Ultrasonic Plastic Welding System Research Articles

Study on a Large-Scale Three-Dimensional Ultrasonic Plastic Welding Vibration System Based on a Quasi-Periodic Phononic Crystal Structure

The uniformity of amplitude distribution and amplitude gain are two main factors affecting the performance of ultrasonic welding vibration system. In order to improve the uniformity of amplitude distribution and amplitude gain of welding surface to enhance the performance of the vibration system, a new design method of a large-scale three-dimensional ultrasonic plastic welding vibration system based on a quasi-periodic phononic crystal structure is proposed. In this method, the composite horn combined with a conical section and a cylindrical section can effectively improve the output amplitude gain of the welding surface. In addition, the method forms a quasi-periodic phononic crystal structure by slotting in a large-scale three-dimensional tool head, and utilizes the band gap property of the structure to effectively suppress lateral vibration of the tool head and improve the amplitude distribution uniformity of the tool head’s welding surface. However, when the size of the tool head is relatively large, the quasi-periodic phononic crystal structure cannot suppress the lateral vibration very well. Therefore, the paper processes fan-shaped slopes on the output surface of the tool head which can further improve the uniformity of the amplitude distribution and amplitude gain. Finally, the simulation analysis and experiments show that the design method can optimize the large-scale three-dimensional ultrasonic plastic welding system, improve the uniformity of the vibration distribution and increase the output amplitude gain of the welding surface.

Two-dimensional ultrasonic plastic welding system based on phononic crystal dislocation theory

When the lateral dimension of the tool head is close to or greater than a quarter of the longitudinal wave length, the tool head will produce severe lateral vibration. The coupling of the lateral vibration and the longitudinal vibration makes the amplitude distribution of the tool head’s radiation surface uneven, which seriously affects the welding quality. To solve the problem of uneven amplitude distribution of the two-dimensional tool head’s radiating surface, in the paper we conduct an optimized design study on a two-dimensional ultrasonic plastic welding system. First, using the theory of phononic crystal dislocations, we construct a nearly periodic phononic crystal homogenous dislocation junction on a large-sized long strip tool head, and use the homogenous dislocation junction to change the regular lattice arrangement of the phononic crystal structure to adjust the position of the band gap and increase the width of the band gap, so that the operating frequency of the two-dimensional ultrasonic plastic welding system can be located in the band gap of the lateral vibration of the tool head, and the effective control of the lateral coupling vibration of the tool head can be achieved, thus optimizing the amplitude uniformity of the radiating surface of the tool head and increasing the amplitude gain. Although the homogenous dislocation junction structure improves the amplitude uniformity of the radiating surface of the tool head, the lateral dislocation effect of the homogenous dislocation junction causes the sound waves in the band gap frequency range to propagate along the dislocation channel, while the dislocation line channel is located in the middle of the tool head, which results in a larger displacement of the middle part of the tool head’s radiating surface, and a smaller displacement on both sides. Therefore, the further optimizing of the two-dimensional tool head is required. In this study, the nearly periodic phononic crystal inclined groove structure is used to better optimize the amplitude distribution uniformity of the radiating surface, and the influence of the inclined groove structure parameters on the longitudinal resonance frequency and amplitude distribution uniformity of the ultrasonic plastic welding system are analyzed, that is, the inclined groove can better improve the uniformity of the amplitude distribution than the straight groove, but the angle of inclination of neither the inner nor outer inclined grooves should be too large: the optimal range is 3°－6°. In addition, the difference in inclination angle between the inner inclined groove and the outer inclined groove should not be too large, and the angle difference from 0° to 2° is best. The simulation results show that the nearly periodic phononic crystal homogenous dislocation junction and inclined groove structure can optimize the two-dimensional ultrasonic plastic welding system, which provides a basis for further research on the theory of lateral vibration suppression.

Optimization on ultrasonic plastic welding systems based on two-dimensional phononic crystal

Large-sized tools are needed for plastic welding of large objects. However, the displacement distribution at the radiation surface of the tools is not uniform due to the strong lateral vibration. In this paper, two-dimensional (2D) phononic crystal (PnC) is introduced by processing periodically arranged grooves in large-sized tools. This method is different from the traditional experience-based grooving method. The lateral vibration is suppressed due to the characteristic of PnC. In this paper, six kinds of ultrasonic plastic welding systems based on 2D PnC with different groove width and height are designed. The vibration characteristics of ultrasonic plastic welding systems were simulated and experimented. The band gaps of large-sized tools are analyzed. The results show that the lateral vibration is suppressed when the operating frequency of the ultrasonic plastic welding system is within the band gap of the large tool. The displacement distribution at the radiation surface of the tools is more uniform. A theoretical support is provided for the design of large-sized ultrasonic plastic welding systems.

Suppression of lateral vibration in rectangular ultrasonic plastic welding tool based on phononic crystal structure

Ultrasonic welding is one of the main applications of high-power ultrasound and is used in the automotive industry and aerospace. Transducers and tool are important parts of the ultrasonic welding system. Different tools are required for different welding objects. For larger plastic welded parts, it is necessary to weld them with large-sized welding tools. Due to the large size of the welding tool, under the excitation of the transducer, the tool will produce a coupling effect of longitudinal vibration and lateral vibration. Lateral vibration will cause the radiation surface of the tool to be non-uniformly displaced, and the working efficiency and welding results of the welding system will also be affected. So, in this paper, the phononic crystal bandgap theory and coupling vibration theory are used to study the coupled vibration of large-sized rectangular plastic ultrasonic welding tools. In order to improve the work efficiency and radiation surface's displacement uniformity of the tool, the phononic crystal structure is used to suppress the lateral vibration of the large-sized plastic ultrasonic welding tool, and the lateral vibration band gap of the phononic crystal structure is calculated. The longitudinal resonance frequency of the system is designed in the band gap range of the lateral vibration of the tool. So the lateral vibration of the tool can be effectively suppressed. The longitudinal vibration displacements on the radiation surface of the rectangular tool before and after vibration suppression are analyzed and compared with each other. The vibration mode of the ultrasonic welding system is simulated by the Comsol Multiphysics finite element software. The large-scaled tool with phononic crystal structure has a radiation surface displacement compared with the tool without phononic crystal structure, and the results show that the radiation surface displacement with phononic crystal structure will increase and tend to be uniform, greatly optimize the welding effect, improve the working efficiency of the welding system, and meet the needs of practical engineering. It is concluded that the longitudinal resonance frequency of the ultrasonic plastic welding system within the lateral vibration bandgap on the phononic crystal structure can not only suppress the lateral vibration, but also make the longitudinal displacement of the radiation surface more uniform and larger. Therefore, the work efficiency is greatly improved.

Temperature Rise and Welding Characteristics of Various-Frequency Ultrasonic Plastic Welding Systems

Welding characteristics and temperature increases of ultrasonic plastic welding parts over a frequency range from 27 to 94 kHz are studied. Using 27, 40, 67, and 94 kHz ultrasonic plastic welding systems, temperature increases at welding surfaces of lapped 1.0-, 2.0-, and 3.0-mm-thick polypropylene plates and polymethyl methacrylate plates are measured using 0.1- and 0.2-mm-diameter thermocouples inserted between plates, and temperature distributions at cross sections of lapped plate specimens are measured using a thermotracer. The 94 kHz vibration system used for ultrasonic plastic welding consists of a bolt-clamped Langevin-type longitudinal vibration source using four 30-mm-diameter piezoelectric ceramic (PZT) rings, a stepped horn (vibration velocity transform ratio N=3.0) and a catenoidal horn (N=3.13) with an 8-mm-diameter welding tip. The other vibration systems have similar configurations. In the case of using a higher-frequency system, increases in temperature measured at the welding parts are larger. Temperature rises are larger for lapped plate specimens than that for a one-piece specimen owing to the vibration loss of welding surfaces.

Frequency Characteristics of Ultrasonic Plastic Welding: (27 kHz to 180 kHz Ultrasonic Plastic Welding Systems)

Welding characteristics and temperature rises at plastic welding part over frequency range from 27kHz to 180kHz were studied. Ultrasonic plastic welding systems of 27, 40, 67, 94, 150 and 180kHz were developed and direct welding characteristic of lapped plastic sheets were measured. The temperature rises at welding surfaces of lapped 1.0-mm-thick polypropylene and polymethyl methacrylate plates were measured using thermocouples inserted between plate specimens. And also, temperature rise distributions in cross sections of the lapped plate specimens were measured using a thermotracer. The longitudinal vibration systems used for ultrasonic plastic welding consisted of a bolt-clamped Langevin type longitudinal vibration source using two or four piezoelectric ceramic (PZT) rings, a stepped horn and a catenoidal horn with a 4-mm- or 8-mm-diameter welding tip. Using higher frequency system, temperature rise measured at the welding part were higher. Maximum temperature rise measured using thermocouples and a thermotracer was over 350°C under excessive condition.

Temperature Distributions in Welding Specimens for Ultrasonic Plastic Welding Systems Using Various Frequencies

Welding characteristics and temperature increases of plastic welding parts over a frequency range of 27 kHz to 94 kHz are studied. Using 27 kHz, 40 kHz, 67 kHz and 94 kHz ultrasonic plastic welding systems, temperature increase at welded surfaces of 1.0-mm-thick polypropylene plates and polymethyl methacrylate plates is measured using thermocouples inserted between plates, and temperature distributions at cross-sections of lapped plate specimens are measured using a thermotracer. The 94 kHz vibration system used for ultrasonic plastic welding consists of a bolt-clamped Langevin type longitudinal vibration source using four 30-mm-diameter piezoelectric ceramic (PZT) rings, a stepped horn (vibration velocity transform ratio N=3.0) and a catenoidal horn (N=3.13) with an 8-mm-diameter welding tip. The other vibration systems have similar configurations. Using a higher frequency system, increases in temperature measured at the welding parts are higher. The maximum temperature increase measured using thermocouples and a thermotracer was over 330°C.

P1-34 Temperature Rise and Welding Characteristics of Various Frequency Ultrasonic Plastic Welding Systems

P1-34 Temperature Rise and Welding Characteristics of Various Frequency Ultrasonic Plastic Welding Systems

Configuration of a 30-mm-diameter 94 kHz Ultrasonic Longitudinal Vibration System for Plastic Welding

Vibration and welding characteristics of a 94 kHz ultrasonic plastic welding system are studied. The 94 kHz ultrasonic plastic welding systems consist of a 30-mm-diameter bolt-clamped Langevin-type PZT longitudinal transducers with four PZT rings, a stepped horn (vibration transform ratio N = 3.0) with a supporting flange at a nodal position and a catenoidal horn (N = 3.13) with an 8-mm-diameter welding tip. Maximum vibration velocity of the 94 kHz welding tip was 3.2 m/s (peak-to-zero value) at loaded condition. The welding characteristics of the 1.0-mm-thick polypropylene sheet specimens using the 94 kHz welding system were studied. Using the 94 kHz system, a weld strength of more than 370 N per one welded area was obtained at a vibration velocity of 2.7 m/sp-0 (peak-to-zero value), welding time of 0.8 s and static pressure of 600 kPa.

Welding characteristics of 27, 40 and 67 kHz ultrasonic plastic welding systems using fundamental- and higher-resonance frequencies

The welding characteristics of 27, 40 and 67 kHz ultrasonic plastic welding systems that are driven at only the fundamental-resonance frequency vibration were compared, and also those of the welding systems that were driven at the fundamental and several higher resonance frequencies simultaneously were studied. At high frequency, welding characteristics can be improved due to the larger vibration loss of plastic materials. For welding of rather thin or small specimens, as the fundamental frequency of these welding systems is higher and the numbers of driven higher frequencies are driven simultaneously, larger welded area and weld strength were obtained.

P2-66 Temperature Distributions of Welding Specimens Using Various Frequency Ultrasonic Plastic Welding Systems(Short presentation for poster)

P2-66 Temperature Distributions of Welding Specimens Using Various Frequency Ultrasonic Plastic Welding Systems(Short presentation for poster)

L-2 Welding Chracteristics of a 180 kHz Ultrasonic Plastic Welding System

L-2 Welding Chracteristics of a 180 kHz Ultrasonic Plastic Welding System

Welding Characteristics of 67 kHz Ultrasonic Plastic Welding System Using Fundamental and Higher-Resonance-Frequency Vibrations

The welding characteristics of a 67 kHz ultrasonic plastic welding system using fundamental and higher-resonance-frequency vibrations were studied and compared with those of the 27 kHz and 40 kHz systems. At high frequency, welding characteristics were improved due to the larger vibration loss of plastic materials. The 67 kHz welding tip vibrates at a maximum velocity of more than 2.3 m/s (peak-to-zero value) at a fundamental resonance frequency and there are several higher resonance frequencies up to 94 kHz whose vibration velocities are more than one-fourth that of the fundamental frequency. The welding characteristics of lapped 1.0-mm-thick polypropylene sheets were measured for the cases where the vibration system was driven using combined driving voltages of both fundamental and higher resonance frequencies. The welded area and weld strength increased when fundamental and higher resonance frequencies were driven simultaneously. The welding characteristics of the 67 kHz ultrasonic plastic welding system were improved significantly compared with those of 27 kHz and 40 kHz welding systems by driving fundamental and higher resonance frequencies simultaneously.

Welding Characteristics of 40 kHz Ultrasonic Plastic Welding System Using Fundamental and Higher-Resonance-Frequency Vibrations

The welding characteristics of 40 kHz ultrasonic plastic welding system using fundamental and higher-resonance-frequency vibrations were studied. At high frequency, welding characteristics can be improved due to the larger vibration loss of plastic materials. The 40 kHz welding tip vibrates at a maximum velocity of more than 3.0 m/s (peak-to-zero value) at a fundamental resonance frequency and there are several higher resonance frequencies up to 107 kHz whose vibration velocities are more than one-fourth that of the fundamental frequency. The welding characteristics of lapped 0.5-mm-thick polyvinyl chloride and 1.0-mm-thick polypropylene sheets were measured in the cases where the vibration system was driven using combined driving voltages of both fundamental and higher resonance frequencies. The welded area and weld strength increased as fundamental and higher resonance frequencies were driven simultaneously. The welding characteristics of ultrasonic plastic welding were improved significantly by driving fundamental and higher resonance frequencies simultaneously.

Characteristics of Two-Vibration-System Ultrasonic Plastic Welding with 90 kHz and 20 kHz Vibration Systems at Right Angles

The direct welding characteristics of an ultrasonic plastic welding system with an upper 90 kHz longitudinal welding tip with a small vibration amplitude and a lower 20 kHz low frequency torsional vibration welding tip with a large vibration amplitude at right angles are studied. By using a combination of high and low vibration frequency systems with small and large vibration amplitude welding tips, the welding characteristics are improved, resulting in a smaller required vibration amplitude and less damage to the specimens due to vibration than those using conventional systems. The two-vibration-system welding equipment consists of a 90 kHz upper longitudinal vibration source with six bolt-clamped Langevin-type piezoelectric ceramic (lead-zircon-titanate; PZT) transducers 15 mm in diameter, a 20 kHz torsional vibration system 40 mm in diameter and a welding frame. The total required velocity amplitude of the two-vibration-system welding equipment is decreased and the welding characteristics are improved significantly compared to those of conventional one-vibration-system for both soft and hard plastic sheet welding.

Ultrasonic Plastic Welding Using 90 kHz Upper and Lower Vibration Systems

Direct and transmission welding characteristics of an ultrasonic plastic welding system using 90 kHz upper and lower vibration systems are studied. By using high frequency, welding characteristics of plastic specimens may be improved because ultrasonic vibration absorption by plastic material increases as vibration frequency increases. The 90 kHz ultrasonic vibration source designed consists of a radial-to-longitudinal vibration direction converter with four bolt-clamped Langevin-type piezoelectric ceramic (lead-zircon-titanate; PZT) transducers of 15 mm in diameter. The 90 kHz welding equipment consists of two vibration sources positioned at upper and lower parts and a welding frame. In the case of direct welding of various sheet specimens, the required total velocity of 90 kHz upper and lower welding tips is less than 60% that of 27 kHz welding tips. Direct and transmission welding characteristics of a 90 kHz welding system with two vibration sources are significantly improved compared with those of conventional systems.