JP2008106848A - Al-based composite screw and its manufacturing method - Google Patents

Abstract

An Al-based composite material screw that can be easily and inexpensively manufactured by plastic deformation at room temperature and a manufacturing method thereof.
An Al-based composite material screw 10 is a composite material in which reinforcing material particles are dispersed in an Al-based metal of the same type as the shaft core portion 12 outside the shaft core portion 12 mainly composed of an Al-based metal. The screw thread part 14 which consists of has the structure formed continuously with this axial core part 12. As shown in FIG. The screw 10 generates an Al-based melt 42 in which reinforcing material particles 44 are dispersed in the mold 22, and the Al-based melt 42 is moved so that the reinforcing material particles 44 move to the peripheral portion of the Al-based melt 42. It is manufactured by applying an electromagnetic force to the molten metal constituting, solidifying the Al-based melt 42, taking out a solid rod made of a composite material from the mold 22, and forming a thread on this by a rolling method.
[Selection] Figure 1

Description

  The present invention relates to an Al-based composite material screw made of a composite material made of metal Al or an Al alloy and ceramics, and a method for manufacturing the same.

  Recently, in fields where weight reduction of engines, bicycles, and the like is desired, there has been a widespread movement of replacing screws used for assembly from those made of conventional iron or stainless steel to those made of lightweight aluminum.

  However, the aluminum screw has a drawback that it is difficult to retighten because the strength is small and the screw thread is easily plastically deformed. Therefore, for example, stainless steel screws are used for assembling the frame member of the aluminum sash window. For this reason, in the aluminum recycling process after dismantling, it is necessary to remove all the screws, which is costly.

Therefore, for example, a screw made of a composite material in which a metal is used as a matrix and ceramic particles are dispersed as a reinforcing material has been studied (for example, see Patent Document 1). However, in such a composite screw, it is necessary to form a screw thread by warm forging or cutting, and there is a problem that the processing cost increases.
JP 2000-343178 A (paragraphs [0009], [0010], [0016], etc.)

  The present invention has been made in view of such circumstances, and an object thereof is to provide an Al-based composite material screw that can be easily and inexpensively manufactured by plastic deformation at room temperature and a manufacturing method thereof. And

  In the Al-based composite material screw according to the present invention, the shaft core portion is mainly composed of an Al-based metal, and a thread made of a composite material in which reinforcing material particles are dispersed in the same Al-based metal as the shaft core portion. The portion has a structure formed on the outside of the shaft core portion so as to be continuous with the shaft core portion.

  Such an Al-based composite screw includes a step of generating an Al-based melt in which reinforcing material particles are dispersed in a mold, and an Al-based melting so that the reinforcing material particles move to the peripheral portion of the Al-based melt. A step of applying electromagnetic force to the molten metal constituting the body, a step of solidifying the Al-based melt and taking out a solid bar made of a composite material from a mold, and a step of forming a thread on the solid bar by a rolling method Manufactured by going through.

  According to the present invention, the outer peripheral portion is made of a composite material of an Al-base metal and a reinforcing material, and the shaft core portion (center portion) is made of an Al-base metal. Al-based composite screws can be manufactured using widely used rolling methods. Thereby, a high-strength screw can be manufactured easily and inexpensively with high productivity.

  Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the structure of a screw made of an Al-based metal-ceramic composite material (hereinafter referred to as “Al-based composite material screw”).

  As shown in FIG. 1, an Al-based composite material screw 10 is formed continuously with an axial core portion 12 mainly composed of an Al-based metal and an axial core portion 12 outside the axial core portion 12. It has a threaded portion 14 made of a composite material in which reinforcing material particles are dispersed in the same Al-based metal as the core portion 12. With such a structure, the Al-based composite material screw 10 exhibits higher strength than a pure Al screw.

  The head portion 16 of the Al-based composite material screw 10 is also made of an Al-based metal at the center, and a composite material at the outer peripheral portion. This is derived from the manufacturing method of the Al-based composite screw 10 as described later.

As the Al-based metal, pure Al, Al—Mg-based alloy, or the like is preferably used, but is not limited thereto. Further, as the reinforcing material particles, ceramic particles such as SiC, Si ₃ N ₄ , Al ₂ O ₃ , and AlN are preferably used, and only one kind of these may be added to the Al-based metal. More than seeds may be added to the Al-based metal. Further, the reinforcing material particles are not limited to these, and may be a metal material having a melting point higher than that of the Al-based metal and not forming an alloy with the Al-based metal, for example, metal Si precipitated from the alloy.

Next, a method for manufacturing the Al-based composite screw 10 having such a structure will be described. FIG. 2 shows a schematic configuration example of a solid bar manufacturing apparatus used for manufacturing the Al-based composite material screw 10. The manufacturing apparatus 20 is provided so as to surround the casting mold 22 with a bottomed cylindrical mold (crucible) 22 for melting the Al-based metal, a pedestal portion 24 that supports the casting mold 22 in a vertical posture, and the casting mold 22. An induction coil 26 and a high frequency power supply 28 for supplying a high frequency current to the induction coil 26 are provided. The mold 22 is made of a material that is not easily affected by high-frequency induction heating of the metal raw material filled in the mold 22 and electromagnetic separation (AC magnetic field application) of the Al-based melt in the mold 22, specifically, SiO _2. Those made of (quartz glass, synthetic quartz) are preferred. The pedestal portion 24 can use heat-resistant bricks or the like. The wire diameter and the number of turns (the number of turns) of the induction coil 26 are appropriately set in consideration of the size of the mold 22 and the melting ability of the metal put into the mold 22. The high frequency power supply 28 has a function of adjusting the frequency and output so that high frequency induction heating of the metal raw material filled in the mold 22 and electromagnetic separation of the Al-based melt in the mold 22 can be performed.

  In addition, a cooling water spray device for spraying cooling water for cooling the mold 22 on the outer periphery of the mold 22, a stirring rod for stirring the melt in the mold 22, the mold 22, and the like It is also preferable to provide a protective pipe that is installed so that the cooling water spray pipe is accommodated therein and the induction coil 26 is disposed outside thereof.

  In addition, the manufacturing apparatus 20 has a configuration in which one induction coil performs both high-frequency induction heating and electromagnetic separation, but the high-frequency induction heating coil and the electromagnetic separation coil are separately provided, It is good also as a structure where each drive power supply was connected.

  The solid rod used in the manufacture of the Al-based composite screw 10 is manufactured by first filling the mold 22 with the Al-based metal powder (or lump) and the reinforcing material powder in a predetermined ratio, and subjecting this to high-frequency induction heating. By doing so, an Al-based melt in which reinforcing material particles are dispersed is generated. It is also preferable to stir the Al-based melt to make the distribution of reinforcing material particles uniform.

  The raw material is not limited as long as an Al-based melt in which reinforcing material particles are dispersed can be generated. For example, first, pure Al is put into the mold 22 to produce an Al melt, and reinforcing material particles are added to and mixed with this, or an Al-based metal containing reinforcing material particles is added and dissolved and mixed. Such a method is also preferably used.

  After making the temperature of the Al-based melt constant, the high-frequency induction heating power supply is turned off, and then an alternating current of a predetermined frequency is passed through the electromagnetic separation coil. Thus, electromagnetic force is applied to the Al-based melt in the mold 22 to move and accumulate the reinforcing material particles on the peripheral portion of the Al-based melt.

  FIG. 3 schematically shows the movement mechanism of the reinforcing material particles. An electromagnetic force 36 is generated by the interaction between the AC magnetic field 32 generated by applying an AC current to the induction coil 26 and the induction current 34 induced in the Al-based melt 42, and the reinforcing material does not generate this electromagnetic force 36. A force is applied to the particle 44 in a direction opposite to the electromagnetic force 36. Since the opposite direction is the direction toward the outer periphery of the Al-based melt 42, the reinforcing material particles 44 can be accumulated on the peripheral portion of the Al-based melt 42 using this action.

  From such an electromagnetic separation mechanism, it can be seen that the combination of the Al-based metal and the reinforcing material particles only needs to have a difference in conductivity, and the concentration of the reinforcing material particles is not limited.

  As a method for supplying power to the electromagnetic separation coil, a method of flowing a current continuously for a predetermined time is preferably used.

Control of the reinforcing particle accumulation width (hereinafter referred to as “skin thickness”) can be adjusted by the frequency of the current flowing through the coil during electromagnetic separation. This skin thickness δ is δ = (πμ _e σf) ^−1/2 (permeability μ _e = 4π × 10 ⁻⁷ H · m ⁻¹ , conductivity σ = 3.80 × 10 ⁶ Ω ⁻¹ m ^{− 1} , f: frequency).

  Accordingly, in FIG. 1 shown above, the entire thread portion 14 is formed of a composite material. However, only the surface is made of a composite material, and the inside thereof is an Al-based composite having a thread portion made of an Al-based metal. It can be seen that the material screw can also be manufactured by controlling the concentration of the reinforcing material particles and the electromagnetic separation conditions.

  Subsequently, when this electromagnetic separation process is completed, the mold 22 is cooled to solidify the Al-based melt. As a result, a solid rod made of a composite material in which a metal component is a main component in the mold 22 and the reinforcing material particles are accumulated and dispersed in the outer periphery is formed in the mold 22.

  The solid bar is taken out from the mold 22 and a thread is formed on the solid bar by a rolling method. The rolling method is a kind of cold plastic deformation process, and is well known as a general method for manufacturing screws. A round bar (solid bar) is a plurality of cylindrical molds (rolls) in the form of screws. ), And a round bar material is plastically deformed by pressing it while rotating and making a screw thread shape.

  Thus, in the manufacturing process of the Al-based composite material screw 10, the solid composite rod in which the reinforcing material particles are dispersed in a desired portion is referred to as melting of raw materials in the mold 22, accumulation of reinforcing material particles, and solidification. This can be done with a simple operation. In addition, since a screw forming technique that is widely used for forming threads can be used, the productivity is high and the screw can be manufactured at low cost.

  In this example, a simplified mold configuration was shown. However, a solid bar was prepared by continuously supplying Al-based metal from one end of a pipe-shaped mold and providing a cooling mechanism at the other end after electromagnetic separation. Continuous casting is also possible by pulling out.

(Example 1)
Using a manufacturing apparatus having the structure shown in FIG. 2 and configured according to the standards described in Table 1, first, a predetermined amount of pure Al is melted by high-frequency induction heating (frequency: 30 kHz) in a mold. And kept at 750 ° C. Subsequently, while continuing high-frequency induction heating, this molten Al was mixed with an SiC-dispersed Al alloy (manufactured by Hydro Aluminum, Si 9%, Mg 6%, the balance Al, SiC: 23% by weight, SiC average particle diameter: 13 μm (calculated from the volume-based particle size distribution of SiC particles alkali-extracted from this alloy by means of a HELOS particle size distribution device) so that the SiC concentration in the Al-based melt finally becomes 4.5% by weight. A fixed amount was added to produce a SiC-dispersed Al-based melt, which was maintained at 750 ° C. The SiC-dispersed Al alloy was dissolved while stirring the Al-based melt in order to prevent electromagnetic separation of the SiC particles.

  High frequency induction heating was stopped after the SiC-dispersed Al alloy was completely dissolved and its temperature was stabilized at 750 ° C. Thereafter, the Al-based melt was further stirred for 20 seconds to disperse the SiC particles. Immediately after that, a 220 ampere current (frequency: 30 kHz) was continuously passed through the induction coil for 30 seconds to perform electromagnetic separation of the Al-based melt. The high frequency power supply was turned off to finish electromagnetic separation, and the sample was naturally cooled and solidified. The shape of the solid bar taken out from the mold was approximately φ11 mm × 100 mm.

  The solid bar was cut perpendicular to the length direction, and the cross-sectional structure was observed with an optical microscope. Further, a thread was formed on this solid rod by a rolling method, and the obtained screw was cut in parallel with the length direction, and the cross-sectional structure was observed with an optical microscope.

  FIG. 4 shows an optical micrograph of a cross section of the solid bar produced. As shown in this photograph, it was confirmed that the SiC particle accumulation layer was uniformly formed on the periphery of the solid bar, corresponding to the skin thickness δ (= 1.49 mm) at a frequency of 30 kHz. It was. In addition, it was confirmed that the central part of the solid bar is mainly composed of metal Al.

  The optical micrograph of the cross section of the produced screw is shown in FIGS. 5B, 5C, and 5D are enlarged photographs of regions (a), (b), and (c) in FIG. 5A, respectively. In the conventional material in which SiC is uniformly dispersed in metal Al, the rolling method could not be used for the production of the screw, but a cylindrical shape in which a SiC integrated layer was formed at the periphery and the center was composed of metal Al. It was confirmed that if a composite material is used, screws can be manufactured by a rolling method.

  As can be seen in the enlarged photograph of the thread portion, the SiC particle accumulation layer is denser in the thread portion than in the state of the solid rod before processing. This is thought to be a result of the SiC particles in the valley of the screw being pushed toward the thread because the thread is formed by compressive deformation.

(Example 2)
As the metal initially put into the mold, Al alloy (Al-7075) was used in place of the pure Al of Example 1, and the SiC-dispersed Al alloy had an average SiC particle size of 21 μm. A screw was produced according to the same procedure as in Example 1 except for two points. An optical micrograph of the cross section of the screw is shown in FIG. 6B and 6C are enlarged photographs of regions (a) and (b) in FIG. 6A, respectively.

As shown in FIGS. 6A to 6C, the shape of the screw thread is not collapsed and cracks are not observed. Therefore, even when an Al-based alloy is used as the main component, the screw can be easily formed by the rolling method. It was confirmed that it can be plastically deformed into a shape. It was also confirmed that SiC particles were uniformly dispersed in the thread portion.

(Torque test)
The screw of Example 2 was manufactured again, and the torque test was performed by the following method. That is, it fixes by pinching with the vise of the axial part of a screw, and a stainless steel nut is inserted in a screw part. A stainless steel long nut was further fitted from above, and the lower nut was fixed with a wrench, and the upper long nut was tightened with a torque in increments of 10 N · m, and a tightening torque value at which the threaded portion was broken was obtained. For comparison, two screws made only of an Al-7075 alloy, which is the base material of the screw of Example 2, were produced, and the tightening torque was measured in the same manner.

  The measurement results are shown in Table 2. The screw standard of Example 2 is M12. As for the screw of Example 2, no deformation of the thread was observed at a tightening torque of 30 to 40 N · m. On the other hand, as shown in Table 2, it was confirmed that when the screw made of only the Al-7075 alloy exceeds the tightening torque of 20 N · m, the thread is deformed. From these facts, it can be considered that the screw of Example 2 is difficult to deform because the SiC particles are accumulated in the thread portion. Therefore, in the conventional aluminum screw, the screw thread is deformed with a small torque and it is difficult to use it repeatedly. However, by integrating SiC particles in the screw thread part, a screw that can withstand repeated use can be manufactured.

Further, the screw portion of Example 2 was broken when the tightening torque exceeded 40 N · m. The specified tightening torque for M12 type aluminum screws is 21 N · m, and the specified tightening torque for general iron-based M12 type screws is 42 N · m. Was confirmed.

Sectional drawing which shows typically the structure | tissue structure of the screw made from Al group composite material which concerns on this invention. The figure which shows schematic structure of the manufacturing apparatus of the solid rod used for manufacture of screws made from Al group composite material. The figure which shows typically the movement mechanism of the reinforcing material particle in Al-based melt. 2 is an optical micrograph of a cross section of a solid bar according to Example 1. FIG. 3 is an optical micrograph of a cross section of a screw of Example 1. FIG. The enlarged photograph of the area | region (a) part in FIG. 5A. The enlarged photograph of the area | region (b) part in FIG. 5A. Enlarged photo of area (c) in FIG. 5A 4 is an optical micrograph of a cross section of a screw of Example 2. FIG. The enlarged photograph of the area | region (a) part in FIG. 6A. The enlarged photograph of the area | region (b) part in FIG. 6A.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Al group composite material screw, 12 ... Shaft core part, 14 ... Screw thread part, 16 ... Head, 20 ... Manufacturing apparatus, 22 ... Mold, 24 ... Base part, 26 ... Induction coil, 28 ... High frequency power supply, 32 ... alternating magnetic field, 34 ... induced current, 36 ... electromagnetic force, 42 ... Al-based melt, 44 ... reinforcing material particles.

Claims (5)

An axial core mainly composed of an Al-based metal;
A threaded portion made of a composite material formed continuously with the shaft core portion on the outside of the shaft core portion, and reinforcing material particles dispersed in the same kind of Al-based metal as the shaft core portion;
A screw made of an Al-based composite material, characterized by comprising:   The Al-based composite material screw according to claim 1, wherein the reinforcing material particles are SiC. Producing an Al-based melt in which reinforcing material particles are dispersed in a mold;
Applying electromagnetic force to the molten metal constituting the Al-based melt so that the reinforcing material particles move to the peripheral edge of the Al-based melt;
Solidifying the Al-based melt and taking out a solid bar made of a composite material from the mold; and
Forming a screw thread on the solid bar by a rolling method, and a method for producing an Al-based composite screw.   The method for producing an Al-based composite material screw according to claim 3, wherein the reinforcing material particles are SiC, and the Al-based melt is a pure Al melt or an Al alloy.   The step of applying an electromagnetic force to the Al-based melt is performed by arranging an induction coil so as to surround the mold and generating an alternating magnetic field in the length direction of the mold. Or the manufacturing method of the screw made from Al group composite material of Claim 4.