A Brief Discussion on the Essential Factors of Blow Mould Design and Manufacturing

Material Design of Blow Mould

The materials used for making blow mould must have high thermal conductivity and sufficient strength to withstand the cutting force of the die opening. Currently, aluminum is the advanced alloy used to make most molds. Because of its good machinability, the mold cavity is usually machined by machine cutting. Copper alloy molds also have high heat transfer and good corrosion resistance. However, the cost is high and the price is expensive. Moreover, its density is three times that of aluminum, which may cause severe wear on the molding machine. Steel alloy molds are easy to repair with welding or inlaying method. The thermal conductivity of cast aluminum molds is worse than that of cutting aluminum molds. The die opening of the mold cavity usually needs to be inlaid with copper alloy or stainless steel because the strength and hardness of cast aluminum cannot meet the requirements of the cutting force of the die opening.

Zinc castings can be made on a steel mother mold. The mold cavity and bottom plate are poured into a predetermined size. Since the strength of zinc is not sufficient to cut the plastic, the operating holes and shoulder areas are inlaid with copper or stainless steel. The bottom and neck are also inlaid with these two metals. Casting molds can also be made of casting copper alloy. In comparison, casting steel molds are relatively easy because they rely on pressure or gravity casting. These molds have many fine parts that can be produced by steel mother molds or ceramic molds.

Cooling Design of Blow Mould

Cooling is a challenging and critical aspect in blow mould design. Drilling-type cooling pipelines are installed where cooling is most needed. To achieve better production control, most molds are designed with several independent cooling zones. The neck and bottom require the most heat dissipation, so the most effective cooling is required.

Die Opening Design of Blow Mould

The depth of the die opening area may be a significant factor in part yield and quality. The die opening area is where excess plastic enters during blow molding. The type and shape of the die opening may determine the welding condition of a part. For harder resins, steel or copper alloy is required as the die opening material. Sometimes the die opening area needs to be blown with air to accelerate plastic cooling, remove excess material, and prevent part distortion.

Exhaust Design of Blow Mould

When blow moulds are formed, exhaust must be made to allow gas to escape quickly. The most common and economical exhaust method is surface exhaust. Deep sandblasting or texture treatment of the mold cavity also helps exhaust. Another important reason for exhaust (for parts where plastic must be blown into tight narrow spaces) is to display details.