Hot runner injection mold design for paper holder

Time：2021-09-13 13:58:49 / Popularity： / Source：

Paper holder is an important part of shell of a certain Japanese brand printer. Product picture is shown in Figure 1. Maximum size of product is 495.45 mm * 348.69 mm * 71.84 mm, average thickness of plastic part is 2.85 mm, material of plastic part is HI-PS, shrinkage rate is 1.005, weight of plastic part is 675.20 grams. Technical requirements of plastic parts are that there must be no defects such as peaks, underfilling of injection molding, flow lines, pores, warpage deformation, silver streaks, cold materials, jet lines, etc.

Hot runner injection mold design for paper holder

Figure 1 Product picture of the paper support
It can be seen from Figure 1 that structure of plastic part is a flat and complex shell. There are local protrusions on both sides of fixed mold to provide guidance for paper output. This surface has multiple paper-through positions, which need to be smooth to reduce contact area between paper and surface to reduce friction. There are multiple bone positions in movable mold part to increase strength and rigidity. Bone position of movable mold is also over paper surface, top of bone position is rounded, it is required to be smooth, and paper should not be prevented from flowing out of this surface to front side. There are 3 undercuts on both sides of plastic part, and slider core needs to be designed. There are 3 undercuts in movable mold part, and it is necessary to design inclined top demoulding.
Please refer to attached PDF for product drawings of plastic parts. Product drawing specifies dimensional tolerances and technical requirements of product in detail. Technical requirements stipulate that mold release agents (release agents) must not be used during injection molding. Injection molding material mixed with recycled materials does not exceed 25%, and detailed dimensional tolerances are shown in the product drawing.
Size of plastic part is large, and mold design cavity is ranked as 1 cavity. When mold design cavity is arranged, three sliders are arranged on operating side and non-operating side of mold. Since gating system uses hot runner injection, mold base is a non-standard mold base 7095, which is a large mold. In order to increase rigidity of mold, 4 ø35 positioning pins are added to fixed mold. Since hot runner system generates a large lateral force in manifold during injection molding, diameter of positioning pin here should not be less than ø30. In most cases, standard guide posts are used instead. In movable mold part, ø20 positioning pins are added between B plate and square iron, between square iron and bottom plate. On four sides of mold base, zero-degree positioning blocks are respectively designed for precise mold clamping. This zero-degree positioning block must be customized by mold blank manufacturer and cannot be added later.

Size of plastic part is larger, bone position of movable mold part is deeper, quantity is larger. Gating system of mold adopts hot runner system, system adopts South Korean YUDO needle valve hot runner system. Gate position is 2 points on top surface, which is marked in product drawing according to results of mold flow analysis in advance. Mold insert design is a very important part of mold design.

Insert design of this set of molds adopts a full insert design. Design of inserts with full inlays is commonly known as broken inserts. It is widely used in design of large and medium-sized molds, is especially suitable for plastic parts with larger dimensions, large fluctuations in height, and more deep bones. Design of inserts for full inlays needs to adopt a design method of comprehensive analysis of three elements, that is, design of gate, parting surface and ejection method.
Design of full inlays requires comprehensive consideration of various factors, and a reasonable determination of number of large inserts. Breaking up and making inserts must take into account design of water transportation, layout of ejection system, and processing efficiency of machine tool. 3D diagram of water transportation is shown in Figure 4. Specific to each insert, it is necessary to consider that each insert has a reasonable processing benchmark, it can be processed by wire cutting or grinder as much as possible, and EDM processing or corner cleaning should be avoided as much as possible. Small inserts are all designed with hanging tables, and screws cannot be used to fix them.

Mold design specifications are documents about mold design specifications. Mold design engineer should check and understand content of mold design style book item by item, mold design drawing should fully meet requirements of mold design style book. Mold design specification book is a document before mold design, which has been introduced in previous article, and this article will be omitted. What is introduced here is mold design pattern confirmation certificate, as shown in Figure 6. Mold pattern confirmation certificate is a guide document for inspection before shipping mold, mold can be packaged and shipped only if inspection meets requirements of document one by one.

DFM is abbreviation of Design for Manufacturability (design for manufacturability), which mainly studies relationship between physical design of product itself and various parts of manufacturing system, and uses it in product design to integrate the entire manufacturing system for an overall optimization. DFM can reduce development cycle and cost of product, so that it can be put into production more smoothly. Export mold customers always ask for DFM documents before placing orders. Mold suppliers have an important responsibility for DFM assessment made by themselves, which will directly affect rationality of mold design and stability during mass production. Be sure to pay attention to details when evaluating, evaluate one by one in accordance with requirements.
Through development of DFM activities, on the one hand, mold manufacturers intervene in customer product design stage to consolidate relationship with customers, assist customers in improving product design capabilities, provide professional knowledge, optimize and improve product quality, reduce potential problems, and provide customers with a full range of solutions. At the same time, they have a more in-depth understanding of customer product design intentions and can better control subsequent costs. On the other hand, for mold manufacturers, since they can fully communicate with customers on various technical issues in the early stage of project during DFM activities, it lays a good foundation for opening a good mold review meeting, which is conducive to parallel development of product and mold design work, thereby shortening product and mold development cycle. Mold DFM file is shown in Figure 5.

Figure 2 Die diagram of paper support bracket

Figure 3 3D mold diagram

Figure 4 3d diagram of water transport in front and rear mold

Gud Mould Industry Co., Ltd

Hot runner injection mold design for paper holder

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