Precision sheet metal folding technology enables kit manufacturing

FIGURE 9. A folding workcell conveys kits of electrical enclosures to feed welding.

As long as manufacturing has existed, those who manufactured sought better ways to do so. Driven by technological advancements in tools and machinery, improved efficiencies boosted margins, built a competitive advantage, opened new markets, met labor challenges, and provided steady improvement in the means and methods of production. Tdc Corner Tool

Precision sheet metal folding technology enables kit manufacturing

As technological advancements make more dramatic changes possible, manufacturers are continually introduced to new process improvement concepts. But limitations caused by a single inefficient process can render downstream improvements impossible to achieve.

The relationship between blanking and bending is a case in point. With no hard tools to worry about, laser cutting has made blanking extraordinarily flexible. Walk downstream, though, and you might see an operator retrieving tools, processing tryout parts, and running through all the checks necessary to start a run on a legacy bending machine. Lengthy, unpredictable setups demand batches of a certain quantity.

Smaller lot sizes become a challenge, and kit-based production—where every piece in an assembly or subassembly is processed in sequence, moving in “kits” from one work center to the next—simply becomes impractical. Certain flexible bending methods, though, have made kit-based production practical and profitable. Today, this includes precision folding technology.

Today’s labor crisis is forcing companies to reevaluate their production methods, and this includes kit production. When employed, kit-based flow can affect production efficiency dramatically, and every downstream process can benefit.

Kit manufacturing produces groups of similar or dissimilar parts that make up sub- or full assemblies. They often directly feed downstream operations like robotic welding or assembly (see Figure 1). Kits are produced in the order of need and delivered just in time to feed the next process.

This type of production is incredibly efficient as it eliminates most of the issues created by the biggest violator of lean manufacturing: overproduction. That said, one requirement prevents most from adopting this incredibly efficient concept: efficient, single-part production. This, again, has to do with setup time—especially if every part in a kit requires a unique machine setup. If a system isn’t flexible (for instance, one tooling configuration can produce a variety of parts), and it can’t change over quickly, producing kits usually isn’t practical.

Throughout the fab shop, though, evolving technology has made the impractical practical. Think back to the early 1980s, when turret punch presses reigned supreme. They typically produced blanks in large quantities to offset non-value-adding setup costs. This lump of product clogged downstream processes and became burdensome to handle. Fabricators sometimes spent large sums of money to manage the problem, yet gained little relief.

Poor utilization and high labor demands made turrets the perfect target for replacement by a high-impact technology: laser cutting. When lasers disrupted the punch market in the mid-1980s, it forever changed how blanks are produced. Lasers introduced the ability to move between material types and thicknesses effortlessly with no tooling restrictions, eliminating the importance of run quantity. Automated lasers quickly followed, and more blanks could be produced than ever thought possible.

No longer held hostage to an inefficient blanking process, companies could schedule production to benefit downstream operations. But because of some inherent inefficiencies in forming, this incredible level of lean blank production could push efficiency only so far.

FIGURE 1. Parts for this truck body subassembly are folded and kitted before being sent downstream for assembly and robotic welding.

Bending technology has evolved significantly. For many operations, though, forming remains an extremely labor-intensive, complicated, and inefficient process requiring highly skilled operators. In typical shops, machines only produce bends about 10 to 15% of the time. Variations in grain direction, thickness, and tensile strength wreak havoc when trying to reliably form accurate workpieces, requiring operators to check and recheck parts. Fatigue sets in as they lift, flip, and position large parts and retrieve tools for changeovers.

An operation might combat these challenges in various ways, like opening forming tolerances to address accuracy concerns and running larger batches to reduce the impact of lengthy machine setups. Yet decisions in forming can send serious ripple effects downstream. Poorly formed parts are a struggle to robotically weld. They require more welding, more grinding, more finishing. Assembly takes longer, involving more people and more effort.

Solutions involving larger quantities hope to improve efficiency through repeated processes and motion. Producing larger batches, though, has a tremendous impact on how work flows through downstream operations. The end result: A fabricator makes more than what’s needed, and downstream operations suffer.

Every extra, unneeded part prevents a needed part from being produced and compromises the ability to quickly respond to customer needs. And if a setup part is in error, how many parts are made incorrectly until the error is discovered and repaired? Extra parts take up precious production space. They need to be stacked, tracked, stored, found, and retrieved when needed again. Parts get damaged, lost, or an engineering change turns that skid of cut and formed parts into scrap.

The ability to go from one part to another with little to no effort or skill is an absolute must to effectively flow kits. Panel benders have supported kit production for years. But parts out of the panel bender’s reach, due to limitations in part size, flange length, or thickness were left to traditional production concepts. This is where folding fills a need, offering flexible and productive forming suited to kit-based production regardless of part size.

After the workpiece is positioned in the folding machine, the upper beam (also called the clamping beam) clamps the material against the lower, or bottom, beam. The folding beam swings in an arc, pivoting the flange on its bend center to the desired angle (see Figure 2).

Modern folders have multiple axes that adjust to the proper tool settings for material thickness, type, inside bend radius, and bend angle. The machine’s axes work together to create the equivalent of an infinitely variable V die, automatically adjusting for material thickness, desired bend radius, and angle (see Figure 3).

Because a folder’s tooling operates independently of material type and thickness, radius bends of any size, hems, and offsets are nothing more than a program. They’re all formed with the same toolset (see Figure 4). A single set of standard tooling is able to form a four-sided box to a depth of 15.75 in., in 0.196-in. mild steel on down to shim stock (see Figure 5). Tool change is simply a matter of stacking the tool segments to the length required to form the part.

Tooling strategy is further simplified by the folders ability to bend bidirectionally, both up and down. Manual tool change typically takes less than three minutes. An automatic tool change accomplishes its task in less than 90 seconds on average and can run in parallel to the operator removing the last part formed and bringing the next blank onto the table. No production time is lost, and part-to-part time is controlled by the machine itself, eliminating any variances caused by operator distractions.

Still, forming flexibility is just one piece of the puzzle. When manufacturing kits, fabricators must handle an extraordinary amount of information. Kit-based flow is extremely efficient—until someone pulls up the wrong program or misidentifies a part.

FIGURE 2. A folder bends the same way a protractor measures. The thickness of the material has no impact on the angle created or measured.

Where to begin? It all starts with a program. The ability to import CAD models, even entire assemblies into the software, and make ready-to-run programs in a matter of seconds is paramount. This is the basis for successfully processing parts that differ from one to the next. Long, drawn-out programming would prevent the kind of efficient throughput required to successfully implement kit production.

Bar or QR code scanners can pull the program into production at the machine and can even contain part size information for variable programming. Recurring kits can be saved, detailing each part and quantity in the proper order, along with how many times the kit is to be run. Folding’s simple processing and tooling strategy helps software quickly determine the bend sequence, optimize the bending process and machine movement, and calculate the tooling stations necessary to perform the task.

Once the tooling is set up, forming begins. This is where the advantages of folding make kit production possible. Because of the way a folder bends, variations in material thickness, tensile, and grain have little to no impact on part accuracy. Bend-to-bend accuracy is controlled by the machine, as the part is affixed to the vacuum gauge that automatically feeds the part from one bend to the next.

Being able to gauge from the back of the part, off the flange, into a notch, or adjacent flange provides multiple reference points for a wide variety of part design. Pneumatic squaring arms also automatically raise and lower as needed. Workpieces of the right size can be run simultaneously, which can be particularly useful for mirrored parts (see Figure 6).

First-part accuracy is a must in kit production. Traditional bending methods may take several trial bends to home-in part accuracy, both flange length and angle. But when running kits, machines often bend one unique part after another. There are no trial bends. The machine forms only one part before moving on to a different part, and if that part isn’t accurate, kit production falters, and the entire process could fail to meet throughput requirements.

The process also needs to be sustainable. Regardless of part size, folding ergonomics relieve the operator of lifting, flipping, or struggling to manipulate profiles. Never is more than one operator needed (see Figure 7), and part size has no impact over part accuracy.

These ergonomic benefits help standardize run times, which is crucial to feeding downstream production. Random and inconsistent bend times make scheduling a challenge—yet run times on a folder vary little. A large part will certainly take longer than a small one, but this is a difference of seconds, not minutes.

Safety considerations are a big factor with any manufacturing process. While light curtains have substantially reduced compression injuries, repetitive-motion injuries are still a major concern with some equipment, and little can be done to prevent them. Operator fatigue quickly reduces output, introduces part error, and increases the risk of injury.

Folding is a safe process, which is even more important as less-experienced operators are being asked to maintain high production velocity. Some systems rotate and reposition the workpiece between bends automatically, and some offer part loading and unloading automation. That has obvious safety benefits, but it also helps with part flow—especially in kit manufacturing.

Kit production demands efficient work transport. After all, the kit really isn’t “finished” forming until the next process can do something with it—and it can’t do anything while the kits sit upstream as WIP.

FIGURE 3. A folder’s axes adjust for different material thicknesses by changing the gap between the folding blade (the tool on the swinging beam that contacts the workpiece) and the theoretical center of bend.

This is where the conveyor can play a critical role (see Figures 8 and 9). It’s set to the table height of the folder, and parts are simply pushed onto it in the proper sequence—that is, in the order welding or assembly (or any other downstream process) needs them.

Carts, customized to a part grouping, are also commonly used for assembling kits and transferring them to the next process. Many shops lack a direct path from one process to the next, and in these scenarios, carts can be the perfect solution.

Maintaining a steady stream of reliably accurate parts is the goal, never flooding or starving the next process. It’s a balancing act, and the fourth industrial revolution is making this balancing act easier with the digitization of data and machine-to-machine communication.

The OPC UA interface makes production-rate information readily available. Data from a machine can even trigger when an upstream operation must begin, properly timing part delivery to the next process in line.

While not for everyone, kit production offers many unique benefits for companies seeking ways to offset the lack of labor and bring some sanity to a shop filled with parts waiting to be used. Overproduction begins a cascade into wasteful practices, which many believe are necessary to maintain production levels. In reality, if parts were produced when needed to feed the next production stage immediately, most would be astounded by the gains in throughput.

Even if going “full kit” is not practical for your particular needs, you could reap enormous benefits by adopting at least some of the concepts. Implementing a technology to form parts more precisely, in a sustainable fashion, with less labor, and in smaller quantities will benefit the entire manufacturing process. Today’s advanced folding technology is suited to satisfy the needs of today’s fabricator seeking that next step in process efficiency.

See More by David Prokop