Here on our blog, we often write about the various standards and specifications governing different fasteners, which usually are authored by a specific federal or third-party specifying agency responsible for that industry. While fastener manufacturing standards may vary across all of these governing bodies, one universally shared detail across all standards is that the produced fasteners are to be checked and controlled for quality after their fabrication. That is to say, a standard is only as good as its enforcement, and ensuring the reliability and integrity of fasteners manufactured all over the world for US consumption is arguably more challenging than designing the fasteners, to begin with.
Traditional standards enforcement was largely left to individual manufacturers and their industry’s respective standards organization, achieved through basic end-of-line lot sampling and inspection. Over time, manufacturers have increasingly implemented automated, inline, upstream quality control systems, catching and correcting manufacturing errors in-situ, both to reduce reject / rework costs as well as to provide more reliable quantity volumes to customers. After a series of high-profile fastener failures in the 1980s, the United States government passed the 1990 Fastener Quality Act, assigned to NIST (National Institute of Standards and Technology), further requiring robust quality control practices as a means of protecting public safety
Today, manufacturers largely use a combination of statistical process control, highly automated inspection instruments, and substantial documentation to make up their Quality Assurance programs and Quality Control practices. Foreign manufacturers supplying into the United States are required to meet these same Quality expectations, though often even more expectations are involved such as additional layers of certification, verification, and third-party laboratory testing to prove conformance prior to shipping out orders.
What Quality Control Parameters are Tested?
Quality Control programs in fastener manufacturing typically measure factors that are most at risk of failure, where harm to humans may be caused if the fastener were manufactured out of compliance with the application’s standards.
Dimensional tolerances, weight, identification stamps and markings, and general physical form are all mechanical properties requiring inspection. These requirements can be numerous and very critical for special applications, measuring every facet of machined fabrication such as thread pitch, thread spacing, run-out, and even aggregate tolerances across paired assemblies (nuts and washers).
Fasteners must be made with the correct alloy and thermal treatment in order to provide the necessary strength, corrosion resistance, and wear characteristics. Checking raw material documentation, heat treatment temperature and time records, and performing spectrometric analysis are a few common methods of confirming material properties.
Manufacturers will always prefer to find failures of their fasteners in their lab and never in the field after installation, often conducting various physical tests on their fasteners such as hardness, deformation, and tensile strength testing.
Whether for decorative or functional purposes, fastener finishes are also inspected upon fabrication to make sure that they meet the correct sheen, roughness, polish, grain, porosity, and color requirements.
For materials that are coated after initial fabrication, further tests are involved to ensure that the coating’s thickness, uniformity, adhesion, tactility, color, and markings are all properly observed.
Do you have a critical fastening application but are unsure of which specialty fastener might be best to use? E&T Fasteners offers expert support and product selection between the above options and more! Contact us to discuss your application, or to see our standard fastener offerings, visit our product selection here.
How are Quality Control Tests Performed?
High-quality and high-volume manufacturers almost always utilize their own internal testing laboratories to perform Quality Control evaluations, and many also use external third-party labs to confirm their findings (often as a requirement of a supply agreement). Smaller fabricators may rely entirely on external evaluators for full testing but may perform general measurement and documentation work internally. Either way, both manufacturers rely on accurate test equipment to help complete their Quality Control battery, such as the examples provided below.
- Hand Tools – tried-and-true traditional hand tooling can provide highly accurate quality inspection measurements. Thread ring gages, pitch gages, plug gages, depth gage, and micrometers are common tools used for first-pass inspections, usually employed for basic measurement or random grab tests.
- Optical Comparator – also known as a Profile Projector, an Optical Comparator is a visual inspection tool that projects an enlarged view of a fabricated part detail against an illuminated screen, allowing for digital measurements and software analysis of precision details on small parts.
- Magnetic Particle Inspection System – a form of nondestructive testing (NDT), Magnetic Particle Inspection imposes a magnetic field across a part’s surface which can then be measured with great accuracy for any surface irregularities (they would display as distortions across the magnetic field).
- Surface Roughness Tester – this tool can quickly measure the roughness depth, texture, and roughness value (Ra) down to micrometer and even micron units.
- Coating Meter – available in several different technologies, a Coating Meter can use ultrasonic, resistive, conductive, thermal, or other means to measure the thickness, uniformity, adhesion, and consistency of coatings, films, linings, and plating applied to fasteners.
- Fatigue Testing – these test systems apply loads to fasteners in multiple directions, varying consistency, and across different amounts of time, all to examine tensile, compression, and alternating load capacities of a fastener.
- Torsion Testing – simply put, a Torsion Test station ‘twists’ a fastener to determine its torsional strength, stiffness, and stress-strain properties.
- Hardness Testing – by applying a specifically-dimensioned load point to a fastener, a Hardness Testing station is able to measure the material’s resistance to indentation, otherwise known as hardness. This can help identify issues with material alloys and thermal treatment processes meant to harden the material.
- Optical Sorting – last but not least, an Optical Sorting station visually examines fasteners for overall profile, appearance, color, and other visual parameters against control samples (via advanced software).
It’s worth pointing out that while the above list of testing equipment represents some of the most sophisticated options available today, these tools only make up half of the overall effort involved in managing a modern Quality Control program. The other half of the battle is to document, study, and learn from all test findings over time, feeding into a Continuous Process Improvement paradigm in which a manufacturer makes statistically-informed, proactive improvements to their processes. These improvements increase successful part production, cut waste, cut costs, and heighten the safety of the systems that these fasteners are supplied.
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About E&T Fasteners
With sales and support teams spanning the Continental US, E&T Fasteners is here to serve your hardware, fastening, and component needs both domestically and internationally. We are a stocking distributor of metallic, plastic, and exotic alloy fasteners, backed by our technical staff directly experienced in your unique applications. We can assist your specifying and selection efforts, providing engineered solutions, record-fast lead times, and stellar customer service from quote through delivery. Please let us know how we can help!