Foundry Design Tips

For designing an ideal framework of a metal casting, a detailed study of the contradictory needs and finding the best solution is required. The designing, quality-benchmarking and cost-effective considerations of the product, plays an important role to work out an ideal structure for metal casting.

There are many considerations required to be avoided while making a framework of a casting design. Conventional rules like:

  • Thumb Rule- At every step of the decision process, we tend to filter out significant information, and rely on flawed rules of thumb, which generally, direct us toward the familiar facts and away from the unknown facts. Hence, limiting are knowledge to few areas.
  • Avoiding heavy sections can improve the designing capabilities of the cast. As heavy sections involves stress concentrations and tears.
  • Avoid sharp edges and sharp re- entrant angles - As sharp corners and edges encourage high thermal gradients. Thus, they should be avoided. Rounded corners (external) and fillets (internal) are trademarks of a casting. Not only do they improve manifestation but also they dispense strains. Either carry the common thickness around a liberal radius or thin it slightly. Use of generous fillets and radii is recommended.
  • Design junctions to avoid mass concentrations- while production; it is proved to be much beneficial by producing close to net shaped parts which can involve varied complicated junctions between sections and generate mass concentrations.
  • To avoid excessive number of sections to minimize stress concentrations.
  • General Do's and Don'ts as found in the casting design manuals and guidelines have limited approach and thus limit the knowledge of the conceptual framework. It becomes very important to explore all the pros and cons of the subject matter before designing the casting.
  • Building simple, extruded, rotated and orthogonal shapes, such as building blocks from refined shapes like plates, bars, tubes, I-beams, and other kinds of extrusions of invariable cross section, etc.
  • To avoid sharp angles and abrupt section changes.
  • Bosses, lugs, and pads should not be used unless absolutely necessary.
  • Allow for material shrinkage and machine finish in dimensional tolerances
  • Fillet all sharp angles.
  • Avoid casting strain.
  • Avoid sharp angles and abrupt section changes
  • Design all sections as nearly uniform in thickness as possible- satisfactory wall thickness range from 1/4 inch to 3/4 inch is required for most sand cast irons. All common metals show expansions when heated as their molecular activity increases. After pouring, the liquid loses heat through the mold by conduction and immediately starts to build the metallic solid shell. Sound casting is possible if the casting's wall is reasonably thin and uniform. But if the casting has heavy walls, thick local section, abrupt transitions, or massive junctions, the center metal may become porous. This is called centerline shrinkage or internal porosity.
  • Design for casting soundness to eliminate shrinkage or porosity - casting soundness is strongly influenced by hydrogen porosity and entrained nonmetallic inclusions. Shrinkage is generally more harmful to casting properties. In isolated cases, hydrogen may actually be intentionally introduced and controlled in specific concentrations compatible with the application requirements of the casting in order to promote superficial soundness.
  • Proportion dimensions of inner walls correctly
  • Design ribs and brackets for maximum effectiveness
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