Overview of Content for Engineers and Designers
Designing for Manufacturabiity Controlling and Reducing Cost
- 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)
- Typically, the deeper the impression, the greater the draft angle
- Parting line and draft consideration- Where is draft taken from : top or bottom?
- 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
(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)
- 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)
- 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
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.
- 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.
- 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.