Flat patterns and bend allowances · Lesson 2 of 4

Flat patterns and bend allowances: materials, standards and design constraints

What K and the inside radius depend on, published values and their limits, painted coil and the 2T rule, gauge tolerance, press brake versus folder, and the limits a blank must fit.

You will be able to: Explain what sets K and the inside radius, read published values as typical rather than AFS values, allow for thickness tolerance and coating limits, and check a blank against AFS limits.

9 min · 12 slides · 7 questions

All lessons in this module

Slide 1 of 12

What K depends on

The Fabricator says K depends on the tooling used, the type of material, its tensile and yield strength, and the forming method.

That is why K is found for each material and thickness on the machine that will bend it.

Sources

Analyzing the k-factor in sheet metal bending (Steve Benson, 2018-09-12, updated 2023-10-20) - The Fabricator
Analyzing the k-factor in sheet metal bending, part II - The Fabricator

Videos for this lesson

What this video shows: K-factor, bend allowance and bend deduction as the options a CAD system uses to size a flat pattern, with bend tables for your own tools and machines. In SOLIDWORKS "bend allowance" names the whole family of settings, not the single quantity this module defines.

Video: What is a K-Factor? | Sheet Metal Bend Allowance Explained by TriMech Group, on YouTube. Chosen from the video's published description.

What this video shows: A Thalmann TD125 double folder forming 24 ga parts, from CIDAN Machinery Group, which acquired Thalmann in 2022; a folder at work, not AFS's machine.

Video: CIDAN Machinery - Thalmann TD125 6.4m Double Folder forming 24ga (.61mm) parts by CIDAN Machinery Group, on YouTube. Chosen from the video's published description.

Glossary

Minimum bend radius: The tightest inside radius a metal can be bent to without damage; set by the metal, its thickness and temper.
T-bend: A bend described by thickness: in Petersen's guide a 180 deg 2T bend has an inside radius of twice the thickness.
Gauge tolerance: The range a sheet's thickness may fall in for its gauge, above and below the nominal.
Air forming: Press brake bending in which the radius forms in the air across the die opening.
Folding beam: The beam of a folder that swings up past the angle to bend the clamped sheet, then releases it; in bump bending it is held in one position, which sets the radius.