Discontinuous Chip Formation Research Articles

切削における刃先での分離作用に関する研究(第2報)

Acoustic emission techniques are tested to detect fracture phenomena of separation process at tool tip in metal cutting. These acoustic emission techniques are simple method in which the output of transducer attached on a specimen is connected to oscilloscope directly. First, calibration tests prior to cutting experiments are performed. They are composed of measure-ments of acoustic emission transducers' frequency characteristics and tensile tests. Tensile tests are carried out with detecting acoustic emission in which acoustic emission events corresponding to stress-strain relation are examined. Next, it is shown that nucleation of cracks can be detected by acoustic emission techniques in discontinuous chip formation. Furthermore, nucleation of cracks due to inclusions in continuous chip formation can be detected in separation process at tool tip and break down of built up edge by fracture also can be detected. Experimental results show that fracture phenomena in metal cutting can be detected by acoustic emission techniques with real time, high sensitivity and precise.

Metallurgical appraisal of instabilities arising in machining

The character of the shear instability in the metal-cutting operation is discussed with reference to results from machining En58C austenitic stainless steel. It is shown that at certain cutting speeds a continuous chip which exhibits large serrations is formed. The sequence of events in a typical cycle of serration formation has been established from a series of photomicrographs of ‘quick-stop’ specimens, and the associated dynamic cutting forces have been recorded. It is shown that the serrated chip formation is not caused by machine-tool vibration but is related to the inherent metallurgical features of the steel, for the machining conditions used. The essential feature of the chip formation is a varying shear strength of the work material at the chip/tool interface: a phenomenon that is similar to the stick-slip conditions described in previous work on the discontinuous chip formation. In a typical cycle, compressive stresses build up ahead of the tool as material sticks on to the rake face; selected shear then occurs on a primary shear plane of decreasing length as the chip moves away with greater velocity. The forms of the slip-line fields for the two extremes of deformation-zone geometry are considered and the effect of the chip formation on tool wear is discussed.

Surface damage during machining of annealed 18% nickel maraging steel Part 1 — Unlubricated conditions

The effect of cutting speed and tool wear land length on the surface damage produced during the machining of annealed 18% nickel maraging steel under dry orthogonal conditions was determined. Machined test pieces were examined with a scanning electron microscope and an optical microscope. Surface roughness was determined with a profilometer. The results of the investigation show that during machining a wide variety of different forms of surface damage is generated. The machined surfaces show extended regions where both coarse and fine scale surface damage have occurred at cutting speeds up to 0.1 m s −1, whereas at cutting speeds greater than 0.1 m s −1 the surfaces show evidence only of fine scale surface damage. It is suggested that the regions of coarse scale surface damage are associated with the phenomenon of partially discontinuous chip formation and the nucleation of cracks in the vicinity of the tool nose region. Several mechanisms of crack nucleation and propagation, which are thought to account for the occurrence of many aspects of the surface topography observed, are presented and discussed. It is suggested also that the regions of fine scale surface damage are associated with the phenomenon of continuous chip formation and interaction between the tool nose region and the freshly machined workpiece surface. It is shown that scanning electron microscopy is more indicative of the true condition of the surface than surface roughness measurements.

Fracture toughness and cutting

Abstract An exploratory model for cutting is presented which incorporates fracture toughness as well as the commonly considered effects of plasticity and friction. The periodic load fluctuations Been in cutting force dynamometer tests are predicted, and considerations of chatter and surface finish follow. A non-dimensional group is put forward to classify different regimes of material response to machining. It leads to tentative explanations for the difficulties of cutting materials such as ceramics and brittlo polymers, and also relates to the formation of discontinuous chips. Experiments on a range of solids with widely varying toughness/strength ratios generally agree with the analysis.

Adiabatic instability in the orthogonal cutting of steel

The reversion of Fe-18.5 Ni-0.52 C tempered martensitic steel to austenite under shear was used to study the formation of discontinuous chips by orthogonal cutting. For certain combinations of cutting speed, depth of cut, and tool rake angle, chips with bands of reverted austenite along their sheared edges were formed. Tensile tests on the same material exhibited transformed austenite on the specimen fracture surfaces for tests conducted below 200°C. Metal cutting theory predicts that continuous plastic deformation during chip formation cannot heat the material to its reversion temperature. Analysis of the machine-sample interaction before chip separation shows that adiabatic instability can occur, resulting in localized shearing and a temperature rise to at leastA s. Only those chips which are heated during continuous deformation to temperatures between 100° and 200°C undergo adiabatic instability and reversion.

砥粒切れ刃による切削現象の研究 (第8報)

Cutting process of an abrasive grain in grinding is transitional and it is not from the beginning of contact between a cutting edge and the metal being cut, but after the plastic region following the elastic one, that cutting chips are generated.Therefore, deformation process of the metal being cut in the plastic region preceding the cutting one should first be investigated to make clear the chip formation mechanism in the transitional cutting.From the above mentioned point of view, the plastic deformation process has been analyzed, paying a special attention to the pile-up phenomena ahead of the rake surface and the chip formation mechanism has been investigated in the low speed transitional cutting.Leading conclusions are as follows;1) In the plastic region, the metal being cut is plastically deformed and piled up ahead of the rake surface. The pile up shead of the rake surface developes with the depth of cut, but the development in similar shape of the pile up with the depth of cut results in no chip formation because the plastic deformation under the rake surface is very stable in the case.2) When the profile angle of the pile up ahead of the rake surface reaches a critical value, a crack originates at the free surface of the pile up. The propagation of the crack leads to discontinuous chip formation.

The cutting of polymers

The variation in the cutting behaviour of two polymers (Kematal and Perspex) as conditions are varied is described. Subject to the proviso that the Merchant shear plane angle is not greater than 45°, cutting force component data are shown to obey theoretical relations derived to account for the cutting behaviour of metals. The transition from brittle to ductile chip formation can be assessed (a) visually (b) in terms of the cutting force variation and (c) in terms of the change in the proportion of the shear zone which is subject to tensile stress; results obtained by each of these assessments are shown to be substantially in agreement. Utilizing the observations, made inter alia, by Banerjee and Palmer, that during discontinuous chip formation, chip material moves up the rake face by a series of “sticks” and “slips”, a hypothesis is proposed wherein it is suggested that such a motion of chip material occurs not solely during discontinuous chip formation but that it occurs during all forms of chip formation and, in particular, during continuous chip formation. In this way the existence of rugosities on the upper side of continuous chips is explained and deductions from this hypothesis are verified using experimental data.

せん断形切りくず生成機構の塑性学的解析(第2報)

The visioplasticity technique which was presented in a concrete form in the previous paper is applied to the analysis of discontinuous and continuous chip formations.The plastic deformation at the initial stage of discontinuous chip formation is essentially E.H. Lee's type pseudo-steady plastic flow although the flow does not last so long as to show any practical importance.Variation of plastic deformation, slip line field and its hodograph with cutting time during a cycle of producing discontinuous chip segment are obtained with the aid of grid lines engraved on a side of the workpiece. The plastic flow, slip line field and its hodograph for continuous chip formation are also obtained using the same technique and compared with the results for discontinuous chip formation. The comparison shows a great resemblance in slip line field and hodograph as well for the both types of chip formation although the grid line deformations are entirely different. This means that instantaneous properties of the each plastic field are es sentially the same, and transition between the two types of chip formation appears to be quite smooth.Under a very high friction condition on tool-face, built-up edge is sometimes formed from half-way of discontinuous chip formation. The possibility of the formation is discussed with the properties of slip line, and hodograph.

せん断形切りくず生成機構の塑性学的解析(第3報)

せん断形切りくず生成機構の塑性学的解析(第3報)

せん断形切りくず生成機構の塑性学的解析 (第1報)

せん断形切りくず生成機構の塑性学的解析 (第1報)

Some Observations on the Mechanics of Orthogonal Cutting of Delrin and Zytel Plastics

An investigation of the mechanics of orthogonal cutting on an acetal resin (Delrin 150x) plastic and a nylon resin (Zytel 101) plastic was carried out. The specimens were in the form of tubes and the rake angles and feeds were varied from −10 to +40 deg and 0.003 to 0.0115 ipr, respectively. It was found that a shear-plane type of analysis and the minimum-energy principle at low tool chip contact friction are applicable. It was found further that some of the reasons for the formation of discontinuous chips for Delrin 150x were excessive strains and induction of tensile stresses into the zone ahead of the tool. By the use of the minimum-energy principle and a constant dynamic shear stress, which appears to correlate with static properties, it was possible to predict the tool forces for Zytel 101 to a satisfactory degree of accuracy.

An Energy Approach to the Mechanics of Discontinuous Chip Formation

After briefly reviewing previous work in this field, the authors propose that rupture of the chip work contact (to give a discontinuous chip) is governed by a limiting shear strain energy condition. Assuming that shear stress and strain at rupture are dependent on the compressive normal stress, a criterion for the direction of the rupture plane is deduced. Using some results given by Field and Merchant, the authors then compare their calculated direction of rupture with that experimentally observed. Some indication that the agreement is not entirely fortuitous is afforded by checking the calculated shear strain energy at fracture with that calculated from force and chip measurements.

フライス切削の基礎的研究(第1報)

The theory of plasticity applied to the non-steady plastic flow produced by a cutting edge which is engaged paralell to the side of a workpiece is proposed. The theory is veri-fied to be in good agreement with the experimental results in slow speed machining.The friction characteristics and the coefficient of friction on the rake face in slow speed machining is discussed in conjunction with the slip line construction of the plastic field whithin the chip.The plastic deformation in discontinuous chip formation appears to be analogous to the non-steady flow in the edge engaging.

An Analysis of the Mechanism of Discontinuous Chip Formation

The mechanism of formation of discontinuous chip in metal cutting was analyzed theoretically with the concept of regional plastic flow in the flow region instead of the conventional concept of single slip along the so-called shear plane. The relationship between formations of continuous and discontinuous chips was reasonably explained. Theoretical expressions for inclination angle of the ending boundary line of the flow region, i.e., fracture surface, the starting boundary line of the flow region, and the shearing strain in the discontinuous chip fragment were deduced and ascertained to be in agreement with the experimental results for carbon steel. Moreover, the shearing stress-strain diagram in metal cutting was discussed and compared with that in static material tests.

An Analysis of the Mechanism of Discontinuous Chip Formation

The mechanism of formation of discontinuous chip in metal cutting was analyzed theoretically with the concept of regional plastic flow in the flow region instead of the conventional concept of single slip along the so-called shear plane. The relationship between formations of continuous and discontinuous chips was reasonably explained. Theoretical expressions for inclination angles of the ending boundary line of the flow region, i.e., fracture surface, the starting boundary line of the flow region, and the shearing strain in the discontinuous chip fragment were deduced and ascertained to be in agreement with the experimental results for carbon steel. Moreover, the shearing stress-strain diagram in metal cutting was discussed and compared with that in static material tests.

Discussion: “An Analysis of the Mechanism of Orthogonal Cutting and Its Application to Discontinuous Chip Formation” (Okushima, Keiji, and Hitomi, Katsundo, 1961, ASME J. Eng. Ind., 83, pp. 545–555)

Discussion: “An Analysis of the Mechanism of Orthogonal Cutting and Its Application to Discontinuous Chip Formation” (Okushima, Keiji, and Hitomi, Katsundo, 1961, ASME J. Eng. Ind., 83, pp. 545–555)

Closure to “Discussion of ‘An Analysis of the Mechanism of Orthogonal Cutting and Its Application to Discontinuous Chip Formation’” (1961, ASME J. Eng. Ind., 83, p. 555)

Closure to “Discussion of ‘An Analysis of the Mechanism of Orthogonal Cutting and Its Application to Discontinuous Chip Formation’” (1961, ASME J. Eng. Ind., 83, p. 555)

An Analysis of the Mechanism of Orthogonal Cutting and Its Application to Discontinuous Chip Formation

Instead of the conventional theory of the mechanics of metal cutting based on a process of shear confined to a single shear plane, the concept of flow region, a fairly large transitional deformation zone which exists between the rigid region of work and the plastic region of steady chip, was developed. The mechanics of orthogonal cutting was analyzed, theoretical equations for angles of boundary lines of the flow region and for strain in chip were deduced in the case of simple continuous chip formation and confirmed in cutting tests on lead. The concept of flow region was also applied to discontinuous chip formation, and theoretical expressions for angles of boundary lines of the flow region were ascertained to be in agreement with the experimental result for carbon steel.

Discontinuous Chip Formation

Abstract The extent of fracture in the chips in a metal-cutting operation varies from cracks that are just discernible under the microscope to complete discontinuity where the metal removed is in the form of discrete particles. The fracture that occurs in all of these cases is either of the ductile shear type (which predominates in metal cutting) or the brittle tensile type. The characteristics and causes of these two types of fracture are first discussed and then applied to the problem of chip fracture. The very limited fracture that occurs at the point of a tool in “continuous cutting” is held to be of the tensile type, and the role of tool sharpness in this connection is discussed. It is shown by means of motion pictures and dynamometer data that completely discontinuous chip formation is entirely different from that in continuous cutting, being better described as a periodic extrusion process rather than one of simple shear. In discontinuous cutting the friction between chip and tool is static rather than dynamic in nature. The normal stress on the shear plane, as influenced by rake angle or tool friction, is found to be an important variable in determining whether a chip will be continuous or discontinuous. Other variables of importance include the cutting speed, depth of cut, number, shape, size, and hardness of inclusions in the metal cut, and tool rigidity. The influence of these several variables with regard to chip discontinuity is discussed and a number of examples are presented to illustrate the principal points that are made.