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issue: April 2003 APPLIANCE Magazine

Assembly & Fastening
Putting It Together


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Lisa Bonnema, Managing Editor

As product cycles get shorter and the word "inventory" becomes taboo, manufacturers are looking for new options when it comes to appliance assembly, hoping to find a synergy between the two crucial aspects of a quality appliance - its design and how it's made.

During the last few years, it seems the industry buzzword regarding appliance assembly is flexibility. According to equipment suppliers, there are several reasons this term has become commonplace on plant floors.

"The newer machine design trend is to be able to change over [tooling] in minutes, maybe simply in the software," explains Pete Doyon, vice president of Product Management for Schleuniger (Manchester, NH, U.S.). "Batch sizes have gone down too, so you can't justify having a machine set up and a long changeover. Also, with all of the manufacturing philosophies, people don't want inventory on the floor. You only want to build today what you ship today. So the machines have to be able to be flexible to be used for a number of jobs. But batch sizes are really what have pushed the pressure on the changeover times."


Bosch Rexroth's newest generation of intelligent SCARA robots - turboscara SR4, SR6, and SR8 robots - offer appliance makers several advantages, including simple programming in a Windows(R) environment, TCP/IP interfaces for data transfer and remote maintenance, and customer-specific man-machine interfacing through Visual Basic or C++ programming. The robots are said to be optimized for fast, precise, and flexible assembly in cleanroom, dust-proof, or standard versions.

David O'Nions, general manager of Siemens Dematic Assembly Systems (Birmingham, AL, U.S.) says that with the current economic conditions, it is also an issue of cost. "The biggest thing right now is the amount of capital investment, especially in the U.S., in this kind of line. You're talking multi-millions of dollars. In order for someone to justify that process versus foreign labor costs right now, we have to offer very flexible lines," he explains. "If a customer just wanted to build a random product order group, they literally could. The goal is to develop systems where there is either little or zero changeover time for the customer to achieve that. That is the ultimate justification right now. The only people that pretty much can afford to do it are the ones that are given the highest level of flexibility."

The obvious question surfaces: What solutions are available that will make my assembly processes more flexible and more cost effective? The answer to that question, however, isn't easy: the options are many.

 

 

Adhesive Statistics

U.S. shipments of pressure-sensitive (PS) tapes are projected to increase 2.8 percent annually through 2006, according to The Freedonia Group, Inc.

PS tape leaders are expected to include double-coated, adhesive transfer, and certain plastic film-backed products. According to Freedonia, growth industries such as electronics and telecommunications are disproportionately using double-coated tapes.

Getting Equipped

Appliance makers - especially those with varied product lines - have much to consider when choosing assembly equipment. Making productive decisions means carefully reviewing the newest technologies and trends while keeping in mind specific applications.

"The type of manufacturing equipment [available] varies as widely as the applications do. If you consider appliances to range in size from, say, electric toothbrushes to refrigerators and dishwashers, you also cover a massive range of different manufacturing strategies," notes Kevin Gingerich, marketing manager at Bosch Rexroth, Linear Motion and Assembly Technologies (Buchanan, MI, U.S.). "In some cases, that might mean manual assembly stations linked with conveyors; in others, it might mean full automation with our turboscara and multi-axis Cartesian robots - or it might mean a mix of the two."

Most assembly equipment suppliers agree that a major trend right now is to offer equipment with increased intelligence. Smarter equipment means less labor, increased productivity, and higher quality.

"All assembly equipment has improved substantially over the years, as the needs of manufacturers get fed back into the engineering departments of capital equipment suppliers. Robots are a great example," says Mr. Gingerich. "The turboscara robots we're selling now are technological light years ahead of the SCARA robot invented by Bosch 30 years ago, and even those sold 10 years ago."

He explains: "For example, all programming software is now Windows-based and has TCP/IP connectivity, so they can even be programmed and tested via the Internet. Let's say a customer is installing a robot in California and is not sure about a certain programming sequence. They can call us in Michigan, give us the access code to their robot, and we can troubleshoot their program online. Capabilities like these not only cut hours or days out of robot installation, they add convenience and cut costs."

Mr. Gingerich adds that many new robots now have absolute encoders so that the robot always knows where it is in its operating cycle. "You don't need to 're-home' the robot every time you power it," he says.

Siemens Dematic offers an intelligent palette-based conveyor system that utilizes radio frequency (RF) tags and is said to allow for quick changeover and flexibility. "The pallet (or fixture) contains universal tooling, where we are perhaps given 10 or 20 products from the customer that they would like to build down the same line, and we build the tooling - either adjustable or very, very quickly changeable - to carry multiple products," explains Mr. O'Nions. The system has several appliance applications, including range, washing machine, refrigerator, air-conditioner, furnace, and dryer production.

"For example, on a range, we're carrying anything from single ovens to very wide double-oven assemblies with cooktops, all on the same pallet," says Mr. O'Nions. "The way we have achieved that is 'stair-step tooling,' where the largest product sits at the highest level, and the smallest product is at the lowest point of the stair step. Each stair step as you go down the tooling is a different product outline. So we achieved, in this case, zero changeover time."

He adds that the specialty is not so much the mechanical solution, but the software solution. "We carry intelligence on the pallet usually in the form of an RF tag that carries the data for the particular product. So we might be only carrying a serial number to start off with, which would be tied to the system. Then we would automatically route the pallet to only the operations that were required for that specific product. That in itself is nothing revolutionary, it's just done on a very large scale, and we tie that in with recording the test results. With a range, for example, you measure gas flow, comparisons, electrical tests, etc. We actually carry the test results on the RF tag until we get to the end of the system," Mr. O'Nions says.

When the appliance reaches the end of the process, the tag's information is downloaded to a host computer system, which records the results. The advantage, Mr. O'Nions explains, is that if a manufacturer ever has testing issues or warranty issues, it has the individual test results of that particular unit by serial number. In addition, once the information is downloaded, the RF tag's memory is wiped clean and can be used again for the next run.

Of course, there are other tactics an appliance producer can use to add flexibility. Another trend is the concept of modularity. While traditional fixed conveyors continue to be the best option for some producers, according to Dynamic Conveyor Corporation (Muskegon, MI, U.S.), light- and medium-duty manufacturing applications could benefit by upgrading to flexible, reusable modular systems. The latest modular conveyor technologies, the company says, can make dramatic improvements in uptime, agility, overhead, ROI, and other critical business issues.

According to Dynamic Conveyor, the term "modular" needs to be clarified in order for a manufacturer to realize the true benefits. Many so-called modular conveyors and accessories, it says, are actually sectional units or adaptable accessories, and may suit only limited production line requirements. While such products, including special belts and flights, may indeed offer significant advantages, the benefits can become much more substantial when the entire conveyor system is designed to be totally modular, the company says.



Henkel Loctite (Rocky Hill, CT, U.S.) offers two patented, industrial-grade, hand-held pneumatic spray applicators for dispensing 1.75-in diam areas with hot-melt adhesives. The Hysol 175-Spray unit achieves 180°C for dispensing EVA hot melts, while the Hysol 175-Spray HT reaches 195°C for polyamide hot-melt dispensing. Both 500-W units feature adjustable flow controls to tailor spray patterns and are said to be ergonomically designed for operator comfort and application control. In addition, both applicators feature automatic end-cycle purge to prevent nozzle clogs, a high melt rate for maximum output, and a fixed-precision thermostat temperature control for consistent heating.

Fastening is certainly one area of appliance assembly that requires manufacturers to carefully weigh solution benefits and drawbacks. Options range from clinching and spot welding (see the sidebar, "The Advantages of Clinching") to self-piercing fasteners and standard rivets.

One joining alternative that is gaining a lot of attention is the self-piercing fastener. AKH Inc. (Indianapolis, IN, U.S.) recently introduced its new Double Headed FAS-NER(R) for appliance applications. The new FAS-NER adds an external head to AKH's existing Headed FAS-NER, giving the rivet additional surface area.

AKH's existing FAS-NER system is a punch-and-die operation that automatically feeds, punches, inserts, and locks the company's patented FAS-NER to form a flush joint.


The pneumatically operated 752V-SS valve from EFD Inc. is said to provide exceptional accuracy and reliability when dispensing UV-cure adhesives on automated and semi-automated assembly lines. Here it dispenses adhesive into a heart pump for a medical application. The valve's design features no seals or O-rings to wear out and leak. Instead, a precision diaphragm rated for tens of millions of cycles reportedly ensures long, trouble-free operation. A fast, clean cutoff at the end of each cycle is said to eliminate waste, dripping, and cosmetic damage.

The new Double Headed FAS-NER works the same as the original FAS-NER, explains Dave Caulk, AKH sales manager. "With this new FAS-NER, we've actually taken that second-generation of our FAS-NER with the head end on it - the one end larger diameter than the smaller punch end - and we just basically put a button cap on top to capture more material for the thinner top layer so it won't pull out," he says. "For applications where the flush surface is not a requirement, this Double Headed FAS-NER is going to give us additional holding capability."

According to Mr. Caulk, this new FAS-NER is appropriate for any application that would have a thin, wrapper material, most notably refrigerator cabinets.
If cost is an issue, Wayne Mundsinger, director or Product Application at Driv-Lok, Inc. (Sycamore, IL, U.S.) suggests using a simple grooved pin. "[Our] grooved pins can replace a higher cost fastener while also providing lower assembly costs in many applications," he says. "Historically, many engineers have chosen ground dowel pins as their mating part locator solution. This requires an expensive pin and drilled and reamed hole. A…grooved pin can perform this function without the cost of a reamed hole."

Uses within the appliance industry include hinges, timers, part-to-part locators, spring anchors, and motor drives. Because grooved pins are shear resistant, they are said to be ideally suited for use in locations without a high degree of end load.
According to Ted Schaumburg, Driv-Lok's director of Research and Development, the grooves of a grooved pin are formed by a swaging operation. Three tools penetrate the nominal diameter of the metal at 120-degree intervals.

This penetration displaces a controlled amount of metal to each side of the grooving tool, forming a raised portion along the side of each groove. When the grooved pin is used, the hole into which the pin is to be inserted is drilled a few thousandths larger than the nominal diameter of the pin.

Inserting the grooved pin into a hole compresses the expanded portion of the metal, generating radial holding forces. These radial forces lock the pin securely into the drilled hole. However, Mr. Schaumburg explains that it only produces limited radial forces because interference is only between the hole and the expanded diameter. This system, he notes, allows the hole size to vary in diameter without generating detrimental radial stresses.

The Assembly Influence

It's no secret that appliance design and production need to go hand in hand in order to achieve today's demand for quick turnaround. While this may require some customization on the supplier's part, OEMs may also find that in order to get the most cost-effective solution, flexibility needs to go both ways.
"There's only a small portion of our appliance products that are standard. Most of the time we sell a dedicated piece of equipment," notes Steve Sawdon, president of BTM Corp. "We have to consider the shape of the customer's part, which depends on how it is designed."

Therefore, he says, it is crucial that manufacturers design their products with assembly in mind. "Sometimes we ask them to redesign their products too. That will help us reduce the tooling cost. We also provide them with flange size and clearance specifications that we like them to have in order to make lower-cost machines to join their products."

Sometimes the relationship between assembly and design is so strong that one literally dictates the other. An example of this, according to Mr. Doyon of Schleuniger, is the use of flexible flat cable (FFC) in appliance design. The cable, currently being used in Europe for automotive applications, also offers major benefits to appliance makers, he explains. The cable is a light-weight alternative to round wire, which makes it ideal for portable appliances and consumer electronic products. It also offers production advantages. "The appliance industry is moving toward using more FFC in manufacturing because it allows for mass termination, which means labor savings, flexibility, and increased quality," explains Mr. Doyon. "The fact that you can mass terminate means that instead of running, say, 12 individual wires and then terminating them and putting them in a connector housing, you basically run one piece and terminate on both ends and just plug and play."

The holdup, according to Mr. Doyon, is the capital investment needed to process the cable. "There is a cost up front to get capability to process FFC. Most appliance makers outsource their wire harness assemblies, so as the sub-contractors gain capability in that area, then it won't be so cost-prohibitive to start using these new technologies in the appliance design," he says.

It is important to note that the equipment is available, Mr. Doyon adds. Schleuniger currently offers FFC Processing Systems that can be customized for any application. "What happens is the customer will have an application, and they'll send us samples and specs. We'll review it, and we'll build a custom system for their application, based on standard modules," he explains. "So, rather than have to redesign from scratch every time, we know that we need to transport a flat cable up to 3-in wide. Once we know what the customer's needs are, we can mount the individual process stations on the various module, and it all ties together with a standard software we developed."

Mr. Doyon says that until appliance OEMs and wire harness suppliers base their decision on value instead of expense, the industry will have to wait. "Some OEMs are even saying, 'We want to use this in our next-generation design,' but the wire harness manufacturers will quote a really low price to do it in the current technology, which is discrete single wires. So, on paper, it looks cost-prohibitive to the OEMs to jump to that new technology," he explains. "But ultimately, there will be some sub-contractors that make an investment up front, and they will go out and look for work. It will happen."

One fastening technique that is rapidly gaining acceptance among appliance producers is clinching, the process of creating a joint via punching and squeezing, without the need for additional fasteners such as screws, rivets, or pins.

According to ATTEXOR, Inc., clinching offers several advantages over other fastening methods, specifically spot welding. "While it is difficult to tell whether a spot weld is a good one or whether a screw thread has been stripped, the quality of a clinched joint can be controlled at any point in time without destroying or disturbing the assembled structure," explains Dr. Hans Bergkvist, president of ATTEXOR Inc. (Springfield, MA, U.S.) and ATTEXOR Tools (Ecublens/Lausanne, Switzerland). "This has been one of the most important arguments in favor of clinching, as well as the fact that clinching works perfectly on pre-coated, enameled, and galvanized material found in the appliance industry without destroying the surface finish."

One of the main advantages of clinching over spot welding is that clinching can easily join material couples that are difficult to weld, Dr. Bergkvist explains. "It is a well-known problem that the punches tend to stick in aluminum, particularly in larger thicknesses, which can be a major difficulty when low-weight aluminum profiles are to be joined with sheet metal. Various ways of solving this drawback have been tried, such as using a 50/50 alcohol and water spray on the punch side. This mixture has the advantage of evaporating without leaving any traces that could have a negative influence on subsequent painting operations. However, installing and maintaining the spray equipment means additional complications and costs."

As an alternative, ATTEXOR has developed patented punch geometries that are said to significantly reduce the sticking problems. These punch geometries use double-stroke clinching, the company's proprietary clinching technology.
Dr. Bergkvist also believes that clinching equipment such as his POT CLINCH(R) Tiger line and the SPOT CLINCH(R) Grip line will replace stitchfolding machines in applications like vending machines, commercial refrigerators, and washing machines. One of the main reasons for this, he says, is operator safety.

"In the stitchfolding process, tabs are cut out of the overlapping material sheets, and they are then folded back to give a staple-like joint where the staples are made from the base material itself. While this process is very fast, it presents additional drawbacks over the risk for hand injuries," Dr. Bergkvist explains. "Operating quickly means that the tool often gets moved laterally before the punches have been fully retracted and as a result, they break. Even if replacing them is rapid, the cost for punches can run up to a considerable amount. Additionally, a stitchfold joint is not foam tight, requiring tape masking of the joined material lips before foam is injected between the outer shell of an appliance and the inner lining."

Steve Sawdon, president of BTM Corporation (Marysville, MI, U.S.) agrees that recent advancements in clinching have made it the ideal fastening method in most cases. Specifically, new tooling materials have allowed his company to further improve its Tog-L-LOC(R) clinching system.

One example of the system's expanded capabilities was a microwave application performed by BTM's German distributor. "The microwave was joined together with the Tog-L-LOC clinching process even though it had some stainless steel components in its wave guide and body," he says. "That is fairly new because stainless steel has traditionally been difficult to join. However, with the advent of some new tool steels, we've been able to accomplish sufficient joint strength, and the tooling is durable enough that it can join this harder stainless steel together and can give the customer acceptable tool life, even in the range of 30,000-50,000 cycles per tool."

According to Mr. Sawdon, because of the tougher tooling, BTM can now join most metals, including ferritic stainless steel and austenitic stainless steel, as well as more ductile metals such as aluminum, copper, brass, and coated steels.

 

For more than 20 years, Sundance Spas, a Chino, CA, U.S.-based manufacturer of acrylic hot tubs for the global market, has accumulated an array of awards and endorsements based on the quality, reliability, and innovations of its products. The company has always credited part of its success to the way it assembles its products.

That's a major reason why the hot tub manufacturer decided to upgrade to a more efficient method of fastening its hoses to plastic fittings. The company had been using gluing as their joining method, which was not only messy, but time consuming.

The gluing process included applying the primer to the fitting, applying glue to the male and female sides, setting the hose to the PVC, and waiting for the glue to dry. In addition, hoses had to be placed on the inside of the fittings, which increased the chance of error because it was often difficult to get exact positioning on how deep the hose was placed. Inspectors also had a difficult time determining whether the proper amount of glue had been used, and if the hose was seated completely against the fitting socket or if had partially backed out.

Sundance then discovered Rotor Clamp's self-compensating constant tension band hose clamps (CTBs). The CTB solution not only enhanced spa performance and increased efficiency by cutting down on defective parts, it also sped up assembly, according to Bruce Walters, director of Product Marketing at Rotor Clamp (Somerset, NJ, U.S.). "Their goal was to save both time and money during manufacturing," Mr. Walter says.

The CTBs made it possible for the hoses to be connected to the outside. Reducing the number of steps made the manufacturing process more efficient and constant. In addition, the design utilizing the CTBs allowed for more flexibility by offering a greater range of tolerance on the hose and fitting specification.

Adjustments on the PVC application were viable with the CTBs, whereas gluing was permanent and resulted in lost resources and ruined fittings if anything ever needed to be adjusted or replaced.


Another major advantage Sundance received from the CTBs was that they eliminated any chances of leakage, says Mr. Walters. The clamps compensate for changes in the joint diameter due to compression set in a hose. This feature eliminates leaks and the need to re-torque the clamp.

The clamps can also be reused. "With any spa or white goods appliance, our clamps are not a 'one-time' item [to be] thrown away," explains Mr. Walters. "Should a warranty issue arise and a repair person is needed to replace a hose, the original clamp can be reused. Crimp-style clamps, however, must be thrown away and a new one must be installed. Old-fashioned screw type clamps can be under- or over-tightened, possibly calling for another service call to the customer. Our constant tension, self-compensating hose clamps are specifically made for each hose outer diameter, making installation fool proof."

There were three major areas of improvement with the barb and clamp method. First, instant-use plumbing eliminated the hour-long wait required for solvent welds to dry before factory testing. In addition, workers no longer were exposed to VOC (volatile organic chemicals) in solvent welding. Connections also appeared clean and neat.

According to Mr. Walters, there was only one challenge when implementing the CTBs into Sundance's assembly process. "The main challenge, like anything new being introduced to an assembly line product, was change. When people on an assembly [line] are used to doing something, they are not as open to change," explains Mr. Walters. "By actually going out on the line with the clamps and special pliers and showing the worker the ease of installation and cleanliness of a steel clamp versus messy glue, the process and ease of installation sold itself."

 

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