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Why thin wall mould cost is so high?

2018/11/7 15:36:47

Some customers wonder why thinwall molds cost so high. Let’s see:

First, comparing with common plastic articles moulds, thinwall moulds have undergone major differences from mold structures, gating systems, cooling systems, exhaust systems, and demolding systems. Mainly in the following aspects:

A. Mold structure: In order to withstand the high pressure during molding, the thin-wall molding mould has a large rigidity and a high strength. Therefore, the moving and fixed plate, and the supporting plate are relatively heavy, the plate thickness is usually thicker than that of the conventional molds. There are many support columns, and there may be more internal locking in the mold to ensure accurate positioning and good side support to prevent bending and offset. In addition, the high-speed injection speed increases the abrasive wear, so the thinwall mold should use a steel with higher hardness, and the hardness of the high-wear and high-erosion areas (such as the gate) should be greater than HRC55.

B. Gating system: Forming thin-walled products, especially when the thickness of the product is very small, a large gate is used, and the gate should be larger than the wall thickness. For the sprue, a cold well should be installed to reduce the gate stress, assist the filling, and reduce the damage when the product is removed from the gate. To ensure that there is sufficient pressure to fill the thin cavity, the pressure should be minimized in the runner system. For this reason, the runner design is larger than the common moulds, and at the same time, the residence time of the melt need limited to prevent degradation of the resin degradation. When it is a multi-cavity, the balance of the casting system is much higher than that of conventional molds. It is worth noting that two advanced technologies, namely hot runner technology and sequential valve gate technology, have also been introduced into the gating system of thin-walled product molds.

C. Cooling system: Thin-walled products can not withstand the large residual stresses due to heat transfer irregularities like traditional wall thickness parts. In order to ensure the dimensional stability of the product, and to control the shrinkage and warpage within an acceptable range, it is necessary to strengthen the cooling of the mold to ensure the cooling balance. Good cooling measures include the use of unclosed cooling lines in the core and cavity modules, increasing the cooling length, and enhancing the cooling effect. High-conductivity metal inserts are added where necessary to accelerate heat transfer.

D. Air venting system: Thin-wall injection molding molds generally need to have good venting properties, and it is best to perform vacuuming operations. Due to the short filling time and high injection speed, it is very important to fully exhaust the mold, especially the exhaust in the flow front gathering area, to prevent trapping. Air is usually discharged through cores, rams, ribs, studs, and parting surfaces. The end of the runners should also be fully vented.

E. Demoulding system: Because the walls and ribs of thin-walled products are very thin, they are very easy to damage, and the shrinkage in the thickness direction is small, so that the ribs and other small structures are easily bonded, and the high holding pressure makes the shrinkage smaller. To avoid topping and sticking, thin-wall injection molding should use a larger number of ejector pins than conventional injection molding.

All 5 points constitute the speciality of the thin-walled injection mold, resulting in an increase in the price of the mold.

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