Tag Archives: Fastening Plastics

Is There Value in Application Engineering?

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Reprint from LINK, Summer 2021

I began my career in the fastener industry over thirty years ago as an Application Engineer. This was a great place to start, and, perhaps, the most cherished time of all my years in the industry. I suppose that Application Engineering can mean different things to different people, but within the fastener realm this role is pretty universally understood as an interface which works with the customer to provide the best fastening solution. This not only means choosing the correct fastener but also the related joint design, fastener heat treatment, finish, packaging, and any number of other design or process related decisions.

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Using Screws to Fasten into Plastic

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Reprint from China Fastener World Magazine, Vol. 53

Very early in my career I worked on a very interesting project. In the U.S. after a new car is assembled, it is either loaded into a truck or onto a train for delivery. In this case, our customer’s new model vehicle was loaded onto a train car for shipment across the country. When it arrived on the other end of its journey the cars would not start and could not be offloaded. It did not take long to discover that the glove box doors were opening in route, causing the glove box light to come on, and the battery to drain down. When the root cause of this problem was investigated it was quickly determined that the plastic ABS bosses which accepted the screws that held the glove box door assembly together were completely cracked and broken. The Type AB screws that had been used exerted so much radial stress on the plastic ABS bosses that they had destroyed them causing the plastic to fall away, the doors to flop open, and the new cars to arrive in an inoperable state.

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Miniature Thread Forming Screws for Plastics and Light Metals for Electronics Applications

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From Fastener World Magazine, May/June 2014, Volume 146

As handheld electronic devices have gotten smaller and lighter, the fasteners that hold them together have had to follow suit. Although miniature metric and imperial machine screws have been used in eyewear, watches, and cameras for many years, it is only relatively recently that very small variants of thread forming screws have become commonplace. It is impossible to explain why this is the case, but probably stems from the fact that thread forming in plastics and light metals is a practice that has itself only recently gained universal acceptance.

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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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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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