Metal Fabricating Process
The advent of CNC-controlled laser-cutting, press-brake and punch-press machinery allows rapid production of parts with little setup—and little cost related to tooling.
CNC punch presses, sometimes referred to as punching machines, manipulate a sheet of material on a table where it is shaped or punched by tools contained in a turret or other tool-holding apparatus. The press chooses, based on instructions, the appropriate tool for that particular operation. These presses contain various standard tools that allow for great machine flexibility in punching, slotting, bending and a host of other operations.
Laser cutters use a laser—typically CO2--positioned over a sheet on a worktable to cut—actually melt or vaporize—the sheet to the desired profile. Shielding gases allow for smoother material edges or increased material combustion.
Press brakes provide bending operations, typically on relatively longer and slimmer workpieces.
Laser cutters and CNC punch presses often are used together in cells, or the two are combined into one machine. Sometimes press brakes are teamed with a robot in an automated bending cell.
Competitive processes: Stamping.
Parts produced: Relatively flat parts with louvers or tightly spaced hole patterns, such as those found in HVAC and electrical/electronic industries are ideal for CNC punch presses. Lasers also accommodate a number of such parts and are useful for prototypes and preproduction parts as well as parts with highly irregular outer contours.
Benefits: Fabricating via CNC punch presses, laser cutters and press brakes requires no specific hard tooling, as is the case with traditional stamping. Fabricating produces parts that usually would require a high number of progressive-die stations, making the stamping option costly. The advent of CNC punch presses and lasers enable quick setup and production of prototypes or parts in small and medium runs, while press brakes are ideal for bending of longer, slimmer material. With material-handling add-ons, such processes can run unattended, thus boosting the size of part runs. Also, the nature of such processes allow rapid changes in part configurations, in essence allowing the designer to conduct design development during the initial phases of production. With such capabilities and minimal setup requirements, lead times are greatly reduced.
Also, lasers allow nearly burr-free holes and can produce parts without the need for prior blanking. After the part is produced, the sheet can be stored for later use.
Capacities: CNC punch presses, depending on machine size, can carry upward of 70 tools and provide as much as 50 tons of forming and forming pressure. Tables on such machines can carry sheet reaching above 80 inches long and wide. Operational speeds range from about 80 to 400 hits/min. based on 1-in. movement of the workpiece between each hit. Such presses, in some cases, can perform as much as 1 in. (vertical) of forming. Lasers can handle similar sheet sizes as CNC punch presses and cut at speeds approaching 800 in./min. on 0.040-in.-thick mild steel. Press brakes are available in various tonnages and bed lengths to handle various bending jobs.
Materials: CNC punch presses generally accept sheet that can be run in stamping presses. Lasers are most productive when working with mild or stainless steel. Aluminum and metals such as zinc and lead reflect light (scatter the laser beam) when molten, requiring greater laser power. Also, aluminum and copper alloys conduct heat away from the cutting area, again requiring more laser power. Press brakes usually can handle all types of material in thicknesses to nearly 1 in.
Should I use it? CNC punch presses, lasers or combination setups as well as press brakes deliver parts quickly without the costs and lengthy setup required for hard tooling. Given that, such machines are limited with respect to workpiece material and vertical part dimensions. Punch-press and laser processes allow flexibility in design, flat-part size and short lead times as well as minimal tooling costs. With CNC punch presses, more sophisticated tooling is warranted and becomes cost-effective with increasing part quantities.
When designing parts for laser production, remember that the process results in localized hardening. This can provide problems when holes are produced that also require tapping, countersinking or reaming. But such hardening can be a benefit in applications where a part must be case-hardened for wear resistance.
