Frame of handrail is shown in Figure 1. The total length is 580mm, width is 200mm, and wall thickness is 2.5mm. Since molded plastic parts have high requirements on deformation, plastic parts are designed with more ribs, and deformation is reduced by increasing rigidity of plastic parts. Digital model of plastic part is processed and filtered by Moldflow CADdoctor to remove small rounded corners, chamfers and other features, import repaired model into Moldflow synergy, divide double-layer mesh and perform mesh repair, then apply mesh quality statistics tool, statistical mesh quality is shown in Figure 3, mesh matching percentage and mutual percentage both reach 90%, mesh matching rate reaches analysis standard, then metal insert model is divided together to make boundary mesh precisely match and increase accuracy of analysis. During injection molding, it is necessary to ensure that metal insert cannot move. Since wall thickness of metal insert is relatively thin, assuming that metal insert does not shrink, it only moves with position of molded plastic part in width direction, length of metal insert and plastic part is basically same. After it is embedded into molded plastic part, shrinkage of plastic part in length direction is limited, but shrinkage in width direction of plastic part is not restricted. If same shrinkage rate is used in X-axis and Y-axis directions, size of molded plastic part may be unqualified. It is necessary to design shrinkage rate of plastic part in X-axis and Y-axis directions separately, and to remove influence of metal insert on support of plastic part. Since plastic parts in X-axis direction are constrained by metal inserts and cannot shrink, shrinkage rate is not designed for X-axis, and only shrinkage rate is designed for Y-axis, and shrinkage rate is 0.4%. In mold flow analysis, metal insert needs to be fixed, node constraints of metal insert are used to simulate influence of metal insert on deformation of plastic part, as shown in Figure 4.

 

 

Plastic part is equivalent to center of symmetry, and there is a long metal insert on both sides of left and right edges. Now consider trying to balance force on metal insert, design gates near metal inserts on both sides to prevent initial feed from causing uneven force on both sides of metal insert to move. There is no appearance requirement for large surface of plastic part, and gate can be set. Considering that material of plastic part is relatively hard, trimming of gate aggregate should be omitted, and a needle valve gate can be used. If filling end is far away from gate, gate area and filling end area are prone to uneven shrinkage, resulting in deformation of plastic part. Gate is also designed at the end of plastic part to be molded to increase holding pressure to reduce difference in shrinkage and improve warpage. Considering that plastic part material contains fibers, plastic part is easily deformed by uneven orientation of glass fiber. Needle valve gate is used to fill in time to improve fiber orientation of glass fiber and reduce deformation of molded plastic part. Plastic part adopts 4-point needle valve sequential injection molding, and there are 2 gate positions to choose from. Figure 5(a) shows gate position one, gate opening sequence is G1→G2→G3, G4, injection pressure of Moldflow simulation analysis is shown in Figure 5(b), and flow process analysis is shown in Figure 5(c). Without considering mold structure, pressure is lower and filling scheme is better. However, mosaic structure needs to be designed at gate G2. Figure 6 shows position of mould-mounted mosaic. There are many small bump holes near gate G2. Considering that pressure near gate is relatively high, edge of small hole is easy to appear Flash, eventually abandoning this gate location. Figure 7(a) shows gate position 2. Since gates G1 and G2 are far apart, injection pressure is relatively high after sequence is opened. Theoretical analysis of injection pressure is shown in Figure 7(b). Injection pressure is too high, which is not suitable for injection molding. Opened gate positions have avoided mosaic position of mold parts, and gate opening sequence is G1→G2→G3, G4. Flow process analysis is shown in Figure 7(c). Considering opening gates G1 and G2 at the same time, injection pressure of the first stage can be reduced. Flow process is shown in Figure 8(a), and injection pressure is shown in Figure 8(b) after software simulation, normal injection molding can be performed. Finally, choose gate position 2 scheme and open gates G1 and G2 to inject melt at the same time.

 

 

 

 

Customer provided 2 kinds of materials, one material grade is B6, and the other material grade is B10. Injection pressure results obtained by using same molding process for these two materials through Moldflow software simulation analysis are shown in Figure 9. Injection pressure of material B6 is about 92MPa, injection pressure of material B10 is about 41MPa, and injection pressure of material B10 is lower than that of material B6. The lower injection pressure, the smaller impact force on metal insert, the smaller risk of movement, and the easier it is to meet molding requirements of metal insert. The lower injection pressure, the smaller force on mold cavity, the smaller deformation of plastic part after molding, and material properties meet product requirements, so material B10 is finally selected to form plastic part. Armrest frame is a non-appearance part, but affected by its function, deformation requirements of plastic part are stricter, mainly shape and position of small hole of plastic part. Plastic part material contains glass fiber, and deformation of plastic part is generally affected by orientation of glass fiber. Now, 80% of maximum injection pressure is used as holding pressure. Holding time is set to 10s, and needle valve will automatically close after 30s. Results obtained after warpage analysis are shown in Figure 10. The total deformation under all effects is 1.34mm, deformation of plastic part in X direction is 1.0mm, deformation in Y direction is 1.3mm, and deformation in Z direction is 1.8mm. Deformation of molded plastic part is small, which meets customer's requirements. After actual plastic part is formed, shape and position tolerance of small hole of plastic part are mainly detected. After the first part is produced, there was an out-of-tolerance problem in local small hole tolerance, small-hole insert was adjusted according to out-of-tolerance value. After another mold test, it was verified that it was good, size of final molded plastic part was qualified.

 

 

Molding material of plastic part contains glass fiber, and it is required that deformation of plastic part is small during actual assembly. In order to prevent excessive workload of mold modification in the later stage and high manufacturing cost, mold adopts an inlay design, and insert can be replaced later to adjust deformation of molded plastic part. For holes with positioning requirements, small inserts are designed. It can be seen from Figure 1 that there are many holes on both sides of plastic part. These hole structures are undercuts in demoulding direction, and the overall large sliders are designed on both sides of mold, as shown in Figure 11. It should be noted that metal insert should be placed in mold before mold is closed, and metal insert must be positioned stably in the cavity. If metal insert floats or falls off, final molded plastic part cannot be used normally, and even mold will be damaged. In order to prevent metal inserts from moving in cavity, mold is designed to be more inserted, positioned in fixed mold and movable mold, small inserts are added inside large sliders on both sides, as shown in Figure 12. Final design of mold structure is shown in Figure 13. After mold test verification, mold parts move smoothly and metal inserts do not move. Working process of mold: After mold is closed, injection molding machine injects molten plastic B10 into cavity, and it is formed after injection, pressure holding, feeding and cooling; mold is opened, movable and fixed molds are opened along parting surface, molded plastic parts are pressed by slider and stay in movable mold, then slider retreats under pressure provided by hydraulic cylinder, retraction amount is about 5mm larger than undercut on plastic part. Finally, ejection mechanism starts to push molded plastic part out of mold, manipulator pushes molded part out. Actual molded plastic part is shown in Figure 14.