Warping Deformation and Weld Seam During Plastic Molding

Influence of Residual Thermal Stress on Warping and Deformation of Products:
In the injection molding process, residual thermal stress is an important factor that causes warping and deformation, and has a greater impact on the quality of injection molded products. Since the influence of residual thermal stress on product warpage is very complex, mold designers can analyze and predict it with the help of injection molding CAE software.
There are many factors that affect the warpage of injection molded products. The structure of the mold, the thermophysical properties of the plastic material, and the conditions and parameters of the injection molding process all have varying degrees of influence on the warpage of the product. Therefore, the research on the warpage deformation mechanism of injection molded products must comprehensively consider many factors such as the entire molding process and material properties.

Free lace buckle plastic parts

Plastic molding with welded seams
When the molten plastic meets the insert hole, the area where the flow rate is inconsistent, and the area where the filling material flow is interrupted in the cavity and merges in multiple strands, a linear weld seam is produced because it cannot be completely fused. In addition, when the gate injection mold filling occurs, a weld seam will also be generated, and the strength and other properties of the weld seam are very poor. The main reasons are analyzed as follows:

Aviation plug cable plastic parts

1. Processing problems:
(1) The injection pressure and speed are too low, the barrel temperature and mold temperature are too low, causing the molten material entering the mold to cool prematurely and weld seams appear.
(2) When the injection pressure and speed are too high, jets will appear and weld seams will appear.
(3) The speed should be increased, and the back pressure should be increased to reduce the viscosity of the plastic and increase the density.
(4) Plastics should be dry well, and recycled materials should be used sparingly. If the amount of release agent is too much or the quality is not good, weld seams will also appear.
(5) Reduce the clamping force to facilitate exhaust.

Plug wire harness plastic parts

2. Mold problems:
(1) If there are too many gates in the same cavity, the gates should be reduced or set symmetrically, or set as close to the weld joint as possible.
(2) The exhaust at the welding seam is poor, and an exhaust system should be installed.
(3) The sprue is too large, the size of the gating system is improper, and the gate is opened to prevent the melt from flowing around the hole of the insert, or use less inserts as much as possible.
(4) If the wall thickness changes too much, or the wall thickness is too thin, the wall thickness of the workpiece should be uniform.
(5) If necessary, a fusion well should be opened at the welded joint to separate the welded joint from the workpiece.
3. The plastic problem:
(1) For plastics with poor fluidity or heat sensitivity, lubricants and stabilizers should be added appropriately.
(2) The plastic contains a lot of impurities, so replace it with good quality plastic if necessary.