Generator

The generator converts electrical power from the single-phase mains to the correct frequency and voltage for the transducer to convert into mechanical vibrations. The microprocessor unit controls the welding cycle and feeds back key welding information to the user, via the user interface. The user interface also allows the operator to enter the required welding parameters.

Welding stack

This is the part of the machine that provides the ultrasonic mechanical vibrations. It is generally a three-part unit consisting of transducer, booster, and welding horn, mounted on the welding press at the center-point of the booster section. The stack is a tuned resonator, rather like a musical instrument tuning fork. In order to function, the resonant frequency of the tuned welding stack must closely match the frequency of the electrical signal from the generator (to within 30Hz).

Transducer

The transducer, also known as the converter, converts the electrical energy from the generator to the mechanical vibrations used for the welding process. It consists of a number of piezo-electric ceramic discs sandwiched between two metal blocks, usually titanium.

Between each of the discs there is a thin metal plate, which forms the electrode. As the sinusoidal electrical signal is fed to the transducer via the electrodes, the discs expand and contract, producing an axial, peak-to-peak movement of 15 to 20µm.

Transducers are delicate devices and should be handled with care. Once the elements are broken, the transducer will not function.

Booster

The booster section of the welding stack serves two purposes, primarily to amplify the mechanical vibrations produced at the tip of the transducer and transfer them to the welding horn. Its secondary purpose is to provide a location for mounting the stack on the welding press.

The booster expands and contracts as the transducer applies the ultrasonic energy.

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 wavelength.

Welding horn

The welding horn is the element of the welding stack that supplies energy to the component being welded. 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. Aluminum 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.