Laser Assisted Machining

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Laser Assisted Machining

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Laser Assisted Machining

  1. 1. Laser-assisted machining of hardened 4130 steel parts with surface integrity analysis <br />Hongtao Ding, Ph.D. <br />Mechanical Engineering, Purdue University<br />https://engineering.purdue.edu/CLM/<br />
  2. 2. Outline of the Contents<br />Thermal modeling of laser-assisted profile turning<br />Laser-assisted machining of hardened 4130 steel parts with surface integrity analysis <br />2<br />
  3. 3. Thermal Modeling of Laser-Assisted Face Turning<br />24<br />Fig. 4.1 Sketch of laser-assisted facing<br />Fig. 4.2 Sketch of the laser in the machined chamfer<br />3D finite volume thermal model, fully implicit scheme <br />
  4. 4. Thermal Modeling of Laser-Assisted Profile Turning<br />25<br />Fig. 4.3 A representative case study of laser-assisted profile turning<br />Fig. 4.4Preliminary simulations <br />The laser-assisted profile turning process is applied to cylindrical parts with complex geometry features, which require straight longitudinal turning, face turning, taper turning, convex and concave circular arcs, etc. <br />
  5. 5. One-step LAM process of Hardened 4130 Steel <br />Fig. 5.1 Current and proposed methods for machining a transmission shaft of hardened steel<br />Fig. 5.2 LAM experimental setup <br />Fig. 5.3 Geometry of the hollow shaft of varying-thickness<br />Workpiece material is softened by intensely and locally laser heating. Traditional cutting tool removes material.<br />Workpiece integrity should be maintained.<br />26<br />
  6. 6. Thermal and Optical Properties of AISI 4130 <br />Table 5.1Absorptivity <br />Fig. 5.4 Temperature-dependent thermal and mechanical properties<br />Fig. 5.5 An absorptivity test for the graphite coated surface to the Nd:YAG laser <br />27<br />
  7. 7. Thermal Modeling and Temperature Measurement<br />Fig 5.6Lasers in the machined chamfer<br />Fig. 5.8 IR camera temperature measurements<br />Fig. 5.7Predicted temperature distribution<br />Condition: cutting speed of 180 m/min, feed of 0.075 mm/rev, depth of cut of 0.36 mm, CO2 laser power of 1,100 W, Nd:YAG laser power of 300 W<br />28<br />
  8. 8. LAM Test Conditions<br />Table 5.2 LAM experimental conditions<br />The key parameter is the average material removal temperature, Tmr.<br />CO2-only setup: <br />Two-laser setup:<br />29<br />
  9. 9. Cutting Force and Surface Finish<br />Fig. 5.10Surface finish <br />Fig. 5.9 Specific cutting energy <br /><ul><li>Specific cutting energy during LAM drops by about 20% as the Tmr increases to above 200°C
  10. 10. The oxidation must be avoided for the finish process, which limits the Tmrbelow 300 °C.
  11. 11. Generally, a nice surface finish (Ra of 0.2~0.4 µm) is achieved at the feed less than 0.1 mm/rev. </li></ul>30<br />
  12. 12. Dimension Control in LAM<br />Fig. 5.11Size control<br /><ul><li>To study the size control in LAM, same cutting position was applied in the radial direction, regardless of the variation of the original part sizes.
  13. 13. The depth of cut will be 0.035 mm more than that in conventional machining due to: 1) More thermal expansion in LAM 2) the low stiffness of the work and tool holding setup used in this study </li></ul>Precise size control is achievable by improving the machine rigidity and finding a suitable LAM depth of cut to minimize the dimensional error.<br />31<br />
  14. 14. Surface and Subsurface Hardness<br />Fig. 5.12 Surface hardness of the parts before and after LAM<br />Table 5.3 Effect of carbon concentration and % martensite on the as-quenched hardness of AISI 4130 (M, martensite). <br />Fig. 5.13 Subsurface hardness<br />32<br />
  15. 15. Residual Stress<br />Fig. 5.14 Surface and subsurface residual stress<br /><ul><li>The samples produced by conventional machining display about twice the variance in hoop stress than those produced by LAM.
  16. 16. The residual stress becomes more compressive in both the hoop and axial directions as the feed decreases from 0.1 to 0.05 mm/rev. </li></ul>33<br />
  17. 17. Summary on LAM of Hardened 4130 Steel<br />34<br /><ul><li>Thermal model accurately predicts temperatures within a hollow varying-thickness shaft undergoing LAM.
  18. 18. A nice surface finish, Ra of 0.2~0.4 µm, was achieved for a feed less than 0.1 mm/rev
  19. 19. Compared to conventional machining, the specific cutting energy during LAM dropped by about 20% as the Tmr increased to above 200°C.
  20. 20. Hardness of the machined surface is more uniform after LAM.
  21. 21. During LAM, the actual depth of cut is slightly larger, but the resultant diameters were consistent, indicating that depth of cut can be precisely controlled to achieve the desired dimension.
  22. 22. The samples produced by conventional machining display about twice the variance in hoop stress than those produced by LAM. The residual stress becomes more compressive in both the hoop and axial directions as the feed decreases from 0.1 to 0.05 mm/rev. </li>

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