MULTI OBJECTIVE OPTIMIZATION ON PRECISION DIE DESIGN OF HIGH PRESSURE DIE CASTING tối ưu hóa đa mục TIÊU TRONG THIẾT kế CHÍNH xác KHUÔN đúc áp lực CAO

This paper focuses on the following issues: filling simulation, defect analysis by computer aided simulation, finally the use of the Taguchi analysis to find out optimal parameters and f

MULTI-OBJECTIVE OPTIMIZATION ON PRECISION DIE DESIGN OF

HIGH PRESSURE DIE CASTING

T ỐI ƯU HÓA ĐA MỤC TIÊU TRONG THIẾT KẾ CHÍNH XÁC

KHUÔN ĐÚC ÁP LỰC CAO

Anh Tuan Do a , Tien Hung Do b

Hung Yen University of Technology and Education,

ABSTRACT

Precision high-pressure die casting (HPDC) for non-ferrous casting applications is

increasingly used in the foundries For die design of HPDC, it needs well-design of gating,

runner system, die cavity This paper focuses on the following issues: filling simulation,

defect analysis by computer aided simulation, finally the use of the Taguchi analysis to find

out optimal parameters and factors to increase the aluminum A380 die-casting quality and

efficiency After analysis the results of optimum are: gate area of 40 mm2, group 2 location of

gate, gate velocity 50 m/s, liquid alloy temperature 640°C Based on the results of calculation

parameters, we conducted design die by computer aided with the main objective is to optimize

the die design parameters The use of this integrated solution can shorten the cycle of die

design and manufacture, and result in the production of high quality die castings in the

shortest time with the biggest profit

Keywords: die design, Taguchi method, die-casting, shrinkage porosity, A380 aluminum

TÓM T ẮT

Độ chính xác đúc áp lực cao (HPDC) cho các ứng dụng đúc kim loại màu được sử dụng

trong các xưởng đúc Đối với thiết kế khuôn đúc áp lực cao, cần thiết kế tốt cổng rót, hệ thống

rãnh, lòng khuôn Bài báo này tập trung vào các vấn đề sau: mô phỏng điền đầy, phân tích lỗi

với hỗ trợ của máy tính, cuối cùng là sử dụng các phân tích Taguchi để tìm ra các thông số tối

ưu và các yếu tố để tăng chất lượng đúc và hiệu quả của hợp kim nhôm A380 Sau khi phân

tích các kết quả tối ưu là: khu vực cửa khẩu là 40 mm2, nhóm 2 vị trí của cửa khẩu, vận tốc

cổng 50 m/s, nhiệt độ hợp kim lỏng 640°C Dựa trên kết quả của các thông số tính toán,

chúng tôi tiến hành thiết kế khuôn bằng hỗ trợ của máy tính với mục tiêu chính là để tối ưu

hóa các thông số thiết kế khuôn Việc sử dụng các giải pháp tích hợp này có thể rút ngắn chu

trình thiết kế khuôn và sản xuất, và dẫn đến việc sản xuất các vật đúc khuôn chất lượng cao

trong thời gian ngắn nhất với lợi nhuận lớn nhất

Từ khóa: thiết kế khuôn, phương pháp Taguchi, đúc áp lực, xốp co ngót, nhôm A380

1 INTRODUCTION

High-pressure die casting (HPDC) process is significantly used in the industry for its

high productivity and less post-machining requirement Due to light weight and good

forming-ability, aluminum die casting plays an important role in the production of

transportation and vehicle components It has a much faster production rate in comparison to

other methods and it is an economical and efficient method for producing components with

low surface roughness and high dimensional accuracy All major aluminum automotive

components can be processed with this technology The development of industrial die-casting

and requirements for higher quality product, shorter development times and more complex

geometry, the use of computer aided simulation has become essential to stay competitive

The HPDC castings production process has many defects, such as: shrinkage porosity, misrun, cold-shut, blister, scab, hot-tear Several previous studies of defects in aluminum alloy by the method of HPDC and disability solutions Techniques such as cause-effect diagrams, design of experiments (DOE), casting simulation, if-then rules (Fuzzy Logic Controller), genetic algorithms (GA) and artificial neural networks (ANN) are used by various researchers for analysis of casting defects Dargusch et al [1] used pressure sensor in the cavity to make a confident statement of aluminum that molten metal velocity increases and porosity development with high pressure die- casting Guilherme [2] used the design of experiments (DOE) to find out the best parameters in production and notice that: porosity low indices are related with low speeds from slow and fast shots and high upset pressures Mousavi Anijdan et al [3] used genetic algorithm (GA) methods to determine the optimum conditions leading to minimum porosity in aluminum alloy die casting Tsoukalas, V.D [4,5] used the design of experiments (DOE) and genetic algorithm (GA) methods to determine the optimum conditions leading to minimum porosity in aluminum alloy die castings Syrcos, G.P [6] used Taguchi method to determine the optimum conditions leading to casting density in aluminum alloy die castings S Yue et al [7] used CAD/CAE/CAM simulation and analysis with the purpose the quality of the die castings improved greatly in a shorter time Prasad K.D.V.Y et al [8] used the artificial neural network (ANN) methods to determine the optimum conditions in aluminum alloy die castings P.K Seo et al [9] used CAD/CAE simulation and analysis with purpose minimizing the porosities and hot-spots for applying in die casting However, most researchers were used to predict solidification and optimize aluminum alloy casting process parameters in the condition of production foundry factory Little was published die design in die-casting, gating and die casting parameters Approximately 90% of defects in die casting components are due to die design errors (F Shehata [10]) Die design is

a very difficult work and the company often does not publish because of economic competition In order to good die design it requires extensive knowledge in mechanical engineering and experience in die-castings foundry factory

In this paper, the ProCAST® Software commercial is used for analysis casting defects and die filling simulation to enhance the quality and efficiency of die casting The Taguchi method control with design of experiments will be developed to improve aluminum die casting quality and productivity in the cold chamber die casting method After conducting a series of initial experiments in a controlled environment, significant factors for die casting processes are selected to find the optimal parameters to increase the aluminum die casting quality and efficiency Based on the results from analysis by considering the influence of defects on quality castings, we conducted die design to die-casting with optimal parameters It

is suggested to reduce casting defects, reduce time and money, increasing with better casting product quality and die design die-casting efficiency

2 MATERIAL AND METHODS

2.1 Basic design

Fig 1 The model 3D of automobile

Die casting of this study is provided through aluminum die-casting factory, so the casting body no changes The 3D solid model of automobile start motor casing part is shown

in Fig 1

The 3D drawings of objects cast to represent the color with different meanings Accordingly, the white light is the portion need to be machined or cut later Depending on the material molding, casting method and mechanical processing methods after casting product finished that the designer will select the size, tolerances, metal machining appropriate for requirements The nature of the material will directly affect the quality of the casting and die-casting parameters configuration, this study selects die-casting material as the aluminum alloy A380 The chemical composition of the aluminum alloy used in the experimental procedure is given in Table 1

Table 1 Chemical composition of the alloy A380 used

The die with a specific gating system will perform differently on different die-casting machines Only by considering both the die and machine characteristics could optimal flow conditions be achieved Therefore, P-Q2 technique is employed to predict the best gate area, flow rate, filling time and gate velocity This will avoid excessive calculation and ensure that the gating system is designed properly With the computer aided design software, we design the simply filling system with die casting gate and runner; therefore, there is no overflows port, gate and runner design based on the P-Q2 diagram and Bernoulliz flow according Bernoulli equation [11] In this basic study, we mainly focused on the choice of the in-gate area, location of gate and velocity of molten alloy A380 at the gate

From the 3D solid of a part is supplied and ordered from casting factory, we design the 3D of the die casting including the information of machining allowance, shrinkage and casting tolerances by using the CATIA® V5R19 software Our designs include 3 locations of gates with the basic shapes as Fig 2

Fig 2 The location of gate

The in-gate area calculation formula is as shown in formula (1):

T v

G A

g g

ρ

where: T: pouring time, Sec; G: casting weight, g;

Ag: Cross-sectional area of the gate, mm2

We can also use following formula (2) to calculation Ag as:

2 2

2 2

g d

Q A

C

ρ

where: p: metal pressure, kg/mm2

ρ: metal density, g/cm3, A380 as 2.580 g/cm3 g: Gravity (9.81 m/Sec2)

Q: liquid metal flow, mm3/Sec

v: gate velocity, m/Sec

Cd: Eject factor, aluminum is 0.5 ∼ 0.6, 0.5 used in this paper

In addition, cross-sectional area of the gate for the use of formula (1) or the ProCAST® Software commercial built in the PreCAST module to calculate for speed of molten alloy At that filling time, there is a period of liquid metal flows from the gate until the entire die cavity Based on data provided by the NADCA (North American Die Casting Association) formed by the die casting thickness of about 3.2mm, filling time between 0.42 to 0.71 seconds [11], and with the formula (1) on the design criteria for the location of the gate [12] to find the appropriate location of the gate, together with the calculated step to complete the gate system Analysis software is used as a ProCAST® commercial with finite element method (FEM) analysis for a casting process In this paper, all parameters can be able to affect the analysis process, choice of material is aluminum alloy die casting A380, cold chamber die casting method with the die material is H13 FEM based simulation software systems help the designer to visualize the metal flow in the die cavity, the temperature variation, the solidification progress, and the evolution of defects such as shrinkage porosity, cold-shut, hot-tear Z Sun et al [13] used Taguchi analysis and CAE technique to predict the filling velocity and shrinkage porosity numerically, based on the results receiving the author performed optimal parameters for the gating system D.R Gunasegaram et al [14] used the design of experiments (DOE) determined that a thicker mold coat and a higher mold temperature would modify temperature profiles in the casting Q.C Hsu et al [15] used Taguchi analysis and CAE technique to study the shrinkage porosity formation in HPDC, the authors have found these factors affect the molding process and improve quality aluminum die casting and productivity in the cold chamber die casting method This paper focused on analysis of shrinkage porosity defect, the percentage fill rate to determine the experiment

2.2 Experiment and analysis

Taguchi method is one of the solving tools to upgrade the performance of products and processes with a significant reduction in cost and time involved The Taguchi′s parameter design offers a systematic approach for optimization of various parameters with regard to performance, quality and cost (Tsoukalas, V.D [4,5], Syrcos, G.P [6])

Shrinkage porosity formation in pressure die casting is the result of a so much number

of parameters Fig 5 shows a cause and effect diagram that was constructed to identify the casting process parameters that may affect die casting porosity In this case, holding furnace temperature (Liquid alloy temperature), speed of molten alloys of the gate (Gate velocity), cross section of the gate (Gate area) and location of the gate (Gate location) were selected as the most critical in the experimental design The other parameters were kept constant in the entire experimentation Gate velocity has an influence on mechanical properties of the casting and on the properties in the casting surface quality High gate velocity produces higher mechanical properties and less porosity than lower gate velocity New High Pressure Die Casting machines are capable of producing gate velocity up to 100 m/s, but the die erosion started to increase already around 60 m/s For that reason the higher gate velocity

range from 60 m/s to 100 m/s is not very practical (F Shehata [10], ZHANG Weishan et al [16]) Based on technical parameters of high pressure die casting machine SD-500CF from LIKW Enterprise Corp-Taiwan, we select the velocity of the liquid alloy in range: 30∼50 m/s Shrinkage porosity can be reduced without raising the gate velocity by designing the gate and runner system to maintain smooth, continuous flow profiles and by designing the casting so that no backflow occurs This paper used cast material is A380 with the melting temperature is range (540∼595) °C, experiential from foundry factory range (540∼595) + (100∼120) °C is superheated the need to use Solution temperature range (640∼720) °C are selected in this paper The selected casting process parameters are calculated by formula (1), (2) and Bernoulliz flow given in Table 2

Fig 3 Fish-bone diagram

Fish-bone diagram [2], [4], [5], [6], [7], [17] of the configuration shown in Fig 3, in which the head is shrinkage porosity die casting defect, and the objective to be taken

“smaller-the-better”

According to cause and effect diagram of the factor level table, as shown in Table 2, on behalf of the L9 orthogonal array as Table 3

Table 2 Factor level table Table 3 Experimental layout using an L9

orthogonal array

For the amount of inspection shrinkage casting part used for the ViewCAST module function for quantitative analysis The parameters are taken from Table 3 and conduct nine experiments In each experiment we took five elements with the coordinates determined at the important positions in the working conditions of automobile starter motor casing Each experiment was repeated five times sampling in order to reduce experimental errors, as shown

in Fig 4 Data from nine experiments with five sampling times in each simulation are summarized as in Table 4 From this table we conducted quality characteristics analysis

Fig 4 Castings measurement

Shrinkage porosity area

Table 4 The experimental data

The parameter design study involves control and noise factors Measure of interactions between these factors with regard to robustness is signal - to - noise (S/N) ratio S/N characteristics formulated for three different categories are as follows: the bigger the better, the smaller the better, the nominal the best This paper focused on studying the effects of four input parameters (A, B, C, D) to defect shrinkage porosity in the process of casting, so the criteria "the smaller the better" is selected

The smaller the better (for making the system response as small as possible):













−

=

n

i i

n N

S

1 2 1 log 10

where:

n: number of sampling, n=5 (each experiment was repeated five times sampling);

yi: value of shrinkage porosity at each time sampling

Analog measurement data, calculated by formula (3) after sorting out the S/N response table as Table 5 and S/N response graphs in Fig 5, by the responding graph learned that the best combination in this study for aluminum die casting shrinkage defects: A3B2C1D3

Table 5 S/N response table

-4.400000 -4.300000 -4.200000 -4.100000 -4.000000 -3.900000 -3.800000 -3.700000

-3.600000 A1A2A3 B1 B2 B3 C1 C2 C3 D1D2D3

A B C D Average

Fig 5 S / N Response graphs

Analysis of variance (ANOVA): Through the contribution rate calculated results shown

in Table 5.6, and the contribution of each factor is organized in the chart, as shown in Fig 6

Table 5.6 The ANOVA table

Fig 6 Contribution rate histogram

In this study, the results of the optimum parameters via Taguchi design are: the gate area of 40 mm2, group 2 of the gate location, the speed of the liquid metal at the gate is 50 m/s, the temperature of molten aluminum 640°C The casting process simulation by ProCAST can determine the location of shrinkage formed by the temperature field and the solid fraction, and it is also to understand the reasons for the formation of defects Therefore, it can help in

further design priority to avoid shrinkage porosity defect

2.3 Computer aided die design

High pressure die casting (HPDC) with the gating system consists of a biscuit or a sprue, runners system, a gate, overflows and vents There are two basic gate types: tangential and fan-gate (Gating manual, NADCA, USA 2006 p.56 [18], S.H Wu et al [19], B.H Hu et

al [20]) Both gates are usually designed with converging cross sectional area The selection between the gate types depends on the part requirements Fan-gate is the simplest in structure and easier to machine Tangential gates are more difficult to design and machine, but the design is flexible and easy to adapt to different technical requirements The designer should ensure that the gate and runner system to maintain smooth, continuous flow profiles and by designing the casting so that no backflow occurs or two lines overlap Based on the technical side-core and molding direction we design two types of gate systems with components of a biscuit (diameter: 70 mm), a runner, a gate, overflows Two types runner is designed as Fig 7 and Fig 8 with a cross section of gate: 40 mm2

Fig 7 Die-casting with full inlet Fig 8 Die-casting with half inlet

The results of the optimum parameters via Taguchi Design will be installed in ProCAST software with parameters for two cases (full inlet and half inlet):

- gate area of 40mm2

- gate location: group 2

- speed of the liquid metal of the gate is: 50 m/s

- the temperature of molten aluminum: 640° C

- the temperature of die: 180° C

- water cooled

With full inlet filling of the liquid metal flow in the die cavity is good In case of half inlet, not fill in all the volume of die cavity, high pressure increased The shortage metal

occurs as Fig 10 mean that having a disability and the option half inlet design cannot be used for further study

Fig 9 Shortage of the casting with half

inlet Fig 10 Shrinkage porosity of the casting

with full inlet

Shrinkage porosity analysis as in Fig 10 with full inlet case shows that need additional overflows in some locations important to reduce this phenomenon shrinkage porosity Fig 11 shows solid 3D of dies with full gating system

Fig 11 3D solid model of die casting dies Fig 12 Shrinkage porosity of castings

The simulation results with the parameters setting on the ProCAST are calculated in the previous steps The result of test is the liquid metal fill in full of die cavity Fig.12 show that the casting no defects and shrinkage porosity acceptable

3 RESULTS AND DISCUSSION

The die for this study is the result of collaboration between the LIKW Enterprise Corp, Taiwan and Department of Mechanical Engineering - Hung Yen University of Technology and Education

The entire die will be installed on the SD-500 CF casting machine as Fig 13 with the parameters setting on the machine are calculated in the previous steps

Fig 13 Casting in SD-500CF die-casting machine

Fig 14 The product after casting

The product after casting to the naked eye without disabilities, show in Fig 14

Fig 15 X-ray film testing of samples casting

Tested X-ray by ERESCO 160 MF4-R machine for samples casting with parameters: 2% sensitivity, 30 Sec time exposure in the critical sections of castings Results showed no defects shrinkage porosity and no cracks inside, good quality castings, as shown in Fig 15 The results between simulation and experiment indicate that the liquid metal in the mold filling full, no cracks inside, shrinkage porosity acceptable That means the die are designed and manufactured optimization in accordance with the conditions of the foundry factory production

CONCLUSIONS

The experiments, that are conducted to determine the best levels, are based on

"Orthogonal Arrays", are balanced with respect to all control factors and minimum in number One method of casting defect analysis is proposed and studied which is a combination

of design experiments by Taguchi method and Computer aided casting simulation technique for analysis of the optimal die design

The results of the optimum parameters via Taguchi design for the gate area of 40 mm2, group 2 of the gate location, the speed of the liquid metal at the gate is 50 m/s, the temperature of molten aluminum 640° C

For analysis of defect such as shrinkage porosity computer aided casting simulation technique is the most efficient and accurate method The quality of the casting product can be efficiently improved by computer assisted casting simulation technique in the shortest possible time and without the conventional trial and error on foundry factory This in turn implies that the resources (materials, saving time and money) required for the experiments are also minimized It saves very much helpful and a great effort and money

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