Material used for Pattern.

• Material used for patterns in casting:
  
  1. Common pattern materials (with uses, advantages & disadvantages):
  
  Wood (softwoods, hardwoods, plywood):
• Typical use: low-volume sand casting, prototype patterns, large simple shapes, core boxes, match-plates backing.
• Types: straight-grained softwood (pine, cedar) for cheap patterns; hardwoods (mahogany, maple, beech) or high-quality plywood (marine/birch) for better durability and stability.
• Advantages: inexpensive, easy to shape/repair, good for hand work and one-off patterns, light weight.
• Disadvantages: absorbs moisture and can warp; limited life in repeated production; surface wear from sand; needs coating for durability.

Metal (cast iron, steel, aluminum, brass):

• Typical use: large production patterns, match-plates for automatic molding, shell molding, high-precision master patterns, long-run core boxes.
• Advantages: excellent dimensional stability and durability, resists wear, can be machined to tight tolerance, long life.
• Disadvantages: costly and heavy; harder/longer to machine; higher upfront cost justified only for moderate-to-high production.
• Tooling boards / machinable plastics / resin blocks (rigid urethane, epoxy tooling boards, phenolic boards):
• Typical use: CNC-machined prototype and medium-run patterns, master patterns for moulding processes, patterns with complex geometry.
• Advantages: easy to CNC, good dimensional stability, predictable machining, can be finished to smooth surface, repeatable.
• Disadvantages: costlier than simple wood; life depends on resin type and surface treatment (some wear faster than metals).

Plastics & thermoplastics (ABS, HDPE, nylon, acrylic):

• Typical use: prototype patterns, low-to-medium volume production, patterns for lost-wax/investment (thermoplastic wax alternatives), cores in some processes.
• Advantages: stable, can be machined or 3D printed, good surface finish, lighter than metal.
• Disadvantages: some plastics deform at elevated temperatures; wear resistance varies.

3D-printed materials (FDM plastics, SLA/SLA castable resins, SLS nylon):

• Typical use: rapid prototyping, complex shapes, investment-casting patterns (castable resins), low-volume sand or foam patterns.
• Advantages: rapid iteration, no tooling needed, complex internal geometry possible, SLA castable resins can be used directly in investment casting (lost-resin).
• Disadvantages: layer lines may require finishing; material strength and heat behavior vary; some prints are single-use or limited life in production molds.

Wax (paraffin / beeswax blends, injection molded wax):

• Typical use: investment (lost-wax) casting patterns, injection-molded wax trees.
• Advantages: excellent surface finish, burns out cleanly for shell, easy to inject into reusable molds for high-precision castings.
• Disadvantages: fragile, limited handling life, requires special equipment for wax injection.

Expanded Polystyrene (EPS - foam):

• Typical use: lost-foam casting (pattern left in mold and vaporized by molten metal).
• Advantages: pattern can be made to final shape; no parting line on casting; good for complex shapes; low cost.
• Disadvantages: fragile; requires careful handling and coating; not reusable.

Fiberglass / Composite (GRP):

• Typical use: large swept or sculpted shapes, body patterns, repeated medium-run shapes.
• Advantages: lightweight, durable, good surface finish, dimensionally stable.
• Disadvantages: more expensive to produce initially; repair requires composite work.

2. Special pattern types & matching materials to processes:

• Sand casting (green sand / CO₂): wood, patternboard, metal, resin tooling boards, 3D-printed patterns. For high volumes choose metal or durable resin boards.
• Shell molding: metal patterns are common (to retain heat and repeated use).
• Investment casting: wax patterns or 3D-printed castable resins.
• Lost-foam: EPS foam patterns (coated).
• Die casting / permanent mold: patterns are the dies — metal only.

3. How to select pattern material:

1. Production volume:

   • Low (1–10): wood or 3D print.

   • Medium (tens–hundreds): tooling board, aluminum, composite.

   • High (thousands): metal (cast iron/steel matchplates).

2. Required dimensional accuracy & surface finish:

   • High accuracy: metal or high-grade tooling board / SLA castable resin.

3. Complexity of shape:

   • Complex internal details → 3D printing or multi-piece pattern + cores.

4. Thermal/chemical compatibility:

   • For processes where pattern interacts with binder/heat, choose compatible material (e.g., wax for investment; metal for shell molding).

5. Cost & lead time:

   • Budget + quick turnaround → 3D print or wood; longer runs justify metal.

6. Tooling & machining capability:

   • If CNC available → tooling boards and metals are easy to produce accurately.

7. Handling & weight:

   • Large patterns benefit from lightweight composites or aluminum.

4. Pattern allowances & design considerations:

1. Shrinkage allowance: To compensate metal solidification shrinkage (depends on alloy). (Verify exact value from alloy/foundry — it varies by metal and casting size.)

2. Draft allowance: Taper on vertical faces to ease pattern removal (common: ~1°–3°; more for very deep cavities).

3. Machining allowance: Extra material left for machining of critical surfaces.

4. Distortion allowance: For shapes that distort during cooling (thin long sections, flat plates).

5. Parting/shake allowance: To account for the molding process and removal.

5. Surface treatment & pattern protection:

1. Seal & harden wooden patterns: shellac, varnish, lacquer or epoxy coatings to reduce sand wear and moisture uptake.

2. Parting compounds: talc, graphite, clay, silicone or commercial parting sprays to ease removal and improve mold surface finish.

3. Wear protection: metal plates or hard-facing where pattern contacts molding machine or parting surfaces frequently.

4. Finishing: sanding/filling and final varnish or paint for smooth mold surfaces.

6. Maintenance, storage & repair:

1. Wood: control humidity, re-varnish, store flat; repair with wood filler or epoxy.

2. 3D prints/resins: inspect for cracks; reprint replacements if damaged.

3. Metal: inspect for wear; re-machine as needed.

4. Regular inspection: check key dimensions, parting lines, core seats and core prints.

5. Spares: keep spare loose pieces/segments for rapid replacement.