Blog 30: Different types of casting process?

Introduction:

A method known as casting manufacturing involves pouring a liquid substance, such as molten metal, into the cavity of a mold that has been specifically created and then waiting for it to set. After solidifying, the workpiece is taken out of the mold to either go through various finishing processes or be used as the finished product. Cast items are utilized in a variety of applications, such as automotive components, aerospace parts, etc., and are normally produced using casting procedures to produce complex solid and hollow shapes.

Also read: Different types of Casting Defects.

There are different types of the casting processes.

Different Types of Casting and the Casting Process

Despite being one of the oldest manufacturing processes known to man, casting has given rise to a wide variety of specialized casting techniques because of recent advancements in casting technology. Each hot forming method has distinct advantages for production, including die casting, investment casting, plaster casting, and sand casting. Selecting the casting process that is most appropriate for a particular production run can be aided by comparing the benefits and drawbacks of the popular types of casting processes.

1. Sand Casting Process

Any metal alloy, ferrous or not, can be cast using the flexible casting method known as sand casting. It is frequently employed in industrial settings for mass manufacturing of components for automobiles made of metal casting, such as engine blocks, cylinder heads, crankshafts, etc.

A synthetic or naturally-bonded sand mold constructed of silica-based materials is used in the procedure. Casting sand typically consists of spherical grains that have been finely powdered and can be closely packed together to provide a smooth mold surface. Cope (the upper half) and drag are the two components of the mold surface (the lower half). Using a pouring cup, molten metal is poured into the design, where it is then allowed to harden and take on its final shape. Finally, surplus metal is removed so that the finished metal casting product can be finished.

By permitting a modest amount of elasticity and shrinkage throughout the cooling portion of the process, the casting is made to lower the possibility of tearing, cracking, or other faults. Clay can also be added to the sand to reinforce it by tightening the link between the particles.

Making patterns, molding, melting and pouring, and cleaning are some of the processes involved in sand casting. The cope is taken off and the pattern is extracted once the sand has been sufficiently compacted to duplicate the design. The cope is then replaced once any new inserts, known as core boxes, have been inserted. After the metal has been poured and solidified, the casting is taken out, cleaned of any scale and adhering sand, and the risers and gates used during the pouring operation are removed.

Sand casting’s main advantages as a casting process include:

  • Relatively inexpensive production costs, especially in low-volume runs.
  • The ability to fabricate large components.
  • A capacity for casting both ferrous and non-ferrous materials.
  • A low cost for post-casting tooling.
  • Recyclability

Some of the main disadvantages of the casting process are:

  • Sand casting yields a lower degree of accuracy than alternate methods
  • It can be difficult to sand cast components with predetermined size and weight specifications.
  • The process has a tendency to yield products with a comparatively rough surface finish.

2. Gravity Die Casting

Gravity dies casting, commonly referred to as permanent mold casting, produces metal and metal alloys using reusable molds consisting of metal, such as steel, graphite, etc. This kind of metal casting can be used to create many different items, including wheels, engine pistons, pipe fittings, gear housing, and gears.

In this method, molten metal is directly poured into the cavity of the mold while being pulled downward by gravity. The die can be angled to manage the filling for greater coverage. The items are created by allowing the molten metal to cool and solidify inside the mold. As a result, this method increases the prevalence of casting materials such as specific bronzes, cast iron, and alloys of lead, zinc, aluminum, and magnesium.

In contrast to conventional pressure casting procedures, this casting method fills the mold from the bottom up. However, compared to sand casting, the method has a higher casting rate. But because expensive metal molds are used, the price is significantly greater. Review its benefits and drawbacks below

The following are the advantages of Gravity casting:

  • Production of thin-walled products
  • Provides better surface quality of products due to rapid solidification
  • Casting products have high precision and tight tolerance
  • Reusable molds save time and increase productivity which reduces production costs
  • The products possess better mechanical properties

The following are the disadvantages of Gravity casting:

  • Casting complex objects is difficult.
  • Manufacturing costs of molds are higher
  • At times, the ejection mechanism to remove the casting from the mold forms a dent in the product

3. Pressure Die Casting

Depending on the pressure, there are two different forms of pressure die casting. both high-pressure and low-pressure die casting, to be exact. For mass production of complex geometries requiring fine precision, high pressure dies casting is more common. Conversely, low-pressure die casting is a better casting technique for manufacturing large and straightforward parts.

This kind of metal casting involves the high-pressure injection of non-ferrous metals and alloys including zinc, tin, copper, and aluminum into a reusable mold that has been coated in lubricant. In order to prevent metal hardening, high pressure is maintained throughout the quick injection procedure. After the procedure is finished, the casting is extracted and finished to eliminate any superfluous material.

When it comes to filling the mold, pressure dies casting differs from gravity die casting. Whereas high-pressure injection of molten metal into the metal mold is used in pressure die casting. The needed product is subsequently made by quickly solidifying the molten metal.

Its advantages are summarized below.

  • High precision and dimensional tolerance.
  • High efficiency and good product quality.
  • Reduced need for post-casting machining.
  • Rapid cooling of molten metal pertaining to faster production rates.
  • The process can run for longer hours without the need to replace the die

Its disadvantages are summarized below.

  • Relatively high tool costs.
  • Limited to non-ferrous materials.
  • Difficult to ensure the mechanical properties of products, therefore, it is not used for structural parts.
  • Complete setup requires a large capital investment

4. Investment Casting

Investment casting, commonly referred to as lost-wax casting, is a procedure in which wax is injected directly into a mold, removed, and then coated with refractory material and a binding agent, typically in numerous stages to build up a thick shell. The patterns are inverted and fired in ovens to remove the wax before being filled with molten metal to create metal castings when the shells have solidified. Investment casting is an expensive and labor-intensive process that can be used to create metal casting products such as gears, bicycle trunks, motorcycle discs, and replacement parts for blasting equipment in large quantities or in intricate castings.

Investment casting is extremely accurate but frequently more expensive than other comparable casting procedures. It is usually only economically viable when sand or plaster castings cannot be used. However, because investment castings produce high-quality surfaces, the cost may occasionally be offset by lower machining and tooling expenses.

Below summarizes its advantages

  • It can produce parts with thin walls, more complexity, and high surface quality
  • Reduces the need for post-casting machining
  • Can cast hard-to-melts alloys such as stainless steel, thin steel, etc
  • Breaking away of the shell mold, allows for casting 90- degree angles
  • High dimensional accuracy in products
  • Shrinkage allowance in the mold
  • The capacity for casting both ferrous and non-ferrous materials.

Below summarizes its disadvantages

  • Requires labor for use
  • The production cycle is a loner
  • Higher manufacturing costs of molds
  • New die requirement for the creation of wax patterns for each casting cycle

5. Plaster Casting

With the exception of the mold being composed of a substance known as “Plaster of Paris,” the plaster casting procedure is similar to sand casting. Plaster cools the metal more slowly than sand due to its limited thermal conductivity and heat capacity, which aids in achieving high precision, especially for pieces with thin cross-sections. However, high-temperature ferrous materials cannot be used with it.

In particular, the plaster mold casting process can be used to create small castings of 30 grams and big castings of 45 kilograms. The figure below, for instance, illustrates a cast component made using this method with a 1 mm section thickness.

Learn more about its advantages

  • Smooth surface finish
  • Great dimensional accuracy than sand casting
  • The ability to cast complex shapes with thin walls
  • Learn more about its advantages

The process tends to be more expensive than most casting operations

  • Limited application to aluminum and copper-based alloys
  • May require frequent replacements of plaster molding material
  • Not suitable for high melting material
  • Longer cooling times, affecting production rates
  • Unstable material as compared to sand, which can affect the complete process

6. Centrifugal Casting

Roto casting, commonly referred to as centrifugal casting, is a method for producing cylindrical pieces industrially using centrifugal forces. In this kind of metal casting, molten metal is poured into a hot spinning die. The high-pressure molten metal is distributed throughout the die with the aid of centrifugal forces. The de Lavaud technology, originally developed to produce symmetrical pieces like soil pipe and huge cannon barrels using water-cooled molds, has the advantage of generating items with a low riser count.

There are three types of centrifugal casting: vertical centrifugal casting, semi-centrifugal casting, and genuine centrifugal casting. In contrast to genuine centrifugal casting, semi-centrifugal casting uses a sprue to entirely fill the mold. However, because of the constant rotation used in genuine centrifugal casting, the molten metal adheres to the sides. On the other hand, vertical centrifugal casting involves directional molding and the same procedure as genuine centrifugal casting, as the name implies.

Typically, rotational geometries like cylinders are produced through centrifugal casting. especially components such as cylinder liners, clutch plates, piston rings, and bush bearings Additionally, pouring the metal into the mold’s center helps to minimize flaws like blow holes, shrinkage, and gas pockets. It is not, however, appropriate for all metal alloys.

Advantages of Centrifugal casting:

  • Improved process yields and reduced wastage
  • Casting has high density and almost no defects
  • The process is convenient to manufacture barrel and sleeve composite metal castings
  • No requirement of gates and risers

Disadvantages of Centrifugal casting are:

  • Centrifugal casting requires high investments
  • Requirement of skilled labor
  • Specific shapes production

7. Lost-Foam Casting

The distinction between investment casting and lost-foam casting is that the former employs wax for the pattern while the latter uses foam. Following the creation of the pattern, the refractory ceramic is coated using dipping, coating, spraying, or brushing. The finished product is then created by pouring the molten metal into the mold.

This method can be applied to a variety of materials, including ferrous alloys, alloy cast iron, carbon steel, and alloy steel. The lost-foam casting process is particularly used to produce items like pump housing, fire hydrants, valves, and fittings.

High production precision and accuracy are just a couple of the benefits of lost foam casting. This technique, however, has a few drawbacks that make it unsuitable for low-volume applications.

Advantages of lost foam casting:

  • High precision casting
  • Allows flexible design
  • Clean production
  • Economic for high volume production

Disadvantages of lost foam casting are:

  • High pattern costs for low-volume production
  • Low strength causes distortion or damage to the pattern
  • Many production processes and longer delivery time

8. Vacuum Casting

The manufacturing of vacuum casting, as the name suggests, takes place under a vacuum pressure of 100 bar or less in order to exhaust gas from the mold cavity. In this procedure, bubbles and air pockets are removed by pouring molten metal into the mold cavity inside a vacuum chamber. The die cavity is evacuated under a vacuum to prevent gases from becoming trapped there during the metal injection process. The metal is then taken from the mold after being cured in a heating chamber.

Many industries, including those in the automotive, aerospace, electronics, marine, and telecommunication sectors, use the vacuum die-casting method. As a result, structural chassis components and vehicle body elements are some components produced by this manufacturing technique.

Advantages of vacuum casting:

  • Reduce porosity, improve mechanical properties and surface quality of die casting
  • Production of thin-walled products
  • Welding and heat treatment of products is possible
  • Welding and heat treatment of products is possible
  • Suitable for low-volume production
  • No requirement for expensive hard tool finishing
  • Diminishes air pockets and bubbles at early stages

Disadvantages of Vaccum casting are:

  • High tooling cost
  • The mold used in the process has a short life
  • Potential hollowness issues

9. Squeezing Casting

Squeeze casting, also known as liquid forging, is a hybrid metal forming method that combines die forging with permanent mold casting in a single stage. In this procedure, a predetermined volume of molten metal alloy is pumped into a die and shaped under pressure. The metal component is then heated to the melting point and removed from the die.

Squeezing die casting, in particular, is a possible casting method for safety-critical components in automobile systems. For instance, chassis frames, brackets, nodes, space frame joints, aluminum front steering knuckles, etc.

The advantages of casting and forging processes are combined in this kind of metal casting. For instance, the intense pressure used during solidification aids in preventing porosities and shrinkage. However, it is less common than other casting methods for mass production due to unique tooling needs.

The advantages are as follows:

  • Eliminates internal defects like pores, shrinkage holes, and shrinkage porosity
  • Low surface roughness
  • It can prevent casting cracks
  • High strength components
  • No wastage of material

The disadvantages are as follows

  • Requires accurate controlling, slowing down the overall process
  • Less flexibility in part geometry
  • Lower productivity
  • High machining requirements

10. Continuous Casting

It enables the consistent mass manufacture of metal profiles having a fixed cross-section, as the name would imply. In the manufacture of steel bars, this kind of casting is frequently used. Additionally, semi-continuous casting products like billets, ingots, bars, etc. are produced by the vertical cast. A surface of the solid metal can form on the liquid metal in the center of the mold by carefully controlling the rate at which molten metal is injected into the open-ended, water-cooled mold. Therefore, metal solidification occurs from the outside in. After this procedure is complete, metal strands can be constantly removed from the mold. Mechanical shears or moving oxyacetylene torches can cut goods off at predetermined lengths.

Generally, the products created using continuous casting are homogeneous, consistent, and dense. However, it also limits its use to such applications.

Some other advantages are:

  • Diverse size range of casting products varying from a few millimeters thick strip to larger billets and slabs
  • Lower costs due to continuous production
  • Lower material wastage

Some other disadvantages are:

  • Requirement of continuous cooling of the molds, otherwise, center-line shrinkage develops
  • The casting of only simple shapes with a constant cross-section
  • Requires large ground space and high initial investment

11. Shell Molding

Shell molding is a mold casting procedure that is disposable. The only difference between it and sand casting is that the mold cavity is formed by a solid shell of sand rather than a flask of sand. The sand used is finer than that used in sand casting, and it is combined with resin to enable heat treatment and hardening into the shell surrounding the pattern.

Industrial items including gearbox housing, connecting rods, small boats, truck hoods, cylindrical heads, camshafts, valve bodies, etc. are produced using shell molding.

The casting products have accurate dimensions and a nice surface finish. The size and weight restrictions on the parts are one of this type of casting’s limitations, though.

Some other advantages are:

  • The casting of thin and complex parts
  • Semi-skilled labor
  • No further machining required
  • Accounts for surface defects

Some other advantages are:

  • Not suitable for small-scale production
  • Special metal pattern is required which makes it expensive for large casting
  • Limitations on size and weight

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