Analysis of the technology of microinjection molding in injection molding industry

- Jan 26, 2018-

According to a report in the injection molding processing, injection molding industry in the context of the current market increasingly diversified, broaden also in unceasing development, appeared such as multi-color injection molding, gas assisted, mould sticker, new injection molding process. Also in the injection molding machine specifications, also in two directions - large tonnage of injection molding machines and micro-injection molding machines are constantly updated.

The microinjection molding process is developing rapidly.

In recent years, micro products demand more and more, whether it is the electronics industry, watch industry or in the military industry, there are a lot of small injection molded parts requirements, the requirements on the precision of injection molding products in size and is very high. Injection molding processing

Under such a premise, the micro-injection molding process also faces a huge challenge, how can the injection molded parts meet the size requirements of microns, and also have a good appearance and performance? The following is a brief introduction to the differences between the mold, equipment, materials and process of micro-injection molding.

Die processing and key points.

In the aspect of mold, the requirements of micro-injection molding for processing equipment are much higher than that of traditional injection molding.

Micro injection molding in the aspect of mould processing usually has two trends: the first is the mirror spark machining, in order to ensure high precision, best graphite electrode for edm is used, because the wastage of the graphite electrode is much smaller than ordinary copper electrode.

Processing which are frequently used in the second way is to use an electric molds, electroforming process can ensure high precision, but the disadvantage is that the processing cycle is long, each hole to separate processing, and in production if there was a slight damage cannot be repaired, can only replace the damaged point.

Mold temperature is also a very important parameter for micro injection molding. In the face of high-end customers, the current practice is to borrow the concept of high-gloss injection molding, and introduce fast heating and cooling system.

Theoretically, anti-embrittlement temperature is helpful for micro injection molding, can prevent the thin wall filling difficult, short of materials, for example, but high mold temperature will bring new problems, such as cycle lengthened and molding shrinkage deformation, etc. So import new mold temperature control system is very important, in the process of injection mold temperature can increase (which can be used more than plastic melting point), makes the melt quickly fills the cavity, prevent the melt temperature is reduced too quickly and cause in the process of filling packing is not complete; When the mold is removed, the mold temperature can be reduced rapidly, and the mold can be kept at a lower temperature than the plastic thermal deformation temperature, and then the mold can be pushed out again. Injection molding processing

In addition, because of the micro injection molding is the quality level for mg products, if the ordinary pouring system for injection molding products, even if in the optimization, improved products and material quality than still the gating system of 1:10. Only less than 10% of the material is molded into miniature products, which produce a large amount of pouring system coagulation. Therefore, the micro-injection molding should adopt the hot runner system.

Material selection highlights

In terms of material selection, it is suggested that some general engineering plastics with low viscosity and good thermal stability can be selected in the early stage of development.

Choose low viscosity materials because the melt viscosity is low, in the process of filling the gating system is relatively small, the resistance of the filling fast, can guarantee the melt filled cavity smoothly, also won't have significantly lower melt temperature, otherwise easy to form cold seam on the products, and molecular orientation in the process of filling is little, the performance of the products more evenly.

If you choose high viscosity plastic, not only fill slowly, and fill material for a long time, because of the shear flow is easy to make supplementary food chain molecules along the direction of shear flow orientation, in such cases when cooled to below the softening point orientation state were frozen, which to a certain extent, the freezing of orientation is easy to cause the internal stress of products, and even cause products stress cracking or buckling deformation.

Requirements of plastic good reason is due to the thermal stability of the material stay a long time in hot runner or screw shear effect is easy to cause thermal degradation, especially for heat-sensitive plastic, even in a short cycle time, also because material injection quantity is small, stay in the gating system for a relatively long time, causing considerable plastic degradation, so the heat-sensitive plastic is not suitable for the micro injection molding. Injection molding processing

Equipment selection

In terms of the selection of equipment, the injection machine should be selected as a milligram-grade injection machine due to the size of micro-injection molded parts in micron-sized products.

The injection unit of this type of injection machine generally adopts the screw - plunger assembly type, which completes the plasticization of the material by the screw part, and the melt is injected into the cavity by the plunger. The screw plunger type injection molding machine can combine the high precision of the screw and the high speed of the plunger device to ensure the precision and filling speed of the production process.

In addition, the injection machine is usually composed of a mould - oriented mechanism, injection system, pneumatic stripping mechanism, quality testing mechanism and automatic packaging system. A good quality inspection system can guarantee the yield of miniature precision injection products and monitor the fluctuation of parameters in the whole process.

Injection molding process points.

Finally, we look at the requirements of the injection molding process. In the injection molding process, we need to consider the gas mark and stress problem of the gate, usually the multi-stage injection molding is needed to ensure the material can be filled in a steady flow state.

In addition, it is necessary to consider the size of the pressure protection time. The small pressure pressure will cause the product to shrink, but the excessive pressure will cause the stress concentration and the size to become larger.

In addition, the time spent in the material in the material pipe also needs to be strictly monitored. The material will stay in the material pipe for too long, which will cause the degradation of the material to affect the function of the product. It is suggested that standard parameter control should be carried out in the process parameter management, and it is better for each product to do DOE verification before delivery, and all the changes in production should be tested again for size and function.

Micro injection molding as a branch of the field of injection molding are moving in the high dimensional accuracy, high functional requirements, the direction of high appearance requirement, only by tooling, equipment, materials, technology and the strict control of each process and technology continuously improve to meet the development of the market.