According to the molecular structure of plastic resins, plastics can be divided into two categories: the crystalline plastics and non crystalline (or amorphous) plastics. The main difference between crystalline and non crystalline plastics is from a molten state to the condensation, resin molecules can form a certain ordered design. If it can form a kind of regular arrangement, known as the crystalline, otherwise says it shows non crystalline.
There is a significant difference between crystalline plastics and non crystalline plastics, not only in mechanical properties, but also in the viscous flow transition from glass to state, their contraction rate difference is very big, crystalline plastic shrinkage rate is usually 210 times of the non crystalline plastics shrinkage.
At the same time, the crystalline plastics, if cooling rate of each part is not consistent, it can also cause the crystalline parts within the product have different degrees of internal stress, the difference in crystallinity will WIP, resulting in the deformation and cracking products. Therefore, for the crystalline plastics, Mold cooling system design is an important aspect related to the product the deformation degree.
In addition to the resin raw materials, mechanics usually add some padding to improve plastic electrical, optical and thermal properties. These fillers in injection molding due to the shear flow will form the molecular orientation. Analysis of the fiber orientation distribution is given by using the Mold flow software. Orientation will make the products in different directions on the shrinkage rate have significant differences.
Therefore, for the glass fiber reinforced plastic products, non uniform orientation of packing is often the main cause product deformation. In practice, in order to improve or eliminate the deformation of products resulting from this, people usually adopt measures to change the position of gate and adjust injection speed etc.
So The effect of deformation of injection product has 5 factors, respectively is: forming material, forming method, product design, mold design and injection molding process conditions.
