Manufacturing Processes Grinding(연삭), E DM DM(방전)

Grinding, EDM 

Manufacturing Processes 

© 2012 Su-Jin Su Jin Kim GNU 


Grinding(연삭 

Grinding 연삭), , EDM EDM(방전) 

Associate Professor Su-Jin Kim 

School of Mechanical Engineering 

Gyeongsang National University

Contents 

1. Abrasive and mechanics 

2. Grinding 

3. EDM (Electrical discharge machining) 

4. Water Jet Cutting 



© 2012 Su-Jin 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. 




©김태용, GNU

Abrasives (연삭입자) 

• Abrasives are harder than conventional cutting‐tool 

materials. 

1. Aluminium oxide, Al2O3 2. Silicon carbide, SiC 

3. CBN (Cubic boron nitride) 

4. 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 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 




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) 




Chip 

ф 

Workpiece 

α 

Grain 

v 

Material Specific energy 

(GPa, J/mm 3 ) 

Aluminum 7~27 

Cat iron 12‐60 

Low carbon steel 14‐68 

Tool steel 18‐82

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. 




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. 

• Bond fracture(결합재파괴): if bond is too Grain strong, dull grains 




cannot be dislodged 

Bond 

Bond fracture 

Porosity 

Wear 

Micro crack 

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. 


http://www.ehow.com/video_4418709_dressing-grinding-wheel-sharpening-tools.html Dressing 



vitrified bonded dressing tools single grit diamond dressing tools

Surface grinding (평면연삭) 

• Surface grinding involves grinding flat surfaces. 


http://ma.gnu.ac.kr/vod/Machining/Grinding_Machine.MP4 Surface grinding machine 



Grinding wheel 

25~50 m/s 

Workpiece 

0.2~1 m/s 

Small depth 

0.01~0.05 mm

Cylindrical grinding (원통연삭) 

• Cylindrical grinding, internal grinding and thread 

grinding are done on cylindrical grinders or centerless 

grinders 




Grinding wheel 

Workpiece

Centerless & Creep‐feed grinding 

• Centerless grinding 

• Creep‐feed grinding : low feed, large depth 




Grinding 

wheel 

Work-rest 

blade 

Regulating 

wheel 

Large depth 

1~6 mm 

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 F c and F n . 

Solution 

Material removal rate is 

Power consumed is 

Power 

uMMR 682. 5811. 

966 

1342 

W 6.1183 

kg - m/min 8210. 

76 m - kg/min 




MRR 

dwv 

 

3 

0. 005082. 

54152. 

4 

1. 

966 cm /min

Ex) Forces in surface grinding 

Solution 

Since power is defined as 

Since thrust force is about 30% higher than the cutting force, 




Power T 

8210. 

76 

Fn 

F 

 

c 

25. 

4 

Fc 

 

2 

25. 

8 kg 

24000 1. 325. 

8 

33. 

54 kg

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 material‐ 

removal process. 

3. Lapping & polishing: Two surfaces are 

rubbed together with an abrasive 

between them to creates a smooth and 

shiny surface 




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 




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. 




Power 

supply Transducer 

Tool 

Workpiece 

Abras 

slurry 

©갈창우, GNU 

http://ma.gnu.ac.kr/vod/machining/Ultrasonic_Machining.MP4 Ultrasonic Knife

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. 

Insulating 

coating 

Workpiece 




DC 

power 

supply 

(+) 

(-) 

Pump for 

circulating 

electrolyte 

Tool electrode 

Tank 

Electrolyte 

©갈창우, GNU 

http://www.youtube.com/watch?v=Z_U_ZZty5Ns

Electrochemical Grinding (전해연삭) 

• Combines the processes of electrochemical machining 

and conventional grinding. 




EDM (Electrical‐Discharge Machining, 방전가공) 

• 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). 

• 50~380 V, 0.1~500 A, 50~500 kHz, 1~100 μm3 /Hz 




Spark 

http://www.youtube.com/watch?v=q4FinKsDfww EDM 

Electrode 

Workpiece

EDM (Electrical‐Discharge Machining) 

• Usedto machine high hardness metals like as die by 

copper of graphite electrode. 

• Metal removal rate (mm 3 /min) = Exp const x Current (A) 

/ Meting temperature (°C): MRR = 4x10 4 I T w ‐1.23 




http://ma.gnu.ac.kr/vod/Machining/EDM.WMV Machine

Wire EDM( Wire Electric Discharge Machining) 

• 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. 

+ Workpiece 




- Wire electrode 

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. 




Water‐Jet Cutting 

• Water jet acts like a saw and cuts the material. 

• Advantages: start at any location, no heat, no deflection, 

environmentally friendly. 




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. 




Abrasive waterjet: http://www.youtube.com/watch?v=GCBsTumaIhs

Manufacturing Processes Grinding(연삭), E DM DM(방전)

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