Methods to solve common quality problems in SMC material molding process
2017-08-04
1104
SMC material molding process is a high-power production method in the molding process of fiberglass/composite materials. SMC molding process has many advantages, such as accurate product size, smooth appearance, good repeatability of product appearance and size, one-time molding of complex structures, and no need to damage the product during secondary processing. However, in the SMC molding production process, there may also be adverse phenomena, mainly manifested in the following aspects
(l) Shortage of materials:
Shortage refers to the incomplete filling of SMC molded parts, which often occurs at the edges of SMC products, especially at the root and top of corners.
Cause analysis:
(a) Low material discharge, (b) poor activity of SMC material, (c) insufficient equipment pressure, (d) too fast curing.
Mechanism and countermeasures:
① After SMC material is heated and plasticized, its melt viscosity is high. Before the cross-linking and solidification reaction is completed, there is no sufficient time for the melt to fill the mold cavity due to pressure and volume.
② The storage time of SMC molding material is too long, and the styrene evaporates too much, resulting in a significant decrease in the activity performance of SMC molding material.
③ The resin paste has not penetrated the fibers. During molding, resin paste cannot drive fiber movement and result in material shortage. The direct solution to the shortage caused by the above reasons is to remove these molding materials during cutting.
④ Lack of feeding amount leads to material shortage. The solution is to appropriately increase the amount of material added.
⑤ The molded guess is wrapped in too much air and a lot of vapor. The treatment methods include adding appropriate exhaust times; Appropriately increase the feeding area and regularly organize the mold; Properly increase the molding pressure.
⑥ The pressure was applied too late, and the molded material had already completed cross-linking and curing before filling the mold cavity If the mold temperature is too high and the cross-linking curing reaction is premature, it should be cooled appropriately.
(2) Stomata
There are regular or irregular small holes on the surface of the product, which often occur at the top and center of the thin wall of the product.
Mechanism and countermeasures:
① SMC molding is wrapped in a lot of air and has a high content of evaporated substances, resulting in poor exhaust; The thickening effect of SMC material is insufficient and cannot effectively remove gas. For the above causes, useful control can be obtained by combining the method of adding exhaust frequency and organizing the mold.
② If the feeding area is too large, reducing it appropriately can achieve control. In the actual operation process, human factors may also form sand holes. For example, if the pressure is applied too early, it may make it difficult for the gas trapped in the molded material to be discharged, resulting in the appearance of pores on the surface of the product.
(3) Warping and deformation
The primary reason for the occurrence is the uneven solidification of the molding material and the shortening of the product after demolding.
Mechanism and countermeasures:
During the resin curing reaction, the chemical structure changes, causing a reduction in volume. The uniform curing results in a tendency for the product to warp towards the side that is cured first. Secondly, the thermal expansion coefficient of the product is greater than that of the steel mold. When the product cools, its unidirectional shrinkage rate is greater than the unidirectional thermal shrinkage rate of the mold. Therefore, the following methods are selected for processing:
① Reduce the temperature difference between the upper and lower molds to make the temperature spread as evenly as possible;
③ Using cooling fixtures to constrain deformation;
④ Properly increasing the molding pressure, adding structural compactness to the product, and reducing the shortening rate of the product;
⑤ Extend the insulation time appropriately to eliminate internal stress.
⑥ Adjust the curing shortening rate of SMC material.
(4) Bubbling
Rise in a semi-circular shape on the surface of a cured product.
Mechanism and countermeasures:
It may be due to incomplete solidification of the material, excessively high temperatures in some areas, or high levels of evaporation in the material, resulting in trapped air between the sheets and causing the semi-circular appearance of the product.
① Appropriate progress in forming pressure
② Extended insulation time
③ Lower the mold temperature.
④ Reduce the discharge area
(5) Uneven color distribution on the surface of the product
Mechanism of occurrence and countermeasures
① The mold temperature is uneven and some parts are too high. The mold temperature should be properly controlled;
② The activity of the molded material is poor, resulting in uneven fiber dispersion. Generally, the activity of the melt can be improved by adding molding pressure;
③ During the process of color paste distribution, pigments and resins cannot mix well.
Reading source: SMC molded product manufacturer www.jmlicheng.com
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