Title of Invention

METHOD OF PRODUCING DIAMOND SEGMENTS FOR CUTTING TOOLS

Abstract

Abstract The invention relates to a method of producing diamond segments for cutting tools. According to the invention, forging is used in order to apply a high pressure to parts which are preformed from metal powders and which are brought to high temperatures, thereby enabling the porosity of said materials to be fully closed. The metal is densified by means of hot dynamic energy transmission. The aforementioned forging technique is particularly suitable for the production of diamond segments, using mixtures of low-cost metal powders. The forging operation involves the closed die application of a mechanical pressure of between 400 MPA and 700 MPA, the application time being of the order of several seconds and the forging temperature being below 1000 DEG C.

Full Text

Method of producing diamond segments for cutting tools. Background of the invention The invention relates to a method of producing a diamond segment for a cutting tool by sintering, consisting in successively performing: - mixing of metal powders with diamond particles, - preforming of the mixture by cold compression to obtain a handleable preform, - and hot presintering of the preform to eliminate the compaction residues and de-oxidize the preform while performing a beginning of sintering. State of the art Manufacturing diamond segments of cutting tools is based on powder metallurgy which consists in consolidating metal powders of predetermined composition with grains of natural or synthetic diamond by thermal and mechanical effect. The product obtained is a body composed of sintered metal having characteristics that depend on the nature of the basic metal powders and on the sintering conditions. The following different techniques are commonly used for manufacturing diamond segments: - free sintering: consolidation is performed in a furnace under a neutral or reducing atmosphere without any mechanical energy being provided, - pressure sintering: consolidation is performed in a furnace under a neutral or reducing atmosphere with additional energy being provided by pressure (gas or mechanical). The free sintering technique is performed at a temperature comprised between 900°C and 1200°C at atmospheric pressure. The manufacturing cycle time is fairly long (a few hours), and the compactness obtained for the sintered material is about 92% to 95%. The residual porosity of the parts after sintering is then liable to impair the mechanical strength of the sintered material and of the diamond. The thermostability of the diamond is in fact considerably affected when the temperature at low pressure exceeds 1000°C. The mechanical pressure sintering technique is performed at a temperature comprised between 700°C and 1200°C at a pressure of 250 to 400 bars (25 to 40 MPA). The cycle time is about 15mn and the compactness is comprised between 97% and 99%. This technique requires considerable manpower, and the use of graphite pistons to apply the loading increases the cost of the consumables. The gas pressure sintering technique is performed at a temperature comprised between 700°C and 1000°C and at a pressure of 2000 to 2500 bars (200 to 250 MPA). The compactness achieved is 99% to 100%, with cycle times of a few hours. This technique also requires considerable manpower, and costly investments for the manufacturing installation. Whatever the sintering technique used, the standard manufacturing steps of the diamond segments by sintering are as follows: - mixing metal powders with the diamond grains, - preforming the products by cold pressing causing compaction of the mixture, - assembling sintering cells, - free or pressure sintering, - recovering the sintered products, - finishing the sintered products. The presence of the diamond in the diamond segments means that the manufacturer has to work at as low temperatures as possible to avoid damaging the diamond. In addition, to have a correct lifetime and cutting qualities, the residual porosity must be low, notably less than 2%. These two imperatives lead to the following constraints: • use of a sintering process wherein a pressure is applied; • use of costly fine powders having a granulometry of less than 50 microns, enabling the sintering conditions to be reduced. This results in a considerable additional manufacturing cost of the diamond segments in comparison with free sintering. Low-cost metal powders commonly used in metallurgy exist, but they are rougher, in particular more than 50 microns. These materials cannot be used for diamond cutting tools manufactured according to one of the above-mentioned sintering techniques, as the temperature and pressure used are too low to correctly reduce the porosity of the sintered structure. The document CH 471 641 describes a method for manufacturing diamond tools using a cold compressed powder containing a hard carbide and a ferrous metal, the impregnation temperature being at least equal to the melting temperature of copper and at most equal to 1130°C. Object of the invention A first object of the invention consists in developing a method of producing diamond segments for cutting tools, based on sintered metal powders, enabling a homogeneous structure with a low residual porosity to be obtained, and with improved mechanical characteristics. According to the invention, this object is achieved by the fact that, after presintering, the preform is subjected to a forging operation by closed die application of a mechanical pressure comprised between 400 MPA and 700 MPA, the application time of said pressure being about a few seconds and the forging temperature being less than 1000°C. The residual porosity of the forged part is less than 2%. The die is previously heated to a temperature comprised between 200°C and 450°C and the mechanical forging pressure is applied to the preform by means of a press stamp. Preferably, before presintering, dewaxing of the preform is performed between 420°C and 560°C followed by cooling under a nitrogen flow. A second object of the invention concerns the use of a low-cost metal powder containing iron as binder in manufacture of diamond segments by hot sintering, thus enabling the porosity to be eliminated to increase the density of the structure. The binder contains for this purpose a mixture of 50% - 100% in weight of a steel powder containing Fe, C, Ni, and Mo, with a granulometry of less than 300 microns, and 0% to 50% in weight of an element A able to be either bronze, tungsten carbide, or any other element or compound designed to modify the characteristics of the binder. The composition of the steel powder contains in % of weight: - 90% - 97% of Fe, - 0.01%-0.1% of C, - 1%-3%ofNi, - 0.1%-0.8% of Mo. - Possibly other elements such as Chromium, Vanadium or Manganese. In the case where the element A is bronze, the composition of the steel powder is preferably in % of weight: - 1.8% -2% of Ni, - C content less than 0.06%, - 0.5%-0.6% of Mo, - 0.15% «0.25% of Mn, - Fe balance with 20% of bronze. The bronze of the element A can advantageously be irregular 90/10 bronze with a granulometry of less than 400 mesh. In the case where the element A is tungsten carbide, the composition of the steel powder is preferably in % of weight: - 1.5%-2% of Ni, - 1.35%-1.65% of Cu, - C content less than 0.01 %, - 0.45%-0.6% of Mo, with 10% of tungsten carbide. The tungsten carbide of the element A has a granulometry of less than 35 microns. Brief description of the drawings Other advantages and features will become more clearly apparent from the following description of particular embodiments of the invention given as non-restrictive examples only and represented in the accompanying drawings, in which: Figure 1 is a synoptic view of the steps of the method of producing according to the invention; Figure 2 shows a schematic cross-sectional view of the closed and heated die forging step. Detailed description of the invention The invention relates to the use of the forging technique to apply a high pressure to preformed parts made from metal powders, heated to high temperatures, enabling the porosity of these materials to be fully closed. Densification of the metal is obtained by hot dynamic energy transmission. Such a forging technique is particularly suitable for manufacturing diamond segments using mixtures of low-cost metal powders to replace conventional sintered binders. Two examples of compositions of metal powders used in the method according to the invention will be given hereafter. Example 1: Steel and bronze based powder Mixture of 80 % weight of a steel powder comprising: • Fe : >90% • C : • Ni : 1%-2% • Mo : 0.5% - 0.6 % • Mn : 0.15%-0.25% Granulometry: + 250^i: 0 % 150μ1-250μ : and 20 % weight of irregular 90/10 bronze This mixture is particularly suitable for producing tools for cutting hard concrete. The diamond composition is variable and adapted to the type of cutting, to the diameter of the tool, and to the power of the machine. Example 2: Steel and tungsten carbide base powder Mixture of 90 % weight of a steel powder comprising: • Fe : >90% • C : • Ni : 1.58% -1.93% • Cu : 1.35%-1.65% • Mo : 0.45% - 0.55 % Granulometry: + 212 \x : 0 % 180μ-212μ: 150 μ-180μ: balance 150μ-212μ: 45μ- 150μ: balance This mixture is particularly suitable for producing tools for cutting asphalt. The diamond composition is variable and adapted to the type of cutting, to the diameter of the tool, and to the power of the machine. Adding various elements such as graphite, ferro-alloys either carburized or not, bronze, copper... enables properties to be obtained making these binders suitable for any cutting use with a diamond tool. The different steps of the method for producing the diamond segments are illustrated in figure 1: Step 1: Preparation and mixing of the powders The metal powders according to one of the two examples 1 or 2 are first mixed together and with the diamond particles in a predetermined proportion. Step 2: Cold compression This compaction operation by cold compression of the mixture is performed in conventional manner with the suitable mould on a hydraulic or mechanical press to obtain a handleable preform. The pressures typically range from 100 to 600 MPA depending on the nature of the metal powders of the mixture. Step 3: Presintering This operation is essentially designed to eliminate the organic compaction residues, to deoxidize the parts, and to perform a beginning of sintering. Prior dewaxing is performed between 420°C and 560°C for a period of 5 to 30 minutes. Presintering is then performed in a furnace between 820°C and 900° C for 3 to 30 minutes under a reducing gas flow. Presintering may be carried out in the same enclosure as dewaxing. After cooling, the presintered segments can receive an oxidation protection layer. A D17A type graphite spray is used for this purpose. If the parts have been cooled, heating is finally performed under a neutral or reducing gas at forging temperature, for example 870°C. Step 4: Forging for closing the porosities The forging operation is performed by applying a pressure in a cold die, previously heated to between 200°C and 450°C and lubricated. The press used can be a mechanical or hydraulic screw press. The mechanical pressure is applied on the presintered part PR by means of a stamp 10, as illustrated in figure 2. The pressures vary according to the working conditions and the material. For the aforementioned examples, the values are as follows: - forging pressure between 400 MPA and 700 MPA, - effective forging temperature at die input of about 750°C - 850°C, - pressure application time less than 5 seconds. Step 5: Subsequent treatments The forged parts are then sand-blasted and cooled, possibly with a thermal treatment, and final machining. Using the forging technique according to the invention is less costly than conventional mechanical pressure sintering, as it enables low-cost rougher powders, more or less greater than 50 microns, to be used while keeping a relatively moderate temperature of about 750°C to 950°C to avoid damaging the diamond. Moreover, the mechanical properties are considerably improved on account of the fact that a compactness of more than 98% is obtained. Increasing from a density of 7.6 to 7.85 (100 % density) gives a 40 % gain in tensile strength, whereas the elongation at break is multiplied by 5. Reducing the porosity enables the resilience to be multiplied by 6, whereas it varies little between 95 % and 98 % compactness obtained with conventional sintering. The mixture of powders according to the aforementioned example 1 or 2 can thus easily be forged and can advantageously replace the conventional sintered binders to produce diamond segments for cutting tools. The preform is preferably handled in a gas flow for protection against oxidation. The mixture of powders contains 50% - 100% in weight of a steel powder containing Fe, C, Ni, and Mo, with a granulometry of less than 300 microns. in addition, the steel powder can contain 0.1% - 0.8% of Mn or 1% to 2% of Cu. Claims 1. Method of producing a diamond segment for a cutting tool by sintering, consisting in successively performing: - mixing of metal powders with diamond particles, - preforming of the mixture by cold compression to obtain a handleable preform, - and hot presintering of the preform to eliminate the compaction residues and de-oxidize the preform while performing a beginning of sintering, characterized in that, after presintering, the preform is subjected to a forging operation by closed die application of a mechanical pressure comprised between 400 MPA and 700 MPA, the application time of said pressure being about a few seconds and the forging temperature being less than 1000°C. 2. Method of producing according to claim 1, characterized in that the die is previously heated to a temperature comprised between 200°C and 450°C. 3. Method of producing according to claim 1, characterized in that the mechanical forging pressure is applied to the preform by a die - stamp assembly. 4. Method of producing according to claim 1, characterized in that, before presintering, dewaxing of the preform is performed between 420°C and 560°C. 5. Method of producing according to claim 4, characterized in that the preform is covered after cooling by a graphite layer for protection against oxidation. 6. Method of producing according to claim 4, characterized in that the preform is handled under a gas flow for protection against oxidation. 7. Diamond segment for a cutting tool manufactured by hot sintering of a mixture of metal powders containing: - 50% -100% in weight of a steel powder containing Fe, C, Ni, and Mo, with a granulometry of less than 300 microns, - and 0% to 50% in weight of an element A able to be either bronze, tungsten carbide, or any other element designed to modify the characteristics of the metal die, characterized in that the diamond segment is produced according to the method of one of the claims 1 to 6. 8. Diamond segment according to claim 7, characterized in that the composition of the steel powder is in % of weight: - 90% - 97% of Fe, - 0.01%-0.1% of C, - 1%-3%ofNi, - 0.1%-0.8% of Mo. 9. Diamond segment according to claim 8, characterized in that the steel powder also contains 0.1% - 0.8% of Mn. 10. Diamond segment according to claim 9, characterized in that the composition of the steel powder is in % of weight: - 1.8%-2% of Ni, - C content less than 0.06%, - 0.5%-0.6% of Mo, - 0.15%-0.25% of Mn, - Fe balance with 20% of bronze. 11. Diamond segment according to claim 8, characterized in that the composition of the steel powder contains 1% to 2% of Cu. 12. Diamond segment according to claim 11, characterized in that the composition of the steel powder is in % of weight: - 1.5% -2% of Ni, - 1.35%-1.65% of Cu, - C content less than 0.01%, - 0.45%-0.6% of Mo, with 10% of tungsten carbide. 13. Diamond segment according to claim 10, characterized in that the bronze of the element A is irregular 90/10 bronze. 14. Diamond segment according to claim 12, characterized in that the tungsten carbide of the element A has a granulometry of less than 35 microns. 15. Method of producing according to claim 1, characterized in that the forging temperature is preferably comprised between 750°C and 900°C. 16. Method of producing according to claim 1, characterized in that the residual porosity of the forged part is less than 2%. English translation of the claims of the PCT application n°PCT/FR2005/000035 as modified according to article 19 [received by the International Bureau on May 18, 2005 (18.05.2005) :Claims 7-14 have been amended, claims 1-6,15 and 16 stay unchanged] Claims 1. Method of producing a diamond segment for a cutting tool by sintering, consisting in successively performing: - mixing of metal powders with diamond particles, - preforming of the mixture by cold compression to obtain a handleable preform, - and hot presintering of the preform to eliminate the compaction residues and de-oxidize the preform while performing a beginning of sintering, characterized in that, after presintering, the preform is subjected to a forging operation by closed die application of a mechanical pressure comprised between 400 MPA and 700 MPA, the application time of said pressure being about a few seconds and the forging temperature being less than 1000°C. 2. Method of producing according to claim 1, characterized in that the die is previously heated to a temperature comprised between 200°C and 450°C. 3. Method of producing according to claim 1, characterized in that the mechanical forging pressure is applied to the preform by a die - stamp assembly. 4. Method of producing according to claim 1, characterized in that, before presintering, dewaxing of the preform is performed between 420°C and 560°C. 5- Method of producing according to claim 4, characterized in that the preform is covered after cooling by a graphite layer for protection against oxidation. 6. Method of producing according to claim 4, characterized in that the preform is handled under a gas flow for protection against oxidation. 7. Method of producing according to one of the claims 1 to 6, characterized in that the mixture of metal powders contains: - 50% - 100% in weight of a steel powder containing Fe, C, Ni, and Mo, with a granulometry of less than 300 microns, - and 0% to 50% in weight of an element A able to be either bronze, tungsten carbide, or any other element designed to modify the characteristics of the metal die. 8- Method of producing according to claim 7, characterized in that the composition of the steel powder is in % of weight: - 90%-97% of Fe, - 0.01%-0.1% of C, - 1%-3%ofNi, - 0.1%-0.8% of Mo. 9. Method of producing according to claim 8, characterized in that the steel powder also contains 0.1% - 0.8% of Mn. 10. Method of producing according to claim 9, characterized in that the composition of the steel powder is in % of weight: - 1.8%-2% of Ni, - C content less than 0.06%, - 0.5%-0.6% of Mo, - 0.15%-0.25% of Mn, - Fe balance with 20% of bronze. 11. Method of producing according to claim 8, characterized in that the composition of the steel powder contains 1% to 2% of Cu. 12. Method of producing according to claim 11, characterized in that the composition of the steel powder is in % of weight: - 1.5% -2% of Ni, - 1.35%-1.65% of Cu, - C content less than 0.01 %, - 0.45%-0.6% of Mo, with 10% of tungsten carbide. 13. Method of producing according to claim 10, characterized in that the bronze of the element A is irregular 90/10 bronze. 14. Method of producing according to claim 12, characterized in that the tungsten carbide of the element A has a granulometry of less than 35 microns. 15. Method of producing according to claim 1, characterized in that the forging temperature is preferably comprised between 750°C and 900°C. 16. Method of producing according to claim 1, characterized in that the residual porosity of the forged part is less than 2%.

Documents:

2485-CHENP-2006 AMENDED PAGES OF SPECIFICATION 22-12-2011.pdf

2485-CHENP-2006 AMENDED CLAIMS 01-05-2012.pdf

2485-CHENP-2006 AMENDED CLAIMS 22-12-2011.pdf

2485-CHENP-2006 AMENDED PAGES OF SPECIFICATION 01-05-2012.pdf

2485-CHENP-2006 CORRESPONDENCE OTHERS 02-03-2012.pdf

2485-CHENP-2006 CORRESPONDENCE OTHERS 21-06-2011.pdf

2485-CHENP-2006 CORRESPONDENCE OTHERS 01-05-2012.pdf

2485-CHENP-2006 CORRESPONDENCE OTHERS 26-12-2011.pdf

2485-CHENP-2006 ENGLISH TRANSLATION 26-12-2011.pdf

2485-CHENP-2006 FORM-13 01-05-2012.pdf

2485-CHENP-2006 FORM-3 02-03-2012.pdf

2485-CHENP-2006 FORM-3 22-12-2011.pdf

2485-CHENP-2006 OTHER PATENT DOCUMENT 22-12-2011.pdf

2485-CHENP-2006 EXAMINATION REPORT REPLY RECEIVED 22-12-2011.pdf

2485-CHENP-2006 POWER OF ATTORNEY 22-12-2011.pdf

2485-chenp-2006-abstract.pdf

2485-chenp-2006-claims.pdf

2485-chenp-2006-correspondnece-others.pdf

2485-chenp-2006-description(complete).pdf

2485-chenp-2006-drawings.pdf

2485-chenp-2006-form 1.pdf

2485-chenp-2006-form 3.pdf

2485-chenp-2006-form 5.pdf

2485-chenp-2006-pct.pdf