A criterion for judging good injection molding conditions:
  1.The moling process is stable and unstable for production,
  2.Whether the efficiency is maximized.
Plastic injection modling and mold maker

injection molding from China–Longterm

 In the injection molding process,  after a period of production, the product will have defects such as burnt and lack of glue.

 

 To eliminate these problems and achieve production stability, We should know more about the injection material temperature, mold temperature and cycle time   in the molding parameters .
The material is driven by the rotation of the screw at the hopper and is pressed into the barrel. It is heated and melted while entering the barrel. The material is pressed from the end of the barrel to the front end.
 In this process, the material will become a high temperature and high pressure fluid. Then through the thrust of the screw, the molten material is injected into the mold, and the mold is cooled and shaped, and the final product is the product.

What are the main factors that will be affected in this process?

Pressure, speed, time, and temperature are all the main factors, we mainly talk about temperature here. In the process of material from solid to fluid to solid, the temperature changes are very large, generally from the material drying temperature (80 ° ~ 140 °) to the molding temperature (200 ~ 400), and then to the demolding temperature (mold Temperature and material determination). In this process, the barrel temperature, mold temperature and cycle participate in the process to obtain qualified products.
Each material has a range of temperature requirements. Within this range, how much is the best?  Temperature is an energy. A material changes from a solid to a fluid, from a low temperature to a high temperature. It needs to absorb heat, the fluid becomes a solid, and the high temperature becomes a low temperature, and it needs to release heat.
Because molding a timed cyclic process, according to the law of conservation of energy, the heat between the two cycles must be balanced, that is, how much heat is absorbed (cylinder heating) in normal production, and the consumption ( Cooling), how much heat must be released in order to achieve energy conservation.
Whether it is heat absorption, heat consumption, or heat release, it takes time and efficiency per unit time. This is the problem of cycle and heat transfer efficiency. Therefore, starting from cycle and heat transfer can solve many problems.
It takes time to heat and cool the temperature. If the temperature is not balanced, the temperature (including the material temperature/mold temperature) in each cycle will be left for the next cycle.
When it is accumulated, the later production temperature will be Get up high, bad appearance. If the temperature is insufficient, it is necessary to replenish the missing temperature in the next cycle.
When it accumulates, the temperature will become lower and lower, and defects will appear. So what is the way to control the temperature so that it can reach equilibrium?
The production temperature depends on 3 factors:
1. Original heat source, 2. Time, and 3 cooling rate.
The heat source is the material temperature we set (the mold temperature is the cooling medium), and the set height directly affects the amount of heat transferred.
Time is mainly cycle time. Whether a balance can be achieved between each cycle, the speed of the cycle is very important.
The cooling rate depends on the size of the temperature difference. That is, the temperature difference between the material and the mold, the smaller the temperature difference, the slower the cooling rate, the greater the temperature difference, the faster the cooling. The use of different temperatures for the mold is to change the cooling rate of the material in the mold so that its appearance and size can meet our requirements. The cooling rate of the material in the mold is different, and the stress, shrinkage, and stretching of the material in the mold have different performances, which are reflected in cracks, whitening, deformation, shrinkage, etc.
The setting of mold temperature is related to materials and molds. Different materials and different molds have different suitable mold temperatures. Set according to actual conditions. If the heat dissipation of the mold is insufficient, the mold temperature will slowly rise, changing the cooling rate, the cooling efficiency will decrease, and the cycle will be lengthened.
The interaction and balance of these three aspects: mold temperature, material temperature, and cycle time, can meet one of our requirements: maximum production stability and efficiency. How these three aspects interact and constrain each other requires experience and technology. Basically, when the cycle is fixed, the mold temperature and the material temperature are determined according to the bad conditions.
For example, short shot may be caused by insufficient material temperature and unstable injection speed, or it may be caused by excessively high material temperature, which leads to better material fluidity and back flow during injection. The size of some products deteriorated in production, and the temperature was not well balanced.
Of course, if you want to have a perfect condition, you need not only these three points, but also many more. This is only an overall requirement and a basic requirement, and you must understand the adjustment of the machine.
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