Pattern making is the process of creating a replica of the final casting used to prepare the mould. The five basic steps in pattern making are designing the pattern, selecting pattern material, adding allowances, shaping and finishing the pattern, and inspecting the pattern.
In foundry practice, pattern making is the first and most critical stage of the casting process. Most textbooks summarize it into five basic steps, from design to final finishing.
In this article:
Five Steps in Pattern Making
Pattern making is the process of creating a replica of the desired casting used to form the mould cavity. It involves a series of systematic steps to ensure accuracy, strength, and ease of moulding.
1. Study of the Component Drawing
What is done?
- The engineering drawing of the component is carefully studied.
- Shape, size, tolerances, and surface finish requirements are analyzed.
Important considerations
- Casting allowances (shrinkage, machining, draft)
- Parting line selection
- Need for cores
- Metal to be cast
Why it is important
- Any mistake here leads to defective castings
- Forms the basis for pattern design
2. Selection of Pattern Type and Material
Pattern type selection
Based on:
- Shape and complexity of casting
- Size of casting
- Production quantity
- Type of moulding process
Common pattern types:
- Solid pattern
- Split pattern
- Match-plate pattern
- Sweep pattern
- Skeleton pattern
Pattern material selection
- Wood (low cost, short life)
- Metal (high accuracy, long life)
- Plastic (lightweight, moderate life)
3. Provision of Pattern Allowances
To obtain accurate casting dimensions, allowances are added to the pattern.
Types of allowances
- Shrinkage allowance – compensates metal contraction
- Machining allowance – extra material for finishing
- Draft allowance – helps easy withdrawal of pattern
- Rapping allowance – compensates mould enlargement
- Distortion allowance – for warping control
Importance
- Ensures final casting meets design requirements
4. Making and Finishing of the Pattern
Pattern making process
- Pattern is manufactured by:
- Carpentry (wood)
- Machining (metal/plastic)
- CNC / 3D printing (modern method)
Finishing operations
- Sanding and polishing
- Painting or lacquer coating
- Colour coding for:
- Machined surfaces
- Core prints
- Unmachined surfaces
Purpose
- Improves mould surface finish
- Increases pattern life
5. Inspection, Testing, and Storage
Inspection
- Dimensional accuracy check
- Shape verification
- Allowance confirmation
Testing
- Trial mould preparation (if needed)
- Fit and withdrawal check
Storage
- Stored in dry conditions
- Protected from damage and warping
Importance
- Ensures consistent quality in production
Summary Table
| Step | Activity |
|---|---|
| 1 | Study of drawing |
| 2 | Pattern type & material selection |
| 3 | Allowance provision |
| 4 | Pattern making & finishing |
| 5 | Inspection & storage |
Conclusion
Pattern making involves studying the drawing, selecting pattern type and material, providing allowances, making and finishing the pattern, and finally inspecting and storing it.
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