Casting Designing Framework

To approach an ideal framework for designing a metal casting requires a detailed study of the contradictory requirements and identifying the best solution. The artifact’s designing, quality-benchmarking and cost-effective considerations play an important role to work out an ideal structure for metal casting.

Advantages of defining framework:
  • To design functionally stable cast products with production techniques using minimal development time.
  • To produce quality casting designs with reduced number of rejections.
  • To maintain a balance between material and energy consumption to increase productivity at lowest costs.

A clever designed casting is required to be competent on one hand and cost effective on the other. However, this technique of designing and creating castings is a complex job. Several considerations are required to define while crafting a framework of the cast and surprisingly, there’s no particular rule to distinguish them. Thus, it involves a thorough analysis of manufacturability and other production stages during the design phase of the metal casting.

Important considerations in the framework:
  • Minimum thickness of the section – To accomplish strength and firmness, casting shapes with the minimal thickness of the walls are designed. This helps in achieving distortion free and stress free castings. Thus by minimizing the variations in the cross section of the casting reduces successive failures in the final product. (Refer Table 1.1 for minimum wall thickness of the common metals)
  • Tolerance-capability of the material being used- It is desirable for the designer to apply higher tolerance. Also, geometric tolerance values for e.g. profile of a surface are required to be specified for composite blended surfaces.
  • Calculation of the shrinkage in the alloys being used- As the material becomes cold, and the sections of the cast component intersect to form ribs; opposite directions starts shrinking. This directs higher stress levels at the intersections, causing immediate cracking.
  • Understanding heat transfer phenomenon of component castings, while undergoing various shapes. The cooling characteristics of the casting play a major role in the metal casting production. Design of the corners of the casting can influence the cooling rates. For e.g. sharp corners stimulate higher thermal gradients.
  • Defining radii changes in the cast sections.
  • Heavy mass-concentrations are avoided, as junctions between the sections produces mass-concentration. The shape of the casting component which requires section thickness change, should have measured and progressive blends. Thus avoiding heavy mass-concentrated sections.
  • A pre-defined objective is required for post manufacturing process and inspections. Jigs or fixture points should always be designed in such a way that they lie away from the line of symmetry or parting line of the cast component.

Table – 1.1 – Table showing minimum wall thickness chart of the common metals

Metal Pattern Oversize Factor for each direction Finish Allowance (smaller number for larger sizes) Minimum Wall thickness mm (inches)
Aluminum cast alloys 1.08 - 1.12 0.5 to 1.0 % 4.75 (0.187)
Copper cast alloys 1.05 - 1.06 0.5 to 1.0 % 2.3 (0.094)
Gray Iron for casting 1.10 0.4 to 1.6 % 3.0 (0.125)
Nickel cast alloys 1.05 0.5 to 1.0 % N/A
Steel cast 1.05 - 1.10 0.5 to 2 % 5 (0.20)
Magnesium cast alloys 1.07 - 1.10 0.5 to 1.0 % 4.0 (0.157)
Malleable Irons for casting 1.06 - 1.19 0.6 to 1.6 % 3.0 (0.125)

An approach towards defining solutions gives the competitive edge over struggle to control the production process within the initial stage of designing. It facilitates the base of implementing solutions to work for the benefits. Based on the above extensively differing, yet noteworthy perspective; cost effective metal casting designs can be achieved proficiently.

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