Plastic welding is a process that involves creating a bond from the 2 similar plastics. The use of welding allows the bond to have a superior level of strength and shorter cycle times. The steps to welding are: pressing, cooling, and heating. It’s easy to differentiate between plastic welding processes by paying attention to their heating methods. Using force while also allowing time for cooling is something that vary between both process and welding machine.
What are the plastic welding processes?
There are several plastic welding processes. Listed below are a few of these methods:
- Ultrasonic Plastic Welding
- Vibration Welding
- Laser Welding
- Spin Welding
- Infrared Welding
- Hot Plate Welding
Ultrasonic Welding
What is Ultrasonic Welding?
Ultrasonic Welding is an industrial technique that applies ultrasonic acoustic vibrations to work pieces that are held together under pressure. It is typically used for metals and plastics and is mainly used for dissimilar materials. In ultrasonic welding, there are no connective nails, bolts, soldering materials, or adhesives needed to bond materials to one another. When ultrasonic welding is used on metals the temperature stays below the melting point of either material. This prevents properties that may not be wanted and which may result from high temperature exposure of either material.
Video credits to Engineer’s Academy. It explains what Ultrasonic Welding is in great detail.
Vibration Welding
What is Vibration Welding?
Vibration welding moves a single part out of 2 horizontally while pressure is placed on it. Vibration welders operate at lower frequencies operate at lower frequencies, much greater clamping force, higher amplitudes. The electromagnetic heads that linear vibration welding is designed with eliminate the lubrication and wear that’s typically associated with bearing surfaces.
Video credits to Lee Alex. It discussed a vibration welder made by Hornwell Ultrasonic.
Laser Welding
What is Laser Welding?
Laser welding is a welding process used to bond both metals and thermoplastics that utilizes laser beams to create a weld. Since the heat source is so incredibly concentrated, when used to weld thin materials high welding speeds can be achieved (of several meters per minute). Not only that, but even when used to weld thicker materials laser welding can produce deep, narrow welds. Laser welding can be used in two different modes: Keyholes welding and conduction limited welding.
Video credits to Kelly Xu. It discusses handheld laser welding.
What is conduction limited welding?
Conduction limited welding is typically used battery and electronic applications that require a high depth to width ratio. A laser beam or top hat distribution is typically used to produce conduction spot welds.
What is Keyhole Welding?
Keyhole mode heating achieves weld penetration using a power density great enough that the metal being welded gets hot to a point just beyond melting or in other words the metal begins to vaporize. The metal then creates an expanding gas that pushes outwards and creates a keyhole from the surface of the materials down to the depths of the weld. The keyhole follows the laser as it moves across the surface which creates a narrow, deep weld. The keyhole will remain open as long as the laser’s power is great enough and there isn’t excessive travel speed.
Spin Welding
What is spin welding?
Spin welding is a process of welding that uses heat generated by rotational friction to form a bond between thermoplastic parts with circular joints. Spin welding machines apply force axially while rotating one part against it’s stationary mate. The friction resulting from this friction generates heat that melts both parts at the interface. Once rotation stops the thermoplastics cool and harden which forms a welded assembly. Welders stop rotation at particular points and angular orientation for cases where parts must have a particular orientation.
Video credits to Max Willson. It shows how to spin weld on rotational molded tanks.
Infrared Welding
What is Infrared welding?
Infrared welding is a form of non-contact welding process that creates air tight welds in thermoplastic materials. When we use infrared radiation or electromagnetic radiation in a tight, controlled manner we can heat thermoplastic parts to molten temperatures very quickly and in a way that very closely resembles hot-plate welding. The infrared energy used in Infrared welding is generated via encased infrared emitters. The atoms within each conductor produces different oscillation frequencies but only a few of them are used for the actual welding of plastic materials. The infrared wavelengths we typically see used for plastic welding are:
- 2.0 – 2.5uM peak
and
- 1.0 – 1.2uM peak
Video credits to Branson Ultrasonics. It goes over the Infrared Welding process.
What factors influence proper plastic welds?
The factors that influence a proper infrared weld are:
- Mold release agents
- Fillers
- Moisture
- Transition time between melts and weld steps
- Infrared Intensity
- Incoming line voltage
- Polymer uniformity
- Part dimensional stability
- Dissimilar materials
Also not that infrared absorption or what’s needed for it to melt the part interface depends on the type, color, and polymeric uniformity of the plastic being welded. Every thermoplastic has a characteristic absorption curve / weld time, and welds can be produced at an point along the curve. One typically wants to choose the highest possible intensity using the shortest time so that cycle times can be minimized.
Hot Plate Welding
Hot plate welding is the process of used a heated plate to melt the surfaces of two halves of thermoplastic parts. Both halves are brought into contact with a heated plate (precisely heated plate) for a specified time. After plastic interfaces are melted both parts are brought together to form a permanent, molecular, and typically hermetic bond. Properly designed joints welded while under precise control tend to exceed the strength of most other part areas.
A properly designed joint welded under precise process control often equals or exceeds the strength of any other part area.
Video credits to Branson Electronics. It discusses the hot plate welding process.
