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Abstract

The gating system design for a die-casting die is a non-trivial task that involves a number of steps and computations, in which many factors related to part design, material, and process need to be accounted. In case of a multi-cavity die-casting die, the non-triviality of the gating system design increases manifold. The main contribution of this article is to develop a computer-aided system for design of gating system for multi-cavity die-casting dies. The proposed system applies design knowledge and rules, accounting for various influencing factors to design gating system elements and generate their computer-aided design models in an efficient manner. To demonstrate the capabilities of the developed system, the results for an industrial case study part are presented. We expect that the proposed system would help reduce manufacturing cost and lead time, alongside bridging gaps between design and manufacturing of the die-casting process.

Keywords

Die-casting die-design multi-cavity gating system computer-aided design

Introduction

The die-casting is one of the most economical manufacturing processes for producing near net-shaped, high-precision metallic components in large volume. The parts produced by this process are widely used in products such as automobile, aerospace, and consumer goods.¹ In the die-casting process, liquid non-ferrous metal is injected in a die cavity under high pressure, and the die-cast part is ejected from the die after solidification. The die-casting die-design involves steps such as design of cavity layout, gating system design, cooling system design, core-cavity design, ejection system design, and side-core design.

The gating system is a channel or a passage in the die through which the molten metal reaches the cavities. The gating system design refers to the design of its various elements, such as gate, runner, overflow, and biscuit, which are discussed in section “Elements of gating system.” The design of a gating system is crucial because it not only affects manufacturing of the die but also the quality and cost of the parts produced.

The gating system design is a non-trivial task, which depends on the designer’s experience and technical knowledge, and requires a number of iterations, resulting in a longer lead time and increased die cost. Today, when use of computer-aided design (CAD)/computer-aided manufacturing (CAM) tools is quite common in the die-casting industry, it is desirable to develop computer-aided tools that help in the design of a gating system. With the available CAD/CAM tools, a die-designer needs to do a lot of effort and use his or her experience and heuristics for the gating system design. The die-casting industry will highly benefit if a suitable system is developed that provides step-by-step guidelines for gating system design with the instantiation from the part product model and alongside takes care of various other tasks, such as the design of cavity layout. The availability of such a system will improve consistency in the decision-making, besides significantly reducing dependency on a die-design expert.

This article presents a new system, which helps the designer to design the gating system elements and generate their CAD models for a multi-cavity die-casting die. The developed system uses a generative approach and works as an add-on application of an existing CAD software. The following paragraphs describe the important features of the developed system:

The design of the gating system is instantiated with the information about the number of cavities and cavity layout, which is derived from the system developed by Kumar et al.^2,3

The parameters of the gating system elements are generated using various factors, such as the number of cavities, material information, part application type, cavity volume, and wall thickness of the die-cast part.

The generated parameters are verified with the industry recommendations, and the information is displayed to the user with the help of a graphic user interface (GUI).

The generated gating system parameters are used to make CAD models of the gating system elements with the help of a gating feature library.

The user has the facility to modify the generated parameters as per the requirements. The effect of any change in the parameter of a gating system element (such as gate) on other gating system element (such as runner) can be quickly visualized by the user through the GUI. The user can see the effect of such change in parameters on the design of gating elements.

To help the designer, the system displays important guidelines at various steps of the gating system design. These guidelines have been compiled based on the information available from the published literature and understanding industry best practices.

The system performs P-Q² analysis to select a compatible die-casting machine for effective metal flow in the gating system elements.

The system has a good level of automation and requires minimal interference from the user to make decisions in the process of gating system design.

The rest of the article is divided into the following sections. Section “Elements of gating system” discusses the elements of the gating system. Section “Literature review, research gaps and objectives of this research” discusses literature review and objectives of this research. Section “Design guidelines for gating system design” presents important guidelines for the design of gating system elements. Section “Gating system design” deals with the gating system design that includes (1) the determination of gating system parameters, (2) generation of CAD models of the gating system elements, and (3) placement of the generated gating system elements in the die. Section “System architecture, implementation and results” discusses architecture of the developed system, system implementation, and results. Finally, section “Conclusion” discusses conclusions drawn from this research work.

Elements of gating system

Figure 1 shows the various elements of gating system of a die-casting die, which are briefly explained in the following paragraphs:

Gate: it is the entry point for the molten metal to the cavity. Generally, it provides the smallest restriction in the molten metal flow path to the cavity.

Runner: a runner (or main-runner) is the passage that connects the metal-receiving hole of the die to the gate, where the molten metal enters the cavity (or cavities). A runner can be divided into three sections:

Gate-Runner: the portion of the runner which connects to the gate is known as a gate-runner. A gate-runner leads the metal into the die cavity through the gate.

Branch-runner: a branch-runner connects the gate-runner to the main-runner.

Main-runner: the main-runner is the passage, which connects the biscuit to the branch-runners.

Overflow: an overflow is a small pocket located around the edge of the cavity. It acts as a reservoir for the first metal, which flows through the cavity. Strategically placed overflows can be used to add heat in a cold area of the die.¹

Biscuit: a biscuit is the excess of ladled metal that remains in the shot sleeve of a cold chamber die-casting machine. It is part of the cast shot and is removed from the die along with the casting.

Flow angle: flow angle is the angle at which the metal flows into the cavity. As shown in Figure 2, it is measured relative to a normal to the gate. A high flow angle may cause the metal to flow out to the sides of the cavity, and a zero flow angle indicates that the metal flows directly across the cavity from the gate.¹ Therefore, the flow angle $(φ)$ ranges between 10° and 45°. The symbols used for flow angle for fan and tangential gate-runner are ϕ_f and ϕ_t, respectively.

Figure 1.

Elements of the gating system of a die-casting die.

Figure 2.

Flow angle representation with gate-runner and cavity.

Literature review, research gaps, and objectives of this research

Here, we discuss previous attempts made by the researchers in the gating system design for die-casting dies. Previous research attempts,^4–9 to automate the design of gating system for injection molding, provide a good insight into the concept but are not directly applicable due to higher complexity of the die-casting process. A summary of the literature surveyed is also presented in Table 1 for ready reference. Later, we discuss research gaps and objectives of this research.

Table 1.

Summary of the previous literature.

Authors (year)	Issue addressed
Authors (year)	Design guidelines	Multi-cavity gating parameters	Multi-cavity CAD model	Remark
Singh et al.¹⁰ (2013)	No	No	No
Wu et al.¹¹ (2007)	No	Yes	No	Does not consider important factors, such as part application types and cavity fill time to decide gating parameters
Woon and Lee¹² (2004)	No	No	No
Yue et al.¹³ (2003)	No	No	No
Lin¹⁴ (2002)	No	No	No
Wu et al.¹⁵ (2002)	No	Yes	No	Does not determine overflow parameters. Only considers up to four numbers of cavities
Choi et al.¹⁶ (2002)	No	No	No
Fuh et al.¹⁷ (2002)	No	Yes	No	Does not determine gating parameters
Reddy et al.¹⁸ (1994)	No	Yes	No	Determination of overflow parameters was not considered. Limited to axis-symmetric components only
Weishan et al.¹⁹ (1997)	No	No	No
Hu et al.²⁰ (2000)	No	No	No

CAD: computer-aided design.

Literature review

Singh et al.¹⁰ proposed a system for the gating system design for die-casting dies, which uses process knowledge to determine different gating system parameters. It uses a feature library together with the parametric design to generate a CAD model of the gating system elements, but is limited to few features and single-cavity die-casting dies only.

Wu et al.¹¹ proposed a system for the gating system design, using API of a CAD modeling software.²¹ The system comprises databases, design modules, and design evaluation module. The system needs further enhancement since the gating design varies according to the part shape.

Woon and Lee¹² developed a prototype, die-design system that combines feature-based and constraint-based modeling in a parametric system and applies geometrical and topological information extraction technique from the part B-rep model. It helps the die-designer in layout planning of the cavities, insertion of gates, and design of the runner and overflows. However, it does not address the design of gating system parameters.

Yue et al.¹³ developed a system for design, analysis, and manufacturing of the die-casting dies for aluminum and magnesium alloys using Pro/Engineer and Magmasoft software. The design of gating system elements is carried out manually using the empirical relation. However, it does not determine parameters of the gating system.

Lin¹⁴ uses simulated annealing (SA) optimization algorithm to find out optimal position of the gate on free-form surface part. However, their study does not determine gate parameters.

Wu et al.¹⁵ developed a semi-automated approach to the gating system design of a die-casting die. The system has a user-defined gating feature library for easy retrieval and placement. However, it only considers three types of gates, two types of overflow wells, and four types of runner layouts. The system is limited to four-cavity layouts only, and the user needs to select the type of gating element and its dimensions and position.

Choi et al.¹⁶ developed an automated system for the gating system design for die-casting using AutoCAD platform. It addressed the issues of gate design, runner design, and overflow design. However, the system has applications to single-cavity layout only and does not consider undercut features.

Fuh et al.¹⁷ developed a prototype die-casting die-design system, which uses the API of Unigraphics software. The system is structured by several functional modules, namely, data initialization, cavity layout, and gating system design. It uses P-Q² approach to select the initial process parameters. However, the selection of gating system elements is user-dependent.

Reddy et al.¹⁸ developed a software package for providing intelligent assistance in several tasks involved in the design of die-casting dies. The tasks include material selection, parting line location, gating design calculations, and die layout. The gating module calculates the gating dimensions. However, the system is limited to axis-symmetric components only.

Weishan et al.¹⁹ presented a die-casting die-design system, which can determine the location, shape, and dimension of the runner and gating system. It uses the P-Q² technique to check the suitability of the die according to the process parameters. However, it does not help in the design of the gating system.

Hu et al.²⁰ developed a system to design and optimize the runner and gating system for hot chamber magnesium die-casting using Magmasoft software. They optimized runner and gating system based on the homogeneous filling pattern through visual analysis. However, the system does not consider the multi-cavity dies.

Research gaps and needs

Despite very useful work of the researchers, there are still research gaps that need to be addressed; the prominent gaps are mentioned below:

A system that interactively provides information about design rules, guidelines, and industry best practices for design of gating system elements for a die-casting die is not available.

Most of the previous systems have limited applications as far as determination of parameters of the gating system elements is concerned. This is because they do not consider important influencing factors and the maximum number of cavities is limited.

Systematic decision support to select the type of gate, runner, and overflow is not available.

A system that can determine the parameters of the gating system elements for a multi-cavity die and use that information for generating their CAD model is also lacking.

Need and motivation

After having identified the gaps in the previous research, we found that there is a need to develop a knowledge-based system, which can help in the design of gating system for multi-cavity die-casting die. The system should provide step-by-step guidelines for design of gating elements for a given part model. It should be capable to generate a CAD model of the gating system and help place it in the selected cavity layout. Furthermore, it should have a good level of automation and require minimal inputs from the user to make decisions in the process of gating system design.

With the increased use of CAD/CAM systems for die-casting die-design and manufacturing, developing a system for the gating system design of a commonly used CAD system would provide the benefit of CAD/CAM data integration.

Objectives of this article

This work is an attempt to develop a computer-aided system for design of gating system for a multi-cavity die-casting die from the part CAD model. The developed system named multi cavity die designer uses a knowledge-base of gating system design and is supported by die-casting machine and material databases. The objectives of this article are mentioned below.

Provide information to the die-designer for basic design rules, guidelines, and industry best practices interactively for the design of gating system elements.

Determine parameters of the gating system elements for a given part model in an automated manner using established gating knowledge-base with minimal interaction from the user.

Generate CAD model of the gating system elements for a multi-cavity die-casting die. Help the die-designer to place the gating system elements in the die by joining it with the existing arrangement of cavities.

The scope of this research article is to provide a system that helps the designer to design gating system elements for a multi-cavity die-casting die and generate their CAD models. The article minimizes the efforts of the designer using a structured approach that takes help from a knowledge-base of guidelines and rules that are well established in the industry and literature. The knowledge-base can be updated time-to-time as per the requirements of the industry.

Design guidelines for gating system design

While designing a gating system for a die-casting die, a number of guidelines need to be taken care of, most of which are based on the physics of the process and industry best practices. The guidelines have been compiled based on the information available from the published literature and understanding industry best practices. In the proposed system, most of the gating system design guidelines are incorporated in the system; however, some of the guidelines, which require the designer’s input, need to be taken care by the user. The guidelines are accessible to the user of the system through its GUI and are of a great help. These guidelines, which pertain to different elements of the gating system, are explained in the following paragraphs.

Gate design

The gate should be positioned to direct the flow across the shortest cavity dimension, which reduces the metal flow distance.

The gate should be so placed to use the natural part shape to direct the metal flow. In some cases, this may be an exception to guideline (1) mentioned above for choosing the shortest flow distance.

For round and oval shape cavity, the gate should be placed in such a location that central portion of the cavity be filled first.

If possible, that area of the part, which has special quality requirements, such as high surface finish and porosity, should receive direct flow and be close to the gate.

If possible, the gates should be placed along the thickest section of the part.

If possible, the gate should be away from any projections (These projections may be due to a boss or hole feature of the part, which may require a projection (negative impression of the feature) in the cavity.) that exist in the cavity.

In a multi-cavity die, where the cavities are identical, gate all of them in the same manner.

Gate height should not exceed 75% of the wall thickness of the part, which helps in trimming without distortion or break out of the part.

The ratio of the gate width to the gate height should be more than 10.

Runner design

The cross-sectional area of the runner must be larger than that of the gate to ensure an increase in flow velocity along the flow path. This reduction in the area should be smooth.

For a multi-cavity die, the cross-sectional area of the main-runner should be larger than the sum of the cross-sectional area of all the branch-runners.

The runner should always be joined with smooth bends to minimize turbulence and pressure losses.

Going upstream from the branch-runner to the main-runner, increase the runner cross-sectional area by 3%–5% at every bend and 3%–10% at a “Y” junction.

In general, the flow angle varies between 10° and 45°; however, flow angle of 30° is most commonly used.

If possible, the runner should be kept straight for half an inch just before connecting with the gate-runner.

Overflow design

An overflow should be placed at a point where the metal flow reaches the last. Alternatively, an overflow can be placed at a point where the two flows meet.

It is always better to have many modest overflows than a few large ones for the purpose of the distributed flow within the part.

The sum of out-gate (Out-gate cross-sectional area is the area of the metal’s entry to the overflow(s).) cross-sectional areas should be approximately one-half of all in-gate (In-gate cross-sectional area is the area of the gate.) cross-sectional areas.

Biscuit design

The cross-sectional area of the biscuit must be greater than the cross-sectional area of the runner.

Minimum recommended thickness for a biscuit is 20 mm.

The biscuit should be of at least the same thickness as the runner height.

Gating system design

In this section, gating system design for a multi-cavity die-casting dies is discussed. The entire process of gating system design is divided into three major steps, which are below mentioned:

Determine gating system parameters;

Generate CAD models of the gating system elements;

Place the generated gating system elements in the die.

The above-mentioned steps are discussed in the following paragraphs.

Determine gating system parameters

In this section, the steps to determine gating system elements are discussed. The determination of gating system parameters first requires determination of parameters for filling the hot metal/alloy to the cavity, such as cavity fill time, pressure, and flow velocity.

The following paragraphs discuss two important parameters, namely, cavity fill time and gate velocity. In the die-casting process, P-Q² analysis, which is often used to evaluate the performance of the die viz-a-viz the selected machine, is also discussed. The determination of parameters of the gating system elements, namely, gate, runner, overflow, and biscuit, is discussed thereafter.

Determination of cavity fill parameters

Cavity fill time $(t)$

Cavity fill time is the time required to completely fill the cavity and overflow wells. One of the well-known formulas used by the industry to calculate fill time for a given die-cast part is mentioned in equation (1)²²

t = K {\frac{T_{i} - T_{f} + SZ}{T_{f} - T_{d}}} T

(1)

where t is the maximum fill time (s), K is the empirically derived constant related to the die steel (s/mm), T_i is the metal temperature at the gate (°C), T_f is the minimum flow temperature of the metal alloy (°C), T_d is the die surface temperature just before the shot (°C), T is the wall thickness of the die-cast part (mm), S is the percent solids at the end of fill (%), and Z is the solid’s unit conversion factor (°C/%).

Gate velocity

The gate velocity influences the mechanical properties and surface quality of a die-cast part. Higher gate velocity produces better mechanical properties and less porosity. New die-casting machines are capable of producing gate velocities up to 100 m/s. However, die erosion starts to increase when the gate velocity reaches 40 m/s. Therefore, in normal practice, a gate velocity higher than 40 m/s is normally not used.

Table 2 presents recommended gate velocities based on the type of alloy and its intended application. As mentioned in the table, the gate velocity is minimum for decorative parts and maximum for pressure-tight parts, while the mean value is taken for engineering parts.

Table 2.

Recommended gate velocity for typical die-casting alloys.

Alloy	Gate velocity range (m/s)	Recommended gate velocity (m/s)
Alloy	Gate velocity range (m/s)	Decorative parts	Engineering parts	Pressure-tight parts
Aluminum	20–60	20	40	60
Zinc	30–50	30	40	50
Magnesium	40–60	40	50	60
Copper	20–50	20	35	50

P-Q² analysis

The P-Q² analysis helps to evaluate the performance of the die viz-a-viz the selected machine. Here, it is worth mentioning that the die-casting machine is selected using the algorithm developed by Kumar et al.² The machine’s characteristic curve describes the amount of pressure ( $P_{m}$ ) the machine applies to the metal at a given flow rate (Q). The metal pressure ( $P_{m}$ ) can be calculated using equation (2) after selecting the gate velocity. The gate velocity is selected by the system from the database taking into account the information of die-cast part material and part application

P_{m} = [\frac{ρ}{2 g}] x {[\frac{v_{g}}{C_{d}}]}^{2}

(2)

where P_m is the metal pressure (Pa), ρ is the metal density (kg/m³), g is the gravitational constant (m/s²), v_g is the gate velocity (m/s), and C_d is the coefficient of discharge (0.45–0.5).

The metal pressure creates a breaking force, F, which is proportional to the projected area of the cavity, A, and is found using equation (3)

F = P_{m} \times A

(3)

The breaking force should be less than the machine tonnage capacity (clamping force), and in such a case the system displays the message of P-Q² check is OK. In case the machine does not pass the P-Q² check, a die-casting machine with a higher capacity needs to be selected from the machine database, which also requires modification of cavity layout design.

Gating system parameters

In this section, the procedure to calculate parameters of the gate, runner, overflow, and biscuit is discussed. The system uses the bottom–up approach to determine gating system parameters, which means that the parameters of the gate are determined first, followed by the parameters of other gating system elements, namely, gate-runner, branch-runner, main-runner, and biscuit.

Gate parameters

A gate should be designed to make the injected metal flow smoothly into the whole of the cavity. The following paragraphs discuss the determination of gate parameters, namely, gate area, gate height, and gate width, which are critical for the injection speed of the molten metal.

Gate area

The gate area represents the cross-sectional area of a gate and is determined using equation (4)

A_{g} = \frac{V_{Part} + V_{o}}{v_{g} xt}

(4)

where A_g is the gate area (mm²), V_Part is the part volume (mm³), V_o is the overflow volume (mm³), v_g is the gate velocity (m/s), and t is the cavity fill time (s).

The procedure to determine overflow volume $(V_{o})$ is discussed later in section “Overflow parameters.” In case of a multi-cavity die, the amount of metal flowing through all the gates is the same since all the cavities are identical. The gate area for each cavity of a multi-cavity die is also determined using equation (4).

In some cases, a cavity may be provided with multiple gates to satisfy its metal filling requirements; in such situations, the gate area determined using equation (4) is divided by the number of gates of the cavity to find the cross-sectional area of each gate. However, the present system cannot handle multiple gates for a cavity.

Gate height and width

The gate height depends on the selected gate velocity and alloy density and is found using equation (5)

v_{g}^{1.707} * H_{g} * ρ ⩾ J

(5)

where H_g is the gate height (mm), $ρ$ is the alloy density (kg/m³), and J is the constant, 998,000 for aluminum, magnesium, and zinc alloys.

Equation (5) provides the minimum value of gate height. However, the user can interactively choose another suitable value of gate height that fulfills the gating requirements, in which case the gate width is modified and displayed to the user through the GUI. The developed system takes care of gate design guidelines 8 and 9 discussed in section “Gate design,” for selecting a suitable value of gate height. Typical gate height is 0.7–3 mm for aluminum alloys, 0.7–2.2 mm for magnesium alloys, 0.35–1.2 mm for zinc alloys, and 1.5–4 mm for brass alloys.

Runner parameters

The function of a runner is to deliver the metal to the gate and to generate the desired flow pattern within the cavity. The ratio of the runner area ( $A_{r}$ ) to gate area varies with the part design, which usually ranges between 1.1 and 1.4. However, a larger ratio of 1.6 is used in the case of small parts. The system by default takes the runner area as 1.4 times of the gate area.

Mostly, trapezoid and round cross-sectional shapes are used in the runners. For trapezoid shape runners, the height ( $H_{r}$ ) is calculated using equation (6).

The runner width ( $W_{r}$ ) is taken as twice of the runner height

H_{r} = \sqrt{\frac{A_{r}}{1.6}} ~ \sqrt{\frac{A_{r}}{2}}

(6)

For round shaped runners, the diameter (D) is calculated using equation (7)

D = \sqrt{\frac{4 \times A_{r}}{π}}

(7)

The area of a branch-runner is determined considering the cross-sectional areas of all the gate-runner to which it feeds the molten metal. Equations (6) and (7) are also used to determine the cross-sectional area of a branch-runner. The system takes care of the runner design guidelines (2) and (4) discussed in section “Runner design” to determine the parameters of the main-runner and branch-runner.

Overflow parameters

An overflow collects the initial contaminated metal that traverses the cavity, provides local heat to the far side of the cavity, and acts as a base for ejecting the casting from the die. The parameters of the overflow are discussed here. The shape and size of an overflow with gate-land details are shown in Figure 3. The inlet area of an overflow is approximately half of the inlet area of the cavity. The system therefore takes inlet area of an overflow $(A_{O})$ as 50% of in-gate area by default. In some cases, when more than one overflow is used for a cavity, the overflow area is divided equally to cater all overflows.

Figure 3.

Shape and size of an overflow with detail of gate-land (The shape and dimensions for the gate-land, which is the straight portion of an overflow, depend on the part material. The ranges of parameters for gate-land are as follows: A = land length (2–5 mm); B = overall length of the overflow gate (5–8 mm); C = overflow gate height (Al: 0.6–1.2 mm, Zn: 0.3–0.8 mm, Mg: 0.8–1.5 mm); angle = 30°–45°.) parameters.

The overflow width ( $W_{O}$ ) and overflow height $(H_{O})$ are calculated using equations (8) and (9), respectively, considering rectangular cross section of the overflow. Similarly, the length of the overflow is calculated by dividing the overflow volume with overflow cross-sectional area considering the cuboid shape of the overflow

W_{O} = \sqrt{A_{O}}

(8)

H_{O} = \frac{A_{O}}{W_{O}}

(9)

The overflow volume required to determine the overflow parameters depends on the factors of volume, wall thickness, shape, and surface finish requirement of the part. Table 3 provides a decision matrix to determine the overflow volume that considers the above-mentioned factors.

Table 3.

Relationship of overflow volume and part wall thickness.

Wall thickness of the die-cast part (mm)	Overflow volume (% of cavity volume)
Wall thickness of the die-cast part (mm)	Excellent surface quality	Some cold defects allowed
0.9	150	75
1.3	100	50
1.8	50	25
2.5	25	25
3.2	10	10

Biscuit parameters

A biscuit is formed by the excess of ladled metal remaining in the shot sleeve of the die-casting machine. After solidification of the metal, the biscuit becomes part of the cast shot and is removed from the die with the casting. The shape and size of the biscuit depend on the plunger of the die-casting machine. The diameter of the biscuit is always equal to the plunger diameter and is taken by the system from the machine database. A minimum value of 20 mm is recommended for biscuit thickness.

Generating CAD models of the gating system elements

In this section, the methodology for generating CAD models of the gating system elements is discussed. For generating CAD models of the gating system elements, selection of the type of gate-runner and main-runner is required. In the following paragraphs, the selection of the type of gate-runner and main-runner is discussed, followed by a discussion on the CAD model generation of the gating system elements.

Selection of a type of gate-runner and main-runner

Two types of gate-runners, namely, fan and tangential, are widely used in the die-casting dies. Normally, both types of gate-runners are designed using the concept of converging cross-sectional area. Figure 4 shows a snapshot of the fan gate-runner, whereas two types of tangential gate-runners, namely, single-tangential and double-tangential, are shown in Figure 5.

Figure 4.

Fan gate-runner.

Figure 5.

(a) Double-tangential gate-runner. (b) Single-tangential gate-runner.

The type of gate-runner is selected taking into account the factors of part shape and geometry. Table 4 shows the relationship of part shape with the selection of the type of gate-runner. Generally, a fan gate-runner is recommended when the length-to-width ratio of a cavity is close to 1, which needs a central fill pattern. The tangential gate-runner is used when the length-to-width ratio of a cavity is 1.5 or more, which needs uniform flow pattern over the entire length of the die-cast part. A double-tangential gate-runner is generally used to feed symmetrical or near-symmetrical parts. Hybrid gate-runner, which is a combination of fan and tangential gate-runner, is also used for complex shape die-cast parts to fulfill metal flow requirements. The system helps the user to select a suitable gate and runner by displaying the above-mentioned criteria to the user. The user input, such as flow angle of gate-runner, is used to determine its length. The length of the gate-runner is further used for generating its CAD model that is discussed in the next section.

Table 4.

Relationship of part shape with the selection of type of gate-runner.

Part shape	Gate-runner type
Trapezoid, square	Fan gate-runner
Parallelogram, rectangle	Tangential gate-runner
Complex shape	Hybrid gate-runner

CAD model generation of gating system elements

This section presents the methodology to generate CAD models of the gating system elements, namely, gate-runner, main-runner, overflow, and biscuit.

Gate-runner

As discussed in section “Elements of gating system,” a gate-runner is the channel or blended portion of a gating system, which connects the gate with the runner. Generating CAD model of the gate-runner is a crucial step both in the design of the gating system and manufacturing of the die. In section “Gating system design,” the determination of the gate and runner parameters is discussed; the next step is to use these parameters to generate a CAD model of the gate-runner by taking flow angle as the input. The following paragraphs discuss CAD model generation of two types of gate-runners, namely, fan and tangential.

Figure 6 shows a CAD model of a gate-runner with various transitions in the cross sections between the gate and runner sides. North American Die Casting Association (NADCA) recommends nine section profiles to get desired gate-runner,²² but use of five section profiles is also quite common in the industry. The profile of a gate-runner here means the determination of the height and width of each section. The developed system uses five section profiles to generate a CAD model of a fan gate-runner using the formulas given in Table 5.

Figure 6.

CAD model of a fan gate-runner with the cross-sectional profiles.

Table 5.

Determination of gate-runner cross-sectional profiles.

Section No.	Height	Width
1 (Runner side)	$H_{r} = A_{r} / W_{r}$	$W_{r}$
2	$H_{1} = H_{g} + 3 / 4 (H_{r} - H_{g})$	$W_{1} = [A_{g} + 3 / 4 (A_{r} - A_{g})] / H_{1}$
3	$H_{2} = H_{g} + 1 / 2 (H_{r} - H_{g})$	$W_{2} = [A_{g} + 1 / 2 (A_{r} - A_{g})] / H_{2}$
4	$H_{3} = H_{g} + 1 / 4 (H_{r} - H_{g})$	$W_{3} = [A_{g} + 1 / 4 (A_{r} - A_{g})] / H_{3}$
5 (Gate side)	$H_{g} = A_{g} / W_{g}$	$W_{g}$

A_g: gate area (mm²); H_g: gate height (mm); W_g: gate width (mm); A_r: runner area (mm²); H_r: runner height (mm); W_r: runner width (mm); $H_{1}, H_{2}, H_{3}$ and $W_{1}, W_{2}, W_{3}$ : height and width of section profile at respective section (mm).

The length of the gate-runner is determined using equation (10)

Length of gate runner = \frac{W_{g} - W_{r}}{2 \times \tan φ_{f}}

(10)

The information about the sectional profiles and length of the gate is used to generate its CAD model using specific gate-runner feature from the pre-defined feature library.

Tangential gate-runner

A tangential gate-runner tapers toward the ends, connects tangentially to the part, and has a width equal to the full length of the part. A tangential gate-runner may be curved, straight, or bent, and ideally located on the longest side of the part. It is also recommended that a tapered gate-runner be extended to provide a “shock absorber” to absorb the excess of kinetic energy, which otherwise may create localized die erosion. The shock absorber is a channel located in a tangential position of the gate, whose diameter approximates the square root of the inlet area. Figure 7 shows a tangential gate-runner with the shock absorber.

Figure 7.

Effective and actual gate area for tangential gate-runner.

Because of the flow angle, the effective gate area is smaller than the actual gate area in tangential gate-runner and is found using equation (11). As shown in Figure 7, the gate-runner cross section converges toward the gate borders because of the flow angle

\cos (φ_{t}) = \frac{Effective gate area}{Actual gate area}

(11)

The cross-sectional profile of a tangential gate-runner is shown in Figure 8. The parameters of the cross-sectional area of the tangential gate are approach angle, back wall draft angle, height, moderate width (The moderate width is the width in the middle of the profile.), and aspect ratio (The aspect ratio is the ratio of the moderate width to the height of the gate-runner.). Typical approach and back wall draft angles are 30° and 80°, respectively, and typical aspect ratio is 2. The parameters of cross-sectional profiles are generated using the equations given in Table 6, which require the values of gate-land height and flow angle. CAD model of the gate-runner is then generated using these parameters and specific feature from the pre-defined feature library. A snapshot of the CAD model for a single-tangential gate-runner is shown in Figure 9.

Figure 8.

Cross-sectional profile for tangential gate-runner.

Table 6.

Sample calculation (the calculation has been done by taking gate-land height, h_l = 2 mm, and flow angle, $φ_{t} = 45^{\circ}$ ) for gate-runner parameters.

Plane	Distance from first plane, L (mm)	Gate-runner area A = (L × h_l)/cos(ϕ_t) (mm²)	Gate-runner height h = √A/2 (mm)	Gate-runner width w = 2 × h (mm)
Fifth plane	40	113.15	7.5	15.0
Fourth plane	30	84.87	6.5	13.0
Third plane	20	56.58	5.3	10.6
Second plane	10	28.29	3.8	7.6
First plane nearest to the shock absorber	0	8	2.0 (Equal to h_l)	4.0

Figure 9.

Snapshot of CAD model of a single-tangential gate-runner.

Main-runner

The function of the main-runner is to feed sufficient molten metal to the gate-runner in the case of a single cavity die, or to the branch-runners in the case of a multi-cavity die. The shape and size of the main-runner should be determined by considering the required volume of the molten metal and path to be followed by the runner.

The shape of the main-runner cross section should be trapezoidal with side draft angle of 10°. The main-runner average width-to-height ratio is normally kept between 1 and 3, 2 being the most common. Figure 10 shows a snapshot of a runner cross section that connects with a fan gate-runner, where the average width ( $W_{r}$ )-to-height ratio ( $H_{r}$ ) is 2.

Figure 10.

Snapshot of the cross section of a main-runner connecting to a fan gate-runner.

The cross-sectional parameters of the main-runner are used along with the pre-defined feature library to generate its CAD model. It needs to be added that the runner is kept straight for half an inch just before connecting with the gate-runner while generating CAD model.

Overflow

The main gate, which directly feeds the part, acts as a restriction because it has the smallest area in the metal feeding system. The kinetic energy provided by the metal injection system to the flowing metal passing through the gate needs to be absorbed, which is done by placing a proper size overflow.

The cross-sectional profiles and length of the overflow determined using the procedure mentioned in section “Determine gating system parameters” along with the pre-defined feature library are used to generate its CAD model. Figure 11 shows a snapshot of the system-generated CAD model of an overflow along with the gate-land.

Figure 11.

Snapshot of an overflow CAD model.

Biscuit

The parameters of the biscuit are determined using the procedure already discussed in section “Determine gating system parameters.” CAD model of the biscuit is then generated using a pre-defined library of features. However, to maintain the desired pressure during metal injection, the thickness of biscuits should be modified based on the part volume.

Placement of the gating system elements

Gating system elements of a die-casting die are dimensionally and spatially dependent on each other. For example, the design of the gate-runner depends on the gate and runner cross sections. The design of a gating element needs to be modified if the other gating system element is modified. The modification in the gating system design is usually necessary, as the initial design requires changes due to low success rate of the first time design.

Once CAD models of the gating system elements are available, they need to be placed along with the cavity layout as a step toward the complete design of the die-casting die. This section discusses the steps to place the gating system elements in a multi-cavity die.

Step 1—cavity layout

Cavity layout design is one of the basic requirements to place the gating system elements in the cavity. The cavity layout design in case of a multi-cavity die includes activities, such as determine the number of cavities, orient the cavities, and place the cavities in a die-base with required clearances. All these activities depend on a number of factors influenced by the part design, material, and the die-casting machine. The system proposed in this article makes use of cavity layout design system that has been developed by the authors in their earlier work.²

Step 2—determination of possible gate location

After cavity layout is decided, the candidate sides for the gate location are determined. For this, all the possible alternatives are shortlisted and the best option is chosen by the designer. Although the system for cavity layout design takes care of the undercut position, a number of factors need to be considered for choosing the best option, such as surface finish requirement and type of feeding system.

Step 3—assemble CAD models of gating system elements

The assembly of CAD models of the gating system elements is explained in the following steps:

The gate-runners are placed at the selected locations of the part model.

The main-runner and branch-runners are assembled with the gate-runner using Boolean operations.

CAD model of the biscuit is assembled with the main-runner to complete the gating channel.

The overflows are placed at the selected location using Boolean operations.

System architecture, implementation, and results

In this section, system architecture, implementation, and results of a case study are discussed.

System architecture

This section discusses the architecture of the system for gating design for multi-cavity dies. The information flow diagram of the proposed system for gating system design for multi-cavity dies is presented in Figure 12. The following paragraphs describe the steps of the proposed system:

Load CAD file of the die-cast part, which is used to extract part information.

Determine number of cavities and display the cavity layout design.

The P-Q² check is performed for checking the suitability of the selected die-casting machine. The system shows the message of “P-Q² check is OK” or prompts the user to change the machine.

Gate parameters are determined using various factors, such as the number of cavities, material information, part application type, cavity volume, and wall thickness of die-cast part. The gate parameters are verified with the industry recommendations given in Appendix 1; however, the user is allowed to change these parameters as per his or her preference.

Runner and overflow parameters are determined. These parameters are also evaluated against the recommended values.

If the gating parameters are within the permissible range, and acceptable to the user, he or she may proceed further to generate the gating system elements.

CAD models of the gating system elements, namely, gate-runner, main-runner, overflow, and biscuit, are generated using their parameters and library of features.

CAD models of the gating system elements are assembled using SolidWorks assembly workbench using Boolean operations to generate a CAD model of gating system for a given cavity layout pattern.

Finally, filling simulation is performed to validate the gating system design and to make required modifications. The user has the option to either reselect/modify the gating parameters, or to modify/rebuild CAD models of the gating system elements for necessary improvements.

Figure 12.

Information flow diagram of the system for gating system design for multi-cavity die.

System implementation and results

In this section, first, implementation of the proposed system is discussed, followed by a discussion on the results. The results obtained from the system are also validated using process simulation.

System implementation

The development platform for the system for gating system design for multi-cavity die-casting dies is SolidWorks CAD software using its API with programming in Microsoft VB.NET. The developed system functions as an add-on application of SolidWorks and has the advantage of data integration from part design up to the complete die-design and manufacturing. Figure 12 shows the information flow diagram of the developed system. Most of the computational tasks in the gating system design procedures that need information about the cavities, material, and so on are determined with the help of the developed system. The system provides an option to the user at various steps, either to accept the system recommended parameter or input another desired value. This aspect of the developed system provides flexibility to the user and makes it more useful in an industrial environment.

The representative machine and material databases used in the developed system are given in our earlier publication.² These databases are developed using standard values taken from reliable sources such as NADCA and leading die-casting machine manufactures. The user has the option to alter these databases as per the requirements and the availability of machines and materials in a particular industry. Furthermore, the gating feature library has pre-defined features of gating elements, such as the runner and gate, which are used to generate CAD models of the gating elements on the basis of the system determined parameters.

A knowledge-base has been developed after consulting die-casting industry, available literature, and interviewing die-designers and manufacturers; this knowledge-base consists of design guidelines and thumb rules. These guidelines and rules are incorporated in the developed system by two means. Some of the guidelines are interactively displayed to the designer, enabling him or her to take care of these. Other guidelines and rules have been incorporated in the form of logical reasoning and empirical relations. Furthermore, to make the system useful for the industry, the user has the option to incorporate or modify any new guideline as per the requirements of a particular industry.

Results

The developed system has been tested on parts taken from the die-casting industry. To demonstrate the capabilities of the developed system, the results of the case study of a cylinder head cover are presented in the following paragraphs.

Case study: cylinder head cover

The die-cast part taken in this case study is an automotive part named cylinder head cover, which is shown in Figure 13. The characteristics of the part are as follows: aluminum alloy material, no undercut features in the selected parting direction, and envelope size of 82.8 mm × 65.3 mm × 15 mm (length × breadth × height). The number of cavities determined by the system is four and series layout pattern is selected with a bottom feeding system. Figure 13 shows a snapshot of the GUI of the developed system in SolidWorks platform. The system first performs the P-Q² analysis, which is shown at the bottom of the gating design parameter window. The part application type is selected as Engineering; gate type is Fan, and runner type is Trapezoidal with flow angle of 45°. The determined filling time is 0.028 s, gate area is 40.4 mm², and gate height is 0.7 mm, respectively, which is well within the industry recommended range. The runner parameters determined by the system are also within the recommended range. The recommended value/range for each of the gating parameters is also displayed for ready reference of the user. The final CAD model of the gating system is presented in Figure 14.

Figure 13.

A snapshot of the GUI of the developed system.

Figure 14.

Generated CAD model of the gating system for the cylinder head cover.

Discussion

The design of gating system for a die-cast part is an iterative process. Although, in the developed system, sufficient knowledge is provided to facilitate decision-making at different stages, it may still require alterations/modifications by an experienced user. To take care of this aspect, enough flexibility is provided in the system for the user to alter suggested decisions interactively, which makes the system quite useful and practicable.

Validation

The gating system design needs to be evaluated for the desired level of performance. The primary performance required here is the complete filling of the cavity in the desired time. The design of a gating system is generally evaluated in two stages, which are mentioned below:

Evaluation of parameters and visual inspection: this is a preliminary evaluation of the gating system, which is normally based on thumb rules, knowledge, experience, and judgments.

Process simulation: the metal filling process is simulated under the recommended boundary conditions. This provides sufficient information to the user: about the effectiveness of the gating system design, to understand the metal filling pattern, and to decide if any design modifications are required.

To validate the gating system design, the above-mentioned two steps were used to evaluate the gating system design generated by the system in the following manner:

The opinion of the die-casting experts on the system-generated gating system design was taken. The experts suggested only cosmetic changes in the system-generated design of the gating system.

Metal filling simulation was conducted using a die-casting process simulation software. The filling pattern results for the case study part at four time intervals (out of the available 340) during filling are shown in Figure 15. Die-casting expert’s opinion on the filling pattern was also taken, who gave a positive feedback on the success of the system-generated gating system design. The quality of the metal filling pattern is generally evaluated by the amount of turbulence in the molten metal flow and temperature drop of the molten metal within the die. The molten metal flow in the cavities and gating elements should be turbulence free, and the temperature drop of the molten metal during filling should always be above solidus temperature; both the conditions are fulfilled in this case study.

Figure 15.

Snapshots of filling pattern of cavities at different time steps: (a) at 0.833 s, (b) at 0.841 s, (c) at 0.850 s, and (d) at 0.853 s.

Conclusion

A system for the gating system design of a multi-cavity die-casting die has been developed. The gating system design guidelines, the determination of gating system parameters, CAD model generation of the gating system elements, and placement of the gating system in a selected cavity layout are discussed in detail. The architecture of the developed system is also discussed in detail. The developed system is tested for industrial die-cast parts and the results of a case study part are demonstrated. The developed system uses SolidWorks part file along with the user interaction to generate elements of the gating system for a multi-cavity die-casting dies using a gating feature library. The developed system is an effort to integrate die-casting die-design application into the existing CAD software.

The gating system design is central to die-casting technology. There is perhaps no skill more important to a die-casting die-designer than the ability to design an effective gating system. The design of gating system for a die-cast part may vary as per the designer’s experience, die-casting machine limitations, delivery requirements, and cost factors. The developed system blends the die-casting die-design rules and the industry best practices, along with the flexibility desired by a die-designer in a CAD system environment, and proves to be an effective tool in the hands of a die-designer. Development of systems for die-design for various near net-shape processes^23–31 brings the advantages of lower lead time besides reducing the effort of the die-designers. The developed system significantly reduces the time required for the design of gating system, needs little user interaction, and is very much useful for the industry.

It is assumed that the parting direction is already known to the user. Combining the system presented in the article along with the previously developed systems that address automatic determination of parting direction,^32–36 identification of undercut features and their location^37–39 in an automated manner would make the system more useful and significantly increase the level of automation. Some other characteristics which affect die-cast part quality that have not been considered in the present system are as follows: (1) die runs too hot or too cold due to spray conditions, water flow, hot oil temperature, and so on and (2) the process runs with an inconsistent cycle time.⁴⁰

Design of a multi-cavity die-casting die needs consideration of new characteristics and parameters. The system should also provide a platform to extract new rules and knowledge for improvement of the said design. The authors plan to take such issues in their future research work.

Footnotes

Appendix 1 Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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A system for computer-aided gating design for multi-cavity die-casting dies

Abstract

Keywords

Introduction

Elements of gating system

Literature review, research gaps, and objectives of this research

Literature review

Research gaps and needs

Need and motivation

Objectives of this article

Design guidelines for gating system design

Gate design

Runner design

Overflow design

Biscuit design

Gating system design

Determine gating system parameters

Determination of cavity fill parameters

Cavity fill time ( t )

Gate velocity

P-Q2 analysis

Gating system parameters

Gate parameters

Gate area

Gate height and width

Runner parameters

Overflow parameters

Biscuit parameters

Generating CAD models of the gating system elements

Selection of a type of gate-runner and main-runner

CAD model generation of gating system elements

Gate-runner

Tangential gate-runner

Main-runner

Overflow

Biscuit

Placement of the gating system elements

Step 1—cavity layout

Step 2—determination of possible gate location

Step 3—assemble CAD models of gating system elements

System architecture, implementation, and results

System architecture

System implementation and results

System implementation

Results

Case study: cylinder head cover

Discussion

Validation

Conclusion

Footnotes

Appendix 1

Declaration of conflicting interests

Funding

References

Cavity fill time $(t)$

P-Q² analysis