For years, ultrasonic welding has been used in cleanrooms where plastic components are assembled to complete medical and electronic devices. That is unlikely to change. What is changing, however —rapidly — is the sophistication and complexity of these products and the level of precision and quality required to complete their assembly.
Specialized manufacturers know that cleanliness — especially prevention of particulate contamination — is of paramount importance, and most have already installed the latest in HEPA filtration, air pressure, and temperature control and monitoring systems to comply with all applicable standards. However, it is equally important for manufacturers to fully understand and appreciate that today’s applications require higher levels of performance in welding equipment than they did only a few years ago. Examples of challenging applications include:
- Plastic assemblies containing compressible internal elements, such as elastomeric seals or cores
- Small, thin, or complex plastic parts welded onto plastic structures directly atop sensors or delicate electronics
- Components involving posts or other structural elements that must be ultrasonically swaged or inserted into substrates that vary in hardness or structural consistency, such as composites
- Parts molded from bioplastics and other novel materials with narrow processing windows
It is necessary, then, to stay current with available welding technology. In fact, if ultrasonic equipment is even just seven years old, it may not be up to the task, and the consequences in terms of quality and productivity can range from the inconvenient to the catastrophic.
In ultrasonic plastic welding, parts are brought together under pressure by the acoustic stack, which generates a vibratory motion (amplitude) that is transferred to the part. These vibrations cause friction at the interface between the parts, creating heat and localized melting to form the weld. Ultrasonic welding is an inherently clean process, but it does involve moving parts, and particulate generation is always a possibility. In addition, quality standards — such as ISO 13485 in medical manufacturing — demand real-time control, process monitoring, data storage, and communication capabilities that may not be built into older welders.
State of the Art
Today’s advanced ultrasonic welders, such as the Branson™ GSX-E1 model from Emerson, incorporate technology and features that make them ideal for cleanroom applications. For instance, they are built with electromechanical (servo) actuators, which are far less likely to generate particulates than pneumatically actuated units. The new GSX-E1 welder qualifies for an ISO Class 5.5 cleanliness rating, and, if desired, a special cleanroom-friendly feature package, which includes stainless-steel exterior surfaces to make wipe down easy, can be added.
New power supplies that drive and control the welder also are drawing interest from cleanroom operators. These have transitioned in recent years from analog to fully digital systems that offer closed-loop feedback and tighter control of critical weld parameters. This change is important because, while the welding equipment itself is inherently clean, the specifics of each application — size, cycle times, polymer materials involved, and so on — influence particulate generation. Suppliers can work with customers to test applications and determine the ideal “recipe” to achieve high-quality results while also meeting cleanliness objectives.
For instance, the Branson GSX-E1 welder takes advantage of closed-loop feedback in the actuator to make split-second adjustments to force and amplitude. Both variables can be changed in 10-step increments such that, in a 1-second welding cycle, for example, the setting can be changed every 0.1 seconds to ensure optimal results.
State-of-the-art power supplies also use web services to enable remote connectivity. Medical and electronics manufacturers can control and monitor welding equipment from just about anywhere in a given plant or around the world. They can digitally monitor the health of their assembly systems by tracking key process indicators such as frequency or power draw. Variations in these and other values can provide early indications of problems in the acoustic stack. This, in turn, helps users identify near-term maintenance issues and avoid quality problems and unplanned downtime on the line.
In addition, the advanced data-gathering capabilities of these digital power supplies also enable users to monitor process parameters in real time, set high/low limits on weld results, and configure alarms that flag weld cycles of parts that fall outside process limits. This capability enables automated bad-part processing and data logging that can be indispensable for maintaining superior quality as well as the 100 percent traceability required under standards such as the U.S. Food and Drug Administration’s 21 CFR Part 11.
Cleanroom applications often involve complex parts with very tight welding tolerances or high levels of automation. Applications like these frequently require more advanced welding technology than older systems that optimize welder performance around a single factor that is critical to part quality such as energy (joules per weld), peak power, distance (part collapse depth), or total weld time.
To overcome the limitations of single-factor weld modes, Emerson has developed a new patent-pending dynamic mode that is available on the GSX-E1. Dynamic mode leverages the servo-actuation system, combining computing power and cutting-edge algorithms with highspeed data communications to monitor, recalculate, and adjust the weld process in real time and achieve an optimized target result.
When using dynamic mode, the manufacturer selects the single-factor weld mode — such as energy, distance, or time — that provides the best results in a new application. 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). Then, 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.
Getting to the Right Solution
Focusing on challenging applications in medical and electronic cleanrooms, along with new equipment and technology available to help ensure meeting quality and standards-compliance goals, is critical to advancing applications of new welding technology; however, not every situation will require top-shelf features or be best-served by ultrasonic welding.
Working closely with customers, supplier consultants use their extensive process expertise and consider alternative technologies — like laser welding, for instance — before recommending the appropriate equipment. Branson welding solutions, for example, are backed by deep technical knowledge, decades of application experience, and a global supply chain with sourcing, manufacturing, and customer-support capabilities.