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Several considerations for processing plastic molding

Time：2019-03-09 16:47:11 / Popularity： / Source：

  • Several considerations for processing plastic molding
Injection moulding is one of several aspects of injection moulding. Five elements that meet needs of injection moulding are temperature, speed, pressure, position and time. Keys to quality of controlled molded product is that a qualified product requires control of above factors. Most of quality problems often encountered in injection molding come from quality anomalies caused by five points that are not well controlled.
1. During processing of plastic molding, temperature is the first step of injection molding. Temperature can be divided into: temperature of drying, material and mold. These are some of the most important factors. Drying temperature is to dry polymer in advance to ensure molding quality, dry and wet of polymer are in a certain amount, normalization of plasticizing (melting) of polymer for smooth filling and molding; Temperature is an important condition for skin size, appearance, and molding cycle. Control affects cooling rate of product in cavity and appearance quality of product.
2. In plastic molding processing process, speed is divided into: speed of injection moulding, melt temperature, loosening, opening and closing mold, ejector forward and backward. Increase of injection speed will affect increase of filling pressure. It will increase flow length, ensure product quality. High-speed injection is suitable for long-flow products. Melt speed affects plasticizing ability, which is an important parameter for quality of plasticizing ability. The higher speed, the higher melt temperature, the stronger plasticizing ability. Loosening speed is to reduce melt specific volume, so that internal pressure of melting chamber is reduced to prevent its outflow. Opening and closing speed is One of the important conditions to ensure production and operation of machine. Ejector forward and reverse speed is to ensure that product is smoothly demolded without deforming product and cracking.
3. Pressure is divided into: pressure of injection, holding, back, mold clamping, mold protection, and ejection. During processing of plastic molding, injection pressure is used to overcome pressure loss of melt from nozzle-runner-gate-cavity to ensure that cavity is filled. Holding pressure is to reduce excessive injection pressure of workpiece which cause mold burst or bend. Back pressure is to avoid impurities in the mold under high-speed and pressure state which cause mold crushed. Ejection pressure is to prevent product from being detached from mold surface and causing defects.
4, In plastic molding processing, time is divided into time of cooling, sol, drying, cooling, melting, drying, cycle, injection and pressure holding. Molding of product requires a certain period. Injection time determines size of product. Holding time is to prevent melt backflow, cooling shrinkage. Cooling time ensures product solidifies and prevents deformation. Melting time is to ensure melt is sufficient. Drying time Ensure that product does not become elongated, bad and other factors.
In injection moulding processing, there are often unfavorable causes such as damage to appearance of defective products, wave marks, spray marks, scratches, peeling, bubbles, and film removal that are all affected by above five factors.
5, In plastic molding processing process, position can be divided into position of mold opening, ejection backward stroke, metering stroke, injection stroke, buffer amount. Mold opening position is to ensure normal operation of demoulding take-up. Ejector retracting stroke has effect of partial spring reset on ejector limit protection; Metering stroke is to ensure that there is enough plastic filling mold to ensure product quality. Buffering amount prevents mechanical failure of screw head from coming into contact with nozzle, and precision can be controlled.
  • Precautions for mold opening of injection moulding
Some customers often focus on product development and price when developing products or new product designs, ignoring communication with mold maker. After initial design of product design, it is necessary to communicate with mold manufacturer in advance. Method / step: 
First of all, choice of steel is very important, which is related to life of mold. There are many types of molds. Should be more than ten kinds of molds. According to different requirements of parts materials, physical and chemical properties, mechanical strength, dimensional accuracy, surface finish, service life and cost performance, different types of molds are selected. Molds with high precision requirements need to use high-precision processing equipment, and mold material and forming process requirements are strict. It is also necessary to use CAD/CAE/UG and other mold software to design and analyze.
Secondly, mold manufacturer should have CNC, EDM, wire-cutting machine and CNC copy milling equipment, high-precision grinding machine, high-precision three-coordinate measuring instrument, computer design and related software. Some plastic products have special requirements when designing, and mold structure is more complicated. Mold manufacturer also need to use advanced processes such as hot runners, gas-assisted molding, and oil cylinders.
Generally, large-scale stamping dies (such as automotive cover molds) should consider whether machine has a crimping mechanism, or even a lubricant, multi-station grade. In addition to punching tonnage, it is necessary to consider punching, feeding device, machine tool and mold protection device. Manufacturing methods and processes of above molds are not available and mastered by each mold manufacturer. When choosing a collaborative manufacturer, you must understand its processing capabilities. Gud Mould is professional in terms of hardware equipment, management level, processing experience and technical strength.
Finally, for same set of molds, different mold manufacturer sometimes have a large gap, you should not pay more than cost of mold, and should not be less than cost of mold. Mold manufacturer, like you, must make reasonable profits in business, not too demanding on price, because price may be low, quality may not be guaranteed, so in premise of mutual benefit, it should be more practical in process requirements.
 
Last article：5 major news in plastic molding industry Next article：Three basic principles of mold steel selection

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