Addressing Frequent Issues in Ultrasonic Welding

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The process of ultrasonic amalgamation is globally accepted for the connection of thermoplastic components. It presents numerous merits such as the assurance and consistency of the process, reduced energy expenditure in comparison to other connection methods, conservation of materials due to the absence of necessities like adhesive or mechanical anchors, and savings in manpower.

Just like any other procedure, there are instances where perceived issues with this method could hinder the manufacturing process. The secret to solving and preventing these issues is to comprehend their probable sources.

Welding equipment with a higher frequency is perceived as being “less harsh” when applying ultrasonic energy to components.

The components designated for welding are subjected to a mechanical force, typically facilitated by a pneumatic actuator that secures the booster and horn. This force enables the transmission of mechanical vibrations to the junction of the material surfaces, concentrating the vibrations to generate intermolecular and surface friction. The resultant friction produces heat and a consequent melt, which hardens to form a welded joint.

An ultrasonic system is fundamentally composed of a power supply, an actuator, and a stack. The power supply is responsible for converting the standard 120-240V line voltage into a high-voltage, high-frequency signal. It also possesses the necessary programming to control the actuator and stack to achieve the desired welding result. The actuator, which can be operated pneumatically or by an electric servo, is responsible for moving the ultrasonic tooling towards the parts to be joined, applying the necessary force to facilitate the welding conditions.

The stack is the final piece of the ultrasonic system. It is responsible for transferring the vibratory energy directly to the parts at the sealing/joining surface. The stack is typically made up of three parts: the transducer or converter, which contains the piezoelectric ceramic crystals that oscillate at the frequency of the power supply signal. As these crystals oscillate, they expand and contract, creating a measurable mechanical motion, also known as peak-to-peak amplitude, on the output side of the transducer. The booster, the second section of the stack, has an attached ring in its mid-section and serves dual purposes: It acts as a mounting point for the stack into the actuator and also amplifies or reduces the output motion created in the transducer.

Paying attention to a “minor issue” at an early stage could potentially allow us to pinpoint and solve a challenge before it negatively impacts production.

The last piece of the assembly is the sonotrode, or horn, that interacts with the components to be fused. The shape of the horn is tailored to either fit the exact contour of the rigid components or to include a sealing pattern on its surface for use in film or textile applications. The design of the horn, in conjunction with the other elements of the assembly, aims to achieve the ideal amplitude output for the most effective ultrasonic welding process.

Common Challenges in Ultrasonic Welding

Difficulties typically arise in one of these four sectors:

  • Machinery: The ultrasonic welding machinery or the various welding elements are not appropriate for the task.
  • Operational variables: The settings applied are incompatible with the components being fused.
  • Raw materials: Alterations in the kind, makeup, or physical/mechanical properties of the materials used in the components occur.
  • Component design: Certain aspects of the component’s shape are not conducive to consistent or successful welding.

It’s crucial to highlight that a flaw detected in one domain might reveal a vulnerability or shortfall in another. Let’s begin with the machinery. It’s a common and often rational assumption that the tools and methods that yield successful results in one scenario will replicate the same success in another. However, this isn’t always the case. Globally, ultrasonic welders operating at 20-kHz are predominantly used due to their adaptability, high power, and high-amplitude outputs. They are also compatible with a large variety of tool sizes. For a contract manufacturer that produces ultrasonically welded components, investing in 20-kHz equipment can be a wise decision as it provides the prospect of future use in numerous applications.

Nevertheless, there are circumstances, particularly with small and fragile components, where the high power and high amplitude of 20-kHz equipment might be too forceful for certain assemblies, possibly causing damage. A probable solution could be to decrease the input amplitude, but this may not work if the amplitude used is below the suggested level for the polymer being welded.

Another alternative is to consider equipment operating at a higher frequency, maybe 30 or 40 kHz, given that the necessary tooling for the application is available at this frequency. Higher frequency equipment generates lower amplitude output, but makes up for it by resonating at a higher frequency. Consequently, higher frequency welders are perceived as “gentler” in applying ultrasonic energy to components. Electronic assemblies, particularly those with sensitive timers/oscillators and other components situated on printed circuit boards, have gained from this method. Similarly, components that experience excessive movement of one of the mating parts will often benefit from the switch to higher-frequency equipment.


Bonne specializes in producing machinery and systems for industrial ultrasonic welding technology. This technology serves as a method for permanently joining two metal components, including wire harness welding, terminal welding, metal spot welding, plastic-to-metal welding, and metal rolling welding, among others.

One prominent application of ultrasonic welding lies in the new energy automobile sector, where it is used for connecting instrument panel instruments, center consoles, or engine wiring harnesses. Additionally, ultrasonic welding finds use in various other industries, including the solar energy sector for battery soft pack welding, electronic industry welding, refrigeration industry, and automation equipment.

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