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10 factors that affect quality of injection moulding
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Mold manufacturing is a complicated process. From steps of design, processing, assembly, debugging to final use, there are mainly 10 factors that affect quality of mold throughout life cycle.
Mold steel
Steel is decisive factor for mold quality. Choosing a reasonable steel is the most important factor. Criteria for choosing steel are:
1. Requirements for injection moulding materials
Different plastics should use different steel materials, such as requirements for high polishing, corrosion resistance, etc.
2. Price
Steel used is not the more expensive the better. Considering cost of mold, mold steel should use material corresponding to life of mold to avoid unnecessary waste; life of general P20 material is about 300,000; 2738 materials are no problem at 500,000, H13/2344 is usually more than 80-100 million, and it can be selected according to actual situation;
3. Surface treatment
Surface treatment of mold is also very important. Nitriding can enhance surface hardness of steel and effectively extend life of mold. Electroplating can effectively modify mold steel. For some high-brightness and corrosion-resistant plastic mold parts, electroplating can be used to enhance and improve performance of steel.
Structural design
Moulding process
Standard parts
Collision (flying mold)
Polishing/skinning
Mold assembly
Hot runners or cold runners
Cooling Waterways
Mold maintenance
Mature mold structure not only considers product material properties, shrinkage rate, molding temperature, elastic tensile deformation coefficient, etc., but also consider cooling waterway, speed of opening and closing mold. Reasonable mold structure can effectively extend life of mold and ensure smooth production of mold, improve efficiency and reduce costs.Workers want to be good at things, must first sharpen their tools. Arrangement of moulding process is particularly important, and reasonable process arrangement can speed up production cycle, shorten processing time, and effectively save costs. And more importantly, accurate and reasonable moulding process can ensure stability and longevity of mold during production process. Some machining errors will lead to mold welding. No matter how good welding is, it is a loss to mold; in addition, poor moulding process may affect mold movement, reduce mold life, cause mold to crack, and even broken during production process.The lowest piece of wood that determines capacity of bucket. Everyone understands this truth, but it is often not noticed when doing it. Mold is same, although standard parts are not directly involved in molding, but control operation of entire mold. Good standard parts should be wear-resistant, hard enough, high precision, and not suitable for deformation. Different brands of standard parts are very expensive, so don't blindly bargain. Or your mold will drop from Mercedes to Volkswagen.Experience of mold fitter is against seemingly simple work but the most technical work. The main thing about complex molds is this effort. Flat mold is the simplest, and fractal surface is basically ok as long as there is no flash break. It is very troublesome for a car accessory mold. Not only is fractal surface relatively irregular, but it often includes multiple sliders and top blocks. At the same time, it can improve and perfect other problems of mold through touch, so it is a comprehensive work.Polishing of mold is the last step in mold manufacturing. Polishing is directly reflected on plastic mold parts, so this is the most face-to-face job. Polishing also helps and complements mold movement, especially for demolding. Often some mold production is not smooth because polishing is not in right place, resistance is too large, demoulding is difficult, and even white, top crack and so on.Mold assembly is like assembling a machine. Every component and every screw can't go wrong. Otherwise, consequences will be quite serious. If minor, it will lead to product defects, affecting production; If severe, it will completely damage mold and cause scrapping. Therefore, assembly work must be very meticulous. In assembly process, especially pay attention to cleaning of mold, especially water circuit and screw holes. Be sure to blow off iron filings inside.This actually has the least impact on mold quality, because hot runners are generally branded by customers, especially some large customers. Well-known foreign brands do very well in quality and after-sales service, so there is generally no problem in quality. However, some domestic hot runners have a very different quality. In order to save costs, individual small enterprises strive for price advantages with some unreliable heating and conduction accessories, problems are easy to occur. Main problem with cold runners is how to ensure balance of injection moulding, gate size, injection pressure and so on.Anyone who has experience with molds knows how important cooling is to a mold. Due to increase in prices and labor wages, it is unthinkable to reduce profit from one-second injection cycle when mass-producing products. However, when production cycle is accelerated, temperature of mold will rise. If it is not effectively controlled, mold will be too hot to be formed, and even mold deformation will be scrapped. Therefore, excellent waterway design is particularly important, including arrangement density of waterways, diameters, links between each other, and so on.Mold maintenance is mainly maintenance during production process. Mold is like a car. If it is not used for a long time without maintenance, it may cause mold to be scrapped. Therefore, every time mold is used, it must be fully maintained, especially rust prevention of plastic mold parts and rust prevention of main moving parts. Because mold has to be watered during production process, it may fall into mold during installation or disassembly process, so be sure to dry mold and then apply a layer of oil protection.
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