JPS643921B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is manufactured by powder metallurgy. W.C.
The present invention relates to a manufacturing method for improving the dimensional accuracy of a sintered metal part that is made of at least one of a -Co alloy, a TaC-Ni alloy, a stainless steel alloy, a high-speed steel alloy, and a TiN-Ni alloy and has a non-circular inner diameter. Parts manufactured by the powder alloy method are made into finished products or finished product blanks through the steps of raw material mixing, granulation, powder compaction, and firing. but,
Depending on the precision required for each product field of the finished product, there is a difference whether shrinkage due to sintering is considered to be relatively small or large. Therefore, when shrinkage due to sintering is a problem, factors related to dimensional changes include powder particle shape, powder particle size, powder fluidity,
These include uniform filling into the mold, compaction pressure, amount of binder added, granulation density, firing temperature, firing time, and firing atmosphere, and by controlling these factors, products with dimensional accuracy that can be satisfied for mass production are required. It's not easy to get. The present invention regulates shrinkage deformation and dimensional changes that occur during sintering in sintered alloy parts with a non-circular inner diameter by using a nest that controls the amount and direction of shrinkage that occurs during sintering, The purpose is to suppress dimensional variations, reduce finishing machining allowance, and minimize finishing machining load. In general, the inner diameter of so-called cylindrical or ring-shaped sintered metal parts is determined based on the shrinkage dimension when firing freely in advance. Set to narrow. Figure 1 schematically shows the dimensional variations in free firing when sintering is performed freely and when the dimensions are regulated using a nest (nested firing). Regarding the material of the insert, the material should not melt at the firing temperature, have high-temperature strength that can withstand the shrinkage stress of the sintered body at the firing temperature, have low diffusion of components between the sintered body, and do not cause close contact with the sintered body. It is necessary to satisfy the following conditions: the coefficient of thermal expansion is large compared to the coefficient of thermal expansion, and it is easy to detach from the sintered body upon completion of firing. If the insert is loaded into the fired product immediately after the powder molding process, the non-circular insert 4 and There is a phase shift between the nest and the engaged fired product 5 having a non-circular inner diameter, making it impossible to achieve the objective. This is because at the start of firing, there is a large gap between the insert and the fired product. The structure of the present invention is to manufacture a sintered alloy part that is made of at least one of WC cemented carbide, TaC cemented carbide, TiC cemented carbide, Co-based alloy, and powdered high speed steel alloy and has a non-circular inner diameter. In the method of The sintered alloy is characterized in that the sintered alloy is regulated, and an insert having a larger coefficient of thermal expansion than the sintered alloy is loaded to complete the firing. Incidentally, the sintered alloy of the present invention is intended for a sintered alloy that shrinks upon firing, and is not intended for a sintered alloy that expands. Examples according to the present invention will be described below. The alloy powder having the composition shown in Example 1 was pulverized and mixed in a ball mill to an average particle size of 1.5μ, and was molded into a shape with a non-circular inner diameter as shown in Fig. 3 using a hydraulic press at a molding pressure of 5t/ ^cm2 . molded. This molded body 1
After roasting in a hydrogen atmosphere at 300℃ for 1 hour, roasting was performed at 1220℃ in a 10 ^-3 torr atmosphere in a vacuum furnace.
After firing for 1.5 hours, the shrinkage rate was 16% as shown in Figure 4.
A preliminary sintered body 2 was obtained. Next, the sixth
The insert 4 shown in the figure was loaded and main firing was performed at 1258°C for 1.5 hours in a vacuum furnace in an atmosphere of 10 ^-3 torr.
A completed blank 3 with a shrinkage rate of 17.5% was obtained. Regarding the insert material, the thermal expansion coefficient of the fired body is 18.9×10 ^-6
Since it is ℃, the coefficient of thermal expansion is larger than this.
SUS304, which has a temperature of 20.1×10 ^-6 ℃, was selected, machined, and used. Table 2 5th by nest firing
A comparison between the blank dimensions shown in the figure and the dimensions obtained by firing without using inserts is shown. The number of blanks at this time was 400 for each, and 50 were extracted and measured. As can be seen from this table, when the core firing was performed after pre-firing, the dimensional variation was about 1/6 to 1/10 of that when firing was performed freely. However, as shown in Table 2, when the core firing was performed without performing the pre-firing step, the phase between the core and the sintered body was shifted, and the firing was performed freely. In comparison, dimensional variations gave poor results.

【table】

[Table] Example 2 A WC-10% Co alloy having the same shape as in Example 1 was molded using commercially available WC with a particle size of about 1.5 μm and Co powder with a particle size of 1.3 μm at a molding pressure of 2.5 t/cm ² . Vacuum firing was carried out for 1 hour at a pre-firing temperature of 1320°C to obtain a pre-sintered body with a shrinkage rate of 16.5%. A 99.9% Ti insert was machined into this and loaded into the inner diameter of the preliminary sintered body, and main firing was performed at 1400°C for 1 hour. Table 3 shows the dimensional variations when firing freely and the dimensional variations when firing with size regulation by nesting. As shown in this table, the purpose of improving dimensional accuracy was achieved by the manufacturing method according to the present invention.

[Table] Example 3 Commercially available TaC, Ni powder, and Co powder were ground in a ball mill and molded into the shape shown in Figure 3 at a pressure of 2.5 t/cm ² , followed by vacuum firing at 1350°C for 1 hour. ,5
A pre-sintered body having a composition ratio of %Co-5%Ni-TaC and a shrinkage rate of 16.5% was obtained. A 99.9% Ti insert was machined into this and loaded into the inner diameter of the pre-sintered body at 1420℃
A 1-hour final firing was performed. Table 4 compares the dimensional variations when firing freely and when firing with size control by nesting. As shown in this table, the manufacturing method according to the present invention was able to achieve the objective of improving blank dimensions.

[Table] As described above, the present invention introduces a preliminary firing process,
Since the insert is loaded and fired after this process, the inner diameter dimensional accuracy of sintered alloy parts with non-circular inner diameters is greatly improved compared to the conventional method without a pre-sintering process. The load of finishing machining such as electric discharge machining or abrasive machining can be reduced.

[Brief explanation of drawings]

Figure 1 is a graph showing the variation in dimensions between conventional free firing and nested firing, Figure 2 is a plan view showing the phase shift between conventional fired products and nested firing, and Figures 3 to 5 are graphs showing the variation in dimensions between conventional free firing and nested firing. The plan view of each step of the example, FIG. 6, is as follows:
FIG. 3 is a plan view of the nest of the present invention. 1... Molded body, 2... Pre-fired body, 3... Completed blank, 4... Insert, 5... Fired product.

Claims (1)

[Claims] 1. A method for manufacturing a sintered alloy part made of at least one of WC-based cemented carbide, TaC-based cemented carbide, TiC-based cemented carbide, Co-based alloy, and powdered high-speed steel alloy and having a non-circular inner diameter, Before the process of firing the sintered alloy, 70% to 95% of the shrinkage is completed.
A preliminary sintering step is provided to complete the shrinkage up to %, and after the completion of the preliminary sintering step, deformation and dimensional change are controlled, an insert having a larger coefficient of thermal expansion than the sintered alloy is loaded, and firing is completed. A method for manufacturing a sintered metal part having a non-circular inner diameter, characterized in that: