By Jeffrey Frantz, Branson

Deciding on the best assembly process for your application can be very confusing. There are several options available, from mechanical fasteners and adhesives to heat and friction methods, each with distinct advantages. Further complicating matters is everyone seems to have the "best" solution.

To ultimately make the proper choice, each and every application must stand on its own. Every application has its own particular properties. To begin the process of selecting the proper assembly method, it is imperative to first define and list all of the properties, characteristics and requirements. This includes component material (do not exclude internal components), part geometry and end user requirements.

When selecting the assembly process that is right for your application, here is a thought process that should work for a majority of applications:

1. The first consideration is material. You will see in Chart A (below) that some materials lend themselves to be more readily compatible with a given process. For instance, Olefins are somewhat limited in ultrasonic welding, but are recommended for all of the other process. Ultrasonics are not recommended for TPRs, have limited capabilities in some processes and are recommended for others. Please keep in mind that all aspects of this chart are recommendations gathered through years of experience, and does not mean you can’t get excellent results. It is a guideline.
2. The next consideration is the part geometry. Let’s start with the size of the part. One of the limitations of ultrasonics is the size of tooling: the lower the frequency (15 kHz), the larger the tool (approximate maximum 10x10") and the higher the frequency (40 kHz), the smaller the tool (approximately 2 1/2x2 1/2"). If the parts are larger than these ranges, you will have to consider either multiple hits with ultrasonics or one of the other processes.
3. Going further in the part geometry category, we come to the complexity of the part and weld profile. Some of the processes can accommodate for these features easily and others cannot.
4. Wall thickness and internal walls also must be considered. Vibration welding, due to its linear reciprocating motion, has difficulty welding long, unsupported walls, while other technologies do not have an issue with these part features.
5. Production volumes must not be overlooked. Some processes, such as ultrasonics, spin and laser, will process assemblies in seconds (or faster), while hot plate may take 40-50 seconds. In some instances, multiple parts can be welded in a single cycle to improve throughput.
6. I know it may be difficult, but capital equipment cost should be the last consideration. If a process is selected based on price, there may be long-term processing costs such as scrap, downtime and mold changes.

The best bet in selecting the best process for your application is to go into the decision-making process with an open mind and be “Process Neutral!” Understand the advantages and limitations of each process available, and work closely with equipment/solution providers to develop a solution that works for your application.

Jeffrey Frantz is director of marketing and product development for Branson Ultrasonics. Branson Ultrasonics Corporation, a subsidiary of Emerson, is the industry leader in the design, development and manufacture of plastics joining and metal welding equipment, as well as precision cleaning and liquid processing equipment. For more information, visit www.bransonultrasonics.com. The full article was published in the January/February 2012 issue of Plastics Decorating.