Engineering Specifications

Designing for Manufacturabiity Controlling and Reducing Cost

Draft Angles

  • Forgings made on a hammer must be designed to include draft angles to allow
    the parts to release from the die.
  • Typical draft angle= 7° (tolerance: +2°/0°)
  • Minimum draft angle= 5° (tolerance: +2°/0°}
  • Below 5° (call Trenton Forging engineering to discuss your specific needs)

Draft Notes

  • Typically, the deeper the impression, the greater the draft angle
  • Parting line and draft consideration- Where is draft taken from : top or bottom?

Die Wear

  • Draft angle and wear tolerances are defined as a function of how the dies wear, I e., the tolerances will get bigger as wear occurs.
  • Die wear varies according to the material that is forged and the shape of the forging.
  • Consequently, die wear tolerances for various materials are applied in addition. Generally,
  • carbon content and hardness of the steel define it’s abrasiveness; the higher the carbon content and I or harness, the faster die wear occurs.

Die Wear Tolerances
Forgings Under 30 Inches or 750 mm
Factor (In/Inch)
(mm/millimeter) Over 30 in. or 750 mm Constant in. mm.

carbon, low Alloys      0.005   0.15   3.81
Stainless                   0.007   0.21   5.33
Heat Resistant Alloy    0.0009   0.27   6.86


  • The basic rule is: bigger is better; which is especially true with deep impressions.
  • Minimum radius; .060″
  • Smaller radii are possible (call Trenton Forging engineering to discuss your specific needs)

Surface Finish and Surface Conditions

  • The OKidation of the steel during the forging process can result in sca le pits (small indentations in the surface)
  • If necessary, eKtra care can be taken to reduce scale pits at additional cost .
  • The process of removing flash from the forging (or trimming) produces a surface at the parting line that is different than the as-forged surface.
  • Flash extension will be .015″ to .020″ (see figure 3)engineeringPageSpecsFigue3
  • The parting Line can be hand ground to reduce the flash extension at additional cost .
  • Forged parts are tumbled in a shot blast machine which is used to remove scale and to improve surface finish.
  • Different blast media can be used to provide a different surface finish.
  • Dings and dents can occur during handling; special care can be taken at additional cost if necessary. (call Trenton Forging engineering with Questions).


  • Mismatch occurs at the parting line and is caused by minor shifts between the top and bottom dies(see figure 4)engineeringPageSpecsFigue4
  • Mismatch can be from side-to-side, end-to-end or can be different from side-to-side along the length which is known as twist; the reality is that there is always some variation across the parting line due to setup and slight movements between the top and bottom dies.
  • Typically match tolerance: up to .030″.
  • Tighter match tolerance is possible: reduced to .015″ 
    but possibly at additional cost.


  • Closure is the variation in thickness of a forging (i.e.; across the parting line).
  • Typical closure tolerances= +/- .030.
  • Tighter closure tolerances+/- .010 with post-forging coining operation.
  • Extremely tight closure tolerance is also possible: +/- .005″ (call Trenton Forging engineering with Questions).

Straightness and Flatness

  • Straightness and flatness can be affected by different stages in the forging process, handling, abrasive blast and heat treat and must be preemptively curbed or corrected before shipment.
  • Straightness is a 2-0 characteristic.
  • Stalghtness tolerance: .003″ per inch
  • Flatness Is a 3-0 characteristic.
  • Flatness tolerance: .003″ per inch

Cost Drivers
Raw Material Input

  • The diameter of the raw material is defined by the largest cross-section of the part and how far material must travel to fill the impressions in t he die.

Draft Angles

  • The tighter the draft angle, the more difficult it is to forge and reCJuires more freCJuent die maintenance.


  • Very tight radiuses are more difficult to forge; tight radiuses can result In cracks and premature die wear.

Forging Size and Complexity

  • Part complexity is directly related to the deviation from the shape of the raw material to t he shape of the Impression, and therefore the finished part; Trenton Forging specializes in parts made from round-bar billets.

Production Runs

  • Smaller lot sizes or shorter production runs drive cost by needing multiple setup processes.

Heat Treatment Costs

  • Heat treating charges are based on minimum lot sizes. Small lots cost the same as large ones to process up to the minimum Quantity required.

Additional Resources