PRODUCT DESIGN AND PRODUCTION TOOLING · Sheet metal working: Design consideration for shearing,...

PRODUCT DESIGN

AND

PRODUCTION TOOLING

By

Prof.(Dr) MANOJ KUMAR PRADHAN

B.E, (University College of Engineering , Burla, Odisha)

M.Tech, (National Institute of Technology, Rourkela)

Ph.D, UCE, Sambalpur University, Odisha

Professor and Head

Department of Mechanical Engineering

Gandhi Institute for Technological Advancement (GITA) Bhubaneswar, Odisha

PRODUCT DESIGN & PRODUCTION TOOLING Module I

Product design considerations, product planning, product development, value analysis,

product specification. Role of computer in product design.

Product design for sand casting: design of gating system and risering.

Module II

Forging design: allowances, die design for drop forging, design of flash and gutter, upset

forging die design.

Sheet metal working: Design consideration for shearing, blanking piercing, deep drawing

operation, Die design for sheet metal operations, progressive and compound die, strippers ,

stops, strip layout.

Module III

Design of jigs and fixtures, principle of location and clamping, clamping methods, locating

methods, Drill Jig bushing, Indexing type drilling Jig. Design of single point cutting tool,

broach and form tool. Design of limit gauges.

Process Planning – selection of processes, machines and tools. Design of sequence of

operations, Time & cost estimation, Tooling design for turret lathe and automats.

Text Books:

1. Fundamentals of Tool Engineering design, S.K. Basu, S.N. Mukherjee, R. Mishra, Oxford & IBH Publishing co.

2. Manufacturing Technology, P.N. Rao , Tata McGraw Hill

3. A Textbook of Production Engineering, P.C. Sharma, S. Chand & Co

Reference Books:

1. Product Design & Manufacturing, A K Chitale, R C Gupta, Eastern Economy Edition, PHI.

2. Product Design & Development, Karl T Ulrich, Steven D Eppinger, Anita Goyal, Mc Graw Hill

3. Technology of Machine Tools, Krar, Gill, Smid, Tata Mc Graw Hill

4. Production Technology, HMT

MODULE-I

Introduction to Product Design

Definition of Product Design.

Product design deals with conversion of ideas into reality which aims at fulfilling

human needs.

A designer produces the prototype which issued as a sample for reproducing the

particular goods or, services as many times as required.

In the course of production, on error made by the producer in manufacturing an

item may lead to its rejection, but an error in design, which will be repeated in all

products, may lead to an economic misadventure of enormous, proportions. The

designer’s responsibility is therefore serious.

Design by Evolution – Product Designers are usually asked to develop an existing

design, rather than to design a new product from scratch. Updating successful or

even unsuccessful designs is a regular occurrence in the working life of a Product

Designer.

Take for example the humble and tried and tested pen knife. The existing design,

as seen with the Swiss Army Knife, has evolved slowly over many years. Pen

knifes and multifunction knives have been used for well over a century. Even the

Romans developed multifunctional tools. Manufacturers know from experience,

that they must continue to develop new designs in order to remain successful and

to continue to sell their products.

Design by Innovation –

Following a scientific discovery, a new body of technical knowledge develops

rapidly; the proper use of this discovery may result in an almost complete deviation

from past practice. Every skill, which the designer or, the design team can muster

in analysis and synthesis, is instrumental in a totally novel design.

e.g- Implementation of laser beam.

Product design considerations –

1. Need – A design must be in response to individual or, social need, which can be

satisfied by the technological status of the times where the design is be prepared.

2. Physical realizabilaty – A design should be convertible into material goods or,

service, is it must be physically realizable.

3. Economic worth wholeness – T he goods or services, described by a design ,

must have a utility to the consumer which equals or, exceeds the sum of the total

costs of making it available to horn .

4. Financial feasibility –The operation of designed producing and distribution the

goods must be financially supportable.

Primitive need

5. Optimality – The choice of a design concept must be optimal amongst the

available attentive the selection of the choice design concept must be optimal

among all possible design proposal.

6. Design criterion Optimality must be established relative to a design criterion

which represents the designer’s compromise among possibly conflicting value

judgments which include those of the consumer, the producer, the distributer and

his own.

7. Morphology – Design is progression from the abstract to the concrete. This

gives a chronologically horizontal structure to a design project.

Phase-I

Feasibility Study

Phase-II

Preliminary Design

Phase-III

Detailed Design

Phase-IV

Planning for Production

Phase-V

Planning for Distribution

Phase-VI

Planning for Consumption

Phase-VII

Planning for Retirement

8. Design Process – Design is an iterative problem solving process.

9. Sub problems – During the process of solution of a design problem, a sub-layer

of Sub- Problems appears; the solution of the original problem is dependent on the

solution of the Sub- problems.

10. Reduction of uncertainty – Design is derived after processing of information

that results in a transition from uncertainty, about the success or, failure of a design

towards certainty.

11. Economy worth of evidence – Information gathering and processing have a

cost that must be balanced by the worth of the evidence, which affects the success

or, failure of the design.

12. Bases for decision – A design project is terminated when it is obvious that its

failure calls for its abandonment. It is continued when confidence in an available

design solution is high enough to indicate the commitment of resources necessary

for the next phase.

13. Minimum commitment- In the solution of a design problem at any stage of the

process, commitments which will fix future design decisions must not be made

beyond what is necessary to execute the immediate solution.

14. Communication – A design is a description of an object and prescription for its

production; it will exist to the extent of is expressed in the available modes of

communication. The best way to communicate a design is through drawings, which

is the universal language of designers.

The present day impact of computer added modeling and drafting has resulted in

very effective communication between the designer and sponsor.

Product Planning-

The product planning process takes place before a product development project is

formally approved, before substantial resources are applied and before the large

development team is formed. Product planning is an activity that considers the

components (portfolio) of projects that and organization might pursue and

determines what subset of these projects will be pursued over what time period.

The product planning actuate ensures that product development projects support

the broader business strategy of the company and addresses these questions:

1. What product development projects will be undertaken?

2. What mix of fundamentally new products, platforms, and derivative products

should be pursued?

3. How do the various projects relate to each other as a portfolio?

4. What will be the timing and sequence of the projects?

The product plan identifies the portfolio of products to be developed by the

organization and the timing of their introduction to the market. The planning

process considers product development opportunities indentified by many sources,

including suggestions from marketing, research, customers, current product

development teams and benchmarking of competitors. From among these

opportunities, a portfolio of projects is chosen, timing of projects is outlined and

resources are allocated

The product plan is regularly updated to reflect changes in the competitive

environment, changes in technology, and information on the success of existing

products. Product plans are developed with the company’s goals, capabilities,

constraints, and competitive environment in mind. Product planning dews ions

generally involve the senior management of the organization and may take place

only annually or a few times each year.

Product Development –

Each of the selected projects is then completed by a product development team.

The team needs to know its mission before beginning development. The answers to

these critical questions are included in a mission statement for the team. :

What market segments should be considered in designing the product and

developing its features?

1. What new technologies (if any) should be incorporated into the new

product?

2. What are the manufacturing and service goals and constraints?

3. What are the financial targets for the project?

4. What are the budget and time frame for the project?

Four type of product Development Projects –

A. New product platforms – This type of project involves a major development

effort to create a new family of products based on a new, common platform.

The new product family would address familiar markets and product

categories.

B. Derivatives of existing product platforms – These projects extend an existing

product platform to better address familiar markets with one or , more new

products.

C. Incremental improvements to existing products – These projects may only

involve adding or modifying some features of existing products in order to

keep the product line current and competitive. Product life cycle (PLC) is

one conceptual tool which helps to analyze the requirement, growth,

maturity and decline. Many a time, the third stage of PLC that is maturity

stage of product life cycle, primarily gives clue for making incremental

improvements in existing products to remain competitive and to keep the

product in the market.

D. Fundamentally new products – These projects involve radically different

product or, production technologies and may help to address new and

infamiliar markets. Such projects inherently involve more risk; however, the

long term success of the enterprise may depend on what in learned through

these important projects.

Value Analysis –

Value analysis is defined as an organized creative approach, which has for its

purpose the efficient identification of unnecessary cost i.e, cost which provides

neither nether quality nor use, life, appearance or, customer features”.

A Product or, service is generally considered to have good value if that product

or, service has appropriate performance and cost.

1. Value is always increased by decreasing cost, (While of course, maintaining

performance)

2. Value is increased by increasing performance, if the customer has needs and

wants, and is willing to pay for more performance.

Nature and Measurement of Value –

Value can be perceived as the ratio of the sum of the positive and negative

aspects of an object.

𝑉𝑎𝑙𝑢𝑒 = ∑(+)

∑(−)

In reality, this equation, is more complex, since we are dealing with many

valuables of different magnitudes.

A more descriptive eqn is

).....(

)....(

2

21

n

n

mcmcma

mbmbmbValue

Where, m = the magnitude of a given factor or, criterion

b = a specific benefit

c = a specific cost

Maxm. Value is probably never achieved. The degree of value of any product

depends on the effectiveness with which every usable idea, process material,

and approach to the problem have been identified, studied and utilized.

In a free enterprise system, with competition at full play, success in business

over the long term hinges on continually offering the customer the best value

for the price. The best value determined by two considerations : performance

and cost.

The value Analysis Job Plan –

In the job plan, the problems are recognized and faced, with the functions to be

accomplished clearly in mind. It is a five step process.

(i) Information step –

Record of all the relevant information pertaining to the problem is done by

individuals or by groups of any number of persons.

(ii) Analysis step – In the analysis step, extensive essential “function” thinking

is developed. Functions are “evaluated” and problem setting is made precise;

functions are separated for single study and then they are grouped as needed for

best solutions.

(iii) Creativity step –

When there is a problem to be solved: “Creativity is more important than

knowledge”. Having acquired understanding and information, we have laid the

foundation for the application of various techniques, to generate every possible

solution to the overall problem involved, to the part of problem, and to the

individual problems.

To meet real life situations, the strategy of value engineering must be to

1. provide logic,

2. communicate emotionally in credible terms,

3. Identify new types of knowledge needs.

4. Provide research techniques that will find that knowledge efficiently, and

5. Cause creativity that will usefully combine the knowledge from diverse

sources.

(iv) Use preliminary judgment - Select the approaches that show so much promise

than it is believed. They should be thoroughly studied, extended and judged.

(v) Evaluation – This phase is a feasibility and cost analysis phase.

The alternative ideas suggested during the creative phase were refined and

analyzed with a view to ascertain, whether they could achieve the desired

functions.

This was carried out in two stages:

In the first stage, all suggestions were studied and those which could not be

adopted because of quality, reliability or, other basic reasons were eliminated, and

the others were shortlisted.

In the second stage, the ideas short listed after first evaluation were critically

studied and discusses with the concerned personnel , for feasibility and

practicability of production.

Value Analysis Tests – Each product or, component is subjected to the following

tests :

1. Does its use contribute value?

2. Is its cost, proportionate to its usefulness?

3. Does it need all its features?

4. Is there anything better for the intended use?

5. Can a usable part be made by a lower cost method?

6. Can a standard product be found, which will be usable?

7. Is it made on proper tooling, considering the quantities used?

8. Do material reasonable labouur, overhed and profit total its cost?

9. Will another dependable supplier provide it for less?

10. Is anyone buying it for less?

Product Specifications.

Customer needs are generally expressed in the “language of the customer”.

The term product specifications mean the precise description of what the product

has to do. A specification (singular) consists of a metric and a value. For example,

“average time to assemble” is a metric.

“Less than 75 seconds” is the value of this metric.

The value may take on several forms, including a particular number, a range or, an

in equality values are always labeled with the appropriate units. (e.g., seconds,

kilograms, joules)

Together, the metric and value form a specification. The product specifications

(plural) are simply the set of the individual specifications.

The specifications must reflect the customer needs, differentiate the product from

the competitive products and be technically and economically realizable.

Specifications are typically established at least twice. Immediately after identifying

the customer needs, the team sets target specifications. After concept selection and

testing the team develops final specifications.

Target specifications represent the hopes and aspirations of the team, but they are

established before the team knows the constraints the product technology will

place on what can be achieved. The teams Efforts may fail to meet some of these

specifications and may exceed others, depending on the details of the product

concept the team eventually selects.

The process of establishing the target specifications entails four steps.

1. Prepare the list of metrics.

2. Collect competitive benchmarking information.

3. Set ideal and marginally acceptable target values.

4. Reflect on the results and the process.

Final specifications are developed by assessing the actual technological

constraints and the expected production costs using analytical and physical

models. During this refinement phase the team must make difficult trade-offs

among various desirable characteristics of the product.

The five-step process for refining the specifications is :

1. Develop technical models of the product.

2. Develop a cost model of the product.

3. Refine the specifications, making trade – offs where necessary.

4. Flow down the specifications as appropriate.

5. Reflect on the results and the process.

Role of Computer in product Design The design related tasks which are

performaed by a modern CAD system can be grouped into four functional areas :

1. Geometric modeling. 2. Engineering analysis. 3. Design review and

evaluation. 4. Automated drafting.

1. Geometric modeling.

In CAD, geometric modeling involves computer complatible mathematical

description of the geometry of an object.

In geometric modeling, the designer constructs the image of the object on the CRT

screen of the interactive computer graphies system, by inputting three types of

command to the computer.

1. The first type of command generates basic geometric elements such as

prints, lines and corcle.

2. The second type of command is meant to accomplish translation scaling

(size change), rotation or, other transformations of the elements,

3. The third type of command joins the various elements to give the desired

object.

During the above process, the computer converts the commands into a

mathematical model, stores it in the computer data files and displays it as an image

on the CRT screen.

2. Engineering Analysis

In the formulation of any design project, some sort of analysis is required. The

analysis may be stress stralin calculations , heat transfer computations or, the use

of differential equations to described the dynamic behavior of the system being

designed. The computer can be used to assist in this work. CAD/CAM systems can

be interfaced to engineering analysis software to test a given product design.

Probably the most powerful analysis feature of a CAD system is the finite element

Method (FEM).

3. Design Review and Evaluation –

Checking the accuracy of design can be accornplished conveniently on the

graphics terminal . Semi- Automatic dimensioning and tolerancing routines which,

assign size specifications to surfaces indicated by the user help in reducing the

possibility of dimensioning errors. The designer can zoom in on any details and

closely sorutinize the magnified image. Animation helps in checking kinematic

performance of like mechanisms without resorting to pinboard experiments.

Gear simulations can be carried out and tooth contact analysis can be done.

Interference checking of shaft hole assemblies and the link can be done.

4. Automated Drafting –

This procedure results in saving a lot of time and labour. Computer aided drafting

is known as the design workstation. The CAD work station is the system interface

with the outside world. A good CAD workstation must accomplish five functions.

It must –

1. Interface with the central processing unit of the computer.

2. Generate a steady graphic image for the user;

3. Provide digital description of the graphic image.

4. Translate computer commands into operating function ; and

5. Be user friendly.

Product Design for Sand Casting

Gating systems refer t o all those elements , Which are connected with the flow of

another metal from the ladle to the mould cavity.

The various elements that are connected with a gating system are _

(i) Pouring basin ,

(ii) Sprue,

(iii) Sprue base well,

(iv) runner

(v) runner extension ,

(vi) in – gate .

(vii) riser.

Pouring Bason –

D- sprue entrance diameter The main function of a pauring basin is to reduce

the momentum of the liquid flowing into the mould by setting first in to it in

order that the natal enters into the sprue without an y turbulence, it is necessary

that the pousing basin be deep enough, and also the entrance into the sprue be a

smooth radous of at least 258mm. The pouring basin depth of 2.5 tomes the

sprue entrance diameter is enough for smooth metal flow and to prevent vortex

formation.. Also ,the pouring basin is kept full to avoid vortex formating

Constant conttains of flow through the sprue are established by using strainer

Core cevarnee from fulter

Sprue – Sprue is the channel through which the molten metal is brought in to

the parting plane where it enters the runners and gates to ultimately reach the

mould cavity.

The sprue tapering is obtained by equation of continuity. T → demites top

secton c → demotes choke section

At Vt = AcVc

t

cctV

VAAor ,

From, Bernoulli’s equation )tan2

(2

tConshv

w

p

g

ht

hcAA ct

The square root suggests that the profile of the sprue should be parabolic if

exactly done as per equation. But making a parabolic sprue as too inconvenient

in practice and therefore a straight taper is preferable. A straight – tapered sprue

is able to effectively reduce the air aspiration as well as increase the flow rate

compared to a cylindrical sprue.

The dimensions of the sprue at the top and subsequent top per depends on head

of the metal in the pouring basin . Metal at the entry of the sprue would be

moving with a velocity of gh2

Hence, h

htACAt

Where, H = Actual sprue height & ht = h + H

Theoretical ratios of

Ac

At based on pouring basin depth.

Sprue height (mm) Depth of pouring basin (mm)

50 1.414 1.225 1.155 1.118 1.095

100 .732 1.414 1.291 1.225 1.183

150 2 1.581 1.414 1.323 1.265

200 2.236 1.732 1.528 1.414 1.342

250 2.450 1.871 1.633 1-500 1.414

375 2.915 2.179 1.871 1.696 1.581

500 3.317 2.450 2.082 1.871 1.732

600 3.742 2.739 2.309 2.062 1.897

Sprue Base well -

This is a reservoir for metal the bottom of the bottom of the sprue to reduce the

momentum of the mother metal and there by mould erosion as reduced .

The sprue base area should be five times that of the sprue choke area and the

well depth shold be approximately equal to that of the runner.

For a narrow and deep runner, the well diameter should be 2.5 times the width

of the runner in a two-runner system, and twice its width in a one runner

system.

Runner

It is generally located in the horizontal plane (parting plane), which connects

the sprue to its in gates, thus allowing the metal enter the mould cavity. The

runners are normally made trapezoidal in cross section.

It is a general practice for ferrous metals to cut the runners in the cope and the

ingates in the drag, there by slag are entrapped.

For effective trapping of the slag, runners should flow full.

Figure

Runner Extension

The runner is extended a little further after it encounters the in-gate. This

extension is provided to trap the slag in the molten metal

Gates or in gates

Depending on the application, various types of gates are used in the casting

design.

Top Gate – IN this type of gating, the molten metal enters the mould cavity

from the top. This is sudtable only for simple casting shapes of famous days.

Bottom Gate – When molten metal enters the mould cavity slowly from bottom,

it would not cause any mould erosion. Bottom gate is generally used for very

deep moulds.

Parting Gate – This is the most widely used gate in sand castings. The metal

enters the mould at the parting plane when a part of the casting is in the cope

and a part in the drag.

Step Gate – Such, gates are used for heavy and large castings. The molten,

metal enters mould cavity through a number of in gates, which are arranged in

vertical steps. The size of in gates are normally increased from top to bottom

such that the metal enters the mould cavity from the bottom most gate and then

progressively moves to the higher gates.

Riser – Most of the foundry alloys shrink during solidification. Hence a

reserved of molten metal is to be maintained from which the metal can flow

readily into the casting when the need arises. These reservoirs are called risers.

Material Shrinkage (%)

Medium carbon steel

High carbon steel

No

Morel

Al

Cu

Brass

Bearing bronze

Grey cast iron

Mg

Zn

2.5% to 3.5%

4%

6.1

6.3

6.6

4.92

4.5

7.3

1.9 to negative

4.2

6.5

The metal in the riser should solidify in the end. The riser volume should be

sufficient for compensating the shrinkage in the casting.

The risers are normally of the following types top risers which are open to the

atmosphere, blind risers which are completely concealed inside the mould

cavity itself and internal risers which are enclosed on all sides by the casting.

%100xW

YieldCasting

When , W – actual casting mass

W – mass of metal poured into the mould.

Gating System Design

Pouring Time – There is an optimum pouring time for any given casting.

1. Grey cast Iron, mass less than 450 kg

.sec59.14

41.1, WT

KttimePouring

40,

inchesinironofFluidityKwhere

T = average section thickness, mm.

W = mass of the casting, Kg

2. Grey cast iron, mass than 450 kg

.sec65.16

236.1, 3 WT

KttimePouring

3. Steel castings,

.seclog3953.04335.2, WWttimePouring

4. Shell moulded ductile iron (Vertical pouring)

.sec, 1 WKttimePouring

Where, K1 = 2.080 for thinner sections

= 2.670 for sections 10 to 25mm thick .

=2.970 for heavier sections.

5. Copper alloy casting –

.sec,3

2 WKttimePouring

K2 is constant given by

Top gating = 1.3

Bottom gating = 1.8

Brass = 1.9

Tin Bronze = 2.8

6. Intricately shaped thin walled casting of mass upto 450 kg –

.sec,3 '

3 WKttimePouring

W1 = mass of the casting with gates & risers, Kg

K3 = a constant.

7. For castings above 450 kg and upto 1000 kg.

.sec,3 ''

4 TWKttimePouring

Q- Calculate the optimum pouring time for a casting whose mass is 20 kg and

having an average section thickness of 15mm. The materials of the casting are

grey cast iron and steel. Take the fluidity of iron as 28 inches. Calculate for

grey cast Iron and steel.

Solution – Grey cast Iron

.sec632.72059.14

1541.1

40

28

.sec59.14

41.1,

W

TKttimePouring

Steel,

ond

WWttimePouring

sec5825.8

20)20log3953.04335.2(

.sec)log3953.04335.2(,

Q. Calculate the optimum pouring time for a casting whose mass is 100 kg

and a thickness of 25mm . Fluidity of iron is 32 inches. Calculate both for cast

Iron Steel

Solution –

ond

ttimePouring

Steel

ond

ttimePouringIroncastGrey

sec429.16

100)100log3953.04335.2(,

,

.sec988.24

10059.14

2541.1

40

32,

Choke Area

The choke area can be calculated using Bernoulli’s equation as –

gHdtc

WA

2

Where, A = choke area, mm2

W = Casting mas, Kg.

T = pouring time, s

D = mass density of the molten metal, kg/ mm3

G = acceleration due to gravity, mm/s2

H = effective metal head (sprue height), mm

C = efficiency factor which is a function of the gating system used.

The effective sprue heads can be calculated using the following relations.

Top gate, H = h

Bottom gate, H = h - 𝑐

2

Parting gate, H = h - 𝑃2

2𝑐

Where, h = height of sprue

P = height of mould cavity in cope

c = total height of mould cavity.

Q –

Figure

For the casting sloon, which is to be made in cast iron, calculate the choke area.

Sol – Volume of the casting = 500 x 250 x 50 = 6.25 x 106 mm3

Weight of the casting = 7.86 x 10-6 x 6.25x 106 kg = 49.125 kg

Assuning a composition factor of 4.0 and a pouring temperature of 13000C and

fluidity is 22 inches.

.sec19125.4959.14

5041.1

40

22,

ttimePouring

Calculate effective sprue height , Assuring a top gating system with 100 mm cope

height, Effective sprue height = 100 mm.

Selecting effodency factor C = 0.73

Assumed the density of the liquid metal = 6.9 x 10-6 kg/mm3

2

6648.366

1009800273.019109.6

125.49, mm

xxxxxAareaChoke

In a pressurized gating system, the choke is located in gates, with four ingates, the

ingate area of each is 90 mm2 , each = (15.x6) mm

Gating Ratios –

The gating ratio refers to

Sprue ara : runner area : in gate area.

Depending on the choke area, there can be two types of gating systems :

Non – Pressurized

Pressurized.

A non – pressurized gating system having choke at the bottom of the sprue base,

having total runner area and in-gate areas higher than the sprue area. In this system

there is no pressure existing in the metal flow system and thus it helps to reduce

turbulence. E.g, sprue : runner : in-gate : : 1: 4:4

In the case of a pressurized gating system, normally the in-gate area is the smallest,

thus madntaining a back pressure throughout the gating system. Because of this

bnack pressure in the gating system, the metal is more turbulent and generally

flows full and thereby, can minimize the air aspiration.

e.g Sprue : runner : in-gate : : 1 : 2: 1

Al – 1:2:1 or 1:3:3 or 1:4:4

Al – bronze – 1:2.88:4.8

Brass – 1:1:1, OR 1:1:3 OR 1.6:1.3:1

Cu – 2:8:1 OR 3:9:1

Steels – 1:1:7 OR 1:2:1 OR 1:2:1.5

In gate Design – The in-gates are generally made wider compared to the depth,

upto a ratio of 4. Sometimes of is proffered to reduce the actual connection

between the in-gate and the casting by means of a neck down, wash burn or, dry

sand core so that the removal of the gating is simplified.

In-gate should not be located near a protruding part of the mould to avoid

the striking of vertical mould walls by the molten metal stream.

In-gates should preferably be placed along the longitudinal axis of the mould

wall.

In-gates should not be placed near a core point or a chill.

In-gate cross-sectional area should preferably be smaller than the smallest

thickness of the casting so that the in-gates solidify, forest and isolate the

castings from the gating system.

Slag Trap systems,

Runner Extension

Whirl Gate

Risering Design

Caine’s Method –

Chvorinov has shown that the solidification time of a casting is proportional to the

square of the ratio of volume – to – surface area of the casting.

The constant of proportionality called mould constant depends on the pouring

temperature, casting and mould thermal characteristics.

2

SA

VKts

Where, ts = solidification time, S

V = Volume of the casting

SA = Surface area

K = mould constant.

The ‘freezing ratio’, X, of a mould is defined as the ratio of cooling characteristics

of casting to the riser.

riserVriserSA

castingVtingSAX

/

/cos

In order to be able to feed the costing, the riser should solidify last and hence its

freezing ratio should be greater than unity. For that sphere has the lowest surface

area to volume ratio and hence should be used as a riser. But in a sphere, the

hottest metal being at the centre, it is difficult to use it for feeding the casting. The

next best is the cylindrical type which is most commonly used.

Based on the Chvorinov’s rule, Caine developed a relationship empirically for the

freezing ratio as

cbY

aX

Where , Y = Riser volume / Casting volume.

A, b & c are constants whose values are different for different materials.

Riser – Most of the foundry alloys shrink during solidification. As a result of this

volumetric shrinkage during solidification, voids are likely to form in the castings

unless additional molten metal is fed into these places which are termed as hot

spots.

Hence a reservoir of molten metal is to be maintained from which the metal can

flow reading into the casting when the need arises. These reservoirs are called

risers.

Risering requirements, vary from material to material.

Risers should be designed keeping the following in mind –

1. The metal in the riser should solidify in the end.

2. The riser volume should be sufficient for compensating the shrinkage in the

casting.

The risers are normally of the following types.

(a) Top risers open to the atmosphere.

(b) Blind, risers completely concealed inside the mould cavity.

(c) Internal risers which are enclosed on all sides by the casting.

Out of the above three, the best is the internal riser which is surrounded on all sides

by the casting such that heat Iron the casting keeps the metal in the riser hot for a

longer time. These are normally used for castings which are cylindrically shaped or

have a hollow cylindrical portion.

a b c

Steel 0.10 0.03 1.00

Al 0.10 0.06 1.08

Cost Iron brass 0.04 0.017 1.00

Grey cast Iron 0.33 0.030 1.00

Al – bronze 0.24 0.017 1.00

So - bronze 0.24 0.017 1.00

Q – Calculate the size of a cylindrical riser (height and diameter equal) necessary

to feed a steel slab costing of dimensions 25 x 25 x 5 cm with a side riser, casing

poured horizontally into the mould.

Sonn – Volume of the casting = 25x25x5 =3125 cm3

Surface area of the casting = 2x25x25 + 4x25x5 = 1750 cm2

Volume of the riser = 𝜋

4 D3

Surface area of the riser = 𝜋D2 + 𝜋

4D2 = 1.25𝜋D2

When D – Riser diameter and height

32 25.0/25.1

3125/1750,

DDXratioFreezing

= 0.112D

33

000251.03125

25.0D

D

volumecasting

volumeRiserY

Sub situating in Caine’s eqation , X= 𝑎

𝑌−𝑏+ 𝐶

103.0000251.0

10.0211.0

3

DD

On simplification , D4 – 8.9286D3 – 119.52D = 2490

By trial & error, D = 11.48 cm 12cm

Modulus Method –

If the module of the riser exceeds the modules of the casting by a factor of 1.2, the

feeding during solidification would be satisfactory.

The modulus is the inverse of the cooling characteristic (surface area/ volume) as

defined earlier.

In steel castings, it is generally preferable to choose a riser with a height to

diameter natoo of 1.

3

4DVolume

The bottom and of the riser is in contact with the casting and thus does not

contribute to the calculation of surface area.

222

45

4DxDDareaSurface

The modules of such a cylindrical riser,

MR = 0.2 D

Since MR = 1.2 Mc

= 0.2 D = 1.2 Mc = D = 6Mc

Where, Mc = Modulus of the casting

Thus in this method, the calculation of the riser size is simplified to the calculation

of the modules of the casting. Though this takes into account the cooling effect of

the riser, it does not consider exactly the amount of feeding metal required to

compensate for the shrinkage of the costing.

If allowance is made for the volume of metal to be fed to counteract the contraction

of the costing the equation would be

D3 – 5.46McD2 – 0.05093Vc = 0

Where , Vc = Volume of the casting.

Module of simple Geometric shapes.

Figure

Q – Calculate the size of a cylindrical riser (height & dia. Equal) , using Modulus

Method, necessary to feed a steel slab costing of dimensions 25x25x5 cm with a

side riser, casting poured horizontally into the mould.

Solution – Since it is a slab of dimensions 25x25x5cm, it can be considered as a

long bar with cross section of 25x5cm

cmx

ba

abMcModulus 0833.2

)525(2

525

)(2,

The riser diameter, D = 6Mc = 6x2.08333= 12.5 cm

Naval Research Laboratory Method

In NRL Method a shape factor is used in place of freezing ratio

The shape factor is defined as

Thickness

WidthLength

The corresponding riser volume to casting volume is obtained from the graph

Figure

Ex – Calculate the size of a cylindrical riser (H& Di) using NRL method necessary

to feed a steel slab casting of dimensions 25x255 cm with a side riser, casting

poured horizontally in to the mould.

Solution -

)(47.0,

105

2525

graphfromvolumeCasting

volumeRiseringCorrespond

factorShape

= Riser Volume = 0.47 x (25x25x5) = 1468.75cm3

cmx

D

cmxDD

32.1275.14684

75.14684

3

32

The same can also be directly obtained from graph

Figure

For calculation of shape faction for

1. Circular plates, the length and width are same as that of the diameter.

2. Cylinders, the width and thickness are same as the diameter.

Chills

Chjills are provided in the mould so as to increase the heat extraction capability of

the sand mould. A chill normally provides as steaper temper. Gradient so that

directional solidification as required in a casting can be obtained.

The chills are metallic objects having a higher heat absorbing capability than the

sand mould.

Depending upon the place of applications, chills can be of two types – external,

and internal .

External chills when placed in the mould should be clean and dry. The chills

should not be kept for long to avoid moisture condensation resulting in below

holes.

Internal chills are placed inside the mould cavity where an external chill can not be

provided. The material of the chill should be approximate to the composition of

the pouring metal for proper fusing.

Internal chills should be troughly cleaned before use. However, because of serious

draw backs with use of internal chills, they should be sparingly used.

Grouping of castings

Feeding Aids

To increase the efficiency of a riser, it is necessary to keep the metal in the riser in

liquied form for as long a period as required so that it would feed the casting till it

solidifies. The aids used for thos purpose are called feeding aids.

The feeding aids can be either exothermic materials or, insulators.

The exothermic materials that can be used are graphite or, charcoal powder, rice

husks and thermit mixtures.

For steel costing, an insultating shield on the top of an open riser is very effective

since it reduces heat loss by radiation. Rice husk is used as top insulation.

For non ferrous materials, plaster of pairs is generally used as insulator.

MODULE-II

FORGING DESIGN

Drawing out : Upsetting

Forging Types.- Smith Forging (Open dies)

Drop Forging (Closed impression dies)

Press Forging (closed up dies – Hydraulic Press)

Machine forging (Upsetting)

Allowance –

(i)Shrinkage Allowance – The forgings are generally made at a temperature of

11500C to 1300oC. At this temperature the material gets expanded and when it is

cooled to the atmospheric temperature its dimensions would be reduced It is very

difficult to control the temperature, at which the forging process would be

complete. A Therefore to precisely control the dimensions, a shrinkage allowance

is added on all the linear dimensions.

(ii) Die Wear Allowance – The die wear allowance is added to account for the

gradual wear of the die which takes place with the use of the die.

(iii) Finish Allowance – Machining allowance is to be provided on the various

forged surfaces, which need to be further machined. The amount of allowance to

be provided should account for besides the accuracy, the depth of the decarburized

layer. Also, the scale pits that are likely to form on the component should also be

removed during machining.

FORGING – - No loss of Material

- Blacksmith operation

- Plastic Deformation Process.

Classification – 1 – Hot Forging & Cold Forging

2- Closed –die Forging

- carried out for complex shapes

- For small size, mass pad suitable.

- Close tolerance

- Rough forsing – Blokege pre – Finishing due

Open – die Forging

- Carried out for simple shapes

- For large size

- Production volume less

- Wide tolerance

- carried out in one stage

3- Impact foring

- Pressure is applied suddenly

- Definition is limited to surface

- Hagh velosity of material flow.

- Repeated rapid inpact brows .

- Pressure is max ,at begriming &gradually bows

Press Forging

- Pressure is applied gradually.

- Law velocity of material flow.

- Single step pressure application.

- Pressure is from zero to max.

- Pressure increases as the metal is deformed & is maximum

at the moment the pressure is released

- Deeper Penetration of metal deformation.

Drop-forging Die Design –

The first step in the design of a drop –forging due is the decision regarding what

impressions (or stages) are necessary to achieve the necessary fiber flow direction

to obtain the requisite strength.

A blocking impression becomes a necessity only when the component is to be

accurately made or the component has deep pockets or thin ribs, which are difficult

to be obtained in a single finishing impression. A bending impression is required

when the part is of bent nature and the growth direction is to be along the bend

lone. In such a case, the bending impression is to be obtained before the blocking

impression or finishing impression when no blocking is used. Similarly, a

flattening impression is used when the component is thin and perpendicular to one

plane.

Flash – The excess metal added to the stock to ensure complete falling of the due

cast in the finishing impression is called flash.

Gutter Proportions. Flash Gutter

Stock size

(cm)

Width

(cm)

Thickness(mm) Width (mm) Thickness

(mm)

Upto.35 4.5 0.8 25 3.0

36 to 50 5.3 1.0 25-32 4.5

51 to 65 6.5 1.5 32-38 4.5

66 to 75 8.0 2.0 32-38 4.5

76 to 100 10.0 3.0 38-44 6.5

Forging load is greatly influenced by the flash thickness and width. The forging

load can be decreased by increasing the flash thickness. However, this increases

the scrap losses.

In addition to the flash, provision should be made in the die for additional space so

that any excess metal can flow and help in the complete closing of the die. This is

called gutter. Without a gutter, flash may became excessively thick, not allowing

the dies to close completely.

Stock – As a rule drop forgings do not get upset and therefore the stock size to be

chooser depends on the largest cross –sectional area of the component. To get the

stock size, the necessary flesh allowance is to be provided over and above the stock

volume.

The stock to be used is either round, rectangular or any other section depending on

the nature of the component. Knowing the section of the stock, the length of the

stock can be found out. In addition to stock length, about 50 to 60mm tong hold is

provided for effective handling and movement of the stock in the die.

As the metal is being processed at high temperature, the iron of the forging

combines with atmospheric oxygen to form an oxide which is adhering over the

forging as scale. The loss of metal in this way is about 6% of net weight of forging.

areationcrossgreatestxmetalofDensity

weightGrossstocktheofLength

sec

Impressions in a Multiple Impression Die – Six types of impressions may be

incorporated in a drop forging die for shaping the material progressively from bar

form to the finished forging.

They are –

1. Fuller – This impression is required to reduce the cross – section of a portion of

the forging stock between the ends of the stock.

2. Edger or, roller – This impression distributes the stock so that it will fill the next

impression without excessive waste.

3. Bender impression – Bender impression is included in the die block when curves

or, angles in the forging make it necessary to bend the stock before it will fit

properly in the finishing impression. Bending is a very important operation to keep

the flow lines continuous in a job like crane hook.

4. Block impression – Block impression gives the forging its general shape and

allows the proper gradual flow of metal necessary to prevent laps and cold shuts.

Blocking impression is of same contour as the finished parts but the radio and

fillots are lange to permit the easiest flow of metal. A block impression is without a

flash or, gutter.

5. The finishing impression – This impression bring the forging to its final size.

The finishing impression has both a gutter and flash impression cut round it to

provide space for the excess metal. Both blocker and finisher have a necking or,

running impression so that the forging is still held with tongs.

6. Cut off – It is also part of the die block. It cuts the forging from the bar by

cutting off the tong hold. The flash and gutter are however removed in separate

trimming dies, under punch, presses.

Die – block Dimensions –

The dimensions of the die-block depend upon the length of the finish forging

impression, depth of the impression and the number of impressions in the die

block.

For a single – impression die, the length of the die block may be taken as,

L = l + 3 h (minimum) B = c x b

Where, l – Total length of forging impression,

h = maximum depth of the impression,

b = Maximum width of the impression

c = Constant

= 3 for b upto 5cm

= 2.5 for b upto 25 cm

= 2 for b above 25 cm

The height of the die – block determines the maximum impression depth, since

adequate die material must be there between the bottom, of ompression and bottom

face of the die block to provide strength in the die.

From the strength point of view of the dies and the die wear, the ratio of h and b is

Material h/b

l = b l≥2b

Al, Mg 1.0 2.0

Steel, Titanium 1.0 1.5

For multi impression dies, a gap of at least 25mm should be left between two

adjacent impressions.

a1 - the inter impression distance,

a – the distance of impression from the edge of the die block

H – the height of the die block Dimension in mm

h a a1 H

6

10

40

100

12

32

56

110

10

25

40

80

100

125

200

315

h = the maximum depth of impression.

In terms of the maximum depth of impression, corresponding other values given.

Upset Forging Die Design – (Machine Forging)

In upset forgings, as a rule, no reduction in cross section occurs.

Depending on the shape of the upsetting to be done, the number of passes or blows

in the die are to be designed. The amount of upsetting to be done in a single stage

is limited. To arrive at the safe amount of upsetting in a given pass, the following

rules are to be satisfied, to achieve defect free upset forgings.

Rule 1 – The maximum length of the up supported stock that can be gathered or,

upset in a single pass is not more than three times the diameter of the bar. Beyond

this length, the material is likely to buckle under, the axial upsetting load. In

practice, it is better that the length of the unsupported stock is within 2.5 times the

bar diameter.

Rule 2 – Length of stock more than 3 times bar diameter that is within the limits of

the stroke of machine can be successfully upset made is not more than 1.5 times

bar diameter. If this is kept more than 1.5d, the buckling will be excessive and the

stock will fold in. In practices it is advisable not to exceed 1.3 time bar diameter.

Rule 3 – In an upset requiring more than 3rd in length, when the diameter of the

upset is 1.5d, the amount of unsupported stock beyond the face of the die must not

exceed one diameter of bar.

However if the diameter of the hole in the die is reduced below 1.5d, then the

length of unsupported stock beyond the face of the die can be correspondingly

increased.

Rule 4- Avoid using head diameter greater than four times the stock diameter.

The ratings of Upset forging machines as per Metals Handbook –

Rated Size,

cms

Nominal Rated

capacity kN

Average strokes per

min.

2.5

3.1

3.8

5.0

6.25

7.50

-

1250

3000

4000

5000

6000

90

75

65

60

55

45

10

12.5

15

17.5

20

22.5

8000

10000

12000

15000

18000

22000

35

30

27

25

23

-

Selection of correct size machine necessary to forge a part should be governed by

the following factors.

1. Volume of stock required in the finished forging,

2. Size of stock used.

3. Maximum dimension of the finished forging.

4. Number of blows necessary to complete the forging.

The following steps are formulated in sequences for the purpose of eliminating

guess work.

(i) Calculate the volume of metal in the part to be forged.

(ii) Determine the proper cross section of metal and shape of the metal to be used

to make the forging.

(iii) With the shape and area of the cross – section as well as the volume of the

upset, calculate the length of the metal necessary.

(iv) Calculate the number of blows necessary to complete the forging, using the

general rules that eliminate folding or, buckling.

(v) Make a die layout to determine the size of the die blocks and heading tolls

necessary to accommodate the required number of blows and cavity dimensions.

(vi) Determine the size of forging machine to be used, bearing in mind the size of

the bar to be used, size of the forging to be made, size of the die-blocks necessary

length of header slide, length of stroke, length of gather, length of die opening etc.

(vii) Use hot dimensions on all cavities.

(viii) Provide for clearance between heading tools and their mating dies when

these tolls enter the dies

(ix) Provision should be made for proper grip of the stock.

The length of this grip should not be less than 3d. Also, the cavity diameter in this

area should measure approximately 0.30 to 0.50mm smaller then the diameter of

the bar to be foged.

(x) With the dies and tools designed and the impression machined in the die

blocks, it is advisable to place the tools in the tool holders and make a preliminary

set up of the dies and tools in a face placet for final checking before placing them

in the forging machine.

(xi) Setting of the dies and tools in the forging machine requires a check of

parallelism for the die seats and also the travel of the header slide.

(xii) A small stream of coolant should be directed on the dies and tools to dissipate

the heat and keep the dies free from scale, that may gather in the cavities. The best

is solution of slable oil & water.

Upset forging gives flowing added advantages –

1. A high degree of accuracy in dimensional tolerances.

2. Die life is increased by minimusing the contact time between the dies and

the hot metal.

3. Reduction in the man power required as compard to drop forging.

4. Die setting time is less than drop forging for similar jobs.

5. Die manufacturing cost is less as insert technology is very suitable for

upsetter dies.

6. Preparation of raw material perform design ) is not needed as the bar stock is

directly used in dies.

Design suitable tooling for upset forging of the component shown. The material is

mild steel.

Solution – For the design of the die, all the dimensions will be taken on M.S.

contraction scale.

Volume to be upset.

Since 𝑙

𝑑 is less than 2.5, the forging can be upset in one blow. Applying rule 1-

Total length required for the component

= (43.8 – 5.7) + 8.188 + 0.16 = 46.45 cm

Size of the M/c = Since the bar size is 3.8 cm, so the size of M/c of nominal rated

capacity 3000 KN will be suitable.

Size of the die block = For 3.8cm size of the machine, the die block sizes.- Length

of bar to be gripped = 3d = 11.4cm.

Parting line of the job is taken aling the diameter Half the impression is in the die

block and the other half in the punch.

The length of the conical portion is within two – thirds of the maximum working

length. The unsupported stock beyond the die face is 101mm which is 2.89 times

the stock diameter and is acceptable since it is around 2.5

The average stock diameter after pass 1 is 35+45

2= 40mm

𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑡𝑜𝑐𝑘

𝐷𝑖𝑎𝑚𝑒𝑡𝑒𝑟=

324

40= 8.1

This is still high and therefore one more conical gathering pass is desired.

Length of conical portion = 12𝑥408898

𝜋(402+40𝑥60+602= 205.5mm

The unsupported length is 118.5mm which is 2.96 times the stock diameter and

therefore can be acceptable.

Average stock diameter after pass 2 = 40+60

2= 50mm

𝐿𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑡𝑜𝑐𝑘

𝐷𝑖𝑎𝑚𝑡𝑒𝑟 =

205.5

50=4.11

This is still more than 3 but not too high . Therefore, we may check for the validity

of Rule 2, since it has already violated Rule 1.

Rule 2 is violated since the diameter of 135 mm of the cavity should be

135

50=2.7x stock diameter.

Hence, one more cone gathering is desirable.

Length of conical portion= 12𝑥408898

𝜋 (502+50𝑥70+702) = 143.29 mm

After the third pass, the length to diameter ratio is now 2.388 which therefore can

be gathered in a single pass.

SHEET METAL WORKING

Shearing Action –

The metal is brought to the plastic stage by pressing the sheet between two

shearing blades so that fracture is initiated at the cutting points.

The metal under the upper shear is subjected to both compressive and tensile

stresses.

Clearances - The clearance between two shears is one of the principal factors

controlling a shearing process. This clearance depends essentially on the material

and thickness of the sheet metal. This clearance is given per side as.

C = 0.0032 x t x √𝜏

Where t = sheet thickness, mm

& = material shear stress, MPa

Shearing operations –

In die shearing operations, the shears take the form of the component to be made.

The upper shear is called the punch, and the lower shear is called the die.

Blanking – It is a process in which the punch removes a portion of material from

the stock which is a strip of sheet metal. The removed portion is called a blank.

Piercing – It is also called punching. Piercing is making holes in a sheet.

In the shearing operation, first the material is elastically deformed and then

plastically and finally removed from the stock strip. After the final breaking, the

slug will spring back due to the release of stored elastic energy. This will make

the blank cling to the die face unless the die opening is enlarged. This enlargement

is normally referred as angular clearance or draft.

The normal value is from 0.25 to 0.75 deg per side the die opening increase after

every sharpening of the die because of the provision of angular clearance. So, to

maintain the die size as per the design, the angular clearance is provided in the die

opening along with a straight portion called die land or cutting land. The length of

the cutting land is around same as the material thickness.

Stripper = Due to the release of the stored elastic energy in the stock left on the die,

the stock tends to grip the punch as the punch moves upward. This necessitates the

use of a stripper to separate the punch from the stock.

The stripping force varies from 2.5 % to 20% of the punch force. The stripping

force is given by,

Ps = KLt

Where, Ps = Stripping force, kN

L = Perimeter of cut, mm

t= Stock thickness, mm

K = Stripping constant.

= 0.0103 for low-carbon steels thinner than 1.5mm with the cut at the edge or, near

a preceding cut.

= 0.0145 for low-carbon steels thinner than 1.5mm for other cuts.

= 0.0207 for low-carbon steels thinner than 1.5mm above 1.5mm thick.

= 0.0241 for harder materials.

In blanking the die size is same as the component size whereas in piercing the

punch size is same as the actual hole size to be obtained.

Punching Force – The force required to be exerted by the punch in order to shear

out the blank from the stock can be estimated from the actual shear area and the

shear strength of the material.

It is given by =

P = Lt z

Wher, P = Punching force, N

z = shear strength , MPa

t = Stock thickness, mm

The punching force for holes which are smaller than the stock thickness is

estimated as =

Where, d = diameter of the punch, mm

S = tensile strength of the stock, MPa

Shear

The maximum shear force when shear is applied to the punch or the die, is given as

Where, p = Penetration of punch as a fraction

t1= shear on the punch or, die, mm

The provision of the shear on the punch will change the slug where as shear

provided on the die would make the stock left on the die to bend. Hence, the shear

is provided on the die for blanking and on the punch for piercing.

Q = Determine the die and punch sizes for blanking a circular disc of 20mm,

diameter from a C20 steel sheet whose thickness is 1.5mm Take shear strength of

C20 steel as 294 Mpa.

Solution = The clearance to be provide is given as

C = 0.0032 x t x √𝜏

= C = 0.0032x 1.5 x √294

=0.0823 mm≅ 0.10𝑚𝑚

Since it is a blanking operation,

Die size = blank size = 20mm.

Punch size = blank size – 2C = 20 – 2x0.10 =19.8 mm

If it were a piercing operation ,

Punch size = blank size = 20mm

Die size = blank size +2C

= 20 + 2 x 0.1 = 20.2 mm

Blanking Piercing

Punch size, mm 19.8 20.0

Die size, mm 20.0 20.2

Punching force (P) = Lt z

=𝜋𝑑 𝑥 𝑡 𝑥 𝑧

= 𝜋 𝑥 20𝑥1.5𝑥294 = 27.709𝑘𝑁.

Stripping force (Ps) = KLt

= 0.024 x (𝜋𝑥20) 𝑥 1.5

= 2.262 kN

Q = A 100mm diameter hole is to be punched in a 6mm thick steel plate. The

material is cold rolled C40 steel for which the maximum shear strength can be

taken as 550 MPa. With normal clearance on the tools, cutting is complete at 40%

penetration of the punch. Give suitable diameters for the punch and die, and shear

angle on the punch in order to bring the work within the capacity of a 200 kN

press available in the shop. Solution –

DEEP DRAWING -

Drawing is the process of making cups, shells, and similar articles from metal

blanks. Here, the setup is similar to that used in blanking except that the punch and

die are provided with the necessary rounding at the corners to allow for the smooth

flow of metal during drawing.

Shallow drawing is defined as that where the cup height is less than half the

diameter.

For drawing deeper cups it is necessary to make specific provisions to confine the

metal in order to prevent excess wrinkling of the edges. For this purpose, a blank

holder is normally provided on all deep-drawing dies.

DRAW DIE DESIGN –

Corner Radius on the Punch – The corner radius on the punch varies from four to

ten times the blank thickness. Ideally, the punch radius should be the same as the

corner radius of the required cup, because it takes its form.

Draw Radius on Die –

Drew radius = 4t normal

= (6 to 8 ) t when the blank holder is used.

= 0.8 𝜋 (D-d) t

Where, t = blank thickness

Clearances =

Ideally, the clearance between the punch and die should be same as the blank

thickness. But the blank gets thickened towards the edge because of the metal flow

and hence, the actual clearance provided is slightly higher to account for this

thickening. It varies from 7% to 20% of the blank thickness.

Blank size –

Where, r = corner radius on the punch, mm.

h = height of the shell, mm

d = outer diameter of the shell, mm.

D = blank diameter, mm.

Trim Allowance –

These are only the theoretical blank sizes, based on the surface area of the shell

and blank. Additional trimming allowance is added for trimming of uneven and

irregular rim of the deep-drawn cup. The trim allowance is 3mm for the first 25mm

cup diameter and additional 3mm for each of the additional 25mm of cup

diameters.

Drawing Force –

Where, P = drawing force N.

t = thickness of the blank material, mm

s = yield strength of the metal, Mpa.

C= constant to cover friction and bending. It varies between 0.6 to 0.7

Blank Holding Force = The maximum limit of blank holding force is generally one

third of the drawing force. However it is obtained more by trial and error

depending on the wrinkling tendency.

Ironing force = The objective of Ironing force is to reduce the wall thickness of the

cup. Neglecting the friction and shape of the die, the ironing force =

F=

Where F = Ironing force, N

d1 = mean diameter of the shell after ironing.

t1 = thickness of the shell after ironing.

to = thickness of the shell before ironing.

Sav = average of tensile strength before and after ironing.

Percent Reduction = The drawing operation relies on the ductility of the blank

material. The ductility is affected by the amount of strain a material takes. But

there is a limit to which it can be strained. The amount of straining or, the

drawability is represented by the % reduction which is expressed in terms of the

diameter of the blank and the shell

The percent reduction P is given by,

Where d= Shell diameter (OD)

D = Blank diameter

D

dP 1100

Theoretically, it is possible to get a percentage reduction upto 50, but it is

practicllay limited to 40 Because of strain hardening, the percentage reducation

gets reduced in the subsequent draws.

Reduction in drawing with cup height (% Reduction)

Ht. to dia.

ratio

No. of

draws

First draw Second

draw

Third drew Fourth drew

Up to 0.75

0.75 to 1.5

1.5 to 3.00

3 to 4.5

1

2

3

4

40

40

40

40

-

25

25

25

-

-

15

15

-

-

-

10

Air vent – An air vent is normally provided in the punch to reduce the possibility

of formation of vacuum in the cup, when it is stripped from the punch. For

cylindrical shells, one vent located centrally would be enough, but for other shapes

two vents are provided. The size of the air vent depends on the punch diameter.

Punch dia. (mm) Air- Vent dia. (mm)

Up to 50 4.5

50 to 100 6.0

100 to 200 7.5

Over 200 10

Drawing speed – The speed with which the punch moves through the blank

during drawing is termed the drawing speed. Suggested drawing speeds are =

Drawing Speeds

Material Drawing speed (m/s)

Aluminum 0.9

Brass 1

Copper 0.75

Steel 0.28

Zinc 0.75

Q. A symmetrical cup of circular cross section with a 40 mm diameter and 60mm

height having a corner radius of 2mm is to be obtained in C20 steel of 0.6mm

thickness. Make the necessary design calculations, for preparing the die for the

above cup.

Q. The symmetrical cup work piece as shown is to be made from cold rolled steel

0.8 mm thick. Make the necessary design for the drawing die of this part.

Progressive Dies – In practice, components are produced by combinations of

blanking, piercing, bending or, drawing operations in a certain order. Hence,

practically dies have to do more than one operation for making a finished

component.

The progressive dies perform two or, more operations simultaneously in a single

stroke, of a punch press, so that a complete component is obtained for each stroke.

The place where each of the operations is carried out are called stations. The stock

strip moves from station to station undergoing the particular operation.

The distance moved by the strip from station one to two so that it is properly

registered under the stations is called advance distance.

The feed distance is the amount of stock fed under the punch when the ram comes

for the next stroke. The feed distance may or, may not be the same as the advance

distance. This is because sometimes the sheet is overfed against a stop. The strip is

therefore positioned correctly under the punch by pulling it backwards with the use

of pilots.

Progressive dies contain a large number of stations. It is generally preferred to

have a piercing operation first in the sequence and a blanking or, cut off operation

in the end to get the final component. Any of the pierced holes may be used as a

pilot hole.

The choice of progressive dies is made only when the production is of large

numbers so that the handling costs are saved; stock material is not very thin, so that

movement of the strip by pilots is convenient; stock material is not too thick so as

to avoid the problems of stock straightening and the overall size of the die or, the

press capacity are large.

Compound Die- In a compound die, all the necessary operations are carried out at a

single station , in a single stroke of the ram. To do more than one set of operations,

a compound die consists of the necessary sets of punches and dies.

Compound dies are somewhat slower than the corresponding progressive dies in

operation. But higher tolerances can be achieved in them than in the progressive

dies. This is mainly because the part located in one position under goes all the

operations . Also in compound dies, small strips can be advantageously used,

whereas in progressive dies very long strips are required to cover all the stations.

MODULE-III

Design of Jigs and Fixtures

A jig may be defined as a device which holds and positions the work, locates or,

guides the cutting tool relative to the work piece and usually is not fixed to the

machine table. It is usually lighter in construction.

Jigs are used on drilling, reaming, tapping and counter boring operations.

A fixture is a work holding device which only holds and positions the work but

does not in itself guide locate or, position the cutting tool. The setting of the tool is

done by machine adjustment and a setting block or, by using slip gauges. A fixture

is bolted or, clamped to the machine table. It is usually heavy in construction.

Fixtures are used in connection with turning, milling, grinding, shapping, planning

and boring operations.

To fulfil their basic functions, both jigs and fixtures should possess the following

components or, elements:

1. A sufficiently rigid body (plate, box or frame structure) into which the

workpieces are loaded.

2. Locating elements.

3. Clemping elements.

4. Tool guiding elements (for jigs) or, tool setting elements (for fixtures).

5. Elements for positioning or, fastening the jig or, fixture on the machine on

which it is used.

Jigs and Fixtures are used –

1. To reduce the cost of production, as their use eliminates the layingout of work

and setting up of tools.

2. To increase the production.

3. To assure high accuracy of the parts.

4. To provide for interchangeability.

5. To enable heavy and complex shaped parts to be machined by being held

rigidly to a machine.

6. Reduced quality control expenses.

7. Increased versatility of machine tool.

8. Less skilled labour

9. Saving labour.

10. Their use partically automates the m/c torl.

11. Their use improves the safety at work, thereby lowering the rate of

accidents.

Locating and Clamping –

The overall accuracy is dependnt primarily on the accuracy with which the

workpiece is consistently located within the jig on fixture. There must be no

movement of the work during maching.

Locating refers to the establishment of a proper relationship between the workpiece

and the jig or fixture.

Clamping is to exert a force to press the workpiece agadust the locating surfaces

and hold it there against the action of cutting forces.

Figures

In a state of freedom, it may move in either of the two opposed directions along

three mutually perpendicular axes, xx, yy and zz. There six movements are called

“movements of translation”.

Also, the workpiece can rotate in either of two opposed directions around each

axis, clockwise and anticlockwise. These six movements are called “rotational

movements”.

The sum of these two types of movements, gives the twelve degrees of freedom of

a workpiece inspace. To confine the workpiece accurately and positively in another

fixed body (jig or, fixture). The movements, of the workpiece in any of the twelve

degrees of freedom must be restricted.

(a) The workpiece is resting on three pins A, B and C which are inserted in the

base of the fixed body.

The workpiece cannot rotate about the axes XX and YY and also it cannot move

downward. This wayt, the five degree of freedom 1,2,3,4, & 5 have been arrested.

(b) Two more pins D and E are inserted in the fixed body, ina plane perpendicular

to the plane containing the pins A,B and C. Now the workpiece cannot rotate about

the Z – axis and also it cannot move towards the left. Hence, the addition of pins D

& E restrict three more degrees of freedom, namely 6, 7 and 8.

(c) Another pin F in the second vertical face of the fixed body, arrests degree of

freedom 9.

Thus, six locating pins, three in the base of the fixed body, two in a vertical plane

and one in another vertical plane, the three planes being perpendicular to one

another, restrict nine degrees of freedom. Three degrees of freedom, namely, 10,

11, 12 are still free. To restrict these, three move pins are needed. Buyt this will

completely enclose the work piece making its loading and unloading into the jig or

fixture impossible.

Hence, these remaining three (10, 11, 12) degrees of freedom may be arrested by

means of a clamping device.

This method of locating a work piece in a jig or a fixture is called the “3-2-1”

principle or “Six point location” principle.

Locating devices –

Pins of various designs and made of hardened steel are the most common locating

devices used to locate a work piece in a jig or, fixture. The shank of the pin is press

fitted or, driven into the body of the jig or, fixture. The locating diameter of the pin

is made larger than the shank to prevent it from being forced into the jig or, fixture

body due to the weight of the work piece or, the cutting forces. Depending upon

the mutual relationship between the work piece and pin, the pins may be classified

as:

1. Locating pins 2. Support pins 3. Jack pins.

Principles for location purposes –

1. At least one datum or, reference surface should be established at the first

opportunity, from which subsequent machining will be measured.

2. For ease of cleaning, locating, surfaces should be as small as possible consistent

with adequate wearing qualities. Also, the location must be done from the

machined surface.

3. The locating surfaces should not hold swarf and thereby misalign the workpiece.

For this, proper relief should be provided where burr or, swarf will get collected.

4. Locating surfaces should be raised above surrounding surfaces of the jig or,

fixture, so that chips fall or, can be swept off readily.

5. Sharp corners in the locating surfaces must be avoided.

6. Adjustable type of locators should be used for the location on rough surfaces.

7. Locating pins should be easily accessible and visible to the operator.

Clamping –

If the work piece cannot be restrained by the locating elements, it becomes

necessary to clamp the work piece in jig or, fixture body. The purpose of clamping

is to exert a pressure to press a work piece against the locating surfaces and hold it

there in opposition to the cutting forces i.e, to secure a reliable (positive) contact of

the work with locating elements and prevent the work in the fixture from

displacement & vibration in machining.

Principles for Clamping Purposes –

Since the proper and adequate clamping of a work piece is very important, the

following design and operational factors should be taken care of

1. The clamping pressures applied against the work piece must counteract the tool

forces.

2. The clamping pressures should not be directed towards the cutting operation.

Whenever possible, it should be directed parallel to it.

3. The clamping pressure must only hold the workpiece and should never be great

enough so as to damage, deform or change any dimensions of the workpiece.

4. The clamping and cutting forces should be directed towards the locating pins;

otherwise the workpiece may get bent or forced away from the locating pins during

machining.

5. Clamping should be simple, quick and foolproof.

6. The movement of a clamp should be strictly limited.

7. Whenever possible, the lifting of the clamp by hand should be avoided if it can

be done by means of spring fitted to it.

8. Clamps should never be relied upon for holding the workpiece against the

cutting force. The cutting force should be arranged against a fixed stop or a

substantial part of the fixture body.

9. The clamps should always be arranged directly above the points supporting the

work, otherwise the distortion of the work can occur.

10. Fibre pads should be riveted to the clamp faces, oterhwise soft and fragile

workpiece can get damaged.

11. A clamp should be designed to deliver the required clamping force when

operated by the smallest force expected.

12. A clamp should be strong enough to with stand the reaction imposed upon it

when the largest expected operating force is applied.

13. Clamping pressure should be directed towards the points of support, otherwise

work will tend to rise from its support.

Clamping Devices – The commonly used clamping devices are –

1. Clamping screws 2. Hook blot clamp.

3. Lever type clamps 4. Quick acting clamps.

DESIGN PRINCIPLES COMMON TO JIGS & FIXTURES –

1. Since the total machining time for a work piece includes work handling time,

the methods of location and clamping should be such that the idle time is

minimum.

2. The design of jig and fixture should allow easy and quick loading and

unloading of the workpiece. This wil also help in reducing the idle tiem to

minimuse.

3. The Jig and fixture should be as open as possible to minimize chip or, burr

accumulation and tto enable the operator to remove the chips easily with a

brush or, an air jet.

4. The design features in the jig or fixture will be such that it becomes impossible

to load the work into the jig or fixture in an improper position.

5. Clearance – Clearance is provided in the jig or, fixture body for two main

reasons :

(i) To allow for any variation in component sizes, especially castings and

forgings.

(ii) To allow for hand, movements so that the workpiece can easily be placed

in the jig or, fixture and removed after maching.

6. Rigidity – Jigs and fixtures should be sufficiently stiff to secure the preset

accuracy of machining.

7. To simplify the handling of heavy jigs or, fixtures, the following means can be

adopted –

(i) Eye- bolts, lifting lugs can be provided for the lifting of the jig or, fixture.

(ii) If the workpiece is heavy, then the jig design should allow for side loading

and unloading by sliding the workpiece on the m/c table.

8. The use of ejection devices to force the workpiece out from the jig or, fixture.

9. Inserts – To avoid any damage to fragily and soft workpieces and also to the

fonishied surfaces of a workpiece clamping, inserts of some soft material such

as copper lead fibre, leather, hard rubber or plastic should be fitted to the faces

of the clamps.

10. Design for safety – Jigs/ fixtures must be safe and convenient in use. For that –

(i) Sharp corners on the body of the jig/fixture should be avoided.

(ii) Bolts and nuts should be inside the body of the jig/fixture and protrude on

the suface.

11. Sighting Surfaces – Machining on a workpiece must be clearly visible to the

worker.

12. Simplicity in Design.

13. Economical.

14. They should be easy to set in the machine tool.

DRILLING JIGS –

Drilling jigs are used to machine holes in mechanical products. To obtain

positional accuracy of the holes, hardended drill bushes or, jog bushes are used to

locate and guide drills, reamers etc. in relation to the workpiece. The portin of the

jig into which the hardened bushes are fitted is called bush plate.

Drilling jigs are either clamped to the workpiece in which holes are to be drilled or,

the workpiece is housed and clamped in the jig body. If more than one hole is to be

drilled, the drill jig is made to slide on the table of the drilling machine.

Drilling jigs make feasible the drilling of holes at higher speed, with greater

accuracy and with less skilled workers than is possible when the holes are laid out

and drilled by hand.

Design Principles –

1. A drilling jig should of light in construction consistent with adequate rigidity to

facilitate its handling because it has to be handed frequently during the operation.

2. A drilling jig which is not normally clamped to the machine table should be

provided with jour feet so that it will rock if it is not resting equeare on the

machine table and so warm the operator.

3. The stability of a drilling jig should be as good as possible since it is not usual to

clamp it to the machine table and to ensure this, the feet or, base of the jig should

extend well outside the holes to be drilled.

4. Drill bushing should be fitted in fixed portoon of the jig.

Drill Bushes –

Jig bushings eliminate the elastic spring back in machining and easily locate the

tool relative to the wor.

Drill bushings are classified as

(1) Press Fit bushings.

(ii) Renewable bushes.

(iii) Linear bushes.

(i) These bushings are used when little importance is put on accuracy or, finish.

These bushing are installed directly in the jig body and are used mainly for short

production runs out requiring bush replacement.

(ii) When the guide bushes require periodic replacement (due to the wear of the

inside dia. of the bush, in the case of continuous or, large batch production), the

replacement is simplified by using a renewable bush. These are of the flanged type

and are sloding fit into the liner bush, which is installed (press fitted in the jig

plate). The liner bush provides hardened wear resistant mating surface to the

renewable bush. The renewable bushes must be prevented from rotating or, lifting

with the drill.

(iii) Liner Bushings – also known as ‘master bushings’ are permanently fixed into

the jig body. These act as guides for renewable type bushings. These bushings can

be with or, without heads. A liner bush is always used in conjunction with a

renewable bush.

Design Principles for Drill Bushings –

1. To facilitate easy entry of drills, the entrances to drill bushes should be

extremely smooth and well chamfered or, rounded.

2. There should not be any sharp corners on the body of the bush

3. Loose or, screwed in solid bushes should not be used where accuracy is

important.

4. The effective length of the drill bushing should be sufficient to guide and

support the drill.

5. Adequate provisions must be made for the chips that are produced and for their

easy removal.

6. The hole of the drill bushing should be from 0.00025 to 0.0025cm larger than

the drill size.

Jig bushings can be used to drill from 10,000 to 15,000 holes.

Indexing jigs and Fixtures –

Indexing jigs and fixtures are used when holes or, slots are to be machined to some

specific relationship, in a workpiece.

Indexing Devices – Many indexing jigs and fixtures employ a simple indexing

plate for their operation. Suppose six holes are to be drilled in a flange. The flange

can be mounted on an index plate which has six equispaced slots. The workpiece is

revolved under the drill and each hole is drilled in turn. For this an index plunger is

used which fots by turn into each slot in the index plate. To index the workpiece,

the plunger is pulled out of the slot. The index place and thereby the workpiece is

rotated ---- the next slpt comes in line with the index plunger into which it gets

pushed due to spring action.

Design of Single Point Cutting Tools

The work of a tool, designer consists of following stops

(i) Determining the forces action on the cutting surfaces of the tool and

determining the optimum tool geometry.

(ii) Finding the most producible shapes of the cutting tool and determining the

tolerances on the dimension of the cutting and mounting elements of the tools.

(iii) Calculating the rigidily of the cutting and mounting elements of the tool.

(iv) Making a working drawing of the tool and computing the manufacturing

dimensions.

Rigidity considerations for a single point turning tool - The shank of a single point

tool may be rectangular, square, round in section. The recteangular cross – section

is the most popular.

Square shank tools are used for boring, turret and automatic lathes.

Round shank tools are used for boring & thread cutting.

The permissible size of the shank cross section is determined on the strength basis.

For this purpose the actual bending moment (Mb) acting on the tool is equated to

the moment of resistance of the tool shank (Mb1). Mb = Mb

1

From Fig, Mb = Fc x L.

The tool overhand (L) = (1 - 1.5) H.

The maximum deflection which the tool undergoes durig the maching operation

should also be limited.

The maximum deflection of the tool would occur at the cutting point and could be

found by assuming the tool shank to be a cantilever loaded at the free end. For a

tool having rectangular cross section, deflection is

BROACH DESIGN

Broaching is a process of machining a surface with a pecial multipoint tool called a

broach, whose teeth remove the while maching allowance in a single stroke.

Broaching is widely used in the manufacture of special gears, Bushings and

sleeves, compressor wheels, Rotors, Chain Sprocket teeth, turbine blades etc.

A broach is a multi point cutting tool consisting of a bar having a surface

containing a series of cutting teeth or, edges which gradually increase in size from

the starting or, entering end to the rear end. Broaches are used for machining either

internal or, external surfaces (sizing of hole, straight or, helical splines, gun riflin

and key ways).

Each tooth of the tool takes a thin slice from the surface. Broaching of inside

surface is called ‘Internal or, hole broaching’ and outside surfaces as ‘Surface

broaching’.

Tooth shape of a Broach. H.S.S. is by for the most widely used material for the

broaches. Brazed carbides are used for maching cast iron parts. Carbide tools are

also used on steel casting.

FORM TOOLS

Form tools are cutting tools which are used to machine complex shaped surfaces

with the cross section outlined by curves or, broken lines. Form tools are

commonly used in large lot and mass production. Their use ensures –

-a high output

- uniform contour of all workpieces, and

- accurate dimensions.

Classification of Form Tools –

1. According to their type as – circular, flat and end form tools.

2. According to the setting of flat tools in respect to the workpiece as : Tools with a

radial cutting edge and tangential tools.

3. According to the position of the tool axis as: tools with the axis parallel to the

workpiece axis and tools with an angular location of the axis or, mounting

surfaces.

4. According to the elements of the contoured surface on the tool, as: circular tools

with annular elements, circular tool with helieal elements, and flat tools with flat

elements.

Design features of form tools –

Most form tools are made of H.S.S. However, cemented carbides are also used.

The use of contoured cemented, carbide tips for form tills enables the productivity

to be raised by 30% to 40% as compared to H.S.S.A form tool should have the

proper rake and relief angles.

Relief angel is = 100 to 120 on circular form tools.

=120 to 150 on flat fomr tools.

Rake angles for form Tools

Material Rake angle (degrees)

Al, Cu 20 to 25

Bronze, leaded brass 0 to 5

Mild steel 25

Medium hard steel 20 to 25

Hand steel 12 to 20

Very hard steel 8 to 12

Soft cast iron 15

Hard cast Iron 12

Very hard cast iron 8

DESIGN OF LIMIT GAUGES

Gauges are inspection tools of rigid design, without a scale, which serve to check

the dimensions of manufactured parts. Gauges do not indicate the actual value of

the inspected dimensions of the component. They are only used for determining

whether the inspected part has been made within the specified limits.

Gauging is used in preference to measuring when quantities are sufficiently high,

because it is faster and easier with resulting lower costs.

The design of a limit gauge must ensure proper inspection of the part for which it

is intended. The following points and factors must be kept in mind while designing

the limit gauges:

1. Limit gauge tolerance:

(a) Manufacturing tolerance

(b) Wear allowance

2. Taylor’s principle of gauge design.

3. Fixing of gauging elements (ends) with hands.

4. Provision of Guard.

5. Provison of Pilot.

6. Correct centring

7. Materials.

8. Hardness and surface finished

9. Rigidity.

10. Alignment.

1. Limit Gauge Tolerances –

(a) Manufacturing tolerance –

Gauge maker’s tolerance or, manufacturing tolerance should be kept as small as

possible so that a large proportion of the work tolerance is still available for the

manufacturing process. However, the small the gauge tolerance, the more the

gauge will cost.

The accepted general norms are –

Limit gauges are made 10 times more accurate than the tolerancs they are going to

control that is the tolerance on each gauge whether ‘Go’ or, ‘Not Go’, is 1/10th of

the work tolerance.

There are two systems for the allocation of manufacturing tolerance, Unilateral

system and Bilateral system.

Unilateral system – In this system, the gauge tolerance zone lies entirely within the

work tolerance Zone.

e.g. the size of the hole to be tested be 25± 0.02mm

High limit of hole = 25.02 mm

Low limit of hole = 24.98

Work tolerance = 0.04

Gauge tolerance = 10% of tolerance

= 0.004 mm

Dimension of ‘Go Plug gauge = 24.98 mm + 0.004 – 0.000

+0.000

Dimension of ‘Not Go’ Plug gauge = 25.02 mm

– 0.004.

The disadvantage of this system is that certain components may be rejected as

being outside the working limits when they are not.

Bilateral system – In this system, the ‘Go’ and ‘Not Go’ gauge tolerance zones are

bisected by the high and low limits of the work tolerance zone

Dimensions of ‘Go’ Plug gauge = 24.98mm +0.002/– 0.002

Dimension s of ‘Not Go’ Plug gauge = 25.02 mm+ 0.002 /– 0.002

(b) Wear Allowance –

Mostly the measuring surfaces of ‘Go’ gauges which constantly rub against the

surfaces of the parts in inspection are sufijected to wear and loose their initial size.

To proling the senis lfie of the gauges, wear allowance is taken as 5% of work

tolerance

For above example,

Wear allowance = 5% of work tolerance = 0.002 mm

Nominal size of go plug gauge = 24.98 + 0.002=24.982 mm

Dimensions of Go plug gauge = 24.982 + 0.004 /– 0.000 mm

Dimensions of Not Go plug gauge = 25.02 + 0.000 /– 0.004mm

2. Taylor’s Principle –

This principle states that the go gauge should always be so designed that it will

cover the Maximum Metal Condition (MMC) of as many dimensions as possible in

the same limit gauge, where as a Not Go gauge to cover the minimum metal

condition of one dimension only.

According to this rule, a Go plug gauge should have a full circular section and be

of full length ofc the hole, it has to check. In addition to control the diameter at any

one point this ensures that any lack of straightness or, parallelism of the hole will

prevent the entry of full length go plug gauge.

3. Fixing of gauge elements with handle – Plug gauges can be of solid type in

which the gauging members are integral with the handle or, the gauging elements

can be separated from the handle and suitable fixed together. These are known as

“Renewable” type of gauges. Below 50mm dia., solid type gauges are mostly used.

For larger diameters, the renewable end type of plug gauges is used.

4. Provision of Guard – In case of screw gauges, in order to protect the first few

screw threads from damage, guard extension should be provided. In plug gauges

also, to protect the end, guard extension is provided. If the plug gauge is used for a

blind hole, then guard extension will not be provided.

5. Provision of Pilot – In case of very closely tolerance parts, sometimes it happens

that the plug gauge does not early enter the hole. To overcome this problem,

piloting of plug gauge used.

6. Correct centering –

Centres for high grade job should be very very perfect. Sometimes before grinding,

the centres are even honed after heat treatment.

7. Materials – Most gauges are subjected to considerable abrasion during their use

and must, therefore, be made of wear resistant materials.

High carbon and alloy steel have been used as gauge materials because of their

relatively high harden ability and abrasion resistance. For high volume production

runs, gauge wear surfaces are often chrome plated. The durability of steel gauges

coated with a layer of chrome of 5 to 8 micrometer is 10 to 12 times that of

uncoated ones.

8. Hardness and surface finish –

Recommended hardness for gauges is 62 to 64 Rockwell – C for plain gauges and

56 to 62 Rockwell – C for screw gauges. The recommended surface finish is :

0.127 to 0.254 micrometer, Ra for ground gauges & 0.05 to 2 micrometer, Ra for

lapped gauges.

9. Rigidity – Rigidity is one of the most important features of gauge design.

10. Alignment of Gauge Faces – In a normal gap gauge, the faces must be parallel

and opposite to each other and the points of contract with the work at each face

must lie on a line normal to the gauging face.

PROCESS PLANNING –

Process planning is the systematic determination of method or, process by which

the product is to be manufactured economically and competitively within the limits

of design specification laid down .It consists of devising, selecting and specifying

processes, machine tools and other equipment to convert row materials in to

finished product. Process planning is on intermediate stage between designing the

product and manufacturing it.

The process planning prepares a Plan of manufatur consigning the facto :

1 . The functional requrements of theh product .

2. Volume of output .

3. The necessary operations and their sequence.

4. Tools and equepmant necessary.

5. Estimated manufacturing cost for producing the product .

6. Requarement of tools. labour etc.

So a process planning is mainly concerned with –

(a) Detormation the manufacturing p rocess, sequence of operations,

equipments tools and lobour required for the production of na companent or

a product .

(b) Co – ordinating the effort of all factors in manufacturing the product.

(c) To finish a guide to use the existing or, the proposed facilities.

Function s of process Engineering -----

The process planning or, process engineering is the function of determinating

exactly how a product will be made.

The functions of process engineering are as

1. To determine what parts are to be manufactured and what part to be purchased

from outside.

2. To determine the most economical manufacturing process to be used . dere

3. To determine the sequence of operation to be performed on each component .

4. To determine the blank sizes of materials in process.

5. To prepare materials list for all components of product to invate the purchasing

of row materials.

6. To determine, select and initiate the order for purchasing the equipments/

machine tools needed to manufacture the product.

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