Tips for Controlling Oxidation and Pitting on a Wire EDM

Additives, machine settings, workpiece materials and current technology are factors in avoiding common problems with unwanted rust and surface defects.

Article From: 10/8/2010 Modern Machine Shop, , from GF AgieCharmilles

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Ugly part

Ugly, rusty parts are avoidable on today's wire electrical discharge machines.

Additives:

Additives do help in controlling oxidation and pitting of a variety of materials. These products help a great deal when cutting a workpiece with pre-polished surfaces.

There are a few rust-inhibitor products available on the market, but caution is advised because machine deionization bottles can remove some of these products. Rust inhibitors also require constant monitoring using a refractometer. It is critical that the correct concentration be present. It is recommend that shops get references of the product before installing it. Hirschmann Engineering USA makes a product call H2O Plus and can supply user references and application suggestions.
 
Settings:

When using an EDM with an anti-electrolysis generator, there are no special settings required to prevent oxidation and pitting. A shop basically uses the available technology and certain techniques to reduce oxidation.
 
These techniques are:

Set the water conductivity to 5 microS or less, which is typically recommended for carbide, PCD, titanium, and fine finishes (<10 micro inches). This will also help keep bluing to a minimum on older non-anti-electrolysis generators.

Check water pH. Acidic detergents used to clean parts and tank will have a dramatic effect on parts rusting and will reduce the life of the deionization bottles.
 
De-magnetizing parts is highly recommended. This includes carbide. If the application involves cutting parts in the gap, demagnetizing the blocks will aid in evacuating sludge produced in the kerf. This applies when the slug is the part being produced. To skim the part, it must be held using a tab and skimmed before cutting off.
 
Always keep the workpiece submerged. Workpiece exposure to air increases the rate of oxidation.
 
Use rust inhibitors.
 
Conduct frequent machine maintenance. Neglecting components such as power contacts and cabling will not create oxidation problems, but it will produce poor machining conditions and finishes.
 
Keep parts clean. If a workpiece is making poor contact on the clamping surface, arcing can occur between the two surfaces and produce a poor finish, which resembles pitting. Parts should always be clean and oxidation-free for any type of EDMing.
 
Use recommended micron level filters. Poor quality filters can create many issues when it comes to surface finishes. Water that is not filtered properly will diminish part surface integrity when skimming in the gap.  
 
Mix Workpiece Materials

With all the new and old types of alloys available, material incompatibility may cause surface issues. However, EDM field technicians have yet to document an instance where this situation has occurred.
 
New Machines

Most current wire EDMs are equipped with Anti-Electrolysis generators, some better then others. It basically comes down to how good the technology is and how fine of a surface finish the generator is capable of producing. A machine that is capable of producing a super fine finish (< 5 micro inches) can generate optimum surface integrity.  

One example is the GF AgieCharmilles CUT 1000 that can machine parts with zero corrosion. The CUT 1000 is available in an oil version. With this feature, there is absolutely no electrolysis, corrosion and virtually zero recast.
 

 
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