How to calculate forging weight

[alliedtrans]

I am a gear manufacturer and have newly entered the field. Can someone please tell me the methods to calculate the forging weight which my suppliers calculate or if there is any software available for that. The materials I use are either 20MnCr5 or EN 8.

Any help would be greatly appreciated as calculating costs for my products is getting difficult when I am abroad and not able to get costings from my suppliers.


Thanks
Ankur

 

[CoryPad]

One approach is take the final part design and add the required forging stock for draft, radii/fillets, surface flatness, decarburization, etc. Then, you use CAD or simplified geometrical models to calculate the forging volume and then use a known mass density of the material to calculate the forging mass.

 

[alliedtrans]

Thanks a lot for your reply!

Is there a software I can use where I input the final drawing or dimensions and get the forging weight (net and gross)..

Thanks
Ankur

 

[CoryPad]

None that I know. I believe there are some simple spreadsheets used by high volume users that rely on experience to calculate those numbers.

 

[tbuelna]

There should be a CAD model of the forging, or at least a drawing of the forging that a CAD model can be generated from, provided by your customer. The net weight of a gear forging can vary greatly depending on the forging process used and the configuration of the finished gear. As CoryPad notes, the forging must allow for adequate surface stock removal for decarb, including factors like draft and large fillets. There are also many different types of forgings used for gears, and each will have different net forging weights for a given gear configuration. There are die forgings, there are rolled rings, there are upset forgings, and there are even "near net" forgings where the individual gear teeth are forged.

When pricing the raw material for a forging, you must include the excess material that is usually trimmed from the finished forging. The flash in a die forging, or the prolong in a roll forging.

Gear forgings are normally produced from wrought bar stock. High performance gears are usually produced from vacuum melt wrought bar stock, which can be quite expensive. So minimizing machine stock in the forging can be important.

Good luck to you.
Terry

 

[tbuelna]

alliedtrans-

Don't know if your question was answered. But I'd add that using a forging for many gear applications can be quite cost effective. Even with modest production quantities, the cost of forging dies for a simple spur gear blank will pay-off. This is due to reduced scrap material produced and the high raw material cost of premium gear steels.

 

[alliedtrans]

Hello

Thanks for your replies. Can someone please tell me how to add tolerances for forging stock for draft, radii/fillets, surface flatness, decarburization, etc. I mean what percentage of the net weight should i add for these processes?

I calculate volume and then multiply with the density of 20MnCr5 which is 7.81 g/cm3 to get the mass.

Thanks
Ankur

 

[tbuelna]

alliedtrans,

Stock for draft can be calculated assuming a 4-5deg increase from the min net surface. Stock for removal of decarburized or metallurgically unsound surfaces is typically around 1/8 inch, but once you refine your forging and HT processes you can probably reduce this stock allowance to about half this thickness. Steel die forgings usually require fairly generous fillet and corner radii. If the transitions in the forging sections are too abrupt, it will result in reduced life of the forging dies, and/or forgings with cold laps, seams, etc.