Nowadays, metal casting has been widely used in the manufacturing industry. This kind of casting process can be dated back 6000 years, and still being used to make complex and large parts. As developing of casting manufacturing, the metal casting has finished more complex and large or small parts with automatic process and lower costs.
Metal casting has developed many types. There are two general types of metal casting: expendable mould casting and permanent mould casting.
This article will introduce the differences between the two types of metal casting. Only 5 minutes, you will get the knowledge about the types of metal casting.
Expendable Mold Casting
Expendable mold casting is composed of sand, shell, plastic, plaster, and investment(lost-wax technique) molding. This kind of casting method is temporary, and the molds it created are non-reusable.
What Is Sand Casting?
This kind of casting method creates a sand mold, where the molten metal next poured into. When the metal finished the cooling process, the mold outside will be broken. The sand is reusable to create another mold, while one mold can only use once time.
Sand casting is widely used to cast big metal parts, and the lower cost is the advantage of it for mass casting.
Sand Casting Process:
- Mold-making: The first step of the sand casting process is to create a mold for casting. Manufacturers create sand mold by pouring the sand into each half of the mold, and arrange a pattern inside the mold to create a casting cavity. Then they remove the pattern and clamp the mold, then finish a sand casting mold.
- Pouring: When you finish a sand casting mold, you can pour the molten metal into the mold. People can make the pouring process manually or automatically. Whatever each pouring manner you take, you should ensure that the cavity and all channels are filled by enough molten metal.
- Cooling: Molten metal will solidify after filling the cavity. And when the molten metal finishes its solidification, the final shape of parts is also finished. Manufacturers open the mold only passing the cooling time. While most of casting defects happen during the cooling process, if molten metal cooling quicker than normal time, the part may have shrinkage, cracks, or incomplete sections. To avoid these defects, we should take preventative measures during the part or mold design.
- Removal: After solidification, manufacturers remove the sand mold. People also name the step as shakeout, because a vibrating machine usually used in mold removing process which shakes and removes the sand. Sometimes, there have some sand and oxide remain on the surface after shaking. Manufacturers use shot blasting to remove the sand and oxide.
- Trimming: The final step of sand casting is to cut excess material from the sand casting products
Sand Casting Application
Sand casting can be used for the different metal parts among the 1oz- 450-ton weight, and widely used at making automotive engine block, cylinder head, crankshaft, and other castings.
What Is Plaster Casting?
Plaster casting is familiar with sand casting, and the difference between them is the mould material. Sand casting creates a sand mould for metal casting, while plaster casting uses plaster to make the casting mould. This kind of casting method can create lighten and precise moulds that are very suitable for casting complex parts.
Plaster Casting Process:
- Pattern spraying: Before making plaster casting, manufacturers usually spray parting compound upon the pattern for creating a thin film and avoid plaster sticking to the pattern.
- Mold making: The mixed plaster is used to package around the pattern. Manufacturers pour the plaster over the pattern and shake it for every small feature of pattern is filled by the plaster. Then the solidification of plaster is usually about 15 minutes, remove the pattern. We should put the mold between 120°C and 260 °C to remove excess water.
- Metal casting: After finishing the plaster casting pattern, you can pour molten metal into the mold to cast parts.
Plaster Casting Application
Plaster casting is usually regarded as low-cost substitute method of other casting methods. While it can only work with low non-ferrous and low melting point materials, such as copper, magnesium, and zinc.
What Is Shell Casting?
Shell casting has finer mold material which is made of the hardened shell of sand rather a flask filled with sand. Mixed this kind of mold material with resin, so the mold cavity it created is more smooth and can be quickly heated. Therefore, shell casting is more automatic than sand casting and more precise. It can cast the item of small to medium sizes.
Shell Casting Process:
- Sand Curing: Heating the cast iron pattern between 230 °C to 315 °C and sitting the sand on the pattern for a few minutes to make the sand partially cure. Then remove the excess sand bay inverting the mold, you will have a shell which has the wall between 10 to 20mm. Putting the pattern and shell into the oven for curing the sand, and after finishing the curing process the tensile strength of shell will reach 350 to 450 psi.
- Remove the pattern: After curing the shell, you can remove the pattern.
- Clamping: When you have two half of mold, you can clamp them as one, and finish the shell casting mold.
Shell Casting Application
This kind of casting method can be used to make cylinder heads, engine blocks, connecting rods, manifolds, and machine bases.
What Is Investment Casting?
Investment casting also known as lost-wax casting was created 5000 years ago. This kind of casting method provides accurate, repeatable, and versatile parts with different metal and high-performance alloys. This kind of casting method is suitable for casting smell and precise parts, and more expensive than other casting methods. While as the mass production, the unit cost will decline.
Investment Casting Process:
- Wax pattern making: Investment casting manufacturers should create a wax pattern for their wax casting. Most of investment casting process takes advanced casting wax to finish this step.
- Wax tree assemble: It is expensive to produce single investment casting products, while with wax tree assembly, investment casting manufacturers can create more production.
- Shell building: Make the shell package over the wax tree, and curing it for the next casting process.
- Wax removing: Remove the wax inside will provide an empty cavity, then you can pour the molten metal into the finished shell.
- Shell knock off: After the molten metal solidifying, knock off the shell and you will get the metal casting products tree. Cut them from the tree, and you will get the final investment casting products.
Investment Cating Application
Investment casting application is widely used in metal parts manufacturing. It has a precision casting process and can make high-finished, smooth parts. Therefore, most manufacturers prefer this kind of casting method.
Permanent Mold Casting
Permanent mold casting also known as non-expendable mold casting, uses permanent mold which is reusable in the production cycle. This kind of casting achieves mass production of metal parts. While most of permanent mold casting methods produce simple metal parts, because it needs to open the mold to remove the parts.
What Is Gravity Casting?
Gravity casting has a long history as the process for metal casting. This kind of casting process pouring the molten metal under the force of gravity without other added processes, such as vacuums, or centrifugal force. And it needs a small-scale mold for creating the mold cavity. Usually, the small-scale mold is made of sand, plaster, or tufa stone.
Gravity Casting Process:
- Small-scale mold making: If your metal parts need cavities, you should make small-scale molds to finish the cavity. This kind of mold is made of sand, plaster, or other heat resistant materials. Pouring the materials into the mold, heating the mold, and when the mold solidified, the small-scale mold has finished.
- Pouring molten metal: Put the small-scale inside the final mold, and pour enough molten metal into the mold and fill with it under the force of gravity. After the solidification of metal, you will have a part with a cavity.
- Remove the small-scale mold: Open the mold and remove the metal parts, then you should remove the small-scale mold inside the parts’ cavity. Most of the manufacturers remove the mold by shaking.
Gravity Casting Application
Gravity casting is mainly used in automobiles for manufacturing huge, simple metal parts, such as turbos, brake calipers, engine cylinder heads, etc. Other industries like lighting components or kitchen tools can also use this kind of casting method.
What Is Die Casting?
Die casting is a type of metal casting process. It creates a mold cavity with two hardened tool steel dies, and shapes the metal under a high-pressure, pour the metal into a mold cavity. This kind of casting has a bit of similarity with injecting molding, and it usually forms non-ferrous metal, such as zinc, copper, aluminum, magnesium, etc.
Die Casting Process:
- Die preparation: Using lubricant to spray the mold cavity will help easily control the temperature of the die and remove the parts.
- Filling: Close the mold and injecting molten metal under the high-pressure, usually you should control the pressure between 1,500 and 25,400 psi.
- Ejection: After the parts cooling and solidifying, open the mold and eject it by using ejector pins.
- Shakeout: The final step is to separate the scrap which including the gate, runners, sprues, and flash from short.
Die Casting Application
Manufacturers use die casting for producing high volume metal components, pumps, compressors, automotive powertrain components, hand and power tool housings, etc. With its precise casting process and high-finished final parts, most manufacturers prefer this kind of casting process.