Patent Application
20110016944
1. Field of the Invention
The present invention relates to a method of producing a metallic member. More particularly, the present invention relates to a method of producing a metallic member having a plurality of protrusions of, for example, a gear member or a vibration member of a vibration wave driving apparatus.
2. Description of the Related Art
As a metallic member in which a plurality of protrusions are arranged, a vibration member for a vibration wave driving apparatus discussed in Japanese Patent Laid-Open No. 07-135785 is available. The vibration member is an annular or a disc-shaped member. Many protrusions like the teeth of a comb are provided at one surface (upper surface) of the vibration member, and a base not having teeth of a comb are provided at the opposite surface (lower surface) of the vibration member. A ring-like piezoelectric element is joined to the lower surface of the base. In this type of vibration member, the many protrusions are formed by a forging method or a method of cutting many radial grooves using a grinding tool or a milling cutter having the shape of a disc (a grinding method or a cutting method). The role of the protrusions is to increase vibration displacement when rotating a moving member by transmitting vibration of the vibration member to the moving member by friction force. Depending upon use, a hole extending through an output shaft is provided in the center of the vibration member.
As another example of a metallic member having a plurality of protrusions, a gear such as that discussed in Japanese Patent Laid-Open No. 2001-205385 is available. The gear (such as a bevel gear) having teeth as the plurality of protrusions has a hole portion that does hot have a core for passing a shaft therethrough. The teeth of the gear may also be formed by the cutting method or the grinding method, or by the forging method using a pressing device.
The forging method is lower in cost than the cutting method and the grinding method because the forging method is a processing method that can be simplified.
For forming many protrusions by the forging method, it is possible to provide an annular or a disc-shaped processing object in which a pipe or a round bar is cut into round slices, and to form the protrusions on the processing object by directly subjecting the processing object to a pressing operation.
However, this method has the following problems. When a punch 122 (serving as a pressing mold (male mold)) contacts the processing object 111, stress applied to the female mold is instantaneously increased. As a result, the female mold tends to break. In addition, a force for reducing the thickness of the processing object 111 interposed between the punch 122 and the female mold is applied to the molds at the same time that pressure is applied. Therefore, a large total load is required for a molding operation. From this viewpoint also, the molds tend to break. In particular, the stress concentrates at a thin-walled portion 124a of a die 124 having recesses and protrusions. The thin-walled portion 124a is provided for forming grooves (between the protrusions) in an outer-peripheral lower surface of the disc-shaped processing object. The smaller the widths of the grooves, the thinner the thin-walled portion 124a, thereby reducing the strength of the thin-walled portion 124a. Therefore, during the forging, the probability with which the thin-walled portion breaks is increased. Consequently, for maintaining the strength of the thin-walled portion 124a, the widths of the grooves between the protrusions need to be large to a certain extent, as a result of which limitations are placed on the widths in a peripheral direction of the protrusions of the gear or the vibration member.
The present invention makes it possible to easily mold a plurality of protrusions to any width on a metallic processing object, and to reduce a load on a mold during the molding of the plurality of protrusions.
According to the present invention, there is provided a method of producing a metallic member having a plurality of protrusions. The method includes forming a cup-like member by applying a load to a metallic plate member, the load applied to the plate member having a component that is perpendicular to a surface of the plate member; and forming the plurality of protrusions at an opening end portion of the cup-like member with a mold by applying a load to the cup-like member, the load applied to the cup-like member having a component that is perpendicular to a surface of a bottom portion of the cup-like member.
According to the present invention, when forming a metallic member having a plurality of protrusions, a cutting operation or a grinding operation is not required, so that a load on a mold when forming the protrusions can be reduced. In addition, it is possible form grooves between the protrusions of a molded product to any width.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention will hereunder be described in detail with reference to the drawings. As a metallic member used in the present invention, a vibration-wave-driving-apparatus vibration member having protrusions for increasing vibration displacement, or a gear having teeth for output transmission is used as an example.
In a first embodiment, as a metallic member having a plurality of protrusions protruding in the same direction, a vibration-wave-driving-apparatus vibration member having protrusions for increasing vibration formed on a surface of the vibration member is used as an example, to describe a method of producing the vibration member. The vibration wave driving apparatus includes the vibration member provided with a piezoelectric element (which is one type of electro-mechanical energy conversion element). In the vibration wave driving apparatus, an alternate signal is supplied to the piezoelectric element to generate a traveling wave at a surface of the vibration member, and the traveling wave is used to drive a moving member that contacts the vibration member.
As shown in
As shown in
Further, by molding the side surface 53 so that a slope extending outward with respect to the bottom portion 52, that is, by forming the opening end portion 51 of the cup-like member so that the outside diameter of the opening end portion 51 of the cup-like member is larger than the outside diameter of the bottom portion 52 of the cup-like member, a molding load is reduced when forming the protrusions in the post-processing process. Therefore, performing this is desirable. This is because, since, as shown in
Next, for softening the cup-like member 11-2, for example, an annealing heat treatment at a temperature of 750° C. is performed. The heat treatment is performed to reduce molding load during a forging operation performed for forming the protrusions in the post-processing process, so that the cup-like member tend to undergo plastic deformation. Depending upon the extent of drawing, the hardening of the material does not progress very much and deformation resistance does not increase very much. Therefore, the annealing heat treatment may sometimes be omitted. Thereafter, a lubricating treatment may be performed on the surface of the cup-like member 11-2. In the lubricating treatment, for example, a lubricant whose main component is molybdenum disulfide is applied.
The cup-like member is positioned at an inside-diameter portion of the die ring 33, and the opening end portion of the cup-like member is disposed so as to contact the upper end of the thin-walled portion 34a (a portion of the die 34) for forming grooves between the protrusions.
By the compression molding performed by this forging operation, the protrusions 55 are formed at the opening end portion 51 of the cup-like member, and the width in the radial direction of the protrusions 55 becomes greater than the width of the opening end portion of the cup-like member. The thickness of the bottom portion 54 of the final molded product is less than the thickness of the bottom portion 52 of the cup-like member. Accordingly, in the embodiment, stress applied to each portion of the molds, in particular, to the thin-walled portion 34a during the molding process is gradually increased, and a force applied to the thin-walled portion in the peripheral direction is small, so that the probability with which the thin-walled portion 34a is broken is reduced. Since excess metal that is produced as the bottom portion of the cup-like member is made thinner is used for forming the protrusions at the outer peripheral side, the load on the die and the knockout portion is also reduced, thereby reducing the probability of deformation and breakage thereof. The shape of the side surface of the cup-like member and the shape of the protrusions are not limited to the shapes discussed in the embodiment as long as they can be deformed so that the width in the radial direction of the protrusions, that is, the plate thickness is increased during the forging operation. For example, the protrusions may be inclined not only at the inner peripheral side, but also at the outer peripheral side, or may be formed with the same width.
Further, in the embodiment, as a plate member serving as the processing object, a plate member having a width that is smaller than the width in the radial direction of the groove of the die 34 (that is, the width in the radial direction of the protrusions of the molded product) may be used, thereby reducing costs. The reason will be given below.
In the related method shown in
The vibration member formed in accordance with the embodiment makes it possible for the mass of the protrusions of the vibration member to provide vibration energy, and to reduce the width of the thin-walled portion in the peripheral direction. Therefore, it is possible to cause the width of the grooves formed between the protrusions that are adjacent to each other to be as small as possible. That is, it is possible to increase the width in the peripheral direction of the protrusions, and to increase resistance to wear of the protrusions that contact the moving member.
In the vibration wave driving apparatus, if the width in the peripheral direction of the protrusions formed by the compression molding is increased, not only is the resistance to wear increased, but also undesired vibration is restricted. This is because, since natural vibration frequency of each protrusion itself is small, undesired vibration caused by the protrusions themselves infrequently occurs.
In the present invention, the method of molding the cup-like member by applying a load having a component that is perpendicular to the surface of the plate member to the plate member is not limited to drawing. As long as it is a method of three-dimensionally deforming the plate member, any other method, such as burring, stretch forming (embossing), or dish extrusion (bowl molding) may also be used.
The method of forming the protrusions by applying a load having a component that is perpendicular to the surface of the bottom portion of the cup-like member to the cup-like member is not limited to cold forging. The plate member may also be molded by hot forging, warm forging, or cold pressing.
In accordance with the embodiment, a vibration member formed of stainless steel (SUS420J2), having an outside diameter of 48 mm, whose bottom portion has a thickness of 2.5 mm, whose protrusions have a width of 5 mm in a radial direction, and whose protrusions have a height of 4.5 mm was produced. A mold used for molding the protrusions had a height of 4.5 mm and a width of 0.6 mm (at a thinnest portion) in a peripheral direction of a thin-walled portion of a die. When an attempt was made to form such a vibration member by the related method shown in
Next, a method of molding protrusions of a vibration member according to a second embodiment will be described. The second embodiment differs from the first embodiment in that a hole is formed in the center of a bottom portion of a cup-like member and in that a preliminary molding operation is performed on the cup-like member between a step of forming the cup-like member and a step of forming a final molded product.
The reason that the circular hole is provided to restrain the center position in this way is related to the precision of the shape of the cup-like member 41-1 and uniformity in its plastic deformation. In drawing, considering the plastic deformation of a material itself, the precision of the shape of a molded product is often influenced by the degree of its anisotropy. Anisotropy occurs as a result of aggregate structures differing from each other in connection with, for example, crystal orientation according to material. For example, characteristics, such as stretching, processing hardening coefficient, an elastic limit value, and Young's modulus, in a rolling direction differ from those in a direction orthogonal to the rolling direction. As a result, differences also occur in the Lankford value (characteristic value indicating the anisotropy of a plate material) and a spring-back amount (amount by which the plate material returns to its state prior to processing by a slight opposing force after a bending operation). If the plate member having a high anisotropic property is drawn, the opening end portion 51 of the cup-like member may be curled. The opening end portion 51 of such a cup-like member infrequently has a high degree of circularity.
To overcome this problem, in the embodiment, measures are taken to allow the use of a material having a high anisotropic property. That is, in the embodiment, as mentioned above, for example, a hole that restrains the center position is formed in the cup-like member. This causes deformation in a radial direction to be uniform during the deformation of the cup-like member. As a result, variations in the thickness in a peripheral direction of a molded product that is formed by compression are reduced.
Prior to molding the final protrusions, it is desirable that the preliminary molded product be subjected to intermediate heat treatment (annealing). By the heat treatment, the preliminary molded product is softened, so that deformation resistance is reduced in a final step. As a result, in addition to reducing the probability of seizure and the burden on the mold used in the final step, the probability of cracking of the molded product itself is reduced. The heat treatment is also effective in reducing negative effects caused by the aforementioned anisotropy as recrystallization occurs.
It is desirable that a lubricating treatment also be performed on the preliminary molded product 41-2 whose protrusions have small volumes (grooves between the protrusions are shallow). This is because, stress on the molds in the final molding step, in particular, seizure of the thin-walled portion is reduced. In the lubricating treatment, for example, a lubricant whose main component is molybdenum disulfide is applied.
As described above, in the embodiment, the circular hole 41-2a is formed in the center of the bottom portion of the cup-like member, and the preliminary molding step is provided prior to the step of forming the final protrusions. Forming the circular hole makes it possible to restrain the center position and to reduce variations in the width of the molded product in the peripheral direction. In addition, even in the final molding step, when a load having an out-of-plane component is applied, the circular hole makes it possible for excess metal to be used for the circular hole and to prevent excessive stress from being applied to the molds. In addition, by providing the preliminary molding step, when the final protrusions are being molded, almost no sideways force is generated at the thin-walled portion, thereby making it possible to further reduce the probability of breakage.
Although each of the embodiments is described taking as an example the case in which protrusions for increasing vibration in the vibration member are formed, the present invention is not limited thereto. That is, as long as a metallic processing object having a plurality of protrusions protruding in one direction is provided, the above-described molding method is applicable to parts having shapes similar to those of, for example, a bevel gear and a hypoid gear.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2009-172920 filed Jul. 24, 2009, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-172920 | Jul 2009 | JP | national |
