Currently we have many casting methods in industry, for different materials and different applications; each casting method is designed to produce high quality, high precision products to meet our part production requirements. But how should we choose the most suitable casting method for your project?Today let’s go deeper into the types of metal casting and its advantages and disadvantages
Definition of Castings
Casting parts, also known as castings, are metal forming objects obtained by various casting methods, i.e., the melted liquid metal is injected into the pre-prepared castings by pouring, pressure injection, inhalation or other casting methods, and the objects with certain shapes, sizes and properties are obtained after cooling and subsequent processing means such as grinding.
Castings have a long history of application. In ancient times, people used castings for some household appliances. In modern times, castings are mainly used as machine parts of the blank, some precision castings, can also be used directly as parts of the machine. Castings in machinery products occupy a large proportion, such as tractors, the weight of castings accounted for about 50 to 70% of the weight of the machine, agricultural machinery accounted for 40 to 70%, machine tools, internal combustion engines and others up to 70 to 90%. Various types of castings, with the most varieties of mechanical castings, the most complex shape, the amount is also the largest, accounting for about 60% of the total output of castings. Followed by metallurgical ingot mold and engineering with the pipeline, as well as some of the tools in life.
Classification of casting materials
There are various ways to classify castings.
According to the different metal materials used, it is divided into cast steel parts, cast iron parts, cast copper parts, cast aluminum parts, cast magnesium parts, cast zinc parts, cast titanium parts, etc.. And each type of castings can be further divided into different types according to their chemical composition or metallurgical organization. Such as cast iron parts can be divided into gray cast iron parts, ductile iron parts, peristaltic cast iron parts, malleable cast iron parts, alloy cast iron parts, etc..
Classification of casting Methods
- Sand castings
- Gravity Die castings
- High Pressure die castings
- Low Pressure die castings
- Investment Casting
- Lost Foam Casting
- Vacuum casting
- Squeezing Casting
- Centrifugal castings
- Continuous castings
The basic raw materials for sand casting are foundry sand and sand binder. The most commonly used casting sand is silica sand, and when the high temperature performance of silica sand cannot meet the requirements, zircon sand, chromite sand, corundum sand and other special sand are used. The most widely used sand binder is clay, but also a variety of dry oil or semi-dry oil, water-soluble silicate or phosphate and a variety of synthetic resins for sand binder.
The external sand type used in sand casting is divided into three types of clay wet sand type, clay dry sand type and chemically hardened sand type according to the binder used in sand and the way it builds strength.
Sand Casting Process Steps
- Make the Prototype, same with desired product.
- Prepare sand box(upper and lower) and proper sand.
- Produce Pattern, Gate and Risers.
- Dry the sand mold and core.
- Pouring Molten Metal into the sand mold.
- Break away the pattern and take Rough casting parts out.
- Debug gate and flash, Running CNC Machining.
Advantage and Disadvantage
|Advantage||Clay is abundant and cheap. Most of the used clay wet sand can be recycled after proper sand treatment.|
Short cycle time and high work efficiency in making the casting patterns.
Long service life of the blended sand.
Wide adaptability. Small and large pieces, simple and complex pieces, single and large quantities can be used.
|Disadvantage||Low productivity of sand casting because each pattern can only be poured once, and the Pattern is damaged after obtaining the casting and must be re-molded.|
the rigidity of the castings is not high, and the dimensional accuracy of the castings is poor.
Castings are easy to produce defects such as sand punching, sand trapping and porosity.
Gravity Die Castings
Also known as Metal mold casting, it is a casting method in which liquid metal is poured into a metal casting mold to obtain a casting. The cast mold is made of metal and can be used many times over (hundreds to thousands of times), also known as permanent mold casting.
Gravity Die Casting Process
- Molten Material, Normally A356, AZ101,AZ104
- Preheat the metal mold before pouring, which can slow down the cooling capacity of the mold and is conducive to the filling of the metal liquid.
- Put sand core into mold and located.
- Poured molten metal into the die manually.
- The Casting Part been hold and cool down.
- The die opened ; the casting parts either removed by hand or ejector pins.
|Advantage||Good reusability, “one die,use many castings”, saving molding materials and modeling hours.|
The cooling ability of the metal type to the casting is strong, which makes the casting dense and has high mechanical properties.
The dimensional accuracy of the casting is high, with the tolerance grade of IT12 to IT14, and the surface roughness is low, with Ra 6.3m.
Metal type casting without sand or with less sand, which improves labor conditions.
|Disadvantage||The manufacturing cost of metal type is high, the cycle time is long, and the process requirements are strict, so it is not suitable for the production of single piece small batch castings. |
Mainly applicable to the mass production of non-ferrous alloy castings, such as aircraft, automobile, internal combustion engines, motorcycles, etc. with aluminum pistons, cylinder blocks, cylinder heads, oil pump housings and copper alloy shaft tiles, bushings, etc..
For ferrous alloy castings, it is also limited to medium and small castings with simple shapes.
High Pressure die castings
High Pressure die casting process is to use high pressure to press the metal liquid into a precision metal mold cavity at high speed, and the metal liquid cools and solidifies under pressure to form a casting.
Cold and hot chamber die casting are the two basic ways of die casting process.
Cold chamber die casting
The metal liquid is poured into the chamber by hand or automatic pouring device, and then the press injection punch advances and presses the metal into the cavity.
Hot chamber die casting
Hot chamber die casting process, the chamber is perpendicular to the crucible and the liquid flows automatically into the chamber through the feed port on the chamber. The downward movement of the press punch pushes the metal fluid through the gooseneck into the cavity. After the metal liquid solidifies, the die is opened and the casting is removed, completing a die-casting cycle. also Hot chamber die casting include Zinc die casting and magnesium die casting.
High Pressure Die Casting Process
Advantage and Disadvantage
|Advantage||Good product quality. High dimensional accuracy of castings, generally equivalent to 6~7, even up to 4; good surface finish, generally equivalent to 5~8; high strength and hardness, generally 25~30% higher strength than sand casting, but the elongation rate is reduced by about 70%; stable size, good interchangeability; can die-cast thin-walled complex castings.|
High production efficiency. Machine productivity is high, for example, domestic J Ⅲ3 type horizontal cold air die-casting machine can die-cast 600 ~ 700 times in eight hours on average, small hot chamber die-casting machine can die-cast 3000 ~ 7000 times every eight hours on average; die-casting Mold life is long, one-time pay die-casting mold, die-casting bell alloy, life can reach hundreds of thousands of times, or even millions of times; easy to realize mechanization and automation.
Excellent economic effect. Due to the die-casting size is accurate, the advantages of the table pan clean. Generally no longer mechanical processing and direct use, or processing volume is very small, so both improve the utilization rate of metal, but also reduce a large number of processing equipment and man-hours; casting price is easy; can use a combination of die-casting to other metal or non-metallic materials. Both save assembly time and save metal.
|Disadvantage||Die Casting is easy to produce pores and cannot be heat treated because of the high speed of liquid metal filling the cavity and the unstable flow state, so the general die-casting method is used.|
Die-casting is more difficult for castings with complex internal concavities.
High melting point alloy (such as copper, ferrous metal), die-casting type life is low.
Not suitable for small batch production, the main reason is the high cost of die-casting mold manufacturing, high production efficiency of die-casting machine, small batch production is not economic.
Low Pressure die castings
Low-pressure die casting is a method of filling the casting mold with liquid metal under low pressure (0.02 to 0.06 MPa) and crystallizing under pressure to form a casting.
Low Pressure Die Casting Process
1.The molten metal liquid is poured into the insulated crucible, the sealing cover is put on.
2.The rising liquid conduit makes the metal liquid and the casting mold connected, the casting mold is locked.
3.And dry compressed air is slowly introduced into the crucible furnace.
4.The mold is opened and the casting is removed.
|Advantage||The rising speed of metal liquid and crystallization pressure can be adjusted during pouring, so it can be applied to various casting types (such as metal type, sand type, etc.), casting various alloys and various sizes of castings.|
With the bottom injection type filling, the metal liquid fills smoothly without splashing, which can avoid the involvement of gas and the scouring of the mold wall and core, and the casting has fewer defects such as porosity and slag, which improves the qualified rate of the casting.
Castings crystallized under pressure, castings with dense organization, clear contour, smooth surface and high mechanical properties, especially beneficial for the casting of large thin-walled parts.
elimination of complementary shrinkage riser, metal utilization rate increased to 90%-98%.
Low labor intensity, good labor conditions, simple equipment, easy to realize mechanization and automation
|Disadvantage||The life of the lift tube is short, and the metal fluid is easy to oxidize and produce slag in the process of heat preservation. Mainly used for casting some high quality requirements of aluminum alloy and magnesium alloy castings, such as cylinder block, cylinder head, crankcase and high-speed internal combustion engine aluminum piston and other thin-walled parts|
Melt casting is also called “lost wax casting” when wax is used for the mold. Investment casting usually refers to the casting scheme in which the mold is made of fusible material, covered with several layers of refractory material on the surface of the mold to make the shell, and then the mold is melted and discharged from the shell to obtain a mold without a parting surface, which can be filled with sand and poured after high temperature roasting. Because the mold sample is widely used wax material to manufacture, so often fusion casting is called “lost wax casting”.
The types of alloys that can be produced by investment casting include carbon steel, alloy steel, heat-resistant alloys, stainless steel, precision alloys, permanent magnet alloys, bearing alloys, copper alloys, aluminum alloys, titanium alloys and ductile iron, etc.
|Advantage||High dimensional accuracy. Generally up to CT4-6|
It can improve the utilization rate of metal materials.
Casting complex shaped castings Melt casting can cast very complex shaped castings
Not limited by alloy materials
High production flexibility and adaptability Melt casting is suitable for both high volume production and small volume production or even single piece production.
|Disadvantage||The size of the casting can not be too large process complex casting cooling rate is slow. |
Investment casting is the most complex process and the casting cost is high.
Lost Foam Casting
It is a new casting method in which foam models of similar size and shape to the casting are bonded and combined into a model, brushed with refractory coating and dried, buried in dry quartz sand, vibrated and molded, poured under negative pressure so that the model is vaporized and the liquid metal occupies the model position, solidified and cooled to form the casting.