Ultrasonic TORSIONAL Welding – Understanding the Process Benefits, Expanding Applications and Product Design Possibilities

Interview conducted by Stuart MilneMay 22 2015

Martin Frost – UK sales manager, Telsonic UK the wholly owned subsidiary of Telsonic AG Switzerland, talks to AZoM about the ultrasonic torsional welding.

Can you give a brief introduction to Ultrasonic welding used in Plastics and Metals welding?

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.

Plastic Welding - Conventional Ultrasonic Principle

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.

Ultrasonic LINEAR Metal Welding Principle

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.

What are the limitations of the Ultrasonic LINEAR welding processes?

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.

How does the Torsional Soniqtwist^® Ultrasonic welding process work?

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).

How exactly does Soniqtwist® Torsional welding address the issues in relation to linear ultrasonic welding?

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.

Why did Telsonic take the initiative to develop Torsional welding Soniqtwist® technology?       

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.

Why the emphasis on Soniqtwist® Torsional welding today?

There are 2 main reasons:-

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.

• Ability to weld thin walled components – reduces component cost and/or allows use of different materials
• Ability to weld rigid or flexible part applications with a degree of sealing surface contamination – Reduces reject rate and justifies the desirable use of measurable, controllable energy saving Ultrasonic technology in packaging, especially in medical/pharma and safety critical applications.
• Ability to weld thin walled components with decorative or painted A side surfaces ie pre-painted automotive bumper panels – Supports vehicle weight reduction targets for vehicle life carbon footprint.
• Very high weld strength in critical materials due to molecular bonding action not achievable using linear method. Offers design freedom and product performance
• Can be used for precision forming or swaging of features not possible in injection moulding ie break off features or thin wall features. Offers design freedom and product performance
• Reduction in Particle production due to compact fusion action ie very small melt cavitation is produced. Supports GAMP practice in medical /Pharma applications
• Helium tight welds are possible due to molecular bonding level. Cost reduction against other sealing methods. Offers design freedom and product performance.
• Excellent process capability without detrimental effects on critical internal assemblies including membranes and chemical layers. Allows and justifies use of desirable Ultrasonic technology in this application.
• Can be applied to non- circular products! The process is not limited to circular parts, with rectangular and non- symmetrical shaped components capable of being welded, sealed and joined using this technique. Offers an ideal “process fit” and is peerless if the component is high volume and has delicate assembly parts
• “Punch and weld” possible for high volume small diameter membranes onto rigid filter bodies - Membranes and foils with an inline 2 stage die cut process followed with a Soniqtwist torsional weld. Measurable, fast and clean and an ideal process fit.
• Unwanted Secondary “tack” welding is eliminated within close fit welded assemblies as little vibration is imparted beyond the weld interface into the assembly. Reduces reject rate and design freedom in safety critical assemblies containing components of same family material.
• Ability to Molecular bond dissimilar materials ie Aluminium to high density Ceramics. Fast, measurable and a peerless mature process
• Ability to weld high volume sensors and energy scavengers with delicate assemblies of PCB’s, chemical layers and Piezo crystal parts. Offers an ideal process fit.
• Ability to seal Aluminium rigid or flexible packaging WITHOUT plastic coating – Offering cost reduction and desirable where assemblies must be single parent material.
• Joint preparation involves similar injection moulded features to Linear Ultrasonics with some special tooling face surface preparation - no 3rd party joining material application – Quality control benefit and cost implication. Telsonic will advise on these joint preparation requirements.
• As with any Ultrasonic welding process, energy use is extremely efficient with weld energy on demand – “on demand” Ultrasonic energy can be up to 40 x less than with constant heat processes for a given joint and rate of production.

Can you provide an example case study of Soniqtwist®?

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.

What solutions do you have for the process to be delivered on the factory floor?

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.

Where could  we find out more information about Telsonic group, the process and  see the process in action?

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.

About Martin Frost

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.

Martin has a HND in Mechanical Engineering and an MBA majoring in quality management systems.