Structural composition of ultrasonic plastic welding machine
Ultrasonic welding equipment is composed of press, generator, transducer, horn, welding head and parts support tooling.
1 Ultrasonic generator
The function of the ultrasonic generator is to convert the power frequency (50 Hz or 60 Hz) voltage into the ultrasonic frequency voltage. The microprocessor 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.
Ultrasonic Plastic Welder
2 Welding stack/Acoustic energy system The welding stack provides ultrasonic mechanical vibration, which is generally composed of three parts: transducer, horn and welding head, and is fixed on the welding press in the middle of the horn. The welding kit is a resonator somewhat similar to a tuning fork. The resonant frequency of the welding kit must closely match the frequency of the electrical signal from the generator (with a difference of less than 30 Hz).
2.1 Transducer
The inverse piezoelectric effect converts the ultrasonic frequency voltage from the generator into ultrasonic mechanical vibration of the same frequency. It consists of several piezoelectric ceramic sheets sandwiched between two metal (usually titanium) blocks. There is a thin metal plate between the sheets to form electrodes. When the sinusoidal electrical signal is supplied to the transducer via the electrode, the piezoelectric sheet expands and contracts, producing an axial peak-to-peak motion of 15-20 μm. The transducer is a precision device and should be handled with care.
2.2 Horn
The horn has two functions. Its main function is to amplify the mechanical vibration generated at the end of the transducer and transmit the vibration to the welding head. Another function is to provide a position for the fixing kit on the welding press. When ultrasonic energy is applied to the transducer, the horn also expands and contracts. Like the other parts in the welding kit, the horn is a tuning device, so it must also resonate at a specific frequency in order to transfer ultrasonic energy from the transducer to the welding head. In order to function effectively, the horn must be a half-wavelength or an integer multiple of the half-wavelength of the ultrasonic wave in its manufacturing material. Generally half wavelength.
2.3 Welding head
The welding head is the part of the welding kit that provides energy to the parts to be welded. Like the horn, the welding head is also a tuning device, and mechanical amplification is also provided in most applications. The length of the welding head must be the half-wavelength or half-wavelength of the ultrasonic wave in its manufacturing material
An integer multiple of. This ensures that the end of the welding head has sufficient amplitude to achieve welding. The amplitude is generally 30~120 μm. The design of the parts to be welded and the joint determines the size and style of the welding head. The shape of the welding head is very important, because the stress caused by the axial expansion and contraction of the welding head can cause cracking at high amplitude. In some applications, the welding head is machined with multiple axial slots. This is to ensure that the maximum amplitude is in the longitudinal direction. The end of the welding head transmits ultrasonic energy to the parts to be welded. The ends should be specially designed to match the parts to ensure maximum energy transfer between the welding head and the parts. Usually the end of the welding head is made into a profile matching the contour of the part.
To prevent indentation and reduce wear, aluminum must be plated with nickel or chromium. When impact resistance or wear resistance is required, and when welding filled plastic or embedded metal inserts, steel welding heads are required. Steel welding head has low fatigue strength and is only used in low amplitude occasions. Complex parts, special-shaped or large-size parts usually require composite welding heads (child-female welding heads). At this time, the base welding head is made of aluminum, titanium or steel secondary welding heads are connected to the base welding head and guide energy.
3 Press
The press is used to fix the welding kit and apply the force required for welding. It consists of a base for fixing the fixture and an air cylinder for applying force. The press is equipped with a pressure gauge and a regulating valve to adjust the welding force. It should be noted that the specific gauge pressure set on an ultrasonic welding equipment is not necessarily the same as the welding force provided by another welder with the same gauge pressure. The welding force should be calibrated with a pressure gauge in order to directly compare the welding force between different welders. There is also a flow control valve on the press to adjust the speed of the welding head approaching the part to be welded. Some welding equipment uses electromagnetic force pressurization system to replace the traditional cylinder, which can better control the approach speed, which is beneficial when welding small or precision parts.
4 Support tooling
The press base fixes the tooling that supports the parts during the welding process. The support tooling is specially designed to prevent the lower part from moving when the ultrasonic is applied. It is usually processed into a shape that closely matches the surface contour of the part. Fixtures range from simple to complex, depending on the part design. The lower parts must be firmly placed and supported. The fixture or base should be adjustable to ensure that the part is perpendicular to the welding head. The fixture can be processed from several materials. Stainless steel is the best choice because it is easy to machine and polish. Special fixtures can now be processed directly via CAD data. Larger, complex, odd-shaped or small batch parts are usually clamped by casting soft polyurethane.
