© 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Grinding( 연삭 ), EDM Grinding( 연삭 ), EDM( 방전 ) Associate Professor Su-Jin KimSu-Jin Kim School.

© 2012© 2012 Su-Jin Kim GNU Su-Jin Kim GNU

Grinding, EDMGrinding, EDMManufacturing ProcessesManufacturing Processes

Manufacturing Processes Manufacturing Processes

GrindingGrinding(( 연삭연삭 )), E, EDMDM( 방전 )

Associate Professor Su-Jin Kim

School of Mechanical EngineeringGyeongsang National University



Contents

1. Abrasive and mechanics2. Grinding

3. EDM (Electrical discharge machining)4. Water Jet Cutting



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, SiC3. 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)

ф

Chip

Workpiece

Grain

vα

Material Specific energy (GPa, J/mm3)

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 )

WearGrain fracture

Bond fracture

Porosity

Grain

Micro crack

Bond

• 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



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

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



Surface grinding ( 평면연삭 )

• Surface grinding involves grinding flat surfaces.

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

Workpiece 0.2~1 m/s

Grinding wheel25~50 m/s

Small depth0.01~0.05 mm



Cylindrical grinding ( 원통연삭 )

• Cylindrical grinding, internal grinding and thread grinding are done on cylindrical grinders or centerless grinders

Workpiece

Grinding wheel



Centerless & Creep-feed grinding

• Centerless grinding

• Creep-feed grinding : low feed, large depth

Low speed0.1~1 m/min

Grinding wheel

Regulating wheel

Work-rest blade

Large depth1~6 mm



Assume that you are performing a surface-grinding operation on a low-carbon steelworkpiece 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 rateof the workpiece is v = 152.4 cm/min. Calculate Fc and Fn.

SolutionMaterial removal rate is

Power consumed is

Ex) Forces in surface grinding

/mincm 966.14.15254.200508.0 3dwvMRR

kg/min-m 76.8210m/min-kg 6.1183 W1342966.1581.682 MMRuPower



SolutionSince power is defined as

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

Ex) Forces in surface grinding

kg 8.25

400022

4.2576.8210

c

c

F

F

TPower

kg 54.338.253.1 nF



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.

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

Workpiece

Power supply Transducer

Abras slurryTool

© 갈창우 , GNU

© 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Grinding( 연삭 ), EDM Grinding( 연삭 ), EDM( 방전 ) Associate Professor Su-Jin KimSu-Jin Kim School.

Documents

edm grinding

cnc grinding

sujin kim gnu

gnu slide

dressing slide

fine slide

abrasive material

dislodged slide