Table of Contents

Electrochemical Honing ( ECH )

Introduction to Electrochemical Honing :

ECH is a process in which the metal removal capabilities of ECM are combined with the accuracy capabilities of honing. The process consists of a rotating and reciprocating tool inside a cylindrical component.
Material is removed through anodic dissolution and mechanical abrasion – 8% or more, of the material removal, occurs through electrolytic action
As with conventional ECM, the workpiece is the anode and a stainless steel tool is the cathode.

Tool consists of a hollow stainless steel body that has expandable, nonconductive honing stones protruding from at least three locations around the circumference
The honing stones are identical with those used in conventional honing operations, except that they must resist the corrosiveness of the electrolyte
The honing stones are mounted on the tool body with a spring-loaded mechanism so that each of the stones exerts equal pressure against the workpiece
The length of the stones is selected to be approximately one-half of the length of the bore being processed.

At the beginning of the ECH cycle, the stones protrude only 0.075-0.127mm from the stainless steel body, establishing the gap through which the electrolyte flows
The electrolyte enters the tool body via a sliding inlet sleeve from which it exits into the tool-workpiece gap through small holes in the tool body
After passing through the gap, the electrolyte flows from the workpiece through the gap at the top and bottom of the bore
The mechanical action of the tool is the same as with conventional honing; the tool is rotated and reciprocated so that the stones abrade the entire length of the bore
Electrolytes used in ECH are essentially the same as those used in ECM, although the control of pH, composition and sludge is less critical because the abrasive action of the stones tends to correct any resulting surface irregularities
As in ECM, the electrolytes are recirculated and reused after passing through appropriate filtration, and the most commonly used electrolytes are sodium chloride and sodium nitrate.

Machines are available that deliver up to 6000 amp
Current density at the workpiece can range from 12 to 47amp/cm 2
Working voltages are 6-30 VDC
The electrolyte is delivered to the work area at pressures of 0.5-1 MPa
ECH can remove materials at rates up to 100% faster than conventional honing, the gain being more pronounced as the material hardness increases
Machine capacities are currently able to accommodate bore lengths up to 600 mm and bore diameters from 9.5 to 150 mm.

Increased MRR particularly on hard materials
Since most of the material is removed electrochemically, honing stone life is greatly extended
Burr-free operation
Unlike conventional honing, no micro-scratches are left on the work surface
Less pressure required between stones and work
Reduced noise and distortion when honing thin-walled tubes
Cooler action leading to increased accuracy with less material damage
As with all ECM-based processes, ECH imparts no residual stresses in the workpiece
Capable of achieving surface finishes of 0.05μ and dimensional accuracies of ±0.012mm
By turning off the power to the tool before the end of the honing cycle, the stones can be used in a conventional manner to achieve tolerances of ±0.002mm and to impart a compressive residual stress on the work surface.

Limitations of electrochemical honing :

Bajidbi says:
September 14, 2020 at 9:53 am
Very nice and very easy for understanding. It helps me alot in preparing for my sem exam. Thank you so much.