Standard for dimensioning sheet metal flat patterns

[pdybeck]

Is there a standard for proper dimensioning of features in a flat pattern sheet metal drawing view? Is there a standard way to list bend allowance/K factor, or is this something that isn't defined to well and varies a bit more from company to company and sheet metal vendor to sheet metal vendor? Does anyone typicall dimension features across the bend lines in a flat pattern view? Are these dimensions listed as reference dimensions or noted somehow as to being related to the K factor or bend allowance? What is proper or accepted practice? TIA.

 

[Tunalover]

What I meant was, do you agree that taking the trouble to develope a flat pattern is not worthwhile if you're the end-user and not the fabricator?


Tunalover

 

[ctopher]

I leave the flat pattern up to the fabricator. It is no use for anyone else. I use SolidWorks and create sheetmetal parts. I send the sheetmetal company my files and they can "flatten" the model for use.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP2.0 / PDMWorks 05
ctopher's home site

FAQ559-1100
FAQ559-716

 

[Tunalover]

ctopher-
Sound thinking!


Tunalover

 

[ctopher]

thanks
(I hope by beer isn't flat)

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP2.0 / PDMWorks 05
ctopher's home site

FAQ559-1100
FAQ559-716

 

[McLeod]

Section 18 of Genium's Drafting Manual is "Sheet Metal Practice". In sub-section 7.0, they show three examples. None of them include features which cross a bend, but each includes a note:

Unless otherwise indicated
Tolerances ± 0.04
Mfg. allowances to 2191K450

Does that number refer to a standard, or is it intended to indicate a shop procedure? (We don't work with a lot of sheet metal, so I wouldn't necessarily recognize a common standard in that field.)

In sub-section 5.0, Bending Allowances, they state "Forming radius must be specified on drawing." They do not state that K factors must be specified.

In Section 18.1, Sheet Metal Design Documentation, sub-section 1.4, Blank Development of Parts, states:

Although blank developments of parts are shown extensively throughout this text, the developments are intended principally as tutorial. However, there will be instances when the developed configuration of a part is necessary. Because the predictability of the shaped part (final configuration) cannot always be ascertained with confidence (as in, for example, control of springback), a cautionary note should be written beneath the developed configuration for manufacturing guidance. In other words, the development is provided to assist manufacturing in visualization and material planning. It is not the end product that is fully dimensioned elsewhere on the drawing.

And finally, in Section 18.2, Sheet Metal Design Considerations, sub-section 3.0 states, "It is not general practice to show blank developments on production drawings; therefore, the following formulas are presented only for reference."

Hopefully this answers more questions than it raises...

 

[smcadman]

This may also be a "Company Standard" issue. Even though Solidworks creates the flat patterns for us, we put a note on the flat pattern sheet stating "FLAT PATTERN DIMENSIONS FOR REFERENCE PURPOSES ONLY". This relieves us of any burden in case our flat pattern is wrong, but we also get a fast turn-around for quoting purposes.

Some of our vendors swear our flat patterns are spot-on, but we put the disclaimer above to cover our butts. As a former sheetmetal fabricator, I am very familiar with triangulation and parallel line developement, but there is no competition between the time it would take me to lay a part out, and the automatic flat pattern that Solidworks creates. This also depends on whether you are talking about laying out simple channels with features, or laying out square-to-rounds, offset-cones, or helical-chutes.

Some shops primarily use air-bending, and use 8 x the material thickness as a standard for the press die while others use 6 x the material thickness for the brake press die. Then you can throw in coining, spring-back, and other factors that change the bend allowance/bend deduction.

Finally, when you throw into the mix that some shops do not use k-factors (like Solidworks uses), but use the Emperical Formula (such as aviation engineering bend allowance charts), you might see why it would be a good idea to have a disclaimer on flat patterns.

Flores