Solving fastening problems is about controlling variables or eliminating potential causes that create an unwanted fastening event. Let’s take a look at common unwanted fastening events: Cross threading, thread or component stripping, unseated fasteners, missing screw, nut or bolt (omissions). These are all evident events of failure that we can see with our eyes. Thank goodness for our eyesight, because these are easily recognized.
Fastening problems that we cannot see are our biggest risk. Latent failure can be a big problem, depending on the product or exposure to risk or liability. Latent failure is caused not only by under-torque, but largely by over-torque events.
Most all of us have opened a product package and discovered a screw or nut that came loose in transit. We might have also found one on the floorboard of our car. Many times these screws or nuts are not critical, they may come from the exterior of a product. However, they still concern us. They should. It makes us wonder if something more critical might also fail. Every time we find one of these rogue fasteners, something did not go as planned, thus a torque-related problem or unwanted fastening event has occurred. These occurrences are frustrating, time consuming and many times create delay and cost. You can get rid of them!
Let’s not over-complicate things when we study fastening variables. In our experience, there is only a handful of really complicated fastening problems and most of our customers don’t experience many of these all that often. Generally, it is a simple set of variables that need to be discovered, isolated and removed to solve fastening related headaches.
It’s important to thoroughly investigate in a scientific manner what may be wrong with the fastening scenario. More important is not to freak out and think that everything is wrong, and try to change too many things too fast. The process of elimination is a great tool for solving fastening failure. Fasteners are generally made to a specification that defines physical criteria. The information is public and validating dimensions is not hard. You can do it online or find it in most any handbook.
Step one is to make sure your fasteners are up to snuff.
1. Ensure your fasteners are dimensionally correct and ensure the assemblers are using the intended fastener for the application.
Many times we see bins of fasteners at the assembly line or work cell. There’s not much of a physical difference in size between an M2.5 or M3 fastener and sometimes these get mixed up in the bins, thus we find operators trying to install an incorrect screw. If an operator takes the wrong sized screw and tries to install it — well you get the picture — you may see an unwanted fastening event. Keep fasteners separate, use colour-coded bins, bin partitions or screw presenters that feed a screw to the operators driver tip before installation. These remedies can help ensure operators begin to notice the difference in screws before installation.
2. Tool selection.
In today’s world of the Internet, you can find products of any kind made all over the world. That’s good if you’re buying a tool for the home and even some professional use. It may be great if you know exactly what you need for the application. However, a wrong tool selection may create a fastening problem, depending on the application.
If you look at a DIY or professional tool line up, there is usually a very narrow selection when compared to industrial options. Look for a cordless tool for home use and you’ll find many brands, but most are very generic as these are made in huge volumes to keep the price low for the consumer. For the same industrial-quality tool, you might have a choice of 17 model options.
There’s a simple reason for it. Industrial fastening applications vary greatly depending on what is being fastened and the sophistication required is not built into just one tool. Industrial tools are built in smaller production quantities, use more advanced materials, and have been designed for harsh assembly conditions.
Industrial applications vary in cycles, torque specification, size and length of fasteners, number of fasteners used, strength and/or experience of the assembler, materials used and much more. You can imagine the diversity in selection needed to meet these industrial applications.
Key tip. Study tool options and pick tools that meet the needs of the applications. Specialists in industrial fastening have information on their websites, and moreover, provide sample tools that customers can try before they buy. Find torque specialists and ensure they are able to help you wade through all the choices.
3. Check your parts.
Changes in part tolerance, the material or a vendor often contribute to changes in fastening results. A customer called us after a large tool installation, worried that something had changed with the tool performance. Fasteners were not being seated correctly in the part and operators were complaining the tool did not have enough power to install the screw correctly.
In this example, the tool checked out fine, but what had changed was the blind hole diameter. A new vendor had been adopted to help control manufacturing cost targets, but their tolerance was not consistent and was on the low side of the specification — and many times under specification. This created a tougher than normal fastening event as the threadcutting application caused the tool to work harder cutting threads, and it sometimes stalled before final torque could be obtained.
This type of prevailing torque application is common with threadcutting screws and a specific tool that has the capability to run with more power during threadcutting, and less at installation was needed to support this change in material.
The bottom line: The right tool was selected for the original parts that were tested. However, this tool could not perform effectively given the new parts because it was the wrong tool for this type of fastening application. This is a very common occurrence that we see when we evaluate fastening problems with our customers.
4. Train operators to listen to the sound of their tools.
Basic training about tool performance can help an operator flag a fastening problem. Teaching operators what to expect when a tool is performing, and what to look for when it isn’t, is important information that can identify or resolve a fastening problem you don’t even know is occurring.
Case in point: Walking down an assembly line, experienced tool professionals listen for what is happening with tools. Each tool has a natural sound it makes when it shuts off, clutches, pulses or impacts properly. Tool professionals understand these sounds intuitively and can tell when a tool is not performing properly.
If an impact tool has lost power, the noise from its output is noticeable. When an electric screwdriver limit switch is not working properly, the tool may double click before the clutch shuts off. These are indications of required normal maintenance or tool failure.
Catching these signs early, operators help to improve fastening errors.
5. Error-proof the biggest contributors to fastening failure.
Most industrial tools today can be augmented with error-proofing technology. You can adapt or match a unique failure event to an error-proof technique.
One customer told us that too many screws were being missed during production. They had tried all sorts of training and different quality control (QC) techniques, but nothing was working to solve the problem. A screw counter was introduced to ensure each product finished production with the exact number of screws planned. This simple implementation ensured the operator could not continue to the next product until all screws were installed properly.
Another customer had a parts stripping problem. The
tool selected was capable, but the RPMs were fixed and sometimes stripped the plastic part, causing scrap, frustration and extra assembly time. A variable-speed power supply was introduced to give the operator a slow start feature to allow the fastener to cut through plastic correctly, and then seat and torque properly. The power supply was fixed so the operator could not adjust it, thus creating a consistent, repeatable result.
These five tips are great starters to solving unwanted fastening problems. There are many more.
Using a quality torque tool makes a safer world through accuracy and precision. Controlling torque is essential for companies to ensure that their product’s quality, safety and reliability isn’t compromised. The failure of a three-cent fastener that isn’t properly tightened can lead to catastrophic or latent failures. Fasteners that are insufficiently fastened can vibrate loose and excessive torque can strip threaded fasteners.
These tips were compiled by Mountz – The Torque Tool Specialists, 1080 N. 11th St., San Jose, CA 95112, e-mail: email@example.com. Copyright 2012 Mountz Incorporated.