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VŠB - Technical University of Ostrava

Faculty of Metallurgy and Materials Engineering

TECHNOLOGICAL DESIGN AND

PREPARATION OF CASTING

PRODUCTION (e-learning) Design Technologicity

Lecture notes / case studies / tests

Jiří Hampl

Ostrava 2016

Reviewer: prof. Ing. Tomáš Elbel, CSc.

Title: Technological Design and Preparation of Casting Production

Author: doc. Ing. Jiří Hampl, Ph. D.

Edition: first, 2016

Number of pages: 62

Educational materials for the field of study Modern Metallurgical Technologies (Metallurgical

Engineering study programme) of the follow-up study at the Faculty of Metallurgy and Materials

Engineering Proof-reading: not performed

Intended for the project:

The Education for Competitiveness Operational Programme (ECOP)

Faculty of Metallurgy and Materials Engineering VŠB - Technical University of Ostrava

Number: CZ.1.07/2.2.00/28.0304

Realization: VŠB - Technical University of Ostrava

The project is co-financed with ESF funds and from the state budget of the Czech Republic

© doc. Ing. Jiří Hampl, Ph. D.

© VŠB - Technical University of Ostrava

Table of contents

TECHNOLOGICAL DESIGN AND PREPARATION OF CASTING

PRODUCTION.............................................................................................. 1

STUDY REGULATIONS ................................................................................... 4

TECHNOLOGICAL DESIGN AND PREPARATION OF CASTING

PRODUCTION.............................................................................................. 4

INTRODUCTION ............................................................................................... 5

1 BASIC TERMS AND AIMS OF CASTING TECHNOLOGICAL

DESIGN .......................................................................................................... 7 1.1 Basic terms .............................................................................................................................. 7

Technological design of castings (TDC) ......................................................................................... 7 Technological procedure of production (TPP) of castings .............................................................. 8

2 PRINCIPLES OF CASTING DESIGN IN TERMS OF MOLD

MAKING ...................................................................................................... 16 Principles of the technological design of castings cast into sand moulds ......................................... 16

3 PRINCIPLES OF CASTING CONSTRUCTION WITH REGARD TO

PRE-CASTING OF CAVITIES USING CORES .................................... 25 Core making methods ........................................................................................................................ 26

4 PRINCIPLES OF CASTING DESIGN IN TERMS OF DIRECTIONAL

SOLIDIFICATION ..................................................................................... 36 4.1 Elimination of a size of thermal nodes .................................................................................. 42

5 PRINCIPLES OF CASTING DESIGN WITH REGARD TO STRESS

IN CASTINGS ............................................................................................. 47

6 PRINCIPLES OF A CASTING DESIGN IN TERMS OF FETTLING

AND FINISHING ........................................................................................ 58

STUDY REGULATIONS

Technological Design and Preparation of Casting Production

You have obtained an educational packet including integrated lecture notes for the combined study

comprising also study regulations.

The subject “Technological Design and Preparation of Casting Production” is intended for the 3rd

semester of the follow-up study of the branch Modern Metallurgical Technologies.

Prerequisites

Graduation from the following subjects is a prerequisite for the study of this subject: Technology and

Theory of Metalcasting and Metallurgy of Foundry Alloys

The objectives of the subject and outputs from the education

The aim of the subject is to introduce students to theoretical and practical knowledge on

technological design and technical preparation of casting production. Emphasis is placed on

application of the acquired knowledge in design and technology of castings, ensuring all of their

functions as well as maximum cost-effectiveness of the manufacture.

After studying the subject, a student should

- know the principles of technological design of castings (TDC)

- know basic procedures of the preparation of casting production (PCP)

- be able to apply the principles of TDC and PCP in the casting manufacturing process

For whom the subject is intended

The subject falls within the follow-up study of the field of study Modern Metallurgical Technologies

of the study programme Metallurgical Engineering, but it can also be studied by applicants from any

other branch, on condition of having met the demanded prerequisites.

Recommended procedure for studying each chapter

The lecture notes divided to chapters need to be read-through as a whole at first. Only after that it is

advisable to begin to study the particular chapters.

A way to communicate with lecturers

You can contact the lecturer through e-mail: [email protected] or by telephone:

+420 597 324 206.

INTRODUCTION

The subject “Technological Design and Preparation of Casting Production” covers principles of

the casting design in term of their manufacturability by foundry technologies. A degree of

technological design of a casting: A high degree means a condition, when a casting can be

manufactured at meeting all technical and economic parameters. On the contrary, a low degree

means that a casting can be manufactured under the given conditions only with difficulties - e.g.

an unsuitable design (material) of a casting or improper manufacturing conditions in the foundry

shop for the given casting. This usually results in increased costs caused for example by high

nonconformance (wastage) of the production.

A properly designed “foundry construction“ gives a presupposition for high usable properties as

well as cost-effective manufacture of castings. On the contrary, a design not respecting the applied

foundry technology (non-technological design) typically leads to costly production and only

difficult-to-meet requirements on casting properties.

As a matter of fact, castings can be manufactured from a broad range of foundry alloys without

any limitation in shape. An optimal design is usually a compromise between technical

requirements for a function, shape, strength, quality, service life, reliability on one side and a

technological potential of a foundry shop and economy of production on the other side.

Obr. 1 Flowchart of a good and bad (below) cooperation of a designer and technologist on

preparation of a casting manufacture

In order to achieve an optimal result in the effective casting production, a cooperation of a designer

with a foundry technologist is demanded (needed) for both the sides (Fig. 1). A block diagram of

the casting production procedure from the market demand to the sale is shown in Fig. 2.

MARKET

SCHEME

ENTERPRISOR

SUBMISSION OF A PROJECT

function

operational conditions

service life and reliability

material properties

standards, experience

demanded quantity

DESIGNER

flowchart, shape, kinematics

force flows

strength calculations, selection of

material,

tolerances, roughness, surface

finishing

PRODUCT DESIGN

drawings, specifications

technological properties

of materials

influence of technology on properties

of material

technological possibilities

demandingness of operations

demanded quantity

demanded quality

TECHNOLOGIST

selection of technology

exact selection of material

modification of a shape and thickness

of walls

semi-products, allowances, tapers

sequence of operations

melting, technological

parameters of production

design of fixtures and tools

MANUFACTURING PROCESS

manufacturing capacities

manufacturing machines and devices

areas and transport

experience, personnel

cost and financing

(prices, depreciations, wages, taxes...)

suppliers

occupational hygiene and safety

MANUFACTURER

organization of production

manufacture of fixtures

orders of semi-products

ensuring of cooperation

calculation of cost and price of the

product

ensuring of waste disposal

promotion

PRODUCT

VENDOR

product usable properties (functional,

economical, aesthetical and ecological)

demand for similar products

MARKET PROFIT

Obr. 2 Schematic procedure of a casting production in a foundry plant

1 BASIC TERMS AND AIMS OF CASTING

TECHNOLOGICAL DESIGN

Subchapters:

Basic terms

Objectives

Time needed for the study: individual

Objective: After studying this chapter a student will be able to:

Define basic terms of casting technological design

Define a degree of technological design of a casting

Design an optimal casting construction in term of the applied foundry technology

Lecture

1.1 Basic terms

Technological designing of castings (TDC)

The technological designing of castings (or technologicity) is a broad term involving all

requirements for properties and functions of a designed casting while respecting conditions of its

manufacture. The manufacturing process from an engineering design (deaft), over the manufacture

of a gated pattern, casting, to fettling and finishing, is influenced above all by a designer of a

component – a casting.

A designer designs shapes, materials, dimensions, surface quality and the casting precision. The

designer through his/her design predetermines meeting of all the required parameters of the casting

and mostly also its good or difficult manufacturability, i.e. the technological degree.

General principles of the technological designing of castings

At the beginning of the process (technical preparation) is always a design of the designer expressed

by a drawing documentation or 3D data of a machine component. A design of an optimal

construction of a casting is a complicated process requiring cooperation of a lot of specialists,

above all a designer and a foundry technologist.

In this (preproduction) phase of the design, specific aspects of the foundry technology should be

considered:

- Possibility to create even highly complex shapes of a casting surface including pre-casting

of holes, cavities and reinforcing ribs – without a noticeable increase in production costs

- Application of a broad range of foundry alloys for castings

- Possibility to influence structures of castings in as-cast condition as well as by heat

treatment

- Combination of various materials, such as casting of steel inserts of cylinders into engine

blocks of cast iron

- Casting of metallurgically connected material layers (e.g. multilayer centrifugal castings

of rolls for rolling mill stands etc.)

In principle, it is not recommended to imitate shapes of forgings, weldments or parts manufactured

from semi-products by machining, which do not allow full utilization of foundry technology

advantages. Constructions imitated this way cause troubles during casting and solidification and

typically also impaired properties of castings in operation. For example, in the past it was an

increased failure rate of crankshaft castings (compared to forgings), which was removed by a

properly designed construction respecting the foundry technology. At present, crankshafts are

commonly cast with comparable parameters as for forgings, but at lower production cost.

For a foundry casting design, the most important is a selection of geometry of main functional

parts, which adapt to maximum rigidity and minimum consumption of the casting material, while

achieving maximum cost-effectiveness.

A shape of a future casting is subsequently modified according to the proposed foundry technology

of manufacturing, i.e. a mould type (expendable mould, permanent mould), the casting method –

gravitational casting, pressure casting, precision casting etc.

The aim is to ensure a maximal inner homogeneity of the casting through a proper design.

Principles of the directional solidification including a correct function of risers in order to reduce

a risk of inner defects (shrinkages) in the casting are applied.

Requirements for casting properties are highly diverse, many times antagonistic. Achieving high

strength (toughness) need not always to be the most important demand. Many times a shape

complexity and maximum surface area are preferred to high mechanical properties (radiators,

boiler fuel cells, heat exchangers) or pre-casting of complicated inner cavities (engine heads and

blocks, hydraulic distributions).

So, the technological design is such a structural embodiment of a casting, which ensures all its

required parameters, e.g. mechanical properties, service life and reliability, to be ensured at

maximum production cost-effectiveness.

Technological procedure of production (TPP) of castings

A technologist designs a procedure of a casting production on the basis of the technical

documentation of a component (a technical drawing, 3D data). When designing the TPP, technical

and economic conditions of the production are considered, typically adapted to conditions in a

particular foundry shop.

The technology of a casting manufacture (specified by material and weight) is bound to production

conditions in the foundry plant, i.e. a furnace size, a type of moulding line, types of moulding

materials, a level of automatization, a kind of production (single-piece production, small-lot

production, batch production, large-scale production).

Basic aims of casting technological designing and TPP

a) to ensure the highest quality, i.e. minimization of production risks (nonconformance) at

minimum work expenditure and

b) observance of required (standardized) properties

c) optimal – acceptable costs while ensuring required casting properties, i.e. the optimal quality

d) at minimum work expenditure (minimization of risks in term of nonconformance - wastage

of production)

Principles of the technological designing of castings

1. A casting shape must respect the foundry technology at a maximum extent, i.e. a uniform

wall thickness, smooth tapers, rounding

2. An alloy with an adequate structure, mechanical and physical properties

3. Good metalcasting properties of the chosen material-alloy (low tendency to shrinkage,

fluidity)

4. To prevent defects by respecting the foundry technology – mainly the principles of the

directional solidification

5. Adequate demands for precision – minimization of technological allowances

6. Precise and clearly defined demands for quality - acceptance terms of castings

7. Fast and non-costly technical preparation of production (TPP) – application of the

simulation of solidification and Rapid Prototyping

8. Application of normalization and typification of the whole casting production process

9. Selection of an applicable type of documentation (3D data)

10. Maximal utilization of manufacturing capacities of the foundry plant (existing machinery)

11. Minimization of production and overhead costs

12. Application of mechanization and automatization of production

Obr. 3 Original design of a wheel hub and a casting respecting the foundry technology (on the

right-hand side)

Obr. 4 Substitution of a crankshaft forging by a foundry casting with an enhanced

technological design has increased its fatigue strength from 4.5 to 16 kp/mm2

Obr. 5 Original construction of a ship motor bracket welded from 5 parts

Obr. 6 Casting of a bracket with by 50% higher fatigue limit and 30% lower weight as a

substitute for the original welded construction

Obr. 7 Halfaxle comprising 3 forgings and 5 welded pressed parts

Obr. 8 Halfaxle cast from EN-GJS-500; through improvement of foundry technological design

the production cost dropped by 13%

Influence of a type of serial production on a conception of a casting manufacture

1. Larger-lot production

2. Unification and typification – type ranges, graduation according to a size and weight

3. Heredity, i.e. the maximal utilization of experience from previous productions

4. Construction standardization

5. Normalization – observance of standards ISO,EN - ČSN

6. Identical shape, dimensions, chemical composition

7. The use of industrial robots and manipulators – automated workplace

Technological standardization methods

1. Typification of technological procedures is based on comparing and seeking structural and

technological similarities of manufactured castings and their sorting

2. Typified production procedure involves an essential operation sequence with

specification of the workplace, tools, used technology

3. Assessment and modification of the technological design in groups according to identical

features

4. Designing a type technology for selected groups and elaboration of typified production

procedures

5. Selection of a characteristic representative of a casting, including the equipment for

production

Advantages of the technological standardization

1. Increase in quantity of pieces in a lot, time and cost saving

2. Enhancement of the technologist work quality while decreasing a scope of TPP

3. Reduction in a number of kinds of special tools – cost-saving for the design and

manufacture or purchase of the tools

Rapid prototyping methods

Rapid prototyping – „rapid making of a prototype” (material is added, not reduced). A result of

this process is a component prototype, on the base of which a pattern for the manufacture of

moulds and casting of castings is made.

Stereolithography – UV laser or UV lamp hardens a liquid polymer in a layer by layer fashion.

Sintering (SLS – Selective Laser Sintering) – a layer of powder material is sintered by a laser,

after each cross-section is scanned, the powder bed is lowered by one layer thickness and the

process is repeated.

Deposition – cladding of molten polymer or wax in a shape of beads or droplets (scanning melting

head)

- powdered metal by scanning CO2 laser

- binder for the powder from the scanning jet – hardening of a layer in a furnace

Laminating (LOM – Laminated Object Manufacturing) - layers of adhesive-coated laminates are

successively glued together and cut to shape with a laser.

3D printer (FDM – Fused Deposition Modeling) – “printing” of patterns. The “printer” fuses and

deposits wax, plastic material or powdered metal layer by layer (in areas), which are hardened

immediately.

Advantages:

Possibility to create highly complicated, small components even with details (with small

holes)

Creating of sharp edges, closed hollows

Fast verification of functionality of a prototype, fast obtaining of a model usable for the

mould manufacture

Disadvantages:

Worse quality (roughness) of side surfaces

Limited range of materials for application in this production

Criteria of the technological designing evaluation

Evaluation of the level of the casting technological design can be performed for example through

an old to new product weight ratio, the original and new technology laboriousness ratio:

product old ofweight

product new ofweight 1 m

material used

product. ofweight 2 m

typeold esslaboriousn

typenew esslaboriousn1 p

Methods of the technical preparation of production - TPP

Sequential engineering

The design preparation, technological preparation and production are done in stages one after

another. After one stage is tested and completed, it is left alone and everything is concentrated

on the next task.

Concurrent (simultaneous) engineering

It is used today; the design preparation, technological preparation and production operate at

the same time - simultaneously, thus saving a half of the original time. More construction

variants are tackled at the same time. The particular professions of technology, design and

economy engineers occur in the same time frame.

Summary of terms of this chapter (subchapters)

1. Technological design of castings

2. Basic aims of the technological design of castings

3. Basic aims of the technical preparation of castings

Questions to the topic

1. What are advantages of foundry technology in term of complexity of components?

2. What is a structure of castings in term of macro- and microstructure?

3. Describe principles of the technological production of castings.

4. Explain methods of technological standardization.

5. How can a degree of technological design of castings be determined?

2 PRINCIPLES OF CASTING DESIGN IN TERMS OF MOLD

MAKING

Subchapters:

Basic terms

Objectives



Define principles of a design of castings cast into sand moulds

Design a way of setting a casting in a mould

Design a parting plane (joint) of a mould

Lecture

Principles of the technological designing of castings cast into sand moulds

If possible, a casting should be a connection of simple geometrical bodies with prevailing

planar and cylindrical areas

Where a shape complexity is necessary, obtaining of a required shape without a need of

machining is preferred (parts of pumps, turbine blades, exhaust pipelines etc.)

A casting design is based on a presupposed method of mould making and the used casting

technology

A casting pattern should have as few parting surfaces, free parts, protrusions without sharp

edges, recesses and corners as possible

Parting surfaces of a casting and mould should be planar, if possible

A casting should have adequately large tapers allowing easy withdrawal of a pattern from

a mould

A casting should not have big differences in wall thicknesses, which could support

occurrence of shrinkages (a need to use risers, chills)

To ensure satisfactory molten metal flow rate during filling the mould

Wall thicknesses should increase towards risers

To use gradual transitions, roundings, in case of need reinforcing ribs to prevent occurrence

of hot and cold cracks in wall joints

Large thicknesses and local accumulation of metal increase a tendency for occurrence of

internal stresses and shrinkages

Tapers and parting surfaces (joints) - when making a casting, one needs to consider that

a pattern needs to be fitted with draft tapers and a parting plane to allow its withdrawal

from a mould. From the constructional and technological point of view, a taper size

depends on casting dimensions, manufacturing technology, gated pattern and a casting

material.

Obr. 9 Types of draft tapers a) the most frequently used taper for non-machined surfaces, b)

used when a casting dimension can be reduced, c) for machined surfaces, when a

casting dimension cannot be reduced

Obr. 10 Round edges on very small surfaces of a pattern made using tapers

Tab. 1. Foundry draft tapers (mm) of patterns and core boxes according to ČSN EN 2820

Height H

Taper T

Shallow moulding 1 H/W Deep surfaces 1 < H/W

Hand moulding Hand moulding

Machine

moulding Aluminous

mixtures

Chemically

bound

mixtures

Machine

moulding

Aluminous

mixtures

Chemically

bound

mixtures

To 30 inclusive 1.0 1.0 1.0 1.5 1.0 1.0

Over 30 to 80 inclusive 2.0 2.0 2.0 2.5 2.0 2.0



Over 250 to 1000

inclusive + 1.0 per each further 250 mm of height

Over 1000 to 4000

inclusive + 2.0 per each further 1000 mm of height

W = inner width

A casting shape has to allow an easy withdrawal of a pattern from a mould in the parting plane.

To verify a proper selection of a parting plane a “shadow method” is used – spots on the casting,

which under illumination perpendicular to the parting plane remain in the shadow, disable the

withdrawal of the pattern from the mould.

Obr. 11 Shadow method – left-hand side: wrong – right-hand side: correct

Obr. 12 Application of a) split pattern; b) one-piece pattern

Obr. 13 Shaped parting area for application of moulding boxes of the same height of 400 mm

Obr. 14 Gear wheel with two rims a) splitting of gear rims by a parting plane may cause their

mutual shift – b) correct solution

Obr. 15 Variants (a, b, c, d, e, f ) of a parting plane after casting of an annulus

A selection of the parting plane typically depends on more factors being usually a case of

compromise.

a) the parting plane does not influence concentricity of casting walls

b) creates parallel walls with a standard taper on the circumference and also inside the casting

cavity

c) a need to ensure proper closing of both halves of the mould, so that a casting cross-joint does

not occur

d, e) the solution has the lowest demands for subsequent processing, which is applicable for

difficult-to-machine materials; a risk of a cross-joint of the mould is here, too

f) without tapers in a hole and along the casting circumference, core prints for seating a core

need to be used

Obr. 16 Moulding of a casting of a belt pulley, a one-piece pattern with an cover core

Obr. 17 Moulding on 3 boxes – a split pattern with two parting planes

Obr. 18 Variants of the manufacture of a mould for a pattern of a housing casting (a, b, c) and

after a constructional modification (d, e)

Obr. 19 Moulding with application of a free part of a pattern (1)

Obr. 20 Selection of a broken (top) and planar (bottom) parting surface of a pattern

Obr. 21 Broken parting surface of a mould (a), planar parting surface with a core (b), planar

parting surface without a core (c)

Obr. 22 Moulding of a pattern with more parting planes into four moulding boxes

Obr. 23 Moulding with loose (removable) parts of a pattern I, II, III

Obr. 24 Moulding with cover cores

Obr. 25 Moulding of a casting of a belt pulley with a cover core (1)


1. Position of a casting in a mould

2. Parting plane, tapers and technological allowances

3. Core and cover core


1. What are the criteria for a selection of a position of a casting in a mould?

2. What are the criteria for a selection of a value of technological allowances?

3. What is a loose piece of a pattern and when can be used?

Recommended literature for further study

3 PRINCIPLES OF CASTING CONSTRUCTION WITH

REGARD TO PRE-CASTING OF CAVITIES USING CORES

Subchapters:

Basic terms

Objectives



Determine when to use a core to pre-cast a cavity in a casting

Explain basic methods of the manufacture and application of cores

Choose a way of positioning of cores and their ventilation

Lecture

Cavities in castings

Cavities should have a simple shape, if possible

Shapes of cavities need to be designed with regard to core box filling with a core mixture

and a removal of cores from castings after casting

Shapes of cores have to enable their easy placing into the mould cavities

Shallow, broad cavities, widening towards a parting plane, with a taper min. 3°, which need

not to be created using cores, are ideal

Seating a core and properties of cores

Core prints are used for seating the cores in moulds

Cores are seated in core seats in moulds

Particular attention needs to be paid to degassing of cores and preventive measures against

cracking

A highly important property of cores is their good collapsibility after casting and cooling

of castings

Large and heavy cores are vented and metal grids are placed inside

Core making methods

Cores are manufactured in core boxes (wooden, metal)

Cores, similarly as moulds, are made by machines In single-piece and small-lot production

they are handmade

Machine manufacturing of cores uses pressing, vibrations, jolting, blowing, injection, sand-

slinging or a combination of these methods

Core boxes are typically from the same material as patterns, because the same wear -

service life is assumed

Complicated cores can be “glued” together from individual segments using adhesives

Obr. 26 Expendable (sand) mould with a seated core for pre-casting of a cavity in a casting

Obr. 27 Mould (4,5) with a seated core (3) and a casting (B,1) with a gate (A,6) and an overflow

(C,7)

Obr. 28 Seating a core in a cavity using 1 core print and 2 studs (wrong) and 2 core prints

(better)

Obr. 29 Unsuitable seating of cores (a, b) and more applicable seating of a core through a

construction modification (c, d)

Obr. 30 Deformation of a slim core by buoyancy of the molten metal

The use of cores and their processing

Cores are mostly used for creating inner cavities (shapes) in castings – ‘true’ cores

Cores can be also used for creating an outer surface of a casting, the so-called cover cores

By decomposition of binders and evaporation of moisture during casting, gases and

vapours generate inside the core, concentrating in the centre of the core and being led off

the mould. Whistlers and vents are used for this purpose, leading to the core print part of

the core

A final core manufacturing procedure is usually application of a dressing

Rules for not pre-casting holes

Holes with dimensions with precise tolerances

Holes which can be finished by drilling

Holes the pre-casting of which would endanger a casting homogeneity (misrun, cross-

section reduction)

Holes the pre-casting of which would dramatically increase costs for cleaning

Rules for sizes of pre-cast holes

Round cylindrical holes in steel castings can be pre-cast for d≥20 mm

It also depends on a wall thickness of a casting (s) in which the hole is placed. The limit

dimensions are recommended:

For straight-through holes: d < 2s ; l < d 2s < d < 3s; l<< 3d

For closed holes: d < 2s l < 0.5d 2s < d < 3s l << 2d

A length of elongated horizontal holes of small cross-sections is limited with regard to

buoyancy

For thin-walled castings from heavy alloys l < 10d; from lightweight alloys l < 12d

For thick-walled castings from heavy alloys l < 3d; from lightweight alloys l < 3d

For closed holes these values are reduced to a half or down to a third

Tab. 2. Minimal diameters of pre-cast holes for different materials and types of moulds

Casting material

Sand moulds Metal moulds Ceramic moulds

Exceptionally

Commonly

small

castings

Commonly

large castings

Gravity

casting

Pressure

casting Exceptionally

Comm

only

Steel 15 - 20 50 80 – 100 1.5 2.5

Graphite cast irons 10 – 15 20 40 15

Malleable cast iron 5 10 30

Cu alloys 12 20 30 12 2.3 – 3

Al alloys 5 20 30 6 - 12 1 – 1.5

Mg alloys 5 20 30 6 - 8 1 – 1.5

Zn alloys 5 20 30 6 10

Obr. 31 Design of gudgeons: a) gudgeon with a cut-off core print, b) gudgeon with an enlarged

diameter, with a cut-off, c,d) gudgeons with protrusions

Obr. 32 Method of attaching a core in the upper part of a mould

Obr. 33 Precision of castings and foundry clearances for assembly of a mould with a core

Obr. 34 Rounding of casting edges using cores and enlargement of thicknesses of hole ends

Obr. 35 Elimination of structure heterogeneity and flash

Obr. 36 Elimination of a cover core by enlargement of the technological allowance (right-hand

side)

Obr. 37 Elimination of a cover core by enlargement of the technological allowance (right-hand

side)

Obr. 38 Modification of a casting (left-hand side) by the elimination of a cover core

Obr. 39 Replacement of two cores (left-hand side) by one cover core (right-hand side)

Obr. 40 Variants of forming a bearing bracket

Core studs

Some cavities do not allow providing a sufficient quantity of core prints, so cores are fixed

using metal studs and spacing elements. A calculation of a size and quantity of studs is

based on a calculation of the weight of cores and metallostatic pressure acting on them.

Obr. 41 Examples of used core studs


1. Methods of core making and processing

2. Core and cover core

3. Methods of seating of cores


1. When to use a “true” core and cover core?

2. How is a core seated in a mould?

3. How is gas exhaust from cores solved?

4. Describe core making technologies.


4 PRINCIPLES OF CASTING DESIGN IN TERMS OF

DIRECTIONAL SOLIDIFICATION

Subchapters:

Basic terms

Objectives



Define particular types of inner and open shrinkages (shrinkage cavities and shrinkage

depressions)

Define a casting module, i.e. time of solidification of a riser and a casting

Define a thermal node and a thermal axis of a casting

Define a function of a riser

Define the directional solidification

Define causes of shrinkage occurrence in castings

Lecture

A basic requirement for casting manufacture is to achieve a maximum degree of their

homogeneity, i.e. without occurrence of inner (closed) cavities – shrinkage cavities and porosities.

Obr. 42 Casting section with an outer, primary and secondary shrinkage

Types of shrinkages:

1. Open - a metal level on a casting

surface is depressed due to atmospheric

pressure

2. Primary inner – closed with

underpressure (1% of a casting volume)

3. Secondary dispersed (shrinkage

porosity)

(0.5 % to 1 % of a casting volume)

Obr. 43 Section of a properly functioning riser with an outer shrinkage connected to a primary

shrinkage, and a secondary shrinkage - porosity

A purpose of the directional solidification technology is as effective localization of shrinkages

into risers as possible – the last residues of the molten metal solidify in the riser.

The solidification process is affected by a temperature gradient

In the first phase – by heat removal from the casting surface

In the second phase, in a longer interval – by metal physical properties

In thin-walled castings the velocity of heat transfer from the casting surface prevails

a, d – frontal solidification e – directional solidification - as a result of

allowance

b – partially directional solidification – influence

of thermal conductivity

f – directional solidification by outer cooling

(heating)

c – inverse directional solidification – bottom

gate

Obr. 44 Influence of the directional solidification (temperature field) on formation of shrinkages

in a steel casting

Casting solidification is affected in particular by

a) Thermal-physical properties of an alloy

b) Casting design

c) Properties of a mould and core (ability to remove heat during solidification)

a) Thermal-physical properties of an alloy – specific for each alloy and cannot be changed

Temperature of liquidus and solidus (determining the solidification interval together)

Specific weight in the liquid and solid state

Coefficient of thermal expansion

Thermal conductivity

Heat capacity

Specific latent heat of crystallization

b) Casting design

Objects with the same relative thickness have the same time of solidification under otherwise

identical conditions, the Chvorinov’s rule for predicting the solidification time of steel castings:

cast. = ( M /k )2

cast. – casting solidification time (s)

M – casting module V/S (m)

k – solidification coefficient (m.h- 0.5)

c) Properties of a mould and core – their ability to remove heat during the casting

solidification

The heat absorbing capacity of a mould bf – a complex technological criterion involving

material (sand) of a mould, ramming, moisture etc.

bf = ( . c . ρ)– 0.5 ( W. S0.5. K -1)

– thermal conductivity of a mould, core

c – specific heat capacity of a mould material

ρ – specific weight of a mould material

Obr. 45 Solidification times (s) of moulding sand mixtures with different heat absorbing

capacity coefficients

Open shrinkages – outer open depressions with crystalline and oxidized surface reach into varied

depths, the most frequently occur under improperly dimensioned risers. Shrinkage becomes a

defect, when reaching into a casting, not being located only in a riser.

Causes of shrinkage formation:

Insufficiently dimensioned riser

A thermal node without a riser

Insufficient cross-section of a riser, improper treatment of a riser

High casting temperature

Obr. 46 Schematic depiction of a shrinkage reaching into a casting

Obr. 47 Shrinkages reaching from a riser into a steel casting

Inner closed shrinkages occur in points of thermal nodes, where a principle of the directional

solidification is not observed. They are usually a continuation of an open shrinkage, the so-called

shrinkage porosities.

Elimination of closed shrinkages - shrinkage porosities consists in a proper dimensioning of a

gating system – ensuring an adequate flow rate in critical places in a casting, a positive thermal

gradient, an increase in the mould heat absorbing capacity. A maximum of thermal nodes need

to be placed in the upper part of the mould.

Solidification and volumetric shrinkage – contraction of metals

Volumetric changes during the foundry alloys solidification are accompanied by formation

of shrinkages and dispersed shrinkage porosities in castings.

A size, shape and position of shrinkages depend on foundry properties of the cast metal.

Broad interval = shrinkages; narrow solidification interval (eutectic alloys) = less risk of

shrinkage formation.

The casting temperature field should ensure the directional solidification of a casting.

Achievement of the directional solidification through solving the technological design of a casting

A casting design should respect the directional solidification principles to the maximum

extent.

Reduction of a number of hot spots – uniform wall thicknesses etc.

Application of technological allowances.

Achievement of the directional solidification through technological means:

Applicable positioning and dimensioning of risers

Directed heat absorbing capacity of a mould bf towards risers

Application of external and internal chills for acceleration of solidification

Insulation and exothermic paddings in order to extend the solidification time – particularly

for risers

A casting method – ensuring a high flow rate through the gating system, or through a

casting method (e.g. reverse casting methods)

Obr. 48 Solution of the directional solidification of a hub casting

gate vtok

riser nálitek

shrinkages staženiny

internal chills vnitřní chladítka

external chills vnější chladítka

4.1 Elimination of a size of hot spots

Reduction of a size of hot spots can be simply assessed using a sphere diameter (a circle)

inscribed in an observed place (thermal node) in a casting (Fig. 45)

A size of hot spots and the directional solidification can be determined more exactly on the

basis of a calculation of modules of individual segments of a casting (Fig. 46)

Modules of various parts of a casting should enlarge from the most distant places towards

a riser

Obr. 49 Solution of hot spots – the Heuvers’ inscribed circle method (koule=sphere)

Obr. 50 Determination of a size of hot spot through a calculation of modules of the casting

individual segments

Obr. 51 Technological allowances at a solution of a thermal node using the inscribed circle

method

a) b) c)

Obr. 52 Modification of casting design: unsatisfactory (a) improved (b) the most satisfactory (c)

Obr. 53 Directional solidification of a casting towards a riser, where shrinkage forms

Modification of a casting shape for removal of risers

A design should offer suitable and easily accessible places for attaching a riser. Risers are

difficult to place and remove on oblique and curved surfaces.

Runners of the gating system should be placed into a riser or as close to a riser as possible.

In a case of face risers on the top of a mould, this requirement may collide with a

requirement for quiet bottom filling of a mould.

Reverse casting methods

The methods enable to create an advantageous longitudinal temperature field in a casting during

the casting process. Immediately upon casting, a mould is tilted to such a position, so that the

stream face gets to as low position as possible. This way, intensely through-flow places (including

risers) are as high as possible – a casting is left to solidify in this position.

Only adjacent risers are applied in this method (i.e. to join the gating system). The methods are

applied for castings with a uniform wall thickness and for castings with thermal nodes. The main

advantage of the method is a high technological utilization of metal and very high quality of

castings.

Obr. 54 Partial (acute-angle) reversal at casting into a tilted mould

Obr. 55 Total reversal – after casting the mould is reversed by 180°

Obr. 56 Examples of improper and improved designs of hot spots of castings


1. Inner and outer shrinkage

2. Module of a casting (riser), the solidification time of a casting-riser system

3. The hot spot and thermal axis in a casting

4. The directional solidification of a casting


1. Describe types of shrinkages and methods for their elimination.

2. Describe how to eliminate a hot spot (thermal node) and thermal axis in a casting.

3. Function and positioning of a riser.

4. What is the directional solidification of a casting?


5 PRINCIPLES OF CASTING DESIGN WITH REGARD TO

STRESS IN CASTINGS

Subchapters:

Basic terms

Objectives



Define volumetric changes during solidification of foundry alloys

Define types of stresses and causes of their origination

Optimize a level of internal stresses through modifications of a casting design

Lecture

Shrinkage during a casting cooling

Volumetric changes in a casting cooling after solidification, a cause of which is thermal expansivity

and possible phase changes in the alloy, result in:

A change in dimensions

Origination of stresses in a casting

A change in a shape (deformation, warping)

Discontinuities (hot tears and cold cracks)

Types of stresses in a casting

• The particular parts of a casting neither cool, nor shrink simultaneously. Non-simultaneous cooling

and shrinking result in differences in dimensions between parts of a casting, causing either stress,

or deformation (warping).

• Shrinkage stress results from a resistance of a mould and cores at high temperatures. It depends

above all on a casting shape and also on strength and collapsibility of moulds and cores. The

resulting (delayed) shrinkage of a casting is usually less than the calculated according to

coefficients of the cast metal thermal expansion.

• Thermal stress originates in the area of elastic-plastic deformations. Parts solidifying faster

impose resistance to parts solidifying more slowly.

• Phase transformation stress results from a non-simultaneous formation of various structure

phases in different areas of a casting during a eutectoid transformation.

Thermal stress

The inner thermal stress, which increases during cooling of a casting down to normal

temperatures, originates as a result of cooling of a casting with different wall thicknesses

at the existence of the temperature gradient.

If it exceeds tensile strength, discontinuities in the material occur (high temperature rears

and cold cracks).

)(. 21 TTE

Internal stress (tension)

Internal stress leads to deformations – it is released especially at machining

Reduces a possibility to load a casting (internal stress adds to the external tension)

It is a cause of a premature casting failure due to occurrence of cold cracks

Obr. 57 Time behavior of length changes of cross-sections 1,2 ∆ l1 and ∆ l2 and their differences

(∆ l1 -∆ l2) during solidification of T - section

Obr. 58 Distortion (deformation) of various sections + tension / - compression [2]

Tab. 3. Characteristics of hottears and cold cracks

Hot tears Cold crack

Temperature at origination Above equicohesion temperature

(high temperature above solidus)

Below temperature tkr, in the area

of predominantly elastic

deformations

Time of origination By a gradual development in three

stages

Immediately (at once)

Causes of origination Mostly tension of exogenous

character

Thermal residual stresses and

transformation stresses

Influence of a casting design Low Decisive

Acoustic effect at the origination Often very loud

Shape Faceted, along grain boundaries Straight – across grains

Surface Oxidized Clean (of a specific colour)

Obr. 59 Geometry of a casting of a gear wheel – gear rim with 6 arms

Obr. 60 Beginning of the solidification – zero level of tensile stresses (brown) and an increased

compression stress (green area)

Obr. 61 End of the solidification – an increased level of tensile (light brown) as well as

compression stresses (green)

Obr. 62 Reduced tension in a gear wheel through reduction of originally 6 arms (bottom) to 5

(top)

Five-arm construction of a wheel and the adapted technology

pětiramenná konstrukce kola a upravená technologie

The original design of the construction and

technology

původní návrh konstrukce a technologie

Obr. 63 Reduced tension when connecting walls with different thicknesses – a wrong and good

solution

Application of reinforcing ribs is advisable for strengthening places where crack occurrence can

be expected. Ribs should have thinner thicknesses than connected walls, so that they solidify faster

and do not extend the time of solidification in the joint. Exceptionally even ribs with reduced

weight are used, however, their manufacture is much more costly.

Obr. 64 Examples of application of reinforcing ribs

Obr. 65 Improper design of a wheel with large differences in wall thicknesses

Obr. 66 More applicable design of a wheel with uniform wall thicknesses

Obr. 67 Improved design of a wheel with curved reinforcements eliminating uniaxial tensile

stresses

Obr. 68 Effect of stress in a belt pulley – its deformation - and a potential design solution

Obr. 69 Shrinkage process in time – a rim and hub of a cast steel belt pulley

Obr. 70 Deformation of wheel ribs by pressure of a rim (a), crack origination (b), pull-out of

ribs from the rim (c)

Obr. 71 Original (a) and improved (b) design of a wheel by a modification of shapes of

reinforcements

The most frequent cause of casting deformation is uneven cooling of particular parts and a mould

resistance to shrinkage.

Obr. 72 Elimination of deformation of plates by a design modification – strengthening of edges

and reinforcement

Obr. 73 Casting modification to eliminate shrinkage stress and crack occurrence

Obr. 74 Casting shapes with free shrinkage and shrinkage braking (mechanically and thermally)


1. Shrinkage, phase and thermal stress in castings

2. Mechanism of origination of hot tears and cold cracks

3. Construction modifications for stress elimination in castings


1. Define particular shrinkage, thermal and phase stresses in a casting.

2. Describe methods for elimination of stress in a casting.

3. Characterize causes of origination of hottears and cold cracks.

4. Describe design modifications for elimination of stress in castings.


6 PRINCIPLES OF A CASTING DESIGN IN TERMS OF

FETTLING AND FINISHING

Subchapters:

Basic terms

Objectives



Define casting design modifications to facilitate fettling

Apply principles for cost reduction of finishing procedures

Lecture

Casting fettling costs often cover 15 to 25 % of the rough casting total cost

These costs also include removal of risers and grinding

These costs can be reduced by 30 to 50 % through a design modification

These changes are often simple and non-costly

A casting design has to meet the following demands:

Avoid places where sticking of a sand mixture occurs easily

Ensure an access of a blasting mean into all cavities of a casting. Castings should not have

inaccessible cavities

If possible, a parting plane of a mould should be flat to facilitate removal of flash. If not

possible, these areas should be fitted with additional ribs onto which the flash “displaces”

Avoid thin protrusions and ribs on tiny castings from brittle materials

Ensure easy removal of risers and gating

Obr. 75 Casting design modification – improper and proper placing of a riser

Obr. 76 Improper and proper placing of a riser on a curved surface

Obr. 77 Improper and proper placing of a riser on a flat surface

Obr. 78 Elimination of places (Fig. below) with sharp inside corners, narrow grooves, dense

ribbing

Obr. 79 More applicable solution (left-hand side) of places inaccessible for cleaning

Obr. 80 Elimination of inaccessible corners through a casting design modification

Obr. 81 Displacement of flash by creating a more easily accessible rib (right-hand side)

Obr. 82 Flash formation due to core shifting – a modified solution on the right-hand side

Obr. 83 Elimination of “flash” in a core print part of a core (hatched)


1. Removal of risers

2. Elimination of flash


1. Describe principles for easy removal of cores from casting cavities.

2. Explain principles of design modifications of casting surfaces for cleaning.

3. Describe casting design modifications for elimination of flash on a casting.


Literature

[1] BEDNÁŘ, B.: Technologičnost konstrukce VI. Slévárenská ročenka,2007, s.65-76, ČSS

Brno, 2007

[2] BEDNÁŘ, B.: Slévárenství, LIII, 2005,č.5-6, s.223-228.

[3] Konstruiren + Giessen 29, 2004,H.4, s.26-28

[4] Konstruiren + Giessen 29, 2004,H.4, s.26-28

[5] BEDNÁŘ, B.: Slévárenství, LV, 2007.č. 4, 2007, s.144-148.

[6] CAMBELL,J.?: 10 Rules for Good Castings. Modern Casting, vol 87, IV/1997, s.36-39.

[7] CAMBELL,J. : Castings Practice: The Ten Rules of Castings, Elsevier Science.Oxford,

2005.

[8] ELBEL,T., HAVLÍČEK,F.:Hospodárné konstruování odlitků. Slévárenství, roč. LV, 2007,

č. 4, s. 149-155.

[9] HRBEK, A.: Navrhování litých součástí, Praha, SNTL 1965.

[10] KOŘENÝ, R.: Výrobní postupy odlitků. ES VŠB v Ostravě, 1989.

[11] ČSN 01 3061 Způsob značení postupu na výkresech pro výrobu modelových zařízení.-

07/70.

[12] ROUČKA,J. : Technická příprava výroby ve slévárnách, skriptum VUT Brno, I.vydání,

[13] Rektorát VUT v Brně, Brno 1986, 79 stran.

[14] HAVLÍČEK, F.: Konstrukce odlitků, učební pomůcka, VŠB-TU Ostrava, 1995.

[15] SKARBINSKI, M., SKARBINSKI, J.: Technologičnosť konštrukcie strojov, Alfa,

Bratislava, 1982.

[16] BEDNÁŘ, B. a kol.: Technologičnost konstrukce I, Vydavatelství ČVUT, Praha 2005.

[17] HERMAN, A., SVÁROVSKÝ, M., KOVAŘÍK, J., ROUČKA, J.: Počítačové simulace ve

slévárenství. Učební texty ČVUT Praha, Vydavatelství ČVUT, 2000.

[18] VETIŠKA, A.: Výroba a konstrukce odlitků v otázkách a odpovědích. SNTL, Praha, 1981.

[19] CAMPBELL, J.: Castings, Butterworth-Heinemann. Oxford, 2000.

[20] SCHLEGG,F.P. et al. Technology of Metalcasting , AFS Publication, 2003

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