CNC punch presses were once relegated to fabrication shops as workhorse punchers of holes of various shapes and sizes, and for edge-nibbling of fairly simple shapes. Forming tools then allowed fabricators to add louvers and lances to minimal form heights, 8 mm (0.3 in.) or so, but at a relatively slow speed without extreme precision.

Today, though, punch-press manufacturers deliver machines with comparatively fast forming capabilities and accuracies once relegated to hard-tooled stamping presses. Thanks to technology enhancements to CNC punch-press hydraulic systems, the use of electric punch drives, linear-motor technology and other improvements, traditional stamping houses and tool-and-die shops now see reason to invest in CNC punching machines.

"Many stampers find that CNC punching machines really help fill a void in the area of prototypes. Punching machines allow a stamper that has developed a prototype part, to be produced with a hard tool, supply limited production runs of the part while the stamping die is being machined," says Mike Morissette, punch product manager for Trumpf Inc., Farmington, CT. "Customers used to have to wait for hard tools before production could start. During this period, the stamper risked losing the production job to a competitor. Now, with new high-speed precision punching machines, the stamper can be the sole supplier, from prototype development to short-run production to volume stamping. We see stampers now using CNC punching machines to make part runs of 10,000 to 15,000 while the hard tools are being made-to fill a gap for their customers."

Punching machines also benefit the quoting process, allowing a stamper or tool-and-die shop to provide sample parts with RFQs in one day. This is particularly true with hybrid machines that combine laser cutting and punching. "The last five years have brought a transition to lower volumes and quicker turnaround on RFQs," says Lloyd Keller, national sales manager-forming for Murata Machinery, Inc., Charlotte, NC. "Hybrid machines fit perfectly where shops might run 500 to 2000 pieces. Presses also fit great for aftermarket support, to produce very small runs of parts produced on stamping presses in production. For example, hinges or brackets that might be ordered aftermarket in lot sizes of 50 or 100-a laser-punch combo makes sense here, rather than have to seek out, clean and install the hard tool in a stamping press."

Tighter Tolerances

Improved hydraulics and, in some presses, the use of electrically driven punch heads, have allowed stampers to consider using CNC punching machines on tight-tolerance parts such as card guides used in telecommunications equipment. "Where precision is critical in forms," says Patrick Canning, vice president, Finn-Power, Schaumburg, IL, "shops might look to electric machines, where we can deliver form repeatability of ±0.0004 in."

Improved forming on punching machines also comes thanks to better hydraulics in newer machines, according to Bob Coscarelli, CNC product manager for Amada America, Buena Park, CA. "We see greatly improved control of the stroke-both its distance and dwell -so that the forming of louvers, lances, extrusions and the like occur quickly and very precisely," he says. "These hydraulic enhancements, along with improved controls introduced in the late 1990s, deliver, on average, a 30-percent improvement in productivity and quality for our customers."

Trumpf's Morissette concurs, adding: "Advances in hydraulics allow machines to stroke faster when upforming stiffening ribs. During high-speed beading of ribs, we can stroke at 2800 strokes/min. This higher speed, along with improved hydraulic control over tool-retract height, allows us to do more than form-we're really flowing the material now. This gives improved appearance."

More Form Height

While form height traditionally hit the wall at 0.3 in. or so with these machines, manufacturers have developed enhanced tools to double, or more than double, that height capacity. About 0.75 in. of forming is now possible on most machines, even 1 in. in some cases. More versatility in forming tools comes via different approaches from the manufactures. A punch and form (P&F) feature from Amada, for example, comprises a forming cylinder below the die in the lower turret that pushes the die upward to increase travel and allow a higher form.

Keller (Murata Machinery) adds: "A retractable die assembly prevents the form tool from sitting up higher in the turret than the other tools, as it once had to. Now we can raise and lower the die set for forming tools so that the tool can go anywhere in the turret. There are no more worries about scratching the material as it drags across the turret, or crashes. This allows users to locate the forming operation anywhere in the nest, whereas they used to have to form at the very end of the program, not necessarily optimizing the process. In addition, shops can leave the form tools in the turret even if they're not needed for a job, where before they would have to change it out if not needed to avoid scratching a sheet."

Remote Machine Diagnostics

While CNC punching machines are doing more work than ever before, eliminating the need for many secondary operations so that shops can make complete parts in one setup, timely and accurate machine diagnostics minimizing downtime for maintenance and repair takes on added importance. Shops need to perform maintenance before anything breaks, avoid unnecessary maintenance and machine downtime, and ensure prompt and short maintenance calls to return machines to production ASAP.

"Customers have been asking, particularly within the last five years," says Canning, "for a better way to monitor their equipment in order to optimize run time. A phone-line hookup enables us to now monitor machines for our customers, looking at parameters such as how much oil flows through a machine or how many miles a ballscrew has logged. We can take the data collected and produce reports periodically to trigger maintenance. Half of our new customers that purchase a machine now purchase this type of service-they are so dependent on the machines that they need as much as help as they can get to avoid unnecessary downtime. This means performing maintenance when its needed, not before nor when its too late and a repair becomes necessary. Customers can receive software updates to their equipment online. We can diagnose problems with a machine or controller remotely and send a needed repair part there ahead of the technician so when he arrives, the part he needs is there. This can shave days off the repair process."

Newer PC-based controls also make programming, and program adjustments, a snap. "Data tables for jobs replace M and G codes that used to reside in the controls," says Morissette. "These data tables allow an operator to make an adjustment to a machine, to tweak the stroke depth of a form tool, for example, to fine-tune a bend angle, then the control immediately and automatically applies that correction to the program. So if the same part is nested several times on a sheet, or over several sheets, the operator makes the adjustment on the first part, then the control applies that adjustment throughout the run."

Enhanced forming capabilities of CNC punch presses allow shops to perform upforming, rollforming, wheel forming, punching, extrusion forming, tapping, marking and hemming all in one setup. MF