Surface finishing requirements for hot forgings
Q: I'm searching for information-on an industry standard for surface finish, including nicks and dings, for a 4140 steel hot forging. A customer is causing us to "apple polish" every forged surface prior to shipping. This is costing us dearly, and without some standard industry practice, I don't have a leg to stand on. Any information will be appreciated.
A: Neither the FIA Forging Manual nor the FIA Forging Design Guide contains specifications, per se , on surface finish. The usual print notations (not true specifications) for forgings may go something like this:
As-forged surfaces shall be smooth and free of scale and other pits.
Shot-blasted surfaces are usually considered as adequate on rough forgings (that will be machined).
On forged surfaces that will not be machined, the surface finish shall have a roughness equivalent to a surface finish of 500RMS or finer. It should also be free of scale and scale pits.
I know of no specification for dings or depression-like pits. If they are proven to be within dimensional tolerances, dings would be a cosmetic problem only.
Often, Brinell "dents" are acceptable in neutral locations (low or no stress areas). Beyond these kinds of notations, I would have to know the technical reasons for your having to furnish parts so heavily polished.
For net or near-net forgings, the surface finish can be specified as smooth as the "apple polish" that you mention. In this case, the forgings are usually warm forged and sometimes coined to sharpen up selected dimensions, as well as improving surface finish.
H. James Henning answers forgers' technical and operational questions. For more than 40 years he held key technical positions in the forging industry, most recently as director of technology for the Forging Industry Association. He is president of Henning Education Services, Columbus, OH, specializing in customized education and training in forging technologies.
Send questions to
ASK JIMc/o FORGING1300 E. 9th St.Cleveland, OH 44114-1503
Or e-mail: henningedu@aol.com
Q: I'm searching for information-on an industry standard for surface finish, including nicks and dings, for a 4140 steel hot forging. A customer is causing us to "apple polish" every forged surface prior to shipping. This is costing us dearly, and without some standard industry practice, I don't have a leg to stand on. Any information will be appreciated.
A: Neither the FIA Forging Manual nor the FIA Forging Design Guide contains specifications, per se , on surface finish. The usual print notations (not true specifications) for forgings may go something like this:
As-forged surfaces shall be smooth and free of scale and other pits.
Shot-blasted surfaces are usually considered as adequate on rough forgings (that will be machined).
On forged surfaces that will not be machined, the surface finish shall have a roughness equivalent to a surface finish of 500RMS or finer. It should also be free of scale and scale pits.
I know of no specification for dings or depression-like pits. If they are proven to be within dimensional tolerances, dings would be a cosmetic problem only.
Often, Brinell "dents" are acceptable in neutral locations (low or no stress areas). Beyond these kinds of notations, I would have to know the technical reasons for your having to furnish parts so heavily polished.
For net or near-net forgings, the surface finish can be specified as smooth as the "apple polish" that you mention. In this case, the forgings are usually warm forged and sometimes coined to sharpen up selected dimensions, as well as improving surface finish.
H. James Henning answers forgers' technical and operational questions. For more than 40 years he held key technical positions in the forging industry, most recently as director of technology for the Forging Industry Association. He is president of Henning Education Services, Columbus, OH, specializing in customized education and training in forging technologies.
Send questions to
ASK JIMc/o FORGING1300 E. 9th St.Cleveland, OH 44114-1503
Or e-mail: henningedu@aol.com
