TWI Industrial Member Report Summary 876/2007
By I A Jones
Transmission laser welding of plastics uses sources that will pass through most natural polymers. A suitably placed absorber is used for the laser energy to provide heating at the joint. When welding small or complex parts, precise control of the process is required. Precision may be defined as dependent on two main factors:
- The amount of energy applied. Controlled by:
- Laser power.
- Welding speed or time.
- Amount and absorption properties of the absorber.
- The location of the energy application. Controlled by:
- Dimensions of the heat source - either laser beam or absorber size.
- Accuracy of the manipulation equipment.
Given that the laser power and beam/part manipulation can be accurately controlled, the main additional factors that need to be understood and controlled are the positioning and behaviour of the absorber material and the use of small focused laser sources. These are studied in this work to accurately deliver heat (in amount and location) to the joint.
Precision welding is of practical importance as medical and electronic devices in particular are manufactured to smaller scale and increased complexity. Following advancements in microinjection moulding, lithography and micromachining it is possible to manufacture polymer components with features a few microns in size and joints of the order 100µm wide are often required. The devices are often intended to be single-use and disposable. Hermetic seals are often required, which can be achieved using either adhesive bonding or welding methods. Adhesives have the advantage that they can be specified to give little or no heating of the parts, but application and curing times can be significant. To be applied effectively, a welding method needs to be fast and have a small heat-affected zone to reduce distortion and avoid affecting thermally sensitive coatings or components in medical or electronic devices.
- Determine the minimum weld width available in laser welding as a result of using different laser sources and absorbers.
- Determine changes in the absorption properties of a Clearweld absorber as laser welding proceeds.