Thin-wall injection molding has a short filling time. Many filling times are less than 0.5 seconds. It is impossible to follow the speed curve or cut-off pressure in such a short time. Therefore, a high-resolution microprocessor must be used to control the injection molding machine; in thin-walled products In the whole injection molding process, the pressure and speed should be controlled independently at the same time. The filling process of the conventional injection molding machine is controlled by speed, and the method of pressure control to pressure control is no longer applicable.
The high-speed injection molding machine is mainly for products with relatively high cycle requirements and thin wall thickness requirements. The output per unit time is relatively large, the product structure is simple, and the product cost can be effectively reduced. The most familiar one is the disposable thin-walled lunch box. Disposable cups and other products.
Compared to conventional molds for conventional articles, molds for thin-walled articles have undergone major changes from mold structures, gating systems, cooling systems, exhaust systems, and demolding systems. Mainly in the following aspects.
In order to withstand the high pressure during molding, the thin-walled forming mold has a large rigidity and a high strength. Therefore, the mold should be made of tool steel with higher hardness. The hardness of high wear and high erosion areas (such as gates) should be greater than HRC55.
2. Gating system
Formed thin-walled articles, especially when the thickness of the article is very small, a large gate is used and the gate should be larger than the wall thickness. Two advanced technologies, hot runner technology and sequential valve gate (SVG) technology, have also been introduced into the casting system for thin-walled product molds.
3. Cooling system
Thin-walled products do not withstand the large residual stresses due to heat transfer irregularities like traditional wall thickness parts. In order to ensure the dimensional stability of the product, and to control the shrinkage and warpage within an acceptable range, it is necessary to strengthen the cooling of the mold to ensure the cooling balance.
4. Exhaust system
Thin-wall injection molding dies generally require good venting and are preferably vacuumed. Due to the short filling time and high injection speed, it is very important to fully exhaust the mold, especially the exhaust in the flow front gathering area, to prevent trapping and ignition.
5. Demoulding system
Because the walls and ribs of thin-walled articles are very thin, they are very easy to damage, and the shrinkage in the thickness direction is small, so that the ribs and other small structures are easily bonded, and the high holding pressure makes the shrinkage smaller.