Edge Rounding and Polishing of Tools

1. Edge Rounding and Polishing of Tools Process and application Straubenhardt, 2 June 2008 Dipl.-Ing. (FH) Martin Bott OTEC Präzisionsfinish GmbH Dieselstrasse 8-12 75334 Straubenhardt www.otec.de

2. 2.) Processes for rounding the cutting edges - Sandblasting - Brushing - VIBRATORY DRAG FINISHING

3. 3.) Drag finishing

4. 3.) Drag finishing 3.1) Process description Since the workpieces can not come into contact with each other, the result is a finishing process which is gentle on the workpiece surfaces. In this process, it is impossible for the workpieces to collide. The drag finishing process enables multistage processes such as fine grinding and polishing to be carried out.

5. 3.2) Drag finishing - processing goals 3.2.1) Edge rounding achieves the following: • Removes grinding burs • Stabilizes the cutting edge • Gives uniform surface structure at the cutting edge • Extends tool life • Gives better bonding for coatings • Reduces jaggedness at the cutting edge • Reduces chipping at the cutting edge • Reduces build-up edges

6. 3.2.1) Edge rounding Example of a die

7. 3.2.1) Edge rounding Example of an end milling cutter

8. 3.2.1) Edge rounding Example of an end-milling cutter

9. 3.2.1) Edge rounding unprocessed cutting edge

10. 3.2.1) Edge rounding processed cutting edge

11. 3.2) Drag finishing - processing goals 3.2.2) Polishing achieves the following: • Improves the surface quality • Reduces roughness • Improves chip flow • Improves flow characteristics when drawing • Extends tool life • Gives better bonding for coatings • Reduces cutting forces needed • Reduces tendency to cold welding

12. Unbearbeitet 3.2.2) Polishing Example of forming dies After polishing Before processing After initial grinding

13. 3.2.2) Polishing Example of a forming tool unprocessed processed

14. 3.2.2) Polishing Example of a forming die

15. 3.2.2) Polishing Example of a tool holder

16. 3.2) Drag finishing - processing goals 3.2.3) Droplet removal achieves the following: • Improves surface quality • Reduces roughness • Improves chip flow • Improves flow characteristics when drawing • Extends tool life • Reduces cutting forces required • Creates microscopic lubricant pockets

17. 3.2.3) Droplet removal Example of an end milling cutter

18. 3.2.3) Example: smoothing of a coated surface As a result of the PVD coating process, droplets (tiny balls of material embedded into the surface) often become lodged in the protective coating. This in turn causes friction. The drag finishing process removes these droplets. The miniature “pockets” that remain improve the wetting properties of the surface. These “pockets” serve to store lubricant.

19. 3.3) Key factors 3.3.1) Machine parameters 3.3.1.1) Speed 3.3.1.2) Processing time 3.3.1.3) Direction 3.3.1.4) Immersion depth 3.3.1.5) Angle of holder 3.3.1.6) Control functions

20. 3.3.1) Machine parameters Parameter input Overview

21. 3.3.1.1) Speed Higher speeds give greater rounding values N.B. The rounding at corners increases more quickly

22. 3.3.1.1) Effect of speed

23. 3.3.1.2 + 3.3.1.3) Processing time and direction The processing time and the direction of rotation can be controlled during the process.

24. 3.3.1.2) Effect of processing time Longer processing times give higher degrees of rounding. The increase in rounding values is not linear to the processing time. N.B. The rounding at the corners increases faster than at the edges. Depending on the media, the maximum value can vary.

25. 3.3.1.2) Effect of processing time

26. 3.3.1.3) Effect of direction The choice of direction of rotation affects the flow of media against the workpiece. A change of speed is absolutely essential for homogeneous media flow and uniform processing. Uneven finishing, which is more pronounced on one side than the other, is often undesirable. Differences between the workpiece and the speed or direction of the rotor affect have an effect on edge rounding. (Low workpiece rotations give a uniform finish) (High workpiece rotations give a more pronounced rounding of the corners)

27. 3.3.1.4) Immersion depth Different immersion depths can be achieved by preselecting the operating modes.

28. 3.3.1.4) Effect of immersion depth Because of the static pressure, the contact pressure of the media increases with the immersion depth. In general we can say that a difference of 100 mm in the vertical results in a difference of about 25% in the amount of material removed. In the case of lightweight media with a low bulk density, this effect is less pronounced.

29. 3.3.1.5) Effect of the angle of the holder and/or workpieces An angled position for the holders and/or the workpieces offers advantages for the processing of the workpiece face and of large flat areas.

30. 3.3.1.6) Control functions In addition to the adjustable machine parameters, the following additional parameters are monitored: • Media life for 5 different, freely selectable, media types • Workpiece length (Sensor for avoiding collisions) • Media level (Sensor for measuring the level) Goal: reliable processes

31. 3.3) Key factors 3.3.2) Media H granulates polishing HSC granulates gentle edge rounding 15-20 µm K granulates gentle edge rounding < 15 µm SIX granulates more pronounced edge rounding up to 30 µm QZ granulates more pronounced edge rounding over 30 µm

32. 3.3.2) Media H granulates - Finishing of HSS tools • Polishing, gentle deburring • Gentle edge rounding • Low rate of chip removal, depending on grinding or polishing additive

33. 3.3.2) Media HSC granulates • Finishing of HSS and carbide tools • Polishing of coated tools and removal of droplets • Smoothing and polishing of carbide tools • Edge rounding of carbide materials up to max. 15 – 20 µm • Removal of solder residues • Rate of chip removal medium to high depending on grain size • Creates very high surface qualities (Rz 0.5 for an initial value of Rz 2.5)

34. 3.3.2) Media K granulates • Finishing of HSS and carbide tools • Polishing of coated tools and removal of droplets • Smoothing and polishing of carbide tools • Edge rounding of carbide materials up to max. 10 – 15 µm • Natural granulate bonded with PP1 polishing powder

35. 3.3.2) Media SIX granulates • Finishing of carbide tools • Deburring and edge rounding of HSS tools • Smoothing and edge rounding of chip removing tools in carbide up to max. 30 µm • Finishing of inserts • High rate of chip removal • Creates high quality surfaces

36. 3.3.2) Media QZ granulates • Finishing of carbide tools • Gives especially high degree of edge rounding over 30 µm • Rate of chip removal approx. twice as high as with SIX granulates • Carborundum with grain size of 1-3 mm • Very high rate of material removal • In the case of small edge radii under 30 µm; gives rougher surfaces than SIX or HSC granulates.

37. 3.3.2) Media - Changing the media It is a quick matter to change the media by simply changing the process container. This makes it possible to carry out multi-stage processing very efficiently. The drag grinding or drag finishing process is the only type of vibratory grinding that enables targeted surface finishing such as deburring, grinding, polishing and targeted edge rounding – all from the same machine.

38. 3.3.2) Media - Changing the media

39. 3.3) Key factors 3.3.3) Workpiece 3.3.3.1) Workpiece size 3.3.3.2) Workpiece geometry 3.3.3.3) Workpiece materials

40. 3.3.3.1) Effect of workpiece size In the case of single-drive DF machines, the transmission ratio between rotor and workpiece can not be adjusted. Here the diameter accounts for only about 10% of the effect. In the case of dual drive versions with two motors, the satellite speed can be set independently of the rotary speed. Areas of application: Thread-cutting taps  high satellite speed, low rotor speed Carbide drills  low satellite speed, high rotor speed In the case of high satellite speeds, the diameter of the workpiece has a much greater effect than it does with low satellite speeds.

41. 3.3.3.2) Effect of workpiece geometry Larger workpieces displace more media, which ‘glides’ over the edges and removes more material. The processing has little effect on the central areas of large, flat workpieces. “Scooping” workpieces push the media away from themselves. This reduces the effect of processing. Inner surfaces can be processed to a limited extend. With small bore holes, the media grain size should not be too large.

42. 3.3.3.3) Effect of workpiece materials Workpieces made from hard materials can be rounded more accurately than soft ones.

43. 3.4) Machine specifications

44. 3.4) Machine specifications Independently rotating holder systems Holder type 4-way 2B up to 500 g Holder type 6-way 2B up to 500 g Holder type 4-way 2B up to 2 kg Holder type 6-way 2B up to 2 kg Holder type 4-way 2B SL Holder type 6-way 2B SL Special types on request

45. 4.) Outlook DF-3/4 and DF-5/6 with angled holders

46. 4.) Outlook DF-6 Automation