In plastic welding, conventional LINEAR ultrasonic welding heads are arranged vertically and use a converter, operating at between 20kHz and 40kHz together with a booster, to increase the amplitude. The sonotrode or horn is in turn coupled to the booster, which utilises the change in cross sectional area of the sonotrode to magnify this amplitude at the working face. This configuration of components is known as the Ultrasonic stack. By using a pneumatic actuator in conjunction with the energy being delivered via the sonotrode, the process creates local heat and melt through ultrasonic agitation of the polymer molecules. The pressure from the pneumatic actuator force collapses the molten joint feature and holds it in position until the weld joint has solidified.
When used in metal welding (usually non ferrous metals) LINEAR ultrasonic welding operates in the horizontal plane with the ultrasonic stack in the horizontal mode. This oscillates the top part of the welded assembly about the bottom part as a friction weld. This causes a molecular bonding of the two surface layers.
The LINEAR ultrasonic weld process is widely used across numerous industries but has limitations in critical applications and the physical ways in which it can be applied.
The use of linear ultrasonics as a process for welding, joining and sealing of plastics has been widespread within industries such as automotive for many years. The characteristics of the conventional linear ultrasonic plastic welding process can present issues when applied in certain applications, commonly within the electronics or medical device industries.
This is due to concerns over possible damage to fragile electronic components or perforation of micron thin seals and membranes during the ultrasonic vibration cycle. The vibration is normally imparted into the joint surface, but there is a subsequent risk of damaging vibration being transferred into the lower component part.
In ultrasonic metal welding, the linear process has limitations due to the small size of the contact face area. The process also has a single direction of applied friction and the orientation of the ultrasonic stack creates difficulty in accessing over or into parts in this mode.
TORSIONAL Ultrasonic welding or Soniqtwist® as we have called the process within Telsonic addresses these issues.
The Soniqtwist® technique developed by Telsonic in Switzerland eliminates these problems using small circumferential amplitudes in the horizontal plane on the end of a vertically mounted sonotrode face.
The converter is mounted tangentially to the booster axis thus generating reciprocal circumferential amplitude movement of the specially designed sonotrode face. The Soniqtwist® process creates a reciprocating circular ultrasonic friction weld of the upper contacted film, membrane or rigid part component about the lower component part.
The process relies on the sonotrode and lower anvil to "purchase" on the surfaces of the upper and lower part. This is achieved using textured tool face features such as serrations or fine knurls to deliver positive relative movement. Vibration transmission to the lower part of the assembly is minimal, which is a key benefit of the process.
The vertical force from the electronic proportionally controlled pneumatic actuator used in the Soniqtwist® configuration, collapses the molten joint (or in the case of metal welding creates the molecular surface bonding of the metals). This then maintains the required pressure until the weld joint has solidified.
The amplitude of oscillation is typically a maximum of 60 micron and “centres” on completion meaning no offset of parts. In this process plane, 20kHz frequency is used as the platform for a wide range of amplitudes and achieves weld and seals in typical Ultrasonic cycle times (usually sub 1 second).
In plastics, the Soniqtwist® process allows even the most delicate electronic components and membranes to be joined, welded or sealed as the vibration is delivered in a horizontal plane and not in the “normal” direction/orientation into the part.
This weld delivery mode reduces imparted vibration into the lower part (which usually accommodates the delicate aspects of the assembly) by as much 90%.In the case of a membrane being directly welded or constrained in the assembly, it creates no vertical oscillation negating “diaphragming” fatigue at the membrane centre.
The process also negates unwanted secondary welding of parts in the assembly, which is sometimes seen with linear welding in assemblies with a close fit of similar materials. As an added benefit, in plastic torsional welding the process emits much less noise when compared to the linear process.
In metal welding, the circular reciprocating oscillation friction delivery and the ability to access parts from above, allows applications other than obliquely shaped overlaid parts to be considered.
Telsonic initially developed this process in the early 1990’s as a surface friction weld for circular non- ferrous pressurised metal enclosures where process controllable, strong, fast, hermetic sealing was required in specific markets such as pressurised devices and pharma/medical devices.
Furthermore, the Torsional ultrasonic process creates molecular bonding, meaning that even dissimilar materials could be bonded such as Aluminium to High Density ceramic for the specialist battery industry. It was a unique process developed by Telsonic and was part of our welding range that demonstrated our reputation as an innovative supplier of active ultrasonic industrial equipment.
During early 2000 the application of the technique was extended further by Telsonic into rigid plastics, foils, flexibles and composite polymer based materials with particular focus on tough engineering glass filled plastics applications. Today the process can be applied to most polymer types applied in applications where the conventional linear concept has reached it’s limits.
Releases product design constraints - The Ultrasonic process is highly desirable in the manufacture of any critical plastic high volume component as it is extremely controllable and fits well with the medical, pharma, electronic and sensor industries where processes need to be fast, extensively controlled, validated and clean. Telsonic’s extension of the Torsional Soniqtwist process into plastics supports our market expansion strategy with blue sky thinking, using our extensive experience of the technique while answering new industry challenges. In plastic products, this technical innovation significantly broadens the opportunities for the designer in many new delicate or difficult critical applications, where a design can now allow the use of joining by the Ultrasonic welding, sealing or bonding process previously not viable with the linear technique.
Capitalises on new market Drivers - New opportunities for the process have arisen and we are seeing consequent market substitution for previous processes that now have to change with new product development borne from new legislation, links to eco friendliness and recycle chains. These drivers present new challenges for the designer beyond simply reducing non- recyclable joining elements or mechanical or glue fixings.
Can you provide features and benefits for designers and product manufacturers that support the use of the Torsional Soniqtwist® process?
Here are typical process benefits linked to the market drivers above that should help get product designers into the mindset.
One of the big early applications for us was membrane welding made possible using the Soniqtwist® technique.
Thin films and membranes, which have a typical thickness of only 50μm, are used to create a hermetic air tight seal on medical pots, devices, filters and drug delivery systems. It is essential that any process used to weld the delicate film or membrane media does not induce any defects or damage.
The vertical amplitudes produced across the face of a sonotrode or horn, when using conventional ultrasonic welding techniques, causes a diaphragm effect when welding a thin film or membrane. This in turn may result in perforation of the membrane, effectively rendering the conventional ultrasonic welding process unsuitable for this type of application.
Soniqtwist® however, produces small amplitudes of typically 30μm pp in a circumferential manner at the perimeter of the seal, with the torsional amplitude diminishing to almost zero at the centre of the membrane or film. Soniqtwist® does not stretch the membrane during welding nor does it cause a diaphragm effect or induce perforation of the film.
The Soniqtwist® technique therefore effectively eliminates the risk of perforation, when welding polymer based foils, films and membranes. The technique also has the advantage of speed, with complete weld cycles being achieved in less than 1 second. The unique characteristics of Soniqtwist® also enables multiple membranes, in close proximity to one another, to be processed without causing any previously welded membrane to become dislodged or lose its hermetic seal. This benefit is not guaranteed using conventional ultrasonic welding techniques.
To serve the markets for Torsional welding applications we offer ranges from manual benchtop machines through to equipment for integration into semi and full automation. To support this we have our TSP –E range of manual machines with loading and guarding options with proportional valve control and generator power facility up to 10kW and actuation force up to 8000N.
For Semi Automation and special purpose machine applications we offer a TSV range in proportional valve controlled actuator form up to 6.5kW and 3000N. We also offer a modular range of components without actuation for mount in special purpose machine pneumatic or servo based systems.
Our new TSC5 touchscreen/controller complements the equipment across these ranges and offers a choice of weld modes, with quality windows, Statistical process control, intuitive graphical user interface and data export and network communication. Finally, the horns (or sonotrodes) are specially designed for the torsional process using enhanced FEA techniques by Telsonic to critical dimensions to achieve the torsional amplitudes.
See our website which shows all our processes including Soniqtwist®, our activities and group companies worldwide. All our subsidiaries have demonstration equipment where products can be demonstrated or tested on Soniqtwist® Torsional welding machines. In the UK we also have the Soniqtwist® Torsional process demonstrated on the stand at the annual Advanced Engineering Show at the NEC, Birmingham held in November.
Martin Frost has had an extensive career which began as a time served mechanical engineer progressing into mechanical design, contract management and Industrial sales in various companies primarily engaged in hydraulic systems. He joined Telsonic UK in 1996 and is now UK Sales Manager responsible for UK sales of the Telsonic Ultrasonic portfolio in the North of the UK and the companies UK marketing promotional activity.
Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited (T/A) AZoNetwork, the owner and operator of this website. This disclaimer forms part of the Terms and Conditions of use of this website.
Stuart graduated from the University of Wales, Institute Cardiff with a first-class honours degree in Industrial Product Design. After working on a start-up company involved in LED Lighting solutions, Stuart decided to take an opportunity with AZoNetwork. Over the past five years at AZoNetwork, Stuart has been involved in developing an industry leading range of products, enhancing client experience and improving internal systems designed to deliver significant value for clients hard earned marketing dollars. In his spare time Stuart likes to continue his love for art and design by creating art work and continuing his love for sketching. In the future Stuart, would like to continue his love for travel and explore new and exciting places.
Telsonic UK, Ltd.. (2019, August 01). Ultrasonic TORSIONAL Welding – Understanding the Process Benefits, Expanding Applications and Product Design Possibilities. AZoM. Retrieved on September 15, 2019 from https://www.azom.com/article.aspx?ArticleID=12022.
Telsonic UK, Ltd.. "Ultrasonic TORSIONAL Welding – Understanding the Process Benefits, Expanding Applications and Product Design Possibilities". AZoM. 15 September 2019. .
Telsonic UK, Ltd.. "Ultrasonic TORSIONAL Welding – Understanding the Process Benefits, Expanding Applications and Product Design Possibilities". AZoM. https://www.azom.com/article.aspx?ArticleID=12022. (accessed September 15, 2019).
Telsonic UK, Ltd.. 2019. Ultrasonic TORSIONAL Welding – Understanding the Process Benefits, Expanding Applications and Product Design Possibilities. AZoM, viewed 15 September 2019, https://www.azom.com/article.aspx?ArticleID=12022.
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