Slow-speed Machine Research Articles

On Chip Curl in Orthogonal Machining

The chips produced in course of machining usually exhibit a finite radius of curvature. Though a part of this can be due to differential strains and thermal stresses, the tightly curled chip shape suggest the operation of some other mechanism which can give rise to the small radii of curvatures frequently observed. In this paper a possible mechanism which can give rise to the observed chip curvatures is advanced and the relevant analysis presented. The model advanced is based on optical metallographic analysis of chips produced under slow speed machining conditions. The chip curvatures observed are attributed to heterogeneous shear during chip formation.

平滑面間の重摩擦における四塩化炭素の潤滑性

It has been well known that carbon-tetrachloride (CCl4) exhibits the outstanding performance as a cutting fluid in slow speed machining of metals. However, whether CCl4 really lubricates the tool face or not is still uncertain, since it sometimes yields a higher friction than dry friction when applied into a heavy duty sliding between smooth surfaces. The paper discusses this problem through a carefully designed friction experiments and the following conclusions are obtained.(1) Dry friction is better than the friction with CCl4 only when the surface of the softer pair is protected with a film of oxides or others and the film is not ruptured during the dry dragging process. CCl4 thus lubricates the tool face during machining.(2) CCl4 appears to degenerate or embrittle the protecting films during sliding. Some metallic contacts between the matting surfaces are then produced and, at the same time, metal-chlorides to reduce friction are formed with these contacts. The friction with CCl4 is thus inferior when compared to dry friction with minor metallic contacts.(3) It seems possible to explain all the experimental results reported hitherto with the reasonings above.

Ｃｕ，Ｍｇを含むＡｌ‐Ｚｎ共析系超塑性合金のせん断応力に及ぼす切削速度の影響

A wet, orthogonal and slow speed machining test was performed to determine an independent effect of cutting speed on the shear stress. The test meets the requirements of constant temperature and freedom from a built-up edge. The stress τs on the shear plane (kgf/mm2) are expressed as a function of the cutting speed V (mm/min) or the shear strain rate γ (sec(-1)).τs = τ1Vn(1)τs = τ1'γm(2)Where, τ1: Shear stress when V is 1mm/min, τ1': Shear stress when γ is 1 sec(-1), n: Exponent of cutting speed sensitivity, and m: Exponent of shear strain rate sensitivity. If γ in equation (2) is assumed as shown in equation (3), m equals n.γ=Vs/t1(3)Where, Vs: Shear speed on the shear plane (mm/sec), and t1: Depth of cut (mm). n and m in equations (1) and (2) are changed in the range from 0.052 to 0.092 with the rake angle of the tool and the depth of cut.

Free Machining Steels—The Behavior of Type I MnS Inclusions in Machining

Experimental results obtained by in situ machining within a Scanning Electron Microscope of a resulphurized steel containing Type I manganese sulphide inclusions are presented. The data obtained from slow speed machining tests show that chip formation in these steels involves decohesion and cavitation at the sulphide-matrix interface as well as fracture of sulphide inclusions. While these processes promote fracture in the shearing region during chip formation (confirming an earlier hypothesis due to Tipnis and Cook), it is argued that these phenomena cannot be responsible for better tool life, surface finish, and lowered power requirements usually encountered with free machining alloys under typical industrial cutting conditions. The role of thermal dissipation during machining and its effect in altering the chip formation through thermally induced changes in plastic flow behavior of Type I sulphide inclusions are discussed.

格子線による塑性変形の吟味と解の許容範囲について

Grid line deformations produced in two dimensional flow-type machining of metals of various strain-hardening characteristics are compared with those of Kudo's solutions. In slow speed machining, the solutions fail to account for plastic deformation arising from the pre-flow region, which always appears regardless of strain-hardening in work materials, although they appear to be in success for explaining chip curl and secondary flow along tool-face. In high speed machining, on the contrary, the theoretical patterns using velocity discontinuity appear to be in good agreement with experimental patterns due to disappearance of the pre-flow region. It is also interesting that Kudo's solution with frictional stress of k, maximum shear stress, along whole tool-chip interface does realize in high speed machining.The permissible range of Kudo's solution in the plot of φ against β-α, where φ, β and α are shear angle, friction angle and rake angle respectively, is determined by using the restrictions of possible frictional stres distribution, mass continuity and Hill's theorem. While the range covers almost all of Merchant and Lapsley's experimental results, it is unsuccessful to cover the results in slow speed machining. The reason may lie in the incompleteness of the solutions for explaining the pre-flow region.Some new slip line solutions involving the pre-flow region are proposed in order to cover the slow speed machining data, although they are not complete in theoretical point of view.

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.