WO2019181454A1

WO2019181454A1 - Sintered body production method

Info

Publication number: WO2019181454A1
Application number: PCT/JP2019/008337
Authority: WO
Inventors: 剛志門村; 中西　徹
Original assignee: 日本電産株式会社
Priority date: 2018-03-22
Filing date: 2019-03-04
Publication date: 2019-09-26
Also published as: JP2019167566A

Abstract

[Problem] To provide a sintered body production method with which it is possible to produce a sintered gear with high dimensional accuracy without using dedicated equipment and without performing secondary processing (postprocessing). [Solution] This sintered body production method involves a step for compression molding a raw material powder containing raw material particles with a mold to obtain a molded body, and a step for sintering the molded body to obtain a sintered body. In the step for obtaining the molded body, vibration and a vertical-direction impact force are applied to the raw material particles inside the mold. Further, it is preferable to apply the vibration for a duration of 0.1-5 seconds and to apply the impact force 1-5 times.

Description

Method for manufacturing sintered body

The present invention relates to a method for producing a sintered body.

Conventionally, a sintered gear (sintered body) is manufactured by compression-molding (compacting) raw material powder to obtain a molded body, sizing the molded body, and then firing. The sintered gear manufactured by this method has a dimensional error of about 0.03 mm with respect to the sintered gear to be manufactured.
However, a high-precision sintered gear used for a robot hand or the like needs to be finished to a dimensional error (about 0.01 mm) comparable to cutting.

In order to satisfy such requirements, when forming a molded body, special molding such as hot molding, hot isostatic pressing (HIP), cold isostatic pressing (CIP) or the like is performed, or a sintered body. For example, it has been studied to perform secondary processing such as forging (see, for example, Patent Document 1) and cutting.
However, these methods are not suitable for mass production of sintered gears, because special equipment such as special equipment and incidental equipment is required or a post-process for secondary processing must be added. In addition, since the sintered body has a large number of nests, when secondary processing (particularly cutting) is performed, the nests appear on the surface and the mechanical strength of the sintered gear may be lowered.

On the other hand, when forming a molded body by inexpensive compression molding, it is necessary to further improve the dimensional accuracy of the molded body. Specifically, it is necessary to improve the filling property of the raw material powder into the mold. Usually, when the raw material powder is filled into the mold, the raw material powder is filled into the mold by free fall from the feeder. For this reason, there exists a problem that the filling property to the shaping | molding die of raw material powder is not stabilized.

JP 2002-137039 A

An object of the present invention is to provide a method for manufacturing a sintered body capable of manufacturing a sintered gear with high dimensional accuracy without using dedicated equipment and without performing secondary processing (post-processing).

The exemplary invention of the present application includes a step of compressing a raw material powder containing raw material particles with a molding die to obtain a molded body, and a step of firing the molded body to obtain a sintered body. Is a method for producing a sintered body characterized by applying vibration and impact force in the vertical direction to the raw material powder in the mold.

According to the exemplary invention of the present application, a sintered body with high dimensional accuracy can be manufactured.

It is the top view (a) and sectional drawing (b) which show typically the structure (sintering gear) of the sintered compact which concerns on one Embodiment of this invention. It is a figure which shows schematic structure of the shaping | molding apparatus used in manufacturing a sintered gear.

Hereinafter, the manufacturing method of the sintered compact of this invention is demonstrated in detail based on embodiment shown to an accompanying drawing.
FIG. 1 is a plan view (a) and a cross-sectional view (b) schematically showing a configuration (sintered gear) of a sintered body according to an embodiment of the present invention, and FIG. It is a figure which shows schematic structure of the shaping | molding apparatus used for.

Below, the case where a sintered compact is used as a sintered gear is demonstrated as a representative.
The direction parallel to the central axis of the sintered gear (the direction perpendicular to the paper surface of FIG. 1A) is the “axial direction”, the direction orthogonal to the central axis is the “radial direction”, and the axis is centered on the central axis. The surrounding direction is called “circumferential direction”.
A sintered gear 1 shown in FIG. 1 includes a disc-shaped gear body 2 and a plurality of teeth 3 that are arranged along the circumferential direction of the gear body 2 and project radially outward. The plurality of teeth 3 are provided at substantially equal intervals.

The sintered gear 1 is composed of a sintered body of raw material powder. The configuration of the raw material powder will be described in detail later.
The size of the sintered gear 1 is not particularly limited because it is designed according to the application to be used, but when the sintered gear 1 is a gear for a robot hand (high-precision gear), for example, the following Designed as such.
The tip circle diameter (indicated by “D” in FIG. 1) of the sintered gear 1 is preferably about 3 to 15 mm, more preferably about 5 to 10 mm. The number of teeth of the sintered gear 1 is preferably about 15 to 40, more preferably about 20 to 35.

Therefore, the module indicating the size (tooth thickness) of the teeth 12 is preferably about 0.15 to 0.3 mm, and more preferably about 0.15 to 0.25 mm. Even such a small (high accuracy) sintered gear 1 can be manufactured with high dimensional accuracy by using the raw material powder of the present invention.
The tooth width of the tooth 12 (indicated by “W” in FIG. 1) is preferably about 1 to 10 mm, and more preferably about 2 to 5 mm.

1 is a so-called spur gear, the present invention is not limited to this, and may be, for example, a screw gear, a bevel gear, a worm gear, a hypoid gear, or the like.
Such a sintered gear 1 is manufactured as follows.
Hereinafter, a method for manufacturing the sintered gear 1 (a method for manufacturing a sintered gear) will be described.

The method for manufacturing a sintered gear according to the present embodiment includes: [1] a molding step of compression molding raw material powder to obtain a molded body having a shape corresponding to the sintered gear 1, and [2] firing the molded body. And a firing step for obtaining a sintered body, and [3] a surface treatment step for heat-treating the sintered body to form an oxide film covering the surface thereof. Hereinafter, each process will be described sequentially.

[1] Molding process First, a molding apparatus and raw material powder are prepared.
The shaping | molding apparatus 10 shown in FIG. 2 is provided with the shaping | molding die 20 and the feeder 30 which accommodated the raw material powder.
The molding die 20 includes a die 21 having a through hole 211 that penetrates in the thickness direction, and an upper punch 22 and a lower punch 23 that are inserted into the through hole 211 of the die 21. The shape of the inner peripheral surface of the die 21 that defines the through-hole 211 corresponds to the shape (uneven shape) of the outer peripheral surface of the sintered gear 1 to be manufactured.

In the present embodiment, inside the lower punch 23, a core pin 231 extending along the axial direction,
A vibrating body 232 that applies vibration to the core pin 231 is disposed.
Further, although not shown, the molding apparatus 10 has a mechanism for lifting the die 21 and the lower punch 23 vertically upward and then dropping them.
With this configuration, it is possible to impart vibration and a vertical impact force to the raw material powder in the mold 20.

In the molding apparatus 10, a molded body is formed according to the following steps.
[1-1] First Step First, the tip of the lower punch 23 is inserted below the through-hole 211 of the die 21 to form a cavity (space) 212 with the die 21 and the lower punch 23 (FIG. 2). (See (a)). Next, the feeder 30 is slid on the die 21 so as to cover the cavity 212 with the feeder 30, and the raw material powder is filled into the cavity 212 from the feeder 30 (see FIG. 2B).

The raw material powder used to manufacture the sintered gear 1 is preferably configured as follows.
The raw material powder includes raw material particles having a particle size of a module [mm] or less of the sintered gear 1. With this configuration, the raw material particles can be filled not only into the tooth root portion of the cavity 212 but also into the tooth tip portion as necessary and sufficient.
In particular, in this embodiment, when the minimum particle size of the raw material particles is A [mm] and the maximum particle size is B [mm], the particle size of the raw material particles is adjusted so that B / A is 10 or less. Has been. That is, it is adjusted so that the difference in particle size of the raw material particles contained in the raw material powder does not become large.

B / A is preferably 7 or less, more preferably about 2 to 4. By adjusting B / A to the said range, the remarkable fall of the fluidity | liquidity of raw material powder can be prevented. Thereby, raw material powder can be stably supplied to the cavity 212 and can be filled with high density. Further, in this case, it is possible to prevent the amount of the raw material particles to be discarded from being excessively increased, and to suppress an increase in the cost of the raw material powder and consequently the manufacturing cost of the sintered gear 1.
The maximum particle size B of the raw material particles is preferably not more than half that of the module of the sintered gear 1, and more preferably about 0.35 to 0.45 times the module. Thereby, the filling density to the tooth tip part of the cavity 212 of a raw material particle can be raised more.

When manufacturing the high precision (small) sintered gear 1 as described above, the specific value of the maximum particle size B of the raw material particles is preferably about 0.1 to 0.25 mm. More preferably, it is about 0.2 mm. In this case, the specific value of the minimum particle diameter A of the raw material particles is preferably about 0.02 to 0.05 mm, and more preferably about 0.025 to 0.04 mm.
By setting the minimum particle size A and the maximum particle size B of the raw material particles in the above ranges, the raw material particles can be produced without reducing the fluidity of the raw material powder even when the sintered gear 1 with high precision is manufactured. The tooth tip portion of the cavity 212 can be sufficiently filled.
Here, the particle diameter of the raw material particles can be measured, for example, from a projected image by a laser.

The raw material particles can be produced using, for example, an atomizing method such as a pulverizing method, a water atomizing method, a gas atomizing method, a reduction method, a carbonyl method, or the like.
Examples of the constituent material of the raw material particles include Fe (iron) alone, various metal materials such as an alloy containing Fe as a main component and an arbitrary element, and various ceramic materials such as apatite-based ceramics. Examples of elements added to the alloy include Cr (chromium), Mo (molybdenum), Mn (manganese), Ni (nickel), Cu (copper), W (tungsten), V (vanadium), and Co ( Cobalt), Si (silicon), C (carbon), and the like.

Such raw material powder may contain a lubricant. Thereby, the fluidity | liquidity of raw material powder can be improved more.
Examples of the lubricant include fatty acids such as stearic acid, metal salts thereof, derivatives thereof (eg, amides, esters, etc.), fluorine resins, and the like. These compounds can be used individually by 1 type or in combination of 2 or more types.
In this case, the amount of lubricant contained in the raw material powder is not particularly limited, but is preferably 5% by mass or less, more preferably about 0.1 to 3% by mass.

In addition, in this embodiment, since the raw material particle | grains with a relatively small particle size are removed, the fluidity | liquidity of the raw material powder itself which does not contain a lubricant is high. Therefore, the fluidity of the raw material powder can be adjusted to a sufficiently high value by containing a small amount (about 0.1 to 0.5% by mass) of a lubricant.
The specific fluidity of the raw material powder is preferably about 25 to 50 sec / 50 g, more preferably about 30 to 40 sec / 50 g. A raw material powder having such a fluidity can be supplied to the cavity 212 with high stability. Here, the fluidity can be measured in accordance with a metal powder-fluidity measurement method defined in JIS Z 2502 (2012).

[1-2] Second step (overfill step)
Next, the die 21 and the lower punch 23 are relatively approached to reduce the volume of the cavity 212 (space 211), and a part of the raw material powder is returned to the feeder 30. Thereby, the packing density of raw material powder can be raised more.
[1-3] Third Step Thereafter, the feeder 30 is slid on the die 21 to be retracted from the cavity 212. At this time, surplus raw material powder is scraped off.

[1-4] Fourth Step Next, the vibrating body 232 is operated to vibrate the core pin 231. Accordingly, vibration is applied to the raw material powder in the cavity 212 through the lower punch 23. At this time, the raw material particles in the cavity 212 are rearranged, and the packing density of the raw material powder can be increased.
The time for applying vibration is preferably about 0.1 to 5 seconds, more preferably about 0.5 to 3 seconds. By applying vibration to the raw material powder in a relatively short time, the packing density can be further increased while preventing the raw material powder from scattering.
The frequency of vibration is not particularly limited, and is appropriately set according to the particle size of the raw material particles, the fluidity of the raw material powder, and the like in order to increase the packing density of the raw material powder into the cavity 212.

[1-5] Fifth Step Next, the die 21 and the lower punch 23 are lifted vertically upward and then dropped. Hereinafter, this operation is also referred to as “tap”. Thereby, an impact force in the vertical direction can be applied to the raw material powder in the cavity 212. Thereby, the packing density of the raw material particles in the cavity 212 can be further increased.
The number of times of applying the impact force (number of taps) is preferably about 1 to 5 times, and more preferably about 2 to 3 times. When the number of taps is within the above range, the density of the raw material powder can be further increased without disturbing the arrangement of the raw material particles rearranged in the cavity 212.
Further, the height at which the die 21 and the lower punch 23 are lifted is not particularly limited, but is preferably about 1 to 10 mm, and more preferably about 3 to 7 mm. Thereby, an appropriate impact force can be imparted to the raw material powder.

[1-6] Sixth Step Thereafter, the tip of the upper punch 22 is inserted into the cavity 212, and the raw material powder is compressed by the lower punch 23 and the upper punch 22 (see FIG. 3C).
The pressure at which the raw material powder is compressed (molding pressure) is not particularly limited, but is preferably about 0.5 to 3 tons, and more preferably about 1 to 2 tons.
As described above, the molded body 11 having a shape corresponding to the sintered gear is obtained in the cavity 212.
[1-7] Seventh Step Thereafter, the die 21 and the lower punch 23 are brought relatively close to each other, and the molded body 11 is discharged from the cavity 212.

[2] Firing step Next, the obtained molded body 11 is fired to obtain a sintered body.
By this sintering, in the molded body 11, diffusion occurs at the interface between the raw material particles, leading to sintering. At this time, the molded body 11 is entirely contracted to obtain a high-density sintered body. In the present invention, since the raw material powder as described above is used, the effect is particularly high.
The firing temperature is not particularly limited because it is set depending on the composition, particle size, and the like of the raw material powder used in the production of the molded body 11, but is preferably about 950 to 1300 ° C., and preferably about 1000 to 1200 ° C. Is more preferable.

The firing time is preferably about 0.2 to 3 hours, and more preferably about 0.5 to 2 hours.
The atmosphere during firing is not particularly limited, and examples thereof include an air atmosphere, an oxidizing atmosphere, a reducing atmosphere, an inert gas atmosphere, or a reduced-pressure atmosphere obtained by reducing these atmospheres.
Since the sintered body obtained in this way has extremely high dimensional accuracy, the sintered gear 1 can be formed without performing secondary processing such as forging and cutting. The secondary processing refers to processing that mechanically changes the shape of the sintered body, and the secondary processing does not include surface treatment (heating treatment) described later.

The error between the dimension in the radial direction of the sintered gear 1 to be manufactured and the dimension in the radial direction of the obtained sintered body is 6σ, preferably 0.02 mm or less, more preferably 0.005 to 0. About .015 mm. By using the raw material particles having a particle size as described above, it is possible to obtain the sintered gear 1 with high dimensional accuracy.

[3] Surface treatment step Next, the sintered body is subjected to a surface treatment for forming an oxide film on the surface.
By this surface treatment, the smoothness of the surface of the sintered gear 1 is increased. Further, by forming an oxide film on the surface, the sintered gear 1 with an oxide film can further reduce a dimensional error with respect to the sintered gear 1 to be manufactured.
The surface treatment temperature is not particularly limited, but is preferably about 500 to 1000 ° C, more preferably about 700 to 950 ° C.

The surface treatment time is preferably about 0.5 minute to 1 hour, more preferably about 1 to 45 minutes.
The atmosphere for the surface treatment is not particularly limited, and examples thereof include a steam atmosphere, an oxidizing atmosphere, an inert gas atmosphere, or a reduced pressure atmosphere obtained by reducing these atmospheres.
[3] The surface treatment step may be performed as necessary and may be omitted.

As mentioned above, although the manufacturing method of the sintered compact of this invention was demonstrated based on suitable embodiment, this invention is not limited to these.
Further, the sintered gear 1 is not only an industrial machine part such as a robot hand, but also, for example, an automobile part, a bicycle part, a railway vehicle part, a marine part, an aircraft part, a space transportation part, etc. It is used for parts for electronic equipment such as parts for transportation equipment, parts for personal computers and parts for portable terminals, parts for electric equipment such as refrigerators, washing machines and air conditioners, parts for plants, parts for watches, and the like.

Furthermore, the sintered body is not limited to the sintered gear 1 and may be, for example, a bearing, a cylinder, or the like.

Next, examples of the present invention will be described.
1. Manufacture of sintered gear with oxide film

(Example 1)
[A] First, raw material particles containing Fe as a main component (maximum particle size B: 0.212 mm, manufactured by Höganäs) were prepared.
[B] Next, particles having a particle diameter of less than 0.032 mm were removed from the raw material particles using a sieve. Therefore, B / A is 6.6.

[C] Next, the raw material particles and N, N′-ethylenebisstearamide (made by Kao Corporation, “KAO WAX EB-FF”) as a lubricant are mixed with a V-type mixer for 30 minutes to obtain a raw material. A powder was obtained. The amount of N, N′-ethylenebisstearamide contained in the raw material powder was adjusted to 0.2% by mass. Further, the fluidity of the obtained raw material powder was measured by using a fluidity measuring device (in-house manufactured, conforming to JIS Z 2502 (2012)), and was 30 sec / 50 g.

Next, this raw material powder was compression molded using a molding apparatus shown in FIG. 2 to obtain a molded body.
First, the raw material powder was filled into the cavity from the feeder. After applying vibration to the raw material powder in the cavity for 1 second, an impact force was applied by two tapping operations. Thereafter, the raw material powder was scraped off by a feeder and then compressed with an upper punch and a lower punch. The pressure during compression molding was 1.1 ton and the temperature was room temperature.

[D] Next, the obtained molded body was fired at 1200 ° C. for 1 hour in an air atmosphere to obtain a sintered gear (sintered body). The shape of the sintered gear was a tip diameter 9 mm, a module 0.3 mm, and 27 teeth.
[E] Next, the obtained sintered gear was heat-treated at 750 ° C. for 1 minute in an air atmosphere to form an oxide film having an average thickness of 0.01 mm on the surface of the sintered gear. As a result, a sintered gear with an oxide film was obtained. The average thickness of the oxide film was measured by a cross-sectional observation method.

(Example 2)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that an overfill operation was performed before applying vibration to the raw material powder.
(Example 3)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the time for applying vibration and the number of taps were changed.
Example 4
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the shape of the sintered gear was 6 mm in tip diameter, 0.2 mm in module, and 28 teeth.

(Comparative Example 1)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the application of vibration to the raw material powder in the cavity was omitted.
(Comparative Example 2)
A sintered gear with an oxide film was obtained in the same manner as in Example 1 except that the application of the impact force by the tap operation to the raw material powder in the cavity was omitted.

2. Measurement of dimensional error The dimensional error 6σ of the molded body and the sintered gear obtained in each example and each comparative example was measured with a factory microscope (measurement microscope). In addition, the dimension error in the thickness direction was measured for the molded body, and the dimension error in the thickness direction or the radial direction was measured for the sintered gear.
The measurement results are shown in Table 1 below together with the composition of the raw material powder.

As described above, by applying vibration and impact force to the raw material powder in the cavity, the dimensional error 6σ in the thickness direction of the molded body can be reduced, that is, the density of the molded body can be increased. . The sintered gear of each example obtained by firing such a molded body had high dimensional accuracy.
Moreover, the said effect showed the tendency to improve by adding overfill operation.
On the other hand, if the application of vibration or impact force to the raw material powder in the cavity is omitted, the density of the molded body could not be increased. The sintered gear of each comparative example obtained by firing such a molded body was inferior in dimensional accuracy.

DESCRIPTION OF SYMBOLS 1 ... Sintered gear 11 ... Molded body 2 ... Gear main body 3 ... Teeth 10 ... Molding device 20 ... Mold 21 ... Die 211 ... Through-hole 212 ... Cavity 22 ... Upper punch 23 ... Lower punch 231 ... Core pin 232 ... Vibrating body 30 ... Feeder

Claims

Compressing raw material powder containing raw material particles with a molding die to obtain a molded body;
Firing the molded body to obtain a sintered body,
In the step of obtaining the molded body, a method for producing a sintered body, wherein vibration and an impact force in a vertical direction are applied to the raw material powder in the mold.
The method for producing a sintered body according to claim 1, wherein the time for applying the vibration is 0.1 to 5 seconds.
The method for producing a sintered body according to claim 1 or 2, wherein the number of times of applying the impact force is 1 to 5.
The mold has a die, and an upper punch and a lower punch inserted into the die,
The step of obtaining the molded body is a state in which the space formed by the die and the lower punch is covered with a feeder containing the raw material powder, and the raw material powder is filled into the space from the feeder;
Applying the vibration to the raw material powder in the space via the lower punch;
Dropping the die lifted vertically upward and the lower punch to give the impact force to the raw material powder in the space;
The method for producing a sintered body according to any one of claims 1 to 3, further comprising: compressing the raw material powder in the space with the lower punch and the upper punch to obtain the formed body. .
The step of obtaining the molded body further includes a step of reducing the volume of the space and returning a part of the raw material powder to the feeder between the step of filling the raw material powder and the step of applying the vibration. The manufacturing method of the sintered compact of Claim 4 which has these.
The sintered body is a sintered gear;
The raw material particles have a particle size of the sintered gear module [mm] or less;
The sintered body according to any one of claims 1 to 5, wherein B / A is 10 or less when the minimum particle diameter of the raw material particles is A [mm] and the maximum particle diameter is B [mm]. Manufacturing method.
The method for manufacturing a sintered body according to claim 6, wherein the module of the sintered gear is 0.15 to 0.3 mm.
The method for producing a sintered body according to claim 6 or 7, wherein after the sintered body is obtained, the sintered body is used as the sintered gear without subjecting the sintered body to secondary processing.
The error between the dimension in the radial direction of the sintered gear to be manufactured and the dimension in the radial direction of the obtained sintered body is 0.02 mm or less at 6σ. The manufacturing method of the sintered compact of this.