A METHOD OF PRODUCING A CUTTING TOOL INSERT

Abstract: A method of producing a cutting (30) edge on a layer (20) of diamond or other ultra-hard material includes the steps of providing a plate of the material, which plate has major flat surfaces (D1, D2) on opposite sides thereof, laser cutting the plate transverse to the major surfaces (D1, D2) to produce two or more layers (20) each having a cutting edge (30) defined on a surface (26) produced by the laser cut and exposing the cutting edge (30) to an ion bombardment etch. The layer of diamond or other ultra-hard material having an edge produced in this manner is useful as a tool insert, particularly a surgical blade.

Description: A METHOD OF PRODUCING A CUTTING TOOL INSERT BACKGROUND OF THE INVENTION This invention relates to a method of producing cutting tool inseπs such as surgical blades made from single crystal or polycrystalline diamond. Diamond has successfully been used since the early 1970's as the ultimate material for surgical scalpels, in particular, for use in eye operations (ophthalmology). Its hardness, strength and perfect crystalline nature allow the manufacture of cutting edges that are defect free under microscopic examination at for instance 100 x magnification, as required for ophthalmology. Surgical instruments equipped with diamond scalpels outperform steel scalpels by lowering cutting resistance and creating less deformation of the tissue being cut thus allowing better precision in the operation. This is particularly important as some operations require operating precision down to 1/100 of a millimeter or better. The relatively high price of natural diamond and the associated cost of processing this ultra-hard material have limited this application to certain market segments. In recent years synthesis methods have been developed for polycrystalline diamond films at significantly lower cost than natural diamond. Even more important, it is now possible to manufacture diamond plates with a diameter of more than 10 centimeters. This makes it possible to manufacture products with much larger dimensions. Natural diamonds in sizes over, say, one centimeter are rare and very expensive. In practice, surgical scalpels are limited to sizes under 8 millimeters in length for this reason. Although the basic properties of polycrystalline diamond make it suitable for use in surgical scalpels, the conventional methods for working monocrystalline diamond are not suitable when applied to polycrystalline material. For example, the time needed to polish a single facet on a monocrystalline scalpel is of the order of minutes. Using the same method on polycrystalline material many hours are required thus losing the cost advantage of the material. In addition, the resulting cutting edge will fail to reach the quality required as it is extremely difficult to avoid chipping the cutting edge during the polishing process. A practical method to shape diamond products known in the diamond industry is to laser cut the material, usually with a Nd-YAG laser beam. This method produces a typical profile as represented in Figure 1. Referring to this figure, it can be seen that at the laser beam 10 entry side, the material edge 12 is rounded producing what is called a shoulder. When the objective is to produce a sharp cutting edge characterised by a small edge radius and an included angle of less than 60 degrees, for example, this shoulder is a disadvantage. An alternative is to use the exit of a laser beam 14 to create a cutting edge 16 (Figure 2). This method is the subject of EP-A-720887. This approach does produce a small edge radius and a low included angle, but the quality achieved on the exit edge is limited by irregularities in the form of waviness and a rougher facet inherent in laser cutting. SUMMARY OF THE INVENTION According to the present invention, a method of producing a cutting edge on a layer of ultra-hard material includes the steps of providing a plate of the material, which plate has major flat surfaces on opposite sides thereof, laser cutting the plate transverse to the major surfaces to produce two or more layers each having a cutting edge defined on a surface produced by the laser cut and exposing the cutting edge to an ion bombardment etch (also known as ion beam milling). The cutting edge is typically defined between the surface produced by the laser cut and a major surface of the plate. Further according to the invention, the method includes the step of ion beam smoothing the other surface or one or both of the major surfaces of the plate prior to or after the laser cutting. It has been found that ion beam smoothing reduces the friction during cutting and can lead to an improved initial cutting edge being produced by the laser cut. The cutting edge which is produced may be a single faceted or multifaceted cutting edge. Alternatively, two or more such cutting edges may be provided. The cutting edge or edges may be straight or curved, or a combination thereof. The cutting edge may be non-symmetric or symmetric. Non-symmetric cutting edges in the context of blades are those in which one of the two intersecting surfaces forming the cutting edge is a surface of the blade itself. Symmetric cutting edges in the context of blades are edges in which neither of the two intersecting surfaces forming the cutting edge is a surface of the blade itself. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 illustrate schematically a diamond plate cut by a laser beam according to the prior art, Figure 3 is a graph illustrating the typical etch rate in relation to the incident angle of an ion bombardment etch for diamond, Figures 4 and 5, and 6 and 7, show, respectively, sectional side views and perspective views of two embodiments of the invention, Figures 8 and 9 show a plan view and perspective view, respectively, of a further embodiment of the invention, Figure 10 shows a sectional side view of a further embodiment of the invention, and Figure 11 illustrates the apex radius of a cutting edge. DESCRIPTION OF EMBODIMENTS The invention has application to producing cutting blades for cutting tools and, more particularly, for diamond cutting tools. The diamond may be single crystalline or polycrystalline in nature, although the invention has greatest application with diamond which is polycrystalline in nature. The diamond may be natural, but is preferably produced synthetically, and more particularly by chemical vapour deposition (CVD). The laser beam which is used to effect the laser cut may be any known in the art. typically a Nd-YAG beam. The ion bombardment etch is achieved using an ion beam, preferably neutralised, with argon as the preferable gas source. The ion bombardment will etch away the material at a rate which depends on the nature of the material. In the case of diamond, the rate will be approximately 0,05 to 10/xm per hour. It has been found that the etch rate is a function of the angle of incidence. The maximum etch rate has been measured at a 54 degree incident angle, as can be seen from the graph illustrated by Figure 3. The maximum etch rate will typically occur around 54 degrees but this angle (α) is dependent on the condition of the etch. An example of suitable ion bombardment etch conditions using argon are a voltage of 250 to 1500 volts to accelerate the ion beam and a current density of between 0,2 mA/cπr and 20 mA/cπr, these conditions being maintained for a time suitable to remove a layer of thickness between 1 and 50μm from a surface of the material. Conditions similar to the ion bombardment etch may be used for ion beam smoothing one or more of the surfaces of the plate or layer. The incident angle of the ion beam will typically be about 0 degrees (normal to the surface) and may be stationary or oscillating. The invention is capable of producing very fine cutting edges and ones which have an apex radius of less than 50nm. and preferably less than 20nm. The method of the invention may be used to produce a high quality, sharp cutting edge for a cutting tool insert, particularly a surgical blade. Further, the invention can also be used to improve the surface quality of a surface or facet which leads to a cutting edge. This has particular importance for surgical blades as it reduces the t p value (this is an accepted standard measure for the smoothness of a surface) of such a surface thereby reducing the blade's resistance during tissue cutting. In an embodiment of the invention, a polycrystalline CVD diamond plate is cut into two, producing two layers of polycrystalline CVD diamond as illustrated by Figure 1 or Figure 2. Edges of the layers, e.g. edges 12 or 16. may thereafter be subjected to an ion beam etch to produce a sharp cutting edge. It is preferred that the major flat surfaces of the plates, indicated as DI and D2 (if not polished), are ion beam smoothed prior to the laser cut being effected. A consequence of the diamond removal that is achieved during the etching process, is that at a 0 degree incident angle, i.e. the ion beam is normal to the surface, an edge will be formed with an included angle ( ), as can be seen from Figures 4 and 5. With reference to these Figures, a diamond cutting blade 20 has opposed flat longitudinal surfaces 22, 24 and a transverse surface 26 created by a laser cut. The ion beam, preferably a neutralised ion beam, is directed at the cutting tool in the direction of the arrows 28, i.e. normal to the surface 24. This, as mentioned, produces an included angle ( ), at the cutting edge 30. This angle is independent of the initial cross section and thus the method of the invention eliminates the laser cut shoulder and edge radius as is found in prior art laser cuts (see Figure 1). It is possible to reduce the included angle resulting from the ion beam etch by appropriately tilting the ion beam and choosing an angle of incidence greater than 0 degrees, for example, 10 degrees. Further, the method of the invention can also be applied effectively on multifaceted products, by rotating the product during the etching process. It is possible to reduce the included angle (a) even further, as is illustrated by Figures 6 and 7. In these figures, like parts to those of Figures 4 and 5 carry like numerals. Using an ion beam etch, a layer of material can be removed from one of the surfaces 22 leaving a substantially reduced included angle (a) and a very sharp and fine cutting edge 30. This ion beam etch also has the effect of smoothing the surface 22. The etching or smoothing may be achieved, for example, by ion etching the diamond under an incident angle, as shown by the arrows, which may be tilted parallel to or away from the cutting edge 30. The cutting edge 30 is defined between surface 22 of the blade and surface 26 produced by the laser cut and is thus a non-symmetric cutting edge. The incident angle is generally greater than 50°C to prevent a microfacet forming on surface 22. It is possible to produce a multifaceted cutting blade from the blade illustrated by Figures 4 and 5. This multifaceted blade is illustrated by Figures 8 and 9. Again, like parts carry like numerals. Oscillation of the ion beam in the direction of the arrow 3, and as shown in Figure 8, produces a multifaceted blade. The multifaceted blade has cutting edges 32, 34 meeting at point 36. For the remaining numerals, parts which are similar to those in Figures 4 and 5 carry like numerals. Oscillation or rotation of the ion beam is needed only for angles other than zero. For zero degree etching no rotation or oscillation is necessary. Curved cutting edges may be produced in a similar manner. A cutting edge with no waviness can be achieved by polishing a microflat on to a laser shaped cutting edge and thereafter polishing a microfacet on to the now blunt edge. This embodiment is illustrated by Figure 10 where parts similar to those of Figures 4 and 5 carry like numerals. Referring to these Figures, the surface 26 produced by the laser cut may be polished to create a microflat 38 and thereafter a microfacet 40 is polished on to the now blunt edge. This polishing can be mechanical or thermomechanical. As the amount of material being removed is very small, this can be done relatively quickly. The blade is then sharpened by ion beam etching, as described above in relation to the embodiment of Figures 4 and 5, to remove the remnants of the small facet 40, as shown by the dotted line 42. This gives a very sharp, smooth cutting edge. The cutting edge is identified as 44. However, since the removal of material at 38 and 40 is so small, the ion beam etching effectively sharpens the cutting edge 30 defined between the laser cut surface 26 and the surface 22. As mentioned above, the invention is capable of producing very fine cutting edges and ones which have an apex radius of less than 50nm, and preferably less than 20nm. For all cutting edges, no matter how fine, there will be an apex radius. This apex radius is "r" shown in Figure 11. The cutting edge is 44 and the surfaces leading to the cutting edge are 46, 48.

Claims: CLAIMS 1. A method of producing a cutting edge (30) on a layer (20) of ultra-hard material includes the steps of providing a plate of the material, which plate has major flat surfaces (DI, D2) on opposite sides thereof, laser cutting the plate transverse to the major surfaces (DI, D2) to produce two or more layers (20) each having a cutting edge (30) defined on a surface (26) produced by the laser cut and exposing the cutting edge (30) to an ion bombardment etch. 2. A method according to claim 1 wherein the cutting edge (30) is defined between the surface (26) produced by the laser cut and a major surface (DI, D2) of the plate. 3. A method according to claim 1 or claim 2 wherein one or both of the major surfaces (DI , D2) of the plate are ion beam smoothed prior to the laser cutting. 4. A method according to any one of the preceding claims wherein the angle of incidence of the ion beam for the ion bombardment etch is 0°. 5. A method according to any one of claims 1 to 3 wherein the angle of incidence of the ion beam for the ion bombardment etch is other than 0° . 6. A method according to any one of the preceding claims wherein the ion beam for the ion bombardment etch is a neutralised ion beam. 7. A method according to any one of the preceding claims wherein the gas source for the ion beam of the ion bombardment etch is argon. 8. A method according to claim 7 wherein the ion bombardment etch conditions are a voltage of 250 to 1500 volts to accelerate the ion beam and a current density of between 0,2mA/cm : and 20mA/cm 2 , these conditions being maintained for a time suitable to remove a layer of thickness between 1 and 50 microns from the surface of the material. 9. A method according to any one of the preceding claims wherein the ultra- hard material is diamond. 10. A method according to claim 9 wherein the diamond is single crystal diamond. 11. A method according to claim 9 wherein the diamond is polycrystalline diamond. 12. A method according to any one of claims 9 to 11 wherein the diamond is CVD diamond. 13. A method according to any one of claims 9 to 12 wherein the ion bombardment etch removes material at a rate of 0,05 to lOμm per hour. 14. A method according to any one of the preceding claims wherein the cutting edge produced has an apex radius of less than 50nm. 15. A method according to any one of claims 1 to 13 wherein the cutting edge produced has an apex radius of less than 20nm. 16. A cutting tool insert comprising a layer (20) of ultra-hard material having a cutting edge (30) produced by a method according to any one of the preceding claims. 17. A cutting tool insert according to claim 16 which is a surgical blade.

Inventors: BARTEN JOHANNES CORNELIUS FRAN, LEMMENS ERIK, NELISSEN WILHELMUS GERARDA MAR, SPAAY PAULUS GERHARDUS HENDRIK, BARTEN, JOHANNES, CORNELIUS, FRANCISCUS, LEMMENS, ERIK, NELISSEN, WILHELMUS, GERARDA, MARIA, SPAAY, PAULUS, GERHARDUS, HENDRIKUS, MARIA
Applicants: BARTEN JOHANNES CORNELIUS FRAN, DRUKKER INT BV, LEMMENS ERIK, NELISSEN WILHELMUS GERARDA MAR, SPAAY PAULUS GERHARDUS HENDRIK, BARTEN, JOHANNES, CORNELIUS, FRANCISCUS, DRUKKER INTERNATIONAL B.V., LEMMENS, ERIK, NELISSEN, WILHELMUS, GERARDA, MARIA, SPAAY, PAULUS, GERHARDUS, HENDRIKUS, MARIA
Application year: 1997
Main classification: B23P15
IPC codes: A61F9, B23P15