Thin wall injection mold has requirements on injection moulding machine, mould, and plastic. This article discusses the thin walls characteristics, economic benefit, and devices design.
What's the thin wall?
In a simple view, when the wall's thickness is less than 1mm, it is called thin wall. More comprehensively,the definition of thin wall is related to the procedure /thickness ratio, the plastic viscosity and the heat transfer coefficient.
Mahishi and mabney make a definition on the thin wall like that the injection whose L/t=100 or more than 150 is called thin wall injection moulding. L procedure from the moulds sprue to the farthest point of the product, and t stand for the products thickness t. L/t is called the procedure /thickness ratio.
thin wall injection mold plastic product
Why we need thin wall injection mold?
The cost of plastic is always in the majority of product's cost, such as 50-80%. Thin wall injection moulding will reduce the cost. Due to consumptive electronic equipments such as cell phone, MP3, digital camera, palmtop computer, are smaller and more convenient, the related plastic parts are thinner.
Thin wall injection mold machine.
Conventional injection moulding machine is difficult to be useful in the thin wall injection moulding. For example, the injection time of thin wall injection moulding is very short, it is unable to follow the speed curve in such a short period time. Therefore, an injection moulding machine with high-resolution MCU is necessary. In the whole thin wall injection moulding process, the pressure and the speed should be controlled independently. While conventional injection moulding machine is controlled by speed in the injection period and pressure in the holding period.
The barrel of thin wall injection mold machine is smaller than it in conventional injection moulding machine. Because the thin wall products need less plastic materials, so if the barrel is as big as the usual one, it will result in the material’s dissociation due to the long residence time. And each inject 35%-75% of the maximum injection volume is the best. It should be cautious to choose a thin wall injection moulding machinery company.
The mould in thin wall injection mold
The mould for thin wall injection moulding should be designed specially. The moulds structure, feed system, cooling system, venting system, and ejection system are all may change a lot.
thin wall injection mold
In order to withstanding high pressure when moulding, thin wall injection moulding mould must have a large rigidity and a high intensity. So the bottom clamp plate , the top clamping plate and the support plate should be thicker than conventional mould. There are more locking and positioning mechanism in the mould to ensure the accurate positioning and good collateral support, and avoid bending and offset.
When forming thin wall plastic product, especially the thickness of thin wall plastic product is very small, edge gate is necessary, and the gate should bigger than the wall thickness. If the gate is direct gate, it should set slag well to reduce gate stress and help filling, and ease the damage when wiping off the gate in the same time. In order to ensure the enough pressure to filling the cavity, it should be to minimum the pressure drop in the runner system as far as possible, and the runner pressure drop should not upper than 15% of the pressure offered by injection machine. Therefore, the runner sectional area should be designed bigger than the usual one, and limiting the residence time of melting materials to avoid plastic dissociation.
Some feed system in thin wall injection mould imports hot runner technology and sequence valve gate (SVG) technology. The hot runner technology enable the melting plastic provide high pressure at the gate after through a long path. However, the hot runner is easy to result in plastic degradation and degradation in a high temperature for a long residence time, so the residence time must be limited. SVG technology is a new class type hot runner control technology developed by U.S.,GE in the process of thin wall injection moulding. SVG can reduce moulding pressure efficiently. It plays an important role in producing large thin wall injection moulding plastic.
thin wall injection mold plastic, unlike the conventional thin wall plastic, can't withstand the large residual stress which is created due to nonuniform heat transfer. In order to ensure the plastic dimension stability, and control the shrinkage and warpage in an acceptable range, we must strengthen the mould cooling to ensure the cooling balance.
thin wall injection mold generally requires a good venting, it's best to operate in a vacuum. The mould’s abundant venting, especially the venting in the flow front gathering area, is very important to prevent trapped gas ignition because of the short injection time and high injection speed.
thin wall injection mold plastics wall and tendons are thin, they are very easy to damage, the contraction along the thickness direction is small, and the high holding pressure make it to shrink smaller, these make the tendons and other small structure easy to glue. thin wall injection mold requires more and larger ejection pins when compared with conventional injection Mold.
Thin wall injection mold requires a lot, but MICON MOULD do well in it. Their thin wall high speed injection mould is popular in the market.