K-Factor Tables

A press brake doesn't bend every sheet with one K-factor: where the neutral layer lies through the sheet depends on the material and on how tight the bend is, the ratio of the inside radius to the thickness (R / T). Press-brake makers give it as a table. ParametrIQ keeps such tables for each sheet-metal material and takes each bend's K-factor from its material's table at that bend's own R / T.

Where a drawing's K-factors come from

A sheet-metal drawing made with File › New and a sheet-metal material (see Materials) starts with the material's block, which names its table in the variable KTABLE, and its K-factor worked out from it:

SELECT T,"Sheet"
    "Mild steel 2 mm" = 2, R=2, KTABLE="Mild steel" DEFAULT
    "Aluminium 2 mm" = 2, R=2, KTABLE="Aluminium"
END
K=KFACTOR(KTABLE,R,T),"K-factor"

K is the table's K-factor at the drawing's own radius R: choose another material, or change R or T, and K follows. A bend of another radius takes the table's K-factor at its own R / T:

the bend table, the DXF with bend data, the 3D page and the STEP solid: a bend whose Bend Line note gives its own radius (UP 90° R6) is bent with the table's K-factor at 6 / T;
the Bend Line and Flat Pattern tools: a radius other than R writes the bend's allowance with KFACTOR(KTABLE,radius,T) instead of K;
Unfolding 3D Models: each bend is unfolded with its material's K-factor at its own R / T.

A drawing with a K of its own and no KTABLE works as before: every bend uses K. Type a number for K to use one K-factor at R while keeping the table for other radii.

The tables that come with the app

Typical values for air bending (check them against your press brake's tables):

R / T	0	0.5	1	2	3	5	10
Mild steel, Galvanised steel	0.33	0.38	0.41	0.44	0.46	0.48	0.50
Stainless steel	0.35	0.40	0.43	0.45	0.47	0.49	0.50
Aluminium	0.30	0.35	0.38	0.42	0.44	0.47	0.50

Copper, Brass and DIN 6935 (the standard's formula, k = (0.65 + 0.5 lg(R / T)) / 2 up to R / T = 5) are there too. Between rows the K-factor is interpolated in a straight line; below the first row or beyond the last it is that row's.

Your own tables

The tables are kept in the sheet-metal materials file, under kFactorTables (see Materials): copy it into your own Materials folder and change or add tables there. Each table has a name (the material's KTABLE names it), a description, its rows (each a ratio, R / T, and its k) and, if it is only for sheets up to a thickness, upTo (in the file's units): a material may have several tables, the thinnest one that fits the sheet is used.

"kFactorTables": [
  { "name": "Mild steel", "upTo": 3, "rows": [ { "ratio": 0.5, "k": 0.36 }, { "ratio": 2, "k": 0.43 } ] },
  { "name": "Mild steel", "rows": [ { "ratio": 0.5, "k": 0.38 }, { "ratio": 2, "k": 0.45 } ] }
]

A table of yours replaces the app's of the same name (and thickness).