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New improvement process (after edm) for suface finish of moulds and dies.

Compare surfaces before and after ECP: - By using the EDM finish electrode; - Remove the recast and heat affected layers from wire and penetration EDM'ed moulds and dies; - Polish in complex ways (texture can be done after this process); ECP can give shine to textures.

All across europe, ecp is only available at PMM-Moldes (Marinha Grande - Portugal)

The surface finish of moulds and dies is very important for all kinds of forming operation, whether it is plastic moulding, die casting of light metals, hot forging of steel or sheet metal forging and stamping. The surface finish of the tools not only influences the quality of the product but also the working life of the tool. A surface finish produced by Electro-Chemical Polishing (ECP) has no micro-cracks or porosity - as is always the case after Electro Discharge Machining (EDM). An ECP finished tool has no surface imperfections where fatigue can start. The ECP process effectively and uniformly removes the 'white layer' or 'recast layer' which is produced by the EDM process. The resulting surface is smooth and glossy and has surface properties that are identical with those of the base material. The use of ECP can, therefore, generate significant savings for both the manufacturers and the users of moulds and dies. It is also possible to use ECP to generate surface topologies which are practically impossible to produce using conventional manufacturing methods.

Electro-Chemical Polishing with the ECHODE-method is significantly different to conventional 'electropolishing', where dangerous acids - phosphoric-, perchloric and chromic acids - are used and poisonous gases and chemical by- products are produced. The ECP-technique with the ECHODE-method uses the fact that a homogeneous electrostatic field is built up in the gap between a mould surface and a mating electrode if a voltage is applied between them. If there is an electrolyte in the gap between tool and electrode, a current will flow. The current will have uniform density if the gap is uniform: the current density used for ECP is very high, typically 40-80 A/cm2 , and evenly distributed over the whole tool surface. The size of the gap may be chosen between 0,1 to 0,5 mm, but must be uniform over the whole surface. The current forces the negative nitrate ions to the positive pole, which is the tool, where they react chemically with the material. These nitrates dissociate immediately - because the pH -value of electrolyte is around 8.5 - forming an insoluble sludge of hydroxides, for example, Fe(OH)2. Thus, the surface of the tool will be dissolved step by step, and after dissolution of a layer about 0,1 mm thick, a metallically clean, uniform and glossy surface will be created, which is completely free from the 'recast layer', micro-cracks and/or mechanical stresses, which are generated by Electrical Discharge Machining (EDM) or conventional milling and grinding.

The machining time for ECP is always the same, independent of the size and form of the mould or die cavity. The only requirement is that a suitable, matching electrode is available. The electrode can be of the same material and geometry as used for rough EDM, with a gap of >0.15 mm. Indeed, if the electrode used for EDM shows little wear or damage it can be used as the ECP electrode as well! The ECHODE 53-A6 machine can polish tools with an area of up to 660cm2 . The maximum current delivered by the power supply of this machine is 24000 A and work-pieces of up to 500Kg can be polished. At present, P.M.M.-Moldes, Lda. is the only company offering contract ECP polishing services in EUROPE. If a 'mirror like' finish is needed, manual polishing with fine diamond or alumina is typically required after ECP. An advantage of ECP is that this is made much easier as the hard ‘recast layer’ is removed entirely. For final polishing it is often sufficient to use diamond paste of size 6-3-1µm. The 6µm diamond paste can often be replaced with 2000/4000 mesh wet SiC grinding paper.

By reducing or removing the need for medium and fine EDM and manual polishing, significant cost savings, both direct and indirect, can be achieved. By increasing the surface quality of the tools produced, ECP removes the need for monotonous manual hand finishing procedures.

The emission of noise and dust is almost completely eliminated and the working environment improved.

Most steels, pure metals and alloys – as Al and brass – can be processed by ECP. The degree of improvement of surface quality depends upon the actual material and the electrode surface conditions. In all cases, the recast layer can be uniformly removed leaving a clean and smooth metallic surface with physical properties identical to those of the base material. This surface also readily accepts manual polishing to a mirror- like finish. he best results are obtained with steels produced by powder metallurgical, ESR– and ESH-methods.

The parameters influencing the surface roughness produced by ECP are the quality of the work-piece material, its heat treatment, surface roughness (Rmax) before ECP and again, the material and surface quality of the electrode.Better mould and die finishing can be achieved if the electrode is manufactured out of copper. The surface finish of the electrode is also very important, as its imperfections and defects will be copied onto the tool surface.

The parameters influencing the surface roughness produced by ECP are the quality of the work-piece material, its heat treatment, surface roughness (Rmax) before ECP and again, the material and surface quality of the electrode.Better mould and die finishing can be achieved if the electrode is manufactured out of copper. The surface finish of the electrode is also very important, as its imperfections and defects will be copied onto the tool surface.