Thanks to computerized weld modes, medical manufacturers routinely use ultrasonics to weld, insert, or stake plastics and other parts into a wide range of medical device assemblies with the expectation of high consistency and quality. Popular weld modes optimize welder performance around a single factor critical to part quality, such as energy (joules per weld), peak power, distance (part collapse depth), or total weld time. These modes, along with increasingly precise digital control of actuator force and down-speed, weld amplitude, and other parameters, make real-time performance monitoring and quality tracking possible.

Yet, for all of the advancements available in ultrasonic technology, there are certain component, material, or application characteristics that can make assembly quality very difficult to control using single-factor weld modes. Examples of such hard-to-handle applications include:

  • Welding parts atop plastic assemblies containing compressible internal elements, such as elastomeric seals or cores.

  • Welding small, thin, or complex plastic parts onto plastic structures directly atop sensors or delicate electronics.

  • Ultrasonically swaging or inserting posts or other structural elements into substrates that vary in hardness or structural consistency, such as composites.

To solve assembly problems like these, ultrasonic suppliers and manufacturers often choose to augment single-factor weld mode controls with additional information collected during the welding process, such as external measurements, data points, or signals.

These data, collected before or during the weld process, can be used to assist a single-factor weld mode in achieving a more precise, consistent result in such areas as weld or insertion depth, insert pull strength, or part dimensional stability. However, the cost and complexity of developing and using external measurement or sensing devices to augment weld mode controls can be significant, especially when mass production is required.

To overcome the limitations of single-factor weld modes and eliminate the need for external measuring devices, a new patent-pending dynamic mode has been developed by Emerson and is now available in its most advanced ultrasonic welder, the BransonTM GSX-E1 2.0 welder. Dynamic mode leverages the welder’s advanced electromechanical actuation system, combining computing power and cutting-edge algorithms with high-speed data communications to monitor, recalculate, and adjust the weld process in real time and achieve an optimized target result.

To use the welder with dynamic mode, the user selects a single-factor weld mode, such as energy, distance, or time that is providing the best application results so far. Then, the user enters two additional scores, which act as limits for dynamic mode activity. The first is a material density score that, essentially, characterizes the hardness or resistance of the material that is to receive the welded, staked, or inserted part (e.g., a low density score equates to a harder, more resistant material). The second is a weld reactivity score, which is used to adjust the degree of variability allowed in the target result (e.g., a low reactivity score equals a more homogenous result).

In operation, dynamic mode monitors each weld cycle, using the density and reactivity limits to adjust the cycle in response to specific part-to-part variabilities throughout the production run. To get a better sense of how dynamic mode works, consider the following application examples.

Sealing a Fluid-Proof Cover over Medical Electronics

Imagine the need to weld a watertight plastic cover onto the shell of a very small medical device. The cover is contoured to fit around sensitive electronic components and complete the device’s protective structural shell.

  • Problem: The close-tolerance plastic cover must be bonded gap-free and watertight, but the weld process and cover structure cannot exert undue compressive force on the sensitive electronics. Reliance on a single-factor weld mode, such as distance, could in some cases result in excessive pressure on the cover and potential damage to internal electronics.

  • Solution: The combined material density and reactivity scores in dynamic mode can optimize distance mode in each weld cycle, allowing the actuator to achieve part-collapse depth sufficient for watertight sealing, yet detect and avoid levels of resistance that equate with the compression of electronic components.

Welding a Sealed, Elastomer-Core Plug

Consider a sealed, two-way connecting plug. The outer shell of the plug consists of a molded plastic cup and lid that contain holes through which metal connecting pins protrude. Inside, connecting pins are embedded in a compressible core of elastomeric plastic. Because the finished plugs must be air- and water-tight, the weld-on lid is designed to compress the elastomer radially around the connecting pins. A flat “fit” is essential for the lid, as is a consistent exposed length for the connecting pins.

  • Problem: The height of the plug’s elastomeric core may vary by up to 10 percent, so achieving consistent positioning, shell contact, and weld quality for the lid is very difficult. Use of a single-factor weld mode like distance mode would likely result in variances in the height of the lid/plug assembly and the exposed length of the connecting pins.

  • Solution: The density score in dynamic mode can adjust for the varied consistency of the elastomer by requiring not only that the actuator travels the required distance but also that it feels the required amount of resistance (e.g., contact with the harder material on the plug’s rim) before welding commences.

The new dynamic mode in the Branson GSX-E1 2.0 ultrasonic welder from Emerson recalculates and adjusts welds in real time to compensate for the varying depth and resistance of compressible plastic parts. (Credit: Emerson)

Inserting Structural Pins into a Substrate

Consider the need to insert structural plastic pins into plastic substrates that vary in hardness, like composites, while achieving consistency in insertion depth and pull strength. The structural pins fit into grooves essential for assembly of the larger product.

  • Problem: Inserts must deliver consistent strength despite variability in material hardness, the depth and diameter of drilled holes, and molded insert quality (surface roughness, flash). Use of a single-factor weld mode like energy to deliver precisely the same force for each insert could, as a result of multiple variances, result in overinsertion and substrate or insert damage or result in underinsertion, misalignment, or pull-out.

  • Solution: By augmenting energy mode with material density and reactivity scores, the dynamic mode feature is able to measure and moderate the input of weld energy for each insert, aiming for a target condition — a uniform measure of insert resistance — that equates with insert pull strength.

Conclusion

For many medical device and medical product manufacturers, current single-factor weld modes, together with continued advances in equipment precision and data-gathering capability, may well provide adequate margins of weld, assembly, and medical product quality. However, for manufacturers facing significant or unexpected application challenges, such as the need to manage multiple part- or material-related variables, new assembly technology like dynamic mode weld controls may be just what an assembly process needs. Instead of thinking about how to redesign a hard-to-assemble part or augment an existing weld processes with new sensors, ask an assembly technology supplier for help. The solution to an assembly problem may already be available.

This article was written by Tarick Walton, Global Product Manager – Ultrasonics for Branson Welding and Assembly, and Christoph Manger, Product Manager for Ultrasonics in Europe, Branson Welding and Assembly, Emerson, St. Louis, MO. For more information, visit here .


Medical Design Briefs Magazine

This article first appeared in the May, 2021 issue of Medical Design Briefs Magazine.

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