Grinding EDM Grinding Electric discharge machining Professor SuJin

Grinding, EDM Grinding, Electric discharge machining Professor Su-Jin Kim Grinding, EDM © 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 © 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 ± 2. 5 μm. Grinding, EDM © Su-Jin Kim GNU How to grind (9 min) : https: //youtu. be/7 Fw. L 55 Erf. DI ©김태용, GNU

Abrasives (연삭입자) • Abrasives are harder than conventional cutting-tool materials. 1. Aluminium oxide, Al 2 O 3 2. Silicon Carbide, Si. C 3. CBN (Cubic Boron Nitride) 4. 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 / 1 g • Mesh(체) No. wire # / inch Grinding, EDM © Su-Jin Kim GNU

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 Grinding, EDM © Su-Jin Kim GNU Cheil grinding wheel (8 min): https: //youtu. be/KZ 27 Ua. SFduw

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) Grain Chip ф Workpiece Grinding, EDM © Su-Jin Kim GNU α v Material Specific energy (GPa, J/mm 3) Aluminum 7~27 Cat iron 12 -60 Low carbon steel 14 -68 Tool steel 18 -82 (10 X machining)

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. Grinding, EDM © Su-Jin Kim GNU

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 © 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 Grinding, EDM © Su-Jin Kim GNU single grit diamond dressing tools CNC grinding, Dressing, Fluid (SME): https: //youtu. be/Nn 8 j 3 hp_z 6 M

Standard marking system • Standard marking system of grinding wheel ANSI standard B 74. 13 -1970 (연삭 숫돌 표시 기호) Abrasive A Al 2 O 3 Si. C CBN PCD Grinding, EDM © Su-Jin Kim GNU Grain size 46 8 -24 Rough 30 -60 Mid 100 Fine 400 Very Fi Grade Structure L A Soft | Z Hard 5 1 Dense | 16 Open Bond Manuf V Vitrified B Resin Silicate Rubber 23 Manufactur e’s private

Surface grinding (평면연삭) • Surface grinding involves grinding flat surfaces. Grinding wheel 25~50 m/s Workpiece 0. 2~1 m/s Grinding, EDM © Su-Jin Kim GNU Small depth 0. 01~0. 05 mm http: //ma. gnu. ac. kr/vod/Machining/Grinding_Machine. MP 4 Surface grinding machine

Cylindrical grinding (원통연삭) • Cylindrical grinding, internal grinding and thread grinding are done on cylindrical grinders or centerless grinders Grinding wheel Workpiece Grinding, EDM © Su-Jin Kim GNU Ti. C Internal grinding (3 min): https: //youtu. be/FVLhyg-_ch 8 Cylindrical grinding machine (6 min): https: //youtu. be/NHq. Mc 4 z. Xph 8

Centerless & Creep-feed grinding • Centerless grinding Regulating wheel Grinding wheel Work-rest blade • Creep-feed grinding low feed, large depth Large depth 1~6 mm Low speed 0. 1~1 m/min Grinding, EDM © Su-Jin Kim GNU Centerless grinding: https: //youtu. be/8 P 4 Mlq. ID 8 yo

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 (mm 3/min) Power consumed P = u MRR (W) = T ω (Torque x angular speed) Torque T = Fc r (Cutting force x radius) Grinding, EDM © 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 © Su-Jin Kim GNU

Finishing Operations 4. Honing: Abrasive stone scrubs metal woekpiece to improve a surface texture. http: //www. youtube. com/watch? v=f 6 CEkk. G-j 8 s&p=9 B 6 D 9 EAE 75875 D 9 D Honing engine block Grinding, EDM © Su-Jin Kim GNU

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 Current (A) Electrode - 5 80 V Spark + 50 Time (ms) Grinding, EDM © Su-Jin Kim GNU Workpiece https: //youtu. be/q 4 Fin. Ks. Dfww Ram vs. Wire EDM 4 min

Sinker EDM • Shape of soft electrode (copper or graphite) is copied to hard workpiece (mold steel, tool steel). https: //youtu. be/L 1 D 5 DLWWMp 8 SME 1 min Grinding, EDM © Su-Jin Kim GNU http: //ma. gnu. ac. kr/vod/Machining/EDM. WMV Machine

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 On-time (ms) MRR Current (A) Grinding, EDM © Su-Jin Kim GNU

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 Grinding, EDM © Su-Jin Kim GNU http: //www. youtube. com/watch? v=p. Bue. Wfzb 7 P 0 Wire. EDM http: //ma. gnu. ac. kr/vod/Machining/Wire. EDM. wmv Wire. EDM

Small Hole EDM • EDM drill rows of holes into the leading and trailing edges of turbine blades used in jet engines. Grinding, EDM © Su-Jin Kim GNU

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. DC power supply Insulating coating (-) Pump for circulating electrolyte Tool electrode (+) Tank Workpiece Electrolyte ©갈창우, GNU Grinding, EDM © Su-Jin Kim GNU http: //www. youtube. com/watch? v=Z_U_ZZty 5 Ns

Electrochemical Grinding (전해연삭) • Combines the processes of electrochemical machining and conventional grinding. Grinding, EDM © Su-Jin Kim GNU

Laser-beam Cutting • High power (k. W) laser melts and evaporates material. • CO 2 & Nd: YAG lasers are used for industrial cutting. Mirror Nd: YAG crystal Xenon Flashlamp Mirror Laser Grinding, EDM © Su-Jin Kim GNU http: //ma. gnu. ac. kr/vod/Machining/Laser_beam_machining. MP 4

Laser-beam Cutting • Standard roughness ∝ material thickness / laser power, cutting speed : r ∝ t 0. 5 / (P 0. 5 v 0. 3) • Cutting rate ≈ laser power / evaporation energy per volume, thickness, width of laser: v ≈ P / (e t w) Laser beam Focusing lens Gas Material t Grinding, EDM © Su-Jin Kim GNU w

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. Grinding, EDM © Su-Jin Kim GNU http: //www. youtube. com/watch? v=51 d 6 g. Qxg 1 KI

Laser-beam welding • Laser welding of diff-case. Laser welded Section Bolted Grinding, EDM © Su-Jin Kim GNU Press 10 ton + Laser welding

Laser Welding Machine • Multi axis machine used for laser cutting, welding, marking. Grinding, EDM © Su-Jin Kim GNU http: //ma. gnu. ac. kr/vod/Joining/Laser_Welding. wmv Machine

Laser drill • Non-contact, a wide range of materials, accuracy and consistency, as small as 10 – 20 microns. Aerospace part: http: //www. youtube. com/watch? v=83 OQTZZ 4 ML 8 Grinding, EDM © Su-Jin Kim GNU Glass: http: //www. youtube. com/watch? v=CS 60 Vz. Akhxk

Water-Jet Cutting • • Water jet acts like a saw and cuts the material. Advantages: start at any location, no heat, no deflection, environmentally friendly. Grinding, EDM © Su-Jin Kim GNU 5 -axis: http: //www. youtube. com/watch? v=2 jm 4_Hik. Mqk&p=9 B 6 D 9 EAE 75875 D 9 D

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 © Su-Jin Kim GNU Abrasive waterjet: http: //www. youtube. com/watch? v=GCBs. Tuma. Ihs

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 Abras slurry Tool Workpiece Grinding, EDM © Su-Jin Kim GNU ©갈창우, GNU http: //ma. gnu. ac. kr/vod/machining/Ultrasonic_Machining. MP 4 Ultrasonic Knife

Reference • CHEIL GRINDING WHEEL IND. CO. (숫돌) http: //www. grinding. co. kr • 유일연삭기: http: //www. youilmc. com (연삭기) • 대한EDM: http: //www. daehanedm. com (EDM) • 원일정기: http: //www. avg. co. kr/wire-edm • 우진기공: http: //www. wjmc. kr • 국일공작소: http: //kookil. com Grinding, EDM © Su-Jin Kim GNU