Factors For Selecting Pattern Material
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| Factors For Selecting Pattern Material In Casting |
Pattern materials are selected for pattern based on numerous factors for producing casting in the sand casting process.
The following factors govern the selection of pattern material for pattern making.
- The casting volume to be manufactured (Eg. Match plate pattern and gated pattern are used for producing casting in high numbers).
- Minimum casting thickness (Shell moulding/casting produces thin casting made from shell mould utilising metal pattern).
- The complexity of casting to be cast (Investment casting produces complex casting using metal and wax patterns).
- The shape, size and weight of the casting (Large size patterns such as cope and drag patterns are difficult to handle in a foundry for pattern makers).
- The surface finish of the final casting (Metal material pattern with good finishing will give a better surface finish and quality of casting).
- The flexibility in the design of the pattern (3D patterns made from rapid prototyping have higher flexibility in design for pattern makers.).
- The flexibility of change in the design of the pattern (Difficult to change the metal pattern once cast but wooden pattern sections can be easily changed, replaced or corrected at a lesser cost).
- The thickness of the final casting (3D printed patterns provide more flexibility in designing thinner sections of the casting).
- Dimensional accuracy of the final casting (Metal pattern cast or metal & plastic 3D printed pattern have better accuracy than the wood pattern).
- Cost of the pattern material (Wood pattern material is cheap than metal pattern material for producing larger casting).
- The pattern should be able to sustain wear, abrasion and rough handling.
- The production cost of casting, handling, storage and pattern making.
- Types of moulding processes such as green sand moulding, dry sand moulding and skin-dried sand moulding.
- Type of moulding material (sand, additives etc) used during the moulding process.
- Pattern storage time or shelf life of the pattern should be higher.
- The pattern material selected should reduce the overall cost of final casting production.
- Material handling equipment is available in the foundry to handle and carry patterns.
- The master pattern material chosen for producing metal patterns should have good castability.
- Machines, equipment, labour, resources and pattern production setup are available to make patterns in the foundry.
- The material selected for producing the pattern should be reliable material.
- Waterproof material (eg plastic) or waterproof coated pattern material must be selected when choosing a pattern (As patterns are in continuous contact with the moulding sand it becomes important to choose pattern material which can sustain moisture in the green sand in the green sand moulding process).
The selection of pattern material factors is explained in detail below:
There are various types of pattern material used in the casting process for pattern making.
Pattern material is selected based on the properties of pattern material.
Wood as pattern material is selected for making prototype casting to large-size casting depending upon the size of the final casting.
Metal pattern is used for producing a casting in large quantities and high quality.
Wax, plastic and gypsum material can be moulded in die making a very complex shape pattern for producing casting.
Pattern-making flexibility is high for wax and plastic patterns as compared to metal and wood pattern material.
Metal, plastic and wax material patterns produce final casting with good surface finish and dimensional tolerance as compared to the wood pattern.
Metal as a patterned material is best for small to medium-size casting for large-volume production. But casting with large-size wood as a material is used as its cost is low compared to metal.
Pattern material should be strong during handling with minimum wear, tear and abrasion.