In order to improve the cutting geometry of the drill bit and optimize the cutting data of the new material, we need to conduct a test inspection. Using the data measured on the vehicle and drill combination test bench, a method for calculating the process force during drilling was developed. The basis of this method is the characteristic data obtained in the orthogonal rotation test.
If the borehole process is simulated using the existing data successfully measured during turning, the drilling process can be better understood and checked
Drilling is one of the most important cutting processes. On typical rotating parts, drilling takes about 30% of the time. When drilling or turning, the cutting edge or cutting edge is always in a continuous cutting process and the same cutting tool material is used. In this regard, the drilling process is similar to the cutting process. of.
The main difference between car and drill
The main difference between a car and a drill is that there are more than one edge cutting at the time of drilling; the cutting speed on the bit edge changes between 0 and the actual cutting speed, which means that the lower the cutting speed, the worse the cutting conditions are. Despite this, the feed to the center of the twist drill bit is still large. The geometry of the bit along the edge of the drill varies greatly (cutting angle, relief angle, wedge angle, tilt angle). The cutting edge of the drill bit has a significant influence on the axial force of the drill bit depending on the degree of sharpness; since the space in the drill hole is closed, the drill cuttings are greatly hindered from being discharged from the drill hole and are periodically discharged or controlled under the control of the chip. Cooling lubricant circulation can improve this situation.
Figure 1 Correlation of drilling and rotation processes
If the borehole process is successfully simulated using the data measured while turning, all of these challenges, as well as the difficulties encountered in conducting trial investigations with twist drill cuttings, can all be better resolved.
Cutting force is the basis of drilling tests
Considering that the cutting angle and inclination angle along the cutting edge of the drill bit vary greatly, the cutting speed depends on the radius, and the cutting data should be obtained from cuttings using similar cutting edge geometry, or by conversion from orthogonal cutting experiments. The condition of the force at the time of drilling was simulated and checked by a realistic drilling experiment. At the same time, it should be estimated that the cutting speed is very small compared to the feed speed at the center of the bit in the center of the bit. The drilling process can not only be described in terms of the Kienzle cutting force model, but must also be expanded by the share of deformation force. Figure 1 shows this method, and the resulting possibility of optimizing the drilling geometry. On the drill bit, the cutting angle γ typically varies between -50° on the chisel edge and +30° on the outer diameter. Due to the chisel edge or the diameter of the drill tip, the main edge is not located on the radius ray. This means that it obtains a tilt angle λ depending on the radius by an offset of k/2. FIG. 2 shows the drill bit geometry analysis obtained from the CAD data and the confocal measurement microscope by optical measurement.
Figure 2 shows the drill edge geometry features a) the CAD model creator and b) the optical measurement method and the effective cutting angle of the drill bit in the radius c) function
Drill holes are distributed in concentric sectors
In order to be able to take into account changes in the geometry of the drill edge along the edge of the drill bit in the analysis, the borehole can be divided into concentric sectors (see Figure 3). If it is simply assumed that the cutting performance within a sector is constant, then the data from a series of tests using the corresponding blade geometry and cutting data must also be converted to the drill hole. The cutting force is the sum of all holes drilled in all sectors.
Fig. 3 Dividing the concentric sectors of boreholes in simulations a) and b)
Since the idea of ​​segmenting a sector model requires a large number of turning trials based on the bit geometry and cutting data adjusted by the drill bit, a new model needs to be developed, which can be derived from the orthogonal cutting reference for turning. Force and torque on the drill. For this reason, it is necessary to understand the influence of various angles and cutting speeds on the blade to the force. In order to model the drilling process, the effects of these parameters on specific cutting forces and feed forces must first be calculated. According to the volume fractions of the radii, they are different, and the corresponding forces of the full boreholes are calculated by summation using the Kienzle formula. In order to determine the parameters of the model, a large number of measurements are required in the processing tests of the car and the drill. For this purpose, a Kistler cutting force dynamometer Typ 9121 and a Kistler drilling platform Typ 9271A (see Figure 4) were installed at each machining station on the NC turret tool turret. These tests can be performed under different cooling and lubrication conditions. The basis for calculating the cutting and feed force is the Kienzle equation, which expresses this force as a product of the specific cutting force and the feed force and cutting area, respectively.
Figure 4 Vehicle, drill test rig equipped with force, torque and sound emission (AE) measurement system
Blade geometry affects cutting forces
It is well known that the specific cutting forces and feed forces depend to a large extent on the cutting edge geometry, and the cutting edge geometry varies along the radius on the drill bit. Therefore, in the first step, the dependency of the ratio of the cutting angle and the inclination angle must be measured from a zero car angle cutting orthogonal car test and from a drill hole test using a twist drill bit. For example, the ratio of the cutting force on the main cutting edge of turning and drilling obtained from the measurement is given. These values ​​can be mutually converted by the correction factors of the cutting angle γ(r) and the inclination angle λ(r). The cutting ability of the borehole can also be expressed by the factor AC or BC compared to the turning cutting ability. The translation of the chisel edge is similar to this.
According to Kienzle formula for cutting force
According to Kienzle's force formula, in the second step, the cutting force on the primary and the trailing edge can be determined using the previously determined value of kc1.1(r). At the same time, the correction of the cutting volume when using the chisel edge must also be taken into consideration. This correction meets the fact that the cutting volume of the drill bit at this location constitutes a sharp circular sector rather than the square formed by turning.
Cross-edge area deformation
Fully drilled cutting force is the sum of the cutting force of the main edge and the cutting edge, taking into account the radius of action. The error as a feed function is indicated on the basis of the measured data of the car and the cutting force or feed force ratio calculated for drilling and the force measured at the time of drilling. Therefore, especially in the area of ​​the chisel edge, that is, in the center of the drill bit, the cutting speed here is very low, and the force component of the deformation process there is also required to be modeled.
Fig. 5 Cutting force and feed force on the drill, calculated based on the cutting data of the turning experiment
The modeling of the deformation share is more important for feed forces than for cutting forces. With other factors (lift correction, deformation share), the influence of the cutting speed on the model, as well as the additional deformation share, can be taken into account. At the same time, the deformation share is derived from the tensile strength Rm of the material to be processed. According to this extended model, the distribution of forces on the drill edge is shown in Figure 5. What is particularly striking here is that the feed force depends mainly on the force on the crossblade. It is well known that the sharper the drill bit, the smaller this force component.
The calculation model must continue to develop
An investigation of the force applied to the auger has shown that the Kienzle formula can be used to make a reliable model of the force of the main edge of the drill, taking into account the changes in the cutting and inclination angles. For the chisel edge, in addition to the cutting share with cutting volume correction, an additional deformation share is required, and the first suggestion is made based on the tensile strength of the workpiece material. The models proposed for other drill bit parameters, sharpness, and application in other materials also need to be reviewed and, if necessary, the models continue to be refined.