Rotary Ultrasonic Machining

Materials with unique properties provide irreplaceable applications in many sectors. Those properties often decrease the machinability of those materials. Moreover, parts made of those materials often require high-dimensional precision and superior quality of the surface. Processing of unique materials can be difficult, ineffective, or even impossible. Therefore, advanced machining methods were invented. One of them is the rotary ultrasonic machining. It is suitable for machining hard and brittle materials. It can process electrically and thermally conductive and nonconductive materials. One of the possible applications of rotary ultrasonic machining is for the creation of cutting-edge preparation on the cutting tools. This preparation increases tool life and process stability.

The inception of the industrial application of the ultrasound was conditional of several discoveries and inventions. The human ear cannot hear the ultrasound (it is practically its definition), therefore for the initial stimulus can be considered the discovery, there can exist the sound beyond audible frequency. After that there was a challenge to invent the device, which can produce the ultrasound. When such a device was manufactured, and when ultrasound could be modulated in different frequencies and amplitudes, the researchers could start thinking about its industrial application. The first global usage of the ultrasound in the industry was a military application in the detection of the submarines and aircraft. After World War II, there begin application of the ultrasound for peaceful purpose in the industry and medicine.

When ultrasound began to be used in industrial application, plenty of regularities and influences had to be discovered. The most of the researches in ultrasonic machining were focused on the evaluation of cutting forces, material removal rate, tool wear, surface roughness, accuracy, cutting temperature and power consumption during machining of hard and brittle materials and composite materials. There were made simulations of the process and analysed the removal process. The hybrid processes were developed with a purpose to improve the cutting process of alloys. Ultrasonic assistance of classic machining process was used to improve observable characteristics of machined alloys. Generally, it can be concluded that ultrasound positively affects every aspect of the machining process.

The research in ultrasonic machining is a never-ending process. New discoveries lead to new devices and applications. And they request additional research to fully understand their processes. And during the research could be discovered additional phenomena, which could find application in the future. Moreover, development in the analytical sector allows obtaining new or more precise analyses of the process. The following chapter tries to briefly introduce possible developments in the field of rotary ultrasonic machining.

To fully understand the processes in ultrasonic machining, it is necessary to understand the theory of the ultrasound first. The material affects the spreading of the ultrasonic waves. The damping of the undulation affects the tool material selection. The modulus of elasticity affects the machinability of the workpiece material. To sufficient ultrasonic machining, the amplitude of the undulation has to be high enough. With those and additional knowledge is possible to construct devices for ultrasonic machining. For their proper operation, they have to consist of ultrasonic, transducer, concentrator and tool. Correct selection of the tool material, workpiece material, ultrasonic set-up and machining parameters cause benefits during the cutting process.

The application of the ultrasonic energy into the production process positively affects every aspect of them. In machining, the ultrasound decreases the cutting forces and temperatures and increases tool life a surface quality. It even allows to machine hard and brittle materials. And it is not only machining, which finds out benefits of ultrasonic undulation—even casting, forming, welding and soldering are improved by ultrasound. The successful application of the ultrasound can be found even in cleaning, localization, defectoscopy, metrology, medicine and many more.

The ultrasound is beneficial in the machining of a wide range of materials. However, the device for rotary ultrasonic machining is not cheap. It can reach the full potential when materials are machining, which are not easy machinable by other methods. Those materials include very hard materials, such as technical glass, advanced ceramics and minerals. The application is focused on the processing of synthetic diamond, cubic boron nitride, alumina, zirconia, carborundum, etc. Beside mentioned hard and brittle materials, ultrasound in machining can be used for machining of chromium-cobalt, titanium, wolfram carbide, graphite, martensite, ferrite, vanadium, stainless steel, composites reinforced by aramid/carbon/glass fibres, and many more. Such a range of machinable materials makes rotary ultrasonic machining attractive in sectors, where machining of different kinds of unique materials is needed.

Cutting-edge preparation brings a lot of benefits in the machining process, including increased tool life, process stability and surface quality. Therefore, there were developed several methods to fulfil this edge modification. Those methods differ by principle, application, effectivity and costs. However, create cutting-edge preparation into CBN inserts remains challenging. Those inserts are used for heavy-duty applications, such as machining of hardened steels and cast irons. Their main characteristic is very high hardness, which makes them abrasive resistant. But there is one machining method created to processing hard materials—rotary ultrasonic machining (RUM). This chapter describes and analyses the experiment of application of RUM to produce cutting-edge preparation on CBN inserts. Experiments confirmed the suitability of this process—it successfully creates a chamfer. However, the accuracy was disputable. There are determined possible reasons for inaccuracy and suggested options of solution for increase the precision of achieved cutting-edge preparation.

Ultrasound brings benefits to many sectors, like industry, medicine, metrology, diagnostics, etc. In machining, it causes decreasing in cutting force and heat generation, while the superior surface is achieved. Moreover, it allows the machining of hard and brittle materials. Therefore, it could be used for modification of the cutting tools, especially ones made of very hard materials, like CBN. Preferred modification on the cutting tools is cutting-edge preparation. According to performed experiments can be concluded, that rotary ultrasonic machining is suitable for the cutting-edge preparation of CBN cutting inserts.