GB2204511A

GB2204511A - Cutter

Info

Publication number: GB2204511A
Application number: GB08809073A
Authority: GB
Inventors: Gennady Filippovich Shaturov; Leonid Pavlovich Pozdnyakov
Original assignee: Mogilevskij Otdel Fiz T I
Current assignee: Mogilevskij Otdel Fiz T I
Priority date: 1986-09-16
Filing date: 1988-04-18
Publication date: 1988-11-16
Anticipated expiration: 2008-04-18
Also published as: HUT46577A; GB8809073D0; HU200292B; NO881945L; FI882268A; SE460350B; SE8801628L; FI882268A0; DE3690780T1; WO1988001922A1; JPH01500651A; NO881945D0; GB2204511B; SE8801628D0

Abstract

Cutter comprising a holder (1), a cutting element (4) mounted on an axle (3) and a mechanism (11) for rotation of the cutting element (4). The rotation mechanism (11) consists of a "nut-screw" pair mounted in the holder (1) parallel to the axle (3). The holder (1) serves as the nut whereas the screw (12) is provided with a section (16) shaped as a body of revolution with a quadric surface. The axle (3) is provided with a protrusion (19) contacting with the surface (16) whereby the point (20) of their contact is located beyond the plane of the geometrical axes (18, 8) of the screw (12) and the axle (3).

Description

CUTTING TOOL Technical Field 'The present invention relates to metal-removal processes and has specific reference to cutting tools.

Prior Art There is known a cutting tool (cf. USSR Inventor's Certificate No. 141716, IPC Ba3B 27/12, Bulletin No. 19, 1961) comprising a holder and a round insert which is fixed to a fulcrum pin fitting into the holder with provision for rotating integrally with the insert owing to a ratchet-and-pawl arrangement provided at the end of the fulcrum pin opposite to that where the insert is attached.

The pawl is fitted to the plunger of an electromagnet which, when energized, causes the insert to turn, whereby a portion of its cutting edge which has become blunt is set out of contact with the worKpiece. The angle through which the insert turns (5-150) depends on the number of teeth in the ratchet. If the ratchet has 72 teeth, the minimum angle of turn is 3o0:72=50. By setting the pawl to turn the ratchet through two teeth at a time, the angle increases to 5x2=100. A turn through three teeth mates this angle 5x3=15 . An angle of turn less than 50 can be obtained only by increasing the number of teeth in the ratchet but this leads to an increase in its diameter and in the overall dimensions of the cutting tool.Tnis seems to be impractical.

For the finishing depths of cut, the angle of 5-150 turned wherethrough is the insert roughly equals the angle of insert-to-worKpiece contact which is the angle correspond ing to the arc of this contact. Thus, every time the insert is being turned, a blunted portion of its cutting edge is set outside the zone of cutting defined by the angle of insert-to-workpiece contact and replaced therein by a sharp portion.

It is known that the chip formed within the angle of contact has a tnickness which is anytning but uniform. The load on a cutting edge due to the forces coming into play during machining also varies lengthwise from a minimum where the chip thickness is at a minimum to a maximum where the chip thickness is at a maximum.

The portion of a cutting edge sustaining a maximum load gets blunt and ineffective in the first place while the rest of the cutting edge exposed to a lesser load retains its ability to cut. Since some of the cutting edge has blunted, the insert-must be turned with the result that the sharp length of the cutting edge is rendered redundant.

The end point of cutting edge life is decided in this case by the life of its portion exposed to a maximum load. This is wasteful, resulting in a short specific life of the insert, i.e. in the life of a unit length of cutting edge.

An angle of turn of the insert which is greater than 50 has also an adverse effect on dimensional stability of the worn, impairing the machine tool accuracy. The point is that the distance of a worn portion of cutting edge from the axis of rotation is smaller than that of a sharp portion coming in the wake of the worn one so that in the former case the workpiece is machined to a larger size than in the latter.

Moreover, an angle of turn in excess of 50 causes instability of surface finish nis results from an unceasingly mounting bluntness of the cutting edge on the one hand and from an instantaneous cliangeover to a slurp cutting edge, replacing the blunt one, on the otner hand.

A replacement of the round insert by a well-known polygonal one is hardly practical in the known cutting tool.

A cutting edge formed by two contiguous faces of the polygon would appear outside the cutting zone defined by the angle of insert-to-worpiece contact if the insert is turned through an angle of 5-15 . An impaired machine tool accuracy is unavoidable in this case.

The means of turning the insert of the known cutting tool is of intricate design and its manufacture is labour consuming.

Disclosure of,the Invention The main object of tne present invention is to provide a cutting tool the means of turning the insert whereof is simple and arranged to cover small angles, ensuring thereby dimensional accuracy and quality surface finish of the workpiece.

This object is realized by providing a cutting tool comprising a holder, an insert fixed to a fulcrum pin fitting into the holder and a means of turning the insert integrally with the fulcrum pin relative to the holder, wherein the means of turning the insert is provided according to the invention in the form of a screw pair which is fitted to the holder parallel to the fulcrum pin, the holder forming the "nut" of the kinematic pair and a portion of tne screw being shaped as a quadratic surface of revolution which contacts a projection on a side surface of the fulcrum pin facing title screw, whereby the point of contact falls outside a plane through the axis of the screw and the fulcrum pin.

The above features of design of the means of turning the insert provided in the form of a screw pair the screw whereof is partly shaped as a quadratic surface of revolution contacting a projection on a side surface of the fulcrum pin create conditions for turning the insert through an infinitesimally small angle with the result that the cutting edge is loaded uniformly during macnining and utilized effectively. The specific life of tne insert increases three or fourfola compared vith the known cutting tools.

A small angle of turn of the insert also ensures good dimensional stability of the workpiece and provides for a high machine tool accuracy because of the distance of the cutting edge from the axis of rotation changing insignificantly in this case without an appreciable dimensional fluctuation.

A small angle of turn is conducive to a uniform surface finish, for the transition from blunt to sharp cutting takes place gradually, at shorter time intervals.

The disclosed means of turning the insert can be used in conjunction with one of polygonal configuration which is widely used in metal-removing practice. Polygonal inserts provide for machining not only the workpieces with a rectilinear generatrix but those with a stepped one as well.

It is expedient to provide the quadratic surface in the form of a cone located coaxially with the axis of the screw.

A conical surface poses no manufacturing problems.

A specified angle of turn of the insert can be obtained very accurately and without difficulty because of the speed ratio of the nut-screw-cone-fulcrum pin kinematic chain which is decided by the pitch of thread of the nut and screw, the taper angle of the cone and the distance between the point of contact of the projection with the quadratic surface and the plane through the axis of the screw and that of the fulcrum pin being high in this case.

Any inaccuracy of the angle of turn of the screw has practically no effect on the accuracy of the angle of turn of the insert.

It is also expedient to provide the quadratic surface in the form of a cylinder located eccentrically with respect to the axis of the screw.

Such a plan has a practical meaning when there is a need to obtain a variable rate of advance of the insert in response to a steady rate of advance of the screw as tnis is the case in machining intricate contours under variable cutting conditions.

It is further expedient to provide a cross at an end of the screw which is arranged to turn the screw, Abutting against stops on the machine tool when the cutting tool is on a go, the cross automatically turns the screw and - through the intermediary thereof -- the insert in accordance with a programme without the operator's participation.

Taking it all in all, the cutting tool according to the invention provides for long specific life of the insert, high machine tool accuracy and an invariably good surface finish.

The disclosed cutting tool is simple, compact, handy and reliable in operation, durable and lends itself readily for streamlined production. It may be used on univernal and automatic machine tools.

A preferred embodiment of the invention will now be described in detail by way of example with reference to the accompanying dravJings.

Summary of the Drawings Pig. 1 is a schematic general view of the cutting tool in accordance with the invention; Fig. 2 is a section on line II-II of Fig. 1, turned counterclockwise through 900 Pig. 3 is a view similar to that of Fig. 2, illustrating the arrangement of parts when the quadratic surface is a cylinder located eccentrically relative to the axis of the screw and the cross is fitted to an end thereof; Pig. 4 is a view along arrow A of Pig. 3; Pig. 5 is a fractional Schematic view of the insert and workpiece, showing their relative position in the cutting zone on an enlarged scale.

Preferred Embodiment of the Invention The cutting tool provided in accordance with the invention has a prismatic oblong holder 1 (Pig. 1) ending with a head 2 which extends beyond the top surface thereof.

A fulcrum pin 3 (Fig. 2) giving support to an insert 4 (Pigs 1, 2) is attached to the head 2. The insert 4 is a polygonal plate -- a hexagon in the case under consideration which has three cutting edges 5 (Fig. 1) each shaped as an arc of circle. The cutting edges 5 are spaced equidistantly apart, i.e. are separated by two sides from each other.

ite insert can also be shaped as a circle.

A set screw 6 with a hexagonal head 7 which extends along the axis 8 (Pig. 2) of the fulcrum pin 3 holds fast the insert 4 to the upper end of the pin 3. Two nuts 9, 9f at the threaded lower end of the fulcrum pin 3 and a disc spring 10 interposed between the upper spring 9' (Fig. 2)and the lower surface (Rig. 2) of the holder 1 provide for an interference fit between the fulcrum pin 3 and the holder 1.

A means 11 of turning the insert 4 integrally with the fulcrum pin 3 with respect to the holder 1 is provided in the form of a screw pair, also shown at 11, which is fitted to the holder 1 parallel with the fulcrum pin 3.

The holder 1 or, to be exact, a downward extending portion 2a of its head 2 serves as the "nut" of the kinematic pair.

The screw 12 of the pair 11 fits into an opening 13 of the head 2 and is provided witn a thread 14 which interacts with the nut, i.e. with the portion 2a of the head 2.

A guiding means 15 in the form of a cylinder fitting into the opening 13 is provided above the thread 14, and a quadratic surface 16 of revolution is provided above the guiding means 15.

In the disclosed embodiment of the invention, the quadratic surface 16 is a cone which tapers downwards. A faceted head 17 provided aboveqthe surface 16 is used to turn the screw, a wrench (not shown) being applied tnereto to that end.

The axis 18 of the screw 12 is parallel to the axis 8 so that the conical surface 16 is located coaxially with the screw 12.

A projection 19 (Figs. 1 and 2) which faces the screw 12 and is located on a side surface of the fulcrum pin 3 contacts the surface 16. Wne point 20 of this contact falls outside an imaginary plane through the axis 18 of the screw 12 (Pig. 2) and the axis 8 of the fulcrum pin 3.

The projection 19 has a beveled side surface 19a (Fig. 1) arranged at an anule to said plane through the axes 8 and 18.

Referring to Pigs 3 and 4, the disclosed cutting tool is shown in another embodiment of tne invention. The cutting tool comprises the same elements: a holder 1 (Fig. 4) fitting whereinto is a fulcrum pin 3 (Fig. 3), which gives support to an insert 4 (Pigs. 3, 4), and a means 21 (Fig. 3) of turning the insert 4 integrally with the fulcrum pin 3 relative to the holder 1.

The means 21 of turning is provided in the form of a screw pair, also shown at 21, which is fitted to the holder 1 parallel with the fulcrum pin 3. The holder 1 or, to be exact, a downward extending portion 2a of its head 2 serves as the nut of the kinematic pair. The screw 22 of the pair 21 fits into an opening 13 of tne head 2 and is provided with a thread 23 which interacts with the nut, i.e. with the portion 2a of the head 2. A guiding means 24 in the form of a cylinder fitting into the opening 13 is provided above the thread 23.

A quadratic surface 25 of revolution in the form of a cylinder located eccentrically with respect to the axis 18 of the screw 22 is provided above the guiding means 24, the eccentricity of the axis 26 of the cylindrical surface 25 being e. The cylindrical surface 25 contacts a projection 19 of the fulcrum pin 3, and the point of this contact falls outside an imaginary plane through the axis 18 of tne screw 22 and the axis 8 of the fulcrum pin 3.

The end 27 of the screw 22 below the thread 23 is also threaded and meshing this thread is the thread in a hub 29 of a cross 28 (Figs 3 and 4) which serves to turn the screw 22 (Fig. 3) on contacting stops 30 (Pigs.3.

and 4) on the machine tool (not shown). The cross 28 is fixed to the end 27 through its hub 29 which is threaded.

Arranged in a line, the stops 30 are spaced a distance apart from each other which is decided by the programme of machining a workpiece 31 (Fig. 5).

The cutting tool provided in accordance with the invention and illustrated in Pigs 1 and 2 operates as follows.

In machining the workpiece 31 revolving as indicated by arrow V (Fig. 5), the screw 12 is turned from time to time as the cutting edge 5 wears away within the portion 32 which is an arc corresponding to an angle Y of contact between the insert 4 and the workpiece 31. To turn the screw 12, a wrench is applied to the faceted head 17. The angle of turn varies with the cutting conditions and the speed ratio of the means 11 of turning which, in its turn, is decided by the pitch of the thread 14 of the screw 12, the taper angle of the surface 16 and the distance between the point 20 of contact of the projection 19 with the surface 16 and the plane through the axes 8 and 18. The screw 12 must be turned up before machining so that the point 20 of contact falls into the least diameter of the cone 16.

The nuts i, 9' and the disc washer 10 eliminate play and provide for an interference fit between the fulcrum pin 3 and the head 2 of the holder 1.

In the embodiment of the invention shown in Figs 3 and 4, the screw 22 is being turned automatically from time to time in the course of feeding the cutting tool in the direction indicated by arrow S (!tig. 5). The turning is effected by the cross 28 which is immovably fixed to the end 27 of the screw 22 and alternately contacts the static stops 30 on the machine tool with its arms. The angle of turn equals that made by two adjacent arms of the cross 28.

In turning, the cylindrical surface 25 of the screw 22 which has an eccentricity e relative to the axis 18 and contacts the projection 19 at tne point 20 causes the fulcrum pin 3 to turn integrally with the insert 4. The torgue required to that end is set up owing to tne distance which exists between the point 20 and the plane through the axes 8 and 18, for in either embodiment of the invention the point 20 of the contact between the projection 19 and the surface 16 or 25 is located a distance apart from the above plane.

A pilot cutting tool produced in accordance with the invention has successfully passed tests which have proved a long specific life of the insert, particularly in machining hard and tough materials, high accuracy and good surface finish of work.

The disclosed cutting tool is simple, compact, handy and reliable in operation, urable. It lends itself readily to streamlined production. The disclosed tool is suitable for use on both universal and automatic machine tools; Industrial Applicability he present invention can be of utility in machine building for finishing to various degrees of surface roughness and for machining hard and tough materials, e.g.

heat-resistant steels, using a cutting tool with a polygonal insert.

The cutting tool according to the invention can be used for turning any other structural materials as well.

Claims

C L A I M S

1. A cutting tool comprising a holder (1), an insert (4) fixed to a fulcrum pin (3) fitting into the holder (1) and a means (11) of turning the insert (4) integrally with the fulcrum pin (3) relative to the holder (1), c h a r a c b e r i z e d in that tne means (11) of turning the insert (4) is provided in the form of a screw pair which is fitted to the holler (1) parallel to the fulcrum pin (3) supporting tne insert (4), the holder (1) forms the "nut" of tue sinematic pair, a portion (16) of the screw (12) of tne kinematic pair is shaped as a quadratic surface o revolution, a side surface of the fulcrum pin (3) is provided with a projection (19) facing the screw (12) and contacting the quadratic surface 16 of revolution, whereby tne point (20) of the contact falls outside a plane tnrou$i tne axis (18) of tne screw (12) and tne axis (8) of the fulcrum pin (3).

2. A cutting tool as in claim 1, c h a r a c t e r i z e d in that the quadratic surface (1O) of revolution is shaped as a cone located coaxially with respect to tne axis W18) or the screw (12).

3. A cutting tool as in claim 1, c h a r a c t e r i z e d in tnst the quadratic surface (25) of revolution is snared as a cylinuer locate a eccentrically witn respect of the axis (16) of the screw (22).

4. A cutting tool as in claim 1, c n a r a c d e r i z e d in that a cross (28) arranged to turn tue screw (22) is provided at an end (27) of tne screw (22).