January 16, 2003
It is no surprise that fabricators are always looking for ways to increase productivity; however, many don't realize that a simple solution sometimes can be found right in front of them.
One of the easiest ways to increase productivity is by getting the most out of existing punching machinery. Following are some basic but often overlooked ways to do this.
According to lean manufacturing principles, the more a part is handled, the more it costs to produce it. The shearing process increases part handling and the distance a part travels throughout the factory. So, eliminating the step of shearing material to size makes each part less expensive.
Coiled steel from which sheets are sheared to size can consume a lot of storage space. Instead, material can be purchased in standard sheet sizes of either 4 by 8 feet or 5 by 10 ft. Standard sizes require a smaller storage area, freeing up valuable floor space for more productive applications. In addition, consolidating material sizes can make organizing and retrieving material easier.
Because frequent reloading is not needed with larger, precut sheets as it is needed with sheared sheet metal, machine run time is lengthened, and productivity is increased. This, in turn, frees up the operator to perform other functions, such as operating additional equipment, setting up tools, or inspecting parts.
Many fabricators process multiples of a single part on a sheet; however, nesting dissimilar parts can maximize material utilization. Processing dissimilar parts together allows fabricators to be more creative in how they nest the parts on a sheet. Small parts can be placed in the unused areas among large parts, allowing more parts to fit on a sheet.
Two of the main nesting approaches are kit-based and order-based, or dynamic nesting. Kit-based nesting assumes a family of parts is produced together, usually as a complete component assembly. Different parts are grouped in common multiples across one or several sheets.
Dynamic nesting takes into consideration production requirements on a real-time basis, usually a day at a time, and groups materials with common thicknesses together.
When nesting, tooling requirements and tool rotation capabilities must be considered. Using multitools can increase total tool capacity. If all toolstations are able to rotate, then all parts may be oriented freely at any angle, which makes it easier to fit more parts on a sheet and increases material utilization.
Nesting software determines the best way to optimize material utilization (see Figure 1) and produces programs for each individual sheet based on the daily order requirements.
Nesting software determines the best way to optimize material utilization.
Murphy's law of machine maintenance: Something always goes wrong with a machine at the exact moment when the need for it is most critical.
Equipment failure can be costly. Even if the problem is easy or inexpensive to fix, a down machine costs time and money. It may seem obvious, but keeping machinery in tip-top shape through regular maintenance and repair is an easy way to ensure higher productivity.
Manufacturers' requirements regarding lubricants and scheduled maintenance should be reviewed. Unfiltered oil in the hydraulic circuit can destroy any hydraulic system. Fortunately, advances in hydraulic technology have improved reliability and functionality. Hydraulics now can eliminate wear and reduce the overall maintenance time required.
Setting up a routine weekly and monthly maintenance schedule should include cleaning the machines every couple of days. Keeping the capital investment clean keeps the boss happy and creates an atmosphere of quality and responsibility that influences other employees.
Most important, keeping the machine clean prevents dirt from getting into vital machine components and damaging the machine.
In addition, equipment manufacturers can provide a detailed list of the most commonly used spare parts. Keeping some low-cost replacement parts or items on hand might help fabricators avoid being caught "in a pinch " when those parts wear out.
Performing tooling maintenance and setup for the next job while the machine is running production takes advantage of the machine's cycle time and decreases costly downtime.
Forming tools, piercing tools, and other tools with tight die clearances should be set up offline. Doing so and checking the punch-to-die alignment at this time may prevent a collision while the machine is running.
Proper tool maintenance, particularly sharpening, is critical to producing quality parts.
Programming tooling setup sheets or automatic tool tables at the controls enables the operator to prepare for the next job. While the machine is running another job, the operator can review the machine tool tables and prepare additional tools required for the next program.
Proper tool maintenance, particularly tool sharpening, is critical to producing quality parts (see Figure 2). Not only do sharp tools reduce the tonnage and noise, they last longer and produce the best part edge quality.
It's a good idea to sharpen tooling with a wet grinder to maintain tool hardness. The heat produced by dry grinding reduces the tool's hardness, making it more susceptible to wear and tear. Burrs, small particles that have broken off the grinding wheel and tool steel during the sharpening process, create an abrasive edge. It's important to "dress " or remove any rough burrs to maintain the quality, accuracy, and life of the punch. Lightly honing the tool with a whetstone and demagnetizing it will remove the burrs.
Generally, the more operations can be consolidated, the less part handling is required. Combining different operations also can improve part accuracy.
For example, a part with several tapped holes usually requires punching and then a secondary, often manual, tapping operation. Using the punching machine for the tapping operation consolidates the steps into one operation. This is accomplished by taking advantage of the punching machine's ram rotation, loading in a tapping tool, and programming the tool rotations in and out of the metal. This process also reduces the possibility of human error, such as missing one or more of the holes to be tapped.
In addition, using other forming tools such as countersinks, louvers, and lance forms can help consolidate operations. Advances in hydraulic punching technology allow operators to adjust tooling in increments of 0.001 in. at the control and to set ram penetration depth. With control over optimal forming height on all forming tools, operators can integrate forming operations into a punching job without risk of damaging the forms.
These five important steps can help fabricators get the most from their punching machines. Re-evaluating current punching situations is likely to uncover at least one area in which one or more of these steps can be used to increase punch power.
Jeff McQuarrie is punching applications engineer at TRUMPF Inc., Farmington Industrial Park (CATC), Farmington, CT 06032, phone 860-255-6285, fax 860-255-6424, e-mail Jeff.McQuarrie@us.trumpf.com, Web site www.us.trumpf.com. TRUMPF Inc. produces fabricating machinery for sheet metal processing, including punching, forming, bending, and laser systems.
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.