Electrochemical grinding

Electrochemical grinding is a process that removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged workpiece.^[1] Materials removed from the workpiece stay in the electrolyte fluid. Electrochemical grinding and electrochemical machining are similar but a wheel is used instead of a tool shaped like the contour of the workpiece.

1 Process characteristics
2 Process
3 Tolerance
4 Uses
5 Disadvantages
6 References

Process characteristics

The wheels and workpiece are electrically conductive.
Wheels used last for many grindings - typically 90% of the metal is removed by electrolysis and 10% from the abrasive grinding wheel.^[2]
Capable of producing smooth edges without the burrs caused by mechanical grinding.^[3]
Does not produce appreciable heat that would distort workpiece.^[4]
Decomposes the workpiece and deposits them into the electrolyte solution. The most common electrolytes are sodium chloride and sodium nitrate at concentrations of 2 lbs per gallon.^[1]

Process

The wheels are metal disks embedded with abrasive particles. Copper,^[4] brass, and nickel are the most commonly used materials; aluminum oxide is typically used as an abrasive when grinding steel. A thin layer of diamond particles will be used when grinding carbides or steels harder than Rockwell C65.

An electrolytic spindle with carbon brushes, acting as a commutator, hold the wheel. The spindle receives a negative charge from the DC power supply, which gives the workpiece a positive charge. The electrolytic fluid is applied where the work contacts the tool by a nozzle similar to that which supplies coolant in conventional grinding. The fluid works with the wheel to form electrochemical cells that oxidize the surface of the workpiece. As the wheel carries away the oxide, fresh metal is exposed. Removing the oxidized fluid may only require a pressure of 20 psi or less, causing much less distortion than mechanical grinding. The wheel is subject to little wear, reducing the need for truing and dressing.^[4]

Tolerance

This kind of grinding is mostly used because it can shape very hard metals and also because it is a chemical reducing process, the wheel lasts a longer time than normal grinding wheel can.
This type of grinding has different types of wheels so it can shape metals to whatever they need to be shaped to.
Produces a smoother, burr-free surface and causes less surface stress than other grinding methods.

Uses

Production of tungsten carbide cutting tools.^[5]
Burr-free sharpening of hypodermic needles^[4]
Grinding of superalloy turbine blades
Form grinding of aerospace honeycomb metals
Removal of fatigue cracks from underwater steel structures. In this case, seawater itself acts as the electrolyte. Diamond particles in the grinding wheel remove any non-conducting organic matter, such as algae, before electrochemical grinding begins.^[5]

Disadvantages

Electrochemical grinding loses accuracy when grinding inside corners, due to the effects of the electric field.^[5]

References

^ ^a ^b Nontraditional manufacturing processes: Volume 19 of Manufacturing engineering and materials processing, CRC Press, 1987, pp. 153–160, ISBN 0824773527, http://books.google.com/books?id=xdmNVSio8jUC&pg=PA153
^ Derek Pletcher, Frank Walsh (1990), Industrial electrochemistry, Springer, pp. 464–466, ISBN 0412304104, http://books.google.com/books?id=E_u9ARrm37oC&pg=PA465
^ Valenti, Michael, "Making the Cut," Mechanical Engineering, American Society of Mechanical Engineers, 2001. http://www.memagazine.org/backissues/membersonly/nov01/features/makcut/makcut.html, accessed 2/23/2010
^ ^a ^b ^c ^d Valenti, "Making the Cut."
^ ^a ^b ^c McGeough, J. A. (1988), Advanced methods of machining, Springer, pp. 82, ISBN 0412319705, http://books.google.com/books?id=f7Uj1uTwkosC&pg=PA82