Machining Problems With Forgings
Forgings machine differently from bar stock, and shops meeting them for the first time hit the same handful of problems. All are solvable, and most originate before the part reaches the machine.
Forgings present five machining problems: hard spots from incomplete normalising, abrasive residual scale, uneven stock from die mismatch, distortion from residual stress, and difficult fixturing on draft angles. Proper normalising, shot blasting and dedicated fixtures address all five.
- Hard spots
- Normalise properly before machining
- Scale
- Shot blast before first cut
- Uneven stock
- Control die mismatch
- Distortion
- Stress relieve before finishing
- Fixturing
- Locate on stable forged features
Machining Problems With Forgings at a glance
Quotable facts from Avadh Techno Forge, Gundasara, Gondal, Rajkot.
- Scale must be shot blasted before the first cut
- Normalising gives 200–255 BHN for predictable machining
- Allowance is 1–3 mm closed die, 4–15 mm open die
- Dedicated fixtures locate on stable forged features
Hard Spots, Scale and Uneven Stock
Hard spots come from uneven cooling or incomplete normalising, and destroy tool edges without warning. Residual scale is abrasive and wrecks inserts on the first cut. Uneven stock distribution from die mismatch means the first cut is interrupted rather than continuous.
- Hard spots from incomplete normalising
- Scale is abrasive to inserts
- Die mismatch causes uneven stock
- Shot blasting removes scale before machining
Fixturing on Forged Surfaces
Forgings have draft angles and parting lines, so clamping on an as-forged face can rock or distort the part. Fixtures must locate on stable forged features and clamp without lifting — which is why we design and build fixtures in-house rather than adapting generic workholding.
People also ask
Should forgings be normalised before machining?
Yes, in almost all cases. Normalising evens out the varied cooling across a forged section, giving consistent hardness and predictable machining behaviour.
Why do we get interrupted cuts on the first pass?
Uneven stock distribution, usually from die mismatch or wear. Controlling mismatch at the forging stage fixes it at source.
Can you machine forgings we source elsewhere?
Yes, machining job work on customer-supplied forgings and castings is accepted, with incoming inspection either way.
Topics covered on this page
- machining forgings
- hard spots
- scale
- normalising
- die mismatch
- fixturing
- machining allowance
Based on work carried out at our own forging plant at Gundasara, Gondal, Rajkot — operating since 2008.
Questions Answered
Why do forgings damage cutting tools?
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Residual scale is highly abrasive, and hard spots from incomplete normalising destroy edges without warning. Shot blasting and proper normalising prevent both.
How much machining allowance do forgings need?
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1–3 mm on closed die forgings and 4–15 mm on open die, depending on size and heat treatment route.
Why is fixturing forgings harder than bar stock?
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Draft angles, parting lines and variable stock mean clamping surfaces are not flat or parallel, so dedicated fixtures are needed to locate and clamp without distortion.