FASTENERS & FIXINGS FASTENER QUALITY ASSURANCE
TFC
How to minimise your quality issues
Fasteners play a crucial role in an assembly — yet quality standards are often overlooked by many businesses . If a fastener is not made to specification , manufacturers may be unable to assemble their products , facing long lead times before the right parts arrive . In a worstcase scenario , manufacturers risk sending poor-quality products out to the market , risking loosening or component failure . This would result in product recall , an expensive , extensive and embarrassing process , which can significantly damage a company ’ s reputation . Here Brian Vince , group quality manager at fastener specialist TFC shares insight on common fastener problems , and how to avoid them .
There are numerous reasons a fastener may not meet the required specifications . Perhaps there was a mix up during picking or labelling , and the fasteners have been delivered in an unmarked or incorrectly labelled bag . Maybe the wrong ISO standard of part has been delivered , or the material is not tempered when it should have been . Many common errors are almost impossible to detect with the human eye , so what can we do to be sure our fasteners are the right ones for the job ?
CHECK YOUR MEASUREMENTS The most common problem with fasteners is that they don ’ t match the drawing — the dimensions , thread , head or length is incorrect . This is a relatively easy issue to pick up , taking a measurement using a vernier or a micrometer will identify around 90 per cent of problems . If needed , the next step would be to measure the component using a shadowgraph , which illuminates a shadow of the component that can be zoomed in on to identify any non-uniformities . Quality teams can also use thread gauges or a shadowgraph to check a fastener ’ s thread .
FINISHING Many fasteners are coated to improve their resistance to corrosion , temperature or friction . For example , powertrain fasteners in a vehicle are commonly coated with zinc to enable them to resist corrosion , heat and oil . Polytetrafluoroethylene ( PTFE ) coating is common in the aerospace and oil and gas industries as it is lightweight and provides high-corrosion resistance . Quality professionals should assess whether the coating thickness is uniform across the fastener and within stated tolerances — if it is not , the part could cause problems later on .
Good communication and full traceability between distributor and supplier is crucial .
Hardness testing can also detect quality issues . Quality specialists can assess tensile strength and perform flexure or compression tests to check the material has the desired properties . This will prevent a fastener from going into an application where it is too hard and will snap , or too soft and will bend .
Dependent on the component at hand , other tests can be performed , such as load testing for springs , checking the hardness of rubber parts with a durometer , or testing the smoothness of bolt . If all testing is coming up fine , but a manufacturer experiences problems with quality during assembly , inspecting the part under a microscope means you can interrogate the problem at a very granular level to identify what is wrong .
MATERIAL To check that the fastener is made using the required material , quality professionals can use positive material identification ( PMI ) testing . This technology analyses the full chemical composition and grade of a metal or alloy , which means that the manufacturer can be confident that the material ’ s properties match specification . Material identification is particularly important in the oil and gas sector , where a material mix up could lead to catastrophic failure . For example , a stainless-steel retaining ring in a subsea drive shaft , instead of specified Inconel X-750 could mean drilling operations are forced to halt months before schedule .
If all testing confirms that the part is to specification , it may be a design issue that is causing quality problems . In this case , your supplier may be able to suggest an alternative option that will be more suitable for the application .
64 PECM Issue 47