There are several methods for joining injection molded plastic components
but each one has equipment, cost and labor to consider.
The simplest way to join plastic parts is to design a fastening element such as a hinge or latch into the part. Stronger plastics are required for these because the joint must survive the repeated use, load and strain of assembly.
When working with precision injection molded components, mechanical fasteners like screws, rivets, pins, or nuts tend to be the most common joining methods. The fasteners can be molded in place, forced, glued or expanded into holes. They can also be inserted ultrasonically or with heated probes.
Mechanical fasteners require that the plastic use can withstand the strain of fastener insertion along with the high stress around the fastener.
Threaded fasteners work best on parts with thicker sections. Thread-forming screws are preferred for softer materials and thread-cutting screws work best on harder plastics. Push on lock nuts or clips may be suited better for thinner section parts.
If the fasteners need to be removed a number of times for disassembly because of servicing or replacement, metal inserts are recommended.
Plastics are softened by coating them with a solvent, then clamping them or pressing them together. The plastic molecules mix together and the parts bond when the solvent evaporates. This process is limited to thermoplastics.
The amount of pressure used is critical, as too much pressure causes parts to distort. A day or more at room temperature or several hours at elevated temperatures are also sometimes needed to help cure the bond.
This is a process that utilizes ultraviolet curing with high-intensity ultraviolet light to instantly cure or dry inks, coatings or adhesives. Offering many advantages like increased production speed, reduced rejection rates, and improved scratch and solvent resistance, along with the facilitation of superior bonding. This method is limited to clear materials.