JP6792330B2 - Manufacturing method of pure niobium products using the new forging method - Google Patents

Description

The present invention relates to a forging method that occupies an important position in the plastic working of a metal material, and more specifically, any of the conventional forging methods, hot forging, warm forging, and cold (room temperature) forging. It relates to a method for manufacturing a metal product using a new forging method, which does not belong to the above.

In recent years, in advanced fields such as precision mechanical parts, electrical / electronic parts, and superconducting elementary particle accelerators, demands for workability, processing accuracy, productivity, and economic efficiency have been increasing.
The conventional hot forging method is suitable for heat-resistant materials, the warm forging method is suitable for forging materials that are difficult to forge in cold forging, and the cold forging method is suitable for good workability and good productivity. Have. However, hot forging requires a large amount of thermal energy, and surface oxidation of the metal material and its removal become problems. Warm forging requires chemical conversion treatment and has concerns about bluish brittleness or strain aging. Further, in cold forging, there are many cases where the occurrence of defects such as necking (necking) and cracks cannot be avoided.

Recently, with the discovery of the Higgs boson and the progress of the Big Bang and inflation theory, the construction plan of the International Linear Collider (ILC), which is a long linear accelerator of 30 to 50 km, is being enthusiastically pursued. The core of the ILC is the superconducting high-frequency acceleration cavity, and the device that is the constituent unit is called the "9-unit cavity". The ILC requires approximately 17,000 units of this device. As shown in FIG. 1, it is composed of a center component 2 composed of nine cells and both end group components 3. The end group component 3 is composed of ports (beam pipe 3a, port pipe 3b) for power input and monitoring, as well as a HOM (harmonic) coupler 3c having a complicated shape and the like.

As shown in FIG. 2, the HOM coupler 3c is a combination of the HOM cup 4 and the HOM antenna 5. That is, since the particle beam is electromagnetically accelerated and excites HOM (harmonics) when passing through the cavity, which hinders the acceleration of the beam, it is necessary to suck it out of the cavity and attenuate it. The HOM coupler (harmonic attenuator) is responsible for this function.

The material used for both the center part 2 and the end group part 3 of the 9-series cavity is pure niobium, which is a rare metal. The main reason is that pure niobium has a high superconducting transition temperature of 9.2K, and by using this at 2K, the most important superconducting property, that is, per unit length for improving the ease of acceleration of the particle beam. This is because there is a high possibility that the acceleration voltage of the can be taken high.

Pure niobium is an extremely expensive, difficult-to-press and difficult-to-cut material. The main reason for this is the low plastic strain ratio for press working and the adhesion phenomenon with tools for cutting. Conventionally, in the HOM antenna 5, the actual situation is that a prototype product created by total cutting or water jet processing from a material is commercialized by cutting.

Further, the HOM cup 4 is subjected to full cutting, back extrusion cutting and heat treatment, or press working in a plurality of steps, inter-process heat treatment, and post-working heat treatment insertion.

Therefore, all of them have serious problems in terms of productivity and economy, and in order to solve these problems, it is strongly expected that the construction method will be changed to the advanced press working method.

Therefore, the inventors have researched a technique for converting the HOM cup 4 to ultra-deep drawing, and have already filed domestic and international patent applications (Patent Documents 1 and 2).

However, as can be inferred from the external view of FIG. 2 (D), the HOM antenna 5 is a “difficult-to-process shape product” in terms of press working, and the pure niobium material is machine-cut or pressed. All of them are "difficult-to-process materials". And since the initial plate thickness of the HOM antenna 5 is a "thick plate" of 10 mm, the target barrier is high.

In the HOM antenna 5, the distance dimension of each part is particularly important in order to optimize the superconducting characteristics. At the same time, it is necessary to consider the plate thickness and the R dimension of the edge portion. Originally, when stamping end group parts 3, it is necessary to consider "material technology" and "plastic working technology" at the same time. In addition, since a part of the almost square punched hole is narrowed and stress concentration is likely to occur, it is expected that necking (necking) / cracking, excess / insufficient meat, shaping, residual stress, etc. will occur. Difficulty is high.

Furthermore, CP (chemical polishing) and EP (electrolytic polishing) are performed in the finishing process, but in order to reduce the load as much as possible, pay attention to the adhesion and intrusion of foreign substances and trace impurity elements on the surface surface and on or near the surface. Must.

Therefore, processing methods other than the cutting processing of the HOM antenna 5 and the water jet processing belonging to the high energy processing are not known and have not been established. Further, it is strongly expected that the mass productivity will be dramatically improved and the manufacturing cost will be reduced by changing the construction method from cutting and water jet machining.

Here, as a means to meet expectations, in order to convert the conventional method to full press working, we are still trying "new full press working" by the advanced technology of "new shear punching" and subsequent "new forging". The present invention is the result of development and research for its realization based on an idea that has never been seen.

Here, the existing conventional shear punching process and precision punching method are excluded. In the former case, the punching clearance is usually 5 to 10% of the plate thickness (t), so it is impossible to obtain the required shape and dimensional accuracy, and in the latter case, an expensive dedicated machine and an expensive mold cost are incurred. This is because the difficulty is high and production efficiency can be a problem.

Prior to the examination of the "new shear punching method", the inventors first examined and evaluated the possibility of forming a raw material by "water jet processing", which is a kind of high energy processing method, instead of cutting. did. Since the processing of raw materials by water jet processing is expected to be relatively fast and highly efficient, we are looking at whether the subsequent cutting processing can be replaced with press processing by the well-known "cold forging processing". Various experiments and studies were conducted while putting it in.

As a result, the existence of some technical issues was recognized. The main problem was that the presence of abrasive grains and their embedding in the substrate were confirmed by surface SEM observation and EDX elemental analysis after CP of the prototype (Fig. 3). From SEM image (FIG. 3 (A)), the white point of apparently several mu m ~ number 10 [mu] m are scattered, the color of its surroundings is probably altered by stress field.

In the EDX (Energy Dispersive X-ray Analysis) measurement chart (Fig. 3 (B)) of the observation field (indicated by white circles) in the SEM image, the white spots (particle group) are due to alumina, silica, iron oxide, magnesium oxide, etc. Identified as one. The cause of the presence of these particulate matter is considered to be the "abrasive grains" used when cutting the water jet for manufacturing the raw material. At present, as long as this cutting method is applied, residual abrasive grains are inevitable.

If the abrasive grains are embedded, there is a great risk of promoting the generation of the high-frequency resonance mode, and there is a concern that the cavity performance will be adversely affected. Therefore, water jet processing of this raw material must be avoided. Moreover, it is undeniable that the water jet processing is inferior in productivity and economy to the press shear punching processing. With the HOM antenna 5, it takes about 10 minutes to manufacture one cut piece, which is far more efficient than full cutting, but tens of thousands (acceleration cavity 1). It is difficult to mass-produce (two antennas are required on the table).

On the other hand, in the processing of the raw product into the product shape, the conventional cold forging was first considered. However, as a result of the test, for example, problems such as necking, uneven size, stress concentration, shape problems (who, burrs, excess material, insufficient filling, etc.) or adhesion phenomenon were confirmed. It can be said that the cause common to these is "plastic flow" between the material and the mold.

Among them, it is a serious problem that the necking phenomenon as shown in FIG. 4 occurs in a part after the cold forging test. Experiments were conducted in which the cold forging conditions for technical plastic working were varied, but the occurrence of necking (inside the circle) could not be avoided.

No matter how small the probability of necking occurs, this is an important problem that impairs the function of the HOM antenna 5 and causes the accelerator to stop working even if it is one of all used for the accelerator, so accept it. Can't.

It is certain that this necking was caused by stress concentration, but it is unknown whether the main cause is insufficient strength of the material, insufficient ductility, plastic flow, or insufficient deformation margin in the process of machining deformation.

The residual abrasive grains and necking are phenomena caused by the interaction between the material and processing. Of course, since it is certain that the function of the acceleration cavity such as the control of the resonance mode and the superconducting characteristics will be deteriorated after the combination with the HOM cup 4 and the electron beam welding (EBW), it is necessary to eliminate the occurrence. However, as mentioned above, it is certain that there is a problem of plastic fluidity as the main cause. Therefore, it is extremely important to study a new processing method for the HOM antenna 5 in consideration of both the material and the processing.
That is, from the viewpoints of workability, mass productivity, economy, initial investment, etc., when manufacturing processed products by cold forging, there are recent demands for the use of difficult-to-process materials regardless of whether they are ferrous or non-ferrous metals, and various difficult-to-process shapes. The need for product processing has arisen. In addition, due to strict demands on the accuracy of processed products, various problems such as necking, cracking, dimensional defects, shape (dripping, burrs, excess meat, insufficient filling, etc.), and adhesion phenomenon occur. Furthermore, since there are strict requirements for improvement of defective rate, mass productivity, material yield, and economic efficiency (cost), it is required to develop a new forging method to cope with these requirements.

Japanese Patent Application No. 2013-152686 WO2013 / 115401 A1 Japanese Unexamined Patent Publication No. 07-48589

Therefore, the present invention relates to a forging method that occupies an important position in the plastic working of a metal material, and more specifically, it is a conventional forging method, such as hot forging, warm forging, and cold (room temperature) forging. It is an object of the present invention to provide a method for manufacturing a metal product using a new forging method, which does not belong to any of the above.

As a result of examining the above tests and problems, the inventors have found a new shear punching method and a new forging method, further formed a prototype by the new shear punching method, and used the new forging method to form the product shape. The present invention has been completed by creating a combination technique for molding into a processed product of.
That is, according to the results of the following consideration and verification for the above-mentioned severe needs including economic efficiency and productivity: 1) Material deformation due to processing temperature and various temperature-dependent phenomena occurring on the surface and inside; 2) Forging Basic knowledge of machining, simulation, basic experiment; 3) Consideration of tribology (friction / lubrication engineering), rotational friction test; 4) Macroscopic / microscopic examination of plastic flow; etc.
Then, in the temperature range that has not been seen in the past, using a temperature control device and a press machine equipped with a servo function, special consideration is given to the deformation temperature / distribution effect and deformation speed / motion effect on the forging behavior, and the plastic fluidity of the material. I went and found a new forging method.

More specifically
In order to solve the above problems, the present invention
(1)
The clearance between the outer circumference of the punch for punching the pure niobium plate and the inner circumference of the die is set to a minute clearance of 0.5% or less of the plate thickness of the pure niobium plate, and the pure niobium plate is bound with a binding jig. Thick plate raw material formed by shear punching with heat removal is processed by press compression with a forging die in low temperature range temperature control of 100 ° C to 150 ° C or less to avoid blue heat brittleness. A method for manufacturing pure niobium products using a new forging method, which is characterized by molding into.
(2)
The method for producing a pure niobium product using the new forging method according to (1), wherein the pure niobium plate material is composed of a fine crystal structure having a particle size of several tens of μm.
(3)
The mold used in the molding is a surface-modified mold and is characterized in that a solid film lubricant having temperature-independent lubrication performance is used for the work material in order to prevent seizure (). A method for manufacturing a pure niobium product using the new forging method described in 1).
(4)
Further, a method for manufacturing a pure niobium product using the new forging method according to (1), which comprises measuring the servo of a press machine and including speed and motion control.
(5)
(A) The clearance between the outer circumference of the punch for punching the pure niobium plate material and the inner circumference of the die is set to a minute clearance of 0.5% or less of the plate thickness of the pure niobium plate material, and the pure niobium plate material is used with a binding jig. With shear punching, which forms a thick plate jig with heat removal while binding .
(B) The gold for avoiding bluish brittleness of the raw product and facilitating plastic flow in order to mold the processed product having the product shape of the raw product by press compression processing using a forging die. A heating device that controls the temperature of the mold and the molded product in a low temperature range of 100 ° C. to 150 ° C. or lower, a mold whose surface is modified to improve the moldability of the molded product and minimize surface oxidation, and the above. The press is equipped with a temperature-independent solid film type lubricant to prevent seizure between the die and the die, and a servo mechanism that controls the speed and motion of the new shear punched die. It consists of forging
A method for manufacturing pure niobium products using a new forging method, which is characterized by converting the cutting and water jet processing of pure niobium products to press working.
And said.

INDUSTRIAL APPLICABILITY According to the present invention, various metal products can be formed by forging, for example, a cooperative technique of forging for forming a processed product that does not depend on any of the existing hot / warm / cold forging methods. It enables excellent productivity and economy that are essential for industrial use. Further, in the molding of a raw material, a metal using a new shear press punching process for molding a raw material without using a metal plate as a starting material, cutting or water jet processing, or using a precision punching method. It is possible to provide a manufacturing method of a product, solve the technical problem of the current fine blanking method, and solve difficult productivity and high cost. Examples of the target metal products include a wide variety of metal products such as precision mechanical parts, precision parts in the electrical and electronic fields, and deformed precision parts in advanced fields such as elementary particle accelerators.

As a result, the problem of abrasive grain embedding due to water jet processing and the problem of necking due to cold forging are solved, and the amount used in expensive metal materials such as pure niobium or various steel and non-ferrous metal materials is reduced. , Material cost can be suppressed. Furthermore, in press molding, depending on the required accuracy, it can be a processed product before the finishing process, or the finishing process (finish cutting) can be significantly reduced, so the manufacturing time can be shortened. This makes it possible to significantly reduce manufacturing costs and contributes to stable mass production and parts supply. The technology is not limited to niobium products, and can be applied to various metal materials such as cold-rolled steel sheets, stainless steel, steel, iron, and non-ferrous metal materials. Further, even if it is an accelerator-related part, stable operation of the accelerator can be guaranteed.

It is a photograph of a superconducting high-frequency 9-cell acceleration cavity with a pure niobium end group attached. It is a schematic diagram of the HOM coupler which constitutes a pure niobium end group of a superconducting high frequency acceleration cavity, and the HOM cup and HOM antenna which constitute a HOM coupler. It is explanatory drawing of the water jet processing of the conventional thick-walled pure niobium plate material. (A) is a SEM electron micrograph of the surface of the molded product formed by water jet processing, and (B) is the EDX elemental analysis result of the particles in the white circle of (A). It is a photograph of a processed product formed by cold forging of a raw product formed by conventional water jet processing. (A) is an external image, and (B) is a close-up image in the circle of (A). Occurrence of necking is observed in (B). This is an example of a method for binding thick-walled pure niobium material in shear punching. (A) is a schematic cross-sectional view of BB'of (B) shown together with a material and a tool, and (B) is a schematic view of AA' of (A). It is a figure which shows the blue thermal brittleness phenomenon of pure niobium. It is an external photograph of a servo press machine and a heating / cooling control device equipped with various control mechanisms and dies used for the press working of the present invention. It is a photograph of the shear punched prototype product (A) and the forged product (before finishing) (B) according to the present invention. It is a perspective view (photograph) of a raw material (A) obtained by a new shear punching method from a stainless steel plate, forged products (B) and (B') obtained by a new forging method, and a nozzle vane subjected to a cutting process. ..

Hereinafter, the present invention will be described in detail with reference to FIGS. 5 and 6.

Among the pure niobium end group parts 3 of the superconducting high-frequency acceleration cavity used for accelerating charged particles of the present invention, the HOM antenna 5 is a new shear punching method (1) by the means of the present application and a new forging method. Manufactured from (2), it enables the conversion of the construction method from conventional cutting and water jet machining to press working.

(1) Shear punching process Shear punching process is a step of molding a raw material 5b from a thick-walled pure niobium plate material 5a, in which the gap (clearance) between the die 6a and the punch 6c is reduced, and the thick-walled pure niobium plate material 6 It consists of an appropriate combination of methods, including binding means, high speed punching means, heat removal cooling means, multi-action dies, servo die cushions, and servo control of the press. The means / effects thereof will be described below.

・ Small clearance 6e
As shown in FIG. 5 (A), in order to obtain a highly accurate shear punched product, the minute clearance 6e has a small gap of 0.5% or less of the plate thickness (t) of the material to be processed in the gap between the die 6a and the punch 6c. It is set to. In conventional punching, 10 to 15% of the plate thickness (t) is normal, and in the existing precision punching (FB) method, t ≦ 0.5%. However, the FB method requires an expensive FB (flood control) press and a special die that requires the formation of V-shaped protrusions, the punching speed is slow, and the operation of the press requires skill. There is.

On the other hand, the present invention provides a new shear punching method that is applicable to difficult-to-press stamped materials such as thick-walled pure niobium plate 5a, which does not correspond to the conventional punching method or the FB method, by the following invention.

・ Binding means 6
As illustrated in FIG. 5, this means does not employ, for example, the thick-walled pure niobium plate material 5a without adopting the special mold of the V-shaped protrusion method adopted in the usual FB method. It suppresses and controls the blisters and fluctuations in the plate thickness of the prototype product 5b.

For example, as shown in FIG. 5, a normal plate pressing load Pb is applied to the thick-walled pure niobium plate material 5a from above and below (plate pressing 6d and die 6a). In some cases, a reverse pressing (reverse direction) load Pp is applied to the punching load Pf depending on the degree of sagging of the thick pure niobium plate 5a.

Further, in the present invention, the binding load F is applied to the thick-walled pure niobium plate 5a. The binding load F is composed of a first side binding force F1 applied to the longitudinal side surface of the thick pure niobium plate 5a which is a rectangular material, and a second side surface binding force F2 applied to the short side surface. Note that F1'is the counterload of F1 and F2'is the counterload of F2.

On this occasion,
Pb = F1 + F2 equation (1)
It is important to control so as to maintain the relationship between. As a result, fluctuations in the thickness of the thick pure niobium plate 5a during shear punching can be suppressed to a necessary and sufficient degree.

Here, since Pb is dynamically controlled during machining by a servo die cushion in the present invention, F may be regarded as a factor that fluctuates accordingly in principle.

The thick-walled pure niobium plate material 5a moves at the time of punching regardless of whether it is the V-shaped protrusion method adopted in the ordinary FB method or the ordinary plate presser, and the plate thickness of the raw material 5b is reduced. Recognizing what will happen, he came up with the idea of such an invention element.

-Continuous high-speed punching and heat punching It was found that the shear punching property is improved by increasing the punch speed to, for example, 100 mm / sec or more at the time of punching the thick pure niobium plate material 5a. Such speeding up cannot be realized by the hydraulic servo mechanism in the FB method. Therefore, in the present invention, it is made possible by the press machine mounting function of the electric servo control mechanism described later.

In pure niobium, the mechanism by which punching performance is improved by high-speed punching was unknown, but the inventors, etc., from the viewpoint of materials engineering, the influence of microslip and its tongue ring (entanglement) during processing deformation of pure niobium material. It was found that this is mainly because the strain is reduced by facilitating cross-slip due to the decrease in stacking defect energy.

On the other hand, when the punching speed is increased and continuous processing is performed, the amount of conversion of external force into thermal energy increases and accumulates, a heat generation phenomenon occurs, and the mold temperature rises. Then, the mutual atomic interaction between the mold and the surface of the thick pure niobium plate 5a increases, and the chemical change of the lubricant and the mold surface modification film, mainly the oxidation reaction, occurs, and the "seizure phenomenon" occurs. Therefore, during continuous shear punching, "heat removal" of the material to be processed and the die is required. Therefore, it is necessary to cool the mold with a temperature control device and cool the work material by heat conduction.

・ Multi-action die press machines are usually based on 2-axis external force machining (slide and plate presser), but a device that adds a servo function to a conventional press machine without using a complicated mechanism such as the FB method. By mounting the die, it is possible to operate the "counterforce" (third axial force) in the opposite direction to the sliding force, and it can also be used as a knockout function (3-axis external force machining).

In order to mold a high-precision molded product 5b with a minute clearance 6e, the effect of such a simple compounding device cannot be ignored (corresponding to Pp in FIG. 5). As a result, the initial investment of the shear punching apparatus can be suppressed, and the product cost of the raw product 5b can be kept low in combination with the improvement of productivity.

-Servo die cushion The plate holding load (surface pressure) during shear punching of thick-walled pure niobium plate material 5a is made variable during shear punching, and is installed to improve shear punching performance. Since the processing time is short, it is difficult to perform such dynamically variable operation, but the improvement of the response speed of the feedback sensor has made it possible to put it into practical use. When used in combination with other configurations, this mechanism exerts a synergistic effect and enables high-precision and high-efficiency shear punching.

-Servo (speed / motion) control In press working, it is an already known method / device, but it is important in the present invention characterized by effectively utilizing high-speed / continuous shear punching, speed control, and motion control. It is an element, and such an idea does not exist in the past in shear punching.

(2) Forging processing Next, forging processing is a process of molding a raw product 5d into a processed product 5c having a product shape, and temperature control in a low temperature range (suppression of blue heat embrittlement, minimization of surface oxide film, facilitation of plastic flow). It consists of an appropriate combination of methods, including selection of fine crystal pure niobium, surface modified dies, proper lubricating oil, and press servo control. The means / effects thereof will be described below. A finished product is obtained by subjecting the raw product to a conventional post-treatment or finishing treatment after forging or instead of forging.

・ Low temperature range temperature control In order to make pure niobium blue thermal embrittlement, minimize surface oxide film, and facilitate plastic flow, temperature range above room temperature (RT) (temperature not including room temperature) to 200 ° C. Control the temperature with. It is more preferably higher than 20 ° C. and 200 ° C. or lower, more preferably 50 to 150 ° C.
Traditionally, in forging, in relation to temperature conditions,
Hot forging (above recrystallization temperature, roughly> 800 ° C)
Warm forging (300-800 ° C)
Cold forging (RT (room temperature)) is known.
This low temperature range control temperature range of the present invention is a temperature control means in a new temperature range that does not apply to any of the conventionally known temperature control ranges, and is a new forging process suitable for processing a difficult-to-press work material. It provides the law.

-As a result of investigating the temperature dependence of the static and dynamic mechanical properties of blue hot brittle pure niobium in a wide range (Fig. 6), valuable information on the means and effects of press working of thick-walled pure niobium plate 5a. Was obtained, and the idea of an important element for the new forging method related to the present invention was obtained.

FIG. 6 shows the static uniaxial tension results of pure niobium at 0 to 400 ° C. The horizontal axis is temperature, the first vertical axis (left) is elongation (ductility), and the second vertical axis (right) is tensile strength (strength characteristics). The results of different charges are plotted for EL (total elongation).

From this, it can be seen that the static mechanical properties of pure niobium do not change (increase / decrease / invariant) uniformly with temperature changes. In particular, it is known that the ductility and strength characteristics of pure niobium decrease sharply in the temperature range of 200 to 300 ° C. This is called "blue heat embrittlement" of pure niobium, following the conventional metal engineering.

When the bluish embrittlement phenomenon occurs, the plastic deformability is reduced due to the decrease in ductility and the deformation resistance to the external force of the material is reduced due to the deterioration of the strength characteristics. The risk of necking in concentrated areas increases sharply. Therefore, bluish embrittlement must be absolutely avoided during forging.

The cause of the formation of blue thermal embrittlement is considered as follows. This is related to the "selective use of finely divided pure niobium" described later. As can be seen from the stress-strain flow stress change in the shaded area in the inset in FIG. 6, hydrogen embrittlement invades the grain boundaries and microslip (strain) generation sites in the pure niobium material. This is due to sticking / blocking by solid diffusion of type atoms (carbon and nitrogen).

The diffusion phenomenon (diffusion coefficient D) in ferrite (body-centered cubic crystal (BCC)) such as pure niobium depends on the temperature T.
D = D _O exp (−Q / kT) Equation (2)
It is represented by.
_DO : frequency term, Q: activation energy, k: Boltzmann constant

And the diffusion distance x of the atom at time t is
x = (Dt) ^1/2 formula (3)
Will be.

However, since the D of carbon and nitrogen in the ferrite at 200 to 300 ° C. is about 100 to 1000 mm / sec, it matches with the microslip rate, so that the sticking action occurs and blue heat embrittlement is considered to occur.

Then, as will be described later, at the same time as the "selective use of finely divided pure niobium", "facilitation of plastic flow" must be considered at the same time.

-Minimization of surface oxide film Pure niobium has a small standard free energy ΔG of oxides (mostly Nb ₂ O ₅ ) and is easily oxidized. To remove the scale (oxide film), finish cutting (mechanical / chemical (Cp) / electrochemical (Ep)) or the like is performed after the press forged product (in some cases, finish cutting) is manufactured. In particular, Ep needs to be performed for each "9-series cavity" that is planned to be made to a little less than 20,000. Therefore, reducing the formation of oxide film as much as possible contributes to the improvement of EP processing capacity, which leads to cost reduction.

Therefore, the forging temperature does not exceed as low as possible between the temperature above room temperature (temperature not including room temperature) and 200 ° C., but at the same time avoids bluish brittleness and the stress inserted in FIG. 6 as described above. -Including the response to changes in flow stress near the elasto-plastic limit shown in the strain diagram). This cause is the same as that of blue heat embrittlement, and is due to the fixation of microslip strain of intruding atoms as described above, but it is also called an aging phenomenon and can occur even in the high temperature range below the lower limit of blue heat embrittlement. There is sex. At the same time, in consideration of facilitation of plastic fluidity, which will be described later, it is preferable to control the temperature range of 100 to 150 ° C. around 130 ° C.

-Since the plastic flow facilitation forging process progresses mainly by material deformation due to compressive force, how to cause macroscopic plastic flow of pure niobium material appropriately, uniformly and appropriately according to the required product shape dimensions. It is important to know.

For that purpose, the ductility (especially uniform elongation) indicated by the total elongation (sum of uniform elongation and local elongation) among the macromechanical characteristics is excellent, and the strength and flow stress are lowered in order to reduce the deformation resistance. It is desirable to keep it in. Then, it is desired to avoid the fixing action of the above-mentioned carbon and nitrogen penetrating atoms against microscopic deformation strain.

From this point of view, referring to FIG. 6, it is possible to understand the importance of controlling the temperature in the low temperature range between the temperature exceeding room temperature (temperature not including room temperature) and 200 ° C., but it is desirable that the surface oxide film is minimized. It can be said that it is preferable to select the temperature range control around 130 ° C., which is consistent with the viewpoint described for the conversion temperature. This preferred temperature varies slightly depending on the type of metal material.

In this way, the formation and high precision of all curved surface portions during forging and the surface texture are improved. The present invention, which is derived from development research experiments and theoretical guiding principles, that is, the technology that realizes all press working of pure niobium materials, has not been known so far.

-Selection of fine crystalline pure niobium material There are two points of view to consider. The first point is from the viewpoint of avoiding the seizure (adhesion) phenomenon that occurs between the thick-walled pure niobium plate 5a and the mold. Pure niobium usually has a high crystal grain growth rate due to recrystallization heat treatment, and generally exhibits coarse grains of about several hundred μm.

This is because the pure niobium used for the present application has a high purity of 300 RRR or more (the content of penetrating impurity elements such as carbon and nitrogen is about several ppm), so that the grain boundary movement blocking action is small and the niobium atom It is presumed that this is due to the ease of body diffusion.

When the crystal structure of the material to be processed consists of coarse particles, the interaction between the surface and the surface of the mold due to the random walk of atoms increases stochastically more than in the case of the fine granules, so that a chemical reaction also occurs. The seizure (adhesion) phenomenon is reduced by using a pure niobium material of fine-grained crystals of several tens of μm according to the presumed principle that seizure and wear phenomena are promoted.

It has not been known so far that the grain size of pure niobium material is one of the causes of seizure and adhesion. Further, a technique for adjusting the crystal grain size to the order of several tens of μm is not disclosed.

The other point is that, as can be seen from the above regarding the bluish brittleness and aging phenomenon in FIG. 6, crystals are crystallized by using a fine grain material having a crystal grain size of about 1/10 of the current one as described above. Since the grain boundary area is significantly increased, many of the intrusive elements such as carbon and nitrogen are adhered (trapped) to the grain boundaries even at the same temperature due to diffusion, and the degree of hindering the progress of microslip is reduced. That is. That is, in the forging process under the same temperature conditions, the fine-grained material has less blue heat embrittlement and aging phenomenon than the coarse-grained material, facilitates the forging process, and improves the forging property.

-To prevent seizure (adhesion) between the surface-modified mold and the thick-walled pure niobium plate 5a and to prevent friction and wear of the mold, the surface of the mold is subjected to DLC, low-temperature nitrided or chemical conversion treatment, etc. Modify with. Considering that the material to be processed is soft pure niobium, consideration is given to the thickness of the modified layer and the base treatment, and at the same time, consideration is given to the selection of the mold material.

-Appropriate lubricant Use a solid film lubricant with temperature-independent lubrication performance. For example, a lubricant that does not change the lubrication performance of a solid film from room temperature to 800 ° C., which one of the inventors of the present application was involved in, is known (Patent Document 3), and by using this, a seizure / adhesion phenomenon occurs. It will be relaxed. The lubricant described in Patent Document 3 is a solid lubricant that avoids the load on the human body / environment of the chlorine-added lubricating oil that has been conventionally used to prevent seizure and adhesion, and contributes to the improvement of workability. To do.

・ Servo (speed / motion) control <br/> This function is installed in a conventional press machine to control the speed and / or motion of the slide (stroke) of the press machine, change the requirements for using external force, and thicken. It is intended to improve the affinity of the pure meat niobium plate 5a in the micro and / or macro deformation modes and to improve the plastic workability.

Since the contents of the present invention have been described in detail above, specific examples based on these have been described below with reference to FIGS. 6 and 7. The present invention is not limited to the following examples.

FIG. 7 shows an external photograph of equipment / devices for carrying out the invention. The main device was a press machine, which was equipped with an electric (AC) servo mechanism on a conventional press machine, and also equipped with a servo die cushion and a multi-action die. Basically, from the viewpoint of cost performance, single-shot processing was used in the examples. That is, the new shear punching process for processing the raw product 5b and the new forging process for processing the product before the finishing process were performed separately for each appropriate number. (Needless to say, during mass production, continuous processing will be performed with two presses).

Therefore, the shear punching die and the forging die were exchanged on the way. A QDC was used to replace the heavy mold. The mold material for the examples is SKD11, the surface modification is DLC, and the thickness of the modification layer is about 2 μm. A solid lubricant G2578T (manufactured by Nippon Kogei Co., Ltd.) was used as the lubricant. These mold materials, surface modifications, and lubricants were used for both shear punching and forging.

The temperature control device 7 shown in FIG. 7 was used for cooling control of the new shear punching process and heating control for the new forging process. The temperature control range was -20 to + 300 ° C., a non-CFC refrigerant was used for cooling, and an electric heater embedded in the mold 7a was used for heating. There was a slight time lag between the temperature control of the thick-walled pure niobium plate 5a and the mold, but there was no particular problem.

As the pure niobium work material, a thick pure niobium plate material having a plate thickness of 10 mm was used. This product is obtained by subjecting EBM (electron beam melting) several times, then ingot rolling and plate rolling, and then vacuum annealing after descaling. According to the material mill sheet (inspection table), carbon, nitrogen, oxygen, etc. of impurity solid solution atoms are all at the level of several ppm, and RRR (an index related to electrical resistance, the larger the number, the more the love purity material. ) Was 341. The tantalum content of the same family (Group 5 of the Periodic Table of the Elements) was 280 ppm. The metal crystal grain size is approximately 100 to 300 μm, and is approximately equiaxed. The crystal orientation texture has not been measured. When the hardness was measured, the Vickers hardness was about 90.

The conditions of the examples are as follows.
(1) Shear punching: (fine) clearance 40 μm; plate presser load (Pb) 20 tons; plate presser surface pressure 140 kg / cm ^ 2; binding load (F) is the same as surface pressure; punching load (Pf) 90 tons Reverse pressing load (Pp) 13 tons; Speed 200 mm / sec; Cooling temperature 0 ° C; Servo motion is straight; Number of continuous machining 50 pieces.

(2) Forging: Forging load 160 tons; Forging speed 0.5 mm / sec; Forging die base product 5b Work offset amount 0.2 mm; Machining temperature 130 ° C.; Number of continuous machining 50 pieces.

Under the above conditions, a typical example of the processed products 5b and 5c performed by a new shear punching method for a large number of HOM antennas 5 from a thick-walled pure niobium plate 5a and a subsequent new forging method according to the present invention. Is shown in FIG.

FIG. 8 (A) shows the shear punched raw material 5b, and the shear punching of the soft thick-walled pure niobium plate 5a having a plate thickness of 10 mm and having a high processing difficulty could be performed without any particular problem. .. Of course, there was no embedding of abrasive grains in the processing of the water jet material, and this problem could be completely solved.

FIG. 8 (B) shows a product (processed product 5c) after forging (before finishing (cutting) processing) by the new forging method, which is a continuous process from (A). It was shown that a processed product having the required shape and dimensions can be manufactured with reproducibility by applying the means and conditions.

A considerable number of them were forged, but there was no "necking" that occurred in the conventional cold forging. In FIG. 8, the length dimensions and the plate thickness dimensions of (A) and (B) are shown, and it has been confirmed that there is no problem in the subsequent finishing process.

In particular, the plate thickness is reduced by 1 mm and the length dimension is also reduced by forging, but these are within expectations, and as described above, the offset amount with respect to the design drawing is properly considered in the die.

As can be judged from the above examples, by applying the present invention, all the manufacturing processes except the finishing process, which avoids the conventional cutting and water jet, are pressed from the processed product of the thick-walled pure niobium plate 5a to the HOM antenna 5. We obtained the result that it is possible to switch to the processing method. Therefore, it has become possible to reduce the material yield of accelerated cavity parts, which has been a major bottleneck, reduce costs, and improve mass productivity.

Next, as an example of the present invention, manufacturing (molding) of a nozzle vane 10 (FIG. 9 (C)), which is an important component of a variable-sweep turbocharger for a diesel engine, using a new shear punching method and a new forging method. The method will be described.

The raw material 8 shown in FIG. 9A is obtained by applying a new shear punching method to a rolled material of a stainless steel plate (SUS310S = 25Cr-20Ni-0.06C) having a plate thickness of 10 mm. At this point, the prototype 8 is a punched flat T-shaped plate. It is the present invention that this is a product including a wing portion 8a forged into a wing 9a, a shaft portion 8a forged into a cap 9b and a shaft 9c in the next step.

Conventional nozzle vanes are often molded by fine blanking (FB) or rolling, but they are expensive because of the high introduction cost of FB equipment and high operating skills. There is. At the same time, problems such as high molding difficulty, yield, and cost are inevitable in the next process (cold forging and rolling).

Generally, as a means for manufacturing this product, a "precision casting" method using SCS21 (25Ni-20Cr-0.3C) of stainless steel for casting is adopted. However, in this case, for example, the production volume of this product is said to be several hundred thousand pieces / month, and production by precision casting has many difficult problems such as mass productivity, cost, delivery date, and distribution. In addition, SCS21 contains a large amount of C and produces Cr carbides, σ-phase non-metal inclusions, or Laves phase due to temperature changes during use, resulting in reduced oxidation resistance, resulting in poor mobility and deterioration of durability. There is also a risk of sensitization (intergranular corrosion) and embrittlement (opening fracture / intergranular fracture).

The forged product 9 shown in FIGS. 9 (B) and 9 (B') was obtained by applying a new forging processing method utilizing plastic flow to the raw product 8. FIG. 9 (B') is a photograph from the wing 9a side of FIG. 9 (B). Here, the forging temperature is set to 150 ° C., servo control is performed, the cap 9b is forged by a combined technique with partial punching, and a specially shaped wing 9a is forged. Depending on the part, it will be the final product by new forging. The nozzle vane undergoes the following cutting process to complete the finished product.

The nozzle vane 10 shown in FIG. 9C was completed by performing necessary cutting on the forged product 9 to form cutting portions 10a and 10b. Through the above steps, it becomes possible to manufacture a nozzle vane having productivity and economy. Depending on the part, the finished product is finished by optimum and various necessary polishing.
For example, according to conventional cold forging methods such as special gears, cams, levers, and split rings that belong to the category of precision machine parts, as the strictness of shape and dimensional accuracy increases, the dimensions of necking, cracks, and R parts Although it is inevitable that the incidence of defects such as defects, who, burrs, and excess meat will increase, these technical problems will be solved according to the method of the present invention. This is mainly due to the improvement of the plastic fluidity of the material and the margin of deformation. At the same time, in terms of mass productivity and economy, it is almost comparable to the conventional cold forging method.
In addition, the harmonic coupler (HOM Coupler) of the superconducting accelerating cavity terminal component of the state-of-the-art project ILC (International Linear Collider) was carried out with high-purity Nb material, but the result satisfied the required functions such as accelerating voltage. Has been obtained. As a peculiar effect based on the examples, the new forging of the present invention is performed by converting a deformed / complicated part such as the above-mentioned HOM Coupler part (antenna) into a raw material obtained by a new shear punching method of a metal material or the like. It can be commercialized by applying the processing method.
In common sense and in actual results, it is impossible to process such a complicated shape and high precision product without total cutting or high energy processing method or casting method, fine blanking by multiple processes and rolling. However, the fact that processing can be performed by the new forging method together with the new punching method means that the production time and efficiency can be significantly increased by 1 to 10 to 100, and therefore, it has an excellent and preferable effect.

In addition, for example, it can be applied to automobile turbocharger (supercharger) parts such as nozzle vanes, link plates, and slide joints made of stable high-grade stainless steel (SUS310S or SUS316L, etc.) currently manufactured by the fine blanking method. For example, it can contribute to the effective utilization and purification function of output, torque and exhaust gas at high temperature and long-term use.

From the above, the technology of the present invention has found a new technology that combines temperature, velocity, external force, etc. from the viewpoint of utilization and fusion of material engineering and plastic working science, and has led to the creation of a concrete new means for that purpose. Is.

The most peculiar effect was the discovery of the possibility of replacing the current fine blanking precision punching method. Specifically, compared to investing in a dedicated fine blanking machine, it is a much cheaper response and means, that is, the modification of the general-purpose press machine that each manufacturer already owns and the preparation of the temperature control mechanism. Metal products using a new high-precision precision shear punching method without the need for complicated work techniques and the preparation of expensive special dies for fine blanking. Realized the manufacturing method of. Even when compared to a processing manufacturer who already owns a fine blanking processing machine and has already depreciated it, the new shear punching process shows an advantage over the medium term.

As described above, shearing in microclearance, especially material deformation engineering, macroscopic plastic dynamics related to separation shearing in plastic working, heat treatment and servo mechanism, and technology related to their interaction with material processing deformation. By consideration and experiment, for various metal materials including steel materials, various materials up to about 10 mm in thickness have required dimensional accuracy, good shape with minimal sagging and burrs, good surface texture, and punched side surface. It is possible to manufacture a punched product under appropriate shear punching conditions in consideration of the plastic flow of the material, such as securing 100% shear surface, changing and distributing the plate thickness, and local small rounding inside the loop.

As a result, the present invention provides cooling jigs and equipment to conventional press machines and dies for precision punched parts and products that require deformed high precision, without using the fine blanking method that requires an expensive dedicated press machine. It is installed side by side and has a servo function for 3-axis external force control including stroke and surface pressure automatic control and back pressure, enabling precision shear separation machining.

Parts with high shape and dimensional accuracy by considering high-speed heat removal, surface pressure control, material movement, compression resistance, etc. of the material during shear punching without using the expensive and difficult-to-use fine blanking method.・ Manufacturing of products and raw materials becomes possible under a small width and good material yield.
In addition, by adopting the new forging method, as described above, by generating good plastic flow, blue heat embrittlement, aging effect, oxidation, necking, shape defect, excess / deficiency, sagging, burr It is possible to commercialize a molded product that avoids such problems by eliminating the need for finish cutting or by performing minimal finish cutting.

1 Superconducting high frequency acceleration cavity 2 Center part 3 End group part 3a Beam pipe 3b Port pipe 3c HOM coupler 4 HOM cup 5 HOM antenna 5a Thick-walled pure niobium plate material 5b Raw material 5c Processed product 6 Binding means 6a Die 6b Plate holder 6c Punch 6d Reverse presser foot 6e Micro clearance 6f Binding jig 6g Binding jig 6h Binding jig Pf Punching load Pb Plate pressing load Pp Reverse pressing load F Binding load F1 First side binding force F1'Reverse load F2 Second side binding force F2 'Reverse load 7 Servo press machine 7a Mold 7b Temperature control device 8 Base product 8a Wing part 8b Shaft part 9 Forged product 9a Wing 9b Cap 9c Shaft 10 Nozzle vane 10a Cutting part 10b Cutting part

Claims (5)

The clearance between the outer circumference of the punch for punching the pure niobium plate and the inner circumference of the die is set to a minute clearance of 0.5% or less of the plate thickness of the pure niobium plate, and the pure niobium plate is bound with a binding jig. Thick plate raw material formed by shear punching with heat removal is processed by press compression with a forging die in low temperature range temperature control of 100 ° C to 150 ° C or less to avoid blue heat brittleness. A method for manufacturing pure niobium products using a new forging method, which is characterized by molding into. The method for producing a pure niobium product using the new forging method according to claim 1, wherein the pure niobium plate material is composed of a fine crystal structure having a particle size of several tens of μm. The mold used in the molding is a surface-modified mold for preventing seizure, and a solid coating lubricant having temperature-independent lubrication performance is used for the work material. A method for producing a pure niobium product using the new forging method according to Item 1. Further, a method for manufacturing a pure niobium product using the new forging method according to claim 1, wherein the press machine is servoed to measure speed and motion control. (A) The clearance between the outer circumference of the punch for punching the pure niobium plate material and the inner circumference of the die is set to a minute clearance of 0.5% or less of the plate thickness of the pure niobium plate material, and the pure niobium plate material is used with a binding jig. With shear punching, which forms a thick plate jig with heat removal while binding .
(B) The gold for avoiding bluish brittleness of the raw product and facilitating plastic flow in order to mold the processed product having the product shape of the raw product by press compression processing using a forging die. A heating device that controls the temperature of the mold and the forged product in a low temperature range of 100 ° C. to 150 ° C. or less, a mold that has been surface-modified to improve the moldability of the forged product and minimize surface oxidation, and the forged product. Forging with a temperature-independent solid film type lubricant to prevent seizure between the die and the die and a servo mechanism to control the speed and motion of the new shear punched die. Consists of processing
A method for manufacturing pure niobium products using a new forging method, which is characterized by converting the cutting and water jet processing of pure niobium products to press working.