After graduating in Metallurgy and Materials Science from Birmingham University, Nicki Taylor joined TWI's Plastics Group in 1985. She is currently Technology Manager for Plastics, working in the Advanced Materials and Processes Department.
Dr Christian Bonten has studied mechanical engineering in Duisburg and plastics technology in Aachen, Germany. From 1994 to 1998 he was lecturer and member of the scientific staff of the Institute for Plastics in Mechanical Engineering (IKM), at University of Essen, Germany. Since then he has been head of the department Research & Development at IKM.
A large number of improvements in plastics joining technology have been stimulated by the end user. The influence of the suppliers to the car industry and the car industry itself, along with the telecommunications and construction industries and medical technology, is reflected in recent developments.
Nicki Taylor and Christian Bonten review the latest advances in plastics joining that were exhibited at the 1998 Kunstoffe Show in Düsseldorf.
In addition to new ways of applying energy using laser, infra-red and microwave radiation, development work from the majority of manufacturers was aimed at greater user-friendliness and better ergonomics, in addition to enabling equipment to function more effectively.
Series or mass production welding
Ultrasonic, vibration and hot plate welding are those most commonly used for automated production of welded components. However, after extensive development work, Wegener demonstrated a new piece of equipment - a fully automated extrusion welding robot, with which large engineering components
eg in container construction, can be welded. The robot has a hand strength of 60kg and, thanks to its strength and track regulation, facilitates a reproducible welding process entirely independent of position, even when bridging large tolerances. It is claimed by Wegener that automatic fabrication should be profitable if at least three identical components are to be joined.
In addition to further developments to their engineering in the heating element and vibration-welding sector, Bielomatik was showing its new laser-welding machine. One component to be joined which is transparent to the laser beam can be joined to another component which absorbs the beam in a cycle time similar to that required for ultrasonic welding, if the components are small. In this case the heat is applied almost exclusively directly to the joining area, as a consequence of which weld seams can be realised which are free from bulging and abrasion. According to Bielomatik, this process will be particularly suitable for the medical technology sector.
Leister also showed its new laser welding systems in the Modulas series. When contour-welding, one transparent and one absorbent component to be joined are welded sequentially, ie a laser beam is routed along the seam contour, which may be three-dimensional. When undertaking simultaneous welding, the beam is fanned out optically depending on the seam, enabling welding times to be produced on small components which are similar to those produced in ultrasonic welding.
Branson presented its new developments in the vibration welding sector (PMT-control, PPL-vibrating head) and ultrasonic welding. It is possible to regulate welding speed precisely using a new servo drive for the ultrasonic welding press. During this process peculiarities, relating to the components to be joined and specific to the materials, can be taken into account automatically whilst at the same time increasing the strength of the seam and the particle outflow via improved melt flow.
The digital generators from Hermann Ultraschalltechnik enable the natural frequency of the sonotrode used to be determined at the push of a button in order to guarantee the best possible operating conditions for welding. Rinco Ultrasonics have facilitated a fast tool change for different applications in their ultrasonic welding machines thanks to the modular structure of the latter. The car industry is already said to be benefiting from this.
Telsonic Ultrasonics is using a new generation of microprocessors which can be maintained remotely by modem. Telsonic also uses a servomotor drive and a digitally programmable force/path profile in its ultrasonic welding equipment. The ultrasonic torsion welding process was demonstrated for special applications, eg in medical technology; the longitudinal movement becomes a torsional movement and an ultrasonic friction weld is produced in the joint area. Sonics and Materials work with larger components (300 x 300mm 2) at 15kHz. Here too, an electrical feed and a high resolution load cell are used which enable the precise control of the joint line.
The model of a high frequency welding system on a scale of 1:5 from Albert Früchtling was particularly striking. According to information from the company, the full size welding systems are being used successfully for laminating in the car industry, some of which involves large surface areas, and in the furniture and leisure industries. The hand-held ultrasonic welding unit from Albert Früchtling only weighs 900g and, for example, enables welding work to be undertaken in areas where access is difficult.
Welding of semi-finished extruded products
Hand-held units
The Plastotherm extruder product group from Munsch has been updated visually and mechanically. According to Munsch, the patented compression cone in front of the screw tip generates greater homogeneity in the melt and thus helps to reduce bubbles in the extruded material.
The new generation of extruders from Wegener is currently undergoing customer tests and will be available during 1999. The high level of user-friendliness because of the high power/weight ratio (weight of machine/output) is supplemented by the second handle, which has a variable setting, and the integration of the supply of air and electricity in a single hose.
Leister showed the Weldmax mini-manual extruder which combines the electronics, fan and barrel in a compact form. The handle is below the centre of gravity of the manual extruder, which represents a beneficial further development in so far as ergonomics is concerned.
Machine mounted
With the assistance of Servoplast, Omicron demonstrated a heating element butt-welding unit with servo-drive. According to company information, the servo-drive requires no maintenance and eliminates disruptive influences up to the maximum system power of 10kN. The system can be used for extremely precise implementation of the warming up and welding pressures recommended by the DVS. The operating unit with touch screen and pictogram guidance is extremely user-friendly.
A new generation of heating element butt-welding machines for site use was demonstrated by Rothenberger in its Roweld Varioline series. A special, patented design concept permits the use of a variable working angle and therefore improved ergonomics. Transport rollers in the chassis make transportation easier.
Welding PVDF pipes was demonstrated particularly effectively by Widos. Instead of being routed to a conventional heating element, the pipe ends are directed to a welding head. They are heated volumetrically in the latter using microwaves. The warming process is short and the power consumption particularly low at 250W (this power is only used during the warming process). The welding head remains cold and is therefore user-friendly since it avoids any of the melt adhering to it.
Georg Fischer promises the fastest butt-welding process in pipeline construction with its IR-welding machine for a range of pipe sizes. Instead of conducting heat through a heating element, the ends of the pipe are heated effectively by an infra-red radiation unit. Systematic investigations of the cooling characteristics of the pipes have enabled the time for which the pipe components need to remain clamped to be defined by IR-measurement of the surface temperature of the joint seam. The heating and joining part of the welding machines can be removed and operated remotely enabling welds to be undertaken on existing pipelines, where access is restricted.
Agru exhibited a pressure-dependent control for the IR-welding process. Existing pipelines are mostly welded using an electric sleeve. In this situation, the new automated welding unit from Frank is welcome because, in addition to continuous temperature measurement on the electric sleeve, its new, ergonomic design sets it apart from other units.
From the institutes
It is encouraging that in a number of cases, research institutes had a significant involvement in new developments by the manufacturers. The KTP in Paderborn, for example, undertook the research into basic principles for the laser-welding machine from Bielomatik. The IKP in Stuttgart was responsible, together with the ICT in Pfinstel, for the research into the basic principles for the microwave welding unit from Widos.
The IKV in Aachen presented its investigations in co-operation with Laserline in the through laser-welding technology sector. It was also possible to implement laser transmission impressively through dyed components to be joined as a consequence of knowledge about the connections between laser penetration depth and pigment concentration in addition to pigment size.
The Institute of Polymer Research in Aachen is working on the characterisation of the phenomena of interfaces in polymer-metal bonds. High resolution processes such as atomic force microscopy (AFM) are used for this purpose.
The LKT in Erlangen undertook the first www presentation of vibration welding worldwide. The animated, interactive presentation is extremely user-friendly and is in two languages. In addition to the current state of the art, it also presents the most recent results of the LKT plus examples of applications for vibration welding. In this way learning is made easy.
The IKM in Essen is undertaking investigations into the weldability of cross-linked polyethylene. During this process, research will also be undertaken into what actually happens in a weld seam, and into how the transference of force takes place as fast as possible after cooling down.
Joining using adhesive
New applications for adhesives are often used in the car industry. Substituting adhesive for heavy rivet heads, when attaching friction coatings by applying it over a wide area in clutches and brakes using the adhesive Supraplast from Süd-West Chemie, is only one example of this. According to information from the company, the adhesive, based on phenolic resin, is able to withstand the mechanical, chemical and thermal stresses.
The product Verstamelt from CreaNova (Hüls Group) is a hot-melt adhesive based on polyamide and polyester. It proves its wide range of applications in the car, telecommunications and textile industries.
Technical coatings based on silicone are used in the car (airbag), construction and textile industries. According to information from Wacker-Chemie, these coatings can be attached with adhesive using silicone adhesives from the Elastosil range. Amongst other things, the advantages of this are the good elasticity of silicone over a wide temperature range (-50-200°C), its age-resistance, and the fact that it is difficult to burn.
Joining using mechanical connections
Mechanical joint connections have the advantage that the majority can be subsequently disassembled. This also applies to the plug-in coupling from Böllhoff. This connection element enables rapid assembly and dismantling of engineering components. The new connection element Rivkle-Elastic enables vibrating components, eg in the engine compartment, to be screwed in place securely and simultaneously to be acoustically decoupled.
Ejot offers the new VARIOboss for fixings in car doors and instrument panels with thicknesses of up to 2.5mm. According to information from the company, this fixing can be assembled entirely automatically and offers an integrated sealing function with high resistance to vibration. The new line fixing system FLASH offers the possibility of fixing lines quickly using just one screw per fixing element which can be fixed anywhere, eg vehicle floors.
Weber Kunststofftechnik have a patent on the Klemmfix-System, which enables several lines and pipes, even of different diameters, to be fixed simultaneously to one Klemmfix fixing element without a tool. The lines or pipes can be removed individually and put back in place and fixed again.
The automatic embedding machine HS3000 from PSM was demonstrated for automatic installation of very small inserts especially in the telecommunications sector. Large machines from the same manufacturer are already being used successfully in mass production in the car industry eg for installing inserts in intake pipes.
Nuts and threaded rods made of Durostone, the glass-fibre reinforced epoxy or vinyl ester resin from Röchling, are used in chemical or maritime areas in particular. According to Röchling, the product's excellent characteristics are its corrosion-resistance and high media resistance with simultaneous electrical and thermal insulation plus the saving on weight.
To learn more contact Nicki Taylor .
