The very first thing that comes to mind when you think about joining two or more components together is a common screw or a mixture of bolts and nuts. Although this is easy to perform, it can add costs and complexity to a manufacturing process that might not be necessary. A simplified solution is provided by ultrasonic welding which minimizes cost and complexity while fulfilling the assembly’s reliability criteria.
Ultrasonic welding utilizes thermal stresses produced by mechanical movement of high frequency to melt plastics. The vibration is produced by converting electrical energy through an ultrasonic mechanical horn which uses the heat generated and friction to burn the plastics and form a mechanical molecular connection between the related components.
To join two components of thermoplastic, the properties must be chemically compatible. If that is not the case, there would be no molecular connection, even though the two materials can be melted together. For example, try welding polypropylene to polyethylene.
Although these semi-crystalline substances are similar in structure and share several physical properties, they are not chemically compatible, and so cannot be welded together. They can only weld to themselves or materials with similar chemical properties. The only way two thermoplastics with different chemical properties can be compatible is if their melting temperatures are below 40ºF, and they have an identical molecular structure.