Royal Military College of Canada

Materials Science & Engineering

Welding and polymer processing research

By: Dr. Philip J. Bates

Dr. Bates' welding and polymer processing research can be broken down into four areas:

  1. Vibration welding
  2. Laser welding
  3. Resistance welding
  4. Thermoplastic processing (new process/product development, long/continuous glass fibre)

Vibration welding thermoplastic polymers and composites

Vibration welding is a common technique for joining thermoplastic parts. It is widely used to manufacture automotive air intake manifolds, resonators and fluid reservoirs. It involves bringing two moulded parts together under a clamping pressure. One of the parts is then vibrated at a frequency of the order 200 Hz over amplitudes of the order of 1 mm. The frictional and viscous shear energy melts polymer to create a molten zone between the two solid parts at the weld interface. The molten polymer is forced from the interface as flash as the two parts come together (meltdown). When a preset meltdown distance is reached, the vibration is stopped. The clamping pressure is then maintained for several seconds to allow the molten polymer in the weld to solidify.

The vibration welding lab is equiped with:
  • a Branson linear vibration welder
  • part fixtures for creating butt-, tee-, cup-plate and lap-welds.
  • data acquisition systems for recording meltdown, acceleration, amplitude, and force on the lower component during welding.

This research examines the effect of material, welding and part variables on the resulting strength/microstructure as well as several vibration weldng process measurements. Examples of materials that have been studied include:

  • unreinforced and short glass-fibre reinforce nylon 6 and 66,
  • short and long glass-fibre reinforce polypropylene (ie VertonTM),
  • TPO
  • polypropylene nanocomposites
  • continuous glass-fibre reinforced polypropylene (ie TwintexTM)
  • self reinforced polypropylene (ie CurvTM)
  • amorphous materials such as ABS and PMMA.

Laser transmission welding thermoplastic polymers and composites

Laser transmission welding involves bringing a laser transparent part into contact with a part rendered laser absorbing by carbon black. A laser beam is directed through the transparent part. As the beam reaches the joint interface, it is absorbed by the carbon black thereby generating heat. The heat is thermally conducted to the transparent part. The melting of both parts at the interface generates a melt pool that allows for interdiffusion of the polymer chains. After sufficient cooling, the melt solidifies and a weld is formed.

Our laser transmission welding lab is equiped with:

Current work includes characterization of thermoplastic compounds used in laser welding, process modelling and examination of the effect of small gaps between mated parts on weld strength and microstructure.

Resistance welding

Resistance welding uses energy generated by electrical current to melt surrounding material. Most work on thermoplastic material involves resistive implants (ie wire mesh) that are placed between mated components. Current, passing through the wire, heats up the interface and ultimately causes a weld to form. In some cases, if the thermoplastic materials are conductive enough, no implant is necessary. The contact resistance between the two mated components is sufficient to cause melting/welding to occur.

Our resistance welding lab is equiped with:

Current work includes the resistive implant welding of polypropylene composites to form large lap-welds. Past work has studied the direct resistance welding of conductive thermoplastic composites.

Thermoplastic processing

This general heading covers a number of themes briefly summarized below:

  • New process/product development - Proprietary projects related to sensor development for QC, novel rheometer development, and metal replacement feasibility studies.
  • Long fibre composite research - Study of the melt impregnation process for the manufacture of long fibre composites.
  • Continuous fibre composite research - Study of the behaviour of continuously reinforced thermoplastics during consolidation.