Warpage during injection molding shall be solved in this way

During the processing and injection molding of acrylic products, warpage, deformation, bubbles, cracking, wrinkling, pockmarked surface, shrinkage pit, overflow edge, fusion mark, burn, silver line, jet line and other defects will generally appear. What kind of solution should we adopt when warping occurs?

Cracking is a common defect of plastic products, which is mainly caused by stress deformation. It mainly includes residual stress, external stress and stress deformation caused by external environment.

Cracking caused by residual stress

The residual stress is mainly caused by the following three conditions: excess filling, demoulding and metal inlay. As the crack caused by excessive filling, the solution can be mainly started from the following aspects:

Because the pressure loss of the straight gate is the smallest, if the crack mainly occurs near the straight gate, the multi-point distribution point gate, side gate and handle gate can be considered.

On the premise of ensuring that the resin does not decompose and deteriorate, appropriately increasing the resin temperature can reduce the melt viscosity and improve the fluidity. At the same time, it can also reduce the injection pressure to reduce the stress.

In general, when the mold temperature is low, it is easy to produce stress, and the temperature should be increased appropriately. However, when the injection speed is higher, even if the mold temperature is lower, the generation of stress can be reduced.

Too long injection and pressure holding time will also produce stress. It is better to shorten it appropriately or carry out th pressure holding switching.

Non crystalline resins such as as as resin, ABS resin and PMMA resin are more prone to residual stress than crystalline resins such as polyethylene and polyformaldehyde, which should be paid attention to.

During demoulding and pushing, due to the small demoulding slope and the rough mold glue and punch, the pushing force is too large, resulting in stress, and sometimes even whitening or cracking around the pushing rod. As long as you carefully observe the location of the crack, you can determine the cause.

When metal parts are embedded during injection molding, it is easy to produce stress, and it is easy to crack after a period of time, which is very harmful. This is mainly because the thermal expansion coefficients of metal and resin are very different, resulting in stress, and with the passage of time, the stress exceeds the strength of the gradually deteriorating resin material to produce cracks.

In order to prevent the resulting cracking, as a matter of experience, the wall thickness 7 and the outer diameter of the embedded metal parts, the universal polystyrene is basically not suitable for adding inserts, and the inserts have the least impact on nylon. Because the coefficient of thermal expansion of glass fiber reinforced resin is small, it is more suitable for inserts. In addition, preheating the metal insert before forming also has a good effect.

Cracking caused by external stress

The external stress here is mainly the stress concentration caused by unreasonable design, especially at sharp corners. R / 7 “- 0.5-0.7 can be taken.

Cracking caused by external environment

Chemicals, water degradation caused by moisture absorption, and excessive use of recycled materials will degrade the physical properties and produce cracking.