Process analysis of plastic parts
(1). Analysis of raw materials of plastic parts
The material of plastic parts is made of polyvinyl chloride, which belongs to thermoplastics.
A: From the point of view of the use performance, the polyvinyl chloride material has flame retardancy and self-extinguishing property, no dripping, high strength, weather resistance and excellent geometric stability;
B: From the viewpoint of dielectric properties, polyvinyl chloride has good electrical insulation and chemical stability;
C: From the viewpoint of molding properties, the polyvinyl chloride has good water absorption, poor fluidity of the melt, low shrinkage, and is not easy to form. In addition, the plastic is prone to defects such as insufficient pouring and shrinkage during molding, and the molding temperature is high. Distillation of hydrogen chloride. Shrinkage occurs when the injection speed is too fast. Therefore, attention should be paid to controlling the molding temperature and residence time during molding. The pouring system should be thick and short, the inlet section should be large, and the cooling should not be too fast. Large diameter nozzles should be used.
Analysis of structural and dimensional accuracy and surface quality of plastic parts
A: Structural analysis In order to obtain qualified plastic parts, in addition to rational selection of raw materials for plastic parts, the structural processability of plastic parts must also be considered. The structural processability of plastic parts is directly related to the mold design. Only the plastic parts are designed to meet the requirements. The molding process requires that a reasonable mold structure can be designed to prevent defects such as bubbles, shrinkage, dents, and cracks during molding, thereby achieving productivity and cost reduction.
B: Analysis from the part drawing The part is generally conical, with a Ø36mm, Ø42mm stepped through hole in the center of the cone. The largest round Ø122mm inner diameter has four semi-circular protrusions with a radius of R6mm and a height of 9mm. There is a Ø122mm flange at the bottom of the cone and a convex height of 5mm. Therefore, the lateral parting core-pulling mechanism must be designed during the design of the mold. Moreover, because the surface area of the core-molding surface of the workpiece is large, the flange is relatively shallow, and the drawing distance is relatively small, and other core-pulling mechanisms are not economical and practical in view of the above situation. Therefore, the inclined block core pulling mechanism is used for forming.
C: Dimensional accuracy analysis The dimensions of the parts are Ø36+0.60 0mm, Ø42+0.70 0mm, Ø500 -0.66mm, Ø8+0.30 0mm, Ø1220 -1.30mm, Ø1100 -0.38mm, etc. The dimensions are MT5 (GB/T14486-1993) .
It can be seen from the above analysis that the dimensional accuracy of the part is medium precision, and the corresponding dimensional processing of the relevant parts of the mold can be guaranteed. From the wall thickness of the plastic part, the maximum wall thickness is 7 mm, the minimum is 5 mm, and the wall thickness difference is 2 mm. The wall thickness is relatively uniform, which is good for forming plastic parts.
D: Surface quality analysis The surface of the part is not easy to be realized except that it has no defects, burrs, and insufficient pouring, and there is no special surface quality requirement.
In summary, it can be seen that in the case of better control of process parameters during injection molding, the forming requirements of the parts can be guaranteed.