Injection molding products (Injection molding products) refers to the use of injection molding machine to heat the plastic plastic melting, and then injected into the molding mold cavity molding, cooling and cooling, melt curing after stripping, injection molding machine injection molding products.
4. Mold design stage through the mold flow analysis of product deformation trend, in the design to do optimization, easy to adjust the process.
The treatment of insufficient brightness of injection molded products
1. Liquidity
Different thermoplastics have different process properties, shrinkage properties and physical properties. For crystalline plastics, when the processing temperature is higher than the melting point, its fluidity is better, the cavity can be quickly filled, and the injection pressure is smaller. For amorphous plastics, its fluidity is poor, so the injection speed is slow and the pressure required is large.
Therefore, in the design of the mold, the flow of the plastic can be used as the basis for calculating the size of the runner system, which can not only avoid wasting materials, extend the injection molding cycle, but also avoid the problem of filling difficulties and pressure retention difficulties due to the small size of the runner system.
2. Contractility
When the thermoplastic is transformed from melting state to solidification state, its volume will shrink in different degrees. Under normal circumstances, the shrinkage range of crystalline plastics is 1.0% -3.0%, and the shrinkage range of amorphous plastics is 0.4% -0.8%, so the shrinkage rate and shrinkage range of crystalline plastics are larger than that of amorphous plastics, and are more susceptible to the impact of the molding process. After mold release, crystalline plastic can also crystallize at room temperature and continue to shrink, and its shrinkage depends on the thickness and temperature of the product, the thicker the product, the greater the shrinkage.
3. Rheology
Rheology refers to the relationship between stress, deformation, deformation rate and viscosity during processing. According to the rheology of plastics, plastics can be divided into two types: shear sensitive plastics and heat sensitive plastics. Common shear sensitive plastics are ABS, PS, PE, PP, POM, etc. The viscosity of this plastic will decrease rapidly with the increase of the shear rate. Common heat-sensitive plastics are PC, PA, PMMA, etc., this plastic has a strong dependence on temperature, the higher the temperature, the faster its viscosity drops.
From the perspective of polymer, the shear rate has an effect on the viscosity of the above two kinds of plastics, and the increase of shear rate can reduce the viscosity of the melt to different degrees, so that the melt produces "shear thinning" phenomenon, and the rheology of the injection product will also change.
4. Orientation effect
Orientation effect will be produced during the flow of plastic melt, which can affect the performance of injection molded products. The macromolecules of the plastic melt are stretched under the action of external forces, and then arranged parallel to each other along the direction of flow, and this arrangement will be frozen in solid products before the plastic is cooled and solidified, forming the orientation effect. The orientation effect will weaken the integrity of the product, resulting in uneven shrinkage of the injection molded product and warping deformation.
Causes of deformation of injection molded products and treatment methods
First, the cause of deformation
1. Residual stress caused by the shape of the product, especially the relationship between the forming shrinkage rate and the thickness of the product.
2. Residual stress due to molding conditions
3. Residual stress generated during demoulding
4. Deformation due to insufficient cooling time
Second, the solution
1. Instant: fully cooling and curing in the mold (extending the cooling time timer), increasing the barrel temperature and reducing the injection pressure.
2. Short term: Make the mold cool evenly.
3. Long-term: Avoid the difference in product thickness, set the gate in the place where the product thickness is large, because the straight line is easy to cause warping, make a large R curve, the product reversible bending mold, increase the number of ejecting rods, increase the release slope.
1. If the mold cavity processing is not good enough, such as scars, microholes, wear, roughness and other defects, it will certainly affect the plastic parts, resulting in a large degree of adverse consequences, resulting in the gloss of the plastic parts is not good enough. Therefore, the mold should be carefully processed, so that the roughness on the surface of the cavity can be greatly reduced, and when necessary, you can also choose to polish and chrome plating, to achieve the best results.
2. If there are some untreated clean oil or water stains on the surface of the mold cavity, or the use of too much release agent will make the surface of the plastic parts appear dark and dull. In this case, those oil and water stains should be removed in time, and at the same time limit the amount of release agent.
3. If the demoulding inclination of the plastic part is too small, it is difficult to demoulding, or the demoulding is subjected to too much force, resulting in the surface smoothness of the plastic part is too small, then the demoulding inclination should be increased to ensure the smoothness of the plastic part.
4. If the mold exhaust performance is not good, too much gas will remain in the model, which will also lead to poor luster after the final product is formed. Therefore, it should be checked and corrected to ensure that the mold exhaust system has sufficient exhaust performance to avoid the presence of trapped gas.
5. If the cross sectional area of the gate or runner is too small, or the change fluctuation is large, it will lead to excessive shear force acting on the melt during flow, resulting in turbulent dynamic flow of the solution, which will also lead to poor gloss of the final product. Therefore, the cross-sectional area of the runner and gate should be appropriately increased to reduce the shear force to avoid turbulence and improve the gloss of the product.
