Sheet Metal Guy Blog

24 Aug 2006   11:56:44 am
What k-factor should I use?
Recently I have received a number of comments from our article about bend allowance. They all have one thing in common. “What is the correct k-factor to use?” And the answer is, I can’t tell you. It really starts with all of the variables involved in the manufacturing process. Number one is the material being bent. How hard or soft is the material? Then there is the process, are you air bending or bottom bending? Next is the radius of the tooling in your press brake. That’s right, don’t just sit in your office and say I want a .06 radius on this bend. Get out in the shop and ask what radius punch will be used when the bend is formed. Can you start to see why this isn’t an easy subject? Well how about some answers. Referring to “Tool and Manufacturing Engineers Handbook, Volume 2”, I found a chart on page 10-4 which shows some data for air bending and it includes a bend allowance based on the other data included in the chart. Using the Bend Calculator, I found the k-factor for 90 degree bends to be as follows: Gauge - Thickness - Inside Radius - k-factor - - 20 - - - - 0.036 - - - - - - 0.039 - - - - - 0.3314 - - 18 - - - - 0.050 - - - - - - 0.059 - - - - - 0.3224 - - 16 - - - - 0.060 - - - - - - 0.078 - - - - - 0.3340 - - 14 - - - - 0.074 - - - - - - 0.098 - - - - - 0.3963 - - 12 - - - - 0.104 - - - - - - 0.137 - - - - - 0.3967 - - 10 - - - - 0.134 - - - - - - 0.176 - - - - - 0.4016 So how about a rule of thumb and from there we will discuss this further in the Manufacturing Forum. Thickness > Inside Radius - - - - k-factor = 0.25 Thickness = Inside Radius - - - - k-factor = 0.33 Thickness < 2 * Inside Radius - - - - k-factor = 0.42 Any questions? I’ll see you in the forum.
		Category : Sheet Metal | Posted By : SheetMetalGuy | Comments[66] | Trackbacks [2625]
21 Aug 2006   10:31:38 am
Still plotting your jobs and keeping paper files?
CNC programmers don’t like to change their habits. Back in the dark ages, just being able to plot your program was an exciting feature. As verification that our program was good, we plotted every job, then printed and duplicated the paper tape and setup sheet. This and any other paperwork we could generate was then stored in a file folder in our cabinet for safe keeping. When graphics based programming came to town we continued these habits. Still generating all of the paper print outs and storing them away. But wait. Now if a problem was to arise, you no longer went to the paper file to look at the plot. Rather you called the job up on the screen and checked it out. No more need to make and save the plots. And as for the paper tape, well now they are DNC files. But, why save a print out? If the file is lost or corrupted, you simply call up the job and run the post processor to recreate the DNC file. And the same with the setup sheet. If you are still printing and plotting everything you do, how about taking a few moments to consider whether these items are still needed. It’s time to empty those file cabinets and save the time needed to create all of that paper backup. After all, when is the last time you pulled a plot out of the file cabinet to find an error in your program?
		Category : Sheet Metal | Posted By : SheetMetalGuy | Comments[49] | Trackbacks [3400]
17 Aug 2006   03:26:50 pm
Bend Allowance or Bend Deduction
During the past 20 years, I have worked with people around the world, helping them to unfold their parts. One of the first things I learned is that everyone uses the terms Bend Allowance and Bend Deduction interchangeably. I have visited many shops which have a chart tacked to the wall and labeled Bend Allowance only to be showing Bend Compensation values. On top of this, the chart was created back in the 1960’s or 70’s for 90 degree bends only. But these are two distinctly different things and you must learn their proper definitions if you are going to unfold your parts in your CAD system. Bend Allowance is the length of the arc through the bend area measured at the neutral axis. Meaning somewhere in the material thickness, where the material is neither stretching, nor compressing due to the bend. This is normally represented in the bend formula as the k-factor. By adding up the length of the flat portion of each flange surface and adding one Bend Allowance for each bend area, you then have the flat length. Bend Compensation is a calculated value (the bend allowance minus two times the setback) which you then subtract from the total of the dimensions of the part to get the flat length. Please review the formulas on our web page http://www.sheetmetalguy.com/bending-formulas.htm.
		Category : Sheet Metal | Posted By : SheetMetalGuy | Comments[214] | Trackbacks [3844]
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