Electro-chemical grinding technique has rotation speed control, constant feed rates, and contour control. Hypersonic engine parts of nickel alloys can be almost 100% machined, keeping tool pressure at virtual zero. Technique eliminates galling and permits constant surface finish and burr-free interrupted cutting

Feagans, P. L.

English

NASA Technical Reports Server

NASA TECH BRIEF 
Langley Research Center El S December 1972	 B72-10744 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Electro-Chemical Grinding 
Nickel alloys, used extensively in hypersonic engines, 
are difficult to machine by conventional means. Tool 
pressures are very high, and tool bounce in interrupted 
cuts is excessive. Conventional grinding results in load-
ing the wheel, or breakdown, which makes it difficult 
to hold size, contour, and finish. These conditions make 
it virtually impossible to machine certain engine parts 
such as a conical one that has to be held by a flange 
at the base and machined for several feet down a con-
tour to a sharp end. 
This application of electro-chemical grinding is unique 
in that the control of rotation speed (to maintain con-
stant surface speed), constant feed rates, and contour 
control are so exacting that the parts are almost 100-
percent electro-chemically machined, thus keeping tool 
pressure at virtual zero. Precise control of the surface 
and feed speeds essentially eliminates mechanical grind-
ing, thereby maintaining grinding wheel size. It also 
allows precise control of contour. 
In electro-chemical grinding (ECG) there is essentially 
no danger of galling. ECG permits constant surface 
finish and allows burr free interrupted cutting. Holes, 
slots, and eccentricity of the part are not the problems 
that they are with conventional machining. 
In this application of electro-chemical grinding the 
work piece is mounted on the lathe spindle. The 
aluminum-oxide copper-bond grinding wheel is mounted 
on the compound of the lathe. A very close gap distance 
(0.001 to 0.002 in, or 0.0025 to 0.005 cm) is main-
tained between the work piece and the grinding wheel. 
The grinding wheel is capable of carrying high current 
and is insulated from the lathe bed. It is connected to 
negative direct current (-dc), and the work piece is
connected to positive direct current (+dc). The wheel 
bonding material breaks down at a rate that keeps the 
projection of the abrasive material at about 0.005 cm. 
This gap is filled with high-velocity salt water. The flow 
of the salt water carries away the removed metal and 
dissipates the heat generated by the high current densi
-
ties. The exact rate of metal removal and the type of 
electrolyte salts to be used must be matched to the 
material being machined. 
A hydraulic tracer is mounted on a cross-slide and 
follows a template which controls part contour. A 
reniote speed control also follows a template on the 
cross-slide and maintains the work piece speed of 
rotation so that a constant surface speed is presented 
to the grinding wheel. The lead screw on the lathe is 
used to obtain a constant feed rate in thousandths per 
revolution. 
The grinding wheel, rotating at 5500 SFM, acts as 
an electrolyte pump and maintains a smooth flow between 
it and the work piece. High current densities remove 
94 to 98 percent of the metal as the wheel is fed over 
the work piece. Overall current values are held at reason-
able values, as grinding wheel contact area is com-
paratively small. 
Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23365 
Reference: B72-10744 
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
S
https://ntrs.nasa.gov/search.jsp?R=19720000743 2020-03-17T03:43:59+00:00Z
Patent status: 
Inquiries concerning rights for the commercial use of 
this invention should be addressed to: 
Patent Counsel 
Langley Research Center 
Mail Stop 456 
Hampton, Virginia 23365 
Source: P. L. Feagans of 
AiResearch Manufacturing Co. 
under contract to
Langley Research Center
(LAR-10801)
S 
S 
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B72-10744	 Category 08


Electro-chemical grinding

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