Die casting mold design case: Aluminum alloy flange cover

figure 1 Aluminum die casting flange cover 2D dimensional drawing

An aluminum alloy flange cover is a commonly used part in equipment manufacturing. The part requires high dimensional accuracy, a glossy surface, good denseness, no shrinkage and other defects, and mass production. Pressure casting, referred to as die casting, is a precision casting method that fills the molten metal liquid into the mold cavity at high speed and makes the molten metal liquid cool rapidly under high pressure, thus forming. Die-casting molding process has the characteristics of high dimensional accuracy, surface accuracy, dense die casting organization, high production efficiency, and can achieve the metal parts molding with less cutting or even no cutting.

This article takes the aluminum alloy flange cover die-casting mold as the design object, and the two-dimensional dimensions of the part are shown in Figure 1. For the structural characteristics of the aluminum alloy flange cover, the three-dimensional structure design of the die casting mold is carried out based on the analysis of its molding processability.

Table of Contents

Die casting structure processability analysis

The aluminum alloy flange covers a 3D structure, as shown in Figure 2. The die casting annual design output of 50,000 pieces, material for aluminum alloy ADC12, domestic grade YZAl Si11Cu3, the shrinkage rate of 0.5%, 2.7g/cm3, pouring temperature of 650 ± 20 ℃. The die-casting wall thickness is generally uniform. The overall wall thickness is 2mm; the maximum external dimensions are: 100×90×30mm; the die casting structure is more complex, there are internal through holes, the hole diameter is about 24mm, the depth is about 50mm, the draft slope is 1°; at the same time, there is a diameter of about ϕ50mm sphere inside, so the die casting mold needs to design the side core extraction mechanism. The die casting has high requirements for air tightness and cannot have casting defects such as shrinkage, shrinkage, cracks, and hard partition.

figure 2 Aluminum die casting flange cover 3D dimensional drawing

Die casting molding process analysis

The mold adopts a mold two cavities, the initial choice of 280t force horizontal cold chamber die-casting machine, considering the complexity of the product structure and gas tightness requirements pressure injection ratio pressure to take 116MPa, filling speed 75m/s, injection pressurization time for 6s, cooling time for 8s. Die-casting machine’s main parameters as shown as follow.

Mold clamping force/kN

Mould thickness / mm

Inside distance of goring column /mm

Compression force/kN

Hammer head direct/mm

2800

250~650

560*560

330

60

Injection volume/kg

Diameter of pressure injection chamber flange/mm

Height of pressure injection chamber flange protruding from shaping plate/mm

1.5

101.6

10

 

Mold main structure design analysis

Selection of parting surface

The parting surface is the surface of the moving and fixed die separation. The parting surface should be selected at the largest die casting profile size to ensure the die casting size accuracy and surface quality. The die casting parting surface selection as shown in Figure 3, the parting surface is located at the largest cross-section of the die casting, while conducive to the die casting to stay on the moving die, to facilitate mold processing.

Cavity number determination and layout by measurement

the die casting volume of 33.8cm3, mass of 91.3g, the projection area on the parting surface for 27.7 c㎡. die casting machine injection volume selection for 1.5kg, clamping force of 2 Considering the economy and equipment, the cavity design of one mold and two cavities is adopted, and the cavity arrangement is shown in Figure 4.

figure 4 Cavity layout

Design of the casting system

Structure design of pouring system

The pouring system is the channel for the metal liquid to enter the cavity. The main function is to introduce the metal liquid and transfer the pressure, which generally consists of straight sprue, cross sprue, inner gate, and material handle. Aluminum alloy flange cover requires dense internal organization and high dimensional accuracy. The pouring system has a great influence on molding quality. From the straight sprue to the cross sprue and then to the gate, the cross-sectional area is gradually reduced, which can not only locally pressurize the flowing metal liquid and promote the flow of metal liquid but also reduce the contact between the metal liquid and air to prevent the metal liquid from rolling gas and oxidation.

Inner gate size analysis

Too large or too small inner gate size will affect the filling process. Too large a gate will reduce the filling speed and slow solidification; too small a gate will cause serious metal injection and increase the wear of the core. The equation of the internal gate cross-sectional area is as follows.

Ag=1.25G/ρvt

Where Ag – internal gate cross-sectional area

G – die casting mass, 91.3g

ρ – density of aluminum alloy, 2.7g/cm3

v – filling speed of metal liquid through the inner gate, 75m/s

t–filling time, s

The cross-sectional area of the internal gate Ag=56mm2 is calculated by substituting the above formula.

The wall thickness of die casting is 2mm. According to the empirical data, choose the inner gate thickness h=2.5mm, then the width of the inner gate, and w=Ag/ h= 22mm, considering that the trimming allowance is taken w=22mm, the length of the inner gate is taken according to experience 1=2mm.

 

Overflow system design

The overflow system refers to the exhaust and overflow grooves of the mold. The functions of the overflow system include: eliminating the gas in the cavity, storing cold and dirty metal liquid, transferring the shrinkage, shrinkage, vortex roll gas, and the part that produces hard partition, improving the internal quality of die casting, etc. The flange cover overflow system is designed as shown in Figure 6.

figure 6 Flange cover drainage system design

The flange cover exhaust system is located in two places: ① end of the farthest from the gate. This is one of the last solidification positions of the die casting. It is necessary to design the overflow exhaust slot to improve its molding process. Still, because this position is adjacent to the deep hole side core parting surface, there are certain constraints on the arrangement of the overflow exhaust slot, so the exhaust overflow slot is designed on the side parting surface and the main parting surface, respectively. The overflow groove on the side parting surface is designed as an annulus to facilitate core extraction of the side core and to prevent the metal liquid from being ejected from the overflow system due to excessive casting pressure. The overflow and exhaust groove on the main parting surface is designed to be similar to the shape of a “rubbing board.” The location of the exhaust groove is misaligned with the overflow port, which plays an exhausting role while storing cold and dirty metal liquid to prevent The other end of the spherical side core extraction position. This is where the metal liquid meets, and it is necessary to design an overflow slot to improve the filling capacity of the metal liquid and to ensure the molding quality of the assembly plane in this area.

Side core extraction mechanism design

Design of spherical side core extraction structure

 The spherical side core extraction mechanism is shown in Figure 7. The main components of this side core extraction mechanism are inclined to guide pillar, slider, block, wear block, pressure bar, and 3 side cores, which are used to form the internal spherical structure of flange cover and 2 side holes. As the metal liquid cools around the side cores, thermal expansion and contraction occur, and the size gradually decreases. It will have a tightening effect on the side cores, so the side cores need a certain core extraction force when they are withdrawn, which is calculated as follows.
F = p A (fcosα-sinα) (2)
Where F – core extraction force
p – the unit area of the die casting on the side of the core extrusion stress, aluminum alloy to take 12MPa
A – die castings wrapped around the surface area of the side core, 50cm2
f – friction coefficient, take f = 0.2
α – side core molding part of the mold slope, take 1 °
The core extraction force F = 12k N. In addition, the spherical side concave and side hole depth determine the extraction distance S = 48mm. By the size of the core extraction force and extraction distance, determine the inclined column tilt angle of 20 °, inclined column length L = 280mm, diameter d = 30mm. Slider using inverted T-shaped structure, wedge angle of 22 °, the slider and side cores, guide slots are used to insert the structure, easy to assemble and replace. They can be individually heat-treated to improve wear resistance. And can be individually heat-treated to improve wear resistance and service life.

figure 7 Spherical side core extraction mechanism 3d drawing

Deep hole side core pulling structure design

The design of deep hole side core extraction mechanism is shown in Figure 8. As the internal hole of the die casting is deep (about 50mm), the clamping force is large, so hydraulic core extraction is used. After the side core is reset, in order to prevent the side core from receding under the casting pressure and affecting the dimensional accuracy of the die casting, the integral wedge tightening block is selected to wedge the movable core with a wedge tightening angle of 25°.

figure 8 Deep hole side core extraction mechanism 3d drawing

Cooling system design

Due to the high casting temperature of aluminum alloy (650 ℃), in order to improve production efficiency and the quality and denseness of the flange cover, to extend the service life of the mold, must be the highest temperature in the mold cavity, heat concentration area design cooling system, including cooling water channel and point cooler. For the parts of the mold that are particularly prone to overheating, such as the straight sprue part, a spiral water channel is used for circulating cooling, as shown in Figure 9a. For the main parts of the mold, such as the cross sprue, the stator cavity and the inclined column side core extraction mechanism, the cooling water channel is arranged as shown in Fig. 9b. The diameter of the cooling water channel of the cross sprue and the fixed model cavity is ϕ10mm, and the slider part of the inclined column side core extraction mechanism is seriously overheated, so the diameter of the cooling water channel is designed to be ϕ16mm, in which the cooling water forms a circulating flow to enhance cooling.

figure 9 Cooling water channelarrangement a-Spiral waterway b-Cooling water channel for fixed mold and side core extraction mechanism

For the local heat concentration, high temperature but not convenient to design the cooling water channel parts, such as the moving die part, due to the design of the ejector device, can not make the ejector device (such as the ejector rod) and cooling water channel interference, usually use the point cooling way to cool, point cooler structure as shown in Figure 10a, moving die and hydraulic device side core extraction mechanism point cooler arrangement scheme as shown in Figure 10b.

Push out mechanism design

The push rod is set in the plane of the flange cover part, straight sprue, cross sprue, overflow groove, exhaust groove and other parts as far as possible, evenly arranged, the arrangement scheme is shown in Figure 11. The diameter of push rod is ϕ6mm and ϕ8mm, 15 pieces in total, and the rear end is thickened, and the rigidity coefficient is more than 2.0 after rigidity check, which can meet the requirements of use. The outer dimensions of the push plate (L×W×H) are 320×550×30mm, the outer dimensions of the push rod fixing plate (L×W×H) are 320×550×25mm, and the diameter of the reset rod is ϕ30mm.

Conclusion

In this article, based on the analysis of aluminum alloy flange cover structure technology, the design of die casting mold structure is 1 mold 2 cavities, using curved cross sprue to reduce the distance of metal liquid flow; scientific calculation of the inner gate size, and at the same time, set the overflow exhaust tank at the intersection of metal liquid and metal liquid flow end, to prevent the internal defects of die casting such as air holes and cold partition, and the internal denseness of die casting is good. The hydraulic core extraction mechanism is designed at the deep hole inside the die casting, and the inclined column side core extraction mechanism is designed at the internal spherical side concave, with three-way core extraction to ensure the dimensional accuracy of the die casting. The design of circulating water cooling system at the overheated parts of the mold such as straight sprue, cross sprue, stator cavity, etc., and the setting of point cooling device at the local overheated parts of the moving mold effectively improve the surface quality, productivity and mold life of die castings. Finally, the design of top bar ejection in the casting system, slag collection bag, exhaust tank and other process waste parts can make the die castings ejected with uniform force, and will not leave traces of top bar ejection on the surface of die castings.

 

The mold structure design is reasonable, high production efficiency, good internal denseness and surface quality of die castings, high dimensional accuracy of die castings, suitable for mass production. Need die casting or die casting die, contact V1 diecast experts to help you solve the problem.

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