TOOL FOR CHIP REMOVING MACHINING

Abstract: A tool for chip-removing machining comprises an insert holder (1) and an insert (2) that is mechanically connected with the holder via upper and lower interfaces including first and second contact surfaces (8, 8'; 9, 9') that extend at an obtuse angle ( alpha ) relative to each other. Centrally between said contact surfaces there is a ridge (10) and a flute (11) that are defined by side surfaces (13, 13'; 15, 15') that extend at an acute angle relative to each other. When the ridge engages the flute a proper absorption of transverse forces acting upon the insert is guaranteed, whereby the insert is maintained essentially immovable in its position in order to guarantee a proper machining accuracy.

Description: TOOL FOR CHIP REMOVING MACHINING Technical Field of the Invention This invention relates to a tool for chip removing machining, comprising a disc-shaped insert holder of a first material and an insert manufactured from a different, harder material, said insert being mountable in an outwardly opening recess in the holder, said recess being defined between a lower, shape-stiff front portion of the holder and an upper, elastically flexible arm intended to clamp the insert in the recess, said insert being mechanically connectable with the holder via upper and lower interfaces, of which at least one includes, on one hand, a male means being generally V-shaped in cross-section, said male means having two laterally separated, first contact surfaces that extend at an obtuse angle relative to each other, and, on the other hand, a female means being likewise generally V-shaped in cross-section, said female means having two laterally separated, second contact surfaces that likewise extend at an obtuse angle relative to each other in order to be brought into contact with the first contact surfaces when the insert is inserted into the recess and the male means engage the female means . Background of the Invention Tools of the kind generally defined above are usually used for parting, grooving and slit milling. In connection with such working operations, as well as in connection with other chip removing machining in the modern engineering industry, often very tough requirements are raised as regards the tole- ranees of the machined workpiece. This in turn requires that the insert, on one hand, is mountable in a very precise, pre ¬ determined position in the recess of the insert holder (the so called insert seat) and, on the other hand, is also capable of maintaining this precise position regardless of external action. Thus, the insert should be fixed immovably in its predetermined position relative to the holder not only when it is subjected to such ideal main forces that act centrally or tan- gentially upon the insert (i.e. parallel to the plane of the insert holder) , but also in relation to secondary transverse forces that strive to displace the insert sideways relative to the recess or the insert seat. Also small displacements of the insert sideways may lead to unacceptable tolerance deviations of the finished product. Other requirements, that are basically contradictory in relation to the requirements as regards safe and precise clamping of the insert in the insert holder, are present in connection with the manufacturing of both the insert and the insert holder. Considered only from the point of view of the manufac- turer it is thus desirable with the most moderate tolerance requirements that are possible, especially from the background that the two components are manufactured in different processes and from different materials that among themselves have different properties . Modern inserts are manufactured from hard materials, like cemented carbide or ceramics. The most outstanding property of such cutting bodies is that they have a large hardness and high wear resistance, implying a long life also in connection with machining of comparatively tough materials, like metals. However, a property of the hard body that is less desirable in practice is its brittleness; something that among other things means that the body runs a risk of being cracked or split in connection with unfavourable loading. Even if optimal manufacturing conditions always are sought for, the manufacturing result as regards tolerances may in practice vary most considerably. The insert holders are usually manufactured from steel, this being an essentially softer and tougher material than cemented carbide. Also when the insert holders are manufactured the result in practice vary as regards the achieved tolerances . In theory absolute maximum fixing of the insert in the insert seat would be achieved if as large surfaces as possible of the insert and the insert seat respectively initially could be maintained firmly abutting each other. In connection with practical series production it is, however, not possible, for the reasons given above, to separately manufacture on one hand all the inserts and on the other hand all the insert holders by such high precision that cooperating profile surfaces in the interfaces between inserts and insert holders fit absolutely perfect into each other. In reality it is therefore seen to that the contact between inserts and insert holders in the individual interface is established in two or at most three points or contact spots spaced-apart cross-section-wise (if more than three contact spots are present so called redundant positioning would arise, i.e. the insert would initially be unstable and could tilt between different positions) . A circumstance that per se is not directly unfavourable for the determination of the position of the insert is that the insert after a certain, often short time of operative load imply a certain plastic deformation to the insert holder, said plastic deformation will cause the insert to "settle". However, said deformation must not get so accentuated that the insert is distanced laterally from a central, predetermined position. Neither must the relative movements between insert and insert holder, in connection with plastic deformation, become so large that the more brittle insert runs a risk of being cracked and/or split. Prior Art During the last decades many attempts have been made to manage the problems mentioned above and to create tools that on one hand allow stable fixing of the insert, and thus proper precision, when the workpieces in question are manufactured, and on the other hand to put up moderate requirements as regards tolerances of the inserts and the insert holders respectively when they are manufactured. It is common for the solutions hitherto presented to use male means and female means, said means being V-shaped in cross-section, at at least one of the upper and lower interfaces between on one hand the insert and on the other hand the clamping arm and the holder respectively. It is characteristic for these known solutions that the V-shaped flanks or contact surfaces of said male means and female means respectively have been comparatively flat. Thus the obtuse angle between the contact surfaces is within the range of 120-179°. This relatively large obtuse angle guarantees on one hand that the ability of the surfaces to absorb high radial forces or central main forces upon the insert is satisfying and on the other hand that the risk for splitting of the insert is minimised. Examples of tools according to this prior art can for instance be found in EP 0 059 602, SE 8601533-6, US 5 054 967, US 4 738 570, SE 9201323-4 and SE 9404266-0. From EP 0 417 862 a tool is furthermore known that in the interface between insert and insert holder includes on one hand a cylindrical, convex surface that engages a groove having several, curved convex surfaces that effect only linear contact between the surfaces . A general disadvantage of the previously known tools as defined in the preamble is that the inserts have a poor trans- verse stability since they are rather easily dislodged from a desired position due to action by transverse forces. Objects and Features of the Invention The present invention aims at overcoming the disadvan- tages mentioned above in connection with previously known tools and to create an improved tool. A primary object of the invention is to create a tool whose insert has an initially good stability and safe fixing simultaneously as the requirements of measure accuracy in connection with the manufacturing of both inserts and insert holders are moderate. A further object of the present invention is to create a tool where the risk of cracking or splitting of the insert is minimal. According to the invention at least the primary object is realised by means of the features that are defined in the characterising portion of claim 1. Preferred embodiments of the invention are further defined in the dependent claims. Further Elucidation of Prior Art From GB 21 297 a tool is previously known (said tool may be in the shape of a slotting milling cutter or a circular saw blade) that apart from a supporting body includes a number of detachable teeth that are connected with the body in interfaces that each includes a central ridge and a flute corresponding to said ridge, said ridge engaging said flute. However, in this case there are no inclined side surfaces at the side of the ridge and the flute respectively that together form male means and female means respectively of the kind defined by the present invention, said means being V-shaped in cross-section. In connection with the known solution firm surface contact is required not only between the outside of the ridge and the inside of the flute, but also between the pairs of contact surfaces being present at both sides of the ridge and flute respectively and extending perpendicular to the plane of the body. Such a surface contact will not be successfully realised in connection with the manufacturing technique of the modern engineering industry for reasons presented in the preamble of the above description. Brief Description of the Drawings In the drawings : Figure 1 is an exploded perspective view of a tool comprising an insert holder and an insert spaced apart therefrom, Figure 2 is an enlarged end view of the insert according to figure 1, Figure 3 is an enlarged, schematic cross -section showing the characteristic geometry of the invention in an interface between the insert and the insert holder, said insert being shown somewhat spaced from the insert seat, and Figure 4 is a further enlarged, parallel cross-section showing the left half of the same interface, said insert being shown in contact with the insert seat. Detailed Description of a Preferred Embodiment of the Invention The tool shown in figure 1 includes, on one hand, at least a partly disc-shaped insert holder 1 and, on the other hand, an interchangeable cutting insert 2. The cutting insert is mountable in a recess or an insert seat 3 that downwards is defined by a lower, shape-stiff front portion 4 of the holder and upwards is defined by an upper, elastically flexible arm 5 intended to clamp the insert in the insert seat. At an inner end of the insert seat there is an abutment surface 6 that the insert is intended to contact in active operative position. Preferably, but not necessary, the insert is of an indexable type since it includes cutting edges 7, 7' at opposite ends. The cutting insert is manufactured from a material that is harder than the material of the insert holder. In practice cemented carbide is preferred in the cutting insert 2 and steel in the insert holder 1. The insert is attached to the holder via upper and lower interfaces that in the disclosed embodiment both includes on one hand a generally V-shaped male means, seen in cross-section, and on the other hand a likewise generally V-shaped female means, seen in cross-section. Said means will be described more in detail with reference to figures 3 and 4. In the example according to figures 1 and 2, said male means is, in the upper interface, provided at the lower side of the clamping arm 5 in order to cooperate with a V-shaped female means at the upper side of the cutting insert. In the lower interface the male means is located at the upper side of the front portion 4 in order to cooperate with a corresponding female means at the lower side of the cutting insert. In this connection it should be pointed out that the expressions "upper" and "lower" interfaces respectively are used only for the aim of simplifying the definition of the invention. Thus, in operation the holder 1 does not need to be positioned verti- cally with the clamping arm 5 above the front portion. In other words the tool according to figure 1 may be oriented in arbitrary spatial positions. Reference is now made to figures 3 and 4 that on an enlarged scale illustrate one of two interfaces between the insert and the insert holder, namely the lower interface. From figure 3 appears how the male means mentioned above is formed by two laterally spaced-apart first contact surfaces 8, 8' that extend at an obtuse angle α relative to each other. In the example given these first contact surfaces are provided on the insert holder 1. A corresponding female means of the insert 2 is formed by two second contact surfaces 9, 9' that likewise extend at an obtuse angle relative to each other, i.e. at the same angle α as between the surfaces 8, 8 1 . This means that the pairs of first and second contact surfaces 8, 9 and 8', 9' respectively will contact each other firmly when the insert is inserted into the insert seat . Per se the obtuse angle α may vary but according to the invention it should be in the range of 120-179°, preferably 150-170°. In the disclosed embodiment the angle α is 160°. In relation to a transverse plane perpen- dicular to a central plane C through the insert holder the individual contact surface slopes at a relatively flat angle. This guarantees that the contact surfaces 8, 8' may bear relatively large forces in the main load direction that is parallel with the central plane C simultaneously as the inclination of the contact surfaces to a limited extent assists in counteracting a transverse displacement of the insert when said insert is subjected to transverse forces. To design, in the manner defined above, inserts and insert holders with female means and male means respectively, said means being V-shaped in cross-section and having a large obtuse angle, is well known prior art, as mentioned in the preamble . According to the invention a ridge 10 is designed in a central area between the two first contact surfaces 8, 8', the purpose of said ridge 10 being to engage a likewise central flute or groove 11 between said contact surfaces 9, 9'. This ridge is defined by a top surface 12 and two side surfaces 13, 13' that extend at an acute angle β relative to each other. The flute 11 in turn is defined by a bottom surface 14 between two side surfaces 15, 15'. In the disclosed preferred embodiment the top surface 12 of the ridge is planar and transforms into the side surfaces 13, 13' via convexely rounded transition portions 16, 16'. At their lower portions the side surfaces 13, 13' transform into the first contact surfaces 8, 8' via con- cavely, rounded transition portions 17, 17'. In the example the bottom surface 14 of the flute 11 is arc-shaped in cross-section, e.g. partly cylindrical, the entire distance between the upper portions of the side surfaces 15, 15'. The height E λ of the ridge 10 is less than the depth H 2 of the flute. This depth H 2 is measured from the bottom surface 14 of the flute to an imaginary intersection point (not shown) between the surfaces 9, 15 and 9', 15' respectively. By this difference between the ridge and the flute a play 18 is created between the top surface 12 and the bottom surface 1 . In other words, the ridge does not bottom in the flute. Between each pair of second contact surface 9, 9' and side surface 15, 15' there is a chamfered surface 19, 19'. The angle between said two chamfered surfaces 19, 19' is on one hand smaller than the obtuse angle between the contact surfaces 9 , 9 ' and on the other hand larger than the angle between the side surfaces 15, 15' that likewise the angle β is essentially acute. The chamfered surfaces 19, 19' define together with the transition surfaces 17, 17', located inside of said chamfered surfaces 19, 19', secondary (in cross-section crescent-shaped) plays 20 where the insert is void of contact with the insert holder. Both the side surfaces 13, 13' of the ridge and the side surfaces 15, 15' of the flute may be planar. However, it is also feasible to design one of the two cooperating surfaces, e.g. the side surface 15 and 15' respectively of the flute, slightly arched in a convex way while the other surface remains planar. In an initial state, i.e. before the insert is subjected to an operative load, the width of the ridge 10 in the area of the side surfaces 13, 13' is at least somewhat smaller than the width of the flute between the side surfaces 15, 15'. When the contact surfaces 8, 8' are brought to firm abutment against the contact surfaces 9, 9', as is shown in figure 4, extremely fine gaps 21 are established between the side surfaces 13 and 15 (as well as 13' and 15'), said gaps 21 being void of surface contact . As regards the rest of the geometry in the shown inter- face it should be pointed out that the angle β preferably is within the range of 20-60°, conveniently 35-45°. In the concrete embodiment according to figure 3 the angle β is 40°. The width of the ridge 10, measured as the width B of the base in the area of the transition surfaces 17, 17', should in all cir- cumstances be less than 70% of the width or thickness of the insert holder (i.e. the distance between opposite side surfaces of the holder 1) . In practice the width B should be within the range of 20-50, preferably 25-45, and suitably constitute 30- 35% of the width of the insert holder. The height H x of the ridge 10 should be within the range of 40-70%, suitably 50-60% of the width B. The height H 2 of the flute 11 should be at least 10% larger than the height E-. . In the initial state, when the insert is mounted in the insert seat, but not subjected to any other forces than the spring action from the clamping arm 5, contact is established at two locations in the individual interface, i.e. surface contact between cooperating pairs of first and second contact surfaces 8, 9; 8', 9'. When the insert is then put in operative mode and subjected to forces from the workpiece, i.e. on one hand main forces in the plane C and on the other hand also transverse forces, the ridge 10 is engaged. Initially a certain plastic deformation takes place in the softer material of the insert holder 4. This will have the effect that the ridge pene- trates further into the flute 11 beyond what is shown in figure 4. Hereby present transverse forces are absorbed by bringing the side surfaces 13, 15 of the ridge and the flute, at one side of the ridge, to contact each other, so as to establish a stable three point contact. Due to the fact that the ridge, as well as the flute, has a distinct height and the side surfaces extend at an acute angle β relative to each other, it is guaranteed that the insert is not displaced to any appreciable degree from its initial position; this meaning that a high grade of accuracy is maintained when the workpiece is machined. Despite the forceful engagement of the tall ridge into the deep flute the risk for splitting of the insert may to a considerable degree be avoided by giving a limited width to the ridge; this guaranteeing that the moment arm of the wedge forces is limited, said wedge forces acting from an external side surface of the ridge towards a cooperating internal side surface of the flute. In this connection it should also be pointed out that the penetration of the ridge into the flute is limited by the presence of the initial gap 21 between the side surfaces 13, 15, also in such cases when the plastic deformation of the in- sert holder is considerable. Feasible Modifications of the Invention The invention is not only restricted to the embodiment described and shown in the drawings. It is thus feasible to connect the insert with the insert holder via a combination of ridge and flute only in one of the two upper and lower interfaces. It is also feasible to provide a central flute between the two first contact surfaces that together form a V-shaped male means in cross-section, while the ridge is provided cen- trally between two other contact surfaces forming a corresponding female means. Although two central flutes in the given embodiment is provided upon the insert (as is shown in figures 1 and 2) , while the corresponding ridges are provided in the insert seat, it is further possible to provide the insert with a flute and a ridge in order to cooperate with a ridge and a flute respectively in the insert seat. It should also be mentioned that the ridge per se may be composed of two or more axially spaced-apart projections, this being effected by spaces or recesses, said projections being localised to the inner and outer ends of the insert and insert holder. It should also be pointed out that the insert seat and the seat respectively (and thereby the ridges and the flutes respectively) must not necessarily be linear. Thus, they may be slightly curved or "banana shaped" .

Claims: Claims 1. Tool for chip-removing machining, comprising a disc-shaped insert holder (1) of a first material and an insert (2) manu- factured from a different, harder material, said insert being mountable in an outwardly opening recess (3) in the holder, said recess (3) being defined between a lower, shape-stiff front portion (4) of the holder and an upper, elastically flexible arm (5) intended to clamp the insert in the recess, said insert being mechanically connectable with the holder via upper and lower interfaces, of which at least one includes, on one hand, a male means being generally V-shaped in cross-section, said male means having two laterally separated, first contact surfaces (8, 8') that extend at an obtuse angle (α) relative to each other, and, on the other hand, a female means being likewise generally V-shaped in cross-section and having two laterally separated, second contact surfaces (9, 9') that likewise extend at an obtuse angle relative to each other in order to be brought into contact with the first contact sur- faces (8, 8') when the insert is inserted into the recess and the male means engage the female means, c h a r a c t e r i z e d in that in a central area between the first contact surfaces (8, 8') a ridge (10) is provided - or alternatively a flute - for mechanical cooperation with a flute (11) - alterna- tively a ridge - in a central area between said second contact surfaces (9, 9'), said ridge (10) having a top surface (12) between two side surfaces (13, 13') that extend at an acute angle (β) relative to each other, and that the flute (11) has a bottom surface (14) between two side surfaces (15, 15') that likewise extend at an acute angle relative to each other, that the height of the ridge (10) is smaller than the depth of the flute (11) in order to create a play (18) void of surface contact between said top surface (12) and said bottom surface (14), that in the transition area between adjacent pairs of cooperating side surfaces and contact surfaces on both sides of the ridge and the flute secondary plays (20), void of surface contact, are defined, and that the nominal width of the ridge in the area of said side surfaces (13, 13') is at least somewhat smaller than the nominal width of the flute in the same area in order to provide, between the pairs of side surfaces facing each other, two extremely fine gaps (21) void of surface contact as long as the insert is not subjected to any load, one of said gaps ceasing to exist as soon as the insert during work is subjected to transverse forces that establish obvious contact between one of the pairs of cooperating side surfaces, whereby the insert during work - at least initially - is generally fixed by a three point contact in the interface in question, namely at the two laterally separated contact spots, in the form of said pairs of first and second contact surfaces (8, 9; 8', 9'), and at a third contact spot localised at one side of the ridge. 2. Tool according to claim 1, c h a r a c t e r i z e d in that the obtuse angle (α) between the first contact surfaces as well as the obtuse angle between the second contact surfaces (9, 9') is within the range of 120-179°, preferably 150-170°. 3. Tool according to claim 2, c h a r a c t e r i z e d in that the acute angle (β) between the side surfaces (13, 13'; 15, 15') of both the ridge and the flute is within the range of 20-60°, preferably 35-45°. 4. Tool according to any of the preceding claims, c h a r a c t e r i z e d in that the width of the ridge (10) in an area of lower limiting lines constitutes at most 70% of the width of the insert holder. 5. Tool according to any of the preceding claims, c h a r a c t e r i z e d in that one of the two cooperating side surfaces (13, 15) at one side of the ridge and flute respectively is planar, while the other is slightly curved and has a convex side facing the planar surface. 6. Tool according to any of the preceding claims, c h a r a c t e r i z e d in that each individual secondary play (20) is defined, on one hand, by a concave curved transition surface (17, 17') between a first contact surface and a side surface upon the ridge and, on the other hand, by a pla- nar, chamfered surface (19, 19") that extends between a second contact surface and a side surface of the flute.

Inventors: ANDERSSON CLAES, BRASK KARL-GOERAN, HANSSON PER, HEDBERG ANNA, TAEGTSTROEM PER, ANDERSSON, CLAES, BRASK, KARL-GOERAN, HANSSON, PER, HEDBERG, ANNA, TAEGTSTROEM, PER
Applicants: ANDERSSON CLAES, BRASK KARL GOERAN, HANSSON PER, HEDBERG ANNA, SANDVIK AB, TAEGTSTROEM PER, ANDERSSON, CLAES, BRASK, KARL-GOERAN, HANSSON, PER, HEDBERG, ANNA, TAEGTSTROEM, PER
Application year: 1998
Main classification: B23B27
IPC codes: B23B27