Ch. 28
Advantages of EDM
-Applicable to all materials that are fairly good electrical conductors -Hardness, toughness, or brittleness of material imposes no limitations -Fragile and delicate parts, complex geometries
Abrasive Waterjet Cutting (AWC)
-Can cut hard materials -Abrasives added to a Waterjet to improve efficiency
Abrasive Jet Cutting (AJC)
-Can cut hard materials -Abrasives mixed in high velocity air stream at 1,000 ft/s
Ultrasonic
-Can cut hard materials (great for glass) -Abrasives mixed in a slurry, ultrasonic transducers provide the mechanical agitation to remove the material
Etch Factor (E)
-Describes the undercutting of the mask layer -E=undercut(u)/depth(d)
Anisotropy (A)
-Directionality of the cut -A=1/E=d/u
Disadvantages of ECM (5)
-Initial tooling can be expensive -Environmentally harmful by-products -Current densities tend to concentrate at sharp edges or features (causing extra material removal near corners) -Control of electrolyte flow can be difficult -Parts may have lower fatigue resistance
Functions of Dielectric Fluid
-Local spark conductor -Coolant -Global electrical insulation -Flushes away debris
Waterjet Cutting (WJC)
-Only cuts soft materials like leather, paper, etc. -Water at 60,000 psi and 3,000 ft/s erode the material -Does not rely on abrasive particles
Disadvantages of EDM
-Slow compared to conventional machining -Produces a hard recast surface -Surface may contain fine cracks caused by thermal stress -Fumes can be toxic -Tool wear
Thermal Deburring
-Thermochemical process -Used to remove burrs by exposing workpiece to hot corrosive gases for a short period of time
Plasma Arc Cutting (PAC)
-Uses a superheated stream of electrically ionized gases (plasma) to melt and remove material -Can be used on almost any conductive material and on exotic materials at high rates
Advantages of ECM (4)
-Well suited for machining of complex 2D shapes -Delicate parts may be made (non contact) -Poorly machinable materials may be processed (including very strong, brittle, or tough materials) -Little to no tool wear
Wire EDM -----> ?????
2D
Sinker EDM ------> ?????
3D
Advantages of NTM (5)
Capable of making complex, delicate, and very small features Tight tolerances Often very good surface finish Little to no burring or residual stresses Materials with high strength or hardness can be machined
Common abrasive particle
Ceramics particles
Four basic groups of material removal using NTM processes
Chemical Etlectrochemical Thermal Mechanical
Methods to make a masking layer
Cut-and-peel Scribe-and-peel Screen Printing Photopatterning
In EDM, what fills the gap?
Dielectric fluid which becomes locally ionized
Most widely used tool electrode
Graphite
How do defects in etching occur?
If baths are not agitate properly
Advantages of CMP
Induces no stress or cold working in the workpiece Can be applied to almost any material Large areas can be etched simultaneously Virtually unlimited shapes Possible to make thin sections and very small fractures
Material Removal Rate Equation (MRR)
MRR=(Constant[C]*Current[I])/(Melting Temp.[Tm])
Chemical Machining Process (CMP)
Material is removed from a workpiece by exposing it to a chemical etchant
Nontraditional Machining (NTM) Processes
Material removal using something other than mechanical cutting/scraping
What materials allow Thermal Deburring to be most effective?
Materials of low thermal conductivity
Most important aspect of electrode (tool) material
Melting temperature
Convential End Milling vs. NTM
NTM typically have lower feed rate and require more power consumption NTM are usually slower and more expensive The feed rate in NTM is often independent of the material being processed Some NTM processes can machine the entire surface at once
Electrochemical Machining Process (ECM)
Removes material by anodic dissolution with a rapidly flowing electrolyte Chemical reaction dissolves workpiece but reaction only occurs locally in presence of electricity
Electrical Discharge Machining (EDM)
Removes metal by discharging electric current from a pulsating DC power supply across a thin interelectrode gap
Disadvantages of CMP
Requires handling of dangerous chemicals Disposal of potentially harmful byproducts Material removal rate is slow
Limitations in traditional machining processes:
Residual stresses and/or unwanted distortion of final part Burrs Delicate or complex geometries may be difficult or impossible High strength, high hardness materials are difficult to machine
Ion Beam Machining (IBM) or Focused Ion Beam (FIB)
Similar to EBM, uses a focused beam of charged ions (usually gallium) to remove material on the surface of a workpiece
In EDM, the electrodes are the ________
Tool and workpiece
When is EDM often used?
Tools and dies
True or False: Compared to other NTM processes, etch rates are slow
True
Four Major Forms of Free Abrasive Machining
Ultrasonic Waterjet Cutting Abrasive Waterjet Cutting Abrasive Jet Cutting
How CMP create patterns
Use gel milling thick gel is applied to workpieceonly in areas we want to etch Use a masking material
Electron Beam Machining (EBM)
Uses a beam of high-energy electrons focused on the workpiece to melt and vaporize a metal
Electrochemical Polishing
Uses a slower feed rate to produce a fine surface finish
Electrochemical Grinding
Uses an electrically-charged grinding wheel at low voltage; combination of electrochemical and mechanical material removal
Laser-Beam Machining (LBM)
Uses an intensely focused coherent stream of light to vaporize or chemically ablate materials
Typical expectations of NTM processes:
Very precise Apply very little to no force to the workpiece
Width of Final Geometry
W=(width in mask opening[w])+2*undercut[u]
Electrochemical Hole Machining
When this method is used to drill small holes; possible to achieve very high aspect ratios with this method
Friability
ability to break down into new, smaller particles
In ECM, the workpiece is the _____
anode
In ECM, the tool is the ______
cathode
the anode and cathode are separated by _______
electrolyte, which helps sweep away by-products of reaction
CMP is the common production method in _______
electronic circuit boards
Chemical reaction occurs everywhere the ______ contacts the workpiece
etchant
Masking material
selected areas are covered and the remaining surfaces are exposed to etchant