1. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Grinding( 연삭 ), EDM Grinding( 연삭 ), EDM( 방전 ) Associate Professor Su-Jin KimSu-Jin Kim School of Mechanical Engineering Gyeongsang National University

2. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Contents 1.Abrasive and mechanics 2.Grinding 3.EDM (Electrical discharge machining) 4.Water Jet Cutting

3. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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

4. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Abrasives ( 연삭입자 ) Abrasives are harder than conventional cutting-tool materials. 1.Aluminium oxide, Al 2 O 3 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)

5. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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

6. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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 MaterialSpecific energy (GPa, J/mm 3 ) Aluminum7~27 Cat iron12-60 Low carbon steel14-68 Tool steel18-82

7. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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_z6Mhttp://www.youtube.com/watch?v=Nn8j3hp_z6M CNC grinding, Dressing, Coolant

8. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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

9. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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 toolssingle grit diamond dressing tools http://www.ehow.com/video_4418709_dressing-grinding-wheel-sharpening-tools.htmlhttp://www.ehow.com/video_4418709_dressing-grinding-wheel-sharpening-tools.html Dressing

10. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Surface grinding ( 평면연삭 ) Surface grinding involves grinding flat surfaces. http://ma.gnu.ac.kr/vod/Machining/Grinding_Machine.MP4http://ma.gnu.ac.kr/vod/Machining/Grinding_Machine.MP4 Surface grinding machine Workpiece 0.2~1 m/s Grinding wheel 25~50 m/s Small depth 0.01~0.05 mm

11. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Cylindrical grinding ( 원통연삭 ) Cylindrical grinding, internal grinding and thread grinding are done on cylindrical grinders or centerless grinders Workpiece Grinding wheel

12. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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

13. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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 Ex) Forces in surface grinding

14. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Solution Since power is defined as Since thrust force is about 30% higher than the cutting force, Ex) Forces in surface grinding

15. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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

16. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes Finishing Operations 4. Honing: Abrasive stone scrubs metal woekpiece to improve a surface texture. http://www.youtube.com/watch?v=f6CEkkG-j8s&p=9B6D9EAE75875D9Dhttp://www.youtube.com/watch?v=f6CEkkG-j8s&p=9B6D9EAE75875D9D Honing engine block

17. © 2012 Su-Jin Kim GNU Grinding, EDM Manufacturing Processes 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.MP4http://ma.gnu.ac.kr/vod/machining/Ultrasonic_Machining.MP4 Ultrasonic Knife Workpiece Power supply Transducer Abras slurry Tool © 갈창우, GNU