Fasteners and Sealing


be achieved with ultrasonics welding - such as a maximum joint length of around 250mm - and one type of application that has proved difficult is the welding of membranes to other components; here, the membrane can behave as a diaphragm (drum skin) and vibrate along its axis, thereby incurring damage. In the medical industry in particular, where there is


concern about loose fragments that might be inhaled in certain applications, such damage is unacceptable. Alternative methods have therefore had to be used for joining, say, filter media to housings for medical devices. However, Telsonic has developed an innovative solution to this problem that enables high-quality joints to be made without damaging the membrane component.


Welding with a twist


Traditional ultrasonic welding has the main system components aligned longitudinally. But with the patented Telsonic Soniqtwist technology, the converter is mounted tangentially to the booster, so the sonotrode exerts torsional vibrations on the workpiece rather than axial vibrations (Fig. 1). Membranes are therefore not subjected to any axial vibration, so they can be welded without risk of damage. In addition, some electronic components can be welded using the Soniqtwist technology, whereas conventional longitudinal ultrasonic welding can cause internal damage (Fig. 2). According to Telsonic, the Soniqtwist technology can also be used to join non- ferrous metals to ceramics or glass, with the ultrasonic energy being converted into a molecular surface bond between the dissimilar materials.


Telsonic is the IPA 3505 (Integrated Power Actuator) for spot welding or multi-point


welding (Fig. 3). Traditional ultrasonic welding systems require


a separate generator for each welding head or, alternatively, fewer welding generators and a means of switching so that each generator can serve multiple welding heads - albeit with penalties in terms


of increased system complexity and longer cycle times. In contrast, the PA 3505 is a compact, lightweight


unit that has a fully integrated actuator, miniature generator and converter. Telsonic says that this unit is


cost-effective for use as a standalone fastening device or in larger numbers in fully automated welding systems.


Fig. 3. Telsonic’s IPA 3505 is a compact, lightweight unit that has a fully integrated actuator, miniature generator and converter for spot welding or multi-point welding.


The IPA operates at an industry-standard frequency of 35kHz with a power and force capability of 500W and 350N, respectively. Each self-contained unit has an adjustable 50mm stroke with integral damping and upper and lower stroke sensors.


Laser welding


Target markets for the IPA are the automotive industry, together with industrial and packaging sectors. In the automotive sector, for example, Telsonic says the IPA is useful for oblique face spot welding in heat-sensitive areas such as attaching insulation and sound-proofing materials, plus it offers savings in space and cost for pin swaging and penetrative spot welding of interior trim parts such as A, B, C and D pillars, carpet areas, glove box assemblies and load space components, together with exterior components such as wheel arch liners and engine bay covers. Already IPA units have been used in the manufacture


of door trim panels, where as many as 44 units have been incorporated within a compact machine that produces left- hand and right-hand panels simultaneously. Furthermore, the compact


dimensions and low weight (4.2kg) mean the IPA can be readily mounted on a robot arm for spot welding operations on complex three-dimensional components. Turning to laser welding,


Fig. 2. Whereas conventional longitudinal ultrasonic welding can damage fragile electronic components - such as in these sensors - the Soniqtwist process is said to be safe to use.


there are generally two types that designers could use: direct laser welding and transmission laser welding. Direct laser welding would normally be restricted to the welding of thin films, as the radiation from the CO2


laser is


readily absorbed by the plastic. In transmission laser welding, Nd:YAG, fibre and diode


Another development in ultrasonics from


lasers are used instead, and the radiation from these is less readily absorbed by plastics; by directing the laser at the joint through a transmissive plastic and by selecting a second plastic material that will absorb the laser energy, heat can be generated at the joint interface. However, if the designer cannot specify an absorbing plastic


for the second component, then an alternative is to apply an opaque surface coating at the joint. Transmission laser welding is capable of welding thicker


parts than direct welding, without marking the outer surfaces of the components.


Transmissive plastics


Where two transmissive plastics are to be joined, the traditional approach is to use a carbon black absorber, but today there is a clear product called Clearweld that absorbs infrared. Invented and patented by TWI, and subsequently licensed


to and commercialised by Gentex Corporation, Clearweld enables virtually invisible welds to be made in clear or coloured plastics.


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