Tag Archives: Automotive

Self-tapping Fasteners for Lightweight Designs

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From SAE International, April 2014

Abstract:  As automotive technology rapidly provides advances in lighter weight designs and materials, the technology to fasten and join them must keep pace. This paper will explore two uniquely different fastening technologies that are being used to address some of today’s demanding application challenges in plastics and thin steel and aluminum sheet. These are two areas of application that have historically provided few good options for designers, especially as they attempt to push the envelope with progressive, light weight designs. The first technology is self- tapping screws for plastics that, although not new, are now evolving to enable smaller bosses and shorter thread engagements, and incorporate light weight design options. Although dependent on the demands of the application, these screws can be produced in both steel and, now, lighter weight materials such as aluminum and plastic. The paper will explore how these technologies can be employed by the designer to obtain desired weight reduction initiatives over more conventional threaded fasteners for fastening plastic. The second technology are self-tapping, thermal forming screws that enable fastening of thin metal sheets that normally are unable to safely accommodate a threaded fastener joint because of the minimum sheet thickness. This technology is proving especially useful in automotive body-in-white applications where multiple stacks of aluminum sheet, mixed applications of aluminum and steel, multiple stacks of thin steel, and applications into extruded aluminum or magnesium members, particularly with one-sided access are necessary. This portion of the paper will specifically explore how this technology allows lighter weight aluminum or thinner steel sheets to be used since a robust and secure threaded joint can be formed. (Article No.: SAE 2014-01-0785)

Available for Purchase on SAE International: http://papers.sae.org/2014-01-0785/

Fastening Solutons: Plastic Clip-On Bosses for Thin Sheet Applicatons

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From Fastener Technology International, December 2013

I have an older garden tractor that I use to cut my grass. Several years ago the engine began to puff smoke and quickly deteriorated to where it was evident that I either needed a new tractor or to rebuild the engine. Since a new, comparable tractor was not in my budget, I decided to rebuild the engine on my own. This meant removing the hood and cowlings to gain access to the engine so that I could take it off the frame and rebuild it. On this tractor, each side of the engine compartment is shrouded by a separate metal panel with two clearance holes in the top corners, which allow a screw to pass through and clamp the panel in place with a metal J-type clip located at a connection point behind the panel. Although this type of joint had worked fine for almost 30 years, after removing these screws and reconnecting them a couple of times, the much harder spring steel clip “stripped” the threads off of the softer screws and they began to back-out. Of course this created a problem when the tractor was running because there was no clamp load left and the panels would vibrate loudly.

Initially, my solution was to retighten the screws, later I began rotating them between joints, and finally I replaced the old screws with new ones. None of these solutions worked for long and I finally got fed up with it and decided to fix it for good.

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Strategies To Mitigate Fatigue Failure in Fasteners

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From Fasteners Technology International, August 2013

Although component failures have probably been around for as long as man has been putting things together, it wasn’t until the early to mid nineteenth century that engineers began studying the progressive failure mode that we know today as fatigue. Although highly undesirable, fatigue is a relatively common failure among fasteners and regretfully can lead to some dramatic and even life-threatening consequences. A great deal of progress in understanding fatigue has been made since the nineteenth century, and yet there is still much to be learned. Fortunately, enough is understood today that specific strategies and practices can be employed when a bolt or screw is designed in an application at risk of fatigue failure. This article will look at the basics of fatigue in fasteners and preventative measures that can be adopted to reduce the risk of failure and improve the durability or life of the fastener component.

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The Art of Thread Forming Fasteners, Part Two – Thread Forming Into Plastics, Light Metals, and Steels

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From Fastener Technology International, June 2013

In Part One of this two-part series, we looked at the general principles of thread forming that apply uniformly regardless of screw or material type. In an ideal world, “one size would fit all” and any screw could be universally used in any material. However, anyone that has ever tried to thread a standard sheet metal screw into polycarbonate or into a thick steel plate might attest to catastrophic results. Why? Quite simply, the fastener being used was never designed to perform in these materials.

Therefore, the first ground rule that any Fastener Engineer or Designer must employ is to choose a fastener that was designed to work in the material and the situation intended. There is some excellent fastener technology that works well in the applications it was designed for, but not so well with other materials. So it is incumbent on the Designer to know as much as possible about all aspects of the joint and not to simply assume that because the fastener works well in thread forming such-and-such a material, that it will work well in a different one.

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The Art of Thread Forming Fasteners, Part One – General Principles

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From Fastener Technology International, April 2013

One of the roles of every Fastener Engineer or Designer is to look critically at each new problem and develop an elegant solution that is as simple in form as it is effective in practice and efficient in cost. That often means using the minimal amount of resources to gain the maximum achievement. The “art” of thread forming fasteners provides a powerful tool in the industry arsenal to achieve such results for customers.

When it comes to fastened joints made up of a threaded fastener and some type of nut member, there are really only two varieties, those that start with a nut member thread already in-place and those that depend on the threaded fastener to create its own mating thread. A great deal of technical information can be found where both screw and nut member are threaded, but far less is available and understood on those where the nut member thread is formed by the screw itself.

This two-part article series will attempt to remove some of this mystery. Part One will explore the basic guiding principles of thread forming. These are principles and behaviors that are true regardless of the screw or nut member material. When I am done, it is my hope that the reader will have gained an appreciation for how thread forming works and the general areas of concern for the Fastener Engineer when he or she designs such a joint.

Part Two will explore the more specific and specialized cases of thread forming into thermoplastic, light metal and steel materials. Although not the only materials available for thread forming, these three categories represent the majority of areas where thread forming fasteners are utilized today.

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Is It Worth Its Salt?

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From Fastener Technology International, October 2012

In the early days of my career, when I was occasionally working on new part approvals, and then later when I was overseeing such activity, a common and frustrating event was to discover that parts submitted to the customer for approval did not pass their salt spray test. This was particularly confounding because those same parts would have passed our internal testing and often that of our plating vendor. I would quickly come to learn that this is a common industry problem and one likely experienced by every fastener manufacturer or distributor at one time or another.

To compound this frustration, I learned that although the experts have long debated the pluses and minuses of this test, regardless of which side they fall, they universally agree that this test may not provide similar results between test cabinets (even though all process parameters have been followed) and that the mechanism of failure is so radically different from real world application, that there is no known or accepted correlation between salt spray hours passed and actual performance in real-world service.

One might logically ask then, what the value of this test is, what is really happening amid that salt fog and why other test methods haven’t replaced it. The following is an attempt to understand more about the process and tackle these and other questions regarding this universal and deep-rooted test method in qualifying fastener quality and ability to withstand service corrosion conditions.

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