Start Hole Erosion Machine— 3
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START HOLE EROSION MACHINES
EDM and it’s Types
Electrical Discharge Machining is a controlled material removal process for manufacturing geometrically complex or hard material parts that are extremely difficult to machine by conventional machining processes. EDM is one of the most extensively used non-conventional machining process because of its increasing ability to machine metals at higher speeds. It is a thermal erosion process which works on the principle of spark erosion. Several recurring electrical discharges are created between the cutting tool which in this case is an electrode and the work piece which is electrically conductive. The process takes place in the presence of a dielectric fluid. EDM can be broadly classified into three major types namely: Wire cut EDM, Die Sinking or Ram EDM and Start hole erosion EDM.
What is Start Hole Erosion EDM?
Small Hole EDM is an improved method of utilizing EDM to drill small holes in conductive material at speeds that are typically 10 times faster than those achieved with conventional Die Sinker or Ram EDM process which was earlier used to drilling of holes by electrical discharge machining. Small Hole EDM is now recognized and accepted as the third method of EDM Machining along with Sinker EDM and Wire EDM. Small hole EDM drilling, also known as fast hole EDM drilling, hole popper, and start hole EDM drilling, uses a rotating tubular electrode with a diameter of 0.1 mm to 6 mm to drill holes by means of electrical discharge machining by eroding material from the work piece in the presence of a water dielectric. These holes may have a depth-to-diameter ratio of 30 to 1 or higher. Tubular electrodes are rotated at speeds of about 100 RPM while drilling. As the electrical discharges occur, this rotation aids in flushing and provides for uniform electrode wear.
History of Start Hole Erosion EDM
High-speed EDM hole drilling was designed especially for fast, accurate small and deep hole drilling applications. Small holes that were once almost impossible to drill by conventional machine tools are now being performed with ease. Conventional Sinker EDM was successfully applied for the drilling of small holes, however the process was always considered to be very slow when compared to conventional drilling. Then came the invention of a specialized EDM process for the drilling of small holes in the late 1970’s. Start hole erosion EDM drilling which was considered to be the last resort for drilling of small holes is now widely used for production work. This can be attributed to the higher drilling speeds of up to 2 inches per minute achievable with the process nowadays. And holes can be drilled in any electrically conductive material, be it hard or soft including carbides. With the capability of drilling through virtually any conductive material, the use of this technology is continually expanding.
Construction and Working of Start Hole Erosion EDM Machine
The basic elements constituting a start hole erosion EDM machine are:
- Extrusion Stainless steel work table
- Rotating spindle
- Drill chuck or collet system for holding electrodes
- Ceramic or diamond guides
- Power supply with control panel
- Capacitor box
- Dielectric fluid pump
Start hole erosion EDM works on the same principle of spark erosion as the wire EDM or die sinker EDM. An electrical discharge is produced across the gap between the contactless electrode and the work piece thereby eroding the material from the job. The process consists of using a precision tubular electrode (generally brass or copper) mounted into the drill chuck located on the "Z" axis and held in location on top of the work piece by the ceramic guide. The top of the work piece is located and the drilling depth is set. The electrode rotation is turned on and the deionized water solution, which is pressurized between 50 and 100 kg/cm2, is sent through the tubular electrode as a flushing agent. The power supply parameters are set-which normally consist of on-time, off-time, peak current and amount of capacitance. At this point, the discharge is turned on to begin the drilling cycle. At the end of the drilling cycle, the discharge is turned off and the "Z" axis is retracted above the work piece. A servo drive is used to maintain the gap between the electrode and work piece. If the electrode touches the work piece, a short occurs and in such cases, the servo drive retracts the electrode.
APPLICATIONS OF START HOLE EROSION EDM PROCESS
Small hole drilling EDM has got wider field of applications. As the process is capable of producing burr free holes, it eliminates the usage of any secondary deburring process. And it is considered to be the most cost effective method for drilling fast and accurate holes in any conductive metals. Although originally conceived as a method of economically producing small holes with large depth-to-diameter ratios, Small Hole EDM is now utilized in just about any situation in many industries where conventional drilling a small hole is normally difficult: Automotive- Diesel fuel injection nozzles, Textile– Fiber spinning nozzles, Wire drawing– Small draw dies, Aerospace– Turbine blade cooling holes, Semiconductor– Silicon masks, Tool, Die, & Mold– Small Hole EDM drilling is ideal for putting ejector holes in hardened punches, coolant holes in cutting tools, vent holes in molds,wire EDM starting holes. And as many of the start hole erosion EDM machines utilize distilled water as the flushing agent, it opens up new applications in the medical field as well.
ONA ELECTRO EROSION, Heun Funkenerosion GmbH, Mitsubishi EDM, ANG International, POSALUX, Aristech, Current EDM are some of the worldwide manufacturers of small hole drilling EDM machines.