Imager inner bracket products are shown in Figure 1. Maximum dimensions of product are 213.00 mm * 148.95 mm * 29.70 mm; average thickness of plastic part is 3.00 mm, material of plastic part is ABS, shrinkage rate is 1.005, and weight of plastic part is 92.46 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 1 Product picture of inner bracket of imager
It can be seen from Figure 1 that plastic part is a flat shell. Size of plastic part is large, there is a gap on the edge, there is a large square hole on top surface, there are also many small round holes and small square holes. Key points of mold design for plastic parts with multiple holes on the top surface were introduced in previous article on electronic calculator surface shell mold design. Plastic parts with this structure will make flow of molten plastic difficult, glue lines will be formed on the edge of each hole, and shrinkage rate of plastic parts will also decrease accordingly. Sides of both ends of plastic part are zero-degree vertical planes, and slider core must be designed. This zero-degree vertical surface cannot be designed with a demoulding slope, nor can it be suggested to customer to make a demoulding slope. Because zero-degree vertical surface here is a surface with functional requirements, not just an appearance surface.

 

Figure 2 3D drawing of mold
Size of plastic part is large, and mold design cavity is 1 cavity. 3D view of mold is shown in Figure 2, and parting surface of mold is shown in Figure 3. If necessary, make corresponding technical documents and submit them to customers for confirmation. At present, common practice is to carry out layout work of mold design before mold manufacturing and processing. Through inspection of layout, hidden dangers can be eliminated, number of rework and trial molds can be reduced, quality of molded plastic products can be guaranteed, cost can be reduced, and the overall design of mold can be optimized.

 

Figure 3 Die parting surface diagram

 

Figure 4 3D diagram of rear mold core
Design for Manufacturing (DFM for short) is to study relationship between design and manufacturing, and integrate manufacturing system into mold design for overall optimization. Mold DFM is an important part of concurrent design. Its purpose is to consider manufacturing-related issues in the early stage of design, so as to reduce and find design errors as early as possible, shorten mold development cycle, and reduce costs. In DFM of mold factory, designers need to consider various factors in mold manufacturing process, generally including product material, shrinkage rate, number of mold cavities, gating system, insert division and parting line, type and position of ejector mechanism, core-pulling form or lifter, whether product has sufficient demoulding slope, whether there is undercut affecting molding, etc.
In order to fully understand mold process performance and molding requirements of customer's products, following issues must be understood during process review of product drawing, mainly referring to problems that affect appearance of product, and also directly affect mold structure plan. Therefore, it is necessary to communicate with customer, understand customer's requirements and obtain approval of customer when mold is arranged.
1 Shape and position of parting line PL and penetration position of through hole;
2 Gate position, gate quantity and gate size allowed by product and weld line (grain) position and quantity allowed by product;
3 Front and rear mouldings, traces of stitching lines and sliders; edge of rear mold core formed by seam of edge of plastic part is raised, which can be directly processed by CNC, and it is not necessary to make an insert. If it is concave, it must be cut. See Figure 4.
4. Front and rear mold insert thread traces and step difference;
5 Are wall thickness, rib thickness, column thickness, etc. reasonable? Is wall thickness at root of all ribs, columns, etc. 0.6 times that of top? What changes can be made?
6 Front and rear mold drafting angles, etch number and lettering content, height, position and other dimensions;
7 Size and direction of basic demoulding slope where demoulding slope is not noted;
8 For injection molding material and color of product (dark or transparent, brown), is it allowed to leave traces such as push rods, push blocks, sliders, and lifters?
9 Is there any glue position interference in direction of movement of slider and lifter? What to do?
10 Contents and positions of signs such as embossed characters, symbols, dates, and material names on product;
11 When one mold has multiple cavities, positions of mold cavity numbers (1, 2, 3, ...) should be arranged in order;
12 When mold has many inserts, it is necessary to mark same number on the bottom of insert the insert hole of inner mold to ensure one-to-one correspondence;
13 Fillet processing (process fillet, absolute sharp corner, inlay, original processing fillet, and whether to cancel fillet);
14 Strength and stiffness of slender core;
15 Metal insert loading method (embedding before injection molding or hot pressing after injection molding, etc.);
16 Accuracy requirements such as dimensional tolerance and geometric tolerance, surface treatment (engraving, etching, mirror surface...);
17 Surface treatment method of product after injection molding (oil injection, electroplating...), electroplating parts must have a flow channel connection;
18 Solution to product deformation;
19 Is product to be machined after injection molding? Such as: gate removal, drilling, etc.
20 Assembly structure of each plastic part in this project: whether there is a gap between matching parts, and whether there is an aesthetic line between cooperation of appearance parts (to prevent misalignment and hide ugliness);
Core-pulling mechanisms of the two sliders all use inclined guide pillars for core-pulling, which is stable and reliable. Ejection adopts dome needle ejection.