November 6, 2003
Press brake forming always has been a labor-intensive process. Shrinking lead-times and smaller lot sizes demand more frequent setups, which cut into productive output hours and put more pressure on manufacturing efficiencies. Fabricators need to find ways to reduce machine downtime for setup and operator adjustments.
|A critical benefit of offline programming and bend simulation is that fabricators can determine upfront whether the part can be bent, avoiding shop floor trial-and-error.|
Traditionally, press brake operation has required skills that could be acquired only through years of on-the-job experience. In the past, machine setups were performed by experienced specialists, and then operators ran production. As the workforce ages, however, setup specialists are rapidly retiring and increasingly harder to replace.
To deal with today's economic business climate, global competition, customer demands for smaller lot sizes, and loss of setup specialists, many shops require operators to perform their own setups. Typically, this means that the operator, equipped with only his part-making experience and a part drawing, must select tool cross sections, determine tool locations, choose bend sequences, and program the press brake.
Too often this strategy comes up short, resulting in long trial-and-error setups and unnecessary scrap. On shorter part runs, programming and setup time can be as long as or longer than the actual production time. Press brake utilization rates may drop below break-even levels.
Faced with these circumstances, shop owners and managers are looking for technology to help. Recent major advances in press brake technology and forming productivity focus on bringing computer help and virtual expert coaching to the human side of the process—to the operators.
Many CNC press brakes were purchased initially to increase productivity through part program storage, enabling faster setups on repeat jobs. While machines with CNC are commonplace today, program storage was never effectively implemented in some shops. Many CNCs have limitations that impede program storage utilization:
Caught between limited time to overcome these complications and daily production requirements, some fabricators abandon the program storage and backup step, even though this feature may have been a significant portion of the purchase justification. As a consequence, they increase their reliance on operators with varying degrees of skill and preferences to make independent programming decisions.
The results may include step repetition, under-realized productivity, trial-and-error setup, and inconsistent part quality. For example, bend sequences may vary based on individual operator preference or the blank size may be incorrect if the operator selects improper tooling.
Previous-generation CNC technology brought productivity improvements, but often not to the extent desired. Benefits tended to be isolated to each machine. Efforts at sharing processing knowledge across the organization (or even across the aisle) have been thwarted, limiting overall gains in forming productivity.
PC-based controls are a key to increased productivity.
Advanced PC-based controls (see Figure 1) are designed to eliminate handicaps and limitations by providing open platforms and communications capabilities:
Networking from a common database allows operators to retrieve a part program, including detailed setup information. This avoids duplicating work already done by others. Part program files provide the operator with an important job setup page, which displays tool names, segment lengths, tool locations, and setup notes detailing important instructions (see Figure 2).
A job setup page, which displays tool names, segment lengths, tool locations, and setup notes helps the operator avoid duplicating work already done by others.
Best practices can be captured and institutionalized as standard operating procedures. Parts are processed repeatedly with the same program settings, tools, and bend sequences, which is critical to reducing variation to meet tighter process and quality control requirements, such as statistical process control programs.
Operators are guided through the forming process by 3-D graphical software (see Figure 3). Graphics show the forming sequence, tool locations on the bed and ram, and part handling for each step. This can be a major advantage on complex parts that require multiple bends and staging of more than one set of tools. Graphic rotation capability through 360 degrees allows a part to be viewed from different vantage points to prevent confusion about part orientation or bend sequence.
In many cases, the pictures are worth the proverbial thousand words—making clear what can be difficult to explain through setup notes on parts with complex bends. The "see-and-do" instruction and "how-to" sharing enhance speed, repeatability, productivity, and part quality consistency, even with less experienced operators.
Advanced PC-based control software also helps the operator to program new parts. Simple jobs can be programmed, run, and edited from one screen with minimal steps using fast touch data entry or control CAD facilities. Programming is initiated by drawing the part shape in a cross-section or flat-pattern view.
Tools can be viewed and selected from a graphical tool library displaying the tool profile. The software automatically creates a part program from the part shape. The most advanced machine controls can import an existing CAD file, automatically determine a valid bend sequence, and simulate forming in 3-D views.
On complex parts, offline programming offers greater productivity benefits (see introductory photo). Offline programming and bend simulation allow fabricators to create an optimum process, maximize both programmer and operator efficiencies, and reduce machine downtime that results when an operator programs the job on the shop floor. A critical benefit is being able to determine upfront whether the part even can be bent with tooling on hand, avoiding shop floor trial and error.
3-D graphical software shows the forming sequence, tool locations on the bed and ram, and part handling.
Offline programming makes it possible for shops to take fullest advantage of skills, similar to the way shops once used setup specialists for complex and difficult jobs. A program can be developed and proved offline in a fraction of the time needed for physical setup and forming trials. This expertise then can be stored and accessed anytime the same part needs to be run again for repeat productivity gains. In addition to leveraging machine hours, simulation minimizes forming errors, scrap, and rework.
Program creation offline begins by importing a CAD file, which may be the same file used to produce the blank on a laser or punch press. If a CAD file is not available, the software provides CAD facilities to draw the part shape in a cross-section or flat-pattern view. The software can unfold parts, calculate flat-blank dimensions, and export new flat-pattern CAD files.
The programmer adds or identifies bend lines on the part, selects tools from a tool library shared with the machine control, manually selects a bend sequence, or requests a computer-generated bend sequence. Bend sequences are validated by automatic checks for part interferences with tooling and machine components. Tool positions, including multiple die setups, are graphically displayed (see Figure 4).
Tool positions, including multiple die setups, are graphically displayed.
Three-dimensional graphic simulations allow the programmer to preview the process through unbent and bent stages while rotating the view through 360 degrees for clarity. The simulation verifies the forming process without generating scrap or wasting operating time, typical with traditional part programming and setup.
After the programmer accepts the simulation, the software automatically creates a part program. Some software packages will automatically optimize ram settings and backgauge positions. The software may provide additional process optimizations, such as minimizing part turns or flips and controlling front-to-back part weight ratio. Safeguarding methods should be carefully evaluated and employed by the user to ensure operator safety.
Not only can programmers create a customized process, they can base it on tooling on hand. Programmers can create tool libraries containing only tools in inventory and use the software to specify tools with the appropriate cross section. Some software also provides utilities specifically for segmented tools. These utilities can track tool segments stored in inventory and provide an autocalculate function to help the programmer determine the segment combinations needed to build a tool of the desired length, rather than cutting one to length.
Offline programming and simulation software offer additional productivity benefits. They can be used for training to speed the learning curve for new and inexperienced employees. The software capabilities can even help to attract young people to the business who may be comfortable with computers but have little or no hands-on shop experience.
Simulation software can aid job scheduling and estimating. It allows a job estimator to visualize the tools and setup necessary to produce a part, resulting in more accurate and competitive estimates of setup and processing times.
All the productivity advantages of PC-based controls may not be enough to convince a fabricator to replace a sound CNC press brake with a new machine just to get an advanced control, especially if the brake is paid off. Some press brake manufacturers offer PC-based control upgrades to existing CNC models. Retrofits and offline bend simulation programming software may also be available.
Today's advanced control capabilities allow fabricators to make the most productive and profitable use of both their press brakes and their human resources. Forming expertise can be captured and shared, raising overall shop proficiency and part-making consistency. Touchscreen convenience and powerful graphics provide visual coaching for faster setup and effective forming sequence. Offline programming and bend simulation software help reduce machine setup downtime, scrap, and rework.
The FABRICATOR® is North America's leading magazine for the metal forming and fabricating industry. The magazine delivers the news, technical articles, and case histories that enable fabricators to do their jobs more efficiently. The FABRICATOR has served the industry since 1971. Print subscriptions are free to qualified persons in North America involved in metal forming and fabricating.