Using proper press brake setup procedures

WWW.THEFABRICATOR.COM OCTOBER 2002

August 29, 2002

By:

Think about it: If your setup is off, the rest of your press brake operation will soon follow. Take the time to do your setup right, and you won't be doing it a second time.

The most expensive part of any press brake operation is setup.

During setup no parts are being made, and the longer setup takes, the longer the list of costs becomes. The efficiency and the profitability of a press brake are measured by the number of completed and correct parts you can produce in a given period of time. When setup takes too long, less time is devoted to making parts, so the cost per part escalates.

On older machines, the only way to reduce the cost per part is to make a large number of parts with the same setup. The goal of every operator should be to learn all the tricks of setting up quickly and correctly so that more parts can be made for less cost.

While setup time is critical, remember that accuracy is just as much so. Therefore, you must try to reduce setup time while improving your accuracy. Having and following a standard setup procedure can help with this and have a profound effect on your press brake's efficiency.

One typical setup procedure has 10 important steps:

  1. Review the drawing.
  2. Select the tooling.
  3. Determine the tonnage.
  4. Select the press brake.
  5. Determine the tooling position on the bed.
  6. Install the tooling.
  7. Program the press brake.
  8. Test-bend.
  9. Correct the program.
  10. Run parts.

Review the Drawing

Operators need to know their parts completely. If the parts have been made before, a review of the drawing may not be necessary; but at some point, the operator must know:

  • Material type and thickness.
  • Flange dimensions and flange tolerances.
  • Angles required and angle tolerances.
  • Inside radius of angles.
  • Blank size.
    • If any of this information is missing, the operator will have to guess. This leaves the part at risk for inaccuracy. Having complete and accurate drawings is a critical first step.

      Select the Tooling

      Tooling selection is based on the drawing. Your choices are air bending, bottom bending, coining, or a special application.

      For example, if the drawing specifies an inside radius equal to metal thickness, then bottoming tooling gets the call. If the radius is at least 1.25 times the metal thickness, air bend tooling works. A radius less than metal thickness may require coining.

      You should select tooling that is at least as accurate as the tooling manufacturer specifies for that particular type of tooling. Worn tooling cannot produce accurate parts, regardless of the press brake's accuracy.

      Determine Tonnage

      Estimating the tonnage requirement should be second nature to operators.

      Tonnage charts are available for air bending. For bottom bending, a good estimate is four times the air bend tonnage. Coining requires some eight times the air bend tonnage. For special-application tooling, the manufacturer will provide tonnage estimates. A bend should never be attempted until the tonnage requirement is determined and compared to the tonnage available.

      Select the Press Brake

      This step is not important if there is only one press brake in your shop. However, if you have two or more brakes, be sure that the one chosen is best-suited for the job at hand.

      Every press brake has a tons-per-inch limit in the center of the machine. To determine the tons per inch for your brake, simply multiply the distance between the side frames by 0.6 and divide the machine tonnage by your answer. For example, if you have a 150-ton brake with 10 feet between the side frames, multiply 120 in. by 0.6 and divide 150 by your answer (72 in.) for a sum of 2.1 tons per inch.

      Therefore, for a 12-in.-wide part, the maximum tonnage should not exceed 25 tons in the center of the machine. Exceeding 25 tons over 12 in. produces a concentrated overload. This is not a good idea, because it can cause permanent damage to the ram. If a tonnage control is available (either CNC or manual), always adjust the tonnage to provide just the amount needed to bend the part, but do not exceed the tonnage limit in the center.

      Also, remember that you cannot overload a press brake when air bending, only when bottoming, coining, or using special-application tooling.

      Determine Tooling Position on the Bed

      If the tonnage requirement exceeds the concentrated load limit in the center of the machine, you may be able to do the job off-center.

      Before doing so, however, you should make sure that the press brake manufacturer allows off-center loading on your machine. It is OK to work off-center within the guidelines of the machine builder, but not outside them.

      Install the Tooling

      Once you have determined the tooling position on the bed, you should install the tooling and align the upper and lower tooling for making the bend.

      Tooling installation is the most time-consuming, and therefore the most costly, step in the setup procedure.

      If your brake has manual clamp bars for the tools, you will need to loosen them enough to slide the tools into position. Install the lower tool (die) first and leave it loose for a moment. Lower the ram so that the distance above the die is about 1/4 in. more than the height of the punch.

      Now slide the punch over the die with the tang behind the clamp bars. In this procedure, the die is supporting the weight of the punch. Follow the same procedure whether or not a safety tag is on the punch.

      Now snugly tighten the clamp bars against the tang and lower the ram to seat the punch and align the die. Then tighten the die set screws and the clamp bars.

      Using a hydraulic clamp for the tooling makes this procedure easier and faster; using snap tooling is even more efficient. Both of these features are available as retrofit systems for all press brakes.

      Program the Press Brake

      Whether manual or CNC, the brake should be programmed properly for making the bend. Manual programming may take some trial and error, but a CNC machine usually can be programmed very quickly.

      The second most time-consuming step of the setup procedure is programming.

      Perhaps one reason programming takes so long is that some operators are not trained properly. Operators spend a great deal of time learning how to operate brakes, but seldom is much time spent on programming. Of course , programming a CNC brake takes less time than programming a manual one does, but proper training in the concept is critical for both CNC and manual machines.

      Make a Test Bend

      Make a test bend on a scrap part so you don't ruin a good blank. Use a production blank only after completing a good test bend. Every blank costs money, after all.

      Correct the Program

      Corrections to the program should be made during the testing phase. However, be careful not to change a program after a good part has been formed.

      Test bending and program correcting should be done at the same time. Program corrections should not be made after an acceptable part has been formed, as long as the program does not change during forming. Here again the operator's programming expertise of the operator in programming is crucial to a complete and efficient setup procedure.

      Run Parts

      After proper setup, you're ready to run good parts. However, don't assume that every part will be perfect. Your supervisor will establish a testing review procedure for the parts you are making.

      Commit your setup procedure to memory and follow it for every different part you form. You soon will find that your setup time will decrease while your accuracy improves substantially.



Bob Butchart

Contributing Writer
Press Brake & Shear Clinic
254 Somers Loop
Reidsville, NC 27320
Phone: 336-342-4393
Fax: 336-342-4129

More in Bending from TheFabricator.com

Published In...

www.thefabricator.com

Read more from this issue

comments powered by Disqus