Ultrasonic Solutions

Ultrasonic welding process overview

Ultrasonic welding machine involves the use of high frequency sound energy to soften or melt the thermoplastic material at the joining point. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations usually at a frequency of 20, 30 or 40kHz. The ability to weld a component is dependent on various factors likedesign of the equipment, the mechanical properties of the material to be welded and the design of the components & joints which includes the weld line.

An ultrasonic welding machine consists of four main components:

Power Supply		Changes mains electricity at a frequency of 50-60Hz, into a high frequency electrical supply operating at 20, 30 or 40kHz. This electrical energy is supplied to the converter

Converter		This power supply Within the converter (Discs of piezoelectric material are sandwiched between two metal sections) changes the electrical energy into mechanical vibratory energy at ultrasonic frequencies (above the audible range)

Booster (Amplitude modifying device)		The vibratory energy is then transmitted through the booster, which increases the amplitude of the sound wave. The sound waves are then transmitted to the horn

Horn (Acoustic tool also known as Sonotrode)		The horn is an acoustic tool that transfers the vibratory energy directly to the parts being assembled, and it also applies a welding pressure. The vibrations are transmitted through the workpiece to the joint area. Here the vibratory energy is converted to heat through friction - this then softens or melts the thermoplastic, and joins the parts together

A benefit of Ultrasonic welding process includes energy efficiency, high productivity with low costs and ease of automated assembly line production.Ultrasonic welding is very fast (weld times are typically less than 1 second) and easily automated, Ultrasonic strengths are Cost-effective process, Large batch sizes and very short cycle time.

The main limitation of the process is that the maximum component length that can be welded by a single horn is approximately 250 mm. This is due to limitations in the power output capability of a single transducer, the inability of the horns to transmit very high power, and amplitude control difficulties due to the fact that joints of this length are comparable to the wavelength of the ultrasound.

Types of Joining

Different types of Ultrasonic joining techniques are like Welding, Staking,Inserting, Swaging/Forming, spot Welding, Slitting, Textile/Film Sealing.

Typical applications

Appliance		In this high-volume market, hermeticity, strength and also cosmetic appearance are important. Applications include: steam iron, pump housing, vacuum cleaner wand, and dishwasher spray arm.

Automotive		Hermetic seals in applications such as lenses, filters and valves. Other applications include: glove box door, instrument cluster, air diverter and mass airflow sensor.

Business		"Clean" assemblies with reduced particulate matter are produced on information storage discs. Other applications include the assembly for ribbon cartridges, and audio and video cassettes.

Consumer		Precision welding, staking and forming operations are used in the manufacture of the Swatch®.

Electrical		Multiple staking and inserting applications are often automated for high-volume production requirements with consistent reliability. Applications include: terminal blocks, connectors, switches (e.g. toggle, dip, rotary quick and diaphragm), and bobbin assemblies.

Medical		Non-contamination and the ability to be operated in a clean room are as important as the strength of the weld. Reliable, repeatable assemblies for critical life-support devices are produced with new capabilities in process control. Applications include: arterial filter, cardiometry reservoir, blood/gas filter, face mask and IV spike/filter.

Packaging		From aseptic packages to toothpaste tubes, the ability of ultrasonic assembly to seal through product contamination in the joint area is a major advantage. In addition to good cosmetic appearance, ultrasonic assembly provides tamper-evident seals for blister packs. Applications include: condiment dispenser, blister package, juice pouch, juice carton and plastic coated paper cups.

Toys		In this highly competitive industry, the elimination of adhesives, screws and solvents, or other consumables is a bonus added to strong, safe, flash-free assemblies.

Ultrasonic Welding Boosters

The booster, like other elements in the welding stack, is a tuned device therefore it must resonate at a specific frequency in order to transfer the ultrasonic energy from the transducer to the welding horn. In order to function successfully, the booster must be either one half of a wavelength of ultrasound in the material from which it is manufactured, or multiples of this length. Normally, it is one half wave lengths.

Welding Horn

The welding horn is the element of the welding stack that supplies energy to the component being welded. Design of the welding horn is critical to successful welding. It is strongly recommended that welding horn manufacture should only be carried out by companies specializing in ultrasonic welding.

The welding horn, like the booster element, is a tuned device, which, in the majority of applications, also provides mechanical gain. It is typically manufactured in either aluminum or titanium. Aluminium welding horns tend to be used for low volume applications since wear can be a particular problem with this material. Some welding horns have specially hardened tips to reduce wear during welding.

As with the booster element, the length of the welding horn must be either one half of a wavelength of ultrasound in the material from which it is manufactured, or multiples of this length. This ensures that there is sufficient amplitude at the end of the welding horn to effect welding.

The amplitude is typically between 30 and 120µm. The shape of the welding horn is important since stress, caused by the axial expansion and contraction of the horn, could lead to cracking in high amplitude applications. In some applications the welding horn is manufactured with slots in the axial direction. This is to ensure that the maximum vibration amplitude is in the longitudinal direction.

The tip of the welding horn delivers the ultrasonic energy to the component being welded. The tip should be specifically designed to match the component. This will ensure that maximum energy transfer between the horn and the component is achieved. Usually, the tip of the horn is profiled to match the contours of the component.

Support tooling

Finally, the base of the machine press supports the tooling that supports the components during the welding operation. The support tooling is designed to prevent movement of the lower component while the ultrasound is applied. It is often machined to match the contours of the component surface intimately.

Types of Joints

Shear Joints	Step Joints	Tongue & Groove joint

The Shear joint is a very strong, self-aligning joint that is particularly useful for creating hermetic seals and right-angle joints. It is ideal for crystaline materials such as Nylon, PPS, and PPO, and can also be used with larger parts made of amorphous materials. Note that this joint can leave flash when parts are joined.	The Step joint is a stronger, self-aligning joint that provides an excellent appearance. It is suitable for use with amorphous materials.	The Tongue and Groove joint eliminates flash caused by the welding process as the weld occurs between two walls and is an excellent choice for hermetic seals. Not recommended for thin walled parts.

Ultrasonic welding design is based on part geometry, including wall thickness and required strength. For more information on designing parts for ultrasonic welding, see:

Ultrasonic plastic compatibility chart

The term plastic can be used for thermoplastic or thermoset materials. Most thermoset material can not be ultrasonically bonded as they burn when heated. Thermoplastics are normal categorised as amorphous or crystalline.

Amorphous material exhibits a random, spaghetti like structure. They are good at transmitting the ultrasonic energy to the part that needs to be bonded. Amorphous material include: ABS, Polycarbonate and Acrylic.

Crystalline materials have an ordered pattern, and have a well defined melting temperature. Crystalline materials include: Acetal, Nylon, Polyester, Polyethylene and polypropylene.

The following grid can be used to assist with plastics suitable for ultrasonic welding. E=Excellent, G=Good, F=Fair, P=Poor, NO=Not suitable for ultrasonic welding.

THERMOPLASTIC	SPOT WELDING	STAKING	INSERTING	NEAR FIELD WELDING	FAR FIELD WELDING

ABS	E	E	E	E	G

ABS/polycarbonate	G	G	G	G	F

ABS/PVC	G	G	F	G	F

Acrylic	G	F	G	G	F

Acrylic multi-polymer-xt polymer	G	G	G	G	F

Acrylic/PVC	G	G	F	G	F

Acrylic-impact modified	F	F	P	F	P


AMORPHOUS POLYMERS	SPOT WELDING	STAKING	INSERTING	NEAR FIELD WELDING	FAR FIELD WELDING

Butadiene-styrene(bds)	G	G	G	G	F

Cellulosics-ca,cab,cap	P	G	E	P	NO

Modified phenylene oxide	E	E	E	E	G

Polyarylate	F	F	G	G	F

Polycarbonate	G	F	G	G	F

Polyetherimide	G	G	E	E	G

Polystyrene, g.p.	F	F	G	E	E

Polystyrene, impact modified	F	F	G	G	P

PVC-rigid	F	G	E	P	P

PVC-flexible	P	NO	NO	P	NO

San-nas-asa	F	F	G	E	E

Styrene-maleic-anhydride	E	E	E	E	G

Sulfone polymers	F	F	G	G	F

Crystalline Polymers


CRYSTALLINE POLYMERS	SPOT WELDING	STAKING	INSERTING	NEAR FIELD WELDING	FAR FIELD WELDING

Acetal copolymers	F	F	G	G	F

Acetalhomopolymer	F	F	G	G	F

Fluoropolymer	NO	NO	NO	P	NO

Nylon	F	F	G	G	F

PC-pet	G	G	E	E	G

Polyester-pbt	F	F	G	G	F

Polyetheretherketone	G	G	E	E	G

Polyethylene (ldpe,hdpe)	G	F	G	P	P

Polyethylene (uhmw)	NO	NO	NO	NO	NO

Polymethylpentene	G	F	E	F	P

Polyphenylenesulfide	F	P	G	G	F

Polypropylene	E	E	G	F-P	P