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Information about Grinding

Published on March 13, 2014

Author: SOUNDAR300


Manufacturing Processes : Manufacturing Processes Grinding ( 연삭 ), EDM ( 방전 ) Associate Professor Su-Jin Kim School of Mechanical Engineering Gyeongsang National University Contents: Contents Abrasive and mechanics Grinding EDM (Electrical discharge machining) Water Jet Cutting Grinding (연삭): 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 ( 연삭입자 ) Abrasives are harder than conventional cutting-tool materials. Aluminium oxide, Al 2 O 3 Silicon carbide, SiC CBN (Cubic b oron 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 wheel (연삭 숫돌): 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): 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/mm 3 ) Aluminum 7~27 Cat iron 12-60 Low carbon steel 14-68 Tool steel 18-82 Temperature: 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. CNC grinding, Dressing, Coolant Grinding Wheel Wear (연삭숫돌마멸): Grinding Wheel Wear ( 연삭숫돌마멸 ) Wear Grain 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: 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 Dressing Surface grinding (평면연삭): Surface grinding ( 평면연삭 ) Surface grinding involves grinding flat surfaces. Surface grinding machine Workpiece 0.2~1 m/s Grinding wheel 25~50 m/s Small depth 0.01~0.05 mm Cylindrical grinding (원통연삭): 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 & Creep-feed grinding Centerless grinding Creep-feed grinding : low feed, large depth Low speed 0.1~1 m/min Grinding wheel Regulating wheel Work-rest blade Large depth 1~6 mm 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 . S olution Material removal rate is Power consumed is Ex) Forces in surface grinding Ex) Forces in surface grinding: S olution Since power is defined as Since thrust force is about 30% higher than the cutting force, Ex) Forces in surface grinding Finishing Operations (마무리작업): Finishing Operations ( 마무리작업 ) Coated abrasives (Sandpaper) is u sed 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: Finishing Operations 4. Honing: Abrasive stone scrubs metal woekpiece to improve a surface texture. Honing engine block Ultrasonic Machining (초음파가공): 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. Ultrasonic Knife Workpiece Power supply Transducer Abras slurry Tool © 갈창우 , GNU ECM (Electrochemical Machining, 전해가공): 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 Electrochemical Grinding (전해연삭) : Electrochemical Grinding ( 전해연삭 ) Combines the processes of electrochemical machining and conventional grinding. EDM (Electrical-Discharge Machining, 방전가공): 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 ). EDM Electrode Workpiece Spark EDM (Electrical-Discharge Machining): EDM (Electrical-Discharge Machining) 50~380 V, 0.1~500 A, 50~500 kHz, 1~100 μ m 3 /Hz Metal removal rate (mm 3 /min) = Exp const x Current (A) / Meting temperature (°C): MRR = 4x10 4 I T w -1.23 1 st RC EDM EDM (Electrical-Discharge Machining): EDM (Electrical-Discharge Machining) Used to machine high hardness metals like as die by copper of graphite electrode. Machine Wire EDM( Wire Electric Discharge Machining): Wire EDM ( Wire Electric Discharge Machining) WireEDM WireEDM - Wire electrode + Workpiece 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. Small Hole EDM: 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 Cutting Water jet acts like a saw and cuts the material. Advantages: start at any location, no heat, no deflection, environmentally friendly. 5-axis: Abrasive-Jet Cutting: 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: Reference: Reference 제일연마 : ( 숫돌 ) 진영정기 : ( 연삭기 ) 우진기공 : 국일공작소 : 두산인프라코어 : ( 방전가공기 )

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