Before you buy: Considerations for turret punch press shoppers

March 10, 2009
By: Terry Stewart

Making an intelligent, economically sound punch press purchasing decision requires careful consideration of many factors, including material size and thickness, material handling capabilities, part complexity and volume, and turret capacity. Take the time to accurately determine your needs. Is that great deal really a wise investment?

Laser Punch Machine

In today's economy it's especially important to approach any new equipment purchase with a clear understanding of your manufacturing requirements. While special pricing and promotions may be tempting, price should not be the most important factor in selecting a machine.

If a new turret punch press is on the horizon, here are guidelines for what to consider before you buy.

Material Size and Thickness

First, define the machine size. Machine table size is determined by the method used to process flat sheet metal parts. Two commonly used methods are single-part processing (one-up) or full-sheet nesting (shaker parts).

The one-up manufacturing technique, which uses blanks cut to exact dimensions required for the final part, eliminates shearing, reduces scrap, and simplifies the picking and sorting of dissimilar parts. A punch press with a small 4-ft. by 4-ft. table best suits this application. Small-table machines also are ideal for cellular production because cells usually have a small footprint.

Large-volume production of flat-pattern sheet metal parts typically is performed using the shaker-part method. This involves tabbing parts together into a large nest and removing the entire sheet of punched parts from the machine. The machine table size appropriate for this application is standard sheet sizes, either 4 ft. by 8 ft. or 5 ft. by 10 ft.

Using the shaker-part method, sorting and stacking parts is moved off the machine to increase the green-lightor machine-ontime.Parts can be removed, sorted, and stacked manually, or automation can be incorporated to complete the process. The shaker-part method is preferred when floor space is available and large sheets can produce high yields with minimal scrap.

Once you can identify the appropriate table size, consider tonnage. Punch presses are typically offered in 20- or 30-ton configurations. The use of laser cutting machines to handle thicker materials has greatly diminished the need for 30-ton punching equipment. As a result, today's punch press applications usually are well below 20-ton capacity.

Determining the proper size and tonnage of your new machine is strictly a function of the application.Company size and volume have no bearing on this selection.

Material Handling Capabilities and Part Volume

If labor utilization is an issue or lights-out production is a goal, evaluate automation options. Automation addresses non-value-adding functions, such as sheet loading, offloading, sorting and stacking parts, and removing skeletons. Automated systems produce completed parts, ready for the next operation, without operator intervention.

An automated system is optimal in high-volume flat sheet metal production. Many fully automated systems require a consistent application with steady volume. Others, including those with robotic material handling, provide broader options for flexibility in processing various part shapes, sizes, and volume.

Part Complexity and Turret Capacity

Now that you have determined table size and tonnage for your machine (with or without automation), consider turret capacity.

Part complexity determines tool capacity and how many turret stations are needed. Simple part geometry requires fewer tools and, therefore, a smaller turret, for example, 21 stations. Complex part geometry demands a larger tooling inventory and more turret capacity.

Large-tool-capacity turrets with up to 48 tools are designed to accommodate parts that have complex geometry.Purchasing a large turret capacity when the application does not require it adds unnecessary cost to the machine purchase.

Setup Reduction and Productivity

A time study will help you evaluate a punch press based on the processing speed. Most time studies performed today indicate the time it takes the machine to complete the part from cycle start to cycle finish. It is important to recognize that sheet loading, tool changes, and relocating work clamps – all non-value-added operations –typically are not included in a manufacturer's time analysis.

Beware: Nonvalue operations easily can add up to compromise the perceived value of a faster machine. The fastest punching machines on the market beat slower counterparts by mere seconds. A typical sheet metal part completed in 20 seconds on a faster punch press might take 26 seconds on a slower model. What is the benefit of saving six seconds if 10 minutes are lost with cumbersome setup procedures associated with the faster machine?

Consider innovative tooling, machine features such as indexable autoindex stations, and ways to reduce tool setup and changeover as means to weigh the value of your investment and to add capacity to your machine.

Most punch presses are able to take advantage of the latest tooling advancements, which can increase production and improve part quality significantly. Wheel tools can cut material faster without overlapping punch marks. Tapping operations can be performed on the machine, which eliminates additional material handling and/or a secondary operation. Indexable multitools can add tool capacity and eliminate the need to interrupt punching operations for a tool change.

In addition, punch press machines incorporate different methods to use and change tools. Look for the quickest method to change tools, such as quick-change die bases that permit tool changeover in seconds.

Automating work clamp movement between jobs and during a punching cycle also helps reduce setup time and increase productivity. Consider programmable work clamps, which never require manual adjustment and thus eliminate the potential liability of operator injury associated with manually positioning heavy work clamps. CNC work clamps can be automatically relocated during the program for total sheet utilization without a time-consuming progressive move.

Parts removal is another time-consuming operation to address. Small-part evacuation can eliminate the labor required to remove parts from nests and tabs from parts manually and produce parts that are ready for the next operation immediately. A parts chute should be able to accommodate a minimum 12-in.-square part and should evacuate the part quickly, without interrupting the punching cycle for more than a few seconds.

For added versatility, consider adding a laser. Combining laser cutting and punching operations on one machine reduces setup time and expands capability. The laser can process complex part contours impossible to produce using conventional punches and dies, while the punch press can more quickly handle parts with interior holes or forming requirements.

Thinking Ahead

If a new punch press machine is not in the immediate plan, but you are considering taking advantage of tax incentives perhaps closer to year-end, take the time now to outline your requirements and identify the punch press that would best suit your needs. Doing so will position you to readily take advantage of tax incentives when they become available.

Stay the Course

When it comes to purchasing the right turret punch press for your requirements, there is no one-size-fits-all solution. Evaluate and prioritize your needs, identify solutions that are most important to your specific business situation, and make your equipment purchase based on the machine that satisfies those specific needs. Stay focused on your needs and don't let price be the only factor. Price is important, but the least expensive machine saves you money only once.

Terry Stewart

Contributing Writer
punching machinery at LVD Strippit
12975 Clarence Center Road
Akron, NY 14001
Phone: 716-542-4511