Automated bending cells aid in shopping cart manufacturing

Among people who work in manufacturing, it’s no secret that tube and pipe are two of the unsung heroes that make modern life possible. Whether used for a flashy, high-profile application—like a fancy set of golf clubs or an aftermarket, custom-made exhaust system for an exotic sports car—or something as common as a bicycle frame or a flag pole, tube and pipe components and assemblies are everywhere. Few of us go more than a couple of hours without seeing or using one.

Many of the common hollow products are straight lengths—hand rails, electrical conduit, broom handles—but one often overlooked and underappreciated tube-based assembly comprises tube with numerous punched holes and several bends. It’s not the most elaborate item, but it’s one of the most utilitarian. It’s a shopping cart, and unlike a golf club or a bicycle, it’s an item that nearly everyone uses from time to time.

Shopping cart manufacturer Technibilt, Newton, N.C., has thrived in this market for decades. The company has grown as the domestic supplier base consolidated and the market has expanded, and Technibilt has made substantial technology improvements along the way. In the past, improvements were small steps; advancing was a matter of training workers on a new process or a new machine, but usually it was a refinement or an upgrade to a previous process. These days, as foreign competitors that rely manual methods and inexpensive labor vie for market share, Technibilt is advancing by taking big strides. It invests in automation, which is an entirely different way of making improvements.

However, automation does have some limitations. While an assembler can compensate for a tube that isn’t quite straight and a welder can deal with a gap that is a little wider than expected, machines aren’t very good at that sort of thing. Modern machines and automated manufacturing lines can provide big productivity gains compared to decades-old, manually intensive manufacturing processes, with two caveats: the incoming material must have sufficiently tight dimensional tolerances, and the automated processes likewise must be consistent and repeatable because they often feed other automated processes.

Shopping Cart Manufacturing Basics

Shopping cart construction hasn’t changed substantially over the decades. The basket is made in three basic steps: workers cut a series of wires to length and lay them out in the required spacing, use resistance welding to join them, then fold the assembly to form the basket. Other workers cut, bend, and punch the tube to form the frame. The last two steps are assembling the basket to the frame and affixing the wheels. From there, the shopping cart goes through a manual inspection process to ensure that all four wheels contact the ground—which prevents the dreaded phenomenon in which one wheel twirls erratically and uselessly—and then the cart is sent off for a final inspection before shipping.

However, the manufacturing processes used at Technibilt have changed, and changed markedly, over the past few decades.

Finding the Seam. In bending tube, a primary concern is proper orientation of the weld seam. When the weld seam is aligned with the bend axis, splits happen. The weld seam is harder than the parent material, so whether the seam is subjected to tension or compression, it’s not likely to withstand the stress. Preventing this is a matter of finding the weld seam and rotating the tube so the weld seam is aligned with the neutral axis.

One of Technibilt’s early weld seam detectors was a mechanical system that relied on a bit of weld flash on the ID. The bender’s mandrel was equipped with a spring-loaded blade; after the mandrel was inserted, the tube would rotate until it contacted the blade.

“It needed 0.012 to 0.018 in. of weld flash to work,” said Plant Manager Alan Deal. The problem was consistency. Too little weld flash made the seam impossible to find; too much weld flash made the mandrel impossible to insert. Relying on a specific thickness of weld flash is difficult because it varies from one lot to the next and even from one tube to the next. Technibilt would need a different technology to automate this task.

Bending the Tube. “We’re on our third or fourth generation of tube bending equipment,” Deal said. In the mid-1980s, the company made shopping cart frames from several short lengths of tube. The process comprised cutting tubes to length, making holes on a punching machine, bending them on a vertical bender, and welding the tubes together to make an assembly. Around 1991 or so, the engineering team came up with a new way: The frame would be made from one long lengths of bent tubing, each with five or six bends per side. The bending process would be more complex, and while anything more complex is prone to a drawback or two, the engineering team was confident that it would be an improvement. The team anticipated that eliminating the time needed for welding several short tubes together would overcome any drawbacks, expected or not. Ultimately the new process was a big advancement in bending and welding time, but this isn’t to say that the first cycle went smoothly as expected. The primary lesson learned was the importance of bending clearance.

“The first bend broke a light,” Deal said.

After establishing the proper clearance, the company got up to speed and soon was making 300 frames a day. However, this didn’t stop the company from searching for a better way to bend tubing, and it found one in a twin-head bender. This allowed it to make the entire frame from a single tube, which doubled its output to 600 frames per day.

Like its predecessor benders, the twin-head bender was a hydraulic unit. Capable and robust, hydraulic units have a drawback in process consistency. As the hydraulic fluid temperature changes, the bender needs adjustment to keep the bends consistent. Hydraulic units also require fluid changes from time to time and they leak in two ways, pooling on the floor or shooting spectacular distances, so hydraulic system users spend no small amount of time and effort on hydraulic fluid containment and spill remediation.

As servo drive technology emerged as a viable option for industrial machines, Technibilt realized that it had a new option if it chose to go that route. The technology—a combination of servo motor and controller—uses a closed-loop control system to provide a precise and consistent process, which provides improved dimensional consistency from one part to the next.

Punching the Holes. Making a hole or two isn’t necessarily a problem, but locating, making, and verifying a large number of holes can be a hair-raising task. Technibilt traveled down this path on an earlier occasion when it automated a punching process. Shopping cart frames need a substantial number of punched holes, and it was a challenge to locate the tube properly, punch the hole, then verify that the hole had been punched. The system was too complex, relying on a large number of sensors and switches, and it wasn’t long before sensors were breaking off. A second system had too few sensors; it occasionally made bad product. Technibilt learned from these systems to stake out the middle ground.

Keeping it Simple. You have to be careful with automation,” Deal said. “If a system like this has a sensor on every component—every gripper, every die, and so on—it adds to the complexity of the software that runs it, and it adds to the difficulty in troubleshooting it when things go wrong,” Deal said. “Everywhere you have a switch, you need the software to generate an error code when the switch doesn’t close. When the system stops running, you need a troubleshooter who understands the software—you need someone who can think like the machine thinks.” This might not be a big problem in Cleveland, Detroit, or Chicago, but in Newton, N.C., population 13,000, the small local workforce isn’t teeming with this skill.

Likewise manufacturers benefit from a system that has simplicity in tooling changeovers. At first blush, making fast, frequent changeovers doesn’t sound too important for shopping carts, because they’re all pretty much the same, aren’t they? Well, no, they’re not.

The number of shopping cart designs made by Technibilt is in the dozens and climbing. This relates to changing shopping habits as much as it does to the company’s growing market share.

“The shopping experience has changed a lot,” Deal said. “Years ago, many people went grocery shopping twice a month. These days, many go several times a week, and some people shop for groceries every day.” Shopping more frequently means smaller purchases. For many shoppers, the traditional shopping cart is too big and the handheld basket gets a little too heavy, so small shopping carts are increasingly common.

Another trend in shopping cart design is a shorter wheelbase. As the population ages, more people rely on walkers. A cart with a shorter wheelbase handles more like a walker and is a little easier to maneuver than a standard-length cart. Rather than one big basket, this type has two baskets, one low and one high. Another design, one intended to ease the burden of lifting groceries from a deep basket or low basket, has a single, shallow basket.

Technibilt is responding to these trends by transitioning from 2-D to 3-D wire benders. The additional axis frees the engineering team to pursue new possibilities in cart design. All this means that as time goes on, Technibilt adds one to two new cart designs each year. Because the company is committed to supporting the many established retailers that need to replace a few legacy carts a year, its attrition rate is zero. The company made about 10 models 30 years ago; these days it makes more than 60.

To keep up with the many designs, the company took an early foray into automation regarding its shopping cart handles. Although the system ran well, the changeover time was about two hours. This was entirely too long, effectively wiping out the productivity improvement it gained from the system.

The company never intended to make every frame design on its new automated system, but when the project was in the planning phase, the goal was to use it for as many of its biggest sellers as possible. The company makes 10 unique frames and 10 unique handles every day. Changeover time is critical.

Looking for Better Shopping Cart Manufacturing Processes

O.M.G. di Menon Guglielmo, Vicenza, Italy, put together a plan to develop an automated manufacturing cell for Technibilt. O.M.G. makes equipment for fabricating and machining tube, including bending (twin-head and roll benders), swaging, drilling, tapping, milling, turning, punching, and cutting. Its manufacturing cells include transfer systems for fabricating processes and robots for assembly work. Using this experience as a foundation, the company proposed a cell that would retrieve tube from a bundle, load it into a punching machine, punch the necessary holes, remove it from the punching machine, detect the weld seam, orient the tube for bending, load the tube into the bender, bend it, unload the tube from the bender, and move it to a storage rack.

Before O.M.G. could get started, Technibilt had quite a bit of preparation to do, which gave its engineering staff an idea of just how much time and effort would go into developing this manufacturing cell.

“Our part drawings that had enough information for manufacturing, but they didn’t have enough information for designing an automated system,” Deal said. Technibilt had to convert from 2-D to 3-D part drawings, because an undertaking like this one requires more information than 2-D drawings provide.

System Complexity. Rather than rely on a multitude of sensors and switches, the new system runs largely on a timed sequence. In addition to eliminating the extra hardware, this type of system is more streamlined, going smoothly from one step to the next rather than waiting on an input from a sensor or a switch.

The engineers at O.M.G. designed the system for downtime simplicity as well. To keep up with the demands of the industry, Technibilt’s new system easily handles 10 changeovers a day.

Seam Detection. The system’s original third-party seam detector was based on a camera that detected the color difference between the parent material and the weld material. The drawback was that the camera needed a substantial color difference, and the color difference varied among Technibilt’s suppliers. Technibilt came up with two potential solutions. The first was to adjust the camera every time it processed a batch of material from a different supplier; the second was to set the camera for a worst-case scenario. Both strategies delivered good results, but as time went on, Technibilt discovered a laser-based system that is much more consistent.

The laser-based system didn’t resolve every issue. One that remains concerns the amount of bow in the raw material. On occasion Technibilt processes a length of tube that is bowed to the point that the laser beam doesn’t reflect back to the laser’s receiver—it ends up going every other direction, of course—so some tubes have to be scrapped. Even so, it provides much more consistent results than the camera did, at one-tenth the cost.

Bending. The new system uses a twin-head bender, which is ideal for making symmetric parts, and it uses servo technology for bend consistency. The difference in bend consistency isn’t much to a casual observer, but to a robotic welder, the difference is substantial.

“We’ve had robotic welders for 10 or 12 years,” Deal said. “We used to use them to weld parts that had two or three bends.” That was the maximum. Since the company has been using electric benders, the bend tolerances are so close that the robots can weld 12-bend parts.

Angling for Supermarket Share

Grocery cart manufacturers don’t spend a lot of time worrying about domestic competition. Technibilt has just two U.S.-based competitors, and new contenders aren’t likely to emerge anytime soon. Making a single grocery cart isn’t all that difficult, but an upstart would have to master dozens of designs. Another barrier to entry is sheer volume. Technibilt ships 800,000 carts each year. It would be a steep challenge for a new competitor to establish a toehold in this industry.

However, this doesn’t mean that the company can rest. The company’s continuous investments in machines and software have yielded extraordinary productivity improvements.

“Thirty years ago, we had about 300 people making 150,000 carts each year,” Deal said. “These days we have about 300 people making 800,000 carts every year.”

This has kept it in business as the industry consolidated from six suppliers down to three. It also has kept out foreign competition, which is quite an achievement, considering that many of the processes used to build grocery carts require manual labor, an area in which many foreign competitors have a cost advantage.

In fact, Technibilt has done much more than keep out imports. The company exports shopping carts to retailers in Mexico, where the average factory wage is roughly 10 percent of the U.S. factory wage.

O.M.G. di Menon Guglielmo is represented in the U.S. by Innovative Tube Equipment Corp., 1807 W. Sunnyside Ave., Chicago, IL 60640, 866-574-8823, info@tube-equipment.com, www.tube-equipment.com.

Technibilt, 700 Technibilt Drive, P.O. Box 310, Newton, NC 28658, 828-464-7388, technibilt.com

Big Hearts, Niche Shopping Carts

The executive team at Technibilt showed what it was made of when it had an opportunity to give something back to the retail community. Parent-turned-inventor Drew Ann Long devised a shopping cart for children and adults with special needs. Handling a wheelchair and a shopping cart simultaneously is inconvenient at best, and as Long’s special-needs daughter outgrew the traditional shopping cart, Long realized that a typical shopping experience would soon be difficult and possibly out of reach for her daughter.

Long came up with a design that incorporates a rear-facing seat big enough for an adult and outfitted with a safety harness so a parent or other caregiver can shop with confidence. The cart has brakes on all four wheels to keep the cart stationary and it has handles to assist in getting into and out of the seat. This is far more than a shopping cart. For people who use one, it’s mobility, and mobility is freedom.

Long got a patent and contacted Technibilt about turning her idea into a reality.

The only drawback to manufacturing such a cart is cost justification. This is a high-volume industry, one in which a typical shipment is hundreds of units, so a product that ships in ones or twos can’t be justified by any reasonable accounting practice. Fortunately for the many people who need mobility assistance to participate in the retail shopping experience, the executives at Technibilt ignored the balance sheet, helped Long refine the concept for manufacturability, and turned the concept into reality. The cart is easy to spot—just look for a shopping cart with a rear-facing seat adorned with a yellow heart and labeled Caroline’s Cart™. Technibilt even tracks sales by store, so anyone interested in using one can search for stores with Caroline’s Cart at www.carolinescart.com/find-a-store.