What should be noted in heat-resistant ABS injection molding?

In this article, we will discuss the processing points of heat-resistant ABS resin molding from five aspects: mold design, material drying, molding temperature, holding pressure and time, and mold temperature.
1. Product mold design
Product wall thickness requires uniformity, and the wall thickness difference of ABS products should be controlled within 25% to prevent local stress concentration caused by excessive wall thickness difference. The root of the column with weaker strength needs to increase the R angle or add reinforcement to prevent the column from fracture. Fastener design, the root of the fastener needs to be chamfered R angle, the size of R angle depends on the wall thickness of the product, the ratio of R angle to wall thickness should be above 0.3, with the increase of the ratio, the internal stress gradually decreases, while also taking into account the shrinkage of the product surface. The design of the cooling channel of the mold should ensure the uniformity of cooling to avoid the internal stress caused by uneven cooling and shrinkage.
2、Whether the material is dry or not
Generally, heat-resistant ABS resin will absorb moisture from the air during storage and transportation. Water absorption varies with air humidity and is generally between 0.2-0.4%, so the material must be dried sufficiently to reduce the water content of the material. Less than 0.05%, preferably less than 0.02%, otherwise surface defects such as water splashes and silver filaments may appear. The drying temperature of heat-resistant ABS resin is higher than that of ordinary ABS, generally 80-95℃, and the drying time is 3-4 hours.
3、Forming temperature
The molding temperature is a parameter that requires special attention during the processing of heat-resistant ABS. The basis of setting is to ensure the full plasticization of heat resistant ABS. The molding temperature range recommended by the supplier should be used as much as possible. Increasing it will significantly reduce the viscosity of heat resistant ABS, increase the fluidity of the resin, and make the flow distance longer to ensure that the material has sufficient filling capacity.
4、Holding pressure and time
For heat resistant ABS, the setting of holding pressure and time is reasonable and directly affects the internal stress of the part. The increase of holding pressure will make the molecular gap smaller, the range of motion of segments decrease, the volume of melt decreases, the density becomes larger, and the intermolecular force increases, which can improve the shrinkage and internal quality of the product, but will lead to a larger internal stress, so a lower holding pressure should be chosen as much as possible under the premise of ensuring the appearance quality of the product.
The holding time is set according to the time when the gate cools and solidifies, the screw pushes forward and no longer applies pressure to the molded product. If the holding time is too long, the material will be easily overfilled, the molecular gap will become smaller and the internal stress will become bigger; if the holding time is too short, the product will be easily shrunk and the size will be unstable. The setting of holding time should be the best holding time when the weight of the product no longer changes.
5、Mold temperature machine
The mold temperature machine is used to control the mold temperature of heat-resistant ABS molding. The recommended mold temperature is 60-80℃. Higher mold temperatures tend to produce good flow, higher weld line strength and lower internal product stress, but the molding cycle time will be extended. If the mold temperature is lower than the recommended temperature, it will result in excessive internal product stress, reduce product performance, and may cause undesirable phenomena such as product cracking, screw hole cracking, or paint cracking.