阅读说明：本技术 烧结齿轮的制造方法 (Method for manufacturing sintered gear ) 是由 岛内一诚 上野友之 伊志岭朝之 野田宗巨 于 2020-04-28 设计创作，主要内容包括：一种烧结齿轮的制造方法,具备：准备圆筒状的压粉体的工序；利用滚刀对所述压粉体进行切齿加工的工序；以及对切齿加工后的所述压粉体进行烧结的工序,所述滚刀的每1周的刃数与条数之比超过8。(A method for manufacturing a sintered gear, comprising: preparing a cylindrical green compact; a step of performing gear cutting processing on the pressed powder body by using a hob; and sintering the green compact after the gear cutting process, wherein the ratio of the number of blades per 1 cycle of the hob exceeds 8.)

1. A method for manufacturing a sintered gear, comprising:

preparing a cylindrical green compact;

a step of performing gear cutting processing on the pressed powder body by using a hob; and

a step of sintering the green compact after the gear cutting process,

the ratio of the number of blades per 1 circle of the hob to the number of the blades exceeds 8.

2. The method of manufacturing a sintered gear according to claim 1,

in the step of gear cutting, a feed speed of the hob at one end surface of the green compact on the side from which the blades of the hob are removed is slower than a feed speed of the hob at the other end surface of the green compact.

3. The method of manufacturing a sintered gear according to claim 1 or claim 2,

in the step of gear cutting, the feeding speed of the hob is set to 1.0 mm/rev or less in a region of maximum 5mm or less from one end face of the hob on the evacuation side toward the other end face side in the green compact, and the feeding speed of the hob is set to 2.0 mm/rev or more in the other region.

4. The method of manufacturing a sintered gear according to any one of claim 1 to claim 3,

in the step of gear cutting, the green compact is arranged such that the axial direction thereof is along the vertical direction, and the hob is fed from the lower end surface side to the upper end surface side of the green compact.

Technical Field

The present invention relates to a method for manufacturing a sintered gear.

The present patent application claims the priority based on japanese patent application No. 2019-088650, filed on 8/5/2019, and cites the entire contents of the descriptions in said japanese patent application.

Background

Patent document 1 discloses that a green compact is machined into a gear shape and then sintered.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2017-186625

Disclosure of Invention

The method for manufacturing a sintered gear of the present invention includes:

preparing a cylindrical green compact;

a step of performing gear cutting processing on the pressed powder body by using a hob; and

a step of sintering the green compact after the gear cutting process, wherein,

the ratio of the number of blades per 1 circle of the hob to the number of the blades exceeds 8.

Drawings

Fig. 1 is an explanatory view showing a machining step in the method for manufacturing a sintered gear according to the embodiment.

Fig. 2 is a schematic side view showing an example of the hob.

Fig. 3 is a schematic cross-sectional view showing an example of the hob.

Fig. 4A is an explanatory view showing a feed start position of the hob in the machining process.

Fig. 4B is an explanatory view showing a state during machining in the machining step.

Fig. 4C is an explanatory view showing a feeding end position of the hob in the machining process.

Detailed Description

[ problems to be solved by the invention ]

The hardness of the pressed powder is low compared to the sintered body. Therefore, the cutting work of the compact is easier than that of the sintered compact. However, since the powder compact is obtained by merely compacting and compacting the powder, it is brittle and easily chipped. This makes it easy for the green compact to be chipped during cutting.

A hob is used for gear cutting of a gear. In the hob, a plurality of blades are provided along a thread on an outer peripheral surface of a cylindrical main body. In the case of gear cutting by a hob, generally, a workpiece is disposed so that the axial direction thereof is vertical, and the hob is disposed so that the axial direction thereof is perpendicular to the axial direction of the workpiece. Then, the hob and the workpiece are synchronously rotated, and the hob is fed in the axial direction of the workpiece. The gear is formed by cutting the blades into the outer peripheral surface of the workpiece in sequence.

When the powder compact is subjected to gear cutting by a hob, a notch may be formed in the powder compact. In particular, when the edge of the hob is removed from the end face of the green compact, a notch is formed in the green compact.

An object of the present invention is to provide a method for manufacturing a sintered gear, which can suppress chipping in a green compact during gear cutting by a hob.

[ Effect of the invention ]

The method for producing a sintered gear according to the present invention can suppress the occurrence of chipping in the green compact during gear cutting by a hob.

[ description of embodiments of the invention ]

The present inventors have conducted extensive studies on a method for suppressing chipping generated in a green compact during gear cutting by a hob and as a result, have found the following.

The inventor considers that: in order to suppress the occurrence of chipping, stress acting on the green compact during gear cutting by a hob can be reduced. Therefore, in order to reduce the cutting load per 1 blade of the hob, the present inventors paid attention to the number of blades per 1 cycle and the number of the hob. The larger the number of blades per 1 revolution of the hob, the larger the number of cuts per revolution of the hob. That is, the number of cuts of the blade per rotation of the hob increases. Therefore, the larger the number of blades per 1 cycle, the smaller the depth of cut per 1 blade. In other words, the smaller the thickness of the chip. The depth of cut is the amount of cut in the radial direction of the green compact. Thus, if the cutting depth per 1 blade is reduced, the cutting load is also reduced. As a result, the main force and the feed component force to which the powder compact is subjected become small, so that the stress generated in the powder compact can be reduced. On the other hand, the larger the number of hobs, the higher the processing efficiency. When the number of the hob is n, the powder pressing body rotates for every 1 circle by n pitches. That is, each revolution of the hob produces n pitches of teeth. However, if the number of hobs is increased, the depth of cut per 1 blade is increased accordingly. Therefore, the larger the number of hobs, the larger the cutting load per 1 blade.

Therefore, the larger the ratio of the number of blades per 1 circumference in the hob, i.e., the number of blades/number of blades, the smaller the cutting load per 1 blade, and the stress generated in the powder can be reduced. This can suppress the occurrence of chipping in the green compact. The present inventors have conducted extensive studies and, as a result, have found that: when the ratio of the number of blades per 1 revolution of the hob to the number of the blades exceeds 8, chipping of the green compact can be effectively suppressed.

First, embodiments of the present invention will be described.

(1) A method for manufacturing a sintered gear according to an embodiment of the present invention includes:

preparing a cylindrical green compact;

a step of performing gear cutting processing on the pressed powder body by using a hob; and

a step of sintering the green compact after the gear cutting process, wherein,

the ratio of the number of blades per 1 circle of the hob to the number of the blades exceeds 8.

In the method for producing a sintered gear of the present invention, the cutting load per 1 edge of the hob can be sufficiently reduced by making the ratio of the number of edges per 1 circumference to the number of pieces of the hob exceed 8. Therefore, stress generated in the green compact during gear cutting by the hob can be sufficiently reduced. Thus, the method for producing a sintered gear of the present invention can suppress the occurrence of chipping in the green compact during gear cutting by a hob.

(2) One embodiment of the method for producing a sintered gear of the present invention includes:

in the step of gear cutting, a feed speed of the hob at one end surface of the green compact on the side from which the blades of the hob are removed is slower than a feed speed of the hob at the other end surface of the green compact.

Since the feeding speed of the hob at one end surface on the side from which the edge of the hob is withdrawn in the green compact is slower than that of the hob at the other end surface, the above-described manner can produce the following effects.

The first effect is that a notch generated near one end face of the compact can be suppressed. When the hob is used to perform gear cutting, a notch is formed in the green compact when the edge of the hob is removed from the end face of the green compact. In particular, a notch is likely to be formed in the vicinity of one end surface of the green compact on the side from which the blade of the hob is removed. If the feeding speed of the hob is slow, the feeding amount per 1 blade becomes small. Therefore, the cut length per 1 blade becomes small. In other words, the length of the chip becomes smaller. The cut length is the amount of cut in the axial direction of the green compact. Thus, if the cutting length per 1 blade is reduced, the cutting load is also reduced. As a result, stress generated in the green compact at the time of gear cutting by the hob can be further reduced, and chipping generated in the vicinity of one end face of the green compact can be suppressed.

The second effect is that an increase in the machining time can be suppressed as compared with the case where the feed speed of the hob is constantly reduced. This is because the feed speed of the hob at the other end face of the compact is relatively fast compared to the one end face of the compact.

(3) One embodiment of the method for producing a sintered gear of the present invention includes:

in the step of gear cutting, the feeding speed of the hob is set to 1.0 mm/rev or less in a region of maximum 5mm or less from one end face of the hob on the evacuation side toward the other end face side in the green compact, and the feeding speed of the hob is set to 2.0 mm/rev or more in the other region.

If the feeding speed of the hob is slow, the feeding amount per 1 blade becomes small. Therefore, the cut length per 1 blade becomes small. In other words, the length of the chip becomes smaller. The cut length is the amount of cut in the axial direction of the green compact. Thus, if the cutting length per 1 blade is reduced, the cutting load is also reduced. As a result, the stress generated in the green compact during the gear cutting process by the hob can be further reduced. Therefore, in the above aspect, the notch generated in the green compact during the gear cutting process by the hob can be more effectively suppressed by setting the feed rate of the hob to 1.0 mm/revolution or less.

When the hob is used to perform gear cutting, a notch is formed in the green compact when the edge of the hob is removed from the end face of the green compact. In particular, a notch is likely to be formed in the vicinity of one end surface of the green compact on the side from which the blade of the hob is removed. In the above aspect, the feeding speed of the roller cutter is set to 1.0 mm/revolution or less in the region of 5mm or less at the maximum from the edge evacuation side end face of the roller cutter in the green compact toward the other end face side. Hereinafter, the above-described area is sometimes referred to as an "evacuation area". Up to 5mm or less means: in at least a part of the region within 5mm from the one end face of the green compact, the feeding speed of the hob may be 1.0 mm/turn or less. Of course, the feed rate may be made slower over the entire area within 5 mm. Therefore, the above-described aspect can effectively suppress the occurrence of chipping in the vicinity of one end face of the green compact, which is particularly likely to cause chipping. In the above aspect, the feeding speed of the hob is set to 2.0 mm/rpm or more in the region other than the evacuation region. That is, the feed speed in the withdrawal region is relatively slow. The evacuation area is extremely short compared to the moving distance of the hob from the machining start position to the machining end position during the gear cutting process. Therefore, the time required for the gear cutting process for 1 compact does not increase significantly. This can suppress chipping of the green compact and can suppress an increase in processing time. Thus, the above-described method can efficiently process the pressed powder and is excellent in productivity. The lower limit of the evacuation area is, for example, 0.1mm or more, further 0.5mm or more, and preferably 1mm or more from one end face of the dust compact on the side from which the blade of the hob is evacuated. The powder compact can be sufficiently suppressed from chipping by setting the feed speed of the roller cutter to 1.0 mm/revolution or less in the region of at least 0.1mm, and more preferably 0.5mm, from the edge-evacuation-side end surface of the roller cutter in the powder compact.

(4) One embodiment of the method for producing a sintered gear of the present invention includes:

in the step of gear cutting, the green compact is arranged such that the axial direction thereof is along the vertical direction, and the hob is fed from the lower end surface side to the upper end surface side of the green compact.

In the above aspect, the feeding direction of the hob is upward along the axial direction of the green compact.

[ detailed description of embodiments of the invention ]

Hereinafter, a specific example of the method for manufacturing a sintered gear according to the embodiment of the present invention will be described with reference to the drawings. The same symbols in the drawings denote the same names. It is to be noted that the present invention is not limited to these examples but is represented by the claims, and all changes within the meaning and range equivalent to the claims are intended to be embraced therein.

< method for producing sintered Gear >

The method for manufacturing a sintered gear according to an embodiment includes the following steps.

A first step: preparing a cylindrical green compact.

A second step: and a step of performing gear cutting processing on the pressed powder by using a hob.

A third step: and sintering the pressed powder after the gear cutting process.

One feature of the method for manufacturing a sintered gear according to the embodiment is that a hob with a ratio of the number of blades to the number of bars per 1 cycle exceeding 8 is used. Fig. 1 shows a state in which a powder compact 1 is subjected to a gear cutting process by a hob 2. The white arrows in fig. 1 indicate the rotation direction of the powder compact 1 and the hob 2 or the feeding direction of the hob 2 during the gear cutting process. Hereinafter, each step will be described in detail.

The first step: preparation procedure

In this step, a cylindrical green compact 1 is prepared.

(powder compacts)

The green compact 1 is obtained by compression molding a raw material powder containing a metal powder. The metal powder is a main material constituting the green compact 1 and further constituting the sintered gear. Examples of the metal powder include iron-based powder made of iron (pure iron) or an iron-based alloy. The purity of the pure iron may be 99% by mass or more, and more preferably 99.5% by mass or more. Examples of the iron-based alloy include an iron-based alloy containing an additive element and including iron (Fe) and inevitable impurities as the balance. The content of Fe in the iron-based alloy is preferably more than 50 mass%, more preferably 80 mass% or more, and further preferably 90 mass% or more. Examples of the additive element include 1 or more elements selected from the group consisting of copper (Cu), nickel (Ni), tin (Sn), chromium (Cr), molybdenum (Mo), manganese (Mn), and carbon (C). The additive elements contribute to improvement of mechanical properties of the iron-based sintered gear. Among the above-mentioned additive elements, the total content of Cu, Ni, Sn, Cr, Mo and Mn is, for example, 0.5 mass% or more and 5.0 mass% or less, and further 1.0 mass% or more and 3.0 mass% or less. The content of C is, for example, 0.2 to 2.0 mass%, and more preferably 0.4 to 1.0 mass%. The content of the metal powder in the raw material powder may be 90 mass% or more, and more preferably 95 mass% or more. Examples of the metal powder include metal powders produced by a water atomization method, a gas atomization method, a carbonyl method, a reduction method, and the like.

The average particle diameter of the metal powder is, for example, 20 μm to 200 μm, and more preferably 50 μm to 150 μm. When the average particle diameter of the metal powder is within the above range, handling is easy, and the raw material powder is easily compression molded. Therefore, the compact 1 having a high density and a high density can be easily produced. As a result, a sintered gear having a high density is obtained. The average particle diameter of the metal powder is the average particle diameter of the particles constituting the metal powder. The average particle diameter is a particle diameter (D50) when the cumulative volume in the volume particle size distribution measured by the laser diffraction particle size distribution measuring apparatus is 50%.

In addition to the metal powder, the raw material powder may contain at least one of a lubricant and a binder. The total amount of the raw material powder is set to 100 mass%, and the total content of the lubricant and the binder is, for example, 0.1 mass% or less. Examples of the lubricant include higher fatty acids, metal soaps, fatty acid amides, and higher fatty acid amides. Examples of the binder include resins such as polyethylene, polypropylene, polyolefin, polymethyl methacrylate, polystyrene, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyether, polyvinyl alcohol, and vinyl acetate; waxes such as paraffin wax. The lubricant and the binder may be added or not added as necessary.

The green compact 1 can be produced by filling a raw material powder in a mold and performing uniaxial press molding. A typical configuration of a mold for forming the cylindrical powder compact 1 may include: the die comprises a die, a lower punch and an upper punch embedded in the die, and a core rod inserted into the die. The molding pressure is, for example, 980MPa or more, further 1470MPa or more, and particularly 1960MPa or more. By increasing the molding pressure, the density of the powder 1 can be increased. Therefore, the density of the sintered gear can be increased. The upper limit of the molding pressure is not particularly limited, and may be 2160MPa or less, for example, 2060MPa or less. The green compact 1 can be produced by a known method.

The relative density of the green compact 1 is, for example, preferably 93% or more, more preferably 95% or more, and particularly preferably 96% or more. The relative density of the green compact 1 is preferably 100%, but may be 99% or less in view of manufacturability and the like. The relative density of the green compact 1 can be determined from [ measured density/theoretical density ]. times.100. The measured density can be measured by, for example, the archimedes method. The theoretical density can be calculated from the composition of the raw material powder, for example.

The size of the green compact 1 is not particularly limited as long as it is appropriately selected according to the size of the sintered gear to be produced. The outer diameter of the green compact 1 is, for example, 20mm to 160mm, and more preferably 25mm to 150 mm. The inner diameter of the green compact 1 is, for example, 10mm to 80mm, and more preferably 15mm to 70 mm. The difference in the width, i.e., the inner and outer diameters, of the green compact 1 is, for example, 10mm to 80mm, and more preferably 15mm to 70 mm. The height of the green compact 1, that is, the length in the axial direction, is, for example, 5mm to 120mm, and more preferably 10mm to 110 mm.

The second step: processing procedure

In this step, the green compact 1 is subjected to gear cutting by the hob 2.

(Hob cutter)

Referring to fig. 2 and 3, a schematic configuration of the hob 2 will be described. Fig. 2 is a side view of the hob 2 viewed in a direction perpendicular to the axial direction. Fig. 3 is a sectional view of the hob 2 viewed from the axial direction. As shown in fig. 2, the hob 2 has a plurality of blades 21 along a thread 22 on the outer circumferential surface of a cylindrical body 20. As shown in fig. 3, the number of blades per 1 cycle of the hob 2 is 9.

(Gear cutting processing)

As shown in fig. 1, when the powder compact 1 is subjected to gear cutting by the hob 2, the powder compact 1 is arranged so that the axial direction thereof is perpendicular to the axial direction of the hob 2. Then, the hob 2 is fed in the axial direction of the green compact 1 while synchronously rotating the green compact 1 and the hob 2. The teeth 13 of the gear are formed by cutting the blades 21 into the outer peripheral surface 11 of the compact 1 in sequence. In this example, the green compact 1 is disposed so that the axial direction thereof is along the vertical direction, i.e., the vertical direction, and the hob 2 is disposed so that the axial direction thereof is along the horizontal direction. The compact 1 is rotated in a counterclockwise direction when viewed from above. The hob 2 rotates so that the blade 21 enters the outer peripheral surface 11 of the green compact 1 from above. In this example, the hob 2 is fed from the lower end surface side to the upper end surface side of the green compact 1. That is, the feed direction of the hob 2 is upward, and the hob is forward milling (clinb cut) in which the tooth cutting process is performed from the lower end surface of the powder compact 1. The feeding direction of the hob 2 may be downward, and the hob may be a reverse milling (continuous cut) in which the tooth cutting process is performed from the upper end surface side of the powder compact 1.

In this example, the blade 21 of the hob 2 rotates so as to enter the outer peripheral surface 11 of the green compact 1 from above. Therefore, on the lower end surface side of the compact 1, the blade 21 of the hob 2 is withdrawn from the outer peripheral surface 11 of the compact 1 to the lower end surface. In this example, the case where the gear cutting process is performed in a state where the baffle 3 is attached to the lower end surface of the powder compact 1 is exemplified. The structure of the baffle 3 will be described later.

< ratio of number of blades to number of strips >

The ratio of the number of blades per 1 revolution in the hob 2 to the number of blades, i.e. the number of blades/number of blades, exceeds 8. As described above, the larger the number of blades per 1 cycle, the smaller the depth of cut per 1 blade. Therefore, the cutting load per 1 edge is reduced, so that the stress generated in the dust compact 1 acting at the time of machining can be reduced. On the other hand, the larger the number of the hob 2, the larger the cutting load per 1 blade. Therefore, the larger the number of blades/number of the hob 2 is, the smaller the cutting load per 1 blade is, and the stress generated in the green compact 1 can be reduced. This can suppress the occurrence of chipping in the green compact 1. The number of blades/number of the rotary cutters 2 is more preferably 9 or more, and particularly preferably 10 or more. The upper limit of the number of blades/number is not particularly limited, and may be 27 or less, for example.

The number of blades and the number of the hob 2 may be set appropriately so that the number of blades/number of the hob exceeds 8. The number of blades per 1 cycle of the hob 2 is, for example, 9 to 27 blades, and more preferably 10 to 25 blades. When the number of blades is increased, it is necessary to reduce the blades 21 or increase the outer diameter of the hob 2. When the blade 21 becomes smaller, the strength of the blade 21 decreases. When the outer diameter of the hob 2 is increased, the hob 2 becomes large, and the cost increases. The outer diameter of the hob 2 is, for example, more than 70mm and 140mm or less, and further 80mm to 130mm or less. The number of the rolling cutters 2 is, for example, 1 to 4, and more preferably 2 to 3.

< feed speed >

The feed speed of the hob 2 can be set appropriately. The feed rate is the distance that the hob 2 moves per revolution of the green compact 1, i.e. the feed rate. If the feeding speed is increased, the processing time can be shortened. However, the cutting length per 1 blade increases due to the increase in the feed amount. This increases the cutting load per 1 blade. On the other hand, if the feed rate is lowered, the cutting length per 1 blade is reduced, and the cutting load is reduced. However, if the feeding speed is too low, the working time becomes long, resulting in a decrease in productivity. The feed rate of the hob 2 is, for example, 0.1 mm/rev to 10 mm/rev, and more preferably 0.2 mm/rev to 9 mm/rev. The cutting speed of the hob 2 is, for example, 40 m/min to 280 m/min, and more preferably 50 m/min to 250 m/min.

In the gear cutting process, the feed rate of the hob 2 may be constant during the process or may be changed during the process. A processing example in the case of processing with a feed speed changed will be described with reference to fig. 4. Fig. 4A and 4C show the feed start position and the feed end position of the hob 2, respectively. Fig. 4B shows a state in the middle of the processing, and shows a state in which the blade 21 of the hob 2 reaches the evacuation area a in the green compact 1. In the case of changing the feeding speed, the feeding speed becomes slow at the end surface of the dust compact 1 on the side from which the blade 21 of the hob 2 is withdrawn, that is, in the vicinity of the lower end surface, and the feeding speed becomes fast at the other region including the other end surface, that is, the upper end surface. In this example, the feed speed of the hob 2 at the end face on the machining start side is slower than that at the end face on the machining end side in the green compact 1. Specifically, in a region of not more than 5mm from the lower end surface toward the upper end surface side of the dust compact 1, that is, the evacuation region a shown in fig. 4B, the feeding speed is set to not more than 1.0 mm/revolution. Further, in the other region, the feed rate is set to 2.0 mm/revolution or more. The other region is a region where the blade 21 of the hob 2 reaches the machining end position after passing through the evacuation region a.

When the hob 2 is used to perform gear cutting on the green compact 1, a notch may be formed in the green compact 1 when the blade 21 of the hob 2 is removed from the lower end surface of the green compact 1. In particular, a notch is easily formed in the vicinity of the lower end surface of the powder compact 1. As shown in the above-described working example, the feed speed is set to 1.0 mm/revolution or less in the evacuation area a, and the occurrence of chipping in the lower end surface of the dust compact 1 can be effectively suppressed. Further, in the region other than the evacuation region a, the feeding speed is set to 2.0 mm/revolution or more, so that an increase in the processing time can be suppressed. Therefore, the compact 1 can be efficiently processed, and productivity is excellent.

< baffle plate >

As shown in fig. 1, a baffle 3 may be disposed on the lower end surface of the powder compact 1. In this case, the baffle 3 may be subjected to a gear cutting process together with the green compact 1. When the tooth cutting is performed with the baffle 3 disposed, if the blade 21 of the hob 2 is removed from the lower end surface of the powder compact 1, it is difficult for a notch to be formed in the lower end surface of the powder compact 1. This is because the lower end surface of the green compact 1 is supported by the baffle 3, and a force can be applied in a direction in which the downward force in the direction in which the blade 21 is withdrawn is cancelled.

The material of the baffle 3 may be appropriately selected as long as it has rigidity that can apply a force in a direction in which the downward force is offset, which is a direction in which the blade 21 of the hob 2 is withdrawn. The baffle 3 may be made of metal such as steel or stainless steel.

The shape of the baffle 3 can be enumerated as a circle. The outer diameter of the baffle 3 may be the same as the outer diameter of the green compact 1, or may be larger than the outer diameter of the green compact 1. The difference between the outer diameter of the baffle 3 and the outer diameter of the compact 1 is, for example, 0mm to 0.7mm, more preferably 0.05mm to 0.6mm, and still more preferably 0.1mm to 0.5 mm. If the difference between the outer diameter of the baffle plate 3 and the outer diameter of the powder compact 1 is 0.05mm or more, the entire lower end surface of the powder compact 1 is easily supported by the baffle plate 3. If the difference between the outer diameter of the baffle 3 and the outer diameter of the compact 1 is 0.7mm or less, the diameter of the baffle 3 can be easily prevented from increasing. The thickness of the baffle 3 is, for example, 2mm to 10mm, and more preferably 3mm to 8 mm.

The third step: sintering Process

In this step, the green compact 1 after the gear cutting process is sintered.

The sintered gear is obtained by sintering the pressed powder 1 after the gear cutting process. The sintering may be performed under known conditions depending on the composition of the metal powder. When the metal powder is an iron powder or an iron-based alloy powder, the sintering temperature is, for example, 1100 ℃ to 1400 ℃ inclusive, and further 1200 ℃ to 1300 ℃ inclusive. The sintering time may be set according to the size of the green compact 1, and may be, for example, 10 minutes to 150 minutes, and more preferably 20 minutes to 60 minutes.

(other steps)

The method for manufacturing a sintered gear according to the embodiment may further include at least 1 of the following steps.

Finishing Process

This step is a step of finishing the green compact 1 after the tooth cutting process. This step is performed after the processing step as the second step and before the sintering step as the third step. Examples of the finish machining include chamfering and shaving. The chamfering and shaving may be performed by a known method.

Thermal treatment Process

This step is a step of heat-treating the sintered gear obtained by sintering. This step is performed after the sintering step as the third step. Examples of the heat treatment include quenching and tempering. The quenching treatment may be carburizing and quenching treatment. The quenching treatment, carburizing-quenching treatment, and tempering treatment may be performed under known conditions.

Grinding Process

This step is a step of polishing the sintered gear obtained by sintering. In the case where the sintered gear is heat-treated after the sintering step as the third step, this step is performed after the heat treatment step. The grinding process includes a tooth grinding process. The polishing process may be performed by a known method.

[ Effect ]

The method of manufacturing a sintered gear according to the embodiment can suppress chipping in the green compact 1 during gear cutting by the hob 2. This is because, in the machining process, by using the hob 2 in which the ratio of the number of blades per 1 cycle to the number of bars exceeds 8, the cutting load per 1 blade can be reduced. As a result, stress generated in the green compact 1 during the gear cutting process by the hob 2 can be reduced, and the occurrence of chipping can be suppressed. Specifically, the feed speed of the hob 2 is set to 1.0 mm/revolution or less at the evacuation area a of the green compact 1, and the feed speed is set to 2.0 mm/revolution or more at the other areas. This can more effectively suppress chipping of the powder compact 1 and shorten the processing time.

According to the method of manufacturing a sintered gear of the embodiment, the notch generated in the green compact 1 at the time of gear cutting is sufficiently small. Specifically, the length of the notch formed in the end face of the green compact 1 on the side from which the blade 21 of the hob 2 is removed, that is, the lower end face, may be 0.3mm or less, and further 0.2mm or less. If the length of the notch formed in the end face of the green compact 1 is 0.3mm or less, the notch can be removed by performing a finish processing such as chamfering in a subsequent step. The length of the notch is the length in the axial direction from the lower end surface of the powder compact.

[ test example 1]

The cylindrical green compact was subjected to a gear cutting test using a hob.

A cylindrical green compact having an outer diameter of 45mm, an inner diameter of 20mm and a height of 20mm was prepared.

The green compact was produced in the following manner. A mixed powder of an iron-based powder and a carbon powder was prepared as a raw material powder. The composition of the iron-based powder is Fe-1.9Ni-0.2Mn-0.55 Mo. The content of the additive element is mass%. The average particle size (D50) of the iron-based powder was 155. mu.m. The average particle diameter (D50) of the carbon powder was 5.8. mu.m. The mixing ratio of the iron-based powder to the carbon powder was 99.6:0.4 by mass ratio. The mixed powder was filled into a mold, and a cylindrical green compact was produced by a uniaxial pressing apparatus. The forming pressure was 1940 MPa. The density of the green compact was 7.71g/cm³. The relative density of the green compact was 98.8%.

And (4) performing gear cutting processing on the powder pressing body by using a hob so as to process the powder pressing body into a gear shape.

The specifications of the processed gear are as follows: modulus: 1.4; number of teeth: 29; pressure angle: 17.5 degrees; helix angle: 15.8 degrees.

The NC hob is attached to the hob so that the axial direction thereof is along the horizontal direction, and the green compact is arranged so that the axial direction thereof is along the vertical direction, i.e., the vertical direction. The tooth cutting process is performed by feeding the hob in the axial direction of the green compact while synchronously rotating the green compact and the hob. The feeding direction of the hob is down-milled. In test example 1, the gear cutting was performed in a state where the baffle was attached to the lower end surface of the green compact. The baffle used is a steel melt material. The baffle plate is shaped like a disk with an outer diameter of 45mm, an inner diameter of 20mm and a height of 5 mm. The outer diameter of the green compact is the same as the outer diameter of the baffle.

In test example 1, gear cutting was performed under the conditions of tests A, B and C shown below.

[ test A ]

The specifications of the hob used were: number of blades per 1 week: 24 edges; the number of the strips is as follows: 2, cutting; number of blades/number of strips: 12; the outer diameter is 120 mm.

The processing conditions were such that the feed rate was constant at 4.0 mm/revolution. That is, the feeding speed of the hob from the start of feeding to the end of feeding is kept constant.

[ test B ]

The specifications of the hob used were: number of blades per 1 week: 24 edges; the number of the strips is as follows: 2, cutting; number of blades/number of strips: 12; the outer diameter is 120 mm.

The processing conditions were such that the feed rate in the withdrawal region in the green compact was set to 0.5 mm/revolution. Specifically, the feeding speed in a section of ± 1mm in the up-down direction from the lower end surface of the green compact was set to 0.5 mm/revolution, and the remaining section was set to 4.0 mm/revolution. That is, the feed rate of the blade of the hob up to the position of 1mm in the downward direction from the lower end surface of the green compact was set to 4.0 mm/revolution. From this position, the feed rate was changed to 0.5 mm/revolution, and after performing gear cutting from the lower end surface of the compact to a position of 1mm in the upward direction, the feed rate was changed to 4.0 mm/revolution.

[ test C ]

The specifications of the hob used were: number of blades per 1 week: 16 blades; the number of the strips is as follows: 2, cutting; number of blades/number of strips: 8; the outer diameter is 80 mm.

The processing conditions were such that the feed rate was constant at 4.0 mm/revolution. That is, the feeding speed of the hob from the start of feeding until the end of feeding is kept constant.

(evaluation of notch)

Under each of the conditions of tests A, B and C, 1000 compacts were subjected to gear cutting. The pressed powder after gear cutting under each condition was evaluated for chipping. Evaluation of the notch was performed in the following manner. The lower end surface of each of 1000 green compacts processed under each condition was visually inspected during processing, and green compacts with notches were extracted. The positions where the notches were formed were observed with an optical microscope for the green compacts having the notches under the respective conditions, and the lengths of the notches were measured. The length of the notch is the maximum value of the length from the lower end surface of the powder compact in the axial direction. As a result, in test A, the length of the notch was 0.3mm on average. In test B, the length of the notches has an average value of 0.1 mm. On the other hand, in test C, the average value of the lengths of the notches was 0.5 mm.

(evaluation of processing time)

The machining time for gear cutting of the green compact under each of the conditions of tests A, B and C was examined. The machining time is an actual machining time required for gear cutting of 1 compact, in other words, a time from the start of machining to the end of machining. As a result, in test A, C, the processing time was 10 seconds. In contrast, in test B, the working time was 11.5 seconds.

From the above results, it was found that in test A, B using a hob with an edge count/number exceeding 8, the length of the notch was 0.3mm or less, and the notch was effectively suppressed. The difference between the processing times of test A, C and test B was 1.5 seconds, and the processing time of test B was hardly increased.

Description of the symbols

1 pressing of powder

11 outer peripheral surface

13 teeth

2 Hob

20 main body

21 blade

22 thread

3 baffle plate

And A, evacuating the area.