Machining is the process of shaping a raw material by cutting or shaving parts of the material away. Traditionally, the term “machining” referred to processes such as drilling, milling, turning, boring or planing. These conventional machining processes are giving way to new technologies and techniques, such as electrical discharge machining, electrochemical machining, laser cutting, water-jet cutting and ultra-sonic machining.
Ultrasonic machining schematic – Image by Joelvlss
Also referred to as ultrasonic impact grinding, this process vibrates the cutting tool at ultrasonic frequencies to remove material from the workpiece. The advantages of this technique are that the tool never contacts the workpiece itself and the grinding pressure is never more than 2 pounds, making it ideal for hard, brittle surfaces like glass and ceramics. Very little heat is produced, which helps to create a clean and unmarked finish. Although the tool and workpiece never come into direct contact, the technique still works surprisingly quickly.
Electric Discharge Machining, or EDM, is sometimes colloquially referred to as “spark machining” or “spark eroding”. The process involves creating a desired shape using electrical discharge, or sparks. The tooling tip emits rapidly recurring electrical discharges between two electrodes – known as the “tool electrode” and “workpiece electrode” –which are separated by a dielectric liquid; this helps the sparks to focus on only the part of the workpiece that is intended to be cut or machined.
ET 3000 – Image by OOO “ECM”(PECM IND. LLC) (CC BY-SA 3.0)
Electrochemical machining, or ECM, removes metal by means of an electrochemical process. It’s sometimes referred to as “reverse electroplating” because it’s similar to electroplating, but removes material instead of adding it. A high current is passed through an electrode and the workpiece, and the tool is moved along the workpiece without touching it. No sparks are created, and thanks to the lack of thermal or mechanical stress being transferred to the workpiece, mirror-smooth surface finishes can be achieved.
ECM is ideal for machining extremely hard materials, but is possible only with materials that are electrically conductive. It can be used to cut small or odd-shaped angles and intricate curves and contours.
Water Jet Cutting
Waterjet cutting – Image by Steve Brown Photography (CC BY 3.0)
Also referred to as water jetting, water jet cutting involves using an extremely high-pressure jet of water to cut a material. Straight water-only cutting is used mostly to cut softer materials like food or rubber. It’s also used in situation where other working processes would create too much heat, such as applications in mining and aerospace technology.
Sometimes the water is mixed with another abrasive substance to wear at the workpiece, and this is referred to as “abrasive jetting”. Abrasive jetting can cut into materials as dense as granite and as hard as metal.
Traditionally, laser cutting was used largely for industrial manufacturing applications. Thanks to desktop versions of laser-cutting machines, it’s now being used by schools, businesses and hobbyists. The process involves using computer numerical control, or CNC, to direct the output of a high-power laser at the material to be cut. The material to be removed melts, burns or vaporizes away, leaving an edge with a high-quality finish.
Different laser-cutting processes are used to cut different kinds of materials. Examples of the processes are vaporization, melt and blow, burning, thermal stress cracking, scribing, cold cutting and burning-stabilized laser cutting.