Plastics are more and more widely used in home appliances, auto parts, aircraft parts, electronic products and other fields, and the injection molding technology of plastic products is a difficult problem for mold design engineers, plastic product engineers, and injection molding technicians, especially the design and molding of heterogeneous parts such as windshields in high-speed trains. Moldflow is a plastic product simulation and analysis software, which can assist mold designers in mold design, plastic product engineers in optimizing product design schemes, and injection molding technicians to debug injection molding machine parameters. The software simulates flash, weld marks and injection pressure in the molding of plastic parts, warpage deformation, etc.
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. The mold design engineer can continuously adjust the parameters such as runner, gate shape, gate position and so on on the software; Product designers optimize the design of products through software; The injection molding machine molding technician can continuously correct various parameters of the injection molding machine on the software, which can reduce product waste, shorten the product molding cycle, and improve production efficiency
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. In this paper, Moldflow software is used to design the gate selection of a complex heterosexual plastic part.
<xref ref-type="bibr" rid="scirp.141281-"></xref>2. Plastic Part Analysis
This product is an inner buckle plate of the windshield in the train, and the display in the three-dimensional software is more complex (as shown in
Figure 1
). The main dimensions are 1874 × 44 × 16, there are many through holes, and the maximum thickness of the wall thickness of the gusset is uneven, and the maximum thickness is about 4 mm (at the hook of the gusset plate).
The small thickness is 1.5 mm, with a thin-walled characteristic structure, the material selection is PC + ABS, the color is white, the appearance of the product is not high, and the assembly tolerance MT5 is not very high.
(a) Heads (b) TailsFigure 1. Outline diagram of the inner gusset.
(a) Heads (b) TailsFigure 1. Outline diagram of the inner gusset.
(a) Heads (b) TailsFigure 1. Outline diagram of the inner gusset.
<xref ref-type="bibr" rid="scirp.141281-"></xref>3. Gate Location Analysis of Plastic Parts
<xref ref-type="bibr" rid="scirp.141281-"></xref>3.1. Meshing and Cavity Layout
The structure of the plastic part is a thin-walled part, the surface mesh is divided by hypermesh, the edge length of the grid is set to 1mm, the network aspect ratio is less than 6 after repair, there is no free edge and overlapping overlapping edge, the structure of the plastic part is complex and the thickness is inconsistent, the preliminary consideration is that it is two molds, one mold and one hole.
<xref ref-type="bibr" rid="scirp.141281-"></xref>3.2. Gate Type Selection
From the analysis of product properties, there are two schemes, one scheme adopts 3 gates, and the gate type adopts a sector gate, see
Figure 2(a)
; In another scheme 4 gate, one gate takes a latent gate and the other gate takes a fan gate, see
Figure 2(b)
.
3.3. Analysis of Gate Feeding of Plastic Parts
The three-gate pouring is shown in
Figure 3(a)
, the filling time is 1.13 seconds, and the wall thickness is only 0.5 - 0.6 mm at the place close to the gate position, and the plastic fluid flows to this position with too much resistance and stagnates, which hinders the flow of the plastic fluid, so the short shot phenomenon occurs;
Figure 3(b)
for 4 gates shows that the filling time is 1.2 seconds, and the stagnation may occur for the same reason at the position of the four gates. Considering the use of a four-gate scheme, the following is a filling and warpage analysis of the four-gate scheme.
(a) Three gate pouring (b) Four gate pouringFigure 2. Plastic part gate filling analysis.
(a) Three gate pouring (b) Four gate pouringFigure 2. Plastic part gate filling analysis.
(a) Three gate pouring (b) Four gate pouringFigure 2. Plastic part gate filling analysis.
(a) Three gate pouring (b) Four gate pouringFigure 3. Filling flow analysis.
(a) Three gate pouring (b) Four gate pouringFigure 3. Filling flow analysis.
(a) Three gate pouring (b) Four gate pouringFigure 3. Filling flow analysis.
4. Flow Analysis of Four-Gate Filling4.1. Injection Pressure Analysis4.2. Injection Wavefront Distribution
From the temperature distribution of the injection wavefront in
Figure 5
, it can be seen that most of the filling temperatures are relatively uniform in the filling process, but the wavefront temperature of the plastic parts in the frame shown in the figure drops sharply, resulting in stagnation, and the fluid plastic parts at 2 and 3 places in the frame can be filled to 1 place in the frame in time to avoid short emission of the plastic parts.
Figure 5. Injection wavefront temperature distribution.
4.3. Weld Mark Analysis
The weld mark in the weld mark frame shown in
Figure 6
obviously affects the appearance of the plastic part, but the welding temperature of the weld mark in the frame is high and does not affect the strength of the plastic part, and the plastic part does not have high requirements for appearance, so the weld mark is acceptable.
The layout of the waterway is shown in
Figure 7
, the upper master mold is designed with two waterways with a diameter of 10 mm, and the lower male mold is designed with four waterways directly of 9.5 mm (the baffle is designed to be directly 12 mm).
Figure 7. Layout design of plastic parts waterway.
5.2. Cooling Water Variation
The cooling water changes as shown in
Figure 8
, the 8 water channels are not connected in series, the water temperature rise changes slightly, and the water channel design meets the cooling requirements during molding.
1) The plastic parts are thin-walled parts with complex structures and different thicknesses, all of which do not have high requirements for appearance, meet the basic assembly function, and consider the cost of designing two molds, one mold and one hole.
2) The three-gate scheme and the four-gate scheme were designed, and it was found that the three-gate pouring was prone to short injection, which affected the functional requirements of the plastic parts.
3) The analysis of the results of Moldflow for the four-gate feeding of plastic parts shows that this product needs an injection molding machine with a large cavity, the flash is more serious, the wavefront temperature is reasonable, the product does not have high requirements for appearance, and the weld marks are acceptable.
4) After the waterway design of the product, the warpage analysis of the product was carried out. The total warpage deformation value in the X direction is 0.7839 mm, the total warpage deformation value in the Y direction is 1.8013 mm, and the total warpage deformation value in the Z direction is 0.5629 mm, and the deformation amount is within the tolerance requirements of the plastic parts.
5) The designed scheme is suitable for small batch production. Assuming mass production, it is recommended to design a three-plate mold scheme.
Funds
Hunan Provincial Department of Education (23C0810 high-speed train through the rubber inner windshield injection mold design and injection parameter optimization research).
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