Ultrasonic welding is a widely accepted joining method in the automotive industry due to short cycle times and consistent weld results which can be reproduced across multiple production facilities worldwide. Applications range from interior (side door trims, centre console) to engine compartment (cylinder head cover, engine covers) through to housings and lighting, such as tail-lamp units of daytime running lights. Exhibiting for the first time at Feiplastic, Herrmann Ultraschall presented their solutions for increasingly demanding requirements from the automotive industry.
Automotive components welded ultrasonically (photos: Herrmann Ultraschall)
The requirements of components for the automotive industry have become increasingly complex: tightness, accurate dimensions and flawless surfaces are typical quality criteria. Amorphous and semi crystalline plastics are combined with a large variety of other materials. One good example for a sophisticated application is glass fibre-reinforced material fitted with membranes, as in pressure balancing elements (PBE) like controller housings and brake servo units. Herrmann Ultraschall offers over five decades of experience in ultrasonic welding and has continuously introduced technical innovations to meet growing industry standards. At Feiplastic the company showed the advanced ultrasonic welder HiQ Dialog with weld force profiling and process visualisation for demanding applications.
Ultrasonic welding machine HiQ Dialog (with weld force profiling and monitor for process visualisation)
Focused ultrasonic waves for a precise bonding process
The advantage of ultrasonic welding lies in producing a high-strength, gas-and watertight bond without any additives or consumables simply by means of ultrasonic vibrations. A titanium weld tool vibrating in an ultrasonic frequency of 20 – 35kHz melts and bonds the plastic parts in a precise manner. When introduced into the part the specific energy input starts a locally defined and temporally controlled melting process. Through a special joint design the ultrasonic waves are focused directly into the joint zone. The ideal joint design for injection moulded parts consists of suitable welding geometries with points or edges in the joining area. Hard, amorphous plastics such as PC, PS, SAN, ABS and PMMA have good transmission characteristics for ultrasonic waves. Semi-crystalline plastics such as PA, PP, PE and POM are more difficult to melt and are best welded in the immediate near field of the weld tool, called sonotrode. The ultrasonic supplier has to assume the role of application problem solver for the customer and should ideally get involved early in the design process of the parts. Welded parts can be processed immediately after joining, so that ultrasonic welders can be integrated easily into automation lines.
Visualisation of weld parameters improves process control
A good weld can be displayed visually. The graphical representation of the welding power, joining velocity and weld force permits exact statements about the quality of the joining process. A rapid and linear slope of the joining velocity curve is desired for even melt built-up and good, repeatable results. This avoids unnecessary loads on the parts and guarantees exact reproducibility of the welding process. However, complex parts, dissimilar materials and foreign objects like sealing rings pose challenges to a linear velocity. Only a controlled switchover to a different weld force in mid-process, as featured in the Herrmann HiQ ultrasonic welders, ensures the linear and smooth slope of the curve.
Sample automotive components, welded ultrasonically
Environmentally friendly technology
Because ultrasonic welders need no consumables to bond parts and require low energy consumption, the technology is viewed as being environmentally friendly: in comparison with other thermal joining processes, its overall energy footprint is reduced by 75%. This is due to power only being drawn during the actual weld time. Energy is focused specifically in the area to be joined and only during the actual weld cycle: no heat ramp up or stand by cycle is necessary. In addition there is no power dissipation through heat radiation as with other thermal processes.
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