Advanced Manufacturing Processes: Electrochemical Machining

Electrochemical machining

Index

• Electrochemical machining .............................................................................................................................. 1
• Introduction on chemical machining ............................................................................................................ 1
• ECM: mechanisms and parameters .............................................................................................................. 3
• ECM: components ........................................................................................................................................ 5

Introduction on chemical machining

Chemical processes for machining purposes and surface finishing have been extensively applied in industry. Controlled dissolution of material substitutes the mechanical relative motion between tool and workpiece typical of traditional material removal processes.

Therefore, absence of mechanical forces leads to removal of residual stresses into the part. Moreover, no significant thermal stresses and good surface finish are achieved.

The typical processes are chemical machining, photochemical machining and electrochemical machining. In chemical machining, the workpiece is put in a tank where a chemical reagent and a heating system allow the reaction of the material. A mask is needed to avoid dissolution in pre-defined zones.

Concentration of the chemical reagent and time of exposure are the main parameters of the process. It is used for acid pickling (removal of oxides from a surface), for milling small components and for post-processing deburring.

Photochemical machining shares the same characteristics of CM, but the mask is a photoresist that hardens if exposed to UV light. The hardened parts are etch-resistant, thus it is possible to selectively dissolve the unprotected metal.

This process is more used as a material removal step in lithography or, for example, with components that require a large number of holes, because drilling them one-by-one would require too much time.

ECM: mechanisms and parameters

Electrochemical machining is based upon electrolysis: anodic dissolution of the workpiece through a DC or a pulsed voltage is achieved. The obtained shape is the negative of the tool, which is the cathode.

In the tool there is a tube for the electrolyte feeding. A recycling system is required because material removal generated sludge that is collected by the electrolyte flow through the working area.

Dimensional tolerances of this process are 3±0,03 ≈ 0,1 − 1 . 1,4 / and typical application of ECM is high speed deburring (≈ with = 1000).

Material removal doesn’t depend on mechanical properties of the workpiece – as hardness, toughness or workability – but on chemical-physical ones: density, atomic weight, ionization energy.

Workpiece (+) and tool (-) constitute an electrolytic cell into which a redox happens. Typical electrolyte is a solution of NaCl or NaNO₃.

For example, ECM has a better surface finish than EDM. Generally, these technologies are used as a post-processing step of burrs removal, especially in complex geometries.

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