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Simple, strong and secure - the 'S' type fastening method
Simple, strong and secure - the "S" type fastening method
Plastic hot air staking selected for Jaguar "S" type sub-assemblies
Keywords: Fastners, Assembly
Plastic hot air staking has been selected by leading first tier motor industry supplier, LINPAC Automotive - Witton to ensure secure, vibration-proof fastening of plastic assemblies used in the new Jaguar "S" type saloon.
The application, which is a first for this customer, employs purpose-designed equipment to retain polypropylene trough mouldings to leafscreens located at the base of the windscreen on the luxury vehicle.
According to LINPAC, the hot air staking solution developed and supplied by Bishop Stortford-based PHASA Developments was selected in preference to other fastening methods through its ability to consistently and cost-effectively meet the application's stringent requirements (see Plate 3).
The leafscreen components are moulded in-house to close tolerances and feature an "easy-clean" textured finish that must remain unmarked during the fastening process. In addition, finished assemblies must be able to withstand operating temperatures from -40°C to +95°C without loosening or suffering any ill-effects.
Plate 3Hot air staking was selected by LINPAC in preference to other fastening methods through its ability to provide consistent and cost-effective, vibration-proof assembly
In its evaluation, LINPAC considered a number of alternative fastening methods - including ultrasonic assembly and hot contact staking - in addition to the PHASA hot air system. However, it found that each of these presented its own particular problems, ranging from joint brittleness due to degradation of the base material and stringing of the plastic material as it adhered to the hot forming tools, to the need for operators to be provided with ear defenders. By contrast, the PHASA system offers a number of all-round advantages.
In operation, the 1,422mm long leaf screen mouldings are first loaded on purpose-designed three-piece fixtures mounted in the PHASA machine. The mouldings carry three semi-tubular pegs, which are used to locate the trough mouldings in position by hand. On initiation of the automatic 30 second cycle, the workpieces are transferred to the unit's heating station, where a manifold directs hot air accurately over the tops of the pegs. Once they have reached their plastic state, cold forming tools clamp the two components together, while simultaneously re-shaping the ends of the pegs into rivet heads to provide a permanent, vibration-proof fixing.
The system offers precise control over all process parameters, enabling the risk of heat marking on the all-important visible reverse face to be eliminated. In addition, the resultant joints are impressively strong, with ultimate joint failure occurring through shearing of the material at the base of the peg, rather than at the formed rivet head.
Simple light beam guarding is incorporated within the machine; along with sensors to prevent cycle initiation if components are missing.
"Ease of use is further enhanced by the system's reliability, which means we only need to employ visual inspection methods", LINPAC reports. "This is backed by the ability to achieve rapid production change-overs to accommodate left or right hand drive versions of the finished vehicle.
"Since its commissioning at our Witton site in Birmingham, the PHASA equipment has performed extremely well. As we ramp up to full production, we are confident that it will be well able to meet the projected 1,500 assemblies a week required by Jaguar's Castle Bromwich plant. It's a fast, reliable and attractive fastening method, which mirrors the qualities of the end product itself."