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HPDC vs LPDC Die Casting

 

High-pressure die casting(HPDC)

High-pressure casting is a process in which molten metal is poured into a pressure chamber so that the molten metal fills the mold cavity at high speed and then solidifies under high pressure to form a casting. The flow speed during filling can reach 30-80mm/s, and the time for filling the cavity is extremely short.

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Advantages and disadvantage of HPDC

It has the advantages of good surface finish, stable dimensions, and direct molding of thin-walled structures. It is mainly used for the manufacture of shells and other castings, Its work efficiency is high, and it will also provide a smoother surface for finishing. The surface finish depends on the finish of the mold. This high-quality surface can be directly applied to other paints.

However, the disadvantage is that it generates high operating and investment costs. In high-pressure production, thicker parts may be difficult to cast. Porosity may also occur in high-pressure die-casting parts, which generally cannot be heat-treated and have high operating costs.

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Feature and application of HPDC

High-speed, high-pressure, and metal casting are the main characteristics of pressure casting production. Thin-walled castings with complex shapes can be cast, and fine grains, holes, teeth, grooves, etc. can be directly cast. The dimensional accuracy and surface quality of the castings are relatively high. High, realizing less cutting or no cutting. Due to the high production efficiency of this die-casting machine and the high metal utilization rate, the application in the die-casting production of zinc, aluminum, and magnesium alloys has a growing trend.

 

The strength and surface bending hardness of the casting are higher, and the tensile strength is 25%~30% higher than that of sand casting. However, due to the fast filling speed of liquid metal, the gas in the cavity is difficult to discharge, and it is often filled with gas under the surface Therefore, under normal circumstances, die castings cannot be heat treated or mechanically processed to avoid porosity on the surface of the casting.

 

HPDC mainly used for the mass production of non-ferrous metals such as aluminum, magnesium, zinc, copper, etc., and it is widely used in industries such as automobiles, meters, electronics, aerospace, lighting, furniture, mechanical, hardware, and communication, etc. In recent years, new technologies such as vacuum die casting, new processes, as well as new equipment such as double-punch die-casting machines, horizontal parting full-vertical die casting machines, etc., have continued to emerge. Although the quality of castings has been greatly improved to effectively control casting defects, there are still have pores, shrinkage holes, and shrinkage porosity. At the same time, due to the continuous emergence of new die-casting materials, the scope of application of die casting will continue to expand.

Low-pressure die casting(LPDC)

LPDC is to make the liquid alloy fill the cavity from bottom to top under lower pressure, and crystallize under pressure to cast the casting part. Therefore, compared with high-pressure casting, the pressure is different and the direction of liquid metal flow is different, and it can be heat treated.

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Advantages and disadvantage of LPDC

Due to the stable filling of LPDC and the same direction of liquid flow and airflow, the castings produced by casting have fewer defects such as porosity and slag inclusion; the structure is dense and the mechanical properties of the castings are high; the filling ability is strong, which is conducive to the formation of clear and clear contours. Castings with smooth surface, so important aluminum alloy castings will be low-pressure casting.

Although LPDC has a dense structure and better mechanical properties, its productivity is low. After HPDC, the surface quality is better, but there are inevitably some pores inside, and its productivity is high, so it is more suitable for thin-walled castings, but the castings are shrinkage and loose, not dense, and are not used for castings with high airtightness requirements.

 

Feature and application of LPDC

LPDC is used when selecting castings with high air-tightness requirements. The production batch is large, and small and medium-sized non-ferrous metal castings without tightness requirements are HPDC. The difference is that LPDC parts can be strengthened by heat treatment, and the toughness can be greatly improved. Therefore, the design depends on the product wall thickness and the weight of the entire product. If the wall thickness is thicker and the product weight is heavier, the LPDC process should be selected. Otherwise, if the wall thickness is lighter, the HPDC process should be selected.

 

The feature of LPDC as below:

  • LPDC can use sand, metal, graphite, etc., and has the following advantages:

  • Filling with pure molten metal improves the purity of castings.

  • The molten metal fills smoothly, thereby reducing the formation of oxide slag.

  • The casting has good moldability. The molten metal is filled under pressure, which can improve the fluidity of the molten metal, which is beneficial to the formation of castings with clear contours and smooth surfaces, and is more beneficial for the molding of large thin-walled castings.

  • The casting is solidified under pressure, and the structure of the casting is dense.

  • Convenient production and operation, good working conditions, high production efficiency, and easy realization of mechanization and automation.

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