Xingye Die Casting Manufacturer Co.

  Draft | Ejector Pin Mark | Flash | Gate | Porosity | Shrink Mark | Surface Finish | Tolerance
Designing a die cast part is different from designing a screw machined part. The following items are the most common characteristics for a die cast part that a designer need to consider:
  1. Flash -A thin web or fin of metal on a casting which occurs at die partings, vents and around moveable cores. This excess metal is due to working and operating clearances in a die. 
  2. Gate vestige -- Passage for molten metal which connects runner with die cavity. Also, the entire ejected content of a die, including castings, gates, runners, sprue (or biscuit) and flash. After cast, the cast part is cut off from the runner but a protruded part (vestige) will be left on the part. This required a secondary operations such as hammering, saw cutting, sander or milling to make the gate vestige smaller or flush with the adjacent part. To completely make the mark invisible requires sand blasting or painting or anodizing.
  3. Draft -- The taper given to walls, cores and other parts of the die cavity to permit easy ejection of the casting. Typical draft angle is 2 degree per side. When designing a part please please allow draft angle at the mold separating direction.
  4. Ejector marks -- Marks left on castings by ejector pins. Designer must first allow a supporting spot for the ejector pins to eject the casting, then allow a round pin mark on the surface.
  5. Porosity -- Voids or pores resulting from trapped gas, or shrinkage during solidification. Porosity is inevitable but the degree can be controlled. 
  6. Shrink mark -- A surface depression which sometimes occurs next to a heavy section that cools more slowly than adjacent areas. Try to design with uniform thin wall and avoid any heavy section. Heavy section would also result in residual stress in the casting which is a  contributor to the future in-service cracking and failure.
  7. Surface finish -the as cast surface finish is smooth in general but cosmetically not appealing due to the existence of flow line, gas mark, heat mark and lubricant residue, etc. However these cosmetic appearance issues can be easily minimized or eliminated or by cleansing, sand blasting, anodizing or powder coating. Other surface defects include soldering due to the adherence of molten metal to portions of the die.
  8. Dimensional Tolerance - Compared to other casting method die casting can achieve the best precision. When the dies are properly made, casting may be accurate within 0.001 inch or even less and a limit of 0.002 or 0.003 inch per inch of casting dimension can be maintained on many classes of work. However try to design a less tight casting will lower the manufacturing cost, especially in mass production, tighter tolerance will result in more scraps and more frequently tool maintenance. So be careful of the tolerance you choose. 
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