Mech 311 Lecture 1 1

Lecture 1

Introduction

Credits: 3.75 Session: Fall

Time: _ _ W _ F 13:15 - 14:30

MECH 311 Manufacturing Processes

–Section X

Instructor: Sivakumar Narayanswamy

Objective of the course

To provide the basic understanding of

• Measurements,

• Tolerancing and

• Design and understanding of different manufacturing methods ( Conventional and non-conventional).

• Feel for manufacturing:

– What machine at what situation?

– What is possible by existing manufacturing methods?

– Cost effective routes!

– Feel for numbers!

How to Ensure?

what we produce is what we want.

Inspection

Manufacturing Processes

Measurement: Fundamental exercise of inspection; Act of measuring or being

measured.

Why measure? Manufactured parts correspond to the specs of the product:

(QA) Confirm functionality, performance, reliability, process capability, etc.

How to measure? Attributes ( Qualitative, go or not-go, Gaging, decisions)

Variables (quantitative, dimensions, useful for analysis and decision)

What to measure? Size/geometry of tools

Size/geometry of a part from a machine tool

Benefits Determines capability of a process.

Indicates the need of maintenance.

Feedback of manufacturing.

Attribute Vs Dimensional

• Qualitative

• Fast and economical

• Pass or fail

• Mostly for standard and

less severe applications

(Automobile)

• Useful after process

development

• Large production volume

• Quantitative

• Slow and expensive

• Exact dimension is needed

• Useful for highly reliable

applications (Aircrafts)

• Needed for development

• Small production volume

Standard Measurements:

Issues Units are different => Conversion scales

Linear Standards

Metric Systems ANSI System

1in ~ 41,929.399 wavelengths related to human body

sizes Of orange-red light Kr86

Standard set of rectangular gage blocks with ±0.000050-in.

Wrung-together gage blocks

in a special holder, used with

a dial gage to form an

accurate comparator.

Screw gage blocks wrung together to build

up a desired dimension.

Length Standards: Gage blocks or slip gages (Alloy

steel with Rc65)

Standard gages of meter – exist in any workshop ( standard blocks); need to calibrate

every specific period ( various precision).

Calibrated at 20°C

Accuracy Vs. Precision

Accuracy: ability to reach the aimed size

Precision: repeatability of accuracy

(Left):Accuracy versus precision. Dots in targets represent location of shots.

Cross (X) represents the location of the average position of all shots.

Allowance and Tolerance:

Allowance: intentional desired difference between the dimensions of 2 mating parts

Tolerance: undesirable but permissible deviation from a desired dimension.

Most manufacturing processes products with dimensions distributed normally

( clustering around the average)

n

x x

i

n

i 1

   

n

xxi

n

i

2

1

  

The manner in which the distributions of the

two mating parts interact determines the fit.

UNTL upper natural tolerance limit =  3 LNTL, lower natural tolerance limit =   3

When mating parts are designed,

each shaft must be smaller than

each hole of a clearance fit.

Wear or lack of process control  shifting

Clearance?

Range of Fit?

MMC?

LMC?

Bilateral?

Unilateral?

Limits

How to Specify Tolerances?

ANSI – 8 classes of fits

•Class 1. Loose fit: large allowance. Accuracy is not essential.

•Class 2. Free fit: Liberal allowance. For running fits where speeds are above 600 rpm and

pressures are 600 psi ( 4.1 MPa) or above

•Class 3. Medium Fit: Medium allowance. For running fits below 600 rpm and pressure below

600 psi ( 4.1 MPa) and for sliding fits.

•Class 4. Snug Fit: Zero allowance. No movement under load is intended, and no shaking is

wanted. This is the tightest fit that can be assembled by hand

•Class 5. Wringing fit: zero to negative allowance. Assemblies are selective and not

interchangeable.

•Class 6. Tight fit: slight negative allowance. An interface fit for parts that must not come

apart in service and are not to be disassembled or are to be disassembled only seldom. Light

pressure is required for assembly. Not to be used to with stand other than very light loads.

•Class 7. Medium force fit: an interference fit requiring considerable pressure to assemble;

ordinarily assembled by heating the external member or cooling the internal member to provide

expansion or shrinkage. Used for fastening wheels, crank disks, and the like to shafting. The

tightest fit that should be used on cast iron external members.

•Class8. Heavy force and Shrink fits: considerable negative allowance. Used for permanent shrink on steel members.

ISO System of Limits and Fits • Clearance fits

• Transition fits/ Location fits/ Assembly fits

• Interference fits

Shaft-basis and hole-basis system for specifying fits in the ISO system

What is Hole based or Shaft based system?

WHY?

Geometric Tolerances: Permitted tolerance on shape/geometry/form/position

(Left) Geometric tolerancing symbols; (Right Up) Feature control symbols for

part drawings; (Right Down) Example of use of geometric tolerancing

(tolerancing for flatness)

MMC – Parts are made with the largest amount of material possible

LMC - Parts are made with the least amount of material possible

RFS – Regardless of feature size

Datums- Concept/Feature common for design, manufacturing and inspection

Inspection methods for measurement

Metrology: measurement laboratory selected according to certain criteria:

• Gage capability ( rule of 10)

Measuring device has to be 10times more precise than the tolerance measured:

Eg. +/-0.001  +/-0.0001  +/-0.00001

•Linearity

Linear working range (Input Vs Output)

•Repeat accuracy

Repeatability of the measurement

•Stability

Retaining calibration over time, no-drift

•Magnification

Amplification of the output portion of the device, bigger dials.

•Resolution

Sensitivity; smallest input value that can be detected or measured

Measurement instruments ( linear)

* Ruler (0.5mm) * Combination set

* Vernier Caliper(0.01mm) * Micrometer caliper

* Optical Comparators (0.001mm) * Laser/ interferometers(0.0001mm)

Combination set.

Three styles of calipers in common use today

Internal and external

Digital Micrometer for measurements

from 0 to 1in., in 0.0001-in.

graduations.

Vision Systems of measurement

Optical Comparator,

measuring the contour on a

workpiece. Digital indicators

with in/.mm conversions add

to the utility of optical

comparators.

Coordinate measuring

machine with inset showing

probe and a part being

measured.

Coordinate Measuring Machines

(CMM)

Interference bands can be used to measure the size of objects to great accuracy

a a)(bottom left) Calibrating the X-axis linear table displacement of a vertical

spindle milling machine; b) ( top right) Schematic of optical setup ; c) ( bottom

right) Schematic of components of a two frequency laser interferometer. Resolution ~ 10nm

The principle of the optical flat

Angle Measurement

• Sine Bar: 1sec of arc

Setup to measure an angle on a part using a

sine bar. The dial indicator is used to

determine when the part surface X is parallel

to the surface plate

(Top) Plain plug gage having go member

on one end and not-go member on other

other; (Bottom) Ring gage with stepped go

and not-go member

Go and not-go ring gages for checking a

shaft.

Gages for Attributes ( mass production):

Ring Gage

GO

Ring gage

No GO

100+/- 0.1

Shaft

100.1 99.9

Plug gage

GO

Plug gage

NO GO

100+/- 0.1

Hole

99.9 100.1

Top) Microtopographer, a stylus profile device used to measure

and depict surface roughness and character (surface profile);

Bottom) Typical surface-roughness profiles.

Schematic of surface profile as produced

by stylus device showing some typical y