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Digitizing the Press-Brake Bending Process

By: Scott Ottens

Sunday, May 01, 2011
 

For many years, the blanking and laser-cutting stages of the sheetmetal-fabrication process have advanced to realize the advantages of offline programming. However, many shops have been slower to adopt this practice for the more-complex 3D bending process.

As computing power has increased to handle the 3D models required to process folded shapes, fabricators now can experience the advantages of virtually processing their formed parts. Fabricators working in a low-volume high-mix production environment can take advantage of offline processing and enjoy huge benefits in time, efficiency and costs.

Opening the Box

 
Fig. 1—Nonproductive activities account for 72 percent of the typical press-brake operator’s time, while green-light time making parts comprises only 28 percent of an operator’s day.

Prior to the blanking process, part data is imported into computer-aided manufacturing (CAM) software, used by a programmer for part processing on a specific machine. The program contains information on the tools required, as well as lines of code that the machine tool’s computer numerical controller (CNC) uses to process the part. This program downloads directly to the machine (laser-cutting machine or turret punch press, for example) with tool-setup information. The machine operator needs to do little more than call up the required program, install tools according to the information downloaded with the program, load material, make some minor adjustments to the machine and begin processing.

Since the program typically is saved, this becomes a highly repeatable operation, minimizing setup time since much of the work is done ahead of time while the machine processes other parts. An added benefit: The skill level of the machine operator need not be high, and operators are more easily trained for the job.

 The greatest benefit of bending CAM programs: They externalize a significant percentage of the setup pie. Bend-sequence planning, tool selection and layout, and press-brake programming are removed from the floor, increasing green-light time.
In many shops, press-brake bending remains a black box, with one or two talented individuals having the high skill level necessary to take material from a flat state to 3D formed parts. Many factors, such as tool selection, bend-sequence development, material properties and machine capabilities must be considered. All of this requires operators of high intellectual capability to generate a machine program that will produce parts within specifications. Often, this lengthy setup procedure occurs at the machine, at the expense of performing value-added work.

A Focus on Green-Light Time

To get a better understanding of the benefits possible with digital processing, consider a typical nine-step bending process, from setup through production:

1) Find materials—Locate material and part information, such as drawings and process instructions.

2) Tool/bend sequence and selection—Specify the required tools for the job, and determine the sequence of bends.

3) Tool setup—Insert tooling into the machine.

4) Program creation—Enter bend data into the machine control.

5) Machine setup—Make all of the required manual adjustments to gauges, jigs, supports, etc.

6) Test bend—Make iterative setup adjustments to obtain the specified angle and flange dimensional tolerances.

7) Processing—Actual part production.

8) Inspection—Inspect parts before and during processing.

9) Data entry—Log the job and miscellaneous shop document requirements.

Studies performed in the bending area of many shops, including typical job shops and OEM facilities, have uncovered a poor ratio of value-added activities to nonvalue-added activities (Fig. 1). Nonproductive activities account for 72 percent of the typical press-brake operator’s time, while green-light time making parts comprises only 28 percent of an operator’s day. With the current trend of high-mix/low-volume processing, where many shops experience more job changes than ever before, green-light time can be even further reduced. New jobs usually require more lengthy setups, since the setup person must start from scratch when determining bend sequence and tool assignments. If this information is not recorded for future repeat runs of the job, this series of events repeats itself. Even if the setup person records the elements of the setup, most times it remains in his possession, unavailable for use by others.

With the pool of highly skilled brake operators getting shallow, shops will continue struggling to maintain a good level of accuracy and efficiency in their bending area. Additionally, differences in setup practices among setup personnel lead to inconsistencies in part specifications and quality. These inefficient practices all contribute to low green-light times, making press-brake bending a labor-intensive process and a bottleneck for many shops. Most fabricators address a bending bottleneck by adding more machines, shifts and operators, or upgrading to faster machines—none of which improve the ratio of value- to nonvalue-added time.

The Virtual Bending Solution

 
The 3D simulation generated by a virtual bending program displays on the machine’s control, providing a bend-by-bend graphical representation of part placement along the machine. This reduces cycle time and minimizes the risk of misformed parts due to incorrect part placement or sequence errors.
A better solution exists in the form of software used to program press brakes offline. Press-brake software and controls have evolved to help operators crack the complex operation of press brakes in an offline, virtual environment. Sophisticated 3D graphical programs accurately depict the bending environment of machine, tools and part geometry. This allows an operator to virtually bend a part before he wastes time performing this process on the floor. The trial-and-error setup process for new production runs can now take place offline.

These virtual bending programs take electronic part data existing in the shop as 2D data (dxf or iges files) or as 3D models, and create bending programs guaranteed to be successful on the machine. Further, virtual bending solutions can be used to determine the manufacturability of a new part, or its tooling requirements, before valuable resources are wasted on jobs determined to have special requirements that a shop may not offer. Then, if a shop discovers that it may need to acquire new tools for a job, it can order the tools confident that they will work.

Many parts come from customers with poorly calculated blank sizes. Since bend deduction can’t truly be determined without knowledge of the tooling used, many flat parts come to the press brake that cannot meet spec when formed. Also, many bending CAM programs allow corrected blanks, based on actual tooling, to be exported back to punching and laser programming before processing. This provides the press-brake operator with the correct blanks and reduces the time spent adjusting flange lengths to keep the entire part in spec—or worse, sending out poor-quality parts and hoping for the best.

The greatest benefit of bending CAM programs: They externalize a significant percentage of the setup pie. Bend-sequence planning, tool selection and layout, and press-brake programming are removed from the floor, increasing green-light time. Yes, this process shifts the burden to the design room, but some CAM programs can batch-process large quantities of parts autonomously to minimize this burden. Further, the software can be trained to scan the database for revisions to drawings and then automatically reprogram parts when necessary. This eliminates the processing of parts based on outdated drawings due to engineering oversight.

Lastly, once a shop has centralized part information in a digital database, it can easily reprogram parts to run on different brakes in the shop when production-scheduling changes become necessary.

New Generation of Controls

In the past five years, the capabilities of press-brake controls have risen to take full advantage of the latest generation of bending CAM programs. This new generation of PC-based controls has Ethernet capability, allowing them to join a shop’s existing network structure to take full advantage of the benefits offered by offline programming.

Virtual bending externalizes the intellectual process of creating a bending solution for a part. The program generated includes useful information that can streamline setup and production. Then, when an operator opens the program on the control, he immediately sees a tooling setup sheet, displaying complete information regarding tool type and layout. Quite often, this information is represented graphically. Further, some controls offer interactive touchscreens, which also will interact with a press brake’s backgauge or LED lights that indicate for the operator exact tool placement. This reduces setup time at the machine.

With tool setup complete, the operator now turns his focus to bending. The 3D simulation generated by a virtual bending program displays on the machine’s control, providing a bend-by-bend graphical representation of part placement along the machine. This reduces cycle time and minimizes the risk of misformed parts due to incorrect part placement or sequence errors. With the bend program downloaded to the control, all of the time previously spent entering data into the control is eliminated.

The next setup issue to address: test bend/inspection. Many factors affect a shop’s ability to achieve the target bend angle when forming on a press brake, including variation in the workpiece material’s thickness, hardness and grain direction. Many press-brake builders offer systems engineered to correct bend angle in-process for these material variations—probes, sensors or laser devices that measure and adjust bend angle on-the-fly. These systems will eliminate the time and material demands of test bending, and also can be used to monitor and adjust the bend process, reducing the need for in-process inspection.

A Final Word

By capitalizing on the skill of the best operators in the shop by leveraging the capabilities of offline-programming software, fabricators can gain a more consistent and repeatable process with fewer mistakes and better-quality parts, all while keeping costs down. The programs generated by this process remain the intellectual property of the company, ensuring that future runs can be processed even if skilled operators become hard to find. MF

 

See also: Amada North America, Inc

Related Enterprise Zones: Fabrication


Reader Comments

Posted by: Ralph Sanders on 7/12/2012 9:13:13 AM
In fig 1, the values only add up to be 80%. Has a 20% slice of the pie been left off or have the slices been mistakenly given the wrong values? What is the 9% Test Band slice referring to? Also, does the Enter Data slice refer to writing programming or to recording data after completion for future setup and production runs? When the bend-sequence planning, tool selection and layout, and press-brake programming are removed from the floor by off-line programming, which increases the green-light time and other factors, do you have any data to illustrate the % values the floor should now witness?

 

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