EBM (Electron Beam Machining)

     Electron beam machining (EBM) uses a focused stream of electrons. The process is widely used for welding, melting, material removal and annealing. Since the stream may have many technical applications, its power density can various (power density is defined as a relation between the beam power and its cross-section). Cutting requires the biggest densities. Smaller densities are used for welding and boring. 
     The energy of an electron beam, changes into heat, while in contact with working material. Due to that a local increase in heat appears which highly exceeds the melting point of every possible material, accompanied by rapid vaporization. Electrons must have enormous speed while going from the electron gun. Huge accelerations may be achieved by applying big value of accelerating voltage.
     Current of an electron stream emission is a current of an electron beam, emitted by a cathode. The current is very small (only few mA) and depends on a cathode material, its temperature and an accelerating voltage.

Electron Gun Working Principles

AWJC (Abrasive Waterjet Cutting)

The abrasive waterjet cutting (AWJC) technology is one of the recently introduced machining methods, used as a machining tool for cutting from soft to hard-to-machine materials. High pressure waterjets were first used to cut soft materials in the early 70’s. Research led to the invention of the abrasive waterjet in 1980, which increased the range of the materials which can be cut.

Pure & Abrasive Waterjet Types

The working principles are both simple and extremely complex. Water simply flows from a pump, through plumbing, to a cutting head. However to generate and control water at pressures of 350 ÷ 600 MPa a sophisticated technology is required. Pump is the heart of the waterjet system. It pressurizes the water and delivers it continuously so that a cutting head can then turn that pressurized water into a supersonic waterjet stream. There are two main types of pumps: direct drive pumps and intensifier based pumps. The direct drive is a triplex pump that gets the movement of the three plungers directly from the electric motor. These pumps are very simple in design although 10-25% weaker than intensifier pump units.
The intensifier pump consists of an electric motor (25 to 200 HP), hydraulic pump, oil reservoir, manifold, and piston biscuit/plunger. The electric motor powers the hydraulic pump, which pulls oil from the reservoir and pressurizes it to 20 MPa. The oil is next send to the manifold where manifold’s valves create the stroking action of the intensifier by sending hydraulic oil to one side of the biscuit/plunger assembly, or the other. The hydraulic oil is then cooled during the return back to the reservoir. The 3,000-psi oil pressure is “intensified” twenty times, yielding 350 ÷ 600 MPa water pressure.

Intensifier Pump Working Principles

LBM (LaserBeam Machining)

     Laser beam machining (LBM) works on a principle of LASER (light amplification of stimulated emission of radiation). The basic principle of laser operation is Bohr’s law. It states that stimulated emission is made by the transition to basic atom’s state from excited state. Laser uses almost completely monochromatic and highly coherent, focused light, to create huge energy density with temperatures 8000÷10000 K. The stream of photons which provides such enormous temperatures gives an explosive erosion of all possible materials. Focused photon stream is a powerful tool for erosion cutting, welding, engraving, soldering, hardening and imbueing. In the laser’s head the focus of photons can be made by: solid laser, gas laser, semiconductor laser or a fluid laser. For the laser beam machining purposes the solid lasers are commonly used.

Solid Laser Working Scheme

Gas Laser Working Scheme

EDM (Electrical Discharge Machining)

     Electrical Discharge Machining (EDM) is a controlled metal-removal process that is used to remove metal by means of electric spark erosion. In this process an electric spark is used as the cutting tool to cut (erode) the workpiece to produce the finished part to the desired shape.

Electrical Discharge Machining Working Scheme

     Due to electrical discharge, there is a very big temperature (8000÷12000 K) between electrodes. Electrodynamical forces and large point internal stresses, caused by temperature difference, cause the erosion. The discharge time is extremely short, so heat applied is very short and shallow.
     Working principles of electro-discharge machining are very simple. The workpiece and the electrode are immersed in a dielectric fluid such as oil or deionized water. The electrode and workpiece are separated by a small gap and voltage is applied. When there is enough voltage, the dielectric breaks down. A spark jumps the gap, striking the workpiece and vaporizing part of the material. The high speed electrons then impinge on the job and ions on the tool. The kinetic energy of the electrons and ions on impact with the surface of the job and tool respectively would be converted into thermal energy or heat flux. Such intense localised heat flux leads to extreme instantaneous confined rise in temperature which would be in excess of 10,000 K. The intense heat also melts a small portion of the material. The current then is pulsed off, and the dielectric flows into the area carrying away most of the melted material in the form of small chips.

Types of Erosion Machining

     In order to receive a part, the material must be machined. The machining plays a very important part in manufacturing. It is about making components from raw materials by getting rid of a preestablished volume of material. One group of methods for shaping the material are erosion processes. Erosion machining belongs to material removal processes. It is used for creating different machine parts and uses other forms of energy than only mechanical energy. It is acomplished by eroding, melting and vaporizing the material.

Classification of Erosion Machining Types

     The main classfification of erosion machining is due to the type of energy that is used. It may be an energy of electrical discharges, chemical, ion, electron or photon energy. Erosion machining may be also classified due to the machining purpose (cutting, drilling, etc.). Additional classification may be done due to the kind of cutting tool that is applied. It can be either a stream or a working electrode.The different types of erosion machining have its own uniqe properties and drawbacks. In order to apply them properly it is important to understand them properly.