Inventor Sheet Metal k-Factor: Sample Bend Tables & Instructions

By Luke Davenport

Alan Mawdsley of Bootle Containers has very kindly provided some of his company’s tried and tested sheet metal bend tables for CADline to share with the community – download these below!

Thanks to Alan and Bootle Containers – Why not check out what these guys are doing with sheet metal here http://www.bootlecontainers.co.uk/

By default, Inventor uses a K-Factor for calculating bend allowances. The default K-factor is 0.44, which simply means that Inventor is assuming that 44% through the cross section of the part, the material is not stretched or squashed when bending, and therefore this slice of the folded part will give the true length of the flat pattern. In reality, how a real metal part will stretch as it bends depends on a number of physical factors (tooling, material homogeneity etc.) which can’t be accurately replicated using a ‘fudge’ K-factor. Most sheet metal shops will produce their own bend tables by physically bending test pieces to specified angles and taking accurate measurements of the bent lengths – this will allow Inventor to ‘interpolate’ between the discrete bend angles (20 degrees, 25 degrees, etc) to give the most accurate result possible.

As the tooling is such a critical factor in producing an accurate bend table, we would recommend that you produce a few test pieces and apply a correction factor to every entry in the bend tables if your machines are producing different results.

Thanks again to Bootle Containers!

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