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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

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