Effect of Increasing Spindle Speed at a Constant Chip Load on Cutting Force Behaviour of Hastelloy X

Cutting force is vital in machining nickel-based superalloys due to their excellent mechanical properties, thus creating difficulty in cutting. In the current scenario of metal machining, milling processes require high spindle speed and low chip load, which result in a low cutting force. However, low chip load not only result in low cutting force but also result in a low material removal rate (MRR). It is contrary to the ultimate high-speed machining (HSM) goal, which is to improve productivity and cost-effectiveness. Therefore, the emergence of an approach for achieving simultaneous low cutting force and high MRR is crucial. This paper presents the effect of increasing spindle speed at a constant chip load on the cutting force of Hastelloy X during half-immersion up-milling and half-immersion down-milling. In both half-immersions, the simulation results and experimental results are in good agreement. The percentage contribution of feed force, normal force and axial force to the resultant force can be arranged descendingly from high to low as axial force > normal force > axial force. Moreover, feed force, normal force, axial force and resultant force have a U-shaped behaviour. The spindle speed of 24,100 rpm and a chip load of 0.019 mm/tooth were found to achieve both low cutting force and high MRR.

Comparison of Rotary and Linear Cutting Methodology in Determining Specific Cutting Energy of Granite

Single polycrystalline diamond compact (PDC) cutting is a practical technique to understand the rock-tool interactions in drag-bit type geothermal drilling operations. This paper introduces a rotary cutting method to determine specific cutting energy (SCE) and compares it with the conventional linear cutting method. In this work, granite is selected to represent hard rock formations in geothermal drilling. Cutting tests are conducted on a CNC machine with a realistic cutting speed of 12.7 m/min and several chip loads ranging from 0.08 to 0.25 mm. The cutting force is measured using a dynamometer, and then converted to SCE. The results show that the rotary method produces an inverse relationship between SCE and chip load, whereas the linear method shows the opposite. As a result, the produced SCE by the rotary method tends to be lower than that of the linear method at a higher chip load at and over 0.16 mm. The difference may be attributed to the cutting configuration and associated force components.

Measuring and modelling of process forces during tapping using single tooth analogy process

For machining internal threads, tapping is a commonly used process. However, due to the complex geometry of the tapping tool, each tooth has a unique geometry resulting in individual forces. Since the forces act synchronously during the process, they partly compensate each other. However, since resulting forces in tapping can cause undesired deflection of the tool which can lead to threads that are not true to gauge or tool breakage, the knowledge of the forces is crucial. To predict the occurring forces on each tooth, different modelling approaches can be used. An approach based on the chip load-cutting force relationship is the mechanistic modelling. Therefore, a suitable force model is of central importance. An empirical force model can be established using an analogy process. Within this work a single tooth analogy process is presented to measure the forces of each tooth separately. By means of a geometrical analysis of the real tool, the chip sizes, such as the cross-section area of the undeformed chip are calculated. Merging the measured process forces from the analogy process and the actual chip sizes, an empirical force model is set up using multivariate regression. The model is validated by implementing it in an existing framework and comparing the results to experimental data.

An Oblique Cutting Based Mechanical Model For Insertion Torque of Dental Implant

The insertion torque of a dental implant is an important indicator for the primary stability of dental implants. Thus, the preoperative prediction for the insertion torque is crucial to improve the success rate of implantation surgery. In this present research, an alternative method for prediction of implant torque was proposed. First, the mechanical model for the insertion torque was established based on oblique cutting process. In the proposed mechanical model, three factors, including bone quality, implant geometry and surgical methods were considered by defined bone-quality coefficients, chip load and insertion speeds, respectively. Then, the defined bone-quality coefficients for cancellous bone with the computed tomography (CT) value of 235~245, 345~355 and 415~425 Hu were obtained by a series of insertion experiments of IS and ITI implants. Finally, the insertion experiments of DIO implants were carried out to verify the accuracy of developed model. The predicted insertion torques calculated by the mechanical model were compared with that acquired by insertion experiments, which were agreed match with the relative error less than 15%. This method reduces the time consumption on establishing the fitting equations for different implants and enhance the predicted accuracy by considering the effects of implants’ geometries and surgical methods.

Effect of chip load and spindle speed on cutting force of Hastelloy X

Research on cutting force revealed that the cutting force decreases as cutting speed increases, which is in line with Salomon’s Theory. However, the fundamental behaviour was never clearly explained because most studies had focused on increasing the cutting speed by increasing spindle speed without retaining the rate of chip load. On that note, the effect of increasing spindle speed while chip load is constant on the cutting force of Hastelloy X is presented in this paper. Third Wave AdvantEdge software was applied and half-immersion up-milling simulations were conducted in dry condition. Result showed that the resultant force was primarily affected by the axial force, followed by normal force and feed force. Trend-lines indicated that the behaviour of cutting force components and resultant force was quadratic. Desirability Function Analysis (DFA) results revealed that the optimum combination of chip load and spindle speed led to lowest cutting force components and resultant force was at 0.013 mm/tooth and 24,100 RPM. Furthermore, the optimum cutting conditions that led to the lowest cutting force components and resultant force at chip loads of 0.016 mm/tooth and 0.019 mm/tooth was 24,100 RPM also. Therefore, increasing Material Removal Rate (MRR) while minimizing cutting force components and resultant force can be achieved by increasing the amount of chip load at spindle speed of 24,100 RPM.

Modeling of Dynamic Instability Via Segmented Cutting Coefficients and Chatter Onset Detection in High-Speed Micromilling of Ti6Al4V

Miniature components with complex shape can be created by micromilling with excellent form and finish. However, for difficult-to-machine materials, such as Ti-alloys, failure of low-flexural stiffness microtools is a big limitation. High spindle speeds (20,000–100,000 rpm) can be used to reduce the undeformed chip thickness and the cutting forces to reduce the catastrophic failure of the tool. This reduced uncut chip thicknesses, in some cases lower than the cutting edge radius, can result in intermittent chip formation which can lead to dynamic variation in cutting forces. In addition, the run-out and the misalignment effects are amplified at higher rotational speeds which can induce dynamic force variation. These dynamic force variations coupled with low-flexural rigidity of micro end mill can render the process unstable. Consequently, accurate prediction of forces and stability is essential in high-speed micromilling. Most of the previous studies reported in the literature use constant cutting coefficients in the mechanistic cutting force model which does not yield accurate results. Recent work has shown significant improvement in the prediction of cutting forces with velocity–chip load dependent coefficients but a single-function velocity–chip model fails to predict the forces accurately at very high speeds (>80,000 rpm). This inaccurate force prediction affects the predicted stability boundary at those speeds. Hence, this paper presents a segmented approach, wherein a function is fit for a given range of speeds to determine the chip load dependent cutting coefficients. The segmented velocity–chip load dependent cutting coefficient improves the cutting force prediction at high speeds, which yields much accurate stability boundary. This paper employs two degrees-of-freedom (2DOF) model with forcing functions based on segmented velocity–chip load dependent cutting coefficients. Stability lobe diagram based on 2DOF model has been created for different speed ranges using Nyquist stability criterion. Chatter onset has been identified experimentally via accelerometer data and the power spectral density (PSD) analysis of the machined surface topography. Critical spatial chatter frequencies and magnitudes of PSD corresponding to onset of instability have also been determined for different conditions.

Segmented Cutting Coefficient Based Chatter Modeling for High-Speed Micromilling of Ti6Al4V

Miniature components with complex shape can be created by micromilling with high surface accuracy. However, for difficult-to-machine materials, such as Ti-alloys, failure of low flexural stiffness micro-tools is a big limitation. High spindle speeds (20,000 to 100,000 rpm) can be used to reduce the undeformed chip thickness and the cutting forces and hence the catastrophic failure of the tool can be avoided. This reduced uncut chip thicknesses, in some cases lower than the cutting edge radius, can result in intermittent chip formation which can lead to dynamic variation in cutting forces. These dynamic force variations coupled with low flexural rigidity of micro end mill can render the process unstable. Consequently, accurate prediction of forces and stability is essential in high-speed micromilling. Most of the previous studies reported in the literature use constant cutting coefficients in the mechanistic cutting force model which does not yield accurate results. Recent work has shown significant improvement in the prediction of cutting forces with velocity-chip load dependent coefficients but a single function velocity-chip model fails to predict the forces accurately at very high speeds (>80,000 rpm). This inaccurate force prediction affects the predicted stability boundary at those speeds. Hence, this paper presents a segmented approach wherein a function is fit for a given range of speed to determine the chip load dependent cutting coefficients. The segmented velocity-chip load cutting coefficient improves the cutting force prediction at high speeds. R2 value is found to be improved significantly (>90% for tangential cutting coefficient) which yields the better forces prediction and hence more accurate stability boundary. This paper employs two degrees of freedom (2-DOF) model with forcing functions based on segmented velocity-chip load dependent cutting coefficients. Stability lobe diagram based on 2-DOF model has been created for different speed ranges using Nyquist stability criteria. Chatter frequency ranges between 1.003 to 1.15 times the experimentally determined first modal frequency. Chatter onset has been identified via a laser displacement sensor to experimentally validate the predicted stability lobe.