Thin-wall Injection Molding Processing Requirements For Injection Molding Machines And Molds

- Apr 24, 2018-

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 molding machines for filling thin-walled parts. However, due to the continuous decrease in 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 has 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, which 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. In order to withstand the high pressure of the new injection molding machine, the minimum clamping force must be 5 to 7 tons per inch (projected area). In addition, when the wall thickness reduces injection pressure increases, large stencils help reduce bending. The ratio of tie bars to stencil thickness for injection molding machines for thin-wall products is 2:1 or lower. When producing thin-walled products, die-cycle 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 barrels are often too large. The recommended injection volume is 40% to 70% of the barrel capacity, and the total molding cycle of thin-walled products is greatly shortened. It is possible to reduce the minimum injection volume to the barrel capacity of 20 % to 30%. The user must be very careful when molding, because for the material, a small injection volume means that the material stays in the barrel longer, which can lead to a decrease in the performance of the product.     

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           Speed is one of the key factors in the success of thin-wall injection molding. Rapid filling and high pressure can inject the molten thermoplastic material into the mold cavity at a high speed, thereby preventing the gate from being cold solidified. If a standard part is filled in two seconds, then the mold thickness is reduced by 25% and it is possible to reduce the filling time by 50% for 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 decreases, the molding cycle can be cut in half. The rational arrangement of the melt conveyor means that the hot runners and runners do not impede the shortening of the molding cycle. Using 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 conventional 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 additional safety factors to thin-walled molds. However, the cost of a strong mold may be higher than that of a standard mold by 30% to 40%. However, the increased costs are usually offset by increased production performance.