As we all know, SMC molding process has many advantages, such as accurate product size, smooth surface, good product appearance and size repeatability, complex structure can also be one-time molding, secondary processing does not need to damage products. It can be said that SMC material molding process is one of the most efficient in FRP / composite molding process. However, in the SMC molding production process, there will also be defects, resulting in defective products, mainly in the following aspects, Ningguang mold and friends to analyze:

1. Shortage of materials:
The lack of material refers to that the SMC molded parts are not fully filled, and the parts are mostly concentrated on the edge of SMC products, especially the root and top of the corner.

Cause analysis:
(a)Less discharge (b)The fluidity of SMC is poor (c)Insufficient equipment pressure (d)Curing too fast

Production mechanism and Countermeasures:
① The melt viscosity of SMC is high after heat plasticization, and there is not enough time, pressure and volume to fill the mold cavity before the crosslinking and curing reaction is completed.
② The fluidity of SMC molding material is obviously reduced due to the long storage time and excessive styrene volatilization.
③ The resin paste did not soak the fiber. The resin paste can not drive the fiber flow during molding, resulting in material shortage. The most direct solution to the shortage caused by the above-mentioned reasons is to eliminate the molding materials when cutting.
④ Lack of material is caused by insufficient feeding amount. The solution is to increase the feeding amount properly.
⑤ There is too much air and a lot of volatiles in the molding material. The solutions are as follows: properly increase the number of exhaust; properly increase the feeding area, burp a certain time to clean the mold; properly increase the molding pressure.
⑥ If the pressure is too late, the molding material has completed the crosslinking curing before filling the mold cavity. ⑦ If the mold temperature is too high, the crosslinking curing reaction will be advanced, and the temperature should be properly lowered.

2. Stomata
There are regular or irregular small holes on the surface of the product, which are mostly produced at the top and middle thin wall of the product.

Production mechanism and Countermeasures:
① SMC molding material is wrapped with a large amount of air and volatile matter, and the exhaust is not smooth; the thickening effect of SMC is not good, and can not effectively drive out the gas. For the above reasons, it can be effectively controlled by increasing the number of exhaust and cleaning the mold.
② If the feeding area is too large, properly reducing the feeding area can be controlled. In the actual operation process, human factors may also cause sand holes. For example, the pressure is too early, which may make the gas wrapped in the molding material difficult to discharge, resulting in the surface defects of the product surface.

3. Warpage deformation
The main reason is the uneven curing of molding materials and the shrinkage of products after demoulding.

Production mechanism and Countermeasures:
In the process of resin curing reaction, the chemical structure changes, resulting in volume shrinkage, and the product tends to warp to the side of the first curing. Secondly, the thermal expansion coefficient of the products is larger than that of the steel mould. When the product is cooled, the unidirectional shrinkage is greater than that of the die. Therefore, the following methods are adopted to solve this problem:
① Reduce the temperature difference between the upper and lower die to make the temperature distribution as uniform as possible.
③ Use cooling clamps to limit deformation.
④ Properly increase the molding pressure, increase the structural compactness of the products, and reduce the shrinkage rate of the products.
⑤ The holding time should be prolonged to eliminate the internal stress.
⑥ Adjust the curing shrinkage of SMC materials.

4. Blistering
A semicircular bulge on the surface of the cured product.

Production mechanism and Countermeasures:
It may be that the curing of the material is incomplete, the local temperature is too high or the volatile content in the material is large, and the air trapped between the sheets causes the semicircular bulging of the product surface.
① Increase the molding pressure properly.
② Extend the holding time.
③ Reduce mold temperature.
④ Reduce the discharging area.

5. Uneven surface color of products

Production mechanism and Countermeasures:
① The mold temperature is not uniform and the part is too high, so the mold temperature should be properly controlled.
② The poor fluidity of the molding material results in the uneven distribution of the fibers, which can generally increase the molding pressure and increase the fluidity of the melt.
③ In the process of color paste mixing, pigment and resin can not be well mixed.