Fasteners
Mechanical fasteners are the joining method of choice to speed assembly and aid recycling.
People will always have to hold things together. Fasteners ease and speed assembly and lower costs. Although most fasteners are conventional threaded products, carbon spring steel and injection moulded ranges of fasteners very often offer faster and easier assembly.
Fasteners continue to change as the materials to be joined change. Innovation is constantly required and there is now a phenomenal range of fasteners available.
Manufacturers encounter specific assembly problems and it is up to the fasteners industry to come up with solutions.
Adhesives are not kind to a manufacturing environment, whereas industrial fasteners inserted in holes automatically locate parts together in space and allow very immediate joining. And, compared with both adhesives and welding or brazing, they also allow assemblies to be easily disassembled.
This is no small matter. For example, regulations on vehicle disposal due to come into force in 2003, will make manufacturers responsible for end of life disposal and recycling.
Customers increasingly need to rationalise their supply base by only going to one vendor.
Among recent industry developments are the following examples of manufacturing ingenuity.
Captive fasteners.
A captive fastener that uses its D-Snap technology to allow it to be installed in a moment in suitably stamped cut-outs, combines the functions of a captive screw and captive nut or cagenut.
The Joiner is pushed into the cut out, at which point a riveted leaf spring widens to prevent the component from falling out and makes it captive. It is then inserted into a cut out in the rear panel, which can be made oblong for tolerance adjustment, where is its kept in position by D-Snap wedges. This ensures alignment of two panels.
Full insertion into the second panel securely fastens the two panels together. To disengage, an insert in the fastener, formed either as a knob or screwdriver insert, is turned. This pulls the snap wedges backwards so that the front panel can be disengaged from the back panel. The component then remains held in the front panel by the leaf spring.
In applications requiring more than one fastener, each is pre-released by turning the inserts and pulling them until the leaf springs touch the front panel. When all have been released, the front panel can be removed from the back panel.
.Flat pack fasteners.
A single component can speed flat pack fastening.
A single fastener type and a system of tee shaped slots and holes greatly eases the assembly of flat pack furniture.
The Lock Fast consists of three elements: a screw-in pin with a stubby padded head; a keyhole-shaped cut-out or tee shaped slot in panels; and a plastic moulded block to cover the hole.
The pins are screwed or pressed into one panel while the keyhole shapes and slots, which are undercut, are machined in the panel to be attached.
At first sight, it looks as if constructions might come loose, but by ingenious design of the overall construction – which becomes rigid when all parts are locked together - a piece of furniture can be assembled in a few seconds, taken apart again, then re-assembled with no loss of integrity.
While the system has been developed purely for the assembly of chipboard panels, it could be equally applicable to the assembly of plastic parts. The development is protected by patent applications.
MAThread screws
A new screw uses a special tip and thread form start that eliminates cross threading.
The ‘MAThread’ screw from Arnold Umformtechnik has a ‘dog point’ that ensures optimum feed into the application. MAThread is a US company that holds the patents on a screw thread design that ends in a special section that forces the screw and hole helices to align every time, regardless of how the screw is put into the hole.
The end starts with the ‘dog point’ after which the thread starts as a cam profile prior to the commencement of the thread form. MAThread offers three basic designs: one for general usage... the ‘Dog point’ for “very difficult application or when prying components into place during installation”... the ‘P’ point for “applications when point clearance is not an issue” and “with thick stack ups of multiple components”. There is also a “very Short” MAThread for use where point clearance is a problem and angular mis-alignment is limited.
The company also offers custom designed MAThreads for “parts used in special applications”.
The MAThread has become standard for OEMs such as General Motors, DaimlerChrysler and Ford as well as suppliers such as Visteon. MAThread claims that more than 7 billion screws and bolts based on its licensed designs have replaced standard fasteners since their introduction in 1996.
Thread forming screws
Thread forming screws cut costs while improving safety.
Direct fastener technology is gaining increasing acceptance, particularly in the automotive industry, where high volume manufacturing and assembly occurs. Thread forming screws, for example, are particularly useful when used to join plastic parts together.
But the functional capabilities of direct fasteners are being thoroughly tested in low volume production too.
The principle of direct screwing is that, as it is screwed in, the screw takes over some of the steps of the manufacturing process that, in conventional manufacturing, would need to be carried out as separate work procedures.
As the fastener is screwed in, a gimlet incorporated into the tip, first forms the appropriate through-hole diameter, after which the screw taps into the bore thread with its own thread. There is no need to drill the hole and cut the thread, so assembly time is less. It saves machining costs too, and saves on wear, so assembly costs go down.
The patented thread geometry provides the fastening with a considerably higher strip load and offers a greater difference between screw-in torque and overturn torque than the traditional 30° low angle screws. The screws, which are therefore consistently tight, provide additional safety room - particularly necessary under extreme conditions.
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