What is sand casting?
It is a process that utilizes non-reusable sand molds to form metal parts – usually aluminum, brass, and zinc. A pattern that is usually CNC machined or 3D printed according to your 3D model, is placed into a sandbox. Then the cavity is formed with sand around the pattern. With other features on the mold, for example pouring cup, sprue, and runner, operators can fill molten metal into the cavity of the sand mold to produce the part.
Process – Sand Casting
Part – Motor Supporter
Material – Steel
What are the advantages of sand casting?
1. Low Mold Cost
The sand mold is much lower than the die casting mold. It makes sand casting a good choice for lower volume production. The cost saving can be significant when the part is big and has complex features.
2. Wide Material Suitability
Sand casting is good to make almost any material – aluminum, steel, brass, bronze, and zinc. Sand mold has very high fire resistance than steel mold making it suitable for high melting temperature materials like steel and copper.
3. Good Geometry Adaptability
Sand casting suits any part small or large, simple or complex. The advantage is very obvious for large and complex parts. It is good for making thin wall features or under-cuts.
4. Short Lead Time
It requires a much shorter time to build a sand mold – as short as one week depending on the complexity of the part.
Permanent Mold Casting (Gravity Casting)
What is permanent mold casting?
Permanent mold casting is a process of forming metal parts with reusable steel molds using gravity to fill them. Some people call it gravity casting. Technically it is one of the gravity-casting processes because sand casting is also gravity-casting. Because the molds are usually steel, the surface quality is better than sand casting. The molds usually are CNC machined and then coated with a refractory material to prevent the parts from sticking to the mold. Molten metal is poured into the mold through the pouring gate. Open the mold to take the part out after material solidification.
Process – Permanent Mold Casting
Part – Machinery Frame
Material – Aluminum Alloy
What are the advantages of permanent mold casting?
1. Low Mold Cost
Compare to sand casting, the permanent mold cost is higher, but it is much lower than die casting. It is a very good process for medium volume, for example, several thousands of parts.
2. High Accuracy
The molds are cut from steel, the accuracy is higher than sand mold.
Investment Casting (Lost-Wax Casting)
What is investment casting?
First, an injection mold is needed to make wax patterns. Then coating the wax patterns by dipping them in refractory slurry and spraying fine sand. Usually, there 3 to 5 layers of coating are needed to make the SHELL(mold) mechanically robust enough depending on the complexity of the part. After that, the well-coated and cured wax patterns are placed into temperature controlled oven to melt the wax away from the SHELL. Then pouring molten metal, for example, steel or aluminum into the mold. After the parts are cooled down, break the mold to take the parts out.
Process – Investment Casting
Part – Turbo Wheel
Material – Stainless Steel
What are the advantages of investment casting?
1. Capability to mold complex part
The mold is to be broken to take the parts out. So there is no restriction of mold release, which means it is good to make any complex features, especially with undercuts.
2. Versatility of Alloy Selection
Because the temperature of the mold can hold is high, it is suitable for various materials, for example bronze, aluminum, tool steel, stainless steel, and stellite.
3. High Surface Finish
Investment casted parts have very good smooth surfaces. It reduces the post machining and the associated time and cost.
4. Low Mold Cost
The cost of the mold is low and the lead time is short. It is a very good process for low volume high complexity parts.
Die Casting
What is die casting?
Die casting is a process of forming metal parts by forcing molten material under high pressure into a hard and precise mold (called a die). The molded part is ejected out from the die once it is cooled to a solidified temperature. It is a very popular process for high volume and tight tolerance parts, usually for aluminum, zinc, copper, and magnesium.
Process – Die Casting + Post Machine
Part – Heat Sink Bench
Material – Aluminum Alloy
What are the advantages of die casting?
1. High Dimensional Accuracy and Mechanical Strength
With high pressure applied on the molten material, die casted parts have good dimensional accuracy and density. The molding cycle and molding parameters are fixed, so the variation is small. Tolerance of the dimensional can be +/-0.05 to 0.10mm depending on the features. Most of the time, no secondary machining is needed.
2. High Production Efficiency
Melting metal, pouring molten material, forming, cooling, and demolding are all fully automated. The molding cycle of die casting is short, usually 30 to 60 seconds per shot depending on the size of the parts. Multi-cavity mold scales up the production capability too.
3. High Surface Quality
The molds are hardened are well polished for a good surface finish. There is no residue or grease on the surfaces.
4. Low Part Cost for High Volume Production
Once the mold is properly built, the process of die casting is very simple and the efficiency is very high. So the part cost is low for high volume production.
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