Aluminium components have been used in the automotive industry since the early 20th century. Automotive experts have long compared the economic efficiency and suitability of different processes for manufacturing these components. Here, we compare low-pressure and high-pressure die casting.

Low-pressure die casting

As with high-pressure die casting, the two halves of the mould are fixed to fixed and moving machine plates, but the machine is aligned vertically. A holding furnace for the molten metal is located below the fixed plate. A pressure of up to 1 bar is applied to the furnace, which pushes the molten metal (usually aluminium, but also magnesium) upwards through an air inlet into the mould cavity - usually a permanent mould, but it can also be a sand mould. The upward movement of the molten metal is against gravity. After filling the mould, the pressure is maintained while the metal cools so that more molten metal can be added to offset any volume deficit (shrinkage cavities) as the metal changes from the molten state to the solid state. This naturally ensures that solidification from top to bottom is as uniform as possible.

Advantages

Very good strength values

Complex geometries can be realized due to the possibility of using sand cores

Higher material utilization, no feeders required

High dimensional accuracy

The entire process is very suitable for automation

Not too complex machine and mold technology

Disadvantages

Slower casting cycle

Minimum wall thickness of about 3 mm (in the mold)

High-pressure die casting

One half of the mold is fixed to a fixed platen and the other half to a movable platen on the horizontally aligned die casting machine. Due to the pressures of up to 1,200 bar used during pouring, the bolts that hold the two halves of the mold together must have a high locking force. Cold chamber die casting machines are mainly used for aluminum alloys due to the relatively high melting points of these alloys. Here, the cast component is located outside the melt. The molten metal is fed into the shot chamber, from where the piston pushes the metal into the mold. As soon as the metal cools and solidifies, the two halves of the mold open and the casting is automatically ejected from the mold by means of an ejector pin.

Advantages

Short casting cycles

Suitable for thin-walled components

Smooth surfaces

Well suited for automation

Disadvantages

High investment and operating costs

Complex and expensive molds

Suitable only for die castings without undercuts, as sand cores cannot be used

Reduced strength values

The die casting weight is limited by the machine clamping force

The first thing to say is that there are processes that are best suited for both low-pressure and high-pressure die casting. This depends largely on the complexity of the component, the number of parts and the manufacturing budget. Therefore, it makes sense to compare the working principles of low-pressure and high-pressure die casting processes at this point.