When we design plastic parts, we will inevitably encounter warpage deformation defects. Warping and deformation of plastic parts is one of the most likely defects, and it is also one of the most difficult defects to solve. So, why the plastic parts will warp deformation. The fundamental reason is the uneven shrinkage of the plastic.
If the plastic part shrinks uniformly in all directions during the injection molding process, the plastic part will become smaller in size at the same time, but will maintain the correct shape and will not warp and deform.
However, if the shrinkage in any one direction is not consistent with the other directions, this will lead to internal stress, and when the internal stress exceeds the strength of the plastic part itself, the plastic part will be warped after ejection.
The structural design of electronic products is mostly composed of plastic and thin steel plates, and the importance of stiffness design is much more than strength design, which is an important difference from ordinary mechanical design. Usually, plastic parts are easily deformed under high temperature, and the prevention of deformation of plastic parts is mainly considered from the use of reinforced plastics, changing the shape of the parts, improving the injection molding process, surface coating, and dispersing the work load.
1-Adding glass fiber to plastics to improve stiffness
With a high level of plastic can certainly improve the stiffness of plastic parts, but this will increase the cost, so in terms of materials mainly never improve the cost of materials, the use of low-cost plastic and then strengthen the method to solve the problem. Adding glass fiber is a common and proven method. Adding glass fiber can also improve the creep performance of the material.
- About Glass Fiber
The diameter of glass fiber added in plastic is 0.05-0.01mm, length is 3-4 mm, tensile strength is 700-2300MPa, hundreds of times of PP plastic, melting point is above 1000℃. Adding glass fiber (10-30%) to ABS and PP can greatly increase the stiffness of the material and improve the creep characteristics without increasing the cost.
- The disadvantage of adding glass fiber and solutions
The disadvantage of adding glass fiber is that the melt viscosity is large when injecting, the fluidity becomes poor, and there are floating fibers on the surface of the parts, which can be solved by the following methods:
- Raise mold temperature and injection molding temperature
- Increase injection speed and pressure
- Enlarge the gate and shorten the runner
- Disadvantages that cannot be overcome after adding glass fiber
After adding glass fiber, the surface gloss of the products will be kind of reduced, so you can’t do high-gloss paint-free parts; after adding glass fiber, the wear and tear of the injection molding machine screw increases, and the life of the screw is shortened. If used continuously, the screw should be replaced in 1-2 years. Therefore, the injection molding cost would be creased.
2- Improve stiffness when designing the part
- Make wall thickness even, reduce the inner stress, so as to avoid deformation.
- Avoid flat structure, make it solid as possible.
- Avoid large area flat surface, make it a little bit cambered.
- Add some ribs in the part. (Reasonable distributed and suitable ribs)
- Increase the wall thickness, though it creases cost as well.
3-Increase injection pressure.
The weight of a 500g part can vary by 50g due to the size of the injection pressure, and when the part is light, the density becomes smaller and the stiffness becomes worse. The prerequisite for high pressure injection is high accuracy of the mold, otherwise there will be flashes
Especially when the pricing parts by weight or by number when outsourcing the orders, there will be low density parts produced in some factories, to reduce costs.
4- Electric plating on the surface
Aluminizing or Cu+Zn plating or chroming on the surfaces of plastic parts, can improve the stiffness and the surface hardness.
5- Distributing the workload
Increases more support points, thus achieving the purpose of dispersing the work load.
Warpage of plastic parts is always a difficult problem. On the basis of understanding the shrinkage unevenness, plasitic injection mold maker can prevent and solve this problem from plastic materials, plastic parts design, mold structure and injection molding process, then warpage/deformation is no longer a problem.