But what about materials that are not similar. Let's address this question by looking at how New Balance has used ultrasonic welding to assemble athletic shoes. Look at a pair of athletic shoes. While traditional shoes may be made of a single material such as canvas or suede leather, many athletic shoes have several materials such as lightweight plastic polymers, suede or synthetic suede, and mesh combined.
These composite materials make the shoes light, flexible, durable and breathable. For example, one style of New Balance athletic shoe has an upper portion which consists of three parts. But how do you put these materials together? Most commonly, shoe companies sew the materials together. About two to three years ago, however, New Balance set out to make the upper part of a shoe without stitching. After experimenting with polymer adhesive films and irons, they came up with a way of making this portion of the shoe using ultrasonic welding.
To assemble the upper part of the shoe, workers start with a piece of synthetic suede material. They use an iron press to bond a thin sheet of hot melt film to the back of the material. Next, an ultrasonic welding assembly presses a pattern vamp into a suede material. Likewise, a similar ultrasonic welding machine presses the saddle eye row from another piece of synthetic suede.
The vamp shape gets cut out of the suede. The saddle eye row and mesh material get welded ultrasonically to the vamp. In the processes, the frictional heat from the ultrasonic welder melts the hot melt film, which bonds the saddle eye row and the mesh material to the vamp. The finished vamp then gets shaped and bonded to the sole and heel pieces using water-based solvents. According to Kenneth Straka, Senior Product Developer for New Balance, the ultrasonic welding methods have increased productivity by saving time.
Not only do the ultrasonic welders distribute heat more evenly than iron presses, they also heat up and cool down faster. So, the assembly process requires fewer steps and is faster than traditional sewing methods. Now that we have seen how ultrasonic welding is used to bond various materials, let's look at the advantages and disadvantages of this technique.
Ultrasonic welding has many advantages over traditional methods. For one, welding occurs at low temperatures relative to other methods. So, the manufacturer does not need to expend vast amounts of fuel or other energy to reach high temperatures.
This makes the process cheaper. It's also faster and safer. The process occurs in fractions of a second to seconds. So, it can be done more quickly than other methods. In fact, it can bond plastics better and faster than glues. For example, the new smart keys in cars have a transponder chip in them. The car can only start when it senses the chip. To make the key, one end of the metal key blank and the chip get placed into one half of the plastic top.
The other half gets placed over them and bonded to the base half. This bonding would usually be done with glue, which takes time to cure. The same task can be done with ultrasonic welding in less than a second. Ultrasonic welding does not require flammable fuels and open flames, so compared to other welding methods, it's a safer process.
Workers are not exposed to flammable gases or noxious solvents. In electronics, copper wires are usually bonded to electrical contacts on circuit boards with solder. The same task can be done using ultrasonic welding in a fraction of the time and without exposing workers to fumes from smoldering lead solder.
Finally, ultrasonic welds are as strong and durable as conventional welds of the same materials -- which is just one of the reasons the method is being used in car manufacturing. To make cars lighter and more fuel efficient, auto makers are turning to aluminum as the main metal in car bodies.
Ultrasonic welding can be used to bond the metal in less time and at lower temperatures than traditional welding. The components to be joined are held together under pressure and subjected to vibrations, usually at a frequency of 20 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 and joint. Ultrasonic welding times are short typically less than one second , which makes the process ideal for mass production.
The process is widely accepted in many applications ranging from automotive light clusters to consumer electronics products, such as mobile telephone casings.
Ultrasonic welding equipment consists of a machine press, generator, converter or transducer, booster, sonotrode or horn, and component support tooling. The machine has a pressure gauge and regulator for adjustment of the welding force.
It should be noted that a particular gauge pressure set on one piece of ultrasonic welding equipment will not necessarily provide the same welding force as another machine set at the same gauge pressure.
Welding force should be calibrated using a load cell so that direct comparison of welding forces can be made from machine to machine. There is also a flow control valve to allow adjustment of the speed at which the welding head approaches the component being welded. Some equipment manufacturers have introduced an electromagnetic force application system in place of the traditional pneumatic cylinder.
This gives better control of the approach rate, and can be beneficial when welding small or delicate components. 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.
Transducers are delicate devices and should be handled with care. Once the elements are broken, the transducer will not function. 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 wave length. The welding horn is the element of the welding stack that supplies energy to the component being welded. A good example would be trying to weld polyethylene to polypropylene.
Both of these semi-crystalline materials have a similar appearance and many common physical properties. However, they are not chemically compatible and are therefore unable to be welded to each other. Like thermoplastics i.
For example, it is likely that an ABS part could be welded to an acrylic part because their chemical properties are compatible. Generally speaking, only similar amorphous polymers have an excellent likelihood of being welded to each other. The chemical properties of any semi-crystalline material make each one only compatible with itself.
When the materials to be welded are compatible, several other factors may affect the adhesive bonding of the parts. These factors include hygroscopicity, mold release agents, lubricants, plasticizers, fillers, flame retardants, regrind, pigments, and resin grades. The joint design of the mating pieces is critical in achieving optimum assembly results.
There are many different joint designs, each with its own advantages. Some of these designs are discussed later in this section. There are three basic requirements in joint design:. There are many advantages to using ultrasonic welding. It is a fast, clean, efficient, and repeatable process.
It produces strong, integral bonds while consuming very little energy, and no solvents, adhesives, mechanical fasteners, or external heat are required.
Finished assemblies are strong and clean.
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