Manufacturing Processes
Grinding(연삭), EDM(방전)
Associate Professor Su-Jin Kim
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
School of Mechanical Engineering
Gyeongsang National University
Contents
1. Abrasive and mechanics
2. Grinding
3. EDM (Electrical discharge machining)
4. Water Jet Cutting
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
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 ±0.0025 mm.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
©김태용, GNU
Abrasives (연삭입자)
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1.
2.
3.
4.
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Abrasives are harder than conventional cutting-tool
materials.
Aluminium oxide, Al2O3
Silicon carbide, SiC
CBN (Cubic boron nitride)
PCD (Poly crystal diamond)
Grit number (입도지수) indicates the size which is a
the function of a sieve(체) size. (10: very rough, 100:
fine, 500 very fine)
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Grinding wheel (연삭 숫돌)
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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
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Mechanics of Grinding (연삭이론)
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•
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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)
Grain
Chip
ф
Workpiece
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
α
v
Material
Specific energy
(GPa, J/mm3)
Aluminum
7~27
Cat iron
12-60
Low carbon steel 14-68
Tool steel
18-82
Temperature
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•
•
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.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
http://www.youtube.com/watch?v=Nn8j3hp_z6M CNC grinding, Dressing, Coolant
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.
Grain
• Bond fracture(결합재파괴): if bond is too
strong, dull grains
cannot be dislodged
Bond
Porosity
Bond fracture
Micro crack
Wear
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Grain fracture
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
Grinding, EDM
http://www.ehow.com/video_4418709_dressing-grinding-wheel-sharpening-tools.html Dressing
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Surface grinding (평면연삭)
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Surface grinding involves grinding flat surfaces.
Grinding wheel
25~50 m/s
Workpiece
0.2~1 m/s
Small depth
0.01~0.05 mm
Grinding, EDM
http://ma.gnu.ac.kr/vod/Machining/Grinding_Machine.MP4 Surface grinding machine
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Cylindrical grinding (원통연삭)
•
Cylindrical grinding, internal grinding and thread
grinding are done on cylindrical grinders or centerless
grinders
Grinding wheel
Workpiece
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Centerless & Creep-feed grinding
• Centerless grinding
Grinding
wheel
Regulating
wheel
Work-rest
blade
• Creep-feed grinding : low feed, large depth
Large depth
1~6 mm
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Low speed
0.1~1 m/min
Ex) Forces in surface grinding
Assume that you are performing a surface-grinding operation on a low-carbon steel
workpiece using a wheel of diameter D = 25.4 cm that rotates at N = 4000 rpm.
The width of cut is w = 2.54 cm, depth of cut is d = 0.00508 cm, and the feed rate
of the workpiece is v = 152.4 cm/min. Calculate Fc and Fn.
Solution
Material removal rate is
MRR  dwv  0.005082.54152.4  1.966 cm3/min
Power consumed is
Power  u MMR  682.5811.966  1342W  6.1183kg - m/min  8210.76 m - kg/min
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Ex) Forces in surface grinding
Solution
Since power is defined as
Power  T
 25.4 
8210.76  Fc 
2 4000
 2 
Fc  25.8 kg
Since thrust force is about 30% higher than the cutting force,
Fn  1.325.8  33.54 kg
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Finishing Operations (마무리작업)
1. 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 materialremoval process.
3. Lapping & polishing: Two surfaces are
rubbed together with an abrasive
between them to creates a smooth and
shiny surface
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Finishing Operations
4. Honing: Abrasive stone scrubs metal
woekpiece to improve a surface texture.
http://www.youtube.com/watch?v=f6CEkkG-j8s&p=9B6D9EAE75875D9D Honing engine block
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Ultrasonic Machining (초음파가공)
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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.
Power
supply
Transducer
Abras
slurry
Tool
Workpiece
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
©갈창우, GNU
http://ma.gnu.ac.kr/vod/machining/Ultrasonic_Machining.MP4 Ultrasonic Knife
ECM (Electrochemical Machining, 전해가공)
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•
High rate of electrolyte movement washes metal
ions away from the workpiece.
It is used for machining extremely hard conductive
materials with soft tool.
DC
power
supply
Insulating
coating
(-)
Pump for
circulating
electrolyte
Tool electrode
(+)
Tank
Workpiece
Electrolyte
©갈창우, GNU
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
http://www.youtube.com/watch?v=Z_U_ZZty5Ns
Electrochemical Grinding (전해연삭)
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Combines the processes of electrochemical machining
and conventional grinding.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
EDM (Electrical-Discharge Machining, 방전가공)
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Based on erosion of metals by spark discharges.
EDM system consists of electrodes(전극) connected to
a DC and placed in a dielectric fluid(방전액).
Electrode
Spark
Workpiece
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
http://www.youtube.com/watch?v=q4FinKsDfww EDM
EDM (Electrical-Discharge Machining)
• 50~380 V, 0.1~500 A, 50~500 kHz, 1~100 μm3/Hz
• Metal removal rate (mm3/min) = Exp const x Current (A)
/ Meting temperature (°C): MRR = 4x104 I Tw-1.23
1st RC EDM
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
EDM (Electrical-Discharge Machining)
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Used to machine high hardness metals like as die by
copper of graphite electrode.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
http://ma.gnu.ac.kr/vod/Machining/EDM.WMV Machine
Wire EDM( Wire Electric Discharge Machining)
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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
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
http://www.youtube.com/watch?v=pBueWfzb7P0 WireEDM
http://ma.gnu.ac.kr/vod/Machining/WireEDM.wmv WireEDM
Small Hole EDM
• EDM drill rows of holes into the leading and trailing
edges of turbine blades used in jet engines.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Water-Jet Cutting
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Water jet acts like a saw and cuts the material.
Advantages: start at any location, no heat, no deflection,
environmentally friendly.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
5-axis: http://www.youtube.com/watch?v=2jm4_HikMqk&p=9B6D9EAE75875D9D
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.
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU
Abrasive waterjet: http://www.youtube.com/watch?v=GCBsTumaIhs
Reference
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제일연마: http://www.grinding.co.kr (숫돌)
진영정기: http://www.kojin.co.kr (연삭기)
우진기공: http://www.wjmc.kr
국일공작소: http://kookil.com
두산인프라코어:
http://www.doosan.com/doosaninfracoremachinetool
(방전가공기)
Grinding, EDM
Manufacturing Processes
© 2012 Su-Jin Kim GNU