The demand for small and light parts has made thin-wall injection molding the most important addition to injection molding machines. 'Thin wall' is usually defined by lightweight electronic parts with a wall thickness of less than 1 mm. In terms of terms, the 'thin wall' can be 2mm. In short, thin-walled products require a change in the processing: higher pressures and speeds, shorter cooling times, changing parts ejection and gate arrangement. The following is thin-wall injection molding Requirements for injection machines and molds.
Injection machine
Standard injection machines can be used to produce a wide range of thin-walled products. The performance of the new injection machines is now more than 10 years ago. Materials, gate technology and design advancements have further broadened the standard injection machine for filling thin-walled parts. Performance. However, due to the 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, the filling time is less than 0.5 seconds and the injection pressure exceeds 210 MPa. of.
The hydraulic injection machine for thin-wall injection molding is designed with an accumulator that can frequently drive injection molding and mold clamping. All-electric injection machines and electric/hydraulic injection machines with high speed and high pressure performance are also available. For the high pressure of the new injection machine, the minimum clamping force must be 5~7 tons/inch (projected area). In addition, when the wall thickness decreases, the injection pressure increases, the large template helps to reduce the bending. Injection for thin-walled products The ratio of the rod to the thickness of the machine is 2:1 or lower. When producing thin-walled products, the infinite loop control of injection speed and pressure and other processing parameters helps to control filling and holding pressure at high pressure and high speed.
As for the injection volume, the large diameter barrel is often too large. The recommended injection volume is 40%~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 will lead to a decline 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 within two seconds After filling the mold, the mold thickness is reduced by 25%, and it is possible to reduce the mold filling time by 50%, which is exactly 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 placement of the melt delivery device allows the hot runners and runners to not interfere with the molding cycle. Shortening. The use of hot runners and sprue bushings helps to minimize the molding cycle. In addition, mold materials should also be considered. P20 steel is widely used in the molding of traditional products, but due to the pressure of thin-wall injection molding High, 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 added cost is usually Will be offset by improved production performance.