What are the requirements for injection molding machines and molds for thin-wall injection molding?
The demand for small and light parts has made thin-wall injection molding the most demanding performance of injection molding machines. "Thin wall" is usually defined by lightweight electronic parts with a wall thickness of less than 1 mm. For large automotive parts, the "thin wall" can be 2mm. In summary, thin-walled products require changes in the processing: higher pressures and speeds, shorter cooling times, changes in part ejection and gate alignment. The following are the requirements for injection molding machines and molds for thin wall injection molding.
Injection machine
Standard injection machines can be used to produce a variety of thin walled products. The performance of the new injection machine is currently more than 10 years ago. Advances in materials, gate technology and design have further broadened the performance of standard injection machines for filling thin-walled parts. However, due to the ever-decreasing wall thickness, a more special injection machine with high speed and high pressure performance is required. For example, an electronic part with a thickness of less than 1 mm is normal for a filling time of less than 0.5 seconds and an injection pressure of more than 210 MPa. The hydraulic injection machine for thin-wall injection molding is designed with an accumulator that can frequently drive injection molding and mold clamping. Full electric injection machines and electric/hydraulic injection machines with high speed and high pressure performance are also available. In order 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 formwork helps reduce bending as wall thickness reduces injection pressure. The ratio of the tie rod to the template thickness of the injection machine for thin-walled products is 2:1 or lower. In the production of thin-walled products, infinite loop control of injection speed and pressure, as well as other processing parameters, helps control filling and holding pressure at high pressures and speeds.
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 total molding cycle of thin-walled products is greatly shortened, and it is possible to reduce the minimum injection volume to 20 barrel capacity. %~30%. The user must be very careful when molding, because for materials, a small injection volume means that the material stays in the barrel for a longer period of time, which can result in a decrease in product performance.
Mold
Speed ​​is one of the key factors for the success of thin-wall injection molding. Rapid filling and high pressure can inject molten thermoplastic material into the mold cavity at high speed to prevent the gate from freezing. If a standard part is filled in two seconds, the mold thickness is reduced by 25%, and it is possible to reduce the filling time by 50%, just 1 second.
One of the advantages of thin wall injection molding is that when the thickness is reduced, less material needs to be cooled. As the thickness is reduced, the molding cycle can be cut in half. The proper arrangement of the melt delivery device allows the hot runners and runners to not interfere with the shortening of the molding cycle. The use of hot runners and sprue bushings helps to minimize molding cycles. In addition, mold materials 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 safety factor to thin-walled molds. However, the cost of a solid mold may be 30% to 40% higher than a standard mold. But the increased cost is usually offset by increased production performance.
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