Picking plastics to laser weld

DuPont Engineering Polymers, Wilmington Del. (www.plastics.dupont.com), for example, offers a wide range of suitable materials for laser welding.

It's relatively easy to produce strong welds with Delrin acetal, Zytel nylon (PA66, PA6, and PA12), and Zytel HTN (high-performance polyamide). Other weldable polymers attain strong welds but have limited processing latitude with respect to wall thickness and certain part configurations. Polymers in this category include Vespel TP, Crastin PBT (polybutylene terephthalate), Rynite PET (polyethylene terephthalate) thermoplastic polyesters, and Hytrel thermoplastic polyester elastomers, Special grades of Crastin PBT and Rynite PET with enhanced laser transparency provide the greatest process latitude in part thickness and welding conditions.

Most natural (uncolored) grades are sufficiently transparent to laser light to produce strong welds. There are also colored options that, though opaque to the naked eye, have enough laser transparency for successful welding. Standard black and some colored grades are suitable for laser-absorbent components of welded assemblies.

Key capabilities of laser welding

• Assembly of sensitive parts: No relative motion of parts being welded. Little or no heating beyond the weld area.
• Excellent aesthetics: No visible scars or flash on exposed surfaces.
• High precision: Tight control of relative part locations.
• Wide latitude in molding related materials. For example, PA66 to high-performance polyamide (HTN) or a rigid structural part made from Crastin PBT to a flexible seal made from Hytrel thermoplastic elastomer.
• Versatility: Suitable for a wide range of part designs and sizes.
• Low cost: Usually competitive with alternative welding methods, and sometimes less expensive.

Automotive door lock covers are made from natural, laser-transparent Zytel PA66 welded to black, laser-absorbing Zytel PA66 housings

How laser welding works

Laser welding joins parts made from the same or very similar polymers. One part must absorb laser light and the other must be at least partially laser-transparent.

The laser beam passes through the laser-transparent part to reach the laser-absorbing component. Absorption of the laser energy melts the material in a localized area. Adjacent surfaces of the laser-transparent part melt via heat conduction. The molten surfaces cool and bond together when the laser beam removes or relocates.