Staged bending strategies for high-product-mix job shops
January 6, 2012
CAM software have made it easier and more affordable for job shops to increase efficiency and productivity without sacrificing quality. Staged bending combined with offline programming offers strategies for reducing downtime, improving part flow, and controlling costs.
Job shops live and die on their ability to maximize throughput. They need to be nimble enough to meet ever-changing customer needs. Efficiency is everything; the less work-in-process, the better. Any bottleneck or additional setup during bending operations can disrupt part flow, prolong lead-times, and even reduce quality.
Fortunately, significant advancements in tooling technology and computer-aided manufacturing (CAM) software have made it easier and more affordable for job shops to increase efficiency and productivity without sacrificing quality. Staged bending combined with offline programming offers strategies for reducing downtime, improving part flow, and controlling costs.
In high-product-mix job shops, the only certainty is that there is no certainty. These manufacturers have no way of knowing what the next job will be or what tooling it may require, so they must have the most flexible press brake tooling available at all times.
Many will try to air-bend as much as they can because it allows greater versatility over a range of material thicknesses. This allows them to keep a smaller tooling inventory to handle many different operations. But because they don’t have a lot of control over what prints and parts their customers will request, air bending alone isn’t enough. Shops usually will need to bottom-bend with some matched-set tools. Some parts might even require high-tonnage coining to form tight inside radii.
Consider a tight-tolerance computer chassis. This requires more than just the 90-degree bends for the corners of the box. The fabricator who can produce a chassis that can accommodate more components—more chips, more fans, and more memory—will win the job. All these components require various louvers, flanges, offsets, card guides, and other complex forms. Offsets and flanges often must be bent over and then flattened.
Traditional bending practices require a separate setup for each and every form. From start to finish, the bending process might require as many as five different press brake setups. Alternatively, the job could be completed with multiple machines: One operator performs the first bend series with one tool set, and then passes the part on to an adjacent operator to perform the next at another press brake. Both arrangements have tradeoffs. The latter ties up multiple operators and machines; the former requires the operator to repeatedly set up the machine.
Staged bending, on the other hand, enables press brake operators to perform multiple bends with a single setup (see Figure 1). Different tools are set up next to each other along the brake bed, allowing multiple bends on a single part to be performed in succession. This simplifies complex short-run jobs by eliminating unproductive and repetitive tasks, significantly reducing setup time, part handling, and WIP.
Staged bending requires that press brake tools have a common shut height to avoid collisions. Early adopters of the practice accomplished this by using a series of shims and risers to create that common shut height. However, this method proved to be both time-consuming and expensive. So, while these early attempts at staged bending reduced setup time, they were very inflexible.
Now suppliers offer press brake tooling that has common shut heights built into the design, a feature that allows operators to arrange multiple tools in a single setup without time-consuming shimming procedures (see Figure 2). By eliminating unnecessary and often repetitive tasks, staged bending with common-shut-height tooling speeds processes throughout the shop and makes tooling inventories more flexible.
There’s nothing worse for part flow than having a job get punched out or laser-cut and sent to the press brake only to discover that the part can’t be formed because the shop doesn’t have the right tools. This disrupts throughput dramatically. A stack of parts sits on the shelf while operators determine which tool is needed, order it from the tool manufacturer, wait for it to arrive, set up for the job again, bring the part off the shelf, and finally bend it and send it on its way. This increases WIP and creates inefficiencies that are largely avoidable with offline programming and bend simulations.
CAM software provides CNC programming of press brake machines, allowing manufacturers to program their press brakes offline as well as provide full 3-D-model simulation of the bending process. Third-party software can be used with multiple types of press brakes and many styles of tooling. It is programmed to recognize the features of each and assists with both machine and tool selection.
The software reviews the shop’s tooling inventory and automatically selects the tools that will best form a component with a single machine setup. It also determines which tools to use and where they need to go on the press brake.
CAM gives the engineer or programmer some early feedback too. Can this part be formed in one staged-bending setup, or are multiple setups required? Which press brakes will be available, and which will be the most efficient for the job? Could the job be performed in one staged-bending setup on a machine with a longer bed? Will there be any interference problems with certain bend sequences or tooling arrangements? Will all the tools be available? The software answers these and other questions before the job is sent to the floor.
Staged bending aims to streamline the process for optimal part flow by performing as many bends as possible with the fewest number of tool setups. This also means arranging tools for the most efficient and suitable bend sequence for the operator. For instance, say the first bend requires a tool set on the far left, the next bend a tool set on the far right, and the next bend yet another tool set in the middle. Repeatedly moving back and force like this isn’t very efficient. Obviously, the operator would prefer a bend sequence that uses tools lined up so he can simply move from left to right to perform the bends—and software helps to make this happen.
Programmers and operators can identify preferred tooling for specific materials and bend radii, so those tools can be carried over from one job to the next whenever possible. Software also allows for advanced forming operations to be combined in a single setup with coining or air bending. An operator may set up several 30- and 90-degree punch and die sets next to a specialty die set that can coin or bottom-bend the metal. For example, the operator could air-bend several flanges and then immediately form a safety edge with a hemming die set—all in one setup.
Just because it can be designed or drawn doesn’t mean it can be fabricated from a sheet. Determining whether a part can be formed before releasing the job to manufacturing is key.
Press brake operators want to know whether the part design can be formed and, if so, that they have the right tools available. After technicians program the staged-bending procedure offline, they can send detailed information to the press brake operator, who views 3-D images of the tooling at the machine controller or at an adjacent PC. The operator then can simulate the forming procedure, zoom in, and rotate views to ensure all process variables—bending sequence, clearances, tool placement, and so on—create an efficient bending procedure.
This all occurs offline. When a job comes to the press brake, the operator knows exactly what tooling is needed, how it should be set up in the press brake, as well as the ideal bending sequence for optimal part flow. CAM software, 3-D bending simulations, and press brake tooling all work together to make this possible.