2.2 SHAPING MATERIALS UNCONVENTIONALLY MECHANICAL ENERGY-BASED PROCESSES The advent of hard materials has made conventional machining methods very difficult and , so other processes, known as "unconventional," have been developed and classified according to the energy they employ: time consuming 1 mechanical, electrical, thermal, chemical, and electrochemical. DO What is the Material Removal Rate (MRR)? 1 Mechanical energy-based processes With mechanical energy-based unconventional processes, unwanted material in the workpiece is removed by mechanical erosion. The most common ones are: Abrasive Jet Machining (AJM), Water Jet Machining (WJM) and Ultrasonic Machining (USM). AJM The process is used for: Abrasive Jet Machining providing a surface finish to hard metallic workpieces; smooth cutting, cleaning and machining semi-conductors (e.g.: silicon, gallium or germanium); making holes and in glass, quartz, mica and ceramics. slots Compressed air or gas is passed into a mixing chamber and a vibrator controls the of some abrasive powder. The two elements are mixed in the chamber, then the mixture is sent to a which produces a abrasive jet used to remove unwanted material from the workpiece. The gas used can be either or . feed nozzle fine carbon dioxide nitrogen 1 MORE The selection of abrasive particles depends on the hardness and the MRR of the workpiece. Most commonly, aluminium oxide or particles are used. 1 silicon carbide WJM The process uses water to produce a high velocity jet to cut a soft workpiece. The water jet strikes the workpiece and its kinetic energy is converted into pressure energy; this causes a high stress on the workpiece until the unwanted particles are automatically removed. WJM is a relatively fast and very precise process which prevents thermal damage to the workpiece because no heat is generated, and which does not produce any hazardous gas (it is eco-friendly), but only soft materials, such as rubber, wood, ceramics, plastics and aluminium can be machined. Water Jet Machining 2 MORE Hard materials can be cut if abrasives are introduced into water, transforming the process into Abrasive Water Jet Machining (AWJM). 2 USM The is a process in which material is removed from the surface of a workpiece by high frequency vibrations of a tool against the surface of the material. Abrasive particles are present: the is formed by mixing fine abrasive grains in water. This method is used to machine both brittle and hard materials with high precision, leaving no in the process. Ultrasonic Machining slurry burr 3 MORE The grains used in the abrasive fluid are usually or silicon carbide, while the fluid medium can be either water, benzene, glycerol or oil. 3 boron carbide
