Product category:
Fasteners, threaded and non-threaded
News Release from: Profil UK | Subject: Pierce fastening technology
Edited by the Engineeringtalk Editorial
Team on 18 August 2004
Pierce fastening technology speeds car
assembly
BMW Group is just one company to harness the advantages of pierce fastening, having specified more than 70 examples of Profil fasteners in the production of its new Mini.
The motor industry is renowned for its relentless quest for better, more cost-effective manufacturing methods And with perhaps 30,000 individual components mounted within the structure of a typical modern car, the provision of high strength threads in sheet metal assemblies continues to be a major focus of attention
This article was originally published on Engineeringtalk on 17 Sep 2008 at 8.00am (UK)
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Profil to showcase latest technology
Profil UK's latest pierce fastening technology will be demonstrated as part of the company's presentation of advanced sheet metal assembly solutions at the Northern Manufacturing Show.
Profil RSN and RND rivet nuts utilised by Audi
Profil has announced that its RSN and RND rivet nuts have been specified by Audi for use in a safety-critical bonnet latch mounting application on its A4 and A5 vehicles.
So, when motor manufacturers set about designing their new models, it's no surprise that they should look for solutions which provide greater benefits than simple rivet or weld type fixings.
Over the past few years, there has been a major shift away from traditional methods - with an explosion in the use of high strength pierce/clinch fasteners to meet both general and "safety-critical" vehicle applications.
BMW Group is just one company to harness the advantages of pierce fastening, having specified more than 70 examples of Profil fasteners in the production of its new Mini.
According to Body Engineering Design Leader, Ian Hill: "Increased automation of assembly methods is one of the main reasons we chose Profil for so many applications on the vehicle".
"Following an intensive assessment session with Profil engineers, we identified several areas that would be ideally suited to pierce fastening methods".
Further reading
Studs chosen for BMW Mini construction
Profil UK's M8 x 25mm steel EBF studs are being uesd to retain rear light clusters on BMW Mini Clubman models.
Stud provides accurate positioning
The stud fasteners are ideal for dynamic, static and shock load applications in materials from 0.6 to 4.0mm thick.
Fastener offers high-strength pivot points
Profil's SBF ball pin fastener provides a fast and cost-effective method of achieving high-strength pivot points in sheet metal components.
"These ranged from simple brackets on components such as the fusebox and foot rests, through to 'safety-critical' areas including the steering column, bumper and subframe mountings".
"It was clear that the Profil system would not only meet our required performance criteria, but that substantial cost, productivity and quality benefits could also be achieved if fasteners were installed as part of each pressing's manufacturing process".
"The use of purpose-designed automatic feed units and the inclusion of setting dies within the progression tooling has enabled this approach to be adopted".
"As a result, new parts - complete with installed fasteners - are now produced with every stroke of the press".
"This represents setting rates of more than 100 fasteners per minute - at least an order of magnitude faster than equivalent rivet nut or welded alternatives", notes Hill.
The consistency and integrity of pierce fastening are also inherently greater than for equivalent welded fixings, which are prone to variations in the base material, surface contamination and operator skill levels.
A further benefit of in-press installation is that parts simply can't be produced without the fasteners in place.
With manual operations, there is always the risk of individual nuts or studs being omitted, which would cause serious disruption during final assembly.
"With all these advantages, Profil clinch nuts and studs have become the preferred fastening method wherever space is available in the press tools to accommodate the insertion dies", says Hill.
As a result, M6 and M8 Profil studs and nuts are now installed on the Mini's fuel tank reinforcing rings, as well as on reinforcers in areas such as the bonnet hinge, door mirrors and handbrake.
In addition, M8 RND nuts are employed on the steering column mounting bracket, and a further six M8 studs secure the vehicle's front bumper assembly.
Profil fasteners are also specified for the dashboard cross-beam mounting, while the heaviest duty pierce nut variants - incorporating large reinforcing flanges - are reserved for the vehicle's subframe anchorage points.
Similar high-strength fasteners from Profil have been specified at the heart of "foolproof" fastening methods on Land Rover's Defender series vehicles.
M8, M10 and M12 pierce nuts are used to secure engine mountings to the chassis via heavy duty adapter plates, as well as to mount all variants of tow hook assembly on this rugged off-road vehicle range.
A detailed chassis review, backed by extensive product trials, led to Profil's selection.
One of the project's key objectives was the introduction of methods to enable the "late configuration" of vehicles to different engine options; a goal that has been achieved through the use of a pair of handed adapter mounting plates secured to the common base chassis using ten M8 Profil nuts.
Several alternative fastening methods, including captive nuts and riveted fixings were rejected in favour of the Profil solution - for reasons ranging from an inability to meet the restricted space envelope requirements, through to panel distortion in an area adjacent to a visible edge.
Likewise, a number of different solutions were evaluated for mounting the vehicles' tow hooks and pintles, which are subject to stringent NATO military specifications.
"The adoption of Profil fasteners for both these safety-critical applications has proved entirely successful", says project Manager John Rolls.
"Not only have we rationalised our product and processes, but we have gained increased flexibility and reliability as well".
The use of Profil fasteners has also been carried through to Land Rover's latest Discovery range, where benefits in vibration and fatigue resistance have been achieved - primarily by eliminating the thermal disruption to panels caused by welding.
Further problems with welded fasteners can arise in terms of initiating corrosion centres, as well as the risk of heat damage to coated or plated surfaces - if they can be welded successfully at all.
By contrast, pierce fasteners avoid the inherent health and safety issues associated with the welding process.
They are ideal for use with corrosion-resistant finishes, as well as galvanised steel and zintec.
Furthermore, the absence of thermal marking or weld spatter ensures that pierce fasteners can even be inserted into panels after painting, without compromising the surface finish or aesthetic qualities of the end product.
This has been used to good effect on the new Discovery's inner door modules, which feature the installation of six Profil M6 nuts and studs after the base panel has been powder coated.
The completed assemblies incorporate window winder motors and mechanisms and, because they operate in a designated wet area, each fastener is also required to achieve a completely water tight seal.
Similarly, corrosion resistance is at the heart of further Land Rover applications based on the use of large flange Profil EMF series nuts.
These steel fasteners carry an inhibiting zinc/nickel black finish and are installed either in the vehicle's steel frame to provide a 5mm standoff for the subsequent attachment of aluminium body panels, or conversely; in alloy brackets used as anchorage points for steel-based components or assemblies.
Ford is another leading vehicle manufacturer to harness the capabilities of pierce fastening technology, having adopted Profil UK's latest multi-functional sheet metal fastener in the assembly of its Fiesta, Ka and new generation Focus models.
Up to six Profil RSN "top hat" nuts are installed in each vehicle, providing high-strength, water-tight mountings for after-market roof racks - as well as significant build quality benefits and cost savings of up to $0.50 per car.
Available with M6, M8 or M10 threads, the new Profil nuts have a completely sealed end and are mounted in the vehicle's roof cant rails at the body-in-white stage.
The new nuts also incorporate a nylon plug, which in turn, carries a "Posidriv" screw head moulded into its exposed end.
The centres of these cross head profiles are used as location points by the laser guided robots that weld the body panels together, underlining the assembly method's ability to achieve absolute positional accuracy of +0.25mm in most applications.
The plastic plugs also act as highly effective thread protectors during subsequent painting operations and are easily unscrewed from the installed steel nut, ready to accept the roof rack's mounting bolts.
The versatility of pierce assembly is also reflected in the wide variety of fastener configurations available.
These range from plain nuts and studs, to large flange, shouldered, conical, ultra-low-profile, high-shear, flush-fitting and restricted access types - as well as Nyloc insert versions.
In addition, products can be developed to incorporate special features, or even custom-engineered for specific applications.
A typical example of this is Profil's ball pin fastener, which is currently used by Peugeot and Alfa-Romeo on bonnet and tailgate assemblies.
The fastener features a 6.5mm diameter shank and incorporates a cold forged head profile compatible with industry-standard gas spring units.
It provides exceptional shear and pull out resistance and deflects less than 1mm under a standard 2kN cyclic load, to consistently outperform equivalent riveted or weld nut anchored pivots.
A further new Profil product is the recently-launched earthing stud fixing, which has already been adopted by Mercedes for its latest A class vehicles.
This new two-piece fastener provides high strength, water tight component or subsystem earthing points in sheet metal panels up to 1.35 mm thick.
Furthermore, it is particularly suitable for the new high strength sandwich steels used by Mercedes in the vehicle bulkhead panel, which incorporates a layer of insulating material between the metallic outer skins.
The new M6 earthing stud is supplied with a special-purpose nut that prevents the ingress of industry-standard E coat or paint finishes prior to final assembly, yet guarantees a large flat area of contact between the nut and shoulder of the stud.
The earthing studs employed by Mercedes are just five of the 43 Profil fasteners installed in every A class bulkhead.
Others include two further examples of the "top hat" nut, which are used purely as location points by robots as they manipulate the finished panel during its assembly process.
Each of the above applications underlines pierce fastening's many advantages for automotive applications.
Quite simply, the process offers a combination of speed, accuracy, strength and cost-effectiveness that is unmatched by any other pressed or sheet metal fastening method in this sector. Request a free brochure from Profil UK ...
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