WO2008102324A1

WO2008102324A1 - Cutting elements

Info

Publication number: WO2008102324A1
Application number: PCT/IB2008/050649
Authority: WO
Inventors: Klaus Tank; Moosa Mahomed Adia; Konstantin Evgenievich Morozov
Original assignee: Element Six (Production) (Pty) Ltd
Priority date: 2007-02-23
Filing date: 2008-02-22
Publication date: 2008-08-28

Abstract

The invention is for a cutting element comprising a layer or table (10) of superhard abrasive material presenting a working surface (14,), a side surface (16,) and a peripheral edge (18) between the working surface (14) and the side surface (16). The peripheral edge (18) is defined by a leading edge chamfer (22) having an edge contiguous with the working surface (14), a trailing edge chamfer (24) and a break-in chamfer (20) between the leading edge chamfer (22) and the trailing chamfer (24). The trailing chamfer (24) is contiguous with the break-in chamfer (20) along a line of intersection (26) which defines a cutting edge for the break-in chamfer (20). The leading edge (22) chamfer may comprise more than one section and its length may be greater than the length of the break-in chamfer (20).

Description

CUTTING ELEMENTS

BACKGROUND OF THE INVENTION

The present invention relates to superhard abrasive material cutting alements, particularly for earth boring bits. More specifically the invention relates to the design of the cutting edge of the cutting elements in order to improve the life and drilling efficiency of the cutting elements, in particular when drilling hard formations. These cutting elements are referred to in the art as "cutters" and comprise a layer or table of superhard abrasive, generally polycrystalline diamond (also known as PDC or PCD), generally bonded to a substrate.

The manner in which a PDC cutter wears is illustrated by Figure 12. ^'he wear area is normally calculated from the width and depth of the wear car.

I. The break-in stage is when the cutter is new and the cutting edge is sharp, and is depicted by a steep increase in wear area. This occurs because the edge is brittle and cutting forces are concentrated on a very small area, resulting in a high stress concentration which causes micro-chipping of the edge. From the literature it is found that this stage is also characterized by a peak in temperature at the edge over a very localized zone no more than 0.5 mm in length and could exceed the degradation temperature of diamond of ~700°C for a short space of time until the peak stresses drop off as the wear flat increases in size

II. The steady-state wear stage occurs after the cutting edge has stabilized and a sizeable wear scar appears and the forces exerted

over the larger area become less concentrated and cutting temperature also drops off. The wear stabilizes to a slow rate until unstable wear starts to take place.

III. The wear-out stage is characterized by unstable and rapid wear associated with large scale break down of the cutting edge.

Much of the prior art in this field {chamfers and edge design of cutters) has been aimed at protecting the new unused diamond or other superhard abrasive on the cutter against impact damage until it has worn substantially from the formation cutting process. After this stage of the cutter life, termed the break-in stage, it is assumed in the prior art that the tendency of the diamond table to chip and spali has been markedly reduced. For some time, it has been known in the art that annular chamfers on the diamond table have enhanced the durability of the cutters. Subsequent to the original invention of Dennis (US Re 32,036), there have been several edge design concepts revolving around chamfer designs by varying chamfer angles and sizes with single and multiple chamfers. The prior art may be classified into two groups, namely, the edge designs which pertain to:

a. "Thin" diamond tables (< 1 mm), and b. "Thick" or "double thick" diamond tables (> 1 mm and < 4 mm).

Generally, single chamfers have been sufficient to enhance the durability of thin tabled PDC. However, these cutters do not have the required life or drilling efficiency when drilfing the widely varying formations drilled today, especially when drilling the harder formations. One such shortcoming is the rapid wear of thin PDC. Attempts to overcome the deficiencies of the PDC have resulted in the development of thick or double thick diamond PDC. There is an optimum thickness of the diamond layer, beyond which sintering of the diamond in the HPHT process becomes difficult, resulting in poor sintering or poor diamond to diamond bonding. This optimum appears to be around 2mm. However, besides manufacturing difficulties, thick PDC presents its own series of problems and in any case suffers from the same impact damage and spalling problem when the PDC is still new and sharp. The problems are in fact worse for thick tables as they tend to be brittle and prone to impact damage resulting in the loss of large volumes of diamond.

In most, if not all, of the cutting elements of the prior art, the intention has been to overcome the initial tendency of the diamond table to chip and spall during the break-in stage of the wear of the PDC. It has been postulated in the prior art that, once this break-in stage has been controlled, and a substantial wear flat is generated, then the cutting forces are spread over a larger area, and the tendency of the diamond layer to chip and spall has been overcome.

Examples of chamfered PDC cutting elements can be found described in US patents nos. 5,706,906, 6,000,483, 6,202,770, 5,437,343, 6,672,406, 5,979,579, 6,230,828, 6,050,354, 4,109,737, 6,935,444 and 5,881 ,830.

In order to increase the life of cutters, using thick diamond tables is one approach, but this is fraught with problems as discussed above. The use of high strength and high hardness diamond tables is another approach. The latter two properties of the diamond table result in very high wear resistance of the table. One negative aspect of this approach is that high strength and high hardness diamond tables are also brittle and have a tendency to chip and spall easily when loaded. Another downside is that the high wear resistance of the high strength diamond tables results in low wear of the cutting edge, resulting in a low wear scar area, which in turn means that the resultant cutting force is concentrated over a much smaller area than if the diamond table were of lower wear resistance. This concentrated load results in a high localized stress which then causes chipping or spailing of the diamond table, if the stress resulting from drilling forces or impact forces exceeds the strength of the diamond table.

The prior art cutters address the problems of chipping and spalling during the break-in stage of the cutting life of a PCD cutter. However, such cutters are prone to chipping and spalling during later stages of the cutting life, namely the steady state wear stage or regime and the wear-out stage. None of the prior art cutters addresses this problem.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a cutting element, particularly one for an earth boring bit, comprises: a layer or table of superhard abrasive material presenting a working surface; a side surface and a peripheral edge between the working surface and the side surface, the peripheral edge being defined by : a leading edge chamfer having an edge contiguous with the working surface, a trailing edge chamfer or landing chamfer, and a break-in chamfer between the leading edge chamfer and the trailing edge chamfer or landing chamfer, the trailing edge chamfer or landing chamfer being contiguous with the break-in chamfer along a line of intersection, which line of intersection defines a cutting edge for the break-in chamfer.

In one preferred form of the invention, the length of the leading edge chamfer is greater than that of the break-in chamfer.

In another preferred form of the invention, the peripheral edge includes a trailing chamfer and a landing chamfer, the landing chamfer being between the trailing chamfer and the break-in chamfer.

The length (or width) of a chamfer is the distance between the major edges of the chamfer. In this preferred form of the invention the leading edge chamfer has a length greater than that of the break-in chamfer. This has the consequence that the angle which the leading edge chamfer makes with the working surface is shallower than that of the break-in chamfer. It has been found that cutting elements of this form of the invention have greater chip and spall resistance than prior art cutting elements during not only the break-in stage, but also during the steady state wear regime and wear-out stages of the cutting life of the cutting element. Thus, the cutting element has excellent chipping and spalling resistance during the entire cutting life. In contrast, the chamfered cutting elements of the prior art are aimed solely at ameliorating chipping and spalling of the superhard abrasive table during the break-in stage, and are worn away soon thereafter.

The length of the leading edge chamfer is preferably as long as possible, and will depend on the overall dimensions of the superhard abrasive table.

The leading edge chamfer may comprise more than one section. If there is more than one section then at least one of the sections may have a length greater than that of the break-in chamfer and/or the sum of the lengths of the sections may be greater than that of the break-in chamfer. The sections are preferably contiguous.

In one preferred form of the invention, the leading edge chamfer forms an angle of 10 to 30 degrees, more preferably 15 to 25 degrees, with the working surface.

The leading edge chamfer and the break-in chamfer are preferably contiguous.

The leading edge chamfer preferably has an edge contiguous with an edge of the break-in chamfer and an opposite edge contiguous with the working surface of the table.

The peripheral edge configuration of the cutting element of the invention also includes a trailing edge chamfer or landing edge chamfer, or both such chamfers. The traiiing edge chamfer is a chamfer which does not come into contact with the workpiece during use of the cutting element. The landing chamfer is a chamfer which does come into contact with the workpiece during use of the cutting element. The trailing edge chamfer or landing chamfer is contiguous with the break-in chamfer along a line of intersection which line of intersection defines a cutting edge for the break-in chamfer. When the peripheral edge configuration includes both a landing chamfer and a trailing chamfer, it is the landing chamfer which will be contiguous with the break-in chamfer.

The provision of a trailing edge chamfer significantly delays the onset of chipping and spalϋng occurring on the trailing edge of the table during cutting, particularly during the steady-state stage of the cutting life of the cutting element.

The landing chamfer is typically short having a length of no more than 0.5 mm. Preferably the landing chamfer has an angle substantially the same as the rake angle, in use.

The trailing edge chamfer can terminate in the superhard abrasive material table. If the superhard abrasive material table is bonded to a substrate, the trailing edge chamfer can extend into the substrate.

According to another aspect of the invention, a cutting element comprises: a layer or table of superhard abrasive material presenting a working surface; a side surface and a peripheral edge between the working surface and the side surface, the peripheral edge being defined by: a leading edge chamfer comprising more than one section and having an edge contiguous with the working surface; a break-in chamfer having an edge contiguous with an edge of the leading edge chamfer and an edge contiguous with the side surface, the edge contiguous with the side surface providing a cutting edge for the break-in chamfer; and the length of the leading edge chamfer being greater than that of the break-in chamfer. In this form of the invention, at least one of the sections may have a length greater than that of the break-in chamfer. The leading edge chamfer preferably forms an angle of 10 to 30 degrees, more preferably 15 to 25 degrees, with the working surface.

The multiple chamfer configuration of ali embodiments and forms of the invention can extend around the entire peripheral edge or around a portion only of the peripheral edge.

Where chamfers in the cutting element of the invention are contiguous, the edge defined between chamfers may be honed to remove surface asperities and/or imperfections.

The surface finish of the multiple chamfer configuration of the cutting element of the invention may be further processed to achieve a polished finish to reduce friction and remove surface damage.

The table or layer of superhard abrasive material may be supported by being bonded to a substrate, generally a cemented carbide substrate.

The table or layer of superhard abrasive material may be substantially planar and may have any suitable shape and preferably has a disc-shape, an ovoid shape or the shape of a segment of a disc or ovoid.

The working surface of the table or layer of superhard abrasive material may be planar or non-planar, e.g. convex or concave. When non-planar, the table or layer may be axisymmetric or non-axisymmetric and may include regions which are concave, convex or a combination thereof.

The superhard abrasive material may be any known in the art such as PDC, PCBN, thermally stable PDC, or CVD diamond, and is preferably polycrystalline diamond (PDC). The abrasive particles for the superhard abrasive material may be monomodal, i.e. the particles have a single average particle size or be multimodal, i.e. the particles have more than one average particle size. For example, if the particles of the superhard abrasive material are bimodal, then the particles will have two average particle sizes.

The thickness or depth of the table or layer of superabrasive material may be thin, i.e. 1 mm or less or thick, i.e. greater than 1 mm and generally less than 4 mm. The invention has particular application to table depths in the range 1.5 to 3mm. It is however anticipated that the invention may have equal or similar benefits where the superhard abrasive layer is thicker than those currently commercially available.

When the superhard abrasive is PDC, the PDC may be relatively soft, i.e. with a low wear resistance, but the invention has particular application to high strength, hard and abrasion resistant PDC. An example of such high strength, hard abrasion resistant PDC is PDC which has a fine diamond particle size, e.g. less than 20 μm in average particle size, and typically a particle size distribution which is multimodal. Such high strength, hard and abrasion resistant PDC, with prior art cutting edge configurations, tend to chip and spall not only during the break-in stage, but also during the steady state and wear-out stages or regimes. The provision of chamfers in the cutting edge region, as described above, substantially reduces the tendency for chipping and spading to occur during both stages and increases the cutting element life.

The high strength, hard abrasion resistant PDC may have an average grain size of less than 20 μm, have a very high wear resistance and an homogenous catalyst/solvent distribution such as that described in WO 2005/061181 and WO2005/110648.

It is also anticipated that the invention may have particular use for finer- grained PDC materials where the average diamond grain size is less than 6 μm and more particularly less than 2 μm. The PDC may also have a region adjacent the peripheral cutting edge which is lean in binder metal, depths of lean phase may be up to 500 microns. Such PDC is described in WO2005/061181 and WO2005/110648. It has been found that the invention provides a further improvement in chip and spall resistance as well as cutter life to that described in WO2005/061181 and WO2005/110648.

The invention extends to an earth boring tool, such as a rotary drag bit, which includes a cutting element, and generally a plurality of cutting elements, as described above mounted in the cutting face of the tool.

The invention extends to the use of a cutting element as described above in the cutting of hard formations, e.g. in the drilling of hard subterranean rock formations, metal machining and cutting tool applications.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional side view of a peripheral edge of an embodiment of a cutting element of the invention;

Figure 2 is a sectional side view of a peripheral edge of another embodiment of a cutting element of the invention;

Figure 3 is a sectional side view of a further embodiment of a cutting tool of the invention, shown in cutting action through a workpiece;

Figure 4 are sectional side and plan views of a peripheral edge of yet another embodiment of the invention; Figure 5 is a series of photographs of a wear scar generated by a cutting edge of an embodiment of a cutting element of the invention in a boring mill test;

Figure 6 is a series of photographs of a wear scar generated by a cutting edge of a cutting element of the prior art in a boring mill test;

Fsgurβs 7a. to 7c are diagrammatic drawings illustrating the cutting action of an embodiment of a cutting element of the invention;

Figure 8 is a series of photographs of a wear scar generated by a cutting edge of a cutting element of another embodiment of the invention in a boring mill test;

⁼igure 9a is a photograph showing a new unused cutter having a high strength high wear resistant PDC table and^' a leading edge chamfer,. a break-in chamfer, a landing chamfer, and a short trailing chamfer;

^:igure 9b is a photograph showing a new unused cutter having a high strength high wear resistant PDC table and a leading edge chamfer, a break-in chamfer, a landing chamfer, and a long trailing chamfer;

igures 10a and 10b are photographs showing the wear scars of a cutter with a multiple chamfer configuration, but with no trailing edge chamfer; and

igures 11a and 11 b are photographs showing the wear scars of the cutters of Figures 9a and 9b, respectively;

igure 12 is a graph showing the manner in which a PDC cutter wears. DETAtLED DESCRIPTION OF THE INVENTION

The invention relates to cutting elements containing a substantially pianar layer or table of superhard abrasive presenting a substantially planar working surface, a side surface and a peripheral edge between the working surface and the side surface. The peripheral edge carries out the cutting action in use and is characterised by a chamfer configuration designed to minimise chipping and spalling of the superhard abrasive table during both the break-in stage of cutting and the steady state regime of cutting.

A first embodiment of a PDC table of a cutting element of the invention is as illustrated by Figure 1. Referring to this figure, the PDC table 10 is bonded to a cemented carbide substrate 12. The table 10 is substantially planar and has a substantially planar working surface 14, a side surface 16 and a peripheral cutting region or edge, generally designated by 18. The peripheral cutting region comprises a break-in chamfer 20, a leading edge chamfer 22, contiguous with the first chamfer 20 and leading to the working surface 14, and a trailing edge chamfer 24 contiguous with the break-in chamfer and having an edge contiguous with the side surface 16. The trailing edge chamfer 24 is contiguous with the break-in chamfer along line of intersection 26, which line of intersection defines the cutting edge of he break-in chamfer. This cutting edge is a sharp cutting edge. The leading edge chamfer 22 is longer than the break-in chamfer 20, as illustrated, and generally defines an angle of 10 to 30 degrees with the working surface 14. The provision of long, shallow leading edge chamfer 22 minimises spaliing and chipping occurring in the PDC table 10 during both the break-in stage of cutting and the steady state regime of cutting. This has been shown experimentally in a boring mill test.

The cutting element used in the test comprised a layer of PDC bonded to a cemented carbide substrate. The peripheral edge of the PDC layer had the leading edge chamfer and break-in chamfer configuration of Figure 1, but no trailing edge chamfer. The PDC was a high strength, hard and abrasion resistant PDC. The test involved using the cutting element to machine into Paarl granite and the wear scar generated was observed.

Figure 5 shows the test results. After 45 passes, the wear scar reached the beginning of the leading edge chamfer but no chipping had occurred yet and after 100 and 170 passes the wear scar was well into the second chamfer but there was still no sign of chipping on the top of the PDC table. Even at end of life of the cutter element, the wear scar did not reach the top of the table and no chipping was visible, although the wear scar exceeded the point where a 45° chamfer would have ended. The 170 pass picture shows the plan view of the worn diamond and the picture shows how surprisingly flat and sharp the wear scar is even after 170 passes. The cutter element failed after 210 passes.

This is to be compared with a PDC cutting element of the same material, but having a single 45 degree chamfer in the peripheral cutting edge. Paarl granite was again used as the workpiece material. This cutting element with a prior art chamfer already showed significant chipping after 50 passes and the cutter failed after 140 passes. The results of this test are shown in Figure 6.

As can be seen from Figure 6a, the standard chamfer serves the purpose amply to prevent chipping and spalling during the break-in stage of wear. The boring mill test is a severe, accelerated wear test and the fact that no chipping has occurred after 35 passes, which is substantially beyond the break-in stage and well into the steady state stage, is considered to be a good performance. Because of the high wear resistance of the diamond table, it can be seen from Figure 6a that the wear scar still occurs only within the chamfer region after as many as 35 passes. Figure 6a also demonstrates that the cutting forces, in particular the normal force, is spread across an area large enough not to initiate chipping. However, it can be observed from Figure 6b after 50 passes that, as soon as the wear scar extends to the top of the diamond table, a chip breaks out on the top of the diamond table, implying that the stress situation has suddenly changed at this stage of the wear development. This chip at the cutting edge causes an uncontrolled loss of diamond, which is the wear resistant element of the cutter, resulting in an acceleration of the diamond wear resulting in a damaged cutting edge. As can be seen from Figure 6c, after 95 passes further chipping has occurred on the diamond table surface and the wear scar size has nearly trebled. Soon thereafter, the cutter failed when a large spall broke out of the diamond table after 140 passes (Figure 6d). This chipping of the top of the diamond table when the wear reaches the top of the diamond table is characteristic of high strength, hard, wear resistant diamond tables.

Thus, the cutting element of the invention achieved a surprising improvement in cutter life of 50% compared with a prior art chamfered cutting element.

Thus, in a preferred form of the invention there is the provision of a long shallow chamfer in the cutting edge region of the PDC table. The manner in which the cutting element of the invention is believed to function in use is illustrated diagrammatically by Figures 7a to 7c. There are two methods by which crack initiation may be prevented in the diamond layer of a cutter (cutting element) by means of edge design, namely:

a. redistributing the cutting forces such that areas of peak stresses are avoided, and b. redirecting (or reducing) the cutting forces in such a way that the lower forces result in lower stresses on the cutting edge.

Figure 7a shows schematically the front view of the PDC cutter as the cutter cuts the rock, where the dotted lines a-b, c-d and e-f in Figure 7a represent various levels of the wear scars. The chamfers have been deliberately exaggerated to aid understanding.

Referring to Figure 7a, the wear scar along line a-b lies within the confines of the first chamfer (break-in chamfer) and is relatively small. The wear scar can be seen to be elongated and narrow. The wear scar of interest to the present invention, is at the level of line c-d, which now intersects the second or shallow chamfer (leading edge chamfer) at points g and h. The cutting edge will be in compression because of the large included angle between the leading chamfer and the wear flat surface. However, the section of the cutting edge which lies on the second shallow chamfer between points g and h is actually curved rather than flat which would be the case had the shallow chamfer not been there.

Figure 7b is a schematic of the foot print of the wear scar as it drags on the rock material, if the cutting element were transparent and if one were looking at the wear scar from the top of the cutter. As the cutter ploughs through the rock, the rock chips slide over the curved surface created by the second shallow chamfer as shown by the arrows. This flow of chips over the cutter is similar to the flow of water around the prow of a ship. In the latter example, the flow of water around the prow allows the ship to cut through the water thereby reducing the friction of the water against the ship and also reduces the resistance to the forward motion of the ship, in a similar manner, the cutting mechanics of the PDC cutter of the invention in the rock is modified to reduce the cutting forces and the friction of the swarf against the face of the cutter, thereby reducing the stresses in the cutter. This reduction in stresses reduces the tendency of the cutter to chip and spall.

in contrast, in the absence of a second shallow chamfer, the cutting mechanics of the rock would be as depicted by Figure 7c, which is a schematic drawing of the wear scar footprint as the cutter ploughs through the rock. The absence of the second chamfer means that the flat face of the cutter will bear down on the rock at the negative rake angle to the cutting direction, and the rock chips will impact the cutter face head-on, and will have no recourse but to be deflected upwards. This cutting action will cause a large resistance to the motion of the cutter, resulting in an increase in cutting forces and, hence, an increase in the stresses at the cutting edge causing the cutting edge to spall easier. A test was carried out to evaluate the efficacy of the shallow second chamfer or leading edge chamfer when used in a cutting element wherein the diamond table is of a softer grade of diamond. Figure 8 shows optical microscope photographs of the wear scar generated by a double chamfered cutting element of one form of the invention in the boring mill test after 45 and 130 passes. The PDC table of the cutting element was a softer grade of PDC than that of the cutting element used in the boring test illustrated by Figures 5 and 6. After 45 passes, the wear scar had already reached the edge of the second chamfer but no chipping can be seen and after 130 passes, the wear scar had reached the top of the table and still no chipping was visible. In both these photographs, the sharpness of the cutting edge is evident. The test was stopped after 130 passes as the wear scar was very large, although the cutter couid have gone on, so no life figure is available. This example is given to demonstrate that the invention has application to softer (less abrasion resistant) diamond layers which can also benefit from long, shallow second chamfers. In this case the benefit is the sharpness of the cutting edge which benefits cutting efficiency.

A second embodiment of the invention is illustrated by Figure 2. Referring to this figure, the cutting element comprises a superhard abrasive table 30 bonded to a cemented carbide substrate 32. The table 30 has a planar working surface 34, a side surface 36 and a peripheral edge region 38. The peripheral edge region is defined by a break-in chamfer 40 and a leading edge shallower chamfer 42 which comprises two sections or chamfers 44 and 46. Each of the sections 44 and 46, in this embodiment, is longer than the first chamfer. However, it is also possible for one or other of the two sections to be longer than break-in chamfer 40 or each of the sections to be shorter than the break-in chamfer. However, the combination of sections must have a length greater than that of the break-in chamfer. The break-in chamfer 40 is contiguous with the side surface 36 along a line of intersection 48 which defines a cutting edge for the break-in chamfer. Figure 3 illustrates a further embodiment of the invention which has a leading edge chamfer, a break-in chamfer, a landing chamfer and a trailing chamfer. Referring to this figure, the cutting element has a superhard abrasive layer 50 having a leading edge chamfer 52, a break-in chamfer 54, a landing chamfer 56 and a trailing edge chamfer 58. The trailing edge chamfer 58 is illustrated as terminating in the layer 50. However, if this layer 50 is bonded to a substrate 64, the trailing edge chamfer can extend into the substrate. The landing chamfer 56 is contiguous with the break-in chamfer 54 along line of intersection 66 which defines the cutting edge for the break- in chamfer. The landing chamfer, in use, makes cutting contact with the workpiece 60 and makes an angle with the side surface 62 of the layer 50 which is the same or substantially the same as the cutting rake angle γ. The depth of cut (DOC) is illustrated by dotted lines. The trailing chamfer 58 makes angle β with the side surface 62 and does not make contact with the workpiece, in use, as illustrated by the drawing

As mentioned above, the peripheral cutting edge for the superhard abrasive table can extend around the entire periphery of the table. Alternatively, the peripheral cutting edge can extend around a portion only of the cutting edge, as illustrated in Figure 4. Referring to this figure, a cutting element comprises a superhard abrasive table 150 bonded to a cemented carbide substrate 152. The superhard abrasive table 150 has a substantially planar working surface 154, a side surface 156 and a peripheral region or edge 158. It will be noted that this edge extends around a portion only of the table 150. The peripheral edge region is defined by a break-in chamfer 160, a trailing edge chamfer 162 and a leading edge chamfer 164 which is longer than the break-in chamfer 160. The trailing edge chamfer 162 is contiguous with the break-in chamfer 160 along line of intersection 166 which defines the cutting edge for the break-in chamfer. It should be noted that whilst the chamfers shown in Figure 4 have straight edges, this invention is equally applicable to a geometry incorporating curved edges.

The use of a trailing edge chamfer to ameliorate chipping of a PDC table at the trailing edge was tested in a boring mill test. Two types of trailing chamfers were tested, namely, a short trailing chamfer which ended within the diamond table and a long trailing chamfer which extended into the carbide substrate. In this test, the multiple chamfer configuration as shown in Figure 1 was used. Figures 9a and 9b show optical microscope photographs of the two edge configurations before the tests commenced. By way of comparison, a test was carried out on a cutter having a high strength high wear resistant PDC table with a triple chamfer edge configuration but without a trailing chamfer, i.e., having leading, break-in and landing chamfers only. Figures 10a and 10b show the wear scar results of the cutter from the reference test, before and after the trailing edge chipped.

Figures 11a and 11b show the wear scar results for the cutters with short and long trailing edge chamfers, respectively. Figures 11a and 11b show the wear scars as they had advanced right up to the interface between the diamond layer and the carbide substrate. Both of these cutters had two trailing edge chamfer configurations. As can be seen, there is no chipping of the trailing edge by comparison with the cutter without a trailing edge as shown in Figures 10 and 10b where chipping was found to occur even before the wear scar reached the diamond-carbide interface. The important point to be made is that there is no cracking of the trailing edge even when the critical thickness from the wear scar to the superhard material interface with the carbide substrate is exceeded. Hence, the objective of ameliorating trailing edge chipping using a trailing edge chamfer is achieved.

The cutter edge configuration shown in Figure 9b is a preferred embodiment. The cutter tested lasted the full duration of the test of 300 passes without chipping or spalling and, hence, did not reach end of life. Therefore, in comparison with the reference embodiment of Figure 6, the improvement in cutter life by the use of the multiple chamfer configuration of the invention exceeded a surprising 100%.

Claims

1. A cutting element comprising: a layer or table of superhard abrasive material presenting a working surface; a side surface and a peripheral edge between the working surface and the side surface, the peripheral edge being defined by: a leading edge chamfer having an edge contiguous with the working surface, a trailing edge chamfer or landing chamfer, and a break-in chamfer between the leading edge chamfer and the trailing edge chamfer or landing chamfer, the trailing edge chamfer or landing chamfer being contiguous with the break-in chamfer along a line of intersection, which line of intersection defines a cutting edge for the break-in chamfer.

2. A cutting element according to claim 1 wherein the peripheral edge includes a trailing chamfer and a landing chamfer, the landing chamfer being between the trailing chamfer and the break-in chamfer.

3. A cutting element according to claim 1 or claim 2 wherein the landing chamfer has a length of no more than 0.5 mm.

4. A cutting element according to any one of the preceding claims wherein the leading edge chamfer has a length greater than that of the break-in chamfer.

5. A cutting element according to any one of the preceding claims wherein the leading edge chamfer forms an angle of 10 to 30 degrees with the working surface.

6. A cutting element according to any one of claims 1 to 5 wherein the leading edge chamfer forms an angle of 15 to 25 degrees with the working surface.

7. A cutting element according to any one of the preceding claims wherein the leading edge chamfer comprises more than one section.

8. A cutting element according to claim 7 wherein the length of at least one of the sections of the leading edge chamfer is greater than that of the break-in chamfer.

9. A cutting element according to any one of the preceding claims wherein the leading edge chamfer and the break-in chamfer are contiguous.

10. A cutting element comprising: a layer or table of superhard abrasive material presenting a working surface; a side surface and a peripheral edge between the working surface and the side surface, the peripheral edge being defined by: a leading edge chamfer comprising more than one section and having an edge contiguous with the working surface; a break-in chamfer having an edge contiguous with an edge of the leading edge chamfer and an edge contiguous with the side surface, the edge contiguous with the side surface providing a cutting edge for the break-in chamfer; and the length of the leading edge chamfer being greater than that of the break-in chamfer.

11. A cutting element according to clam 10 wherein at least one of the sections has a length greater than that of the break-in chamfer.

12. A cutting element according to claim 10 or claim 1 1 wherein the leading edge chamfer forms an angle of 10 to 30 degrees with the working surface.

13. A cutting element according to claim 10 or claim 11 wherein the leading edge chamfer forms an angle of 15 to 25 degrees with the working surface.

14. A cutting element according to any one of the preceding claims wherein each of the chamfers is planar.

15. A cutting element according to any one of the preceding claims wherein the layer or table of superhard abrasive material is substantially planar and the working surface is planar.

16. A cutting element according to any one of the preceding claims wherein the superhard abrasive material is PDC, PCBN, thermally stable PDC, or CVD diamond.

17. A cutting element according to any one of the preceding claims wherein the layer of superhard abrasive material is bonded to a substrate.

18. A cutting element according to claim 17 wherein the substrate is a cemented carbide substrate.

19. A cutting element according to any one of the preceding claims wherein the thickness of the layer of superhard abrasive material is 1 mm or less.

20. A cutting element according to any one of claims 1 to 18 wherein the thickness of the layer of superhard abrasive material is greater than 1 mm.

21. A cutting element according to claim 20 wherein the thickness of the superhard abrasive material is 1.5 mm to 3 mm.

22. A cutting element according to any one of the preceding claims wherein the superhard abrasive material is PDC having an average particle size of less than 20 μm.

23. A cutting element according to any one of claims 1 to 21 wherein the superhard abrasive material is PDC having an average particle size of less than 6 μm.

24. A cutting element according to any one of claims 1 to 21 wherein the superhard abrasive material is PDC having an average particle size of less than 2 μm

25. A cutting element according to any one of the preceding claims for use in an earth boring tool or a metal machining or cutting tool.