Leaning on the turret punch press
A hypothetical tale about adding value in punching
Proper planning and tools lead to greater punching efficiencies as well as smooth part flow throughout the rest of the fabrication operation.
The production manager needs to get moving if he is going to make it to the weekly turret punching production meeting on time. Pushing away from his desk, he thinks about how unpleasant these meetings used to be. Everything was reactive. His team reported on the fires and discussed how they put them out.
That was before the change.
He greets those gathered and calls the meeting to order. In typical fashion, team members report on the problems from the past week and share the solutions they implemented. They make plans for the coming week and discuss anticipated bottlenecks. As the meeting wraps up, he looks around the room. They are the reason for the company's success.
Small Jobs, New Problems
Meetings didn't go this smoothly three years ago, when the company was in serious trouble. The high-volume, long-run orders they had enjoyed for years had dried up. The sales team was bringing in highly variable, low-volume, short-lead-time work to the job shop floor. The production manager wondered how they were going to survive on those kinds of jobs since the turret punching production team was not in a position to support that type of work, let alone be profitable. Things needed to change, and quickly.
Short-run jobs made eliminating non-value-added time on turrets much more important. In the past such activities could be swept under the rug, so to speak—amortized over a long-run job so that in the end it was a tiny contributor to the overall cost. It soon became clear this was going to change. For low-volume, highly variable products, such activity would add major costs to the overall job. Reducing that non-value-added activity became a management priority, requiring the cooperative effort from various departments, including engineering, programming, manufacturing, production, and quality control.
The current state wasn't efficient. Tool change-overs depended on the operator to find the tool, prepare it for use, and install it in the press. The setup time depended on the organization and skill of a specific individual, who also needed to remember which tools were in the turrets. Often the operator would tweak the program at the control because the desired tool was in another station. Such last-minute program changes created opportunities for quality problems. In other words, they were mistakes just waiting to happen.
To develop a fixed turret layout, they standardized programming practices around the tools available to punch the product. This, however, raised discussions about balancing productivity and quality. For example, instead of using a standard tool, a special-application tool could improve quality and might even be faster, even if it required an additional tool changeover. The team decided that those issues would be agreed upon during a new design-for-manufacturability process, during which they would review all new products and programs before introducing them to manufacturing.
They found developing a standard turret configuration to be relatively straightforward for many of the stations, because they already used quite a few common tools. But with numerous orders of disparate products, the team knew they needed variable and special-application punch tooling for certain products.
The team went about tool selection carefully, considering not only individual part geometries, but also entire sheet nests and overall part flow. A tool changeover may increase the time a job spends at the turret punch press, but if the new tool can eliminate a secondary operation entirely, the dramatic reduction in overall manufacturing time would make that additional tool change cost-effective.
Snapping up Nests
They first examined sheet nests. Some new jobs required part profiles with shapes and features that made it difficult or impossible to achieve an efficient nest layout with available tools. When they could, they nested parts on a common line, but parts still required microjoints to maintain sheet integrity. If a microjoint broke in-process, making the part tip up and cause interference, team members historically had just added more, larger microjoints. That supposed "fix" actually caused more non-value-added activity. Operators would simply take longer to shake the sheet on the press table to break the numerous microjoints. Larger microjoints also required more violent shaking, which increased the chances of damaging parts.
Here, specialized tooling came into play. The team used a variant on a standard parting tool that has a linear V-line stencil machined into the face of the upper and lower tools. As the tools penetrate the sheet, they create a line of weakness (a snap line) in the upper and lower surfaces of the sheet material. This allows operators to quickly snap a burr-free part loose from the rest of the sheet (see Figure 1).
Snap lines were also useful for press brake operators. By creating nests of small parts and keeping them attached, they could be bent simultaneously on the press brake. Bending these small parts became much more efficient and safer because the press brake operator did not handle them individually. The individual parts could be snapped out after forming or left together in the nest, if preferred.
In other circumstances, several small parts could be hung on the paint line as one unit rather than individual parts. Here, the punch programming team got even more creative: They programmed the punch to cut out paint hook shapes on certain parts, again separated by a snap line that left a burr-free edge when broken. After painting, operators simply snapped off the paint hook feature (see Figure 2).
To run small quantities and reduce the number of tool changes, the team realized they would need to resort to more nibbling, which in turn would require more deburring. To address that issue, they added another specialized tool that uses a roller to deburr the part while still in the press, eliminating secondary processing. The snap lines were strong enough for the deburring tool to roll over without compromising the nest.
Holes presented yet another challenge. With such small batch sizes and varying parts, how could they minimize tool changeout while efficiently punching such a wide variety of holes? For large holes, another multipurpose tool came into play. A quadradius tool with four radii on the punch circumference could quickly nibble different-sized large-diameter holes common in many parts. This eliminated the need for a specific tool for each hole size.
Standard and Variable Tools
The team separated standard turret tools from the variable tools that weren't used for every job. They made tool installation more efficient by segregating tools to designated areas of the turret, including several adjacent stations for variable tools.
The programming and manufacturing teams developed white boards listing all turret station numbers for each punch press (see Figure 3). They permanently labeled standard stations with the tool shape, size, and orientation, and left space available to write in the die clearance with a dry-erase marker. They also left open space for variabletool stations; when the operator installed those variable tools for a job, he could then write the details (tool size, shape, orientation, die clearance) on the white board.
The team also dedicated two stations to multitool assemblies, which essentially allowed operators to change out several tools simultaneously. One multitool held tools for performing initial pierces followed immediately by the countersink, as required by many of the shop's customers.
Variable tools were highlighted on every setup sheet. In fact, the team's goal was for that setup sheet never to travel without the variable tools the job required. A worker was expected to take both the setup sheet and variable tools to the operator, who would then change over tools as soon as the previous job finished.
A lot had to happen to make this possible.
Previously the turret press operator looked for excessive burrs or stripping problems as telltale signs that a tool needed sharpening. The delayed stripping caused by dull tools was occasionally bad enough to cause an entire sheet to be pulled out of the workholders.
When the operator saw that punches needed attention, he would remove and sharpen them. The problem was that the tool condition determined when it needed to be sharpened. This in turn interrupted production as the operator performed the maintenance. It was all reactive, not proactive.
As a first step, the team organized a centralized toolroom (see Figure 4). Toolroom personnel inspected, maintained, and stored tools, including backup tool sets for all standard tool stations. Essentially, they ensured that tools would be ready when and where needed.
They also took advantage of hit counters. Tools in the press were flagged with an alarm using the hit-counter feature, which told the operator to notify the toolroom when specific tools reached a predetermined maintenance threshold. The toolroom would then send a replacement tool to the press operator, who would perform the changeout during the next setup. The press operator then returned the worn tool to the toolroom. If the tool could have gone longer before sharpening, the toolroom personnel would advise the operator to change the hit count to a new, higher value.
The New Way
The production manager knows that without all those improvements, today's production meeting wouldn't have gone so smoothly. His team understands the shop's capabilities and, most important, communicates those capabilities to the sales team.
Lean initiatives increase a shop's capacity, and salespeople help the shop fill that increased capacity with new work. The support the sales team receives from the production team enables them to provide competitive quotes, creative processes, consistent quality, and fast delivery.
The plan is in place. More small-volume and (quite often) higher-margin work is coming in the door. Things are working again, and the company's balance sheet shows it.
After a quick meeting, the production manager and his team head back to work—with no fires to put out, only organized systems to manage and improve.
Images courtesy of Mate Precision Tooling.
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.