Method for chip forming machining.

0001The present invention relates to a method for chip forming machining, preferably of metallic work pieces, said chip forming machining being carried out by a cutting edge of a cutting insert.

0002From US-A-3.973.308 is previously known a cutting tool having a chip upsetting face and a chip breaking face linked together by a straight contact length. This means that the chip will be laminated by the chip upsetting face and then slide over the straight contact length before it is formed by the chip breaking face. Thus the chip forming takes place in several individual steps.

0003The present invention intends to deform the chip in three steps in quick running in order to decrease the cutting force.

0004This and other aims have been reached by giving the invention the characteristics of the adherent claims.

0005The invention is described in detail in the following with reference to the enclosed drawings disclosing different embodiments by way of example. These embodiments are only intended to illustrate the invention that can be modified within the scope of the patent claims.

0006In the drawings <ul id="ul0001" list-style="none"><li>Fig. 1 shows a top view of a cutting insert with conventional design of the chip upsetting and the chip breaking face.</li><li>Fig. 2 shows a section along the line II-II in Fig. 1</li><li>Fig. 3 shows a top view of an embodiment of a cutting insert according to the invention.</li><li>Fig. 4 shows a section along the line IV-IV in Fig. 3.</li><li>Fig. 5 shows a top view of another embodiment of a cutting insert according to the invention.</li><li>Fig. 6 shows a top view of a further embodiment of a cutting insert according to the invention.</li><li>Fig. 7 shows a section along the line VII-VII in Fig. 6.</li><li>Fig. 8 shows a section along the line VIII-VIII in Fig. 6</li><li>Fig. 9 shows in section still a further embodiment of a cutting insert according to the invention.</li></ul>

0007The details that correspond to each other has been given the same reference numeral.

0008The conventional cutting insert 10 disclosed in Figs. 1 and 2 has a cutting edge 11 that is created by the transition between an upper face 12 and side face 13 of the cutting insert. The upper face 12 constitutes rake face or contact face between the insert and the chip formed during machining and the side face 13 constitutes a flank. The rake face 12 comprises a chip upsetting face 14 arranged in connection with the cutting edge 11 and a curved chip breaking face 15 arranged in connection with the chip upsetting face 14. When the chip disengages the work piece it slides along the chip upsetting face 14, the extension a of said face perpen­dicular to the cutting edge 11 being in the range of 0.4 mm. Then the chip follows the chip breaking face 15, the chip being formed substantially in conformity to the radius of curvature R₁ for the chip breaking face 15, said radius of curvature being in the range of 5 mm. The extension b of the face 15 perpendicular to the cutting edge 11 is in the range of 2 mm. The depth c of the chip breaking face 15 is in the range of 0.5 mm. As can be understood from what is said above the deformation of the chip, i e the lamination and the curving of the chip is carried out in two timely separated steps, said chip breaking work being relatively energy absorbing.

0009In the embodiment of Figs. 3 and 4 disclosing a cutting insert 20′ according to the invention, said insert 20′, like the insert 10, being provided with a cutting edge 21′ at the transition between an upper face 22′ and a side face 23′. The upper face or the rake face 22′ comprises a chip upsetting face 24′ and a curved chip breaking face 25′.

0010Between the chip upsetting face 24′ and the chip breaking face 25′ there is a border line 26′. This border line is to be understood as a straight line that connects the points of the chip forming face 24′ that are located farthest from the cutting edge. According to the invention a number of depressions or recesses 27′ are arranged to bridge the border line 26′. The depressions 27′ are located inside of the cutting edge 21′, i e they do not reach the cutting edge 21′ and are mutually separated along the cutting edge 21′.

0011The extension d of the chip upsetting surface 24′ perpendicular to the cutting edge 21′ between said edge and the border line 26′ is of the same magnitude as the extension a in Fig. 2, i e in the range of 0.4 mm. The radius of curvature R₂ for the chip breaking face 25′ is however essentially smaller than the radius of curvature R₁ in Fig. 2, the radius R² being in the range of 0.5 mm.

0012The extension e of the face 25′ perpendicular to the cutting edge 21′ and its depth f is also essentially smaller than the extension b and the depth c resp in Fig. 2, the extension e being in the range of 0.2-0.4 mm and the depth f in the range of 0.04-0.05 mm.

0013At a cutting insert according to Figs. 3 and 4 the creation of the lamination takes place when the chip disengages from the working piece and slides along the face 24′. Simultaneously an upset of the chip takes place due to the recesses 27′ and runners are created on the lower side of the chip. This friction work in the chip increases its temperature and the deformation of the chip is facilitated. These runners also give rise to a small friction area between the chip and the rake face. This friction area, having reference numerals 28, 29 in Fig. 3, is to be compared to the friction area having reference numeral 30 in Fig. 1, said area being achieved at a cutting insert of conventional design. The decreased friction area is contributing to the increase of the temperature of the chip and thus to further facilitate the deformation of the chip.

0014Due to the fact that the extension e of the chip breaking area 25′ is essentially smaller than the extension b of said area at a conventional cutting insert the chip forming is carried out essentially faster than at a conventional cutting insert. At a cutting insert according to the present invention the lamination creation of runners and the chip forming is happening in quick succession or essentially simultaneously and approximately in half the time that only the lamination requires at a conventional cutting insert. In spite of the fact that the chip very fast looses its high temperature the deformation work is very low and consequently the cutting forces become low due to the fact that the three-step deformation of the chip takes place essentially simultaneously.

0015As can be learnt from Fig. 3 the border line 26′ is constituted from a broken line having portions 31′ that are parallel to the cutting edge 21′. Due to the recesses 27′ the portions 31′ are separated by curved portions 32′ having their centre of curvature located at the side of the portions 32′ that are directed from the cutting edge 21′.

0016The recesses 27 have an extension adjacent to the rear portion of the chip breaking surface 25. In a preferred embodiment the recesses 27′ extend up to the rear border line 33 of the chip breaking face 25′. Said border line 33 is to be understood as a straight line that connects the points on the chip breaking face 25′ that are located farthest from the cutting edge 21′.

0017As can be learnt from Fig. 4 the bottom surface of the recesses 27′ substantially coincide with the bottom surface of chip breaking face 25′ at the portions of the bottom surfaces adjacent to the border line 33. The curvature of the chip breaking face 25′ that is constant at the preferred embodiment having the radius of curvature R₂ is consequently smaller than the radius of curvature of the portions of the recesses 27′ adjacent to the cutting edge 21′.

0018The embodiment disclosed in Fig. 5 corresponds to the embodiment of Fig. 3 and 4 with the exception that the chip breaking face 25˝ at the side directed from the cutting edge 21′ is restricted by a line having alternating straight portions 34 parallel to the cutting edge and curved portions 35 having their centre of curvature located at the side of the portions 35 directed to the cutting edge 21˝. The curved portions 32˝ are arranged opposite to the portions 34 and the straight portions 31˝ opposite to the portions 35. In the preferred embodiment the extension of one of the portions 32˝ in the longitudinal direction of the cutting edge 21˝ is smaller than the extension of one of the portions 34 in this longitudinal direction.

0019In the embodiment of Figs. 6-8 a number of recesses 27‴ are arranged along the cutting edge 21‴. In this embodiment the radius of curvature of the chip breaking face 25‴ is essentially greater than the curvature of the recesses 27‴. The bottom surface of the recesses 27‴ are thus completely below the bottom surface of the face 25‴, said recesses have a border line against the chip upsetting face 24‴ and the chip breaking face 25‴ along the whole circumference, said border line being circular in the disclosed embodiment.

0020The embodiment of Fig. 9 corresponds in principal with the embodiment of Fig. 6-8 with exception for that the rake angle α has been increased, thus somewhat further decreas­ing the cutting forces.

0021The general concept for carrying out the above described three-step deformation is that the depth f of the recesses 27 must be smaller than 0.3 mm. Preferably the depth is smaller than 0.1 mm with preference for values in the range of 0.04-0.05 mm. The chip upsetting face 24 and the chip breaking face 25 have a total extension d + e from the cutting edge of less than 2 mm. Preferably the extension should be less than 1 mm with preference for values in the range of 0.6 mm - 0.8 mm. The extension e of the chip breaking face perpendicular to the cutting edge 21 shall be less than 0.8 mm, preferably in the range of 0.2-0.4 mm. The radius of curvature R₂ for the chip breaking face 25 shall be less than 5 mm. Preferably the radius of curvature shall be less than 2 mm with preference for values in the range of 0.5 mm.