Fastener Technology

Recess Drive Systems for Screws

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Reprint from Hardware & Fastener Components Magazine, Vol. 42

Precariously balancing atop a ladder, you find yourself holding the new light fixture you’re installing in one hand and in the other a screw driver with a screw delicately balanced from the tip. To your chagrin the ladder jiggles a little and the screw drops to the floor leaving you perched on a ladder holding a light fixture you can’t now connect. Whether you are into “do-it-yourself” projects or would never find yourself in this situation, this scenario repeats itself many times a day in many different ways throughout the world. Perhaps ending more successfully than the above example, the screw is driven into place providing the holding power it was designed to give. This is only possible because screws are designed with a drive feature, often an internal recess that accepts a screw driver bit that enables assembly.

Threaded fasteners, since their inception, have had to have some sort of design or feature that allowed them to be driven. Although most internal recesses are relatively new (less than 100 years old), slots have been used for a very long time. Slots are simple, easy to use, and pretty effective. However, newer designs introduce an array of technologies that address many of the challenges that fastener engineers and designers commonly face.

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Fastener Manufacturing Equipment – An Overview

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Reprint from Fastener World Magazine, Vol. 164

It was over thirty years ago that I first walked through a fastener manufacturing plant. I was just completing a cooperative education program with General Motors and looking to complete my engineering education with another summer internship. As luck would have it I was invited to interview with a fastener manufacturer near my home.

That first introduction to manufacturing of fasteners would serve to begin a lifelong interest and appreciation for the way that fasteners are made and, more generally, with all manufacturing processes. I was particularly impressed with my first look at how fastener threads are formed. Never in a million years would I have expected that threads could be formed by squeezing and rolling parts between two, grooved flat plates.

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Screw Threads – Different Designs and Where They Are Utilized

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Reprint from Fastener World Magazine, Vol. 163

In recent years a new addition to public school curriculum has taken the US by storm. This addition is known as STEM, which is an acronym for “Science, Technology, Engineering, and Mathematics”. One of the foundational subjects of the STEM curriculum is education about the “Seven Simple Machines”. As a student of technology, each of these simple machines is an interesting subject, but perhaps none of the seven is more elegant than the screw thread.

Since its first inception and surely its first recorded uses, the screw thread has been faithfully serving mankind in many ways. One of the first recorded deployments of the screw thread was when Archimedes used it to move water from one level to another, and today it’s uses for holding things together are almost limitless and span from the very mundane to the very important and critical. In fact, today many in our society are thankful for screws that hold bones and other body parts together, enabling revolutionary remedies to common health and mobility problems.

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“Drilling Down” – The Basics of Drill Screws

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Reprint from Fastener World Magazine, Vol. 171

Fastening thin metal sheets has presented challenges since screws were first used to connect things. If the metal sheet is very thin the connection is challenging because there isn’t enough thickness to provide sufficient thread engagement, and, thus the ability to withstand stripping. On the other hand, as sheet or gauge thickness increases self-piercing is no longer an option and either a pilot hole is required to accommodate a thread forming or cutting screw or a tapped hole must be prepared to accept a machine screw. In many instances, particularly in construction, the time it would take to prepare each joint to accept such designs is prohibitively long. What, therefore, is the solution to this dilemma?

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The Basics of Stainless Steel

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Reprint from Fastener World Magazine, Vol. 160

In 1913 English metallurgist Harry Brearley was working on a project to develop an improved steel for gun barrels that was more erosion resistant than the current steel of the day. He was experimenting with Chromium alloy steels and happened to try one that had 12.8% Chromium and 0.24% Carbon. As often happens, what begins with one goal in mind results in an entirely different outcome. In this case, Mr. Brearley’s erosion resistant experiments would result in a steel far more corrosion resistant than normal steel. Stainless steel was born.

Today stainless steels are a part of everyday life and are used in a wide variety of applications from appliance coverings, pots and pans, marine components, automotive components, and even fasteners. Stainless steels are a logical choice when the primary goal of the designer is corrosion resistance, although other properties such as appearance and strength may be determining factors in a choice to use them. There are over 300 different iron based alloys containing a minimum of 11.5% chromium that comprise those materials considered stainless steels.

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Solar Fasteners

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Reprint from Fastener World Magazine, Vol. 152

Thomas Edison is attributed with the following quote, “We are like tenant farmers chopping down the fence around our house for fuel when we should be using Nature’s inexhaustible sources of energy — sun, wind and tide…. I’d put my money on the sun and solar energy. What a source of power! I hope we don’t have to wait until oil and coal run out before we tackle that.” Today, many would see his words as prophetic. As concerns have increased over the supply of consumable energy sources and their lasting impact on the earth, cleaner and renewable energy sources have become a topic of intense interest and anticipated source for future energy consumption.

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Characterization of Flow Drill Screwdriving Process Parameters on Joint Quality

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From SAE International, September 2014

Abstract: A state of the art proprietary method for aluminum-to-aluminum joining in the automotive industry is Resistance Spot Welding. However, with spot welding (1) structural performance of the joint may be degraded through heat-affected zones created by the high temperature thermal joining process, (2) achieving the double-sided access necessary for the spot welding electrodes may limit design flexibility, and (3) variability with welds leads to production inconsistencies. Self-piercing rivets have been used before; however they require different rivet/die combinations depending on the material being joined, which adds to process complexity. In recent years the introductions of screw products that combine the technologies of friction drilling and thread forming have entered the market. These types of screw products do not have these access limitations as through-part connections are formed by one-sided access using a thermo-mechanical flow screwdriving process with minimal heat. The friction drilling, thread forming process, hereto referred to as “FDS” is an automated continuous process that allows multi-material joining by utilizing a screw as both the tool and the fastener. The process uses the friction caused by the rotating screw to pierce and extrude the material. Threads are then created in this formed extrusion which allows the fastener to be screwdriven into the parts. A final torquing then securely clamps together the sheets of material. This study explores the quality design space as represented by resultant joint geometry as a function of the critical process parameters of fastener force and drilling speed. Feasible design space regions are explored to determine how process parameters affect joint geometry, and strength testing performed to validate the findings. (Article No.: SAE 2014-01-2241)

Available for Purchase on SAE International: http://papers.sae.org/2014-01-2241/

 

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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