인벤터 판금작업시 유형설정에서요. 릴리프…란?

벤드가 모서리에 가까이 만들어질 때 A 그림처럼 시트메탈이 찢어질(?) 수가 있습니다.
그걸 방지하기 위해 C 그림처럼 벤드 릴리프를 더합니다.

출처: http://www.qualitytool.com/sheetmetalforming.htm

Bend Relief – When a bend is made close to an edge the material may tear
unless bend relief is given. Figure “A” shows a torn part. Figure “B” shows
a part with the edge a sufficient distance from the form. This distance should
never be less than the radius of the bend. Figure “C” shows a bend relief cut
into the part, again the depth of the relief should be greater than the radius
of the bend. The width of the relief should be a material thickness or greater,
preferably a material thickness + 1/64″.

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Gerald Davis가 쓴 “Design tips for sheet metal”이라는 글을 보니
벤드 릴리프가 무엇이고 왜 필요한지에 대해 설명이 잘 되어 있길래 인용합니다.

출처:
http://www.thefabricator.com/xp/Fabricator/Articles/Fabricating/Article244/Article244_p1.xml

When sheet metal makes a transition from a bend to a flat surface, or to another bend,
it tends to rip and tear. To eliminate this, a bend relief is added so the edge of the
sheet metal is perpendicular to the bend. In general, a minimum bend relief is equal to
the material thickness plus the inside bend radius. If it is OK for the metal to rip,
the minimum bend relief is zero.

One benefit of a bend relief is that it makes the part easier to produce. The bigger
the bend relief, the easier it is to align over the end of the tooling. The bend relief
eliminates some burrs and sharp points. Without a bend relief, the part may slip
unpredictably in the tooling as the bend is made.

Another benefit of a bend relief is fracture propagation reduction. If the part is
subject to vibration or flexure, existing cracks may grow rapidly. By eliminating the
cracks before cutting, and by cutting the bend relief with curves instead of sharp
inside corners, the finished part will be stronger and more stable. I think a bend relief
makes the part more attractive.