The low pressure die casting process was developed in the 1940s and is the earliest and oldest counter gravity casting technology. This process is used to produce aluminum parts with complex geometry and high quality. The low pressure casting machine consists of a hydraulic drive system, a server, a molten pool holding furnace, an electrical system, liquid level charging equipment, a grinding tool, and a refrigeration system.
This article discusses the advantages, disadvantages of low pressure die casting process. Also, it explains the LPDC process and its application in various industries.
What is low pressure die casting (LPDC)?
Low pressure die casting is a casting method used to produce symmetrical shapes and design metal parts. For instance, the LPDC process is used to cast steering and wheel rims for automobiles. The most common alloy used in low pressure die casting process is aluminum. Other non-ferrous metals used for low pressure die casting includes brass, zinc, and magnesium alloy.
The low pressure die casting process is categorized as a permanent mold casting process as the molds used to make the casting are permanent and reusable for other cycles. These permanent molds are also known as dies. The destructible molds from permanent molds are then broken to retrieve the casings. The molds include bonded sand molds made from either ceramics or similar materials. But, the bonded sand molds can be used for other low-pressure die casting processes.
Advantages of low pressure die casting
- The pure molten metal filing improves the casting's purity.
- It has a stable liquid metal mold filling and an easy-to-control mold filling speed depending on the structure and materials of the casting. So, during metal filling, overturning impact and slash is avoidable. Also, the casting quality improves while oxidation slag inclusion is reduced.
- Fluidity increases, once the metal used, is filled under pressure making it convenient to pour complex thin-wall castings, thus making the contour of castings clear.
- Low pressure die casting doesn't have strict restrictions on the molds materials, making it equal to those used for general-gravity casting.
- The cast solidifies and crystallizes under pressure, thus improving the casting’s airtightness and sufficient feeding, and is conducive to obtaining casts with high mechanical properties and dense structure.
- Low pressure die casting doesn't have strict restrictions on the mold material. It can be used to wax loss mold, sand mold, graphite mold, metal mold, shell mold, etc.
- It has a relatively simple gating system, and you can omit or reduce the riser. The non-solidified liquid metal flows back to the crucible and reduces liquid metal loss. This process yields as high as 95%.
- Low pressure die casting can be used for various casting alloys, including cast steel and cast iron, with a range of alloy grades applications.
- LPDC has numerous applications suitable for casting different heights, structures, sizes, and wall thicknesses.
- Easy to understand automation and mechanization.
- Can adopt the use of riser and cold iron for castings that has poor sequential solidification and poor sequential.
The disadvantage of low pressure die casting
- Needs significant investment in molds and equipment.
- During aluminum alloy castings production, the riser and crucible contact liquid metal, thus easy to erode and get scrapped.
Applications of low pressure die casting
Low pressure die castings are used to produce magnesium and aluminum alloy parts. The automotive industry tends to be the industry relying heavily on low pressure die casting. It is used to create high-quality aluminum casts. But, because it's a relatively slow casting process, its use is limited to most luxury class automotive markets. Ideally, the automotive industry has reduced the casting cycle time by 50%, thus making low-pressure casting more economical than before.
Though low pressure die casting is the best choice for the automotive industry, non-automotive industries like machine building, electronics, and pipe assemblies rely on the process. Therefore, these industries benefits from low pressure die casting through high volume yield, lower machining costs, and unique quality.
Low pressure die casting is also used for small copper alloy castings like faucets, pipe fittings. When low pressure die casting is used in the production of cast steel, manufacturers use special refractory material.
Low Pressure Die Casting Process
This process involves the use of different types of equipment in each step. We'll look at each stage; Before feeding the molten metal to the crucible, mold manufacturing, and metal smelting process, heat resistant steel is used to make the mold which is the same process for metal smelting. The preparation work for pouring includes crucible seal examination, liquid level measurements, riser tube cleaning up, airtightness test, and more.
Low pressure die casting allows sand cores to be inserted in the die thus, forming the castings inside the structure. Sand core fabrication happens using the machine or manual labor to fill resin sand into the core box. After the sand core solidifies, the core box opened and the sand core is removed.
Step 1: Feeding
The feeding port is used to feed the molten metal into the crucible. The crucible has a heating element that keeps the molten metal at the desired casting temperature.
Step 2: Filling
After feeding, the crucible gets sealed, the pressure gas filled in, and the molten metal forced into the mold cavity through the riser tube. The gas pressure may range between 15 to 100Kpa.
Step 3: Solidification
At this stage, the pr3essure is maintained for a certain period until the mold parts solidify. The pressure is then relieved. The molten metal then goes back to the crucible via the riser tube.
Step 4: Ejection
In the ejection stage, the mold is opened, and ejector pins eject the castings. After that, a lubricant is sprayed on the mold, closed again, and prepared for the next cycle.
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