Metal Stretch Force Calculation (engineering)

1. Jul 19, 2012

johnco_herts

Hi all,

I have started working on a challenge at work.

We have installed a machine for 'stretch forming'. The machine clamps a long sheet of aluminium at both ends, while a convex shape steel die is raised in the centre. The die is raised by a hydraulic system, causing the metallic sheet to stretch over it, hence forming the shape of the die. I am trying to calculate the force required to stretch the sheet, without returning to its original shape(springback), and without necking(rupture). Please see the attached image for a visual representation of the tool.

Now for what I have been using for my method:

1) The sheet being stretch formed is Aluminium 2024 T3 temper.
The Ultimate Tensile Strength(UTS) of the material is 470Mpa
The Yield Strength (YS) is 325Mpa
The sheet is 98.4"(2.5m) wide and 0.120"(0.003048m) thick.
ie) Cross Secional Area is 11.808In² (0.00762m²)

2) Formula:
The UTS=Force(N)/Area(m²)
thus Force(N)=UTS*Area(m²)

3) The above equation would lead to the force required to rupture the material but I just want the force to stretch it, so I need to be between the YS and UTS

4) from points 3&4 I now have Force(N)=((UTS+YS)/2)*Area(m²)
This is the average of YSand UTS, multiplied by the area

5) this is fine for a scenario of tensile testing(see image 'i'), but my questions are:

Q1) Is this the same force for the case I present (image '1' & '2')?
Q2) The die is lubricated prior to forming, so do I need to consider frictional force?
Q3) As the sheet is fixed on both ends, does the force that I apply with the ram replicate a force acting tangential to the sheet edges?

Any help or comments would be greatly appreciated,

John

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• Stretch Forming.jpg
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2. Jul 20, 2012

johnco_herts

anybody able to help here?