1. Grinding, Electric discharge machining
Grinding, EDM
Grinding, Electric discharge machining
Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University 1

2. Contents Abrasive and mechanics Grinding
EDM (Electrical discharge machining)
Water Jet Cutting

3. Grinding (연삭)
In grinding, an abrasive material rubs against the metal part and removes a small amount of material.
Reasons for grinding are: The material is too hard to be machined. Tolerance is less than ±2.5 μm.
Grinding is a finishing process used to improve surface finish and the tolerance on flat and cylindrical surfaces.
In grinding, an abrasive material rubs against the metal part and removes a small amount of material.
Reasons for grinding are: The material is too hard to be machined. Tolerance is less than ± mm.
How to grind (9 min) :
©김태용, GNU

4. Abrasives (연삭입자)
Abrasives are harder than conventional cutting-tool materials.
Aluminium oxide, Al2O3
Silicon Carbide, SiC
CBN (Cubic Boron Nitride)
PCD (Poly crystal diamond)
Grit number (입도) indicates the size which is a the function of a sieve(체) size. (10: very rough, 100: fine, 500 very fine) Surface area / 1g
Mesh(체) No. wire # / inch

5. Grinding wheel (연삭 숫돌)
Abrasive grains are held together by a bonding material to achieve a high material removal rate.
Bond types (결합제) : ceramic bond, plastic based bond, rubber, metal bonds
Cheil grinding wheel (8min):

6. Mechanics of Grinding (연삭이론)
Cutting tool is an individual irregular abrasive grain
The average rake angle of the grains is highly negative
Cutting speeds of grinding wheels are very high
Power = Specific energy x MRR (material removal rate) ф
Chip
Workpiece
Grain v α
Material
Specific energy (GPa, J/mm3)
Aluminum
7~27
Cat iron
12-60
Low carbon steel
14-68
Tool steel
18-82
Cutting tool is an individual abrasive grain.
an individual grain has an irregular geometry
the average rake angle of the grains is highly negative
cutting speeds of grinding wheels are very high
Cutting power and energy
Power = Specific energy x MRR (material removal rate)
Specific energy used in producing a grinding chip has 3 components: Chip + Plowing + Sliding
(10 X machining)

7. Temperature Most of the cutting power transfers into heat.
Temperature rise affects the surface properties and causes residual stress on the workpiece.
Use fluid to prevent excessive temperature rise and to improve the surface finish and dimensional accuracy.

8. Grinding Wheel Wear (연삭숫돌마멸)
Attritious wear(소모마멸): caused by interaction of grain and workpiece
Grain fracture(입자파괴): caused by excessive attritious wear, Friability is the ability of an abrasive grain to fracture into smaller pieces.
Bond fracture(결합재파괴): if bond is too strong, dull grains cannot be dislodged
Wear
Grain fracture
Bond fracture
Porosity
Grain
Micro crack
Bond
Friability is the ability of an abrasive grain to fracture into smaller pieces.
Grit number indicates the size which is a the function of a sieve size. (Smaller the sieve size, the larger is the grit number. )

9. Dressing
Once the sharp edges of the grinding wheel are worn out, they need to be dressed.
Grinding dressers are used for making different profile on grinding wheel. The dressing of a wheel in order to return the wheel to its original shape.
vitrified bonded dressing tools
single grit diamond dressing tools
CNC grinding, Dressing, Fluid (SME):

10. Standard marking system
Standard marking system of grinding wheel ANSI standard B (연삭 숫돌 표시 기호)
Abrasive
Grain size
Grade
Structure
Bond
Manuf A 46 L 5 V 23
Al2O3
SiC
CBN
PCD
8-24 Rough
30-60 Mid
100 Fine
400 Very Fi
A Soft |
Z Hard
1 Dense
16 Open
Vitrified
B Resin
Silicate
Rubber
Manufacture’s private

11. Surface grinding (평면연삭)
Surface grinding involves grinding flat surfaces.
Grinding wheel
25~50 m/s
Small depth
0.01~0.05 mm
Workpiece
0.2~1 m/s
Surface grinding machine

12. Cylindrical grinding (원통연삭)
Cylindrical grinding, internal grinding and thread grinding are done on cylindrical grinders or centerless grinders
Workpiece
Grinding wheel
TiC Internal grinding (3min):
Cylindrical grinding machine (6min):

13. Centerless & Creep-feed grinding
Centerless grinding
Creep-feed grinding
low feed, large depth
Grinding wheel
Regulating wheel
Work-rest blade
Low speed
0.1~1 m/min
Large depth
1~6 mm
Centerless grinding:

14. Ex) Forces in surface grinding
Surface grinding, low-carbon steel workpiece
Wheel diameter D = 250 mm,
width of cut w = 25 mm, depth of cut d = 0.05 mm
Spindle speed S = 4000 rpm, Feed rate F = 1500 mm/min
Calculate cutting force Fc ?
Material removal rate MRR = d w F (mm3/min)
Power consumed P = u MRR (W) = T ω (Torque x angular speed)
Torque T = Fc r (Cutting force x radius)

15. Finishing Operations (마무리작업)
Coated abrasives (Sandpaper) is used in finishing flat or curved surfaces of metallic and non-metallic parts. Surface finish depends primarily on grain size.
2. Wire brushing produces a fine surface texture and serves as a light material-removal process.
3. Lapping & polishing: Two surfaces are rubbed together with an abrasive between them to creates a smooth and shiny surface

16. Finishing Operations
4. Honing: Abrasive stone scrubs metal woekpiece to improve a surface texture.
Honing engine block

17. Electrical Discharge Machining (EDM)
Electrical discharge machining (EDM 방전가공) : Material is removed by electric discharges (spark), between electrode and workpiece, separated by dielectric fluid(oil).
Sinker(Ram) EDM , Wire EDM
Electrode - 5
Current (A)
80 V
Spark + 50
Time (ms)
Workpiece
Ram vs. Wire EDM 4min

18. Sinker EDM
Shape of soft electrode (copper or graphite) is copied to hard workpiece (mold steel, tool steel).
SME 1min
Machine

19. EDM Condition Current I, On-time ton, Off-time toff, Melting temp Tw
Material removal rate: MRR  V I ton / (ton + toff ) / Tw
Roughness Ra  V I ton Ra
MRR
On-time (ms)
Current (A)

20. Wire EDM
A brass wire is fed through the workpiece submerged in a tank of dielectric fluid.
It is used to cut plates as thick as 0.3 m and to make punches, tools, and dies from hard metals.
- Wire electrode
+ Workpiece
WireEDM
WireEDM

21. Small Hole EDM
EDM drill rows of holes into the leading and trailing edges of turbine blades used in jet engines.

22. ECM (Electrochemical Machining, 전해가공)
High rate of electrolyte movement washes metal ions away from the workpiece.
It is used for machining extremely hard conductive materials with soft tool.
Workpiece
Insulating coating
Tool electrode
Pump for circulating electrolyte DC
power
supply
Tank
Electrolyte
(-)
(+)
©갈창우, GNU

23. Electrochemical Grinding (전해연삭)
Combines the processes of electrochemical machining and conventional grinding.

24. Laser-beam Cutting
High power (kW) laser melts and evaporates material.
CO2 & Nd:YAG lasers are used for industrial cutting.
Mirror
Xenon
Flashlamp
Nd:YAG
crystal
Laser
LASER: Light Amplification by Stimulated Emission of Radiation
The high-density energy melts and evaporates small portions of the workpiece.
Surface produced by LBM is rough and has a heat-affected zone.
Laser beams also used for welding, small-scale heat treating and marking of parts.
Laser cutting works by directing the output of a high-power laser at the material to be cut. The material then either melts, burns, vaporizes away, or is blown away by a jet of gas, leaving an edge with a high-quality surface finish. Industrial laser cutters are used to cut flat-sheet material as well as structural and piping materials.
CO2 lasers are used for industrial cutting of many materials including mild steel, aluminium, stainless steel, titanium, paper, wax, plastics, wood, and fabrics. YAG lasers are primarily used for cutting and scribing metals and ceramics.
The carbon dioxide laser (CO2 laser) was one of the earliest gas lasers to be developed. ), and is still one of the most useful. Carbon dioxide lasers are the highest-power continuous wave lasers that are currently available. They are also quite efficient: the ratio of output power to pump power can be as large as 20%. The CO2 laser produces a beam of infrared light with the principal wavelength bands centering around 9.4 and 10.6 micrometers.
The active laser medium (laser gain/amplification medium) is a gas discharge which is air-cooled (water-cooled in higher power applications). The filling gas within the discharge tube consists primarily of:
Carbon dioxide (CO2) (10–20%)
Nitrogen (N2) (10–20%)
Hydrogen (H2) and/or xenon (Xe) (a few percent)
Helium (He) (The remainder of the gas mixture)
The population inversion in the laser is achieved by the following sequence:
1.Electron impact excites vibrational motion of the nitrogen. Because nitrogen is a homonuclear molecule, it cannot lose this energy by photon emission, and its excited vibrational levels are therefore metastable and live for a long time.
2.Collisional energy transfer between the nitrogen and the carbon dioxide molecule causes vibrational excitation of the carbon dioxide, with sufficient efficiency to lead to the desired population inversion necessary for laser operation.
3.The nitrogen molecules are left in a lower excited state. Their transition to ground state takes place by collision with cold helium atoms. The resulting hot helium atoms must be cooled in order to sustain the ability to produce a population inversion in the carbon dioxide molecules. In sealed lasers, this takes place as the helium atoms strike the walls of the container. In flow-through lasers, a continuous stream of CO2 and nitrogen is excited by the plasma discharge and the hot gas mixture is exhausted from the resonator by pumps.
Nd:YAG (neodymium-doped yttrium aluminum garnet; Nd:Y3Al5O12) is a crystal that is used as a lasing medium for solid-state lasers.
Nd:YAG lasers are optically pumped using a flashtube or laser diodes. These are one of the most common types of laser, and are used for many different applications. Nd:YAG lasers typically emit light with a wavelength of 1064 nm, in the infrared.

25. Laser-beam Cutting
Standard roughness ∝ material thickness / laser power, cutting speed : r ∝ t0.5 / (P0.5 v0.3)
Cutting rate ≈ laser power / evaporation energy per volume, thickness, width of laser: v ≈ P / (e t w)
Laser beam
Focusing lens
Gas
Material w t
Standard roughness Rz increases with the sheet thickness, but decreases with laser power and cutting speed. When cutting low carbon steel with laser power of 800 W, standard roughness Rz is 10 μm for sheet thickness of 1 mm, 20 μm for 3 mm, and 25 μm for 6 mm.
Production and cutting rates
The maximum cutting rate (production rate) is limited by a number of factors including laser power, material thickness, process type (reactive or inert,) and material properties.
Common industrial systems (1 kW+) will cut carbon steel metal 0.5–13 mm in thickness. For all intents and purposes, a laser can be up to thirty times faster than standard sawing.
Mild steel 1 mm – 100 mm/s , 13 mm – 20 mm/s

26. Laser-beam welding
Uses a high-power laser beam as a heat source to produce a fusion weld.
Has a high energy density and a deep penetrating capability.
Laser Welding with Ytterbium Lasers
View More Samples
Lasers offer a wide range of welding capabilities such as spot, conduction, penetration and hybrid welding.  Laser welding is performed virtually in every industry as it offers numerous benefits such as high welding speeds, short weld cycles, low heat input, low heat affected zone and minimal distortion.
The good beam quality of the fiber lasers coupled with high CW powers offers deep penetration welding as well shallow conduction mode welding. Modulating these CW lasers offer pulsed laser capabilities with high peak and low average power for low heat input applications. High modulation frequencies up to 10 kW on high power lasers offer very high throughput in pulsed applications. The fiber delivery offers flexibility to integrate into conventional weld head, Galvo heads, robotic are and remote welding systems. Whatever the beam delivery employed, fiber lasers offer unparallel performance.
Typical spot welding applications include Galvo based beam delivery that deliver high speed welding of razor blades and HDD flexures that take advantage of the pulsed capabilities of the fiber lasers. Fiber lasers can be focused to small spot with extremely long focal lengths, thus remote laser welding capabilities with fiber lasers are highly enhanced. The benefit of large stand off in the order of 1-2 meters increases the work area multifold over conventional robotic systems. Such remote welding stations equipped with the fiber lasers include welding door panels, multiple welding of spot and lap welds all over the auto body frame. Other examples of fiber laser welding include full penetration of transmission components, deep penetration welding of thick steels for ships, hermetic welding of battery packs; pressure seals are few to mention.
Application Examples:
Spot welding razor blades and HHD flexures
Hermetic welding of pace makers
Butt welding titanium panels
Conduction welding of diaphragms
Full penetration welding of  transmission gear and shaft assemblies
Welding thick steels
Hybrid MIG welding

27. Press 10 ton + Laser welding
Laser-beam welding
Laser welding of diff-case.
Laser welded
Section
Bolted
Press 10 ton + Laser welding

28. Laser Welding Machine
Multi axis machine used for laser cutting, welding, marking.
Machine

29. Laser drill
Non-contact, a wide range of materials, accuracy and consistency, as small as 10 – 20 microns.
Advantages include non-contact processing, low heat input into the material, flexibility to drill a wide range of materials, accuracy and consistency.
Other benefits include drilling sub micron holes and small holes with large aspect ratios and drilling at angles.
The common techniques used in drilling are percussion hole drilling and trepanning. Percussion drilling is a process where multiple pulses are applied per hole to achieve the desired results. High speed on-the-fly drilling is a percussion type drilling process often used in drilling filter and guide vanes. Trepanning is a process by cutting large holes or contouring shaped holes. The advantages of trepanning include large holes, consistency and ability to drill shaped holes. Trepanning also reduces the holes taper.
Fiber lasers can be focused to spot sizes as small as 10 – 20 microns. The high peak power coupled with short pulse widths, a perfect Gaussian beam of the single mode and Q-switch fiber laser offer very good drilling capabilities in thin sheets, ceramics and silicon. The optics configuration is changed to achieve a different spot size, required for drilling various hole diameters. High power fiber lasers are also currently used for rock drilling applications and for oil and gas exploration industries. The high peak and energy /pulse are also used for drilling thick metals. Contact any of IPG's Application Facilities to arrange complimentary sample processing, evaluation & project planning.
Application Examples:
Drilling of flow filters and strainers
Sub micron drilling in flexography ceramic rolls 
High speed drilling of guide vanes
Hole drilling of silicon
Drilling diamonds for removing imperfections
On-the-fly-cooling holes
Rock drilling
Aerospace part:
Glass:

30. Water-Jet Cutting Water jet acts like a saw and cuts the material.
Advantages: start at any location, no heat, no deflection, environmentally friendly.
Water jet cutting uses a high velocity stream of water to cut through sheet metal. The water typically contains abrasive particles to wear the material and travels in a narrow jet at high speeds, around 2000 ft/sec. As a result, the water jet applies very high pressure (around 60,000 psi) to the material at the cut location and quickly erodes the material. The position of the water jet is typically computer controlled to follow the desired cutting path. Water jet cutting can be used to cut nearly any 2D shape out of sheet metal. The width of the cuts is typically between and 0.06 inches and the edges are of good quality. Because no burrs are formed, secondary finishing is usually not required. Also, by not using heat to melt the material, like laser and plasma cutting, heat distortion is not a concern.
5-axis:

31. Abrasive-Jet Cutting Abrasive water-jet cutting
The water jet contains abrasive particles and increases the material removal rate.
Various thicknesses can be cut in single or multiple layers.
Abrasive-jet cutting
High-velocity jet is aimed at a surface under controlled conditions.
Abrasive waterjet:

32. Ultrasonic Machining (초음파가공)
Material is removed from the workpiece surface by the process of microchipping with abrasive particles with vibrations between the tool and the surface of the workpiece.
Workpiece
Power
supply
Transducer
Abras
slurry
Tool
©갈창우, GNU
Ultrasonic Knife

33. Reference CHEIL GRINDING WHEEL IND. CO. (숫돌) http://www.grinding.co.kr
유일연삭기: (연삭기)
대한EDM: (EDM)
원일정기:
우진기공:
국일공작소: