Cutting insert and method of manufacturing such insert

Abstract: The invention relates to a powder body (10), a cutting insert (20) and a method to manufacture the insert. The powder body is a compacted unit which comprises a lower side (12), provided with a recess (15) and a protrusion (16) located at a certain distance from each other. The insert consists of two identically shaped sintered bodies. The insert includes inner voids (24) in the area around the middle plane (M) of the insert. The method includes the step of sintering the identically shaped powder bodies into one unit.

Description: The present invention relates to a cutting insert and a method of manufacturing such an insert, according to appended claims 1 and 9. Due to complicated insert geometries it has not previously been practically possible to use conventional press tools for pressing inserts having a double-positive geometry, i.e. double-sided inserts having top faces which intersect with adjacent side faces at acute angles. If such previously used double positive inserts would be directly pressed in conventional press tools it would not be possible, without causing damage, to release the powder body from its tool after completion of the pressing. In FR-A-1522955 a method of assembling two portions made of sintered metal powder is described. In accordance with this method two pieces are provided with compatible protrusions and recesses and the pieces are pressed together such that said protrusions and recesses are getting locked together by plastic deformation. These two pieces are not identical in shape and therefore two different types of press tools must be used in manufacture which makes this method time-consuming. Time-consumption is also extended due to the fact that braze material is introduced inbetween the pieces before pressing takes place. This method cannot be used for assembling two powder bodies of hard material due to their brittleness before sintering. The plastic deformation will introduce inner stresses into the material which is objectionable when there is production of cemented carbide inserts due to the small resistance towards tensile stresses that is typical for cemented carbide. In US-A-3 429 700 a pulley wheel is described which is manufactured by joining two sections of substantially identical shape comprising interacting projections and depressions. These two sections are brought together and then sintered. This citation is silent as to hard materials and cutting inserts. Moreover, it does not disclose the production of articles with acute edge angles. It is therefore a purpose of the present invention to provide a cutting insert which can easily be produced. It is another purpose to provide a double-sided insert which inherently has necessary clearance angles. It is another purpose of the invention to provide a simple method for the manufacture of a cutting insert having a complicated geometry. These and other objects have been achieved by shaping the insert and providing a method of manufacture such as described hereinafter in connection with the appended drawings. The invention will now be described more in detail in connection with the appending drawings in which: Fig. 1 is a sectional view of a powder body of the invention taken along line I-I in Fig. 2; Fig. 2 is an underneath view of the powder body in Fig. 1; Fig. 3 is a plan view of an insert of the invention; Fig. 4 is a side view and partly a sectional view of the insert; Figs. 4A and 4B represent enlarged cross-sectional views taken in Fig. 4, Fig. 5 is a cross-sectional view of an alternative insert embodiment of the invention. Fig. 6 is a photograph showing the microstructure of the transition zone in the area A between the two identical bodies at 1000 X after being sintered together. Figs. 1 and 2 show a powder body 10 after being compacted in a press tool (not shown) but before sintering. The powder body consists of a binder material and metal carbides, metal nitrides or ceramic material. The body is a mainly disc-shaped, annularly or polygonally shaped body comprising an upper face 11, a lower face 12 and at least one side surface 13 connecting said upper and lower faces. The upper face 11 intersects each side surface 13 to define an acute edge angle α. The body 10 has a central aperture 14. The upper face might include directly pressed profiles such as chip formers the design of which can be freely chosen. The lower face 12 is mainly planar and comprises, in this ilustrated case, a recess 15 and a protrusion 16. Alternatively one or several recesses and protrusions might have been provided. The recess 15 has a circular cross-section and is provided with decreasing diameter from the lower face 12 to the upper face 11. The recess has a depth d which should not exceed 1/4 of the thickness t of the body. The protrusion 16 which can have a cross-section complementary to that of said recess is in this case provided with approximately polygonal cross-section the dimension of which decreases in a direction from the lower face 12. The protrusion is therefore in the shape of a truncated pyramid. The height h of the protrusion above the lower face is max. 1/4 of the thickness t of the body whilst being somewhat less than the depth d of the recess 15. The protrusion is provided with smoothly rounded corner portions which, as seen in a cross-section parallel with said lower face, are positioned on a circle the diameter of which is less than the diameter of the recess when taken in a corresponding cross-section. The recess and the protrusion are positioned on a circle C the centre point of which coincides with the centre CL of the body 10. The radius R of the circle C is preferably larger than the radius of a standardized inscribed circle of said body. A straight line L can be drawn such that it intersects with said protrusion, said recess and the centre CL in bodies with four corners, such as a body of rhombic or square shape. With a body of triangular basic shape such line L would not pass through the centre CL of said body. The body can be assembled with an identically shaped second powder body and subsequently sintered therewith thereby becoming suitable for chipforming machining. The method of manufacturing an insert 20 of the invention is exercised in the following manner whereby reference is made to Figs. 1 to 4B. The compaction chamber of a conventional press is first filled with powder. This conventional press is only useful for pressing inserts of negative form or simple positive form. The punch and the die of the press which have profiles which are inverted in relation to those of the desired profiles are displaced towards each other so that the powder is compacted or packed. A brittle body 10 consisting of such powder having desired geometry can be removed from the chamber in a conventional way. The pressing procedure which lasts a few seconds is repeated so that two identical powder bodies are obtained. The lower sides 12 of said bodies 10 are oriented towards each other and one body is rotated in the plane of said lower side said rotation being 180° angular rotation in relation to said other body such that the recess 15 and the protrusion 16 are linearly oriented to each other. The bodies are thereafter displaced towards each other so that the protrusions are received in said recesses without there being anything more than a contact between a minor portion of each body, i.e. line contact is established between the wall of the recess and the corners of the protrusion. When the lower sides are thus in contact with each other such package is inserted into a furnace for heating it to sintering temperature so that a sintering occurs, i.e. the lower sides of the bodies and the protrusion and corresponding recess are metallurgically bound together. The normal sintering condition for cemented carbides consisting of 8-10 % Co, 3-10 % TiC + TaC + NbC, rest WC is a temperature of 1350 - 1500°C in vacuum for a time period of 0.5 - 2h. This method makes possible the production of negative inserts having fastening holes which have a decreasing diameter of cross-section towards side surfaces 21 and 22 whilst making possible the provision of a channel system inside the insert around its intermediate plane. Figs. 3 to 4B show a completely sintered insert 20 according to the invention. The insert 20 consists of two identical powder bodies which have been assembled and sintered together. The insert has a double-positive shape which means that upper faces 21 and the lower faces 22 are located at an acute angle α at their intersection with the edge faces 23. The edge faces 23 might be planar or non-planar. Hence, the insert is composed of two identical halves metallurgically bound to each other mainly along the central middle plane M of the insert. There is a remaining play 24 between the recess 15 and the protrusion 16 due to the fact that the height h of said protrusion 16 is about 0.1 mm less than the depth of said recess. The existence of such play 24 promotes an accurate plane abutment between the lower sides of said halves in connection with the sintering. This play 24 might communicate with edge surface 23 via a channel for the purpose of receiving sensors such as electronic circuits in micro scale for measurement of mechanical and/or thermal stresses. Alternatively, special voids might be provided in the middle plane M for housing such sensors. Additionally, channels for instance for transport of cooling media could simply be arranged at the middle plane M by providing slots in the powder body 10 in connection with compacting said body. The insert has a central aperture 25 symmetrically around its central axis CL with convexly decreasing cross-sectional diameter towards the middle plane M . Alternatively this aperture could as shown in Fig. 5 have a concavely increasing diameter towards the middle plane. Hence, the present invention provides a cutting insert, and method for its manufacture whereby a powder body when assembled and sintered together with a similar body can be utilized for chipforming machining whereby said insert makes possible the use of a double positive geometry so that this method also makes possible the usage of new forms of holes and inclusion of measurement sensors therein. Example Compacts according to Fig. 1 - 3 with projections and depressions on the lower side were prepared in four different compositions. Compacts of the same composition were brought together in pairs and then sintered in a laboratory furnace under the following conditions: Composition Sintering conditions 8 % Co, rest WC 1410°C, 1h, vacuum 9.5 % Co, 3.5 % TiC+TaC+NbC, rest WC 1450°C, 1h, vacuum 5.5 % Co, 8.5 % TiC+TaC+NbC, rest WC 1450°C, 1h, vacuum 10 % Co, 6 % TiC+TaC+NbC, rest WC 1450°C, 1h, vacuum The sintered compacts were cut and polished and the transition zone between the two original halves was studied in a light microscope and also in a scanning electron microscope. It was found that the two halves had sintered together completely. The transition zone could be seen as a cobalt band with little or no residual porosity. In some instances the transition zone was almost invisible. An example of a transition zone is shown in Fig. 6.

Claims: Cutting insert of hard material for chipforming machining having cutting edges provided at the intersection between opposed upper and lower surfaces (21, 22) and an edge surface (23) located therebetween, said insert being double-sided, characterized in that the insert comprises two identical powder bodies (10) which by means of sintering are metallurgically bound to each other along a middle plane (M), in that each of the two sides abutting at the middle plane (M) includes at least one recess (15) and at least one protrusion (16), which are separated and located on an imaginary circle having a centre which coincides with the centre (CL) of each powder body, and in that said upper and lower surfaces (21, 22) intersect said edge surface (23) at an acute angle (α). Cutting insert according to claim 1, characterized in that the recess (15) and the protrusion (16) have different forms in a cross-sectional view taken parallel with the middle plane (M) and that the dimension of the recess and the protrusion of each of the two powder bodies decreases and increases, respectively, in a direction towards its surface opposite said middle plane. Cutting insert according to claim 1 or 2, characterized in that the recess (15) and the protrusion (16) have equal or complementary shape in a cross-sectional view taken parallel with said middle plane (M) and that the dimension of the recess and the protrusion of each of the two powder bodies decreases and increases, respectively, in a direction towards its surface opposite said middle plane. Cutting insert as defined in any of the previous claims, characterized in that the recess (15), the protrusion (16) and the centre (CL) of each powder body are located on a common straight imaginary line (L). Cutting insert as defined in any of the previous claims, characterized in that the recess (15) has a circular cross-section and a depth (d) in relation to the the abutting side (12) of the concerned powder body and that the protrusion (16) has the form of a truncated pyramid provided at a height (h) relative to said abutting side (12) whereby the relations are such that said depth (d) is larger than said height (h), thereby forming voids (24) in the cutting insert. Cutting insert according to claim 5, characterized int that sensors are provided in said voids (24). Cutting insert according to claim 5 or 6, characterized in that it is provided with a central fastening hole (25) the dimension of which increases or decreases in the direction towards the middle plane (M) and that the voids (24) are arranged in separate locations on opposite sides of the middle plane. Cutting insert as claimed in claim 7, characterized in that the voids (24) communicate with a channel system within the insert. Method of manufacturing a cutting insert such as defined in any of the claims 1 to 8, including the steps of using a press with a compacting chamber said press having a punch and a die, comprising the following steps: providing a punch or a die, the active surface of which comprises at least one recess and a protrusion. filling a suitable amount of powder in said compacting chamber, compacting the powder for obtaining a powder body (10) the lower side (12) of which has a form which is inverted in relation to said punch or die such that distantly provided recess (15) and protrusion (16) are obtained which are oriented such that the recess (15), the protrusion (16) and the centre (CL) of the body (10) are located on a common straight imaginary line (L), releasing said powder body from the chamber, repeating the last-mentioned three steps to obtain an additional powder body, locating the surfaces (12) of said powder bodies (10) such that those surfaces having recess and protrusion are facing each other, angularly displacing them by rotation in the plane of said surfaces, orienting the protrusions and the recesses so they are linearly located, and displacing them into mating abutment with each other, heating the assembled powder bodies up to a sintering temperature of 1350° - 1500°C in vacuum for a time period of 0.5 - 2h, and cooling said sintered body.

Inventors: JOHANSSON JAN-ERIK, LAGERBERG STIG E V, PETTERSSON LARS T, SILVER BENGT, JOHANSSON, JAN-ERIK, LAGERBERG, STIG E.V., PETTERSSON, LARS T., SILVER, BENGT
Applicants: SANDVIK AB, SANDVIK AKTIEBOLAG
Application year: 1989
Main classification: B22F7
IPC codes: B22F7, B23B27, B22F3