Tool holder having a clamp plate for transmitting clamping forces from a clamping arm to a cutting insert

#The present invention relates to a tool holder intended for chipforming machining of metallic workpieces, and especially to a clamping mechanism for clamping a cutting insert.

#There exists a variety of tool holders for the mechanical clamping of cutting inserts such as rhombic, rhomboidic and triangular indexable inserts with equal angles all around the insert. The material used for such inserts is normally cemented carbide material or ceramic material.

#A commonly used locking system for such indexable inserts includes a pin in the holder extending upwardly into the insert-receiving pocket to engage a hole in the insert located in said pocket, and means for forcing said pin to be subjected to a pivoting movement inwardly towards said holder. The forcing means is arranged to actuate the lower portion of said pin, thus urging both the pin and the insert inwards towards an upwardly extending wall formed on said holder rearwardly of said pocket. Such type of tool holder is disclosed in U.S. Pat. No. 3,314,126. The drawback of such holder, however, is that the forward nose portion of the cutting insert has a tendency of lifting off the shim plate located underneath said insert which sometimes can lead to insert failure.

#The invention will now be described more in detail by reference to the enclosed drawings, which illustrate a preferred embodiment of the invention.

#FIG. 1 is a longitudinal sectional view taken along an axis CA of a tool holder as shown in FIG. 2 according to one embodiment of the invention.

#FIG. 2 is a top plan view of a clamp and the insert of the tool holder shown in FIG. 1.

#In FIGS. 1-2 there is shown a portion of a cutting tool (preferably for turning operations) comprising a partially shown tool holder 10, the forward nose portion of which is provided with a pocket for the receipt of an indexable cutting insert 11 of polygonal shape. This insert has a rhombic basic shape and is manufactured of cemented carbide material or ceramic material. The insert has an upper flat surface 12 and a lower flat surface 13 parallel with said upper surface. The insert has a plurality of side surfaces extending perpendicularly towards said upper and lower surfaces 12, 13, two of which are designated 11a and 11b. The insert is arranged to rest in surface abutment upon a shim plate 14 having a central hole 15 engaged by a screw 16 that is threadably engaged with the holder 10 the central axis of which extends perpendicularly against the flat surfaces 12, 13 of the insert. The insert-receiving pocket includes a bottom supporting surface 17 and two support surfaces 18, 19 extending perpendicularly therefrom.

#There is a clamp arm 20 provided for the clamping of the insert into its pocket in the holder 10, said clamp arm being actuatable by means of a clamp screw 22 that extends entirely through said clamp arm and includes a threaded lower portion 21a that threadably engages a bore 21 in the holder 10. The central axis CL of said screw extends parallel with the central axis of the hole 15 in the shim. The forward end of said clamp is in the shape of a first protrusion 23 intended to engage a clamp plate 24 located between the clamp arm 20 and said insert 11, said clamp plate 24 having a central hole 25. More specifically, said first protrusion 23 is arranged, upon tightening said screw 22, to be received in said hole 25 thereby exerting a downward pressure on the clamp plate which is transmitted to the insert. Preferably, the clamp arm applies a pressure downwardly at pressing points A1 and A2 (see FIG. 2) on an upper surface 55 of the clamp plate (FIG. 8) at respective sides of a longitudinal center axis CA of the clamp arm 20. The central hole 25 is a recessed bore which is of symmetrical configuration about its vertical axis. The hole 25 includes a lower cylindrical wall and a coaxial slightly conical upper wall which expands upwards with gradually increasing diameter in the direction from the lower wall to the entrance opening of the hole 25. The forwardly facing portion (i.e., leftward facing portion in FIG. 1) of the mantle or outer surface of the protrusion 23 is given a corresponding configuration to the wall of the hole 25. The underside 24a of said clamp plate 24 is ground to a planar state and has a large surface area, whilst the lower wall of the hole 25 is cylindrical. This ensures a distribution of the clamping pressure over a large surface of the insert, which is essential, especially in case the insert is manufactured of ceramics.

#The opposite rear part of said clamp arm 20 is in the shape of a second protrusion 28 which has an inclined surface 27 that is preferably convexly shaped and arranged, upon tightening, to come into surface abutment with a correspondingly inclined surface 29a on the holder 10, as is known. The surfaces 27, 29a are inclined at the same angle relative to the central axis CL1 of said clamp screw 22. At 29b there is designated a lower support surface of the holder 10. The clamp arm 20 can be tightened by means of the screw 35 that acts against a spring 31 that is partially received in the bore 21. The spring 31 is inclined to urge the clamp upwardly and rearwardly. Mounted to the holder is a pin 32, acting as stop means, which ensures that the clamp arm 20 does not rotate upon tightening said screw 22.