NEW TECHNOLOGIES | ARTICLE
PRECISION Electrolytic Machining
DON RISKO, PEM TECHNOLOGIES LLC
Theory The Precision Electrolytic Machining (PEM) process is based on subtracting or removing material from the surface of a conductive metal by electrolytic dissolution. That machining process is based on Faraday’s Law of electrolytic action which is the same principle used in electroplating and electropolishing. When an electric field is established between two metal objects by a direct current voltage and the metal surfaces are separated by a distance filled with an electrolyte, electrons will flow between them while ions are released from the positive surface.
PEM Process A preformed metal electrode acts as a machining tool that never touches the surface of the workpiece and never draws a spark. A D.C. pulse from the electrode is used to ionize and release surface atoms from the workpiece in the presence of an electrolyte solution. A precision reciprocating action of the electrode positions the electrode within 10 microns of the surface (termed the ‘gap’), then retracts up to 400 microns. Typical reciprocation rate is 30 to 70 times per second while electrolyte is continuously pumped between the tool and workpiece and flushes the ions removed from the surface during the retracted time. The typical electrolyte solution is a mixture of sodium nitrate and deionized water. The D.C. pulse is programmed to coincide with the electrode proximity to the workpiece surface, hence allowing high-current pulses of short duration that precisely remove surface atoms without boiling the electrolyte in the gap.
Typical machining parameters for the PEM process are: << Figure 1: The PEM400 machine. >>
Feed rate: 0.1— 0.8 mm/min Current density: 100 A/ cm2 Machining voltage: 1—20 Volts Tool oscillation: 0—90 Hz Electrolyte (typical): 6% sodium nitrate Electrolyte flow: 0.1—40 L/min Electrolyte temperature: 20—30 ºC Electrolyte pH: 6.5—8
40 | commercial micro manufacturing international Vol 6 No.6
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