Metal Casting Processes, Pattern, Solidification
- 1. PATTERN • Model of a casting constructed such that it forms an impression in moulding sand
- 2. PATTERN • 1st step- Prepare model (pattern) Differs from the casting Differences Pattern Allowances. • To compensate for metal shrinkage, • Provide sufficient metal for machining • Easiness in moulding • As Shrinkage allowance, Draft allowance, Finishing allowance, Distortion or camber allowance, Shaking or rapping allowance
- 3. MATERIAL 1. WOOD. 2. METAL Al, CI, Brass, 3. For special casting processes, Polystyrene which leaves mould as gas when heated also used. Types- many Simple-Identical patterns; Complex, intricate- with number of pieces. Single or loose piece; Split; gated; Match Plate; Sweep; Segmental; Skeleton(frame, ribbed), skell; Boxed Up; Odd shaped etc. Sketches--
- 4. Material 1. WOOD. (+) Cheap, easily available, light, easiness in surfacing, preserving (by shellac coating), workable, ease in joining, fabrication (-) Moisture effects, wear by sand abrasion, warp during forming, not for rough use. Must be properly dried/ seasoned, free from knots, straight grained Egs. Burma teak, pine wood, mahogany, Sal, Deodar, Shisham, Walnut, Apple tree
- 5. 2. METAL: For durability, strength Egs: Al alloys, Brass, Mg alloys, Steel, cast Iron for mass production (first, wooden pattern is made, then cast in the metal) Type of material depends on shape, size, number of castings required, method of moulding etc.
- 6. TYPES OF PATTERNS 1. SINGLE PIECE PATTERN. • without joints, partings •Cheaper •Takes more time to make •Usually used for large castings of simple shapes
- 7. 2. SPLIT PATTERN (TWO PIECE ) •Use of DOWEL-Pins •Parting surface present •Spindles, Cylinders, Steam valves, Water stop cocks and Taps, Bearings, Small Pulleys and wheels
- 8. 2. a, THREE PIECE SPLIT PATTERN
- 9. 3. LOOSE PIECE PATTERN
- 10. 4. COPE AND DRAG PATTERN • Production of Large castings • Cope and drag parts of the pattern mounted on separate plates. • Cope half and drag half made by working on different moulding machines. • This reduces the separate cope and drag plate preparation. • Generally for high speed mechanized moulding
- 11. 5. MATCH PLATE PATTERN – Pattern generally of metal and plate making parting line metal/wood.
- 12. 6. FOLLOW BOARD PATTERN. For thin sections. THIN PATTERN
- 13. 7. GATED PATTERN - Gating system is a part of the pattern. •To ensure full supply of molten metal •Used for Mass production of small products
- 14. 8. SWEEP PATTERN – For large size castings in small numbers. Template of wood attached to a sweep used. •Used for Circular sctions
- 15. 9. SEGMENTAL PATTERN – For rings, wheel rims, large size gears.
- 16. 10. SKELETON PATTERN.- Stickle board used to scrape the excess sand. Eg. Oil pipes, water pipes, pipe bends, boxes, valve bodies etc. Stickle board
- 17. 11. SHELL PATTERN •Used for Drainage fittings and pipe works •Shell pattern is a hollow construction like a shell and the outside shape is used as a pattern to make the mould.
- 18. 12. BUILT UP PATTERN – Also called lagged up patterns- For barrels, pipes, columns etc
- 19. 13. LEFT AND RIGHT PATTERN – For parts to be made in pairs. Only variation in its base position. Eg: legs of sewing machine, wood working lathe, garden benches, J hangers for shafts, brackets for luggage racks etc.
- 20. • Type of pattern depends on: • Shape and size of casting, • number of castings required, • method of moulding employed, • easiness or difficulties of the moulding operations • other factors peculiar to the casting.
- 21. Metal Pattern Oversize Factor (each direction) Finish Allowance (smaller number for larger sizes) Min Wall mm Aluminum 1.08 - 1.12 0.5 to 1.0 % 4.75 Copper alloys 1.05 - 1.06 0.5 to 1.0 % 2.3 Gray Cast Iron 1.10 0.4 to 1.6 % 3.0 Nickel alloys 1.05 0.5 to 1.0 % N/A Steel 1.05 - 1.10 0.5 to 2 % 5 Magnesium alloys 1.07 - 1.10 0.5 to 1.0 % 4.0 Malleable Irons 1.06 - 1.19 0.6 to 1.6 % 3.0 Pattern, Finish Allowance, and Wall Thickness
- 22. CHARACTERISTICS OF PATTERN MATERIALS CHARACTERISTIC RATING WOOD AL STEEL PLASTIC CAST IRON MACHINABILITY E G F G G WEAR RESISTANCE P G E F E STRENGTH E G E G G WEIGHT E G P G P REPAIRABILITY E P G F G RESISTANCE TO: • CORROSION (by water) E E P E P • SWELLING P E E E E E- Excellent; G- Good; F-fair, P- Poor
- 23. Functions of pattern • Moulding the Gating system; • Establishing a parting Line, • Making Cores, • Minimising casting Defects, • Providing Economy in moulding • Others, as needed