Plastics can be divided into two broad categories based on the molecular structure of the resin in the plastic : crystalline plastics and amorphous (also known as amorphous) plastics. The main difference between crystalline plastics and amorphous plastics is whether the resin molecules can form a certain degree of regular alignment from the molten state to the condensation. If a certain degree of regular arrangement can be formed, it is referred to as a crystalline form, and otherwise it is referred to as an amorphous form.
Crystalline plastics and amorphous plastics not only have significant differences in mechanical properties, but also have large shrinkage rates when changing from viscous flow to glass. The shrinkage of crystalline plastics is usually 210 times that of amorphous plastics. . At the same time, for crystalline plastics, if the cooling rate of each part is inconsistent during cooling, the crystallinity of each part in the product will be different. The difference in crystallinity will cause internal stress in the product, which will cause deformation of the product. Even cracking. Therefore, for crystalline plastics, the cooling system design of the mold is an important aspect related to the degree of deformation of the product.
In addition to the resin, some fillers are usually added to improve the mechanical, electrical, optical and thermal properties of the plastic. These fillers form molecular orientation during shear injection due to shear flow, and are analyzed by Moldflow software. Fiber orientation distribution. The orientation causes a significant difference in the shrinkage of the article in different directions. For example, for a 30 glass fiber reinforced PA66, the shrinkage rate is 0.4 in the flow direction and 1.1 in the direction perpendicular to the flow direction, and the difference in shrinkage in different directions causes internal stress in the article. Therefore, for glass fiber reinforced plastic products, the non-uniform orientation of the filler is often the main cause of deformation of the product. In production practice, in order to improve or eliminate the deformation of the resulting product, measures such as changing the gate position and adjusting the injection speed are generally employed.
It can be seen that there are five major factors affecting the deformation of the injection product, namely: forming raw materials, forming methods, product design, mold design and injection molding process conditions.
Forming material
The influence of the forming raw material on the deformation of the product mainly refers to the molecular structure of the resin in the raw material and the type of the filler.
Forming method
At present, various forming methods such as ultra-high speed injection molding and gas-assisted molding have been developed on the basis of conventional injection molding.
In particular, the application of gas-assisted forming has gradually shifted from the simple shape of handles and handrails to the production of complex products in the industries of home appliances, audio, automobiles, office supplies and toys. The more you come, the more complicated the shape.
Gas-assisted forming breaks through the technical limitations of traditional injection molding and is an innovation of traditional injection molding technology. It not only has the advantages of saving plastic raw materials, eliminating surface shrinkage, shortening the forming cycle, simplifying product design, reducing mold cost, etc. It can reduce the injection pressure, thus reducing the difference in the pressure inside the mold, thereby reducing the internal stress and the deformation of the product. When the automobile accessory bumper adopts the conventional injection molding, the surface of the thin plate is severely deformed and is irregular S shape. After the gas-assisted forming, the whole piece is not deformed, and the surface of the sheet is a smooth arc.
Product design
The influence of product design on deformation is mainly concentrated on the wall thickness of the product, the uniformity of wall thickness, the shape of the product and the rigidity of the structure.
The effect of the wall thickness of the product on the deformation usually varies depending on the type of plastic. For amorphous plastics, the wall thickness is too thin and the orientation is severe.
Therefore, in order to reduce deformation of such plastic products, it is usually appropriate to increase the wall thickness at the time of design, in order to reduce the adverse effects of molecular orientation, and appropriately increase the wall thickness also increases the rigidity of the product to some extent. , thus reducing the deformation of the product.
For crystalline plastic products, the measures to reduce the deformation during design are often to reduce the wall thickness and improve the uniformity of the wall thickness. The reason for reducing the wall thickness is that the crystalline plastic has a large shrinkage rate, and the reduction of the wall thickness reduces the volume shrinkage of the product. It can be seen that the reason for improving the uniformity of wall thickness by Moldflow software is that if the wall thickness is uneven, the crystallinity of the thin wall and the thick wall is different, and the difference in crystallinity of different parts makes the shrinkage of different parts different, thereby generating internal stress. , causing deformation of the product.
Extrusion is a metal forming process , in which billet is passed through a die , to get required cross section of component .
Non cutting process
Production of Fixed cross section
Types of extrusion process
Direct extrusion process
Indirect extrusion process
Impact extrusion process
Hydrostatic extrusion process
Tube extrusion process
Aluminium Extrusion Die,Continuous Extruder Die,High Hardness Extrusion Dies,Continuous Extrusion Mould
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