In order to meet the requirements of small and light parts, thin-wall injection molding has become the most important performance of injection molding machines. According to the definition of lightweight electronic parts, "thin wall" means that the wall thickness is less than 1 mm; for large automotive parts, the "thin wall" can be 2 mm. In summary, thin-walled products require changes in the processing process, higher pressures and speeds, shorter cooling times, and changes in part ejection and gate arrangement. The change of processing technology has also promoted the development of mold, machine and parts design, and put forward higher requirements for injection machines and molds.
The performance of the new injection machine much more advanced 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 continuous thinning of the wall thickness, a more special injection machine with high speed and high pressure performance is required.
With a thickness of less than 1 mm are currently required, filling time of less than 0.5 seconds, and injection pressures exceeding 210 MPa are common. Hydraulic injection machine for thin-wall injection molding, designed with an accumulator that can frequently drive injection molding and mold clamping. In order to withstand the high pressure of new injection machine, all-electric/hydraulic injection machine with high speed and high pressure performance, the minimum clamping force must be 5-7 tons per square inch (projected area). In addition, when the wall thickness is reduced and the injection pressure is increased, the large formwork helps to reduce the bending. The tie bar of an injection machine for thin-walled products requires a ratio of template thickness of 2:1 or lower. When producing thin-walled parts, closed-loop control of injection speed and pressure, as well as other processing parameters, helps to control filling and holding pressure at high pressure and high speed.
As for injection volume; large diameter barrels are often too large. The recommended injection volume is 40% to 70% of the barrel capacity. The shortening of the total molding cycle of thin-walled products makes it possible to reduce the minimum injection volume to 20% to 30% of the barrel capacity. For materials, a small injection volume means that the material stays longer in the simplification, which can result in a decrease in product performance.
Thinwall Mold speed is one of the key factors for successful 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 2 seconds, the thickness is reduced by 25%, which may reduce the filling time by 50%.
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 shortening of the molding cycle, and 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 for 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.