Key points for design of injection mould for test tube holder
The product diagram of the test tube holder is shown in Figure 1. The maximum size of the product is 143.40 mm x 24.50 mm x 105.00 mm, the average thickness of the plastic part is 2.0 mm, the material of the plastic part is PP, the shrinkage rate is 1.016, and the quality of the plastic part is 11.70 grams. The technical requirements of plastic parts are that there must be no defects such as peaks, dissatisfaction with injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.
It can be seen from Figure 1 that the plastic part has a semicircular shape and a simple semicircular cross section. The hook part is provided with a hook hole formed by a long hole and a round hole. The difficulty of mold design lies in the following two points: one is how to judge the direction of mold opening, and further determine the parting surface; the other is the selection of gate location and how to avoid plastic part ejection deformation. The difficulty of mold processing lies in the processing of the parting surface. Since the parting surface is a circular arc surface, the height fluctuations are large, and the plastic is made of PP material, it is easy to run out of the front. Therefore, the processing of the parting surface requires high-speed machining to make the parting Good shape fit.
The production volume of plastic parts is huge, and the mold design cavity ranks 1 out of 4; the mold base is Fu Deba mold base MDC SC3555 A150 B130 C90 H, and the AB plates are made of P20 steel. The mold is exported to Germany. If the mold base used in the early export mold is not the HASCO standard mold base, but the Long Kee or Fu Deba mold base, the customer will require the AB board to be made of P20 steel. Furthermore, the customer will request that the thimble plate is also made of P20, all of which is to ensure the quality of the mold. The two conical positioning parts are designed to be staggered on the parting surface to ensure the accuracy of mold clamping. European and American customers' important concepts for mold design are steel selection and heat treatment hardness. The steel used in this set of molds is 1.2344, and the heat treatment hardness is HRC48~52.
The selection of the mold opening direction is the most important link in determining the mold design plan. In this set of molds, there are two main considerations when selecting the mold opening direction. The first hook hole is designed in the movable mold to make the slider simple; at the same time, the pouring system is at a higher position to make the main runner shorter. The actual mold design is shown in Figure 2. Melting.
After the plastic's autonomous flow channel enters the parting surface, it enters each cavity in 4 ways, and the glue is injected into each cavity one point to dive into the front mold.
The export mold adopts the hard mold design after heat treatment, and the production process needs to be considered. Due to heat treatment, the steel will be deformed. Therefore, the ranking design is that two cavities are on one mold core, and a total of two sets of mold cores are required. Separating the mold core can reduce deformation and facilitate production. The production process of the hard mold is: preparation and fine grinding (flow allowance), rough machining of the cavity, allowance, drilling screw holes, tapping, drilling and transporting water; heat treatment; fine grinding of the shape, lower frame; finishing the cavity. Province mold polishing, etc. Therefore, the design of the hard mold must consider the heat treatment and its deformation, and only precise thinking can design a reasonable mold.
The sliding core pulling system is designed at the hook position, which is driven by an inclined guide post, and the shovel machine backshoes in the rear mold. In molds exported to Europe, when the slider backhoe mechanism can be designed, it cannot be omitted and must be designed. Moreover, the oblique guide column core pulling mechanism is the first choice.
The design of the temperature control system of the mold is very important, which is conducive to controlling the injection cycle and reducing the deformation of the plastic part. While the front and rear molds are designed to transport water, the front and rear molds are designed with heat insulation panels to prevent heat loss.
The ejection of the plastic parts adopts a thimble to eject, which can fully meet the ejection requirements of the plastic parts.
