Die Castings

  • Introduction

Die casting is a metal casting process, which is characterized by applying high pressure to the molten metal using the cavity of the mold. Molds are usually made of higher-strength alloys. This process is somewhat similar to injection molding. Most die castings are iron-free, such as zinc, copper, aluminum, magnesium, lead, tin, and lead-tin alloys and their alloys. Depending on the type of die casting, a cold chamber die casting machine or a hot chamber die casting machine is required.

The cost of casting equipment and molds is high, so the die casting process is generally only used for mass production of a large number of products. Manufacturing die-cast parts is relatively easy, which generally only requires four main steps, and the individual cost increment is very low. Die castings is particularly suitable for manufacturing a large number of small and medium-sized castings, so die casting is the most widely used one among various casting processes. Compared with other casting technologies, the die-casting surface is flatter and has higher dimensional consistency.

Based on the traditional die-casting process, several improved processes were born, including a non-porous die-casting process that reduces casting defects and eliminates pores. It is mainly used for processing zinc, which can reduce waste and increase the yield of direct injection process. There are also new die-casting processes such as the precision die-casting technology and semi-solid die-casting invented by General Dynamics.

  • Process

The traditional die-casting process mainly consists of four steps, or it is called high-pressure die-casting. These four steps include mold preparation, filling, injection, and shakeout, which are also the basis for various improved die casting processes.

The metals used for die casting mainly include zinc, copper, aluminum, magnesium, lead, tin and lead-tin alloys. Although die-cast iron is rare, it is also feasible. More special die-casting metals include ZAMAK, aluminum-zinc alloys and the standards of the American Aluminum Association: AA380, AA384, AA386, AA390 and AZ91D magnesium. The characteristics of various metals are as follows:

Zinc: the easiest metal to die-cast, it is economical to manufacture small parts, easy to coat, high compressive strength, plasticity, and long casting life.

Aluminum: Light weight, high dimensional stability when manufacturing complex and thin-walled castings, strong corrosion resistance, good mechanical properties, high thermal and electrical conductivity, and high strength at high temperatures.

Magnesium: easy to be machined, high strength-to-weight ratio, the lightest among commonly used die-cast metals.

Copper: High hardness, strong corrosion resistance, the best mechanical properties of commonly used die-casting metals, wear resistance, and strength close to steel.

Lead and tin: high density, high dimensional accuracy, can be used as special anti-corrosion parts. For public health considerations, this alloy cannot be used as food processing and storage equipment. The alloy of lead, tin and antimony (sometimes containing a bit of copper) can be used to make manual type and bronzing in letterpress printing.

Die Castings

Advantages and disadvantages
  • Advantages

The advantages of die castings include excellent dimensional accuracy of castings. Usually this depends on the casting material. The typical value is 0.1 mm for the initial 2.5 cm size, and 0.002 mm for each additional cm. Compared with other casting processes, its casting surface is smooth, and the fillet radius is about 1-2.5 microns. Compared to sandbox or permanent mold casting methods, castings with a wall thickness of about 0.75 mm can be produced. It can directly cast internal structures, such as wire sleeves, heating elements, and high-strength bearing surfaces. Other advantages include its ability to reduce or avoid secondary machining, fast production speed, casting tensile strength of up to 415 MPa, and high fluidity metal casting.

  • Disadvantages

The biggest disadvantage of die casting is its high cost. Casting equipment, molds, and mold-related components are relatively expensive compared to other casting methods. Therefore, it is more economical to produce a large number of products when manufacturing die castings. Other disadvantages include: this process is only suitable for metals with high fluidity, and the casting quality must be between 30 grams and 10 kilograms [5]. In normal die casting, the last batch of castings always has porosity. Therefore, no heat treatment or welding can be performed, because the gas in the gap will expand under the action of heat, resulting in internal micro-defects and surface peeling.

Eternal Bliss Alloy Casting & Forging Co, Ltd.

Caesar

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