JP2000063905A - Production of metallic sintered product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the improvement of the production yield in a sintered product and to easily produce the sintered product having high precision and high hardness at a high yield by facilitating the modifying operation for a sintered molded body. SOLUTION: In a state in which a green molded body obtd. by subjecting a molding material contg. the powder of a metallic material and a binder contg. a thermoplastic resin to injection molding is disposed in a heating furnace, by executing heating treatment under the reduced pressure, the binder is removed from the green molded body, and, successively, by executing secondary heating treatment under the reduced pressure, the metallic material powder is sintered to obtain a sintered molded body. After the discharge of the sintered molded body from the heating furnace, quenching is executed to increase the hardness of the sintered molded body and to obtain a sintered product. Before the quenching, the testing of the shape or dimensions of the sintered molded body is executed, and, as for the ones in which the shape or dimensions are judged as defectives by this testing, the quenching is executed after modification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the field of manufacturing technology for sintered metal products, and in particular, the correction of the shape or size of a sintered molded product obtained by sintering a green molded product obtained by metal injection molding. The present invention relates to a method for manufacturing a metal-sintered product in consideration of facilitating the above.

[0002]

2. Description of the Related Art Sintered metal products have been used in a wide range of fields in recent years because of their advantages in mass productivity. As an example thereof, an actuator finger for a circular knitting machine is exemplified.

In a circular knitting machine, an actuator finger is appropriately brought into contact with a knitting needle in a needle selection mechanism section to control a moving path of the knitting needle, whereby a desired pattern can be formed on a knitted fabric to be braided. it can. Such control of the movement path of the knitting needle causes each of a large number of actuator fingers to engage with the action portion of the actuator,
This is done by controlling the actuator in a desired manner by an electronic computer.

The actuator finger is adapted to the tip (acting portion) of an actuator using a piezoelectric element that operates by receiving an electric signal under the control of an electronic computer, and has a first portion that receives a driving force from the acting portion and the first portion. The second portion is fixed to the first portion and appropriately contacts the knitting needle to control the traveling movement route thereof.

Since the actuator engaging portion of the first portion which engages with the actuator needs to accurately follow the minute displacement of the acting portion of the actuator, extremely high dimensional accuracy is required, but it is so high. Hardness is not required. On the other hand, the head portion (knitting needle contact portion) of the second portion that comes into contact with the knitting needle is required to have high hardness in order to reduce wear due to frequent rubbing (contact) of the knitting needle and to prolong life. To be done.

As a method of manufacturing such an actuator finger, a molding material obtained by mixing metal powder with a binder containing a thermoplastic is molded by an injection molding machine to obtain a desired shape corresponding to a molding die. It is possible to use a metal injection molding method (MIM method) in which a green molded body is produced, and then the green molded body is heat-treated to burn or sublimate the binder plastic and to sinter the metal powders in the green molded body. it can. According to this, it is possible to obtain a product (actuator finger) made of a metal sintered body having a shape similar to that of the green molded body, although the dimension of the green molded body is shrunk. This method has an advantage that a large amount of products can be manufactured in a short time as compared with a method of machining a bulk metal material by cutting or the like to obtain a desired shape.

By the way, in the production of a metal-sintered product using such metal injection molding, as the precision required for the shape and size of the product becomes stricter, a heat treatment for obtaining a sintered-molded product from a green compact is performed. There is a problem that deviations from the required values of the shape and dimensions due to the non-uniform contraction of the molded body are accompanied. That is, it may be quite difficult in practice to evenly shrink each part when obtaining a sintered compact from the green compact, especially when the shape of the product is complicated, the self-weight of each part of the green compact. Deformation is likely to occur due to the effect of, and when the frictional force between the green compact and its mounting surface is large, the compact part that comes into contact with the mounting surface due to that effect is equivalent to other parts. At the shrinkage rate, deformation or dimensional error may occur without shrinking. Therefore, in order to improve the manufacturing yield of products that require high accuracy, it is necessary to correct the molded body with inaccurate shapes and dimensions generated as described above and correct it to make it a good product. Is preferred.

In the conventional manufacturing method, when heat-treating a green molded body, first, heating is performed at a relatively low temperature in a debinding heating furnace to remove the binder from the green molded body, and then the debinding process is performed. The molded body is transferred to a sintering furnace, where it is sintered. The sintered compact is carburized and quenched in order to obtain the high hardness required for the second portion of the actuator finger. The straightening operation is performed on the sintered compact having insufficient accuracy after the heat treatment in the sintering furnace is completed.

However, carbon and oxygen adhere to the surface of the molded body during the binder removal heat treatment and transfer of the molded body from the debinder furnace to the sintering furnace, and carbon and oxygen adhere to the surface of the molded body during the sintering heat treatment. By being adsorbed, the surface hardness of the sintered molded body is increased. Therefore, as the hardness is increased, it becomes difficult to correct the sintered compact.

Therefore, the present invention realizes an improvement in the production yield of the sintered product by facilitating the straightening work of the sintered compact, and easily produces a highly accurate and high hardness sintered product with a high yield. The purpose is to do.

[0011]

According to the present invention, in order to achieve the above object, a green molded body obtained by injection molding a molding material containing a powder of a metal material and a binder containing a thermoplastic resin. Is placed in a heating furnace, the first heat treatment is performed under reduced pressure to remove the binder from the green compact, and the second heat treatment is subsequently performed under reduced pressure to the metal material powder. To obtain a sintered molded product, and after removing the sintered molded product from the heating furnace, quenching is performed to increase the hardness of the sintered molded product to obtain a sintered product, a metal sintered product, A method for manufacturing the same is provided.

In one aspect of the present invention, the shape or size of the sintered molded body is inspected before the quenching, and if the shape or size is judged to be defective in this inspection, it is corrected and then Quench.

In one aspect of the present invention, in the second heat treatment, the temperature is raised at a rate of 8 ° C./minute or more.

In one aspect of the present invention, the temperature is raised at a rate of 8 ° C./min or more in the second heat treatment at a temperature of at least 800 to 1050 ° C.

In one aspect of the present invention, the first heat treatment is performed at a temperature of 550 ° C. or lower.

In one aspect of the present invention, the temperature rising rate in the first heat treatment is 3 ° C./min or less.

In one aspect of the present invention, the sintered molded body has a hardness Hmv of 80 to 150.

In one aspect of the present invention, the sintered product has a hardness Hmv of 600 or more.

In one aspect of the present invention, the metallic material has a carbon content of 0.2% or less.

In one embodiment of the present invention, the metallic material is stainless steel or Fe-2 to 8% Ni.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a side view for explaining an embodiment of a method for producing a metal sintered product according to the present invention, and FIG. 2 is a sectional view taken along line XX '. In this embodiment, an actuator finger for a circular knitting machine is used as the metal sintered product.

1 and 2, reference numeral 1 indicates an actuator finger, reference numeral 2 indicates a first portion thereof, and reference numeral 4 indicates a second portion of the actuator finger 1. As shown in FIGS. 1 and 2, the first
2 is a cross-section U that is open downward and extends along a direction orthogonal to the XX 'direction (vertical direction).
It has a V-shaped groove (groove width is, for example, 2.0 mm) 22, and a pair of legs 24 are formed so as to form the groove 22. The second portion 4 has a substantially square through hole (parallel to the groove 22) having a minimum inner diameter of, for example, 1.7 mm 42.
The base portion 44 is formed with a base, a neck portion 46, and a head portion 48 supported by the neck portion. Reference numeral 6 indicates a joint surface between the first portion 2 and the second portion 4.

The first portion 2 and the second portion 4 are made of the same material, and there is no clear boundary, but the first portion 2 is a portion that does not require so high hardness,
The second portion 4 is a portion that requires sufficiently high hardness.

1 and 2, reference numeral 50 indicates a mounting surface in the heating furnace on which the actuator fingers 1 are mounted.

FIG. 3 is a sectional view showing a usage state of the actuator fingers of this embodiment. A pin 10 having a circular cross section that functions as a rotation center support shaft is provided in the through hole 42.
Has penetrated. The pin 10 is arranged in the needle selection mechanism of the circular knitting machine, and is fitted with the minimum inner diameter of the through hole 42 and a minute clearance. Therefore, the actuator finger can rotate around the pin 10 as a center. On the other hand, the upper end (action portion) of the piezoelectric element actuator 12 is inserted into the groove 22 from below with a minute clearance. The actuator 12
Has a lower end fixed to the needle selection mechanism of the circular knitting machine, and is operated by receiving a required electric signal in association with a number of other actuator fingers under the control of the electronic computer. As a result, the upper end of the actuator 12 can be displaced in the left-right direction in FIG. 3 as indicated by the arrow. Along with this, the leg portion 24 which is fitted so as to sandwich the actuator acting portion receives the driving force, the actuator fingers rotate around the pin 10, and the head 48 in FIG. 3 as shown by the arrow. It can be displaced left and right. The displacement of this head 48 is
Since the distance from 2 is larger than the distance from the pin to the actuator acting portion, it corresponds to an enlarged displacement of the actuator acting portion. The maximum displacement of the head 48 is 0.5 mm on one side and about 1 mm on both sides.

The knitting needle of the circular knitting machine (not shown) can come into contact with the head 48 during its movement, and the movement path after contact and separation is controlled according to the magnitude of the displacement of the head. It The foot portion 24 constitutes an actuator engaging portion, and the head portion 48 constitutes a knitting needle contact portion.

The actuator finger as described above is manufactured as follows.

First, a molding material containing a metal material for the actuator finger 1 composed of the first portion 2 and the second portion 4 is obtained. This molding material is, for example, a powder of Fe-2 to 8% Ni having a carbon content of 0.2% or less mixed with polyethylene, paraffin wax and stearic acid as a binder. The amount of binder added is, for example, 40 to 50% by volume. As the material of the metal powder, other materials such as SUS3 having a carbon content of 0.2% or less
Stainless steel such as 16L or SUS304L can be used.

This molding material is put into a molding machine and injection-molded into a cavity to obtain a green molded body.

By subjecting the green compact thus obtained to heat treatment, the binder is removed from the green compact and the metal powder is sintered to obtain an actuator finger as shown in FIGS. This heat treatment
It can be carried out in a vacuum heating furnace according to a temperature curve as shown in FIG. 4, for example.

That is, first, the temperature is raised from room temperature to 100 ° C. in 30 minutes from time 0 to T ₁ , and this temperature is changed to time T 1.
_Hold from ₁ to T ₂ for 4 hours. During this period, the paraffin wax is scattered from the molded body, and the pressure in the heating furnace is reduced to about 10 ⁻⁵ Torr in order to accelerate its removal to the outside of the system.

Next, from time T ₂ to T ₃ , 0.5 ° C./m
The temperature is raised to 400 ° C. with a temperature gradient of in, and this temperature is maintained from time T ₃ to T ₄ for 1 hour.

Next, from time T ₄ to T ₅ , 1 ° C./min
The temperature gradient is raised to 500 ° C., and this temperature is set to time T
Hold for 2 hours from ₅ to T ₆ .

By the above, the binder burns.

Next, from time T ₆ to T ₇ , 10 ° C./mi
The temperature is raised to 1200 ° C. with a temperature gradient of n, and this temperature is maintained for 1 hour from time T ₇ to T ₈ .

Next, from time T ₈ to T ₉ , 10 ° C./mi
The temperature is raised to 1350 ° C. with a temperature gradient of n, and this temperature is maintained for 4 hours from time T ₉ to time T ₁₀ .

As a result, the metal powders are sintered together.

Next, in the heating furnace, it is rapidly cooled to room temperature from time T ₁₀ to T ₁₁ over 4 hours.

Incidentally, time T₂ To T₁₁Until the inside of the heating furnace is
After reducing the pressure to about 10 Torr by introducing the raw gas,
Ku. Time 0 to time T₆ Is the first heat treatment,
Time T ₆ From time T₁₁Is the second heat treatment.

The sintered molded product obtained as described above is
The first heat treatment for debinding and the second heat treatment for sintering are carried out under reduced pressure and further in a heating furnace under a nitrogen atmosphere without being taken out of the furnace, whereby the binder Carbon and oxygen generated by heat treatment,
Furthermore, the amount of carbon and oxygen in the outside air attached to the surface of the sintered compact is extremely small, and therefore the sintered compact has a low carbon and oxygen content and a hardness of Hmv110-140.
For this reason, even when performing correction (for example, correction of the width of the groove 22) for improving the accuracy of the shape and size of the sintered molded body as necessary, the correction work by pressing or cutting is easy (for metal materials, Since the carbon content is 0.2% or less, the hardness of the molded body is little improved by the quenching effect during the process of cooling in the furnace). In addition, in order to perform correction by pressing deformation, Hmv
It is preferably 150 or less, and Hmv 250 or less in order to carry out straightening by cutting.

With respect to the hardness of the sintered compact, a comparison with the conventional method will be made. When Fe-4% Ni is used as the metal material, consistent heat treatment under reduced pressure as in the embodiment of the present invention. In the case where the binder removal and sintering are carried out in, the obtained sintered compact has a total content of carbon and oxygen of 0.01% or less and a hardness Hmv of 110 to 140.
However, using the same material, heat treatment was performed in the debinding furnace in the air as in the conventional case, the molded body was taken out from the debinding furnace and transferred to the sintering furnace, and the sintering furnace was heated in the atmosphere. When the heat treatment was carried out inside, the total content of carbon and oxygen in the obtained sintered compact was 0.05 to 0.1% and the hardness Hmv was 150 to 180.

Therefore, the sintered compact obtained according to the present invention is significantly easier to straighten than the sintered compact obtained by the conventional method. Such a straightening operation can be carried out by inspecting the shape or size of the sintered molded product obtained in the sintering step, and only if the shape or size is judged to be defective in this inspection.

The sintered compacts having the required accuracy, including those that have been straightened as required in the above manner, are subjected to carburizing and quenching treatment. This quenching treatment condition is, for example, 850
120 minutes at ° C. Thereby, the hardness Hmv of the molded body
Is improved to about 650 to 800, and the required hardness required for the second portion 4 is obtained.

In the above embodiment, in the second heat treatment, heating is performed rapidly from time T ₆ to T ₇ ,
Occurrence of non-uniform heat distribution during sintering is suppressed as much as possible to realize uniform shrinkage (shrinkage rate of about 18%), and abnormal deformation can be prevented.

Such an effect of preventing deformation is obtained by the first heat treatment for removing the binder (that is, from time 0 to time T).
After the end of (up to ₆ ), the second for sintering the metal material powder
It can be obtained by raising the temperature at a rate of 8 ° C./min or more in the heat treatment of (that is, from time T ₆ to time T ₁₁ ).

FIG. 5 is a perspective view showing a result obtained by manufacturing a cylindrical metal sintered product by using a molding material equivalent to that of the above embodiment and examining a difference in size of deformation of the sintered product due to a difference in heat treatment. It is a figure. This sintered metal product has an outer diameter of 10 mm as shown in FIG. 5 (a).
It has a cylindrical shape of φ, inner diameter 8 mmφ, and height 10 mm. A method similar to that described with reference to FIGS. 1 to 4 above is carried out, except that the heating rate from time T ₆ to time T ₇ in FIG. 1 is 5 ° C./min, 8 ° C./min, 10 ° C./min and 12 C / min. The dimensions of each part shown in FIG. 5 (b) of the sintered product obtained as described above are shown in Table 1 below:

[0048]

[Table 1] It can be seen that when the heating rate is 8 ° C./minute or more, the deviation from the design dimension is smaller than when the heating rate is less than 8 ° C./minute.

This effect is obtained especially at a temperature of 800 to 1050 ° C.
(Including time T in FIG. 4) ₆ From time T₇ Until
Within the range) is effective. this
Shows that the shrinkage of the molded body occurs most severely within this temperature range.
Therefore, perform rapid heating within this range to reduce the heat generated during sintering.
To suppress the occurrence of non-uniform distribution as much as possible
It is extremely effective in achieving various shrinkages and preventing abnormal deformation.
Because there is.

The first heat treatment is preferably carried out within a temperature range of 550 ° C. or lower, and the temperature rising rate in the first heat treatment is 3 ° C./min or lower to remove the binder. It is preferable for good performance.

[0051]

Industrial Applicability As described above, according to the present invention, it is possible to facilitate the work of straightening a sintered compact, improve the production yield of the sintered product, and achieve a high-precision and high-hardness sintered product. It is possible to easily manufacture with high yield.

[Brief description of drawings]

FIG. 1 is a side view for explaining an embodiment of a method for manufacturing a metal sintered product according to the present invention.

FIG. 2 is a cross-sectional view taken along the line X-X ′ of FIG.

FIG. 3 is a cross-sectional view showing a usage state of an actuator finger for a circular knitting machine manufactured by the method for manufacturing a metal sintered product according to the present invention.

FIG. 4 is a graph showing a temperature curve during heat treatment in one embodiment of the method for producing a metal sintered product according to the present invention.

FIG. 5 is a perspective view showing a sintered product in which the difference in the magnitude of deformation due to the difference in heat treatment is examined.

[Explanation of symbols]

1 actuator finger 2 First part 4 second part 22 groove 24 feet (actuator engaging part) 42 through hole 44 base 46 neck 48 heads (knitting needle contact part)

Claims (10)

[Claims] 1. A green compact obtained by injection molding of a molding material containing a powder of a metal material and a binder containing a thermoplastic resin is placed under a reduced pressure in a state of being placed in a heating furnace.
The binder is removed from the green molded body by performing the heat treatment of 1. and then the second heat treatment is performed under reduced pressure to sinter the metal material powder to obtain a sintered compact, and the sintered compact is A method for producing a metal-sintered product, comprising the steps of quenching after taking out from the heating furnace to increase the hardness of the sintered compact to obtain a sintered product. 2. The shape or size of the sintered compact is inspected before the quenching, and if the shape or size is judged to be defective in this inspection, the quenching is performed after the straightening is performed. The method for producing a metal-sintered product according to claim 1, wherein 3. The method according to claim 1, wherein in the second heat treatment, the temperature is raised at a rate of 8 ° C./minute or more.
2. The method for producing a metal-sintered product according to any one of 2. 4. The metal according to claim 3, wherein the temperature increase at a rate of 8 ° C./min or more in the second heat treatment is performed at least at a temperature of 800 to 1050 ° C. A method for manufacturing a sintered product. 5. The method according to claim 1, wherein the first heat treatment is performed in a temperature range of 550 ° C. or lower.
4. The method for producing a metal-sintered product according to any one of 4 above. 6. The temperature rising rate in the first heat treatment is 3 ° C.
/ Minute or less, The manufacturing method of the metal-sintered product in any one of Claims 1-5 characterized by the above-mentioned. 7. The sintered molded body has a hardness Hmv of 80 to 1
50, The manufacturing method of the metal-sintered product in any one of Claims 1-6 characterized by the above-mentioned. 8. The method for producing a metal sintered product according to claim 1, wherein the sintered product has a hardness Hmv of 600 or more. 9. The method for producing a metal sintered product according to claim 1, wherein the metal material has a carbon content of 0.2% or less. 10. The metal material is stainless steel or F.
The method for producing a metal-sintered product according to claim 9, wherein the content is e-2 to 8% Ni.