Die Casting Design

8/2/2019 Die Casting Design

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A Study on Development of Die Design System for Diecasting

J.C. Choi*, T.H. Kwon**, J.H. Park**, J.H. Kim**, C.H. Kim***

* Dept. of Mechanical Design Engineering, ERC for NSDM at Pusan Nat'l University

** Graduate School, Dept. of Precision Mechanical Engineering at Pusan Nat'l University

*** Dept. of Mechanical Engineering, Dong-eui University

Abstract

Diecasting is one of the forming methods to manufacture large number of products with short period time

and clean surface by high injection pressure of cast alloy. Die design is composed of selection of cast alloy,

design of product, runner and gate design etc. In reality, however, die design of diecasting has been performed by

trial and error method, which cause economic and time loss. This paper describes a research work of developing

computer-aided design of product and die design. Approach to the CAD system has been written in Auto LISP

on the AutoCAD with personal computer.

In this study, die design system of die casting process has been developed to present flow chart for

automation of die design, especially runner-gate system. As generation process and die design system using 3-D

geometry handling are integrated with technology of process planning, die design is possible to be automated. In

addition, specific rules and equations for the runner-gate system have been presented to avoid too many trials

and errors with expensive equipment. It is possible for engineers to make automatic and efficient die design of

diecasting and it will result in reduction of required expenses and time. An example is applied to cap-shaped

product, motor pulley product using proposed flow chart.

Key words : Die casting, Die design system, Rule base, Runner, Gate

Nomenclature

Qa volume of cavity to be filled, cm3

Vg main gate velocity, m/sec

tg filling time, sec

K heat capacity per unit volume, cal

q' the rate heat evolved per unit time during solidification, cal/sec

L latent heat during solidification, cal/g

Cp specific heat of molten metal, cal/g

Tm temperature of molten metal,

Ts solidus temperature,


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Td die temperature,

density of alloy, g/cm3

S radiation area, cm

2

X a half thickness of cast, cm

thermal conductivity of alloy, cal/cm sec

1. Introduction

Die-cast components are being used increasingly in the automobile, aerospace, electronic and other

industries after Doehler manufactured diecasting product by using Al alloys in 1915[1]. Diecasting is not

suitable for a small quantity production because of the high cost. But it has various advantages such as

manufacturing products of complex geometry and thin-wall sections, high productivity, smooth surface of cast

and excellent dimensional accuracy. Therefore diecasting process is developing sharply with establish thousands

of diecasting machines.

Diecasting die design consists of the selection of materials for diecasting alloys, the application of shrinkage, and

the casting plan including designs of cast, gate, runner and overflow. While manufacturing die design is highly

demanded for high precision and shorts the date of delivery, in most of the case, it is designed by determining

product geometry. So it is needed experienced know-how and experts who have a skill for manufacturing die.

In result, such diecasting die design has much economical losses and wastes of time by trial and error method.

Therefore it constructs DB from know-how, designs automatic shape of die and makes a 3D modeling for

diecasting die design & manufacturing by introducing CAD/CAM system.

Diecasting die design includes a process of determining geometrical figure of the product and die and

selecting condition for forming products. Mechanical and external quality of the ultimate diecasting product is

determined by interaction of each variables of the design. Therefore the die designer has to design after due

consideration of the problems that can be caused at the time of production. The traditional die design has been

carried out a designer who experienced for many years and followed a process of trial and error that happens in

the time from designing product and die to producing the ultimate product. Such processes cause the term of

production to extend and have the prime cost rise. As a result, there have been attempts to reduce them in various

ways.

One of them is construction of system that assists initial step developing diecasting product and die

design CAD system. The other is finding formability of product and mechanical defects before manufacturing

process and considering the countermeasure in advance by simulating diecasting process. In the latter study of

diecasting process, C.C Thai used runner-optimization design method and the abdicative network in modeling

the diecasting process according to the experimental data [2,3]. Generally speaking, die design still depends on

experience, due to lack of analytical ability in die and melting metal flow and heat transfer. Current shop floor

practice uses the trial-and-error method to determine die design, when new molds are used. This method is costly


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and results in a lot of wasted casting. To solve this problem a study was done on the runner and gating system to

simulate the molten metal flow and to analyze the pressure and metal movement during the casting process [4].

Although some finite element analysis software is capable of analyzing the melting process and flow conditions

of the products (workpiece) under various injection conditions, they are only giving some limited suggestions

and information to die design.

This research is the former and study on such die design system. W. Zhang et. al. [5] built the applicable

concept of CAD/CAE system for diecasting using by CAD package. J. P. Kruth et. al. [6] applied CAD/CAM

system to mold design. Yuh-Min Chen et. al. [7] developed CAD system using feature-based geometry design

for net shape manufacturing, diecasting and injection mold process. Kishinami T. et. al. [8] developed

CAD/CAM system for modeling of mold cavity and machine manufacturing. Walsham P. A. et. al. [9] developed

the geometry modeling system of CAM for die or mold. These researches are limited to CAD/CAM system for

injection molding. Therefore, so far, the cases applied CAD/CAM system for diecasting die design is scarce. In

this research, we apply CAD system for diecasting die design.

Diecasters usually carry out the diecasting experiments before producing new casts. At the diecasting

stages, the runner-gate part is always repeatedly corrected, which leads to a lengthened processing time and

increased processing cost. The diecasting die design should consider component system factors, such as runner,

gate, biscuit, over flow and airvent. A large amount of experience is essential in manual assessment and if the

design is defective, much time and a great deal of efforts will be wasted in the modification of the die. Thus

human negligence should be minimized.

In this study, die design system for diecasting process has been developed to present algorithm for

automation of die design, especially runner-gate system. In addition, specific rules and equations for runner-gate

system have been presented to avoid too many trials and errors with expensive equipment. It is possible for

engineers to make automatic and efficient die design of diecasting and it will result in reduction of expense and

time to be required. And we developed CAD system for diecasting die design by AutoLISP language under

AutoCAD using proposed algorithm and the database. The detailed contents of the research are described in the

following.

2. Algorithm for die design of diecasting

As shown in Fig. 1, die design is roughly composed of cast design, die layout design and die generation.

At first, 3D geometry of the cast is input and the design of the cast is begun. Each parts such as gate, runner,

overflow and airvent are determined using rule base. After the parts assembled with the cast, the final dies can be

generated.

First of all, the cast must be designed because the dies can be generated from the cast in diecasting die

design. The cast design consists of three parts; cast input, material selection and application shrinkage. In cast

input part, the cast modeling in commercial modeler as IGES file format is input. The input cast is located fitting


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viewpoint from desirable direction. And the parting surface should be determined for detailed die design for

diecasting. But the algorithm that determines the parting surface is not constructed, and in this system it is

supposed that user recognizes the location of parting surface in advance. After inputting the cast in this system,

the material of the cast should be selected. Next, the cast should be applied to shrinkage. The flowchart of cast

design is shown in Fig. 2.

When the cast design is completed, the die layout design for constructing master mold is accomplished.

In the process of die layout design, the gate, runner and overflow are designed for constructing dies. In this

system, the die layout design is divided four parts; gate design, runner design, runner-gate design and overflow

design. In gate design part, the properties are input for gate design and the gate sectional area is determined by

filling speed and time. The runner sectional area is determined by gate its in runner design. The part of

connecting gate and runner can be designed and assembled with cast in runner-gate system. And the overflow

can be designed with an algorithm that is similar with runner-gate system. Fig. 3 shows the flowchart of this

system.

As shown in Fig. 4, the diecasting dies can be generated. The cavity block should be generated first by

using the cast for generating diecasting dies. Hence, it is needed that the cast should be recognized. That is, the

minimum and maximum values of cast geometry should be recognized.

The following is the technique of the geometry recognition. The geometry of cast consists of the line, arc,

circle and spline. The geometry recognition of cast can be made from the understanding this entity information.

The minimum and maximum values of cast can be calculated by changing the current WCS values of this entity

from these of UCS. Here, this transformation is carried out by trans function from AutoLISP. The following is

the detailed content of this function.

But the other entity except line can be generated after defining the essential plan. Specifies the 3D

normal unit vector for this entity. This normal vector is the Z coordinate of OCS of the given entity. Therefore,

the OCS values of this entity should be diverted to WCS values using this function after diverting to UCS values.

Here, the changing UCS values from OCS values are carried out by Z-axis of UCS option. In this process, the

OCS values of this entity are converted into UCS values. And the technique of changing WCS values from UCS

values is equal to line entity. The cast is recognized by this process. Also, the algorithm of geometry recognition

is used for the die generation. That is, this algorithm is used for die splitting.

The cavity block can be generated by geometry recognition and rule base. After generating the cavity

block, the type of dies is determined according to the geometry of the cast. In this system, the types of dies are

set up in two types. Thus, One of them is the case that the cast is located at one side of dies and the other is the

case that the product is divided by parting surface. Here, because of difficulty of detailed geometry recognition

user can determine the selection of die. Consequently, the cavity block is generated and the type of dies is

selected, and ultimately the dies can be generated.


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3. Data Base for die design of diecasting

3.1 Material and Shrinkage DB

Most of the diecasting processes are used to shape or form parts made from both ferrous and nonferrous

metals, principally aluminum, magnesium, and zinc. In this research, it used aluminum alloys. The physical and

mechanical properties of Al alloys are illustrated Table 1.

In establishing dimensions for cavities, an allowance must be added to the dimensions specified for the part

to be cast, for shrinkage of the casting metal. The shrinkage allowances normally used are: 0.005in. per inch for

zinc alloys, 0.006in. per inch for aluminum alloys, and 0.007in. per inch for magnesium alloys. Shrinkage

allowances for copper alloys vary from 0.008 to 0.018 in. per inch, the allowance used depending largely on

foundry experience with the type of alloy being cast. The above values are influenced by several variables,

primarily size and shape of the casting. For castings that have irregular surface contours, die sections and cores

are designed to prevent free shrinkage in specific areas. Die sections or cores so designed are often called shrink

resistors.

For close-tolerance castings, it may be necessary to make an allowance for the expansion of the die cavity

caused by the difference in the temperature at which it was made and the operating temperature. In general, the

calculation of shrinkage allowances at room temperature is illustrated below equation.

)20()20( = tTL (1)

3.2 Gate and Runner DB

The main function of the runner and gating system is to deliver molten metal passed into the mold into

all section of the molten cavity. First, casting material is selected and cavity volume is calculated. Once

mechanical properties of cast are input and filling speed is selected, the gate area is generated.

Table 2 shows the Filling speed according to minimum thickness of cast. The cross-sectional area of the

gate Ag is shown by equation (2).

gg

a

gtV

QA

= (2)

The filling time of die cavity tg is assigned to be that a fraction of solidus comes up to 70 %.

Heat capacity per unit volume, K is given by

XSTTCLKsmp

+= )]([ (3)


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The flow rate heat per unit time, q'is given by

XTTSqdm

/)( = (4)

From the equation (3) and (4), filling time, tg can be obtained.

7.0

=

q

Ktg

(5)

Generally, the gate thickness, t is selected properly, which is between 0.5 and 3.0mm, considering

trimming etc. The width of gateL is determined by following equation from gate area calculated by equation (2).

t

AL

g= (6)

Standards proportions for runner configurations, as established within reasonable limits, are shown in

Fig. 5. To obtain gate-controlled fill of the die cavity, the cross-sectional area of a runner must be larger than

of the gate. However, for minimum heat loss, metal velocity in the runner feeding a gate must be as high as

possible. For these reasons, a runner-to-gate area ratio of 1.15:1 to 1.5:1 is generally used. Oversize runners will

increase metal losses and remelting costs.

Runners should be designed with a stepped increase in cross-sectional area from the gate via branch

runners to main runners, and on to sprue or biscuit, to promote uniform metal velocities and uniform ratios of

cross section to perimeter. The cross-sectional area of a feed runner is equal to, or less than, the sum of the cross-

sectional areas of the branch runners.

On runners of different lengths feeding identical parts, the longest runner should be given a slightly

larger cross section. A runner that converges into a long gate should increase in cross section toward the feed

runner, to keep metal velocities as uniform as possible. Theoretically, these runners should taper out at the ends

to the thickness of the gate, but practical considerations require a compromise. Turns and leading edges should

have generous radii and should be smoothly blended where thickness or width changes occur. Runners should

have a reasonably smooth surface finish.

A thick runner will not solidify fast enough for the cycling rates generally used. A thin, flat runner will

cause the metal to lose too much heat before it enters the gate. As a compromise, a standard width-to-depth ratio

of 1.6:1 to 1.8:1 , side angle is 10~20 and corner radius is over 6mm. has been adopted. This ratio provides for

reasonably fast cooling without excessive heat loss during cavity filling. And then the shape of runner is selected

from database. The width and depth of runner varies with the volume of metal to be injected into the cavity.

Various shapes of a runner are illustrated in Fig. 6.

3.3 Overflow, Airvent and Cavity block DB

The placing of overflows is generally predictable, and their location and size are designed into the gating

system of a die. However, the addition or relocation of overflows is the most frequent cause of failure in the 15%


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of dies for which first-shot success is not achieved. The weight of metal in overflows should be added to the part

weight in calculating the total weight of metal flowing through the gate. Details the shape of overflow are

illustrated in Fig. 7.

Airvent on the die faces usually lead out of overflows. The total of the cross-sectional areas of vents

should be at least 50% of the gate area. Self-cleaning of vents can be ensured by making vents 20 30mm thick,

0.1 0.15mm length. Venting may also be provided by small grooves cut across the parting plane of the die, or

by the clearance around the ejector pins or movable cores and slides.

The shape of the finished component determines the design of a diecasting die. But there are a number of

aspects involved in the design and sizing of a die, which can have an influence and important bearing on die life.

Details the shape of cavity block are illustrated in Fig. 8 [10].

4. Application of system and consideration

4.1 Application of cap-shaped product

The constructed system is applied to some examples as the type of dies in this research. At first, this

system is applied to the cap-shaped product that has one side dies type. As shown in Fig. 9(a), this product is

modeled using by commercial modeler, Pro/Engineer 2000i for diecasting die design.

The geometrical feature of the cap-shaped product is that the parts assembled runner-gate is the plane. In

this case it is simple to apply. And the inner geometry of the cast should be the geometry of die because the type

of dies is one side type. But the recognition of the inner geometry is not accomplished. Therefore, the user

should recognize it.

The geometry that designed the cast and die layout is shown in Fig. 9(b). Here, the ultimate dies are

generated as shown in Fig. 9(c) through the geometry recognition of cast, runner-gate and overflow. In this

system the other parts of dies are not considered.

4.2 Application of motor pulley product

Next, this system is applied to the motor pulley product that has both side dies type. As shown in Fig.

10(a), this product is modeled using by commercial modeler, Pro/Engineer 2000i for diecasting die design.

The geometrical feature of the cap-shaped product is that the parts assembled runner-gate is the cylindrical

plane. In this case, the shape of gate should be modified fitting the cylindrical plane. And the product should be

split the parting surface for generating the dies.

The geometry that designed the cast and die layout is shown in Fig. 10(b). Here, the ultimate dies are


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generated as shown in Fig. 10(c) through the geometry recognition of cast, runner-gate and overflow.

5. Conclusions

The study developed an automated CAD system for die design of diecasting. The primary conclusions of

this study are as follows.

1. This study suggested an algorithm for easy and effective die design system that the die

designer can design diecasting die, especially runner-gating system.

2. This system is constructed using proposed die design algorithm and database in the

circumstance AutoCAD.

3. The constructed system was applied to some examples as the type of dies in this research.

At first, this system was applied to the cap-shaped product that has one side dies type. Next,

this system was applied to the motor pulley product that has both side dies type.

4. A novice who may not have any experience of die design can perform die design only if he

has a little knowledge about diecasting. This system quantifies practical knowledge and

experiences in die designing of diecasting as formulating procedure of design.

Henceforth, the research assignment needs the supplementation of various details that are not considered in this

system. That is, the system that the product having the undercut can be applied should be constructed. And in

this system, the part of user selection should be replaced with accomplishment by an algorithm. Moreover, this

system should be applied to not only the single-impression dies but also multiple impression dies.

6. References

[1] H.H. Doehler, "Diecasting", McGraw-Hill Book Company, 1951.

[2] C. C Tai, J. C Lin, "A runner-optimization design study of a die-casting die", Journal of Materials

Processing Technology, Vol. 84, pp. 1-12, 1998.

[3] C. C Tai, J. C Lin, "The optimal position for the injection gate of a die-casting die, Journal of Materials


[4] Shamsuddin Sulaiman and Tham Chee Keen, "Flow analysis along and gating system of a casting

process", Journal of Materials Processing Technology, Vol. 63, pp. 690-695, 1997.

[5] W. Zhang, S. Xiong, B. Liu, "Study on a CAD/CAM System of Diecasting", Journal of Materials


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[6] J.P. Kruth, "Steps Toward an Integrated CAD/CAM System for Mold Design and Manufacture:

Anisotropic Shrinkage, Component Library and Link to NC Machining and EDM", Annals of the CIRP,

Vol. 35, 1986.

[7] Yuh-Min Chen and Ching-Ling Wei, Compu ter-aided feature-based design for net shape manufacturing,

Computer Integrated Manufacturing System, Vol. 10, No. 2, pp. 147-164, 1997.

[8] KISHINAMI T., et. al., "Development of Interactive Mold Cavity CAD/CAM System", CIRP Annals, Vol.

32, No. 1, pp. 345-349, 1983.

[9] WALSHAM P.A., et. al.., Further Developments of a Geometric Modeling System for the Computer

Aided Manufacture of Dies and Molds , CIRP Annals, Vol. 32, No. 1, pp. 339-342, 1983.

[10] John Worbye, "New Information Points the way to Longer Diecasting Die Life", Diecasting Engineer, pp.

42-54


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ADC1 ADC3 ADC5 ADC6 ADC10 ADC12 ADC14

Density

(Mg/m

3

)

2.65 2.63 2.57 2.65 2.71 2.68 2.73

Specific heat

(KJ/kg/K)

0.96 0.96 0.96 - 0.96 0.96 -

Melting range

(K)

847-855 830-869 808-894 871-913 810-866 788-855 780-921

Coefficient of

thermal

expansion

(10/K)

21.4 22.0 25.0 25.0 21.8 21.0 27.0

Thermal

conductivity

(J/cm/s/K)

1.21 1.13 0.96 1.38 0.96 0.96 1.34

Latent heat

(KJ/kg)

- - - - 394.8 394.8 -

Tensile

strength

(N/mm2)

290 320 310 280 320 310 320

0.2% offset

strength

(N/mm2)

130 170 190 - 160 150 250

Elongation

(%)

3.5 3.5 5.0 10.0 3.5 3.5 -

Table 1 Physical and mechanical properties of aluminum diecasting alloys

Filling speed (m/s )

Minimum thickness (mm)

ADC1 ADC12

1.270 45 46.2

1.905 42 43.5

2.540 40.5 42

3.175 39 40.5


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3.810 37.5 39

4.572 36 37.5

5.080 34.5 36

6.350 31.5 33

Die Temp. 260 C 260 C

Table 2 Filling speed according to minimum thickness of cast

Cast des ign Die Generation

Rule Bas e for dieca sting die

des ign

Die Layout

Design

Cast Input

(3D Wire-

frame )

Material

Selection

Apply

Shrinkage

Gate

Design

Runner

Design

Runner-

Gate

s y s t e m

Overflow

Design

Cavity

Block

Design

Die type

- One side

- Both side

Die

Generation

Fig. 1 Flowchart of die design system for diecasting


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Cast Input Apply ShrinkageMaterial

Selection

IGES file input

( by commercial

modeler)

Aluminum alloy

Zinc alloy

Mag nes ium alloy

Change View

point

Determination of

Parting Surface

( use r )

Mechanical ,

Physical

Propert ies

Calculate

shrinkage (s)

Apply Shrinkage

- Sca ling fac tor

(1+s)

Fig. 2 Flowchart for cast design

Gate

D e s ig nR u n n e r -G a te

S y s t e m

Runner

D e s ig n

Calculate Filling

S p e e d

( by min imum

th ickness )

Ca lcu la t ion o f

runner a rea

( b y g a t e a r e a )

Calculate Filling

Time

Dete rmina tion o f

g a t e a r e a

Se lec t ion

ru n n e r- g a t e t y p e

Dete rmina tion o f

spec if icd im e n s io n

( use r )

Overflow

D e s ig n

Input Value for

g a t e d e s ig n

Se lec t ion o f

g a t e t h i c kn e s s

Dete rmina tion o f

ga te wid th

Se lec t ion

normal line of

pa rt ing surface

Se lec t ion

overflow type

Dete rmina tion o f

spec if icd im e n s io n

( ru le base )

Se lec t ion

normal line of

pa rt ing surface

Se lec t ion

part ing surface

Se lec t ion

part ing surface

Fig. 3 Flowchart for die layout design


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Cavity Block

Design

Die

Generat ionDie Type

Recog ni tion of

c a s t

Determination

die type

- O ne s id e typ e

- Bo th s id e t yp e

Calculate

maximum,

minimum value

Determination of

Cavity Block

Recog nit ion of

s h a p e

Die Generation

Fig. 4 Flowchart for die generation

Width(W)

Radius(R)

Depth(D)

Side Angle

Fig. 5 Schematic drawing of general section shape for runner


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Fig. 6 Schematic drawing of runner type

Cavity

Overf low0.5-0.8mm

3 - 8m m

30 - 45

Fig. 7 Schematic drawing of general shape for overflow


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AB

C

Cavity B lo ck

CastRunner-gate

C : A = 2 : 1

B : A = 3 : 1

Fig. 8 Schematic drawing of general shape for cavity block

(a)


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(b)


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(c)

Fig. 9 Application the developed system for cap-shaped product


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(a)

(b)


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(c)

Fig. 10 Application the developed system for motor pulley product


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Die Casting Design