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8 highlights for plastic injection chair moulds

Aug. 11, 2019

1. How to judge chair molding cycle? If cooling water temperature is 8-12 degree and chair weight is 1700g to 2400g, then its cycle should be 35s-50s. If machine plastics are melted and injection molded under action of accumulator, please check their waterway design. Is waterway straight? Is direction of waterway consistent with shape of chair?
2. How to guarantee life of chair molding? Many people will say that they can guarantee a million times. But who knows how they guarantee this. Can they guarantee that there will be no flash after a mold runs 1 million? If you cut flash by hand, then I think you can use this mold to produce 10 million molds. So you need to check hardness of steel and if the mold has a welded part. Under normal circumstances, hardness of steel should be HRC33.
3. How can you ensure that injection molded chair parting line has no sharp edges? It is dangerous to have a rough parting line on the chair. In order to avoid sharp edges, we must pay attention to many aspects in chair molding designs and mold production process: – Is design of plastic chair injection moulding parting line correct? – Is cavity core thickness sufficient? – How do you process cores and cavities? One processing or multiple processing? Normally we need three processing. From roughing to hardening of steel, we carry out the second stage of CNC milling after steel hardened. We call this stage semi-finishing. Under normal conditions, we will leave a tolerance of 0.3mm and carry out finishing after wait for stress release of steel. Machine operation at this time is very important: 1. We are going to cool in the area of CNC milling; 2. We must ensure depth cannot be greater than 0.08mm during each cutting process. All of this is to prevent steel from deforming after CNC milling and hardening of steel. Deformation can cause inaccurate assembly of core and cavity, which can result in a large amount of manual work on the mold. To do manual work in the typing area, you can’t do a perfect parting line.
4. Whether wall thickness is uniform or not, is one reason of uneven wall thickness. Of course, most reasons is caused by 3D design of plastic chair and poor lighting of cavity core. So when we started a plastic chair molding design, we had to consider wall thickness factor. Sometimes we need to be thicker in some areas to ensure strength of chair. But at the same time we have to think carefully about this issue. Because uneven wall thickness can result in uneven injection molding and uneven cooling. This will slow down injection speed and cause a microcosm. If process of CNC milling is not accurate, you will never get a chair of uniform thickness.
5. How about stack of chairs? When starting chair molding designs, we have to check its superposition effect. At the same time you have to consider possibility of deformation of chair molding.
6. How do you guarantee that injection molded chair is light but strong enough? When designing a chair product, we must consider its weight and strength. You can make bottom of chair strong enough by adding more stiffeners. What about chair legs, chair backs and cushions? About this, you need to analyze strength of each area. In order to make a light chair have good strength, you need to choose a PP material with a low melt index. But premise is: mold must be very strong, injection molding must also be feasible, because you use a plastic with a melt index of 4 or a maximum of 6.
7. How to design exhaust on the back of chair? Back design of some chairs is complex because there are many plastic welds that can cause poor exhaust when material is filled and flowing. So you have to use mold flow to analyze whether some areas of plastic molding need to be vented.
8. How to ensure durability of plastic chair mould polishing? In order to keep core cavity of mold from being corroded by plastic, you must ensure that steel is chrome-plated and has a hardness of more than 33. If you use some recycled materials, chair molding must be chrome-plated. Otherwise, mold should be polished frequently.

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