Bottom shell of diagnostic instrument is shown in Figure 1. Maximum dimension of product is 239.70 mm *181.40 * 52.127 mm; average thickness of plastic part is 2.50 mm, material of plastic part is HI-PS, shrinkage rate is 1.005, and weight of plastic part is 179.95 grams. Technical requirements for plastic parts are that there should be no defects such as peaking, underfilled injection molding, flow lines, pores, warping deformation, silver streaks, cold material, and jetting lines, and meet ROSH environmental protection requirements.

 

Figure 2 3D drawing of mold
Diagnostic instrument is a medical device product of a certain Japanese brand. Product shell is divided into two parts, surface shell and bottom shell. This article introduces design points of injection mold for bottom shell. The overall shape of plastic part is a closed rectangle, height direction is an inclined triangle, and there is a pipe joint on one side, which is a raised cylinder. It is necessary to design a slider core to solve demoulding problem. There is a rectangular sunken structure in the middle of large plane on the top surface of plastic part, which is a data warehouse, which is easy to open at any time. A point gate is located on the plane of this sinker location.
Before carrying out mold design, first carry out mold opening manufacturability review of plastic parts. Plastic part is a regular casing plastic part, its appearance is a polished surface, and geometric tolerances are as follows:

 

Plastic parts have high requirements on appearance, and mold release agents cannot be used during injection molding. Therefore, attention should be paid to exhaust when designing molds to facilitate injection molding. Size of plastic part is large, and cavity design of mold is 1 cavity. 3D drawing of mold is shown in Figure 2. Mold base is fine nozzle base DCH4550. In order to ensure mold processing accuracy and shorten mold making cycle, fine frames of front and rear mold cores are all made in mold base factory. A conical positioning piece is designed on four sides of mold base to ensure that mold can be accurately and precisely closed.

 

Figure 3 Full mosaic structure of rear mold
Back mold of this set of molds adopts insert design method commonly used in Japanese molds, and small inserts are designed with a hanging table, which is fixed without screws as much as possible. There are many small inserts in the front mold core, all of which are fixed by hanging tables. Regarding design essentials of insert hanging table, previous articles have explained many times. When mold plate is thick, if screws are used to fix inserts, small screws cannot be clearly seen in holes, and it is easy to miss the installation, which seriously affects normal progress of injection molding production. There have been many such cases in the past.
For rear mold core, there are relatively many bone positions, and mold design method of full mosaic is often used. So-called full inlay, commonly known as loose inserts, is suitable for large and medium-sized plastic parts. When size of plastic product is above 150*150, and there are many deep bones on the side of moving mold, it is the most common practice to use a fully inlaid structure on moving model. Principle of full inlaid structure is that split position of insert should be beneficial to reduce amount of CNC processing, avoid or reduce EDM corner cleaning process, so that mold parts can be processed by wire cutting or grinding machine as much as possible. Wire cutting or grinding machine processing has high dimensional accuracy and short processing time.
Fully inlaid structure can separate several machine tools for simultaneous processing, effectively improving labor productivity. For large and medium-sized molds, purpose of making inserts is not limited to above points. It is difficult for large and medium-sized molds to use partial inlay design to really improve processing technology. All-inlaid structure is a mold design method that takes manufacturing process of mold core into consideration, shortens mold manufacturing cycle, improves manufacturing precision, and improves injection molding process. Processing cycle, also for convenience of processing, adopts a full-inlay structure design, idea is to divide the entire mold core (usually mainly refers to rear mold core) into multiple inserts for simultaneous processing, which not only simplifies processing time of inserts, At the same time, a large amount of mold steel is also saved. Therefore, fully inlaid mosaic structure has been widely used in Japanese mold design.

 

Figure 4 Die structure diagram
Rear mold core of this set of molds adopts a mold structure with full inlays. Divide back mold core into 4 large pieces on the edge and a large insert in the middle. All inserts are compressed and fixed by squeeze blocks, as shown in Figure 4. When designing full inlays, it is necessary to combine structural characteristics of plastic parts and divide specific cutting parts. It cannot affect appearance of plastic part; it cannot affect ejection and demoulding of plastic part; it cannot affect arrangement of cooling circuit.
When designing squeeze block structure of mold, pay attention to direction of squeeze block. Design in Figure 5 (a) is wrong. When only one side of the mold core has a high open protrusion, squeeze block of mold core cannot be pressed at a high Otherwise, mold core will be deformed, and squeeze block should be placed on the other side, that is, design in Figure 5(b) is correct. During design, mold core can be rotated so that the lower side of mold core is not on reference plane.

 

Figure 5 Design Considerations for Squeeze Blocks
Structure of plastic part is complex, and tightness of rear mold is relatively large. Therefore, ejector pins, flat ejector pins and cylinder ejectors are designed. In order to enable everyone in the forum to effectively understand mold structure, all 2D and 3D mold drawings are attached for everyone to understand and study