injection machine
Standard injection machines can be used to produce a variety of thin-walled products. The performance of the new injection machine is much better than that of 10 years ago. Advances in materials, gate technology, and design have further broadened the capabilities of standard injection machines for filling thin-walled parts. However, due to the continuous reduction of wall thickness, a more special injection machine with high speed and high pressure performance is required.
For example, for an electronic part with a thickness of less than 1mm, it is normal for the mold filling time to be less than 0.5 seconds and the injection pressure to exceed 210MPa. Hydraulic injection machines for thin-wall injection molding are designed with a pressure accumulator to drive injection and mold clamping frequently. All-electric injection machines and electric/hydraulic injection machines with high-speed and high-pressure performance are also available. In order to be able to withstand the high pressure of the new injection machine, the minimum clamping force must be 5 to 7 tons per inch (projected area).
In addition, large templates help reduce bowing when wall thickness decreases and injection pressure increases. The ratio of tie rod to template thickness of injection machine for thin-walled products is 2:1 or lower. In the production of thin-walled products, the dead-loop control of injection speed and pressure, as well as other processing parameters, helps to control mold filling and packing at high pressure and speed.
As for the injection volume, the large-diameter barrel is often too large. The recommended injection volume is 40% to 70% of the barrel capacity. The overall molding cycle of thin-walled products is greatly shortened, and it is possible to reduce the minimum injection volume to 20% of the barrel capacity. %~30%. Users must be very careful when injecting, because for materials, a small injection volume means that the residence time of the material in the barrel is longer, which will lead to a decrease in the performance of the product.
mold
Speed is one of the key factors for the success of thin-wall injection molding. Fast filling and high pressure inject molten thermoplastic material into the cavity at high speed, preventing gate freeze. If a standard part fills in two seconds, a 25% reduction in mold thickness has the potential to reduce fill time by 50%, to exactly 1 second.
One of the advantages of thin-wall injection molding is that there is less material to cool as the thickness decreases. With reduced thickness, the molding cycle can be cut in half. The reasonable setting of the melt conveying device makes the hot runner and runner not hinder the shortening of the molding cycle. Use of hot runners and sprue bushings can help keep molding cycle times to a minimum. In addition, the mold material should also be considered.
P20 steel is widely used in the molding of traditional products, but due to the higher pressure of thin-wall injection molding, the mold must be made very strong. H-13 and other hard steels add an extra factor of safety for thin wall molds. However, the cost of a solid mold can be 30% to 40% higher than that of a standard mold. But the increased cost is usually offset by improved production performance.
