Calculation of flat blank length in press tool design
In any press tool design, the first thing to consider is how to determine the flat blank length of the folded component. I won’t go into the boring theory of how the material behaves during bending and how the individual material property affects the length and spring back. To be frank, I hate all these theories!
During the bending process, the material being bent results in forces: tension and compression. The external portion of the sheet will undergo tension and stretch to a greater length, while the internal portion experiences compression and shortens. The neutral axis is the boundary line inside the sheet metal, along which no tension or compression forces are present. As a result, the length of this axis remains constant. This is the bend allowance that we are interested to know to determine the flat blank length.
There are tones of materials and formulas out there in the cyberspace teaching people how to make calculations. I personally did not use any of these formulas’ during my last thirty years of tool making career.
I applied only one formula for any flat blank length calculation.
@ Pi D/360
where D= circumference of neutral line
@ = Bend angle
Any radius bend smaller than 2x the material thickness, the neutral line will be 1/3 thickness
Any bend radius equal or larger than 2x material thickness, the neutral line will be = 1/2 material thickness.
90 degree sharp bend radius.= 0.4 x material thickness.
+/- 0.05 mm accuracy can be achieved by applying the above method. Of cause, the bending clearances and accuracy of the bend radius does affect the end result.
it was really very helpfull in gettin the concept…
but for bend radius less than twice the thickness of material has neutral axis located at 1/3 of material thickness(as taught by our professor)..
please check it out…
Hi Sandeep
Thanks for the correction. it should be 1/3 of the material thickness.
it should be 1/3 of thickness (why u given 1/3 of nutral axis)
the same its given there Mr. Sandeep
Very good article
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Hello Brook
Thanks for visiting. Cheer!
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Thanks for the visit. I will do my best.
Hello,
I am doing a project on blanking tool (Sheet metal cutting).
Pls help me on basic design procedure.
Thanks
Krishnan
Hello Krishnan
Thanks for visiting, please let me know what information you need.
HAI I WANT TO CREAT A STRIP LAYOUT IN PRO-E
Ya. What can we help?
thanks for your information
if is possibel for you please send me die design handbook
Hello Mohammad
Thanks for the visit.
You can purchase it from http://www.wisetool.com/tdesign.html or from Amazon http://astore.amazon.com/wisetoolcom-20
i need to know,how to make die calculation.like punching force,stripper force,die clearance.and how to minimize punching force with the same.thx
Hey Yulianto
Punching force = cutting length x metal thickness x shear strength
stripping force usually is 10% of cutting force.
Die clearance for steel is usually 5% of thickness. difference material we use difference percentage. In short, harder material bigger clearance and softer material less clearance.
Punching force can be minimized by putting shear angle an the punch’s face.
also wants to know how to calculate the force for forming,bending & embossing.formula with units…thanks
hi..
i need the information about, how compound die can be design for making a blank with inside diameter 28 and outside diameter 62??
plz help
Mr. Kumar
To design a compound for this job is very simple. What can I help?
Kindly help me out in design of progressive tool for stainless steel component of thickness 0.12mm width 13mm length 15mm bend at the centre of width at an angle of 90 + 10 degrees with bend radius 1.5 mm preferably a combination tool. Hardness of stainless steel material is 450 to 500 VPN and the grain direction is perpendicular to the bend axis.
Fantastic blog, I’m just starting out and have a problem figuring out blank sizes in an eyelet machine. The part is .300 in length .162 od, .120 id .020 brass. How do I figure the blank?
Hi Rob,
Please check this out. http://www.wisetool.com/formular/formula.htm