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issue: April 2008 APPLIANCE Magazine

A New Approach to Blind Riveting

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by Harry E. Taylor, Manchester Consulting Group

A patent-pending blind rivet solution is designed to help appliance manufacturers save on necessary blind rivet purchases and reduce unnecessary product waste.

Figure 1. A unique assembled blind rivet solution includes modifications to the installation tooling design and setting method.

Over the past 70-plus years of blind riveting, very little has changed with the basic open-end, break-mandrel blind rivet. Evolving innovations such as closed-end, multigrip, and other variants have been introduced to satisfy unique developing needs and grow the blind rivet market, but the common blind rivet has, essentially, remained unchanged. As raw-material prices have increased, more and more common tapping screws may have even been substituted for blind rivets in appliance and other applications. Now, blind rivets from low-cost countries outside the United States are beginning to find their way into the hands of U.S. and European OEMs.

Blind rivet installation tool modifications have steadily progressed, especially in recent years. Setting tools have gotten lighter as plastics have been introduced and as devices to present blind rivets to the setting tool and collect the spent mandrels have been developed. Other blind rivet fastening system components have also been developed, all utilizing the basic blind rivet which, again, has largely remained the same.

Marketing managers for blind rivet manufacturers have continuously promoted a lower “installed cost” for this unique fastening solution, leveraging more automation or reliability in the setting and mandrel disposal processes. Blind rivet costs have increased with inflationary raw-materials costs, especially when tight dimensional tolerances or specialty designed or packaged blind rivets were required.

Many OEMs in the appliance industry use millions of blind rivets in their manufacturing plants. Still, it is rare to see a blind rivet manufacturer take a focused system approach and provide a unique setting tool design and specialty configured blind rivet that offers the lowest possible installed cost for a specific fastening solution or application. More likely is the gradual disappearance of blind riveting solutions as tapping screws become more cost-competitive and blind rivets are imported from low-cost countries.

Addressing Customer Needs

What appliance manufacturers actually need is simply an installed fastening solution, generally at the lowest possible installed cost. Reducing mandrel length to save cost has frequently been contemplated in the blind rivet industry. U.S. Patent 4,836,728 (filed in 1989) attempted to reduce mandrel length by putting heads on both ends of the mandrel. The patent states: “This shortening of the mandrel entails first, a considerable saving of material, and second, simplification of the removal of the broken-off part of the mandrel stem.” This innovation, however, required a secondary operation and a different setting tool, so added product costs were involved, and the blind rivet was too costly for the appliance industry. This product never reached “the tipping point” and was withdrawn from the market, but the existing customer need for a lower-installed-cost blind rivet that was easier to feed didn’t vanish.

If a lesser amount of material were required for a specific blind rivet fastening solution, and the installed characteristics of the fastener remained unchanged, new appliance applications could be envisioned. U.S. Patent Application 11/654,123 for a unique blind rivet, including modifications to the installation tooling design and setting method, has recently been filed (see Figure 1). These innovations, when implemented and brought to “the tipping point,” will enable appliance blind rivet users to save in necessary blind rivet purchases, and help reduce unnecessary product waste. Since fossil fuel energy is required to produce as well as transport the unnecessary product waste, there might even be a slight reduction in CO2 emissions, and a minuscule contribution to the fight against global warming.

Figure 2. A new setting-tool nosepiece design preserves the ability to use one setting tool to set numerous sizes of blind rivets.

Setting-Tool Nosepiece

A new setting-tool nosepiece design preserves the ability to use one setting tool to set numerous sizes of blind rivets and is illustrated in Figure 2. This nosepiece allows the setting of blind rivets with shortened mandrels. Since the physical characteristics, i.e., the diameter, the tensile strength, and the break load of the mandrel in the new blind rivet are unchanged, the newly installed blind rivet or fastening solution is identical with that in the prior art. The setting time also remains unchanged. If anything, productivity is improved as the shorter spent mandrels are more unlikely to jam in the setting tool, and any spent-mandrel collection bottles will require emptying on a less frequent basis.

The illustrated nosepiece design is capable of gripping a blind rivet mandrel extending 0.5 to 0.6 in. above the blind rivet flange, regardless of diameter. Accordingly, for a 64-size blind rivet with mandrel projection above the flange of generally more than 1.06 in., total mandrel length would be reduced by about 30–40%, depending on the blind rivet manufacturer. This reduction is due solely to nosepiece design.

This shortening of mandrel length and the resulting material savings is critical to reducing installed cost during a period of time when the cost of aluminum, steel, and stainless-steel raw wire continues to escalate. In addition, mandrel wire, on a per-pound basis, is generally more expensive than the body wire in a common blind rivet, so the cost impact, in terms of percentage, can be even greater than the material weight savings for the mandrel.

Other benefits, yet to be measured, include productivity increases from the ability to run mandrel manufacturing and blind rivet assembly equipment faster; savings from packaging additional blind rivets in a standard shipping carton; lower shipping costs; and the ability to more easily feed and automate with shorter blind rivets, thus increasing installation productivity.

Figure 3. Pictured is a blind rivet application “fingerprint” in which setting load (lbs.) is a function of mandrel displacement (in.).

Possible Modification

One embodiment of U.S. Patent Application 11/654,123 is regarded as a disruptive innovation, i.e., the installation of a blind rivet with an even shorter mandrel and a split-second-longer stepped setting process. This method requires an automated setting tool and the use of existing sensor technology. This process will enable blind rivets with mandrel projections under 0.5 in. to be installed in a stepped process that is a function of an application’s unique mandrel displacement-versus-load “fingerprint” (see Figure 3).

Initially, the ultrashort mandrel will be partially gripped with the setting tool jaws and pulled under a low load to a point in Zone C of the “application fingerprint.” At this point, the setting tool jaws will be released from the blind rivet mandrel, and a split-second later, be fully reengaged with a longer blind rivet mandrel. The fully reengaged mandrel will then be pulled to the breaking point to set the blind rivet fastening solution.

These modifications combine to create a disruptive fastening solution. Here, a lower-cost-uninstalled blind rivet will need to be offset against the slightly lower assembler productivity of a two-step process to determine overall installed cost. As with all disruptive innovations, however, this disruptive innovation will continually improve on a new growth trajectory.

Potential Savings

After the first 30–40% mandrel-material savings from innovative design changes is made, another incremental 30–40% may be possible with the stepped setting method. Here, these further incremental savings will be offset negatively by a split-second-longer setting time, but positive productivity savings from rivet feeding and disposal will also be present, and every application will be different, so field-testing for specific applications will be necessary. Conservatively, however, a total 50% mandrel-material savings is estimated from the stepped setting method. Because field-testing will be necessary to quantify all the pluses and minuses, and every application is different, it may be prudent to not overstate the stepped savings at this time.

About the Author

Harry E. Taylor is a management consultant with the Manchester Consulting Group. He holds a BS in mechanical engineering from the Worcester Polytechnic Institute, an MS in engineering science from Rensselaer Polytechnic Institute, and an MBA from the Harvard Business School. If you wish to contact Taylor, please e-mail lisa.bonnema@cancom.com.


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