JPH0127141B2 - - Google Patents

Description

[Detailed description of the invention]

Sintered diamond dies are already on the market today, and the performance of the sintered compact made of fine diamonds is that they have good wire texture when drawing copper wire, aluminum wire, galvanized wire, piano wire, etc., and have a long lifespan. It has amazing high performance, 20 to 100 times that of hard metal dies and 1.5 to 15 times that of natural diamond dies. However, these sintered diamond dies are manufactured by drilling a pilot hole by laser machining or electrical discharge machining and then wrapping, so the minimum diameter of the die is the same as the hole diameter after laser machining or electrical discharge machining. It was impossible to make a die with a diameter smaller than the sum of the altered layers, and it was difficult to use it in the field of ultra-fine wire, where natural diamond dies are used. Therefore, the present inventors conducted intensive research to develop a material that can be used even with these ultra-fine wires and has better performance than natural diamond. First, in order to investigate why the process-altered layer occurs, we used a commercially available diamond sintered body in which diamond particles are bonded with an iron group metal to make a 30μ pilot hole by laser processing, and observed the area around the hole. Around the pilot hole, cracks with a width of approximately 60μ and an altered layer with segregation of iron group metals, which are bonding metals, were observed. The existence of such an altered layer can be estimated as follows. When drilling a pilot hole using a laser, the surrounding area of the pilot hole also becomes hot, and at this time, the iron group metal that is the diamond binding material also expands. This diamond sintered body has a skeleton structure in which diamonds are bonded together, and the iron group metal is trapped between the diamond particles. The coefficient of thermal expansion of diamond is approximately 1.5 to 4.8 × 10 ^-6 , while that of Co, an iron group metal, is approximately 12.5 to 16.0 × 10 ^-6 , and the difference in thermal expansion between diamond and Co causes thermal stress. It is thought that the diamond skeleton part was destroyed and cracks were generated. Furthermore, iron group metals are catalysts for diamond synthesis, and the presence of iron group metals causes the diamond to transform into graphite at high temperatures, which may also be the reason for the enlarged altered layer. Furthermore, the segregation of Co is thought to be due to the Co existing in the pilot hole melting and moving, which is thought to further promote graphite formation of diamond. Therefore, the present inventors eluted the iron group metal in the sintered body by acid treatment, and then prepared a pilot hole in the same manner as described above. As a result, the altered layer was about 20 μm, which was as expected, less than when processing a sintered body containing iron group metals. This sintered body is used to make sintered diamond dies, which are then brass-plated with copper wire (steel cord).
was drawn. As a result, when drawing copper wire, the coefficient of friction was low at the beginning of the wire drawing and the wire drawing was successful, but during the wire drawing the frictional force suddenly increased and the wire broke, making it impossible to draw the wire, and its lifespan was reduced to the iron level. It was shorter than a sintered diamond die that does not elute metal. In order to investigate the cause of this, we observed the inner surface of the die and found that copper was embedded in the recessed areas where iron group metals were eluted, and that this copper and copper wire adhered to each other, increasing the coefficient of friction. . Furthermore, when steel cord was drawn, vertical streaks appeared on the surface of the wire some time after the wire was drawn, and its lifespan was reached, and in this case as well, the performance was inferior to that of a sintered diamond die that did not elute iron group metals. Observation of the inner surface of the die revealed that there was considerable ring wear in the reduction section, which appeared to be caused by diamonds falling off, and diamond particles had fallen off in the bearing section as well, and the inner surface was extremely rough. The reason why this happened is thought to be as follows. When the iron group metal, which is a binder, is eluted from the sintered diamond, each diamond particle is held together only by the bonds between the diamond particles, resulting in a decrease in strength. However, steel cord has a high tensile strength, and the pressure applied to the inner surface of the die during wire drawing becomes extremely high, so it is presumed that the skeleton part, which is the bond between the diamonds, broke and the diamond particles fell out. Based on these experimental results, the inventors of the present invention conducted studies, produced prototypes of various materials, created dies, and conducted wire drawing tests. As a result, the diamond content is 40-95% by volume, and the remainder is 3-55% by volume of carbides of metals from groups 4a, 5a, and 6a of the periodic table, solid solutions or mixtures thereof, and 0.03-5% by volume of iron group metals. and voids 5% by volume
It has been discovered that a diamond sintered body consisting of less than 1% has very little machining-altered layer due to laser or electrical discharge machining, and has excellent performance as a die. The reason why the sintered body of the present invention has excellent performance is presumed as follows. During laser or electrical discharge machining, the temperature around the prepared hole increases, but there are few iron group metals whose thermal expansion is very different from that of diamond.
Since it is a carbide of groups 4a, 5a, and 6a, its coefficient of thermal expansion is lower than that of iron group metals, so it is less prone to cracking due to thermal stress. Also, during wire drawing, the pores were small at less than 5% by volume, so the wire material was not buried in the pores, and the carbide and diamond particles were tightly bonded, so there was no decrease in strength. . The sintered body of the present invention had the best performance as a die, especially when the carbide was WC or (Mo, W)C having the same crystal structure. The content of diamond particles in the sintered body of the present invention is preferably 40 to 95% by volume. When the diamond content is less than 40%, the diamond sintered body loses its characteristic good wear resistance. Furthermore, if the diamond content exceeds 95%, the binding material becomes too small, making it impossible to obtain a sintered body with satisfactory performance. Also, periodic table 4a, 5a,
The content of Group 6a carbides is preferably 3 to 55% by volume. If the carbide content is less than 3%, grain growth will occur if the diamond particle size is 3μ or less, and the content of iron group metals will increase even if diamond particles of 3μ or more are used. The number of pores formed by elution increases, and the performance as a die is no longer achieved. When the carbide content exceeds 55%, the wear resistance of the sintered body decreases because the diamond particle content decreases. The content of iron group metals is preferably 5% by volume or less. If the content of iron group metal exceeds 5%, the altered layer produced during pilot hole machining by laser or electric discharge becomes very large. Further, the number of pores is preferably less than 5% by volume, and preferably 1% by volume or more. When the amount of pores exceeds 5% by volume, the strength of the sintered body decreases, and diamond particles may fall off when drawing a wire with high tensile strength. When the number of pores is less than 1% by volume, the amount of iron group metal increases, and the damaged layer during pilot hole drilling becomes large. The diamond used in the sintered body of the present invention may be either synthetic diamond or natural diamond.
This diamond powder and periodic table 4a, 5a,
Group 6a carbide powder or solid solution or mixture crystal powder thereof and iron group metal powder of Fe, Co, and Ni are uniformly mixed using a means such as a ball mill. This iron group metal may be infiltrated during sintering without being mixed in advance. In addition, the inventors' prior patent application filed in 1972-
As shown in No. 51381, the pots and balls during ball milling are made of a sintered body of compounds such as carbides and iron group metals, and at the same time as the diamond powder is ground in the ball mill, the pots and balls are mixed with compounds such as carbides and iron group metals. There is also a method of mixing fine powder of sintered metal. The mixed powder is placed in an ultra-high pressure device and sintered under conditions where the diamond shown in FIG. 1 is stable. At this time, it is necessary to sinter at a temperature higher than the temperature at which a eutectic liquid phase appears between the iron group metal and the compound such as carbide used. For example, when TiC is used as the compound and Co is used as the iron group metal, a liquid phase occurs at about 1260°C under normal pressure. Under high pressure, this eutectic temperature is several tens of degrees Celsius
It is believed that the degree of Therefore, in this case, sintering is performed at a temperature of 1300°C or higher. The diamond sintered body thus produced is placed in an acid capable of corroding iron group metals, such as aqua regia, to elute iron group metals and create pores. In addition to wire drawing dies, the sintered body of the present invention can be used as cutting tools for cutting non-ferrous metals and the like. This will be explained in detail below using Examples. Example 1 Synthetic diamond powder with particle size of 0.5 μ and WC and Co
The powder was ground and mixed using a pot and ball made of WC-Co cemented carbide. The composition of the prepared mixed powder is as follows.

【table】

[Table] This mixed powder was packed in a container made of Ta and using an ultra-high pressure device, a pressure of 55Kb was first applied, and then a pressure of 145Kb was applied.
℃ and held for 20 minutes to sinter. This sintered body was taken out and placed in heated aqua regia to dissolve the iron group metals in the sintered body. Table 1 also shows the composition of the sintered body after the metal was eluted. Next, a pilot hole of 20 μm was made in each of these sintered bodies by laser machining, followed by wrapping to create a die with a hole diameter of 60 μm. Table 1 also shows the thickness of the process-affected layer around the pilot hole that occurred during laser processing. An ultrafine copper wire was drawn using the die thus prepared. For comparison, a commercially available diamond sintered body using Co as a binder was treated with aqua regia in the same manner as the sintered body of the present invention, and then a die was made and a copper wire was drawn. Also, natural diamond dies were drawn in the same manner. These results are also shown in Table 1. It can be seen that the sintered body of the present invention has few deteriorated layers due to laser processing, and the wire surface after wire drawing is as clean as that of a natural diamond die, indicating excellent performance. Example 2 A pilot hole of 50 μm was made by electric discharge machining on a commercially available diamond sintered body using the sintered body ABCDEF prepared in Example 1 and Co as a binder. Table 2 shows the width of the process-affected layer at this time. Next, a die for steel cord wire drawing with a wire diameter of 150μ was created by wrapping pilot holes in these sintered bodies, and a wire speed of 800 m/
wire drawing in emulsion type lubricating oil. The wire drawing results are also shown in Table 2. It can be seen that the die life is long when the sintered body of the present invention is used.

[Table] Example 3 A mixed powder having the composition shown in Table 3 was prepared. All the sintering conditions were the same as in Example 1, and the diamond sintered body was obtained by sintering using an ultra-high pressure device. These G~
A sintered body of M and a commercially available diamond sintered body made of Co as a binder were acid-treated to dissolve some of the iron group metals, and then a pilot hole of 100 μm was drilled by electrical discharge machining. Table 3 also shows the composition of the sintered body after aqua regia treatment and the width of the machining-affected layer due to electrical discharge machining. Next, the hole diameter is determined by wrapping with diamond particles.
A 0.15 mm die was made, and high carbon steel wire was drawn using this die. As shown in Table 3, the results showed that the sintered body of the present invention exhibited excellent wire drawing performance.

【table】 [Brief explanation of drawings]

FIG. 1 is for explaining the manufacturing conditions of the sintered body of the present invention, and shows the stable range on the pressure and temperature phase diagram of diamond. 1...Diamond-graphite equilibrium line, A...Diamond stability region, B...Graphite stability region.

Claims (1)

[Scope of Claims] 1 Contains 40 to 95% by volume of diamond, the remainder being carbides of metals from groups 4a, 5a, and 6a of the periodic table, or 3 to 55% by volume of solid solutions or mixture crystals of these metals, and iron group metals. A diamond sintered body for tools comprising 5% by volume or less and pores of less than 5% by volume and 1% or more. 2. The diamond sintered body for tools according to claim 1, wherein the remaining carbide is WC or (Mo, W)C having the same crystal structure as WC. 3 Diamond powder and Periodic Table 4a, 5a, 6a
A mixed powder of iron group metal carbides or solid solution powders or mixture crystals of these metals is prepared, and this is powdered or molded by molding, and then heated under high temperature and high pressure at which diamond is stable using an ultra-high pressure and high temperature equipment. A sintered body is created by hot pressing, and the sintered body is treated with acid to elute a part of the iron group metal. Table 4a, 5a, 6a group metal carbides or their solid solutions or mixture crystals 3~
A method for producing a diamond sintered body for tools comprising 55% by volume, 5% by volume or less of iron group metals, and 1% or more of pores less than 5% by volume. 4. The method for producing a diamond sintered body for tools according to claim 3, wherein the remaining carbide is WC or (Mo, W)C having the same crystal structure as WC.