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What are the requirements for injection machines and moulds?

Categories: ZCMIM NewsStars: 3StarsVisit: -Release time: 2019-07-19 08:42:00
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The demand for small and light products has made the manufacture of thin-walled products one of the most important features of injection molding machines."Thin wall" is usually defined by the wall thickness of less than 1mm for electronic parts. For large automotive parts, the "thin wall" can be 2mm. In short, thin-walled products require changes in processing:  higher pressure and speed, shorter cooling time, change ejector and gate arrangement. The following are the requirements of producing thin-wall products for injection machines and molds.

Injection machine

Standard injection machines can be used to produce a variety of thin-wall products. New injection machine performance is much better than it was 10 years ago. Advanced material and  gate design have further expanded the filling capability of standard injection machines. However, as the wall thickness is decreasing, a more special injection machine with high speed and high pressure performance is needed.  For example, it is normal for an electronic part with a thickness of less than 1mm to be filled for less than 0.5 seconds and with injection pressure exceeding 210MPa.The hydraulic injection machine used for thin wall injection molding is designed with a pressure storage device, which can frequently drive injection molding and die.

Fully electric injectors and electric/hydraulic injectors with high speed and high pressure properties are also available. To withstand the high pressure of new injection machine, the minimum clamping force must be 5 ~ 7 tons/inch (projected area). In addition, large templates help reduce bending when wall thickness reduces injection pressure increase. For thin-wall products, the tie bar of injector has 2:1 or lower ratio to the thickness of template.  In production of thin-wall products, endless cycle control of injection speed and pressure and other parameters is helpful to control filling and holding pressure at high pressure and high speed.

As for the injection volume, large diameter barrel is often too large, recommended injection volume for barrel capacity is 40% ~ 70%. The total molding cycle of thin-wall products is greatly shortened, and it is possible to reduce the minimum injection volume to 20% ~ 30% of barrel capacity. Users must be very careful when using injection molding, because a small injection volume means material will remain in the cylinder for a longer time, which will lead to a degradation of product performance.

The mould

Speed is one key factor for the success of thin-wall injection molding. Rapid mold filling and high pressure can inject molten thermoplastic material into mold cavity at high speed, thus preventing gate cooling. If a standard piece filled in less than two seconds, die thickness reduced 25%, potentially reducing the filling time by 50%, just one second.

An advantage of thin-wall injection molding is less material and cool time when the thickness reduced.  As thickness decreases, the molding cycle can be shortened by half. Proper setting of melt conveyer ensures that the hot runner and runner will not hinder the shortening of forming cycle. The use of hot runner and runner bushing helps to minimize forming cycle. In addition, should also consider mold material. P20 steel is widely used in traditional products, but because of higher pressure by thin-wall injection, the molds must be made very strong. H-13 and other hard steels add additional safety features to thin-walled molds. However, the cost of a solid mold can be 30 to 40 percent higher than a standard mold. But the increased cost is usually offset by improved production performance.

Keywords in the article: injection molding machines the mould
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