Published 5/29/2004

Low-Force, Low-Heat Grinding Of Tough Materials

Molecular Decomposition Process (MDP), a new grinding technique rooted in ECG, employs closed loop process control and improved electrolyte filtering capability to mitigate these issues.

Derek Korn

Editor-in-Chief, Production Machining magazine

MDP is used for grinding medical parts, such as syringe tubes, because it delivers a burr-free edge and does not cause distortion.

MDP grinding generates a low amount of heat to allow finishing of rubber-coated parts without burning the coating.

Based on electrochemical grinding principles, MDP softens the surface of hard, conductive materials by flowing electrical current from grinding wheel to workpiece through an electrolyte.

Electrochemical grinding (ECG) uses electrical current to soften the surface of very hard conductive materials for easier grinding. While some shops use ECG for hogging tough alloys or grinding thin parts without burrs, burns or distortion, the process does have its drawbacks. It can be hard to control, and it requires frequent disposal of toxic electrolyte.

Molecular Decomposition Process (MDP), a new grinding technique rooted in ECG, employs closed loop process control and improved electrolyte filtering capability to mitigate these issues. MDP grinding systems are available from Chevalier Machinery, Inc.

Similarly to ECG, MDP flows electrical current from a negatively charged abrasive wheel to a positively charged conductive workpiece through an electrolyte. The resulting electrochemical oxidation produces a soft, hydroxide film on the workpiece surface that is “scrubbed away” by the abrasive wheel at a much lower force than a traditional grinding operation.

Because there is minimum grinding pressure between wheel and workpiece, the process generates very little heat. This eliminates the risk of warping or damaging thin or delicate parts. It also allows grinding of rubber-coated parts without burning the coating.

Closed loop process control monitors electrolyte properties, spindle performance, wheel position, power output and material decomposition rate. The control continuously modulates current per these parameters so that the optimal current level is applied to the workpiece for precise material removal.

MDP’s filtration system removes chips and debris from the electrolyte to help maintain fluid consistency for improved process control and energy efficiency.

The filtration system also reduces the frequency of electrolyte disposal. In liquid form, used electrolyte is a toxic material that is costly to dispose. MDP removes grinding debris from the electrolyte and compresses it into a non-toxic, semi-dry cake, which can be removed and disposed of. This enables the liquid electrolyte to last months longer than is typical with ECG machines before needing to be replaced.