Automated Ultrasonic Welding Equipment For Polycarbonate / Polypropylene

40Khz automated ultrasonic welding machines for polycarbonate / polypropylene

Ultrasonic welding involves the use of high frequency sound energy to soften or melt the thermoplastic at the joint. Parts to be joined are held together under pressure and are then subjected to ultrasonic vibrations usually at a frequency of 20, 30 or 40 kHz. The ability to weld a component successfully is governed by the design of the equipment, the mechanical properties of the material to be welded and the design of the components. Since ultrasonic welding is very fast (weld times are typically less than 1 second) and easily automated, it is a widely used technique. In order to guarantee the successful welding of any parts, careful design of components and fixtures is required and for this reason the technique is best suited for mass production. Benefits of the process include: energy efficiency, high productivity with low costs and ease of automated assembly line production.
 

Parameter:

An ultrasonic welding machine comprises four main components: a power supply, a converter, an amplitude modifying device (commonly called a Booster) and an acoustic tool known as the horn (or sonotrode). The power supply changes mains electricity at a frequency of 50-60 Hz, into a high frequency electrical supply operating at 20, 30 or 40 kHz. This electrical energy is supplied to the converter. Within the converter, discs of piezoelectric material are sandwiched between two metal sections. The converter changes the electrical energy into mechanical vibratory energy at ultrasonic frequencies. 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. 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 work piece 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.

Following are the factors for consideration in the ultrasonic welding process:

Heating Rate
The heating rate in ultrasonic welding is the result of the combined effects of frequency, amplitude and clamp force. In the heating rate equation, clamp force and frequency appear as multipliers. Frequency is usually fixed for a given machine. The heating rate in plastic varies directly and in proportion to the clamp force applied. When more clamp force is applied, the heating rate increases in direct proportion to the change. However, the heating rate varies with the square of the amplitude – if the amplitude is increased, heating rate increases dramatically. Hence, there is an inversely proportional relationship between the frequency of an ultrasonic welder and its output amplitude. If the highest available amplitude yields consistently acceptable results is used, minimal part damage and long sonotrode/horn life usually is desirable.
Plastics Material
An important consideration in the ultrasonic welding process is the material. Softer materials do not carry sound as well as harder materials and will require more amplitude from the tool to get a usable amount of amplitude to the joint. Materials with higher melt temperatures will require more amplitude to reach upto weld temperature before the joint detail is gone. Choosing a machine that is lower in frequency and therefore higher in amplitude is often advisable with soft or high temperature materials. Stiffer materials may be damaged by high amplitude, and may heat so quickly that the process becomes uncontrollable. Welding too quickly also can result in weak welds.
Tool Design Limitations
The laws of physics that govern sonotrode/horn design are related to wavelength. Most of the factors that reduce acoustic performance have to do with transverse dimensions - dimensions perpendicular to the direction of amplitude. If a tool has a longer wavelength (lower frequency), it can have larger transverse dimensions. A lower frequency tool will be simpler and potentially more durable than a higher frequency tool doing the same application.
Machines
High frequency welders typically run small tools - making small, delicate parts with great precision. They typically have small, light slides driven by small air cylinders. Low frequency welders typically run large tools at high amplitudes, making larger parts made of softer materials. They typically have large, heavy slides driven by larger air cylinders.

Types of joining
Ultrasonic vibratory energy is used in several distinct assembly and finishing techniques such as:
Welding : The process of generating melt at the mating surfaces of two thermoplastic parts. When ultrasonic vibrations stop, the molten material solidifies and a weld is achieved. The resultant joint strength approaches that of the parent material; with proper part and joint design, hermetic seals are possible. Ultrasonic welding allows fast, clean assembly without the use of consumables.
Staking : The process of melting and reforming a thermoplastic stud to mechanically lock a dissimilar material in place. Short cycle times, tight assemblies, good appearance of final assembly, and elimination of consumables are possible with this technique.
Inserting : Embedding a metal component (such as a threaded insert) in a preformed hole in a thermoplastic part. High strength, reduced moulding cycles and rapid installation with no stress build-up are some of the advantages.
Swaging/Forming : Mechanically capturing another component of an assembly by ultrasonically melting and reforming a ridge of plastic or reforming plastic tubing or other extruded parts. Advantages of this method include speed of processing, less stress build-up, good appearance, and the ability to overcome material memory.
Spot Welding : An assembly technique for joining two thermoplastic components at localised points without the necessity for preformed holes or an energy director. Spot welding produces a strong structural weld and is particularly suitable for large parts, sheets of extruded or cast thermoplastic, and parts with complicated geometry and hard-to-reach joining surfaces.
Slitting : The use of ultrasonic energy to slit and edge-seal knitted, woven and non-woven thermoplastic materials. Smooth, sealed edges that will not unravel are possible with this method. There is no "bead" or build-up of thickness on the slit edge to add bulk to rolled materials.
Textile/Film Sealing : The use of ultrasonic energy to join thin thermoplastic materials. Clear, pressure-tight seals in films and neat, localised welds in textiles may be accomplished. Simultaneous cutting and sealing is also possible. A variety of patterned anvils are available to provide decorative and functional "stitch" patterns.

Function

1. Frequency auto-chasing: intelligent control system, frequency auto tracking.

2. amplitude adjust Infinitely : amplitude adjust Infinitely , amplitude increase and decrease by 5%;

3. intelligent protection: frequency offset protection, output overloading protection, mold damage protection;

4. electrical components: all pneumatic components and main electronic components of the machine are imported from Germany and Japan;

5. fuselage structure: the frame of the machine adopt special steel structure and made by precision cast aluminum CNC machining processing , the frame is more precise and more stable