Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

MECH339 Manufacturing Processes > Electrochemical Machining > Flashcards

Electrochemical Machining Flashcards

1
Q

What is ECM

A

Electrochemical Machining

  • Based on the chemical (anodic) dissolution of metal by electrolysis
  • known as the “reverse of electroplating)”
  • shaped tool(electrod) is brought close to an electrically conductive workpiece at a constant rate maintaining a gap while submerged in an electrolyte solution
  • tool and workpiece are connected to a dc supply and a high density current passes through the gap and the rapidly flowing electrolyte
  • electrochemical reaction deplates the metal from the anode(workpiece) and gets washed away by the electrolyte before plating on the cathode(tool) can take place
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

ECM process mechanism

A

-electrode is fed into the workpiece at a rate equal to the material removal rate
-feed rate is cnc controlled and vaires from 0.25mm/min to 20mm/min (control less critical than EDM as no tool wear)
maintaining a close gap of 0.05-0.75mm
-electrolyte pumped fast through the gap for a quick removal of metal particles avoiding their deposit onto the cathode; typically 1ltr/min or 15-50m/sec
-dc power of 10-25v kept low to minimise risk of arc forming across the gap
-high current of 40,000A giving the current density of 8-450A/cm^2 to achieve MRR of 1-4mm^3/A-min

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

ECM - MRR

A

-material removal rate
=ranges between 1-4mm^3/A-min

MRR=V/t
V=CIt

where
V=volume of metal removed (mm^3)
C=specific removal rate (based on atomic weight, valence, density of the material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

current flow and resitance of ECM process

A 
-I=E/R
where
I= Current
E= voltage
R= resistance

-R=(gr)/A
goes to
I=(EA)/(g*r)
where
g= gap between electrode and workpiece in mm
-r= resistivity of electrolyte in Ohm-mm
A=surface area between workpiece and tool in the working frontal gap (mm^2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

ECM- Feed rate

A

-removal of volume V over area and time (A*t) for a linear travel rate

V=(C*E*A*t)/(g*r) 
goes to
V/(A*t)=(C*E)/(g*r)=fr 
goes to
fr=(C*I)/A
where
fr=feed rate(mm/sec)
V=volume of metal removed (mm^3)
C=specific removal rate( based on atomic weight, valence, density of a material mm^3/A-sec)
A=frontal area of the electrode(mm^2)
t= time (sec

-feed rate is primarily a function of the current density

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

ECM- surface finish and accuracy

A
  • ranges from Ra 0.4-0.8micrometers depending on electrode and workpiece material and MRR
  • hard and soft materials can be machined with equal speed and precision(stainless steel, titanium, nickle alloy)
  • stress and burr-free surfaces
  • precision accuracy of 0.03mm on one dimensional cuts and 0.1mm on contours
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

properties of electrolyte solution for ECM

A

-function and properties
conductor- allow electric current to flow between the tool and the workpiece
-coolant- to keep temperature of tooling and workpiece constant as teh conductivity of the fluid depends on its temperature
-flushing agent- to carry off deplated material (microscopic particles) from the gap and remove hydrogen bubbles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Medium of electrolyte solution for ECM

A

sodium chloride solution, sodium nitrate with a water base (typically 10%)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

electrodes for ECM- materials

A
  • copper
  • brass-
  • stainless steel
  • bronze
  • titanium
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

desired properties for electrodes (ECM)

A
  • good strength not to deform by flow pressure from the electrolyte bath
  • minimal electrical resistance
  • high chemical resistance
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

tool wear for ECM

A

very little; only caused by flowing electrolyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

electrodes for ECM

A

-generally produced by traditional NC machining methods
-surface of the workpiece does not reproduce exactly the surface of the tool (overcut)
=for best accuracy on the outer surface of t he tool is insulated with thin silicon carbide or coating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Electrochemical grinding

A

-material is a combination of electrochemical decomposition and action of diamond abrasive particals contained in the grinding wheel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Pros of electrochemical grinding

A
  • high grinding ratio with dramatically reduced wheel wear(10x)
  • comparable MRR with normal grinding
  • no heat distortion or danger of burning
  • little mechanical force eliminating burrs or distortion
  • surface finish of Ra 0.2micrometers possible
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Cons of electrochemical grinding

A
  • high initial equipment costs
  • large power consumption, only recommended for hardened material or difficult to machining ones
  • only for electrical conductive material
  • corrosive environment
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

electrochemical grinding - applications

A
  • Sharpening of sintered carbide tools or high strength alloys
  • surgical needles, thin wall tubes
  • fragile parts
17
Q

electrochemical honing

A
  • MRR several times higher than traditional honing especially on hard material
  • up to 5x faster than traditional honing
  • higher accuracy as temperatures are cooler as lower honing pressure resulting in lower tool wear (10x less)
  • very costly
18
Q

Pulsed electrochemical machining (PECM)

A
  • pulsed rather than direct current to eliminate high electrolyte flow rates
  • very high current densities (1A/mm^2)
19
Q

Electrolytic in-process dressing (ELID) mirror-surface grinding

A
  • grind mirror-quality surfaces(Ra 2-10micrometers), no requirement for secondary operation such as lapping
  • use of conventional super-abrasive, metal-bonding grinding wheel and conventional coolant
  • electrolytic action is between a negative copper electrode and the grinding wheel as an anode
  • for optical lenses, mirrors or slicing and surface grind silicon wafers
20
Q

Electrchemical deburring

A
  • removal of burrs or to round sharp corners by anodic dissolution
  • best results when used with a shaped cathode; partially insulated
21
Q

shaped tube electrolytic machining (STEM)

A
  • electrochemical drilling of small diameter, deep holes in a super-alloy materials (diameter of 0.5mm, ratio 300:1)
  • drilling of round or shaped holes using tube (usually titanium) as cathode
  • acid is used as electrolyte and fed through a tube to keep the metal in solution
  • multiple holes can be drilled simulatinuously
  • used for air cooling and weight reduction holes in jet engine blades
  • drilling feeds 2-4mm/min
22
Q

ECM applications

A
  • hard or difficult to machine metal
  • difficult geometry or impossible to manufacture with conventional techniques
  • die sinking, forging dies, and other shaping tools with irregular contours
  • multiple hole drilling
  • deburring
  • micromachining
23
Q

pros of ECM

A
  • any electrically conducting material regardless of hardness can be machined; workpiece can be hardened
  • complex shapes and contours can be machined in one process step with excellent surface finish
  • no distortion as no thermal or mechanical stress
  • little surface damage to the workpiece
  • no burrs
  • little tool wear (only from flowing electrolyte)
24
Q

Cons of ECM (part 1)

A
  • conductive materials (tooling and workpiece) can be machined
  • not suited for sharp profiles (sharp square corners; internal and external)
  • large forces on electrode and workpiece due to small gap and high pressure flow of electrolyte
  • workpiece must be cleaned and oiled directly after machining to avoid corrosion
  • environmental impact with the disposal of electrolytic sludge
25
Q

Cons of ECM (part 2)

A

-expensive equipment and tooling cost
=stainless steel and other corrosion resistant components
=tool making more complex due to insulation for correct conductive paths;make provision for taper (overcut)
=complex plumbing and filtration system including electrolyte regeneration
=safe removal of hydrogen gas required

  • significant power consumption
  • high maintainance to keep equipment clean from electrolyte residue to avoid corrosion

MECH339 Manufacturing Processes (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions