EXPERIENTAL STUDY O AXIAL ORCE AND O TORQUE IN CASE O OLC45 STEEL DRILLING, USING EXPONENTIAL CALCULATION ODEL Adrian TRI 1 and Claudiu ihai NEDEZKI 1 1 Technical University of Cluj-Napoca ABSTRACT: In this paper, the obtained experimental data it will determine the parameters from the equations of the exponential analytical model of the axial force and the cutting moment in case of drilling process of OLC 45 steel. Knowing the influence of drilling parameters on the cutting force and torque allows analysis of the machinability of different types of material; the maximum values of the drilling force and of the torque underlie the design of the drilling machines. KEYWORDS: dry cutting, drill, cutting forces, parameters, exponential model 1 THEORETICAL CONSIDERATIONS The drill is a cutting tool with a complex geometry, conducive to generating full bore. The active part of the drill is provided with two main cutting edges 1-2, joined by the transverse edge 2-2 (figure 1). Drilling of the borehole is effected by means of the helical faces - on the secondary facing faces, - the edges of which form the secondary edges 1-3. Due to the geometric shape of the drill bit and kinematics of the drilling process (cutting movement: drilling speed n [rot / min], feed motion: axial displacement of the drill bit with s [mm / rot]), the material resistance of the material is manifested by - an axial force A and torque t. The axial force and torque act on the workpiece, on the device, on the drill, and on the machine tool, and their maximum sizes are at the basis of drill, of drilling machine and of the device for fixing the workpiece. Since the chisel edge cuts under heavy conditions (low cutting speed and negative rake angle), the axial force resulting in this chisel edge is large and reaches up to (0.5-0.75) A. The torque is less affected by the chisel edge. ig. 1 The geometry of helical drill(a) and drilling forces (b) 2 ACTORS THAT INLUENCE AXIAL ORCE AND TORQUE The main factors considered are: THE ELEENTS O THE CUTTING REGIE: -the cutting depth: because the drill has a cutting depth equal to half the diameter and its increase causes an increase of the section of 84
the non-detached chip, therefore the axial force and torque will increase; - the feed rate: as the feed increases, the section of the non-detached chip increases and consequently increases the axial force and the torque - the cutting speed: Increasing cutting speed results in lower axial force and torsional torque, but only at high velocity when deformation of the material is low. GEOETRIC PARAETERS O THE DRILL: - The rake angle o, the helix angle (on the external diameter) and the point angle 2 r : The three angles are correlated by the relationship: tan D tan o (1) Db sin r This relationship shows that when determining the angles r and take into account the angle o which is chosen according to the processed material. It should be noted that the rake angle o is variable along the edge and increases with the increase in the D of the point on the cut. Angle size is determined by the diameter of the drill and the material to be machined. Increasing the angle (and therefore the angle o ) leads to a decrease in the axial force and the torque but results in a more pronounced weakening in the case of small diameter drills at which angle is chosen smaller. The point angle 2 r results from sharpening the drill. rom the previous relationship, the increase of the angle o results and also the decrease of the axial force and of the torque, with the increase of the angle r. The increase of the angle r increases the thickness of the non-detached chip a s d sin r. Increasing the chip thickness leads to a decrease in the size of the specific pressure force and thus to the decrease in the axial force and the torque. Based on these criteria and on the practical experience, the optimal values of the point angle 2 r are indicated in the literature. -The clearance angle in the frontal plane f slightly influences the size of axial force and of torque. Influence is felt at low f angle when the friction between the clearace face and the cutting surface increases. CUTTING LUIDS: their use in the drilling process causes a decrease of cutting forces and of torque. THE TREATENT applied to the workpiece and its hardness; THE WEAR LEVEL O THE DRILL a.o. 3 EXPERIENTAL STUDY: THE INLUENCE O THE CUTTING REGIE AND THE DIAETER O THE DRILL In order to highlight the influence of the diameter, a number of successive drillings of different diameters will be randomly made in specimens of the same material, keeping the same cutting parameters. Since constant speed maintenance requires a change in rotation, it will be convenient to set the diameters- rotation (D - n) pairs so that the speed variation falls within an acceptable range. To illustrate the influence of the feed rate, a number of drillings with the same drill will be executed using the feed rates of the drill-machine. With the obtained experimental data it will determine the parameters from the equations of the exponential analytical model of the axial force and the cutting moment: A t x y C D s ; C D x s 4 EXPERIENTAL CONDITIONS achine: Drilling machine G40 y (2) Tool:Helix drill with point angle 120º (2 r = 120 0 ) Cutting fluid: Dry cutting Workpiece: OLC45 Dynamometer with resistive transducer (BK 2000): with tensometric stamps linked to Wheatstone bridges. The dynamometer (igure 2) allows the measurement of axial force and torque - by means 85
of resistive electric transducers, - having a computer acquisition and processing system by means of a program designed for that purpose. ounting the test piece on the dynamometer and its respective on the table of the drilling machine is shown in figure 2. The operating principle of the BK 2000 drills dynamometer is similar to the turning process: 1. The force and torque demanding the cutting edge are directed to stimulate the resistive electrical transducers. 2. The resistive electrical transducers convert the deformation into electrical signals they transmit to the electronic circuit. The signals are then amplified and converted by an A/D analog / digital converter. 3. Digital signals are displayed by a microprocessor on its own display. oreover, they are transmitted via the RS232 interface to a connected PC. ig. 2 The BK 2000 drilling dynamometer The calculation formulas: Cutting speed: D n v 1000 [ m / min] ; (3) The model coefficients (parameters) are calculated from the following conditions: 1. s=const.; v=const. (the experiments (5,8),(4,7) and (6,9), (4) (5) (7) (6) Is calculated analogously: then the geometric mean: (8) (9) 2. D=const.; v=const. (the experiments (10,12) 86
, (10) (11) (12) (13) Knowing the coefficients: and considering the 18 experiments, we have: (14) (15) Axial force and the torque: x y x y C D s [ N] C D s [ N m] (16) A t x 0,713; x 2,067; y 0,652; y 0,706; C 1260; C 0,276 Table 1. Recorded results 87
5 RESULTS AND DISSCUSSIONS The obtained experimental data from the equations of the exponential analytical model of the axial force and the cutting moment in case of drilling process of OLC 45 steel are important for knowing the influence of drilling parameters on the cutting force and torque. The cutting force and torque allows analysis of the machinability of different types of material; the maximum values of the drilling force and of the torque underlie the design of the drilling machines. Popescu, I. Scule aschietoare, dispozitive de prindere a sculelor aschietoare. Editura atrix-rom, Bucureşti, 2012. 6 REERENCES Belous, V. Sinteza sculelor aşchietoare. Editura Junimea, Iaşi, 1980. Deacu, L., Kerekes, L., Julean, D., Cărean,. Bazele aşchierii şi generării suprafeţelor, Atelierul de multiplicare, IPCN, Cluj Napoca, 1992. Deteşan, O., Crăciun, lorina, Determinarea expresiei algebrice aproximative a derivatei unei funcţii date prin puncte echidistante, utilizând sistemul PIPE, Conferinţa Ştiinţifică Internaţională TCR 2003, Chişinău, 2003, ISBN 9975-9748-4-8 (vol. 4), pp. 30-33. Crăciun, lorina; Arghir, ariana; Deteşan, O., Necesitate, competitivitate, proiect, Conferinţa Ştiinţifică Internaţională TCR 2003, Chişinău, 2003, ISBN 9975-9748-4-8 (vol. 4), pp. 200-203. Enache, Şt. Tehnologia sculelor aşchietoare. Bucureşti, E.D.P., 1984. Hollanda, D., áté,. Aşchiere şi scule. Editura Universităţii Petru aior Tîrgu- ureş, 2004. Julean, D.Aşchierea metalelor, Editura Dacia, Cluj Napoca, 2000. König, W.ertigungsverfahren, Band 1, Drehen, räsen, Bohren, VDI, Verlag GmbH, Düsseldorf, 1990. Nedezki Claudiu, Julean Dănuţ, Bazele așchierii și generării suprafeţelor: îndrumător de lucrări, Edit. Casa Cărții de Știință, 2017, ISBN 978-606-17-1185-7, 146 pag. Nedezki Claudiu, Bazele așchierii și generării suprafeţelor: suport de curs, Edit. Casa Cărții de Știință, 2017, ISBN 978-606-17-1183- 3, 125 pag. Nedezki Claudiu, Julean Dănuţ.,aşini şi echipamente de fabricaţie îndrumător de lucrări, Editura U.T.PRESS, Cluj-Napoca, 2012, ISBN 978-973-662-734-7, 164 pag. 88