Archives

  • 2018-07
  • 2018-10
  • 2018-11
  • 2019-04
  • 2019-05
  • 2019-06
  • 2019-07
  • 2019-08
  • 2019-09
  • 2019-10
  • 2019-11
  • 2019-12
  • 2020-01
  • 2020-02
  • 2020-03
  • 2020-04
  • 2020-05
  • 2020-06
  • 2020-07
  • 2020-08
  • 2020-09
  • 2020-10
  • 2020-11
  • 2020-12
  • 2021-01
  • 2021-02
  • 2021-03
  • 2021-04
  • 2021-05
  • 2021-06
  • 2021-07
  • 2021-08
  • 2021-09
  • 2021-10
  • 2021-11
  • 2021-12
  • 2022-01
  • 2022-02
  • 2022-03
  • 2022-04
  • 2022-05
  • 2022-06
  • 2022-07
  • 2022-08
  • 2022-09
  • 2022-10
  • 2022-11
  • 2022-12
  • 2023-01
  • 2023-02
  • 2023-03
  • 2023-04
  • 2023-05
  • 2023-06
  • 2023-08
  • 2023-09
  • 2023-10
  • 2023-11
  • 2023-12
  • 2024-01
  • 2024-02
  • 2024-03
  • 2024-04

    • br Methodology To simulate chip flow trajectory the force

    2020-08-13


    Methodology To simulate chip flow trajectory, the force and torque acting on the chips in high pressure coolant are computed based on the control volume method [6]. During the setup, a typical gun drill chip and gun drill bit are imported into ANSYS CFX 14.0 and prescribed as stationary solids. The flow domain is then extracted from the hole, gun drill and chip and subsequently meshed by the CFX solver. In order to accurately capture the boundary layer region, face sizing with 0.1mm element size and five inflation layers on the chip surfaces are introduced. Following that, boundary conditions of pressure at the inlet and outlet of the domain are defined, as shown in Fig. 3. No slip wall boundary conditions were applied to the flow domain and drill surfaces. After the force and torque values are computed, the lateral displacement and rotation of the chip are then determined from the equations of motion:where, is the net force, is the mass of the body, is the acceleration of the chip, is the derivative of velocity with respect to the each time step, is the velocity of the chip, and is the derivative of displacement with respect to the each time step. Eq. (1) can also be expressed in three axes of components as follows:where, are the torques acting on the particle, are the principal moments of inertia, are the angular velocities, and are the derivative of the angular velocities with respect to the each time step. All the values are acting around the principal axes. The new position and orientation of the chip are then updated. With that, a new atp 4 of force and torque computation is invoked to determine the next position and orientation of the chip. A three-step sample is shown in Fig. 4. When the chip comes into contact with the wall (Fig. 5), the re-bound velocities are calculated from the coefficients of restitution:where and are the tangential and normal coefficients of restitution while and are tangential and normal components of the velocity vector. The coefficient of restitution, e, is defined as the ratio of velocity after and before impact. A perfect elastic collision will give e equals to 1 but if the chip stops after a collision then e is equal to 0. The values of the coefficient of restitution are obtained via calibration against experimental data is explained in the Section 3. The overall procedure is summarized in Fig. 6.
    Model calibration To improve the accuracy of the CFD model, it is calibrated with actual drilling experiments using commercial gun drills mainly to determine the coefficient of restitution. Fuchs Ecocool 701 with 12% wt oil was applied at 40bar while drilling speed and feed rate are set at 800rpm and 8mm/min respectively. All the experiments are conducted on the DMU 80p duoBLOCK as shown in Fig. 7. Inconel 718 rods with 8mm diameter are housed in transparent acrylic tubes and mounted on the machine with a vice clamp. 8mm gun drills are then brought into the acrylic tubes from the other side to perform drilling at the aforementioned conditions. After several chips, like the one in Fig. 8 are generated, the process is stopped the spindle and the coolant is applied to flush the chips from the cutting zone. The flow motion of the chips is captured with a Photron Fastcam SA5 at a frame rate of 6000fps. A sample that illustrates collision of the chip against the wall during its evacuation by the flushing coolant is shown in Fig. 9. Each frame has an interval of 1ms. The speed and directional change of the chip before and after collision are derived from the high speed photography and the findings are used to compute the coefficients of restitution. With more than 8 drilling cycles, the tangential and normal coefficients of restitution are approximated to 0.92 to 0.98 and 0.47 to 0.52 using with Eqs. (3), (4) respectively.
    Results and discussions Fig. 10 depicts the trajectory of a gun drill chip. As soon as the chip breaks away from the cutting edges (Fig. 10a), it is carried by the coolant atp 4 towards the wall of the hole (Fig. 10b), resulted in the first collision (Fig. 10c). The chip is then rebounded from the wall (Fig. 10d) and collides against the wall of the gun drill (Fig. 10e), after which it is successfully evacuated (Fig. 10f). The aforementioned is plotted in Fig. 11. The results produced from the CFD model appeared to be in reasonably good agreement with the experiments.