Common quality problems and solutions for drawing hydraulic presses

Although the SMC composite material molding process is the most efficient one in the glass fiber reinforced plastic/composite material molding process. The SMC composite material molding process also has many advantages, such as: accurate product size, smooth surface, good product appearance and size repeatability, complex structure can also be molded once, and secondary processing does not need to damage the product. However, undesirable defects can also occur in the production process of SMC composite material molding, which are mainly manifested in the following aspects:

(1) Lack of materials

Lack of material means that the SMC composite material molded parts are not completely filled, and the production sites are mostly concentrated on the edges of the SMC products, especially the roots and tops of the corners.

Generation mechanism and countermeasures:

①After the SMC material is plasticized by heat, the melt viscosity is large. Before the cross-linking and solidification reaction is completed, there is not enough time, pressure and volume to fill the mold cavity with the melt.

②The storage time of the SMC composite molding material is too long, and the styrene volatilizes too much, resulting in a significant decrease in the flow properties of the SMC composite molding material.

③The resin paste is not soaked into the fiber. The resin paste cannot drive the fiber to flow during molding, resulting in material shortage. For the shortage of materials caused by the above reasons, the most direct solution is to remove these molded materials when cutting materials.

④Insufficient feeding amount causes material shortage. The solution is to increase the feeding amount appropriately.

⑤There is too much air and a lot of volatile matter in the molding material. The solution is to appropriately increase the number of vents; appropriately increase the feeding area to clean the mold at a certain time; appropriately increase the molding pressure.

⑥The pressure is too late, and the molded material has completed cross-linking and curing before filling the mold cavity.

⑦If the mold temperature is too high, the cross-linking and curing reaction will advance, so the temperature should be appropriately lowered.

(2) Stoma

There are regular or irregular small holes on the surface of the product, most of which are produced at the top and middle thin walls of the product. Generation mechanism and countermeasures:

① The SMC composite material is wrapped in a large amount of air and has a large volatile content, and the exhaust is not smooth; the thickening effect of the SMC material is not good, and the gas cannot be effectively driven out. The above causes can be effectively controlled by a combination of increasing the number of vents and cleaning the mold.

② If the feeding area is too large, it can be controlled by appropriately reducing the feeding area. In the actual operation process, human factors may also cause trachoma. For example, if the pressurization is too early, it may be difficult for the gas wrapped in the molding compound to be discharged, resulting in surface defects such as pores on the surface of the product.

(3) Warpage deformation

The main reason is the uneven curing of the molding compound and the shrinkage of the product after demolding. Generation mechanism and countermeasures:

During the curing reaction of the resin, the chemical structure changes, causing volume shrinkage, and the uneven curing makes the product tend to warp to the first cured side. Secondly, the thermal expansion coefficient of the product is larger than that of the steel mold. When the product is cooled, its one-way shrinkage rate is greater than the one-way heat shrinkage rate of the mold. For this reason, the following methods are used to solve the problem