How Does Ultrasonic Welding Simplify The Assembly Of Medical Products

Date:Oct 10, 2019

How Does Ultrasonic Welding Simplify The Assembly Of Medical Products

Since many plastic products are too complex to be molded in a single piece, it may be necessary to assemble their components into a finished product using one of three joining methods: mechanical fasteners, adhesives or plastic welding.

Ultrasonic welding is a popular industrial assembly technique that uses heat and pressure to form a solid state weld between plastic parts. The components are fixed in the tool and then subjected to high frequency (10-70 kHz), low amplitude (1-250 μm) mechanical vibrations, creating intramolecular friction, melting the mating surface and creating strong molecular bonds. Ultrasonic welding is widely used to join thermoformed plastic components because they do not require chemical solvents, adhesives, screws or additives.

The ultrasonic welding process is integrated into the production and automation of high-volume parts because the welding cycle is fast – usually less than a second – and no consumables are required. Typical plastic part designs require only minor modifications to ensure repeatable high-strength ultrasonic welding components. The most common (usually "mold safety") modification adds a small "energy director" to the part interface. The energy director melts and flows to join the two surfaces. Under ideal conditions, the polymer chains from each side of the mating portion migrate at the interface and become indistinguishable from the parent material.

Many thermoplastics, amorphous (such as polystyrene) and semi-crystalline (such as nylon) can be ultrasonically welded. Ideally, the two parts in the weld should be the same material. However, if the melting temperatures (glass transition temperatures, Tg) of the different plastics are very close, ultrasonic welding can be performed on a combination of many different plastics.

Ultrasonic welding can provide significant advantages in the assembly of medical devices that would otherwise have to be connected by screws and solvents. Binders and solvents have longer processing times, may introduce contamination and are difficult to dispense accurately. Minimally invasive surgical instruments such as catheters, cannulas, lures, and trocars have typically achieved great success with ultrasound connections.

For applications where the vibrations used in ultrasonic welding can adversely affect microelectronic components or precision component structures such as membranes or filters, other plastic joining techniques are readily available. Another option is laser welding, a vibration-free process that produces clean and sealed welds between various polymers. These advantages and superior aesthetics make laser welding the technology of choice for plastic components used in many advanced medical applications, from in vitro diagnostic test products to wearable technologies for remote monitoring or microfluidic drug delivery.

There are many choices, problems and challenges in the design, development and production of reliable, repeatable connection process solutions. The expertise provided by the material connection supplier can have a positive impact on everything from proof of concept to prototyping, scalability, data collection, and compliance. Engage experienced engineering experts at an early stage to enable manufacturers to determine the best connection technology for their products. For medical device marketers who design and manufacture on multiple continents, it is also important to work with globally capable technology providers who can provide local welding design and manufacturing expertise and support the implementation of equipment assembly.

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