Six common casting methods and their advantages and disadvantages

Casting is a kind of hot metal processing technology which has a history of about 6000 years.China entered the heyday of bronze casting around 1700 ~ 1000 BC, and reached a rather high level in technology.What are the common casting methods? What are their advantages and disadvantages?

1. Ordinary sand mold casting

The basic raw materials for making sand mold are casting sand and sand binder.The most commonly used foundry sand is siliceous sand, siliceous sand high temperature performance can not meet the requirements of the use of zirconium sand, ferrochrome sand, corundum sand and other special sand.The most widely used sand binder is clay, also can use a variety of dry oil or semi-dry oil, water-soluble silicate or phosphate and a variety of synthetic resin as sand binder.The external sand mold used in sand mold casting can be divided into three types according to the binder used in sand and the way of strength establishment: wet clay sand mold, dry clay sand mold and chemically hardened sand mold.

Advantages:

Clay is abundant and cheap.Most of the used wet clay sand can be recycled after proper sand treatment.Short cycle and high efficiency in mold making;Mixed sand can be used for a long time;It’s adaptable.Small pieces, large pieces, simple pieces, complex pieces, single pieces, large quantities can be used;

Disadvantages and limitations:

Because each sand mold can only be poured once, the mold is damaged after casting and must be remade, so the production efficiency of sand mold casting is low.The rigidity of the casting mold is not high, and the dimensional accuracy of the casting is poor.The castings are easy to produce defects such as sand washing, sand inclusion and porosity.

2. Investment casting

Investment casting is also called “lost wax casting” when the pattern is made of wax.Investment casting usually refers to the casting scheme in which the pattern is made of fusible materials, the pattern surface is coated with several layers of refractory materials to make the pattern shell, and then the pattern is melted out of the pattern shell, so as to obtain the casting pattern without parting surface, which can be filled with sand after roasting at high temperature.Because the pattern is widely made of waxy materials, investment casting is often called “lost wax casting”.The alloys produced by investment casting include carbon steel, alloy steel, heat-resistant alloy, stainless steel, precision alloy, permanent magnet alloy, bearing alloy, copper alloy, aluminum alloy, titanium alloy and nodular cast iron.

Advantages:

High dimensional accuracy.Generally up to ct4-6 (sand casting ct10-13, die casting ct5-7);Can improve the utilization of metal materials.Investment casting can significantly reduce the amount of processing of the product’s forming surface and matching surface, and save the consumption of processing table and cutting tool materials.Can maximize the degree of similarity between the blank and parts, parts of the structural design to bring great convenience.The investment casting of castings with complex casting shapes can produce castings with complex shapes, castings with wall thickness of 0.5mm and weight as small as 1g, and also castings with combined and integral parts.Free from alloy materials.Investment casting can be used to cast carbon steel, alloy steel, ductile iron, copper alloy and aluminum alloy castings, as well as high temperature alloy, magnesium alloy, titanium alloy and precious metal castings.For alloy materials which are difficult to be forged, welded and machined, it is especially suitable for casting by the method of investment casting.High flexibility and adaptability in production. The investment casting is suitable for mass production, small batch production and even single piece production.

Disadvantages and limitations:

The size of the casting should not be too large.Investment casting is the most complicated of all the blank forming methods, and the casting cost is also very high.

3. Die casting

The principle of die casting process is to use high pressure to press the liquid metal into a precision metal mold cavity at high speed.Cold and hot chamber die casting are two basic methods of die casting technology.In cold chamber die casting, the metal liquid is poured into the pressure chamber by manual or automatic pouring device, and then the hydraulic pressure of the metal is injected into the mold cavity by pressing the punch forward.In the hot chamber die-casting process, the pressure chamber is vertical to the crucible, and the metal liquid flows into the pressure chamber automatically through the feed port on the pressure chamber.The injection punch moves downward, pushing the liquid metal through the gooseneck into the cavity.After the liquid metal solidifies, the die casting mold is opened, the casting is removed, and a die casting cycle is completed.

Advantages:

The product is of good quality.High dimensional accuracy, generally equivalent to 6~7 grade, even up to 4 grade;Good surface finish, generally equivalent to 5~8 level;The strength and hardness are higher, and the strength is generally 25~30% higher than that of sand mold casting, but the elongation is about 70% lower.Stable size and good interchangeability;Die-castable thin-walled complex castings;High production efficiency, such as domestic J Ⅲ type 3 horizontal cold empty die casting machine die casting of 600 ~ 700 times on average eight hours, small hot chamber die casting machine die casting of 3000 ~ 7000 times on average every eight hours.Die casting long life, a set of die casting, die casting bell alloy, life up to hundreds of thousands of times, even millions of times;Easy to realize mechanization and automation;Good economic effect.Due to the precise die casting size, table shine and other advantages.Generally no longer mechanical processing and direct use, or very small amount of processing, so both improve the metal utilization rate, and reduce a lot of processing equipment and time;The casting price is easy;Combination die casting can be used for other metallic or nonmetallic materials.Saves both assembly time and metal.

Disadvantages and limitations:

In die casting, due to the high velocity of liquid metal filling cavity and unstable flow state, the general die casting method is adopted, and the casting is easy to produce pores, so heat treatment cannot be carried out.It is difficult to die cast complex castings with internal concave.High melting point alloy (such as copper, ferrous metal), die casting life is low;It is not suitable for small batch production, the main reasons are high cost of die casting mold manufacturing, high production efficiency of die casting machine, and uneconomical production of small batch.

4. Metal mold casting

Also known as hard die casting, it is a casting method in which liquid metal is poured into a metal mold to obtain a casting.A cast is made of metal and can be used many times (hundreds to thousands of times), also known as a permanent cast.Generally, metal molds are made of cast iron and cast steel.The inner cavity of the casting can be either metal core or sand core.There are many types of metal shapes, such as water bisector, double direct and composite.Vertical parting is convenient for opening the inner gate and taking out the casting;Horizontal parting is mostly used to produce thin – walled wheel castings.The upper half of composite parting is made up of two halves of vertical parting connected by hinge, and the lower half is fixed horizontal bottom plate, which is mainly used in the casting of more complex castings.

Advantages:

With good reusability, it can be “one type and many castings”, saving molding materials and molding time.Due to the strong cooling ability of the metal mold, the structure of the casting is compact and the mechanical properties are high.The dimensional accuracy of the casting is high, and the tolerance grade is IT12 ~ IT14.The surface roughness is low, Ra is 6.3m.Metal mold casting without sand or with less sand, improve the working conditions.

Disadvantages and limitations:

It is not suitable for the production of single small batch castings, but mainly suitable for the mass production of non-ferrous alloy castings, such as aluminum piston, cylinder body, cylinder cover, oil pump shell and copper alloy bearing bush and bearing sleeve for aircraft, automobile, internal combustion engine, motorcycle, etc.For black alloy castings, it is limited to medium and small castings with simple shapes.

5. Low pressure casting

Low pressure casting is a method in which liquid metal is filled and cast under low pressure (0.02 ~ 0.06MPa) and crystallized under pressure to form castings.The melting crucible pour liquid metal heat preservation, mount airtight cover, lift catheter with mold, the metal liquid lock casting, slowly to the crucible furnace into the dry compressed air, liquid metal by the effect of gas pressure, from bottom up along the lift tube and pouring system full of cavity, and crystallization under pressure, the casting molding retreat to the pressure inside the crucible, the lift tube of metal liquid drop back to the metal surface in the crucible. Open the mold and remove the casting.

Advantages:

During pouring, the rising speed and crystallization pressure of the liquid metal can be adjusted, so it can be applied to various types of casting (such as metal mold, sand mold, etc.), casting various alloys and castings of various sizes;The bottom injection mold filling is adopted, the liquid metal filling is stable, no splash phenomenon, can avoid the gas involved and the scour of the mold wall and core, the casting defects such as porosity and slag inclusion are few, and the qualified rate of the casting is improved;Casting crystallization under pressure, casting compact structure, clear outline, smooth surface, high mechanical properties, especially for large thin wall casting;The metal utilization rate can be increased to 90% ~ 98% by eliminating the feeding riser.Low labor intensity, good working conditions, simple equipment, easy to achieve mechanization and automation.

Disadvantages and limitations:

The life of the riser is short, and the metal liquid is easy to oxidize and produce slag inclusion in the process of heat preservation.It is mainly used for casting high quality aluminum alloy and magnesium alloy castings, such as cylinder block, cylinder head, crankcase and aluminum piston of high speed internal combustion engine.

6. Centrifugal casting

Centrifugal casting is a casting method in which molten metal is poured into a rotating mold and solidified by filling the mold under the action of centrifugal force.According to the location of the mold rotation axis in space, common centrifugal casting can be divided into two types: horizontal centrifugal casting, casting the rotation axis in the level of state or with horizontal Angle is small (< 4 °) with centrifugal casting.Vertical centrifugal casting: when the rotating axis of the casting mold is in the vertical state, the centrifugal casting is called vertical centrifugal casting.Centrifugal casting with a large Angle between the rotation axis and the horizontal and vertical lines of the casting mold is called inclined axis centrifugal casting, but it is rarely used.

Advantages:

The core, casting system and riser can be saved when the hollow rotary casting is produced by centrifugal casting.Under the action of centrifugal force generated by the liquid metal during rotation, the metal with high density is pushed to the outer wall, while the gas and slag with low density move to the free surface to form the directional solidification from the outside to the inside. Therefore, the reinforcing conditions are good, the casting structure is compact, and the mechanical properties are good.It is easy to pour “bimetal” bearing sleeve and bearing bush. If a thin layer of copper bushing is inserted in the steel bushing, the expensive copper material can be saved.Good filling ability;Eliminate and reduce the consumption of gating systems and risers.

Disadvantages and limitations:

The inner free surface of the casting is rough with large size error and poor quality.Not suitable for alloys with high density segregation (such as lead bronze) and alloys such as aluminum and magnesium.


Post time: Mar-29-2019
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