Limits for Burrs
In our last blog, we dove into Chapter 20 of the Metalforming Design Handbook, also known as the "Red Book." Industry leaders recognize our "Red Book" as the go-to manual for precision metal forming practices. Chapters 22-24 taught us about styles of embossing. Now, join us as we take a closer look at specifications and characteristics of drawn parts in Chapters 25 & 26!
Burrs are ragged, usually sharp, protrusions on the edges of metal stampings.
Common methods of specifying permissible burr:
Unless otherwise specified, an acceptable burr can be 10% of stock thickness.
A note "Conditioned for Handling” is interpreted to mean that normal stamping burrs are to be refined as necessary for average handling.
Remove burrs on specified edges.
Remove all burrs.
Break sharp edges or corners where specified.
Break all sharp edges and corners.
Measurement and Limits of Flatness
Perfect flatness is that condition that exists when all points on a surface lie in the same plane.
Flatness tolerance is the permissible distance between two parallel planes within which all irregularities of a given surface must lie.
Parts may be measured in either unrestrained or restrained conditions. (Recommended limits are applicable to parts measured in the unrestrained condition.)
Bottom surface irregularities are illustrated.
Commonly used flatness tolerances for metal stamping, laser and turret are shown below.
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