Casting Process: It 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 mould called as Casting Process.Casting Process-Importance, Advantages, Mould, Moulding Materials, Methods
Importance of Casting Process:
- This process is widely used to manufacture complex parts.
- All major parts like milling machine bed, the bed of lathe machine, IC engine components, etc. are made by this casting process.
- It produces the best quality sand casting products at the lowest possible cost compared to machining Process.
- High Production rate.
- High complexity shapes: Casting Process can create any complex structures economically.
- Short lead time: Short lead time compared to others and hence, ideal for short production runs.
- Low-cost tooling: Tooling and equipment costs are low compared to some other metal manufacturing processes.
- Design flexibility: The size of an object doesn’t matter for casting.
- Wider material choice: all types of engineering alloys can be cast.
- Dimensional accuracy: Because of shrinkage in the casting, the dimensional accuracy might be at risk. So, the designers must take care of providing the allowance to the product(Pattern) before pouring the molten metal.
- Low strength: Due to high porosity compared to a machined part.
- Post processing: It requires Secondary machining operations in order to improve the surface finish.
- Lower Melting Point: Generally limited to metals of the lower melting point.
- Not suitable for low-volume production.
Mould or Mold:
- It is described as a void or cavity created in a compact sand mass with the help of pattern which (mold), when filled with molten metal produce a casting.
- The mold is made by using the molding sand consists of basic elements such as
- Silica Sand Particles: They are used for producing the required strength of the molding sand. (75-80%) of sand is filled with Silica sand Particles.
- Clay: It is used for producing the bond between the sand particles. (15-20%) of clay is filled in molding sand.
- Water or Sodium Silicate: It is used for initiating the bond formation between the sand particles(6-8%).
|Silica Sand + Clay + Water = Green Sand.
Silica Sand + Clay + Sodium Silicate = Dry Sand.
Green Sand or Dry Sand with 50% Clay is called as Loam Sand.
- The process of making a cavity or mold in the compact sand is called as Moulding.
- A material which possesses high refractoriness can be used for mold making. Thus, the mold making material can be metallic or non-metallic(sand).
- For Metallic Moulds, the common materials are Cast iron, mild steel, and alloy steels.
- For Non-Metallic Moulds: Materials used are molding sand, Plaster of Paris, silicon carbide, graphite, and ceramics.
- Note: Out of all materials, the molding sand is the most commonly utilized non-metallic molding material because of its certain inherent properties namely refractoriness, high permeability, and workability along with good strength. Moreover, it is also highly cheap and it is easily available.
Methods of Moulding Process: [Not in Syllabus]
- Machine molding
- Loam molding
- Skin-dried molding
- .Green sand molding
- Bench molding
- .Pit molding
- Dry sand molding
- Floor molding
- Cement bonded molding
- Shell molding
This is the complete explanation of the casting process with Importance, Advantages, Limitations, etc. If you have any doubts, you can ask from the comments section.
Let’s discuss Types of Pattern in the Casting Process…
Types of Pattern in Casting: Properties, Pattern Materials, limitations, and Applications:
Pattern: It is the replica of the casting to be produced. Replica means, the shape of the pattern remains the same as that of the shape of the casting to be produced.
- The main modifications in the pattern are the addition of pattern allowances and the provision of core prints.
- If the casting is to be hollow, additional patterns called cores are used to create these cavities in the finished product.
- Runner, Ingate, and Riser are the part of the sand casting process used to feed the molten metal into the casting cavity.
- The quality of the casting produced is dependent upon the type of material, its construction, and Design.
- Patterns with high surface finish can reduce the defects in the casting process.
Properties Possessed by the Pattern in casting:
- No moisture absorption by the pattern material would take place.
- Surface finish produced on the pattern material must be good or excellent.
- The material should be of low density.
- Easiness in fabrication.
- It should be cheaper(Pattern Cost).
Types of Pattern in Casting:
The different types of patterns are as follows.
- Solid pattern
- Split pattern
- Match plate pattern
- Cope Pattern and Drag Pattern
Types of Pattern Materials:
The different types of pattern materials used in the casting process are as follows.
Except for moisture absorption, the wood is possessing all other properties which are required as a pattern material and out of all the different woods, the wood which is absorbing less moisture will be used as pattern material.
Example: Teak wood, Mohagaoni, etc.
In the case of metal patterns, the density is high and it is difficult to manufacture the metal patterns.
Ex: Aluminium, white metal, Titanium has low density, but they are of very costly.
Aluminium = 2.7 gm/cc
White metal = 3.2 gm/cc
Titanium = 4.3 gm/cc
When wooden parts are used for producing metal patterns, the double shrinkage allowance must be provided on the wooden pattern.
They are processing all the properties which are required for pattern material.hence in today’s manufacturing industry, plastics are the most commonly used pattern materials.
Ex: Epoxy resin, PVC, Nylon, Cellulose, Polystyrene, etc.
Polystyrene: It is used for producing very large castings where the removal of the pattern is not possible.
Ex: Producing bed of Machine.
It will be selected as a pattern material for producing the complex shape of the pattern, to produce the complex shape of the casting i.e. because of the highest softness of the wax material, it is possible to produce the Complex shape of the pattern easily.
- With wax patterns, removal of the pattern will be easier in the form of a liquid and this liquid wax will be reused.
- When compared to other patterns, the surface finish produced with the wax material will be better.
Disadvantages of using a wax pattern:
- Wax patterns are not effective with green sand molding because the ramming force will be disturbing the pattern shape. So only low ramming force can be applied i.e. only loose sand molds can be produced with Green Sand.
- If a wax pattern is used with Green Sand mold, chances of formation of rat tail defects are high.
- Because of very hair softness, during handling of the pattern due to self-weight, the pattern may get distorted. Hence, to avoid the distortion of the pattern, the maximum size of the wax material is up to 5 kg only.
Applications of using Wax Pattern:
Component Produced are
- Gold and Silver Ornaments
- turbine blades
- a waveguide for a radar system
- surgical instruments etc.
Types of Allowances in Casting Process:
Types of allowances are as follows:
- Shrinkage Allowance
- Machining Allowance
- Draft Allowance
- Shake Allowance
- Distortion Allowance
This is the explanation of Pattern, Types of Pattern Materials, Types of Pattern in Casting, Disadvantages, and Applications in a detailed way. If you have any doubt, you can ask from the comments section.
Also Read:[For Continuation of the Unit]
- Sand Casting Process – Definition, Steps, Diagram, Aspiration Effect, Elements of Sprue, etc.
- Die Casting Process-Principle, Types, Gravity&Pressure Die casting, Applications, Advantages