WO1998051436A1

WO1998051436A1 - Apparatus for breaking chips

Info

Publication number: WO1998051436A1
Application number: PCT/SG1998/000033
Authority: WO
Inventors: Xiaoping Li
Original assignee: National University Of Singapore
Priority date: 1997-05-09
Filing date: 1998-05-07
Publication date: 1998-11-19
Also published as: AU7356698A

Abstract

Apparatus for breaking chips is disclosed in which the chip generated during cutting is broken into small pieces by increasing the shear strain at the shear plane, which is the joint between the chip and the workpiece, until fracture occurs at the shear plane. This is achieved by forming a chip generated during cutting into a lever by guiding the chip using an arcuate surface (97) inclined to the tool cutting edge (19).

Description

APPARATUS FOR BREAKING CHIPS

FIELD OF THE INVENTION

This invention relates to apparatus for breaking chips in metal cutting.

BACKGROUND OF THE INVENTION

In metal cutting, particularly in lathing of ductile materials, continuous chips are usually

generated. Such continuous chips cause serious difficulties in operational safety, chip disposal and quality control of the machined workpiece surface. More seriously,

continuous chips can cause unpredictable jams in the cutting process, which prevent

automation of machining systems. Therefore, in metal cutting it is strongly desired to

have the chips generated in discontinuous forms. Chip breakers for metal cutting processes

are devices used for breaking chips into small pieces. Two types of chip breakers have been proposed in the prior art - obstruction devices separate from a tool insert, and

combinations of grooves and obstacles formed on the rake face of the tool insert. During

metal cutting processes, such chip breakers work to bend the chip after it has been

generated. These chip breakers do not make sure that the chip is broken during cutting and

chip breaking can be achieved only in some machining conditions. It is very difficult to

predict whether the chip will be broken by these chip breakers from a set of given

machining conditions, that is, when these chip breakers are used in metal cutting, it is uncertain that the chip will break. Further, when chips are broken by such chip breakers,

the chips usually fly in many directions and these still cause difficulties in operational safety, control of machined workpiece surface quality and chip disposal. Furthermore,

some of these chip breakers weaken the tool cutting edge and consequently shorten the tool

life. Typical examples of existing chip breakers may be seen in patent specifications

numbers US 5193947, SU 1704939, WO 9427769 and WO 951 1 102.

OBJECT OF THE INVENTION

It is the primary object of the invention to provide an improved chip breaking apparatus.

SUMMARY OF THE INVENTION

According to the invention in the first aspect there is provided apparatus for breaking chips in a metal cutting process in which a chip is parted from a workpiece by a tool at the shear

plane of chip formation, comprising lever forming means for forming a chip into a lever for

exerting a force to increase shear strain at the shear plane until fracture occurs at the shear

plane and wherein the lever forming means comprises an arcuate surface arranged to be

inclined to a cutting edge of the tool.

Preferably the arcuate surface is a two dimensionally arcuate surface for example a section of a cylinder. Alternatively, the arcuate surface may be a three dimensionally arcuate

surface for example a section of a sphere.

The arcuate surface may provide the function of a pivoting surface for bending a said chip

towards a reaction surface and forming a fulcrum point in contact with the chip, a guiding surface for guiding the chip to flow towards the reaction surface and a side flow restricting

surface for restricting sideways flow of the chip.

Lever means may comprise a plurality of arcuate surfaces and several lever means may be

disposed as part of the same chip breaker.

The chip breaker may be formed together with the cutting edge of a tool insert and several

cutting edges may be combined into a tool insert each having associated chip breaking

apparatus.

According to the invention in a second aspect, there is provided apparatus for breaking chips in a metal cutting process in which a chip is parted from a workpiece by a tool at the shear plane of chip formation, comprising lever forming means for forming a chip into a

lever for exerting a force to increase shear strain at the shear plane until fracture occurs at

the shear plane and wherein the lever forming means comprises an arcuate surface arranged

to form a pivoting surface for bending a said chip towards a reaction surface and forming a fulcrum point in contact with the said chip, a guiding surface for guiding the said chip to

flow towards said reaction surface and a side flow restricting surface for restricting

sideways flow of the said chip.

According to the invention in a third aspect, there is provided apparatus for breaking chips in a metal cutting process in which a chip is parted from a workpiece by a tool at the shear

plane of chip formation, comprising a plurality of lever forming means for forming a chip

into a lever for exerting a force to increase shear strain at the shear plane until fracture occurs at the shear plane.

In the described embodiments of the invention, a shear plane fracturing method for chip

breaking in metal cutting is disclosed. In this method, the chips generated in metal cutting

are broken by increasing the shear stress and thus strain at the shear plane of chip

formation until fracture occurs at the shear plane. A leverage chip breaking approach is

also disclosed in which the chip is forced to break into small pieces by a process which

forms the chip as soon as it has been generated from the shear plane into a lever of curled form, in which the head of the chip is the load-lifting point receiving force from a fixed

body, the contact between the chip and the pivoting plane of the chip breaker is the

fulcrum, and the root of the chip is the force-exerting point exerting a force acting along

the shear plane to increase the shear strain until fracture along the shear plane occurs.

The chip breaker of the described embodiments of the present invention breaks the chips

generated during metal cutting processes including turning, facing, boring, parting and other

metal cutting processes in which chip breaking is required, at most combinations of

machining conditions including the workpiece material properties, cooling conditions,

cutting speed, feed rate and depth of cut, into small pieces in forms of less than one circle

of small radius. The chip breaker guides the broken chips to drop gently from the tool main flank to the container of the machine, such that the operational safety, machined workpiece

surface quality and chip disposal efficiency are ensured. The chip breaker reduces the force

acting on the tool cutting edge by sharing the force acting on the tool rake face, reduces

temperature at the tool cutting region by reducing cutting force at the tool rake face and by

breaking the chips frequently, and consequently reduces the tool wear rate and increases the tool life. The chip breaker works with inserts of all kinds of shapes and obviates the need

for geometries constructed on the tool inserts for chip breaking purposes, such that the cost

on tool inserts can be substantially reduced by using flat rake face inserts rather than

inserts with complicated geometry at the rake face. The breaker may be constructed with

the tool insert, in which the chip breaker body is formed on the tool rake face.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example, with reference to

the accompanying drawings, in which:

FIG.1 is an illustration showing the general principle of the shear plane fracturing method

for chip breaking used in the present invention.

FIG.2 is a perspective view showing the structure of a chip breaker using the principle of

FIG. 1 for turning with a rectangular tool insert.

FIG.3 is a perspective view of a chip breaker showing a variation of the chip breaking body

of the chip breaker as shown in FIG.2.

FIG.4 is a perspective view of a chip breaker showing another variation of the chip

breaking body of the chip breaker as shown in FIG.2.

FIG.5 is a perspective view of a chip breaker showing another variation of the chip breaking body of the chip breaker as shown in FIG.2.

FIG.6 is a perspective view of a chip breaker showing another variation of the chip

breaking body of the chip breaker as shown in FIG.2.

FIG.7 is a perspective view similar to FIG. 2 of a first embodiment of the chip breaker

according to the present invention.

FIG. 8 is a perspective view similar to FIG. 2 of a second embodiment of a chip breaker

according to the present invention.

FIG. 9 is a perspective view similar to FIG. 2 of a third embodiment of a chip breaker

according to the present invention.

FIG. 10 is a perspective view of a fourth embodiment of a chip breaker according to the

present invention.

FIG.11 is a perspective view of a fifth embodiment of the chip breaker according to the

present invention in which the chip breaker of the present invention as shown in FIG 10 is

constructed and formed together with the tool.

FIG.12 is a perspective view of the sixth embodiment of the chip breaker according to the

present invention showing a multiple cutting edge tool inserts having compact chip breaker

cutting tools as shown in FIG.11. DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

During a metal cutting process, as shown in FIG.l , a chip 1 is formed from cutting off a

layer of material 2 from the workpiece 3 by the cutting tool 4. The chip formation is a

process of material velocity discontinuation, in which the layer of the work material to be

cut is forced to change its moving velocity from a velocity indicated by vector 5 to a

velocity indicated by vector 6 within a narrow deformation zone 7, the so called "shear

plane". At the shear plane the workpiece material is shear stressed and strained, and is formed into the chip flowing along the tool rake face 10.

In a metal cutting process, the shear strain at the shear plane is a constant when the tool rake angle and the shear angle (the angle between the cutting direction and the shear plane)

are unchanged. Different materials of the workpiece respond differently to the same value of shear strain at the shear plane. A brittle material tends to fracture at the shear plane

after undergoing only a small shear strain and consequently forms discontinuous chips.

Therefore, in cutting of a brittle material, such as a cast iron, discontinuous chips are

usually generated and chip breaking is not a problem. A ductile material tends to fracture

at the shear plane only after it has undergone a large enough shear strain. How large a strain is enough for the fracture to occur depends on the ductility of the material, which is a

function of temperature and strain-rate in the cutting region. The ductility decreases

linearly with the temperature and increases linearly with the logarithm of the strain-rate.

This nature of the material properties means that at low cutting speeds the ductility

decreases with increasing the speed (due to the domination of strain-rate effect), and at high cutting speeds the ductility increases with increasing the speed (due to the domination of

the temperature effect). That is, the value of shear strain leading to fracture at the shear

plane varies with workpiece material ductility which is a function of cutting speed. For the

same material, the value of shear strain leading to fracture at the shear plane is lower in

cutting with a coolant compared to in cutting without a coolant, because the cooling

reduces the ductility of workpiece material in the cutting region. In general, in cutting of

ductile materials, the shear strain at the shear plane due to chip formation is not large

enough to cause fracture, and therefore continuous chips are usually generated, although in

cutting of some hardened steels with cooling or at low cutting speeds, fracture may occur at

the shear plane and discontinuous chips may be generated.

The shear plane fracturing method for chip breaking to be described aims to break the chips

generated during metal cutting processes at all machining conditions, regardless of

differences in the work material properties, cooling conditions and cutting conditions, by

increasing, in addition to the shear strain due to chip formation for workpiece material removal, the shear strain at the shear plane to whatever a value is necessary to lead to

fracture at the shear plane.

The increasing of the shear strain can be provided by the leverage chip breaking approach

of the described embodiments of the present invention. The approach is as shown in FIG.l. The chip 1 is firstly generated from the primary deformation zone (the shear plane 7) and is

secondly deformed along its back in contact with the tool rake face 10 by friction at the tool-chip interface. The secondary deformation causes the chip to curl up ( because of

surface expansion at the back) and flow away from the rake face. Driven by the chip generation at the shear plane 7, the chip flows and then curls further when its head 1 1

reaches the first fixed (on the tool) plane 12, caused by the force from the shear plane 7

acting on the root 8 of the chip and the reaction force from plane 12 acting on the head 1 1

of the chip. The chip then flows up until its head 1 1 reaches the second fixed (on the tool)

plane 14. As soon as the head of the chip reaches plane 14, a reaction force from plane

14 acting on the head 1 1 of the chip will work together with the force from the shear plane

acting on the root 8 of the chip to form the chip into a curled form of small radius. The chip then flows along an arc, with slight elastic spring back in its front portion and with its

side-flow (caused by the side-curl of the chip) being restricted by the third fixed (on the

tool) plane 13, until its head 1 1 is stopped by the fourth fixed (on the tool) plane 9. As

soon as the chip 1 reaches plane 9 with its head 11 , it acts as a lever of curled form, in

which the head 1 1 is the load-lifting point receiving a force from plane 9, the contact

between the chip 1 and plane 12 is the fulcrum, and the root 8 of the chip, joining the workpiece 3 at the shear plane 7, is the force-exerting point exerting a force additional to

the shear force at the shear plane for chip formation until fracture occurs at the shear plane

7.

FIG.2 shows a chip breaker constructed in accordance with the above for turning processes. The chip breaker 22 is clamped together with the tool insert 18 on a tool holder. The bottom face 16 of the chip breaker is in contact with the rake face 21 of the tool insert.

The clamping face 17 of the chip breaker is in contact with the clamp of the tool holder

(not shown). The chip breaking body of the chip breaker is adjacent to the main cutting

edge 19, and comprises a pivoting plane 12 which is inclined to the tool rake face 21, a

side-flow restricting plane 13 which is approximately perpendicular to cutting edge 19, an up-curl guiding plane 14 and a supplementary reaction plane 15. During cutting, the chip

grows from the shear plane and flows along the tool rake face 21 towards plane 12 of the

chip breaker, with an up-curl caused by friction and thermal expansion at the tool-chip

interface and a side-curl caused by differences in the material flow velocities along the

main cutting edge 19 and tool nose 20. Once the head of the chip reaches plane 12, the

body of the chip is bent, and the chip is forced to curl further up when it flows over plane

12, with compressed elastic and plastic defoπnation on the inner-side of the curl and tensile

elastic and plastic deformation on the outer-side of the curl. The larger the feed rate of

cutting, the bigger the plastic deformation on the two sides of the chip. The plastic

deformation will prevent the curled shape of the chip from opening. With the cutting

continuing, due to the side-curling of the chip formation process, the chip is pushed such

that a side of the chip reaches plane 13, and the side-flow of the chip is then restricted by

plane 13. The curled chip will then flow outwards from the chip breaker 22 and then flows

down towards the tool main flank. As soon as the head of the chip has reached the tool main flank face 23, it exerts a force on the flank face 23 and at the same time receives a

reactive force from the flank face 23. The chip is then acting as a lever of curled form, in

which the head of the chip is the load-lifting point receiving a force from the tool flank

face 23, the contact between the chip and plane 12 is the fulcrum, and the root of the chip,

which joins the workpiece at the shear plane, is the force-exerting point exerting a force additional to the shear force at the shear plane. Since the distance from the fulcrum to the head of the chip is much larger than the distance from the fulcrum to the root of the chip,

the force exerted at the shear plane for the additional strain leading to fracture at the shear

plane requires only a small load-lifting force applied on the head of the chip. At this stage,

if the work material is of low ductility or the feed rate is large, the load-lifting force is not large enough to open up the curled form of the chip before the chip acts as a lever to cause

fracture at the shear plane. If the workpiece material is of high ductility or the feed rate is

small, however, the chip once has been generated from the shear plane and bent by plane

12 of the chip breaker, is restricted by both planes 13 and 14 to flow up then down towards

the tool flank. As soon as the chip head has reached the flank face, it acts as a lever

exerting a force at the shear plane as described in the above. In cases like this, there are

two possibilities of breaking the chip at the shear plane. If at the head of the chip the load- lifting force required is not large enough to open up the curled chip before the fracture

occurs, the chip will be broken as described in the above cases with low ductility of

workpiece material or large feed rate. Otherwise, the curled chip will be opened up until

the opening is stopped by plane 15. As soon as the body of the chip, which is on the load-

lifting side of the lever, has reached plane 15, there will be a frictional force between the

chip and plane 15, which is a further load-lifting force of the lever. The lever will then

exert a further force from the root of the chip to the shear plane until fracture occurs at the

shear plane. As soon as the fracture has occurred, the chip will break at its root, the forces

acting on the chip will disappear and the next cycle of chip generating and breaking will

start. The broken chip will then be pushed at its root by the head of the next chip in generation, towards the tool flank, and will drop downwards from the tool flank, before the

head of the next chip reaches the tool main flank face 23.

The broken chips generated in this way are in the shape of a "9". If the cutting feed rate is

large, there is a possibility that as soon as the fracture has occurred, the fracturing zone

which binds the broken chip and the new chip growing from the shear plane will be pushed

out by the new chip and broken on its way towards to the tool flank when it is bent by the opening of the arc formed by the broken chip and the new ship. The opening is caused by

the reactive force on the head of the broken chip. At the mean time for the opening, the

arc formed by the broken chip and new chip may work as a lever to fracture the new chip

at its root (the shear plane). The new fracturing zone will then be pushed out to start

another chip breaking cycle, while the old fracturing zone is bent and broken. The broken

chips generated in this way are in the shape of a "c".

The chip breaking body of the chip breaker as described in FIG.2 can be constructed, by

varying its geometrical parameters, in many forms to suit the needs of practical application

of the chip breaker or to meet production requirements. The geometrical parameters of the

chip breaking body include (see FIG. 2):

1) the angle between the tool rake face 21 and the pivoting plane 12 of the chip breaking

body, α,

2) the distance from the tool main cutting edge to the pivoting plane 12 of the chip

breaking body, b,

3) the width of the pivoting plane 12, w,

4) the angle between the pivoting plane 12 and the up-curl guiding plane 14, β,

5) the length of the upper-side of the pivoting plane which joins with the lower-side of the

up-curl guiding plane, /, and

6) the angle between the side-flow restricting plane 13 of the chip breaking body and the

tool main cutting edge 19, Ψ.

In the chip breaking body of the chip breaker as shown in FIG.2, for simplicity, the angle Ψ is designed to be approximately perpendicular to the tool main cutting edge. An

optimum value for this angle should be determined according to the chip side-flow angle η

which is commonly defined as the angle between the flow direction of the chip at the

cutting region and the normal to the cutting edge in the rake face of the tool (see FIG. 2).

The value of Ψ should be determined such that, during the chip formation and breaking

process, the chip can flow out from the chamber of the chip breaking body and on the other

hand its side-flow is restricted by the side-flow restricting plane 13 so that the leverage

chip breaking process of the present invention can be achieved. Therefore, an optimum

design for the angle Ψ should follow the equation

ψ = 90° - η (1)

In view of the fact that the chip side-flow angle η varies with machining conditions,

especially with the combination of the radius of the tool corner, feed rate and depth of cut

(when the radius of the tool corner varies from 0.4 to 1.2, feed rate varies from 0.1 to 0.3

and depth of cut varies from 0.3 to 4, the chip side-flow angle varies within the range from

5 degrees to 70 degrees), for simplicity, the angle Ψ can be assigned with a fixed value

which is calculated from equation (1) using a usual value of the chip side-flow angle.

FIG.3 shows a chip breaker similar to Fig. 2, having an angle Ψ different from 90 degrees.

In this embodiment the side-flow restricting plane 93 of the chip breaking body in the chip

breaker 22 is perpendicular to the tool rake face 21, and the angle between the plane 93

and the tool main cutting edge 19 is less than 90 degrees measured clockwise from the tool

cutting edge 19. A design for the chip breaking body without having the supplementary reaction plane 15 as

shown in FIG.2 can be constructed by properly determining the geometrical parameters ,

b, w, / and β of the chip breaking body, using the correlations between the geometrical

parameters of the chip breaking body, machining conditions and radius of the broken chips,

such that the chip, when it flows out from the chamber formed by the pivoting plane 12,

side-flow restricting plane 13 and up-curl guiding plane 14, is highly strain-hardened in curled form of small radius, thus the supplementary reaction plane 15 is not needed in the

chip breaking process because the chip under such condition will not be opened up to touch

the supplementary plane 15 before fracture caused by the leverage chip breaking process

occurs at the shear plane.

Expressions for the correlation between the geometrical parameters of the chip breaking

body, machining conditions and radius of the broken chips can be derived from the

geometry of the chip breaking body at the cutting region. By neglecting the elastic spring

back of the chip, the correlation between the radius of a chip broken by the chip breaker, r,

and the parameters b and α can be represented by the equation

b-h r=- tan—

(2)

where h is the tool-chip contact length (see FIG. 2) resulted from machining conditions,

namely the feed rate, tool rake angle and workpiece material flow stress properties which

are functions of strain-rate and temperature. The smaller the value for b, the smaller the

radius of the chip. However, b must be larger than h to allow the chip to be generated naturally from the cutting region. An increase in the angle α will decrease the radius of the

chip, but on the other hand it will also, during the leverage chip breaking process, decrease

the force component exerting from the root of the chip to the shear plane, which is to be

avoided.

The smaller the values for W and β, the smaller the radius of the chip and also the smaller

the size of the chip breaking body. However, W and β have to be large enough to allow

the chip flow out from the chamber of the chip breaking body. The inventor has found that

b ≤ w ≤ 5b (3) and

90° < β < 130° (⁴)

The length / has to be determined such that the chip side-flow is restricted by the side-flow

restricting plane 13 (see FIG.2) to be within the limit required by the leverage chip

breaking process, and on the other hand the chip can flow out from the chip breaking body.

The length 1 should fall in the range:

d≤l≤lOd (5)

where d is the width of cut (see FIG.2).

FIG.4 shows a chip breaker having another design of the chip breaking body in the chip

breaker as shown in FIG.2. In this chip breaker, the chip breaking body is formed by the

pivoting plane 12, the side-flow restricting plane 93 and the up-curl guiding plane 14. The supplementary reaction plane 15 as shown in FIG.2 is not included in the chip breaking

body. In such a design, the geometrical parameters of the chip breaking body, α, b, w, /

and β, are determined, using expressions (2), (3), (4) and (5), such that the chip, when

flowing out from the chip breaking body, is highly strain-hardened in curled form of small

radius and with its side-slow being restricted by the side-flow restricted plane 93.

Therefore, the supplementary reaction plane 15 as shown in FIG.2 is not needed in this design.

In the design of the chip breaking body as shown in FIG.4, the side-flow restricting plane

93 is not needed in cutting under certain ranges of machining conditions, in which the chip,

when it flows out from the corner formed by the pivoting plane 12 and up-curl guiding plane 14, is highly strain-hardened in curled form of small radius with its side-flow being

naturally (without being restricted by the side-flow restricting plane) under the limit

required by the leverage chip breaking process. One of the examples under the certain

ranges of machining conditions stated above is in turning of low carbon steels at the feed

rate equal to and larger than 0.15 mm/rev when the ratio of the radius of the tool corner to

the width of cut is less than or equal to 0.5. In such cutting cases, the side-flow restricting

plane 93 as shown in FIG.4 is not needed for chip breaking, and it can be removed from

the design of the chip breaking body to simplify the structure of the chip breaker. This is

illustrated in FIG.5 which shows a chip breaker, showing another modification of the chip

breaking body in the chip breaker shown in FIG.2. In this embodiment the chip breaking

body is formed only by two planes, the pivoting plane 12 and the up-curl guiding plane 14.

To ensure the chip is broken by the leverage chip breaking method, the up-curl guiding plane 14 shown in FIG.5 cannot be removed for further simplification based on the

structural design as shown in FIG.5, because plane 14 is necessary to ensure that the chip is

formed into a lever for chip breaking. However, the pivoting plane 12 and up-curl guiding

plane 14 in the chip breaker design as shown in FIG.5 can be combined into an up-curl

guiding and pivoting surface which is designed such that it provides both the up-curl

guiding function for forming the chip into a level of curled form and the pivoting function

for the leverage chip breaking process. FIG.6 shows a chip breaker having another design

of the chip breaking body in the chip breaker as shown in FIG.2. In this design, the chip

breaker 22 has a chip breaking body formed by a side-flow restricting plane 13 and an

arcuate up-curl guiding and pivoting surface 96. The parameter b is the same as the one

shown on FIG.2. The radius R, height H and the centre co-ordinates x and y for the arcuate

surface 96 is determined such that surface 96 will work together with the side-flow

restricting plane 13 to form the chip into a lever of curled form, and as soon as the head of

the chip has received a reaction force, it will work, through the contact of the plane 96 with

the back of the chip, as the fulcrum for pivoting in the leverage chip breaking process. As

an example for designing the arcuate up-curl guiding and pivoting surface 96, in turning of

low carbon steels at cutting speeds from lOOm/min to 300m/min, feed rates from 0.03

mm/rev to 0.3 mm/rev, the parameters R, H, x and y can be in the ranges from 1.5 mm to 5

mm, from 1 mm to 6 mm, from 0 mm to 0.5 mm and from 1 mm to 6 mm, respectively.

FIG. 6 shows a first embodiment of the chip breaker of the present invention, in which the

pivoting plane 12, up-curl guiding plane 14 and side-curl restricting plane 13 as shown in

FIG.2 are combined into an arcuate leverage surface 97. In the embodiment of FIG. 2, the

leverage surface 97 is a portion of a cylindrical surface having its axis inclined to the tool main cutting edge 19. The angle between the axis and the cutting edge 19 within a plane

parallel to the tool rake face 21 is determined according to the chip flow angle η as shown

in FIG. 1 and is in the range from η/2 to η. The location of the axis, the radius of the

cylindrical surface and the height H are determined in a way such that the leverage surface

will form the chip into a lever for chip breaking along the shear plane.

The leverage surface can be a 2-dimensionally arcuate surface, that is to say a surface

which curves in two dimensions but is linear in the third, such as that shown in Fig 7, or a

3 -dimensionally arcuate surface, for example a part spherical surface, part ellipsoidal or variably curved surface, or a combination of a number of arcuate surfaces, so long as it

forms the chip into a lever for chip breaking along the shear plane.

A second embodiment of the invention is shown in FIG. 8 in which an arcuate leverage

surface 98 is provided which is part-spherical; the part-sphere being inclined to the tool

cutting edge 19.

A third embodiment of the invention is shown in FIG. 9 in which a plurality of inclined

arcuate segments 99 are connected by side flow restricting planes 99a in a saw-tooth

manner. The segments may be of other desired 3 -dimensionally arcuate surfaces as

envisioned above.

Optimal chip breaking covering a wide range of cutting conditions is provided in a fourth

embodiment of a chip breaker of the present invention in which the chip breaking body is

formed by a number of the leverage surfaces. The fourth embodiment is shown in FIG.10 in which the chip breaking body is formed by 4 leverage surfaces: 100, 101 , 102 and 105

similar to the leverage surface 97 shown in FIG.7. The axis, radius and height of each of

the 4 surfaces are determined independently according to the corresponding ranges of feed

rate and depth of cut such that each surface works most effectively for chip breaking in

cutting under the corresponding cutting conditions.

FIG.11 shows a single cutting edge chip breaker tool insert being a fifth embodiment of the

present invention, in which the chip breaker as shown in FIG.10 is constructed and formed

together with the tool. The tool is designed to have two rake faces. The first rake face 104

has a smaller rake angle for strength of the cutting edge 19. The second rake face 21,

which forms the chip breaking body together with the leverage surfaces 100, 101, 102 and

103, has a larger rake angle such that the leverage surfaces 100, 101, 102 and 103 of the

chip breaking body are sufficiently high without exceeding the top level face 105 of the

tool.

FIG.12 shows a multiple cutting edge chip breaker tool insert being a sixth embodiment of

the present invention, in which each of the cutting edges 105-112 is formed together with

the chip breaking body as shown in FIG.10.

The manufacturing of the chip breaker involves only simple processes of machining and

surface hardening in the case of tool steel manufacturing materials, or compression and

sintering in the case of tungsten carbide or ceramic manufacturing materials.

In the present drawings only embodiments of the chip breaker constructed according to the present invention have been illustrated for lathing processes. This is because problems

caused by continuous chips in those processes are more serious compared to other metal

cutting processes, such as milling. However chip breakers of the present invention are

applicable for other metal cutting processes.

In the above described drawings, embodiments of the chip breaker for cutting with flat rake

face insert tools using tool holders with a clamp on top of the chip breaker have been

illustrated. This is not to be construed as limitative and chip breakers with other ways of

being clamped, such as having a hole in the body of the chip breaker for locating the clamp

or for fixing the chip breaker together with the tool insert on the tool holder, can be

constructed according to the present invention. It is also possible to construct the chip

breaker together with a tool insert to form a chip breaker insert of the present invention, which combines at least one chip breaking body of the present invention and the tool insert.

The chip breaker of this invention works under machining conditions with and without a

coolant. In dry cutting with the chip breaker, the chip will be broken into small pieces of

less than one circle; when a coolant is applied to cutting with the chip breaker, the chip will still be broken into small pieces in less than one circle, which is similar to dry cutting,

and the radii of the broken chip circles will be smaller and more consistent compared to

those in dry cutting, because the ductility of the chip material is reduced by cooling.

Claims

1. Apparatus for breaking chips in a metal cutting process in which a chip is parted from a

workpiece by a tool at the shear plane of chip formation, comprising lever forming means for forming a chip into a lever for exerting a force to increase shear strain at the shear

plane until fracture occurs at the shear plane and wherein the lever forming means

comprises an arcuate surface arranged to be inclined to a cutting edge of the tool.

2. Apparatus as claimed in claim 1 wherein the arcuate surface is a two-dimensionally

arcuate surface.

3. Apparatus as claimed in claim 2 wherein the surface is a portion of a cylinder.

4. Apparatus as claimed in claim 1 wherein the arcuate surface is a three dimensionally

arcuate surface.

5. Apparatus as claimed in claim 4 wherein the arcuate surface is a portion of a sphere.

6. Apparatus as claimed in any one of the preceding claims wherein the lever means

comprises a plurality of said arcuate surfaces.

7. Apparatus as claimed in claim 6 wherein the arcuate surfaces are connected by chip side

flow restricting surfaces.

8. Apparatus as claimed in any one of the preceding claims wherein the lever forming

means is arranged to form a pivoting surface for bending a said chip towards a reaction

surface and forming a fulcrum point in contact with the said chip, a guiding surface for

guiding the said chip to flow towards said reaction surface and a side flow restricting

surface for restricting sideways flow of the said chip.

9. Apparatus as claimed in any one of the preceding claims comprising a plurality of said

lever means.

10. In combination, apparatus as claimed in any one of the preceding claims and a tool

insert, the tool insert having a cutting edge and providing a reaction surface for the lever

means.

1 1. In combination, apparatus as claimed in any one of claims 1 to 9 and a workpiece, the

workpiece providing a reaction surface for the lever means.

12. Apparatus as claimed in any one of claims 1 to 9 constructed together with a tool

insert.

13. A tool insert having a plurality of cutting edges each having associated chip breaking

apparatus as claimed in claim 12.

14. Apparatus for breaking chips in a metal cutting process in which a chip is parted from

a workpiece by a tool at the shear plane of chip formation, comprising lever forming means for forming a chip into a lever for exerting a force to increase shear strain at the shear

comprises an arcuate surface arranged to form a pivoting surface for bending a said chip towards a reaction surface and forming a fulcrum point in contact with the said chip, a

guiding surface for guiding the said chip to flow towards said reaction surface and a side

flow restricting surface for restricting sideways flow of the said chip.

15. Apparatus for breaking chips in a metal cutting process in which a chip is parted from

a workpiece by a tool at the shear plane of chip formation, comprising a plurality of lever

forming means for forming a chip into a lever for exerting a force to increase shear strain

at the shear plane until fracture occurs at the shear plane.