It’s a familiar situation – summer comes, once again hotter than the one before, and precision takes a nosedive. Daytime temperatures exceed 30°C and the nights at 25°C are still are far too warm to deliver dimensionally accurate components. What elements can be influenced and improved with reasonable effort? First we have windows; one kWh per m2 of glass can easily get into the production hall, which adds up to fully 10 kWh with 20 m2 of south-facing windows, the same as 1 kg of heating oil. The room air heated in this manner must be transported out and replaced with cooled outside air.
Relevant heat sources are found in the eroding room: The cooler for the dielectric fluid. Temperatures of 4–6,000°C develop at the electrode-work piece interface, which would quickly heat the dielectric fluid to high levels and cause the work piece in the bath to expand. The dielectric fluid therefore has to be cooled to a constant temperature of 25°C. An investment of three heating calories is needed to produce one cooling calorie. If the dielectric fluid cooler is in the room, it significantly contributes to room heating. The expansion of the EDM components is affected by 30°C during the day and 25°C at night. Repeat accuracy goes out the window. So much for precision.
Safety requirements also have to be considered in eroding. EDM operators are required to observe the safety requirements according to DIN EN ISO 28881: 2014-01, and therefore to comply with the relevant state of the art for capturing emissions in accordance with DGUV information 213-726. For the operator, this means complying with a guiding value of approx. 100 mg/m3. This is according to measurements taken in 2009-2011. The 43 individual measurements with a 95th percentile resulted in a guiding value of 100 mg/m3 for the atmospheric load. A need for extraction exists regardless to prevent the formation of an explosive atmosphere.
Upper and lower explosion limits (UEG and OEG) are provided in the safety data sheets for dielectric fluids. This knowledge is also considered in the DIN EN ISO 28881 standard. It calls for connection to a flue gas extraction system as the result of the underlying hazard analysis. The extraction duct has to be fitted with a flow meter (a sensor, for example) and a safety slider corresponding to the extinguishing equipment. Thus the operator is required to keep corresponding hazard assessments in written form on file with the comprehensible establishment of protective measures. Correctly dimensioned extraction systems are therefore indispensable to obtain fire insurance benefits in case of a fire.