When TCO principals are applied to major elements associated with the operation of the sinker EDM equipment, such as graphite electrode materials, the value proposition and productivity of these elements start to impact profitability of owning and operating the equipment.

Using benchmark data from equipment and graphite vendors, an audit of the EDM process helps identify areas of potential savings by comparing actual costs against accepted benchmarks. Using the TCO model to audit the process may show that additional capacity can be gained from the existing equipment and the EDM hours can be reduced, thus increasing productivity. Once opportunities for improvements are identified, the TCO process is then used to identify the alternative with the lowest total cost, or best value, based on the needs of the company as identified in their business plan.

Just like equipment manufacturers, graphite manufacturers can supply models and benchmarking data to aid in the TCO analysis. The performance of the electrode is largely influenced by the grade of graphite selected. An electrode material should be selected on the ability to achieve a specific surface finish, reproduce critical detail or attain sufficient metal removal rates. Selecting a graphite material without considering the properties of the individual grade can result in poor EDM performance. Using the best graphite for the job can reduce the number of electrodes due to improved wear and reduced polishing because the desired surface finish was reached quickly.

Some graphite manufacturers publish charts or graphs that show metal removal rates, electrode wear and surface finish for specific grades under a variety of operating parameters. This information can be used as a benchmark when comparing various grades of graphite. Another tool to use when comparing graphite is photomicrographs of the microstructure of the graphite. Because the sinker EDM process is designed to produce a mirror image of the electrode shape in the work metal, the quality of the graphite is an important part of the process. Materials that have uniform structure and small grain typically are capable of reproducing a mirror image of the electrode detail in the metal cavity with fewer electrodes. Since the surface finish is also a mirror image of the microstructure of the graphite, large grain size materials with non-uniform structures typically produce finishes that require polishing.
The TCO model looks at the impact that the graphite material has on the EDM-related operations in the shop from electrode fabrication through the mold polishing operation. The goal is to identify productivity increases to reduce production costs. If the graphite grade is the limiting factor in the operation, this factor will continue to affect the operation when new equipment is purchased.

Often a different graphite grade will show enough electrode wear improvement that fewer electrodes need to be fabricated or redressed, thus reducing both consumption of graphite, milling time and tooling. Efficient EDMing with a graphite grade capable of achieving a desired surface finish can minimize polishing time. Adaptive controls respond to conditions in the gap such as excessive debris from electrode wear (graphite grains), reducing the efficiency of the cut.

It is important to use actual conditions rather than an estimate based on short test cuts. Although test cuts are fine for benchmarking or estimating performance, they don’t reveal the true cost of the graphite in EDM time and price of the material when wear and number of electrodes are considered. Comparing two grades of graphite under the actual shop environment shows the impact that graphite performance has on the job.