Sand Casting Design Guidelines
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| Sand Casting Design Guidelines |
- The shape of casting should be simple, reducing mould, core and pattern-making production costs and time. Mould, casting and core should be designed along a straight parting line of the mould.
- The parting line should be along a parting plane. The parting line should be sharp, clear, regular and straight. The parting line should be low for aluminium-based alloys and for steel alloys parting line should be high.
- The core location in the mould should not interfere with the flow of molten metal but should help molten metal flow uniformly through the mould cavity.
- Small-size casting should be manufactured on the drag side of the mould only, without making a cope section of the mould.
- Patterns should be designed for easy removal without damaging the mould cavity during pattern withdrawal, reducing shake allowance.
- Machining allowance should be provided for secondary operations such as drilling, boring and reaming to completely avoid any complex design of the pattern, cores and final casting.
- Green sand moulds should be used where surface finish of casting is not of primary importance at the same time, surface finishing secondary operations can provide better surface finish without using expensive dry sand moulds.
- Complex casting parts should be manufactured separately and welded together, reducing the overall production cost of making sand mould especially for producing multiple-piece patterns.
- Bosses, pads, lugs and undercuts should be avoided in the final casting.
- The use of cores should be avoided wherever necessary. This reduces the production cost of mould sections, cores and chaplets.
- All sections of casting should cool uniformly during the sand casting process without any stress concentration on the solidifying casting. Sand casting should be designed keeping in mind the solidification properties of molten metal and shrinkage allowance.
- Casting should be designed to easily break off the core and separate the sand core from the casting.
- Casting designs are connected to the gating system, gating system in casting should be designed to facilitate proper feeding of molten metal to make a sound casting.
- While designing casting care must be taken that all sections should be of uniform thickness to avoid concentration of molten metal and shrinkage defects.
- Casting should not have sudden changes in thickness and isolated thickness to avoid hotspot defects.
- Care must be taken while designing casting to provide pattern allowances such as machining allowance, shrinkage allowance, draft allowance and rapping allowance should be properly given for sound casting.
- Casting should be designed to eliminate adjacent sections of casting with different thicknesses to reduce warpage defects.
- Proper venting should be provided while using green sand moulding for the escape of gases, water and vapour from the mould as molten metal comes in contact with green sand. This eliminates gas defects such as blowholes and pinhole defects.
- The right combination of round, semi-angular and angular sand grain should be used to give a proper surface finish and at the same time allow the escape of gases out of the mould.
- Casting should be designed with cleaning, inspection, testing, service, and repair in mind. All casting sections should be accessible to cleaning, inspection, testing service and repair.