Clean Infrared Welding
Clean infrared technology (CIT) can be used for clean joining of small, medium, and large parts. Precise plasticization occurs using noncontact heat input by medium-wave, metal-foil emitters that emit the same wavelength spectrum as the absorption range of most common thermoplastics. During the CIT process, the two-part halves to be joined are held in position a few millimeters from the metal-foil-emitter platen that follows the contoured profile of the weld seam. The platen uniformly pre-heats the weld area only, without risk of damage to pre-assembled inner parts. Once plasticization has occurred, the platen is removed, and the halves are brought together under pressure and allowed to resolidify, producing a clean, clear, weld that is virtually particle free.
How to Choose the Right Process
Although the many options available can make it difficult to determine which process is best for a particular application, the following thought process should work for a majority of applications.
The first consideration is material. Some materials are more readily compatible with a given process. Polyolefins, for instance, are somewhat limited when used with ultrasonic welding, but are recommended for all of the other processes. Ultrasonic welding is not recommended for use with thermoplastic rubber or thermoplastic elastomers (TPRs/TPEs), yet has limited capabilities in some applications and is recommended for others.
The second consideration is part geometry, which starts with the size of the part. One of the limitations of ultrasonic welding is the size of tooling. As a rule, the lower the frequency (20 kHz), the larger the tool (approximate maximum, 20 × 20 cm) while higher frequency processes (40 kHz) are limited to smaller tooling sizes (approximate maximum 6 × 6 cm) If the parts are larger than these ranges, it is necessary to consider either multiple units with ultrasonic welding or another joining process.
A second factor in part geometry is the complexity of the part and weld profile. Some assembly processes can accommodate part features easily while others cannot. Wall thickness and internal walls must also be considered. Clean vibration welding, due to its reciprocating motion, has difficulty welding long unsupported walls, while other technologies do not have an issue with these part features.
Production volumes cannot be overlooked. Some processes, like ultrasonic, can bond assemblies in fractions of a second, while other may take considerably longer. In some instances, it is possible to weld multiple parts in a single cycle to improve throughput.
Capital equipment cost should be the last consideration, although that may be easier to recommend than to put in practice. Keep in mind that if the process selected is based on initial price, the decision may not have considered the long-term product or application development: time to market and processing costs such as scrap, downtime, and mold changes.
Choosing a material joining equipment supplier with a broad portfolio of technologies, application engineers, and experience can be a valuable asset within the overall product development strategy. The “total cost of ownership” for the assembly process, including direct and indirect costs, should be considered.
For new or modified medical devices, all parameters — including design, materials, prototypes, and product performance, as well as processing time and costs — should be thoroughly evaluated to ensure that the appropriate joining technique is chosen. Again, start with all of the options by taking a “process neutral” approach.
This article was written by Tom Hoover, Sr. Market Segment Manager, Medical, Branson at Emerson, Danbury, CT. For more information, visit here .