Low Pressure Die Casting

Low pressure die casting process, developed in 1940s, is the earliest counter gravity casting technology.  People use this process to produce aluminum parts with complex geometry and high quality, such as automobile hub, cylinder and cylinder head of auto-engine, piston, missile housing, impeller, inducer etc. Equipment costs are somewhat high, but labor costs are generally low, because the process is now semi or fully automated.

To improve and expand our aluminum casting capability, in 2005 we invested a low pressure die casting line in our foundry. By now, we have 10 set low pressure casting machines, range from 500KG to 800KG. These machines are fully automatic with PLC control, which has enhanced productivity with minimum utilization of resources like manpower. Our low pressure die casting parts cover automotive parts, electrical enlosures/housings, industrial robot parts, medical devices parts, lighting fixture parts, hardware tool parts, etc.

• ASMT Standard: A319, A356, A357, A413
• GB Standard: ZL101, ZL101A, ZL102, ZL107
• BS Standard: LM6, LM20, LM25
• EN Standard: EN AC-42100, EN AC-42200, EN AC-43000, EN AC-43200, EN AC-43300, EN AC-43400, EN AC-44200, EN AC-44300, EN AC-46000, EN AC-46200

In low pressure die casting process, the mold is generally mounted on above the sealed crucible containing molten metal. The riser tube is connected the mold above and extends into the crucible of molten metal below. Compressed dry air exerts a pressure (0.015-0.1MPa) on the liquid surface of molten metal in the crucible, and forces the metal liquid into the cavity from bottom up through the riser tube. The pressure is relieved after casting has solidified in the die, then the molten metal in the riser tube will recede back into the crucible.

The mold for low pressure casting can be die or sand mold. The filling process is different with gravity casting such as gravity die casting and sand casting, or high pressure die casting.

In low pressure die casting process, the molten metal in the bottom of crucible is forced into the cavity through the riser tube, which thoroughly avoids the slag floating on the surface getting into the cavity. So castings made by this  process are with higher purity than by other casting processes.

Molds for low pressure casting have no risers normally, and molten metal in the riser tube will return in the crucible after pressure relief, so the recovery rate of molten metal can be as high as 90%.

The filling process of molten metal is very smooth, and there are no flips, impacts and splashes, which reduces the formation of oxided slag during filling.

The solidification and crystallization of metal is under pressure, which enables this process with good feeding ability and castings with more compact microstructure.

The mold filling properties of low pressure die casting make it very suitable for castings with large surface and thin wall-thickness.

• Mold Manufacturing and Metal Smelting
  Like other permanent mold casting processes, the mold is made of heat-resistant steel. And the metal smelting process is alike as well.
• Preparation for Pouring
  Preparation work includes crucible seal examination, riser tube cleaning up, liquid level measurement, airtightness test, etc.
• Making Sand Cores (if has)
  Like sand casting but unlike high pressure die casting, low pressure die casting allows inserting sand cores in the die to form the inside structure of a casting. Sand core is fabricated by utilizing manual labor or machine to fill the resin sand into the sand core box. After sand core is solidified, open the core box and get the sand core.

• High efficiency — Alike high pressure die casting process, this process is easy to achieve full automation.
• High quality — Parts mde by this process are with some excellent characteristics as tight tolerance, smooth surface, good mechanical properties.
• High material use factor — Since the molten metal will goes back into crucible after pressure relieve, the material use factor is much higher than other permanent die casting processes.

• Both the casting machines and molds are expensive. That makes this process only suitable for big run production.
• The crucible and riser tube are easy to be eroded and damaged since long time storage and contact of molten metal. In turn, the molten metal is easy to be polluted by the Fe element from crucible and riser tube.