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ultrasonic welding of plastics - material suitability guide

The process of ultrasonic welding of plastics is achieved by applying a vibrating metal tool (horn) at 90° to the stationery plastic parts which then vibrate. When combined with pressure, friction produces heat & melts the parts at the horn contact point. Once cooled down a solid homogeneous weld between the 2 parts is created.

 

To give you help with ultrasonic welding of plastics for your application, this ultrasonic welding guide lists the most common unfilled grades of plastic available & their suitability for each style of ultrasonic welding  As a rule, stiffer materials are easier to weld & those with higher melt temperatures need more energy. To weld different materials, they need similar molecular structures - crystalline ones are only weldable to themselves.

 

Plastic Material Type, Abbreviation & A or C Structure Close
Welding
Distant
Welding
Inserting Spot
Welding
Staking
Acetal Co/Homopolymer POM C Good Fair Good Fair Fair
Acrylic PMMA A Good Fair Good Good Fair
Acrylic - Impact Modified PMMA A Fair Poor Poor Fair Fair
Acrylonitrile Butadiene Styrene ABS A Very Good Good Very Good Very Good Very Good
Cellulose Acetate... CA/B/P A Poor Unsuitable Very Good Poor Good
Polyamide 6 & 66 (Nylon) PA6 & 66 C Good Fair Good Fair Fair
Polycarbonate PC A Good Fair Good Good Fair
Polycarbonate/Abs PC/ABS A Good Fair Good Good Good
Polyester - Thermoplastic PBT/PET C Good Fair Good Fair Fair
Polyethylene - Low/High Density LD/HDPE C Poor Poor Good Good Fair
Polyphenylene Oxide PPO A Very Good Good Very Good Very Good Very Good
Polyphenylene Sulphide PPS C Good Fair Good Fair Poor
Polypropylene PP C Fair-Poor Poor Good Very Good Very Good
Polystyrene - General Purpose GPPS A Very Good Very Good Good Fair Fair
Polystyrene - High Impact HIPS A Good Poor Good Fair Fair
Polyvinyl Chloride - Flexible PVC A Poor Unsuitable Unsuitable Poor Unsuitable
Styrene Acrylonitrile... SAN/ASA A Very Good Very Good Good Fair Fair

A (Amorphous) = polymers with a random molecular chain structure. This & their wide softening temperature range enables them to soften gradually without solidifying quickly, thus making ultrasonic welding them easy.
C (Crystalline) = polymers with an orderly molecular chain structure. This & their sharp melting & solidification points makes them absorb vibrations when solid, thus making ultrasonic welding them more difficult.
Close Welding = ultrasonic welding where the horn is applied close to (<6.35mm) the assembly joint - good for welding materials whose low modulus of rigidity dampens vibrations a short distance away from the horn.
Distant Welding = ultrasonic welding where the horn is applied away from (>6.35mm) the assembly joint - good for welding materials whose high modulus of elasticity propagates vibrations without dampening them.
Inserting = ultrasonic embedding of metal components like inserts into preformed holes in the moulding - provides high strength & speed, no stress build up & reduced moulding cycles.
Spot Welding = ultrasonic assembly of parts without premade holes or energy directors - good for large parts
Staking = melting and reforming a post on the moulding to mechanically lock dissimilar materials in place - provides short cycles, good appearance & tight assemblies

 

For more help with plastics, view our ultrasonic welding diagrams or material selection guides