Head blanking
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When forming hemispherical heads in segments, should the unrolling be based on the inner diameter or the mean diameter? In the reference book \"Sheet Metal Unfolding Calculation Method, 2nd Edition, 2014\", the inner diameter is used as the basis ； On the other hand, the book \"New Practical Handbook for Sheet Metal Unfolding Calculations\" compiled by Liang Shaohua is based on the mean diameter for its calculations. Moreover, neither of the above two takes margin into account. I would like to ask the forum’s experts in sheet metal work how to calculate the optimal value.
When developed based on the mean diameter, there is hyperbolic deformation; in fact, this shape cannot be developed, and the cutting allowance for the net material must be taken into account!
What does it mean to be non-developable? Additionally, when using the Jinlin sheet metal unfolding software, there is a \"stretch factor\" in the setting parameters – how should this be considered?
Is there a problem with following the method in the reference book? Should I add more cutting allowance?
I’m not sure what unfolding software you are using. By the machining and cutting allowance I mean that when pressing the spherical segments, straight edges will form along the perimeter of the plate, and these need to be removed through a second cutting step after the segments have been shaped.
It’s not software; it’s a sheet metal lofting book. Do I need to add a margin after lofting according to the radius?
As for the amount to add, it should be determined based on your factory’s processing experience; generally, a secondary cutting allowance of around 50 mm is required around the edges.
The cutting allowance after compression should be considered
50mm is quite a large margin; it should increase after pressing
Do you mean the trimming allowance? How should I think about it? By how much more should I enlarge it based on the lofting diagram? Furthermore, the dimensions obtained from pattern lofting should represent the dimensions after they are arranged in rows; surely there will be stretching and thinning during actual drum manufacturing, so can’t this allowance cover that?