Welding

Plastic parts can be welded using direct mechanical methods such as hot plate, spin, vibration and ultrasonic welding; and indirect processes such as radio frequency, electromagnetic and laser welding.

Hot plate welding:
Since the area of the weld can be very large this is a low cost technique for joints that are mechanically stressed in end use.  Surfaces to be joined are heated to melting with a non-stick metal tool and then welded together under controlled pressure.  Complex joints in several planes can be made.  Throughput is relatively low.

Spin welding:
Parts with circular joint interfaces are joined by holding one part fixed, while the other is rotated at a specified pressure.  This generates frictional heating and creates a melt and subsequent weld.

Vibration welding:
Two parts are rubbed together in a high-amplitude, low-frequency, reciprocating motion, which produces frictional heat and results in a melt at the interface of the two parts.  This method is used in large parts with joints in one plane, however the equipment is relatively expensive.

Ultrasonic welding:
High-frequency (20-40 kHz) vibrational energy is concentrated in a small contact area between two plastic parts of the same material, creating rapid melting along the joint as the parts are pressed together.

Radio Frequency welding:
Heat is created by applying a strong radio frequency field to the selected joint region while clamping pressure is also applied.

Electromagnetic or Induction welding:
A radio frequency magnetic field is used to excite fine, magnetically sensitive particles (either metallic or ceramic) to generate fusion temperatures in thermoplastic materials held together under pressure.

Laser welding:
Laser light is passed through a top (laser transparent) part onto a bottom (laser absorbent) part.  The absorbed laser energy softens and melts both parts.  With externally applied clamping pressure, the parts are bonded upon cooling.

Except for laser welded parts, which require only matching contact surfaces, the type of joint design, material, part configuration, equipment, and process settings are critical parameters for welding thermoplastic parts.  Other factors, such as whether the material is hydroscopic or glass-filled, must also be taken into account.