There are four essential techniques for bonding plastic components.  Each method is associated with equipment, labor and other costs that you most consider.  Let’s take a look at each method in more detail.

1)     Mechanical Fastening

Mechanical fasteners such as rivets, screws, nuts or pins represent the most common joining elements. These fasteners may be molded into place, glued, forced or expanded into holes. In addition, they may be inserted with heated probes or with ultrasound.  When using mechanical fasteners, make sure that both the plastic components and your fasteners are strong enough to survive the pressure applied during installation.

2)     Solvent Bonding

In solvent bonding, the plastic is softened first with a coating of solvent.  The two plastics components are then clamped together. The molecules mix together and the components bond as the solvent dries and evaporates. This process works solely with thermoplastics.

The level of pressure applied is critical, as too much may cause the components to distort. In addition, 24 to 48 hours at room temperature or several hours at a higher temperature may be necessary to facilitate the bonding.

3)     UV Bonding

Ultraviolet bonding utilizes a curing process with high-intensity ultraviolet lighting that instantly dries or cures inks, adhesives or coatings. Moreover, UV bonding works in seconds to bond plastic components even when the plastic material blocks UV light. In addition, plastic adhesives bond together a wide array of substrates making this method an efficient way to bond plastic pieces to other materials, such as ceramic, glass, and metal. This process provides many advantages such as reduced rejection rates, increased production speed, improved solvent and scratch resistance, as well as superior bonding.

4)     Ultrasonic Welding

This process utilizes sonic pulses that are transmitted to the appropriate area with a resonant vibrating device called a horn. The horn causes the two plastic components to vibrate against one another, and the vibration results in heat that fuses the elements together. Thus, no solvents or glue are required. As the horn vibrates, it stretches and then shrinks in length by tiny amounts, and this motion is called the amplitude of the device. The size and shape of the plastic parts generally determine the size of the horn face.

Plastic components and other products, including alloys and blends of a variety of resin families, can be fastened by ultrasonic welding. Moreover, different materials may be joined if the melting temperatures are no more than 30 degrees apart and the compositions are compatible. To ensure the parts are joined appropriately, the elements should have a compatible joint design at the start. Several factors to consider in the design of components to be ultrasonic welded are cost, end use of the product, and the location of the joint surface in relation to the ultrasonic device.

Ultrasonic welding is quick with assembly rates that can exceed 25 parts-per-minute, and the process does not require any secondary operations such as inserting, coating or cleaning. In addition, this process may be used for a wide array of component assembly applications. These include IV components, liquid bearing vessels, monitors, diagnostic components, filter assemblies and hearing aids.

These four methods represent the most efficient and common methods of plastics joining.  Each has positive factors that may be utilized in both complex and simple operations.

What other techniques do you use?  Let me know in the comments section below.

Looking for more information on adhesives?  Download our free Guide to Gluing Plastics.


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