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==Process==
==Process==
The electrochemical grinding process combines traditional electrochemical machining and grinding processes to remove material from a workpiece. A grinding wheel is used as a cutting tool and a cathode and the workpiece is an anode. During the process, electrolytic fluid, typically sodium nitrate <ref name=":0">{{cite book|title = Manufacturing Processes|last2 = Schmid|first2 = Steven|date = 2008|publisher = Prentice Hall|isbn = 9780132272711|edition = 5|pages = 558-561|last1 = Kalpakjian|first1 = Serope}}</ref>, is pumped into the space between the workpiece and the grinding wheel. Other electrolytes used include sodium hydroxide, sodium carbonate, and sodium chlorate.<ref name=":1" /> This electrolytic fluid will cause electrochemical reactions to occur at the workpiece surface which oxidize the surface, thereby removing material. As a consequence of the oxidation which occurs, layers of oxide films will form on the workpiece surface, and these need to be removed by the grinding wheel. Abrasive materials, either diamond or aluminum oxide<ref name=":0" /> , are bonded to the grinding wheel which allows the wheel to remove the oxide layers on the workpiece surface by abrasive action. Appropriate materials used for electrolyte fluid and the grinding wheel abrasives are summarized in the table below.
The wheels are metal disks with abrasive particles embedded. [[Copper]],<ref name="Valenti, Making the Cut."/> brass, and nickel are the most commonly used materials; [[Aluminium oxide|aluminum oxide]] is typically used as an abrasive when grinding steel. A thin layer of diamond particles will be used when grinding [[carbide]]s or steels harder than 65 Rc.
{| class="wikitable"
!Component
!Material
|-
|Grinding Wheel Abrasives
|Diamond, Aluminum Oxide<ref name=":0" />
|-
|Electrolytic Fluid
|Sodium Nitrate, Sodium Hydroxide,
Sodium Carbonate, Sodium Chlorate<ref name=":0" /><ref name=":1" />
|}
Most material removal is by the electrochemical reactions which occur at the workpiece surface. Five percent or less of the material removal is carried out by the abrasive action of the grinding wheel.<ref name=":0" /> The fact that most material is not removed by abrasive action helps increase the life of the grinding wheel, that is, the tool will take a long time to wear down. The electrolytic fluid serves another useful purpose - it flushes out leftover material in between the grinding wheel and work piece. The Abrasive particles bonded to the grinding wheel will help to electrically insulate the space between the grinding wheel and workpiece. <ref name=":1">{{Cite journal|last = Phillips|first = Robert|date = 1989|title = Electrochemical Grinding|url = https://app.knovel.com/web/view/swf/show.v/rcid:kpASMHVM05/cid:kt007WABB4/viewerType:pdf/root_slug:asm-handbook-volume-16?cid=kt007WABB4&page=1&q=electrochemical%20grinding&b-q=electrochemical%20grinding&sort_on=default&b-group-by=true&b-search-type=tech-reference&b-sort-on=default&scrollto=Electrochemical%20Grinding%20Rober|journal = ASM Handbook|doi =|pmid =|access-date = 15 February 2016}}</ref> An equation giving the material removal rate for an electrochemical grinding process is provided in <ref name=":0" /> and is stated here as:

MRR = GI/ρF<ref name=":0" />

where ρ is the workpiece density, G is the total mass of the workpiece, I is the current supplied, MRR is the material removal rate, and F is Faraday's constant.<ref name=":0" />

Some of the main factors which govern the performance of an electrochemical grinding process include current supplied, rotation speed of the grinding wheel, the workpiece feed rate, the type of electrolyte used, electrolyte feed rate, and the workpiece's chemical properties.<ref name=":2">{{Cite journal|last = Jain|first = V.K|date = 2003|title = Electrochemical Hybrid Processes|url = https://app.knovel.com/web/view/swf/show.v/rcid:kpASMHVAC8/cid:kt007P0YAJ/viewerType:pdf/root_slug:asm-handbook-volume-13a?cid=kt007P0YAJ&page=1&q=electrochemical%20grinding&b-q=electrochemical%20grinding&sort_on=default&b-group-by=true&b-search-type=tech-reference&b-sort-on=default&scrollto=Electrochemical%20Grinding%0AAs%20in|journal = ASM International|doi =|pmid =|access-date = 15 February 2016}}</ref><ref name=":1" /> By changing these parameters, one can alter the material removal rate. Increasing the supplied current, rotation speed of the wheel, electrolyte feed rate, or the workpiece feed rate will lead to an increase in material removal rate, while decreasing these properties will do the opposite. If the workpiece is more reactive to the electrolyte used, then the material removal rate will increase. The grinding wheel is usually rotated with a surface speed of 1200-2000 m/min<ref name=":0" /> and supplied currents are around 1000A<ref name=":1" />.

The accuracy of parts made by electrochemical grinding is strongly dictated by the chemical properties of the workpiece and electrolytic fluid used. If the workpiece is very reactive to the electrolyte, and if too much electrolyte is pumped into the space between the grinding wheel and workpiece, it may be difficult to control the material removal which can lead to loss of accuracy<ref name=":1" />. Also, accuracy may be reduced if the workpiece feed rate is too high.


An electrolytic spindle with carbon brushes, acting as a commutator, holds 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.<ref name="Valenti, Making the Cut."/>
An electrolytic spindle with carbon brushes, acting as a commutator, holds 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.<ref name="Valenti, Making the Cut."/>

Revision as of 19:10, 4 March 2016

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 is similar to electrochemical machining but uses a wheel instead of a tool shaped like the contour of the workpiece.

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 electrochemical grinding process combines traditional electrochemical machining and grinding processes to remove material from a workpiece. A grinding wheel is used as a cutting tool and a cathode and the workpiece is an anode. During the process, electrolytic fluid, typically sodium nitrate [5], is pumped into the space between the workpiece and the grinding wheel. Other electrolytes used include sodium hydroxide, sodium carbonate, and sodium chlorate.[6] This electrolytic fluid will cause electrochemical reactions to occur at the workpiece surface which oxidize the surface, thereby removing material. As a consequence of the oxidation which occurs, layers of oxide films will form on the workpiece surface, and these need to be removed by the grinding wheel. Abrasive materials, either diamond or aluminum oxide[5] , are bonded to the grinding wheel which allows the wheel to remove the oxide layers on the workpiece surface by abrasive action. Appropriate materials used for electrolyte fluid and the grinding wheel abrasives are summarized in the table below.

Component Material
Grinding Wheel Abrasives Diamond, Aluminum Oxide[5]
Electrolytic Fluid Sodium Nitrate, Sodium Hydroxide,

Sodium Carbonate, Sodium Chlorate[5][6]

Most material removal is by the electrochemical reactions which occur at the workpiece surface. Five percent or less of the material removal is carried out by the abrasive action of the grinding wheel.[5] The fact that most material is not removed by abrasive action helps increase the life of the grinding wheel, that is, the tool will take a long time to wear down. The electrolytic fluid serves another useful purpose - it flushes out leftover material in between the grinding wheel and work piece. The Abrasive particles bonded to the grinding wheel will help to electrically insulate the space between the grinding wheel and workpiece. [6] An equation giving the material removal rate for an electrochemical grinding process is provided in [5] and is stated here as:

MRR = GI/ρF[5]

where ρ is the workpiece density, G is the total mass of the workpiece, I is the current supplied, MRR is the material removal rate, and F is Faraday's constant.[5]

Some of the main factors which govern the performance of an electrochemical grinding process include current supplied, rotation speed of the grinding wheel, the workpiece feed rate, the type of electrolyte used, electrolyte feed rate, and the workpiece's chemical properties.[7][6] By changing these parameters, one can alter the material removal rate. Increasing the supplied current, rotation speed of the wheel, electrolyte feed rate, or the workpiece feed rate will lead to an increase in material removal rate, while decreasing these properties will do the opposite. If the workpiece is more reactive to the electrolyte used, then the material removal rate will increase. The grinding wheel is usually rotated with a surface speed of 1200-2000 m/min[5] and supplied currents are around 1000A[6].

The accuracy of parts made by electrochemical grinding is strongly dictated by the chemical properties of the workpiece and electrolytic fluid used. If the workpiece is very reactive to the electrolyte, and if too much electrolyte is pumped into the space between the grinding wheel and workpiece, it may be difficult to control the material removal which can lead to loss of accuracy[6]. Also, accuracy may be reduced if the workpiece feed rate is too high.

An electrolytic spindle with carbon brushes, acting as a commutator, holds 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

Disadvantages

Electrochemical grinding loses accuracy when grinding inside corners, due to the effects of the electric field.[8]

References

  1. ^ a b Nontraditional manufacturing processes: Volume 19 of Manufacturing engineering and materials processing, CRC Press, 1987, pp. 153–160, ISBN 0-8247-7352-7 {{citation}}: |first= missing |last= (help); Missing pipe in: |first= (help)
  2. ^ Derek Pletcher, Frank Walsh (1990), Industrial electrochemistry, Springer, pp. 464–466, ISBN 0-412-30410-4
  3. ^ 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
  4. ^ a b c Valenti, "Making the Cut."
  5. ^ a b c d e f g h i Kalpakjian, Serope; Schmid, Steven (2008). Manufacturing Processes (5 ed.). Prentice Hall. pp. 558–561. ISBN 9780132272711.
  6. ^ a b c d e f Phillips, Robert (1989). "Electrochemical Grinding". ASM Handbook. Retrieved 15 February 2016.
  7. ^ Jain, V.K (2003). "Electrochemical Hybrid Processes". ASM International. Retrieved 15 February 2016.
  8. ^ a b c McGeough, J. A. (1988), Advanced methods of machining, Springer, p. 82, ISBN 0-412-31970-5
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