Casting Concepts Engineering Workshop MECHANICAL THEORY

Sand Casting Process, Die casting, Shell Mold casting & Investment Casting process

Sand Casting Process Definition: Casting is a process in which the liquid molten metal is poured into the casting cavity whose shape is same as that of the shape of the casting to be produced, allowing to solidify and after solidification, the casting will be taken out by breaking the mold called as Casting Process.

Steps in the Sand Casting Process:

  1. Pattern making
  2. Mould and Core making
  3. Pouring and Solidification
  4. Fetling
  5. Inspection

Tabular Column:

1. Sand Casting Process

2. Die Casting Process

3.Shell mold Casting Process

4.Investment Casting Process

 

Sand Casting Process Diagram:

sand casting process
sand casting process

Sand Casting Process/Procedure:

The diagram of sand casting was presented below. It consists of

1.Pouring Basin

2.Sprue

3.Runner

4.Ingate

5.Casting Cavity

6.Riser

The detailed explanation of the above sand casting terms is presented below.

1.Pouring Basin:

    • The molten metal is to be poured into the Pouring basin so that it can enter into the mold cavity.
    • The pouring basin  separates the impurities[lighter and heavier impurities present in the molten material]
    • The size and shape of the pouring basin will not have much effect on the flow rate or pouring time of molten metal in the gating system.

2.Sprue:

It is connecting the passage between the pouring basin and Runner. It is always vertical with a straight tapered circular cross-section.

Characteristics of Sprue:

Basically, Velocity of molten metal in the gating system is represented by

          V = Sqrt.2gh

                      Where ‘h’ is the height of the sprue.

The height of the sprue is mainly responsible for producing the velocity of molten metal in a gating system. The height of the sprue is selected such that the velocity of molten metal in the gating system must always ensure laminar flow.

Straight tapered sprue is selected to avoid the aspiration effect in the gating system.

Aspiration Effect/Inhalation Effect/Breathing Effect:

During filling of molten metal into the casting cavity using gating system somewhere along with the gating system due to some reason, if the pressure falls below atmospheric pressure, the pressure difference is existing between the inside and outside of gating system. Due to this pressure difference, the air starts flowing from outside to the inside of the gating system through Porosity property of molding sand called an aspiration effect.

Other Elements in Sprue:

other elements in sprue-Sand Casting Process
other elements in sprue-Sand Casting Process

1.Strainer:

    • Always kept in sprue only.
    • It is used for separating/filtering the impurities present in the molten metal.
    • It is made by using a Ceramic material with high porosity.

2.Splash Core:

    • Used for avoiding sand erosion from the bottom of Sprue.
    • Also made by using a Ceramic material with low porosity.

3.Skim Bob:

    • It is a Semi circular-cut given in Runner.
    • It is used for separating Impurities present in molten metal.

By these additional elements in Sprue, all possible impurities are separated from the molten metal.

3.Runner:

It is a connecting passage between the bottom of the Sprue and in-gate. It is always horizontal with uniform Trapezoidal Cross section.

It is mainly used for minimizing the sand erosion in the casting process.

        Qactual = Cd*Qtheoretical

A trapezoidal cross-section has the highest value of the coefficient of discharge(Cd) and for that reason, it is selected for the design of a runner.

4.Ingate:

It is the last section of the gating system from where the molten metal is entering into the casting cavity. It is also horizontal and uniform trapezoidal in cross-section.

5.Casting Cavity:

It is the cavity in which the molten metal is filled and solidified in order to get the desired product.

6.Riser:

The riser is acting as a Reservoir for supplying the molten metal to the casting gravity for compensating the liquid Shrinkages taking place during solidification.

Parting Line:

It is the line that divides the Cope and Drag.

Vents:

It is a small opening in the mold to escape the gases during solidification.

Chaplets:

Chaplets are used to support the cores inside the mold cavity to take care of its own weight.

Cope and Drag:

The Top Flask is called as Cope and the bottom Flask is called Drag.

This is the complete explanation of Sand Casting Process in a detailed way.



2.Die Casting Process-Principle, Types, Gravity&Pressure Die casting, Applications, Advantages


Die Casting Process-Principle: Die Casting is a metal casting process which is characterized by forcing the molten metal under high pressure or under gravity into a mold cavity. The mold is made by using metal which has been machined into a shape similar to an injection mold during the process. Die Casting process is different from Sand casting process w.r.t. the mold.

In Sand Casting Process, the Mould is made up of Sand whereas, in Die Casting Process, the mold is made up of Metal.
Most die castings are made from non-ferrous metals specifically aluminum, zinc, lead, copper pewter, and tin-based alloys.
Example: Die Steel or Tool Steel.

Die Casting Process-Principle,Types,Gravity&Pressure Die casting,Applications,Advantages
Die Casting Process-Principle, Types, Gravity&Pressure Die casting, Applications, Advantages

Because of the metal mold, the same mold can be used for producing the infinite number of castings.hence the process is also called a permanent mold casting process.

  • Surface Finish: On the metal molds, the excellent surface finish can be produced. Therefore, the surface finish produced in the casting is excellent.
  • Here, no machining is required in the casting process and close dimensional tolerances can be produced directly.
  • Thermal conductivity: The thermal conductivity of metal molds is higher.hence the surface hardening heat treatment effect is taking place.
  • Porosity: There is no porosity property of the mold hence through Risers must be used.
  • low melting point metals: Because of the problem of melting of the metal mold, this process is used only for producing castings with low melting point metals.

To avoid the formation of a bond between casting and metal mold, the Silicon powder will be sprinkled on the mold surface before pouring the molten metal into the casting

Types of Die Casting Process:

Die Casting Process is categorized into two types.
1.Gravity Die Casting
2.Pressure Die Casting

1.Gravity Die Casting:

  • If the flow of molten metal into the mold cavity is due to the gravitational force, then it is called Gravity Die Casting.
  • Because of the problem of flow of the molten metal into the each and every corner of casting cavity due to the gravitational force, the gravity Die casting will be used for producing the simple shape of the castings only.

Ex: IC engine piston made by aluminum alloys.

2.Pressure Die Casting:

pressure-die casting
pressure-die casting
  • If the external pressure is used for molten metal to enter into the mold cavity called Pressure Die Casting.
  • Due to the external pressure, it is possible to flow the molten metal into each and every corner of the complex shape of a cavity. hence the complex shape of the casting can be easily produced.

Ex: Carburettor body made by aluminum alloys

Die Casting Applications:
Die-casting is the largest casting technique that is used to manufacture consumer, commercial and industrial products like

  • Automobiles
  • Toys
  • Parts of a sink faucet
  • Connector housing
  • Gears etc.
  • Most die castings are done from non-ferrous metals like magnesium, aluminum, etc.

Advantages of Die Casting Process:

  • An economical process used for a wide range of complex applications.
  • A process that can be fully automated
  • Post machining can be totally eliminated
  • Parts have high dimensional accuracy, close tolerance, and longer service life.
  • Mold can be used repeatedly because it is made up of metal.
  • No external pressure is required for Gravity Die Casting Process.

The Process was explained briefly with Types of Die Castings, Applications and Advantages. If you have any doubts, you can ask us from the comments section.



3.Shell Mold Casting-Features, Ceramic Slurry, Applications, Adv&Disadvantages:


If the mold is made like a shell called shell mold casting. In this article, all the important points are discussed and underlined which can be helpful to you in any examination. Shell means the thin mold or Hollow mold.

Shell Mould Casting-Features,Ceramic Slurry,Applications,Advantages&Disadvantages
Shell Mould Casting

The material used for mold is a Phenolic resin (Thermosetting Plastic) has the viscosity of (Dynamic Viscosity equal to 1500 to 2000 Centipoise).

  • Dip the pattern into phenolic resin for 1 to 2 minutes.
  • Take the pattern out.
  • Keep it in a furnace at 250 degrees to 300-degree centigrade for 1 to 2 minutes.
  • Take out the pattern from the furnace
  • Remove the top layer of phenolic resin.
  • As it is the phenolic resin will have higher brittleness but to increase the strength and reduce the Brittleness, the sand particles are to be added to the phenolic resin.

Ceramic Slurry:
In Shell mold casting, if the ceramic slurry is used as a mold material in place of phenolic resin it is called a ceramic molding operation.

Features of Shell mold casting:

  • Because of the lower thickness of the mold, the weight of the world is less.hence handling will be easier.
  • Because the time taken for producing a mold is less, the production rate is high.
  • Because the activities used for mold making are standard activities, the process can be mechanized are automated.
  • As there is the lower porosity property of phenolic resin mold, the escape of air or gases can be passed easily through Risers.
  • This method is used for producing the symmetrical and circular shape of castings only.

Applications of Shell Mould Casting:
It is used for producing cylinders and cylinder heads of

Advantages of Shell Mould Casting:

  • Thin and complex sections undergo casting very easily.
  • High dimension, accuracy, and good surface finish are one of the advantages of shell mold casting.
  • No further machining required.
  • It can be operated by a semi-skilled operator.
  • Easily automated.

Disadvantages of Shell Mould Casting:

  • For larger casting components, Special metal pattern required and which makes it expensive.
  • Shell molds are less permeable compared to green sand mold.
  • Size and weight limitation.
  • It is not suitable for small batch production.

This is the detailed explanation of Shell mold casting. Now, let’s discuss the Investment casting process



4.Investment Casting Process: Procedure, Past and Present, Materials Used and Applications


In the Investment Casting Process, the wax is used as a Pattern Material whereas Cement Concrete is used as a Mould Material.

Because of Cement concrete mold, the same mould can be used for producing a few numbers of castings. Therefore, it is also called a Semi-Permanent Mould Casting Process.

Surface Finish:

Due to the cement concrete mold, the surface finish produced will be better.

Thermal conductivity:

Because, the thermal conductivity of cement concrete mold is higher than the sand mold, the heat transfer rate will be high. hence, the surface hardening heat treatment effect will be taking place in the casting.

The casting produced by the investment casting process will always have hard surfaces and soft interiors.

investment casting
investment casting

Because of very low porosity property of cement concrete molds, the thorough Risers must be used for escaping the air or gases.

Investment Casting derives its name from the pattern being invested (surrounded) with a refractory material. The fragile wax patterns must withstand forces encountered during the mold making. Much of the wax used in investment casting can be reclaimed and reused. 

Explanation of the Investment Casting Process:               

    • The process is generally used for small castings but has been used to produce complete aircraft door frames, steel castings of up to 300 kg (660 lbs) and aluminum castings of up to 30 kg (66 lbs).
    • It is generally more expensive per unit than die casting or sand casting, but has lower equipment costs.
    • It can produce complicated shapes that would be difficult or impossible with die casting, yet like that process, it requires little surface finishing and only minor machining.

Past and Present of Investment Casting Process:

    • Investment casting is an industrial process based on and also called low wax casting which is one of the oldest known metal-forming techniques.
    • From 5,000 years ago, when beeswax formed the pattern to today’s high-technology waxes, refractory materials, and specialist alloys, the castings allow the production of components with accuracy, repeatability, versatility, and integrity in a variety of metals and high-performance alloys.

Materials used for Investment Casting Process:                 

    • There are a variety of materials that can be used for the investment casting process, including stainless steel alloys, brass, aluminum, and carbon steel.
    • The material is poured into a ceramic cavity designed to create an exact duplicate of the desired part.
    • Investment casting can reduce the need for secondary machining by providing castings to shape.

Applications of Investment Casting Process:

The materials that can be cast with this process(Investment Casting Process) are Aluminum alloys, Stellite, Bronzes, Valves and fittings, Stainless steels, etc. Glass mold accessory castings, Levers, Gears and Splines are some of the popular usages of Investment Casting Process.

This is the complete explanation of Sand Casting Process, Die casting process, Shell Mould casting process & Investment Casting process in a detailed way.

If you have any doubts, feel free to ask from the comments section. Please Share and Like this blog with the whole world so that it can reach to many.

                                                 

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