Thin-wall Injection Moulding

In order to meet the requirements of small and light injection moulded parts manufacturing, thin-wall injection moulding has become the most important injection moulding process. According to the definition of lightweight electronic plastic parts, "thin wall" means that the wall thickness is less than 1 mm. For large automotive plastic parts, the "thin wall" can be 2 mm. In summary, thin-wall injection moulded parts 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 plastic injection mould, injection moulding machine and injection moulded parts design, and put forward higher requirements for injection moulding machines and injection moulds.

Below are requirements of thin-wall injection moulding for injection moulding machines and injection moulds:
Requirements for injection moulding machine

• Standard injection moulding machines can be used to produce a variety of thin-wall injection moulded parts. The performance of the new injection moulding machine is currently better than 10 years ago. Advances in materials, gate technology and plastic injection mould design have further broadened the performance of standard injection moulding machines for feeding performance of thin-wall injection moulded 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, the electronic part having a thickness of less than 1 mm is normal for the feeding time of less than 0.5 seconds and the injection pressure of more than 210 MPa.
• The hydraulic injection machine for thin-wall injection moulding is designed with an accumulator that can frequently drive injection moulding and mould 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 moulding machine, the minimum clamping force must be 5-7 tons/inch (projected area). In addition, large formwork helps reduce bending as wall thickness reduces and injection pressure increases. The ratio of the tie rod to the template thickness of the injection moulding machine for thin-walled plastic parts is 2:1 or lower. In the production of thin-wall plastic parts, the infinite loop control of injection speed and pressure, as well as other processing parameters, helps to control feeding 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 moulding cycle of thin-wall injection moulded parts is greatly shortened, and it is possible to reduce the minimum injection volume to 20 %~30% of barrel capacity. It must be very careful when moulding, because for materials, small injection volume means that the material stays in the barrel for a longer period of time, which can result in the decrease in plastic parts performance.

Requirements for injection mould

• Speed is one of the key factors for the success of thin-wall injection moulding. Rapid feeding and high pressure can inject molten thermoplastic material into the mould cavity at high speed to prevent the gate from freezing. If a standard part is fed in two seconds, the mould thickness is reduced by 25%, and it is possible to reduce the feeding time by 50%, just 1 second.
• One of the advantages of thin wall injection moulding is that when the thickness is reduced, less material needs to be cooled. As the thickness is reduced, the moulding 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 moulding cycle. The use of hot runners and gate bushings helps to minimize moulding cycles. In addition, mould materials should also be considered. P20 steel is widely used in the moulding of traditional plastic parts. But due to the higher pressure of thin-wall injection moulding, the mould must be made very strong. H-13 and other hard steels add an extra safety factor to thin-wall injection moulds. However, the cost of a solid injection mould may be 30% to 40% higher than a standard injection mould. But the increased cost is usually offset by increased injection mould manufacturing performance.

Thin-wall injection moulding has become a new research hotspot in the plastic moulding industry due to its advantages of reducing plastic parts weight and external dimensions, facilitating integrated design and assembly, shortening injection moulding cycle, saving materials and reducing injection moulding cost.