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issue: May 2004 APPLIANCE European Edition

Assembly & Fastening
Assembling the Evolving Appliance


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by David Simpson, contributing editor

Appliance producers and their assembly and fastening suppliers are responding to thinner metals, pre-painted and stainless steel, and other design changes in the ever-evolving appliance industry.

Montage et attaches d’appareils évolutifs:
Le mode de construction d’un appareil se renouvelle rapidement en raison des changements tout aussi rapides du produit, du lieu de fabrication et du changement de propriétaire de l’entreprise. Les fabricants d’appareils et les fournisseurs des éléments de montage et d’attaches s’adaptent à cette situation en proposant des métaux plus fins, de l’acier inoxydable et prépeint entre autres nouveaux designs propres à l’industrie de l’appareillage en évolution permanente.
Montage und Befestigung:
Montage und Befestigung für die Geräteentwicklung: Aufgrund schneller Änderungen bei Modellen, Fabrikstandorten und Firmenbesitzverhältnissen ändert sich die Gerätekonstruktion ständig. Die Gerätehersteller und ihre Zulieferer für Montage und Befestigung reagieren mit dünneren Metallen, vorlackiertem und rostfreiem Stahl und anderen Änderungen im Design auf die sich immer weiter entwickelnde Geräte-Industrie.
Assemblaggio e Fissaggio per Apparecchi in Evoluzione:
A causa dei rapidi cambiamenti nei modelli, siti di produzione, e proprietà dell’Azienda, il modo in cui un apparecchio è costruito cambia costantemente. I produttori di apparecchi ed i loro fornitori di assemblaggio e fissaggio rispondono fornendo metalli più sottili, acciaio inossidabile e precedentemente sottoposto a trattamento colorante ed altri cambiamenti del modello nell’industria costantemente in evoluzione degli apparecchi.

The times, they are a-changin'. Rapid change in models, manufacturing locations, and company ownership has been a given in the appliance industry for years. Long gone are the days when companies regularly came out with new models every 5 years.


Alloy Fasteners, Inc. (Cranston, RI, U.S.) supplies a range of fasteners for appliance production and installation. The company offers stainless steel fasteners, washers, nuts, and bolts, all of which are available with specialized coatings for superior corrosion protection.
In most segments of the industry, competition is torrid, and pressure is intense to meet market interest with frequent model changes. At the same time, manufacturers are working with suppliers to incorporate materials, designs, and assembly techniques aimed at keeping assembly costs down and quality up.

For instance, some of today's appliance models use thinner sheet metal panels. While keeping material costs and weight to a minimum, such panels have reportedly lead to problems with standard sheet metal screws not holding joints tightly. One solution has been developed by Leland Powell Fasteners, Inc. (Martin, TN, U.S.). Its Grip-Lite screws are said to provide improved drive-to-strip ratios with precision-controlled threads under the head, increased strip-out ratio with full formed thread within one pitch of the head, and increased strip-out torque with special serrations under the head. In addition, a radius screw point reportedly eliminates cutting wire insulation in the assembly, preventing the screw from drilling its own hole if the assembly is misaligned and eliminating sharp points that can cause injuries during assembly.  

On the quality front, the company notes that fewer part numbers means less chance of the wrong screw arriving at the assembly line. With this in mind, it works with manufacturers to standardize fasteners. In one case, it reports that more than 100 different thin sheet metal applications were re-specified to use a single size of Grip-Lite screw and in some cases, even eliminating nuts, clips, or tapped holes.


A new approach is aimed at compressor mounting in base pans for window units, condenser split systems, and other types of A/C systems. The approach, from Richard Associates (Johnson City, TN, U.S.) obsoletes sleeves, shoulder bolts, and welding of weld bolts. It also permits use of pre-painted sheet metal, which can result in dollar savings in welding and painting equipment. The mounting bolt is a combination threaded bolt and stud that is threaded up through an extruded hole in the base pan. Serrations and seal rings under the head prohibit thread stripout and water leaks in window unit base pans, using the splash cooling reservoir in the pan. Also, one standard length will fit many compressor sizes from one to five tons. Once the compressor is set in place, a push nut locks down on the stud portion of the bolt, on top of the grommet, and keeps the compressor secure in place. 
Pre-Paint Impact

The trend toward use of pre-coated sheet metal, aluminum, stainless steel, and plastics has sharply cut traditional resistance or spot welding in major appliance assembly. In this environment, ATTEXOR Inc. (Springfield, MA, U.S.) reports that clinching continues to gain market share. Clinching is a fastener-less assembly method, where a rivet-like joint is produced from the sheets and profiles to be assembled through a cold-flow punching and squeezing action. In addition to avoiding the cost for buying, sorting, and feeding separate fasteners like screws or rivets, the company points out that clinching is clean and silent, as well as fast, with assembly cycle times less than 1 sec. No sparks or fumes or strong electromagnetic fields are associated with clinching.

"We expect clinching to be the dominating assembly method for major appliances in the years to come," notes Hans Bergkvist, ATTEXOR president and CEO. "We are also probably going to see more hybrid assembly, where the point connections of clinching are complemented by the line of surface bonding offered by various types of adhesives. We are working together with leading actors in the adhesives arena to further assess the key parameters when it comes to assembly by clinching and adhesives in combination."

Wide Adhesives Distribution

According to a study from the Adhesive and Sealant Council, the estimated overall volume growth rate for adhesives used in appliances will be 2.5 percent in the next 2 years. The Council points out that most adhesives are used for bonding insulation, labeling, decorative trim, and nameplates. Structural adhesives have found limited use because the need for repair and replacement has generally relied on the use of screws, nuts, and bolts. However, an increase in the use of dissimilar substrates, plastics, and thinner gauge materials in construction may spur additional adhesive uses.

The Mortorq spiral drive system developed by Phillips Screw Company (Wakefield, MA, U.S.) was introduced into the aerospace industry more than 5 years ago. The technology is now applied to other markets, where it reportedly can create an assembly that is smaller, lighter, and cheaper. One advantage is that because of the reduced head height, it is now possible to use thinner materials and still hide the fastener in a shallower countersink. According to the company, without a countersunk screw, the shallower head height will create more clearance for internal parts and more design flexibility.
Adhesives suppliers point out that the ability of an adhesive to distribute a load over its entire bond area rather than in a limited area - as with a mechanical fastener, spot weld, clinch, or rivet - may lead to improved assembly durability and fatigue resistance. "We have a demonstration of 'Bolts versus Bonds' which shows an assembly that is joined with bolts and adhesives being tested to failure," says Scott R. Tremblay, application engineering, Henkel Loctite Corporation (Rocky Hill, CT, U.S.). "The bolted section of the assembly fails before the bonded section due to the fact that the force on the bolted section is concentrated on the leading edge of the bolt shaft, while the adhesive distributes the weight over the entire bond area of the joint."

Mechanical fasteners, however, are said to offer benefits over adhesives at very elevated temperatures. Once temperatures exceed 400°F, structural adhesive options diminish rapidly. But for many applications, adhesive processes work well and may offer cost benefits over mechanical fasteners because of lower total material costs and the elimination of tooling costs associated with the joining operation. Also, the number of parts (bolts, nuts, washers, rivets, etc.) used in the manufacturing is minimized, and the elimination of inventorying and stocking these parts can reduce complexity. In addition, the ability to automate the adhesive assembly process frequently lowers labor costs.

Master Bond Inc. (Hackensack, NJ, U.S.) believes that the wider usage of adhesive technologies for the assembly of appliances has the promise of reducing direct manufacturing costs by as much as 25 to 30 percent due largely to the increasing employment of plastics and elastomers in the design and assembly of appliances. "In the last few years the performance and especially durability in service of newly developed plastics and elastomers has greatly improved," says James Brenner, president. "Designers and hence appliance producers have gained better awareness and recognition of the potential of these improved materials for appliance production."

In the adhesives and gaskets area, many companies are demanding operator-free equipment, with the exception of loading and unloading products, observes Don Leone of Ashby Cross Company (Newburyport, MA, U.S.). The reason, he says, comes down to one word: error. The greater the human intervention, the greater the error rate.

He points out a continued drive toward automatic foam dispensing for gaskets. More generally, computer technology remains important, and his company continues to increase its PC- (microprocessor-) based equipment offerings. "This further drives the equipment to operator-free-operation," Mr. Leone says.

"For some applications it is sufficient to dispense the adhesive directly from the bottle or tube onto the surfaces to be adhered," adds Mr. Tremblay of Henkel Loctite. "In other cases, more precise and automated dispensing and curing is required. To meet this need, adhesive suppliers have developed equipment especially designed to make application of products economical, fast, precise, and clean. The benefits of automated assembly include higher production rates, consistent dispensing and curing, reduced labor, higher production yields to minimize scrap, and improved quality and aesthetics."

Pre-Configured Assembly

Automation continues to be an important part of appliance assembly, and a key component of this involves getting the automated manufacturing process established quickly. To meet this need, many automation suppliers are starting to provide pre-configured and pre-assembled equipment that can be installed quickly, with machinery up and running almost immediately.

New pre-configured, custom Cartesian robot systems from Bosch Rexroth Corporation (Buchanan, MI, U.S.) are one example. "We've taken our standard linear axes and now offer them as pre-configured multi-axis systems," says Kevin Gingerich, the company's director of Marketing Services. "Customers simply specify a few basic parameters and receive a 'plug-and-play' unit customized to their application."

Since pick-and-place cells were frequently custom-designed in the past, the customer can now save time in three places - the design phase, in which the unit is conceived; the purchasing and specification phase, in which the parts to build the custom unit would be sourced and acquired; and the build and start-up phase, in which a custom unit would need to be built, programmed, and brought into operation. The total time savings could easily be weeks and possibly even months, all of which translates into higher profits for the end manufacturer.

"It's a little like outsourcing some of your manufacturing engineering and design work to experts who do that type of automation all the time," says Mr. Gingerich. "We think that manufacturers will continue to focus on cutting as much time as possible out of their new product launch cycles in order to get from idea to cash as quickly as possible. Assembly and fastening suppliers need to help them get there."


The PosiDot valve from Liquid Control Corp. (North Canton, OH, U.S.) helped a medical device manufacturer dispense 1.5 cc's of epoxy into a small cavity on the handle of a medical device known as an ablation wand (inset). The wand is used in a surgical process to help correct heart arrhythmias.

The meter, mix, and dispense valve is said to dispense accurate shots and beads from 0.005 cc's up to 5 cc's, and handle ratios from 1:1 to 25:1 of two-component epoxies, urethanes, silicones, and most reactive resin systems. In this application, there is a wand cavity about 2- to 2.5-in long that is filled with epoxy. The potted section runs from the blue finger grip down to the tube that comes out of the device. The valve was used to dispense epoxy so that the electronic connection in the wand is protected, the PVC tube is securely bonded over a stainless steel tube, and the handle of the device is bonded to the stainless steel tip.

Handling Tight Spots

Achieving optimum assembly efficiency often requires some ingenuity. AEG in Nuremburg, Germany, a maker of clothes washers, needed to automatically feed and drive 17 screws to hold drum halves together. The difficulty was that the screw-holes were placed so tightly next to each other that access with standard feeder tooling was impossible. Therefore, the assembly system needed to be equipped with separate loading, inserting, and driving stations.

The appliance company purchased five identical automatic screwdriving machines from DEPRAG (Amberg, Germany) to address the situation. The supplier designed a holding-mask with screw presence sensors, which allows the screws to be automatically pre-loaded. Once all 17 screws are loaded into the holding mask, magnetic sockets lift the screws out of the mask and insert them into the drum screw-holes.

When all screws are loaded into the drum, the drum advances to the driving station, and 17 automatic screwdrivers drive each screw to the correct torque and depth. A Siemens PLC controls the machines. (For more information see Upside Down Assembly.)

While tried and true assembly methods sometimes continue to work well, it is not a bad idea to do a periodic review. One major appliance company did so and found an alternative to a spot welding operation. Previously, the spot welder was swung into place in a hard-to-reach washer cabinet hole to apply a single weld. This was a cumbersome, non-ergonomic operation.

After a review, the appliance company switched to a Tog-L-Loc system from BTM Corporation (Marysville, MI, U.S.). The appliance OEM reports that the hand-held, air-over-hydraulic clinch lock unit, supported by a balancer, is easier to maneuver and operate. The company feels that nothing is compromised in joint quality with the new approach.

 


A new controller for electric assembly tools monitors the entire fastening process and controls the final torque. When coupled with a tool, the Smart Torq Error-Proofer from ASG (Cleveland, OH, U.S.), a division of Jergens, Inc., automatically learns an assembly's fastener installation characteristics. Once learned, the device monitors the fastening event by comparing learned characteristics to those being experienced while the fastener is installed. By monitoring the event versus just controlling torque, the controller is said to catch problems during the process, such as differences in workpiece characteristics, fasteners, or assembly tool performance. The device monitors the number of fasteners installed and detects cross-threading, premature shut-off, re-hits, cam-outs, and missed fasteners, as well as incorrect torque.

BTM adds that clinched joints are consistently applied, and that the joint expands and contracts at the same rate as the surrounding material. Spot welding, however, may be subject to cold weld, too much flash, the presence of oil, tip conditions, and power fluctuations, which affect the quality and consistency.

Possible inconsistencies aside, spot welding may also be losing ground as many appliance companies go to pre-painted steel. This was the case at HVAC equipment maker Trane's Cullen, LA, U.S. location. Late last year, the company began production of commercial size (5.5- to 20-ton) air handlers, which are the inside portion in split systems. The parts had previously been spot welded and then post painted in another facility. For production in Cullen, Trane decided not to spot weld the now pre-painted steel because of the appearance. Instead, it selected the FAS-NER System from AKH, Inc. (Indianapolis, IN, U.S.). The punch and die operation automatically feeds, punches, inserts, and locks a self-piercing FAS-NER to produce a solid joint in one high-cycle operation.

 

"This has been a good clean operation on the press," Skipper Martin, manufacturing engineer at Trane's Cullen location, tells APPLIANCE. "There is a more consistent and stronger joint than when we spot welded. Beyond that, appearance is nice since the fasteners are flush with the sheet metal surface, and their color has been selected to match that of the pre-finished steel."

 

As appliance designs continue to evolve, appliance companies and their suppliers will surely continue to adjust and improve assembly and fastening processes and materials to meet whatever comes their way.


More Assembly & Fastening

Assembling the Evolving Appliance

Appearance Counts

 

Rotor Clamp, Inc. (Somerset, NJ, U.S.), produces a line of self-compensating hose clamps for low-pressure applications in single wire, double wire, and constant tension band (CTB) configurations. These clamps expand and contract with the hose in response to temperature changes in the application. According to the company, they cannot be over- or under-tightened and are installed and removed easily using either manual or pneumatic tools.

 

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