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Precise electro-chemical machining — or PECM in short — enables precision parts to be serially produced while compensating several machining processes in one and the same machine. It is a technology that dissolves metal ions on the smallest micro scale, and that always stays on the same high level of quality.
PEMTec in Forbach has been engaging with this technology ever since 1995. By now, most of PEMTec's machines are producing precise serial parts for the automotive, aerospace, medical and even the care industry. But the technology is also principally of interest for all branches and areas of industry where precise metal serial parts are required. PEMTec develops, manufactures and distributes these highly precise PECM machines in France and Germany, but by now also has agencies that offer and sell them in many countries around the world. The economic requirements for precise and fast production processes are increasingly gaining in importance worldwide, and this under an intensifying competitive pressure. 'Pemming', as the manufacturing method has come to be called, provides a solution for many parts manufactured by means of PECM.
The technology is principally based on Faraday's Law, which dissolves metals on the anode side with the help of electricity, water and an electrode. PEMTec has perfected this technology and integrated it in a machine. This machines basically works like any other processing machine. The workpieces are placed inside it and then the required shape is reproduced with corresponding electrodes. A TOP-produced electrode can be used on many steels to create finishes with Ra values below 30 nanometres. The ability to manufacture finished parts with an unvarying precision of 2 or 5 µ, for example, in a single workflow is a clearly convincing distinguishing feature of this technology.
How does such a machine work? What can a PEM machine do? Who benefits from it? All these are basically simple questions, and the answers are just as simple. The machine works with salt water as a conductive electrolyte and electricity that is exactly pulsed by means of sophisticated CNC hardware and software which precisely controls and manages the machine, electrolyte and process. And that down to a single µ, while the machine is still easy to operate for the user
In serial production, the machine and/or process offers several benefits at once. PECM is a so-called cold process that will not create any heat at the workpiece itself, i.e. no mechanical or thermal stress in the production of parts. Which also means that there will be no structural changes in the workpiece, and that the process will not give rise to any micro fissures or so-called white layers which would then need to be removed again with great effort. It provides for an absolutely burr-free production method that renders any reworking of the parts superfluous. And these are only some of its truly interesting production characteristics. The electrodes can be used any number of times because the process itself will not cause any electrode wear. Which is also what enables the unvarying quality of the serial parts, possible even on the smallest microscale.
PECM basically enables the finishing of all parts made from conductive materials. This of course also includes all the metallic materials of technical relevance in the metal industry. Very good results are achievable with virtually all types of steel. And even the so-called ‘difficult to machine materials’ such as Inconel, Hastelloy, Crofer, nickel-base alloys, and superalloys can be 'pemmed' very well, as is also the case with alloyed titanium. Precious metals such as gold and silver can meanwhile not be processed with this method. Another type of material that is unsuitable for 'pemming' are hard metals because tungsten carbide, for example, is non-conductive.
If PECM manufacturing is to achieve good results, the electrodes will naturally need to be of a very precise design and contour. For high-gloss finishes requiring a surface roughness of Ra 0.00003 mm (= 30 nanometres), for example, the electrode will of course also need to have the same surface quality at all the desired places. And with standard machines only working in Z-direction, the requirements for the tool are correspondingly high. Serial production tolerances in the smallest µ-range in tool-based manufacturing also calls for a high degree of precision in the toolmaking with the same µ-perfect tolerances. A tool for the PECM technology comprises the electrode unit, a so-called rinse chamber, the workpiece/blank carrier, and the required guide bearings and/or rails.
In comparison with the often overlapping metalworking processes such as eroding, milling or micro milling, PEMTec's PECM process offers inestimable advantages that will be immediately noticeable for the user. These include cost savings brought about by combining several process stages such as roughing, smoothing and polishing in a single operation, and by the absence of rework or labour-intensive de-burring, to name but a few positive characteristics. This technology still harbours immense potentials while the component production range is still in its infancy. The precise ECM technology is unfortunately still not that widely known, and only few colleges go into the topic in any greater detail in their study courses. Given detailed knowledge of this technology, many developers could tackle their subjects and tasks in an entirely different manner. For a number of renowned manufacturers in the mentioned industries, however, the technology has meanwhile become indispensable.
Image captions:
Figures 1-3: Standard machine program.
Figures 4-7: Sample parts for series production.
Figures 8 and 9: Tool Example for series production.