JP5732932B2 - Boss forming jig and boss forming method - Google Patents

Description

  The present invention relates to a boss forming jig for forming a boss with a screw on a metal plate, and a boss forming method.

For information devices such as notebook computers and mobile phones, light metal cases such as magnesium alloys and aluminum alloys are used. This is a light alloy
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In addition to this, it has come to be used because of its high strength and its ease of recycling compared to plastic. As a manufacturing method of these metal casings, for example, a thixo injection molding method or a die-cast molding method is known for a casing using a magnesium alloy.

  However, in these molding methods, there are many post-processing such as deburring after molding, and there are many appearance defects due to the flow trace of the molten metal, so that the manufacturing cost increases. On the other hand, a housing is also manufactured by sheet metal processing using a light alloy plate material. This method of manufacturing a casing by sheet metal processing is excellent in appearance and low cost.

  By the way, the casing needs a boss for fixing the components housed in the casing and the casing or fixing the casings to each other. As a technique for forming a boss on a casing made by sheet metal processing, a method of stud welding a previously prepared boss to the casing is known. A boss forming method using friction welding is also known (herein referred to as friction welding forming method). In this friction welding method, a hollow cylindrical boss forming jig is pressed against a metal plate while rotating at a high speed, and the frictional heat generated between the boss forming jig and the metal plate causes a superplastic phenomenon on the metal of the metal plate. It is expressed and plastically fluidized, and the metal is flowed into a boss forming jig to form a boss (projection).

JP 2007-14967 A JP 2010-23040 A JP 2009-107006 A

  As described above, a housing of an information device or the like is manufactured by sheet metal processing using a light alloy. A stud welding method or a friction welding method is known as a method of providing a boss on a casing made of such a sheet metal.

  The fastening method using a boss is generally a method in which a tapping screw is screwed into a hole opened in the boss and fastened while being tapped, but when a screwed boss is to be fastened using a screw (small screw) There is. For example, a screw is used when dislikes the chips generated when a tapping screw is tightened. In such a case, a threaded boss is required.

  The stud welding method described above involves welding a pre-threaded boss to a metal casing. However, sufficient strength cannot be obtained for joining the boss and the casing, and there are welding marks on the surface of the casing. There is a problem in appearance because it is attached.

  In the friction welding method, a boss with a hole for a tapping screw (here, referred to as a boss hole) is generally manufactured, but it is not known to directly manufacture a screwed boss. In order to obtain a threaded boss, a boss having a boss hole is once created by a friction welding method, and the boss hole is tapped. Therefore, there is a problem that the cost is increased because a tapping process is required after boss molding. In addition, when boss molding is performed on a thin metal plate by friction welding, the metal plate on the back side of the molded boss may generate “sink marks”, which causes a problem of poor appearance. there were.

  The present invention has been made to solve the above-described problems, and provides a boss forming jig and a boss forming method capable of forming a boss with a screw without requiring a screwing step in the friction welding method. The purpose is to do. Also provided is a boss forming jig capable of forming a threaded boss that does not cause “sinking”.

  According to one aspect of the invention, a cylindrical cavity that opens to the bottom surface of a column is formed by aligning the center axis of the column and the cylinder, and the ring-shaped surface of the edge of the bottom surface of the column is used as the processing surface for the metal material A boss forming jig having a boss forming portion which is pressed and rotated, and a rod-shaped screw forming portion whose surface is tapped and arranged so that the boss forming portion can be rotated and moved up and down on a hollow central axis of the boss forming portion. Is provided.

  According to another aspect of the invention, a boss molded part is formed by forming a cylindrical cavity that opens to the bottom surface of the column by aligning the center axis of the column and the cylinder, and having an annular surface at the edge of the column bottom as the machining surface And a boss forming jig, which is arranged on the central axis of the cavity and a cylindrical thread forming part with a tapped surface, is pressed against the metal material to be processed while rotating, and the metal of the metal material is plasticized A step of causing the plastic fluidized metal to flow between the inside of the hollow cylinder of the boss forming portion and the screw forming portion, and forming a boss following the inner wall of the hollow cylinder and the surface of the screw forming portion, There is provided a boss forming method having a step of drawing out a boss formed by rotating in a direction opposite to a direction in which the screw forming portion is tapped.

  Since the threaded core is provided in the boss molding part of the hollow cylinder that defines the external shape of the boss, the boss molding treatment for the friction welding method that enables boss molding with a screw without the need for a screwing process. Tools can be provided.

It is a figure which shows the example of a common metal housing | casing and a boss | hub. It is a figure which shows the boss | molding example by the general friction welding method. It is a figure which shows the structural example (Example 1) of the boss | hub shaping jig | tool of this invention. It is a figure which shows the example of a flow (Example 1) of the boss molding with a screw | thread by this invention. It is a figure which shows the other structural example (Example 1) of the boss | hub shaping jig | tool of this invention. It is a figure which shows the structural example (Example 2) of the boss | hub shaping jig | tool of this invention. It is a figure which shows the example of shaping | molding (Example 2) of the boss | hub with a screw | thread by this invention.

  Prior to the description of the embodiments of the present invention, an example of a boss formed on a metal casing and a general example of boss formation by a friction welding method will be described.

  FIG. 1 is a diagram showing an example of a metal casing of a notebook personal computer. The casing is composed of a plurality of casing parts, and is an example of one casing part among them. The housing part 10 in FIG. 1 is made of a 1 mm-thick magnesium alloy by sheet metal processing, and shows a shape viewed from the back side. As shown in the figure, eight bosses 20 are formed on the back surface by friction welding. Each boss 20 has a boss hole 21 into which a tapping screw is screwed. The tapping screw screwed into the boss hole 21 enters while cutting the inner wall of the boss hole 21 at the cutting edge portion at the tip of the tapping screw and performs fastening. At this time, the above-mentioned chips are generated.

  Next, a general molding method of the boss 20 having the boss hole 21 of FIG. 1 by the friction welding method will be described with reference to FIG. As shown in FIG. 2A, the boss forming jig 30 has a cylindrical shape as a whole, an annular groove 31 is formed at the end of the cylinder, and the end surfaces are processed surfaces 32 and 33. It is a tool. When the boss forming jig 30 is pressed while rotating from above the metal material 40, frictional heat is generated on the processed surfaces 32 and 33, and the metal material 40 is plastically fluidized. The plastic fluidized metal flows into the groove 31 of the boss forming jig 30 as shown by an arrow drawn in the metal material 40 shown in FIG. 2B, and forms a boss 41 having a boss hole 42 in the center. (FIG. 2 (c)). Note that the arrows drawn on the boss forming jig 30 in FIG. 2B indicate the directions of rotation and pressing of the boss forming jig 30.

Example 1
The boss forming jig of the present invention is a jig for forming a screwed boss in the friction welding method. A threaded boss is a boss having a threaded boss hole. FIG. 3 is a view showing the structure of the boss forming jig 100 of the present invention. The boss forming jig 100 includes a boss forming portion 110 for forming the outer shape of the boss and a screw forming portion 120 for forming the screw of the boss hole. It is a configuration that includes.

  The entire outer shape of the boss molded part 110 has a columnar shape, and the tip part (lower end in FIG. 3) serving as the bottom of the cylinder is opened in the same direction as the central axis of the boss molded part 110 and is opened in a hollow cylindrical shape 111. Is forming. The recess 111 defines the outer shape of the boss. The end surface of the recess 111 is a processed surface 112, and the processed surface 112 has an annular shape. In addition, a through hole 113 through which the screw forming portion 120 described below passes is provided in the central axis of the boss forming portion 110. The upper part of the boss forming part 110 is a part that is gripped and rotated by a processing device (not shown). Further, the concave portion 111 formed in the boss molding portion 110 is a space into which a plastic fluidized metal to be described later flows, and corresponds to a cavity in the mold.

  The screw forming portion 120 includes a screw portion 121 and a screw grip portion 122. The screw portion 121 is a rod-like long screw, and is a portion that becomes a mother die for tapping a boss hole. The tip of the screw portion 121 (the lower end portion in FIG. 3) is made to be almost the same height as the processed surface 112 of the boss forming portion 110 here. The height of the tip defines the depth of the screw hole formed in the boss. Therefore, it can be appropriately changed depending on the depth of the screw hole. The screw part 121 is connected to the screw gripping part 122 through the through hole 113 formed in the boss forming part 110. The boss forming part 110 during the boss formation is rotated by the through-hole 113, but the screw forming part 120 is not rotated because the screw holding part 122 is held by a processing device (not shown). The screw part 121 of the recess 111 of the boss molding part 110 corresponds to a core (core) in the mold.

  Both the boss forming part 110 and the screw forming part 120 are made of stainless steel SUS304. However, it is not limited to this material. The surface of the screw part 121 of the screw forming part 120 is coated with diamond-like carbon. As will be described later, the plastic fluidized metal forms a screw following the unevenness of the screw thread formed on the screw part 121, but it is necessary to pull out the screw forming part 120 from the metal after the boss is formed. This is a coating of diamond-like carbon that has a low coefficient of friction so that it can be easily peeled off. This film is not limited to a diamond-like carbon film, and may be a fluorine film, a urethane film, an inorganic glass film, or the like.

  The dimensions of each part of the boss forming jig 100 are as follows: the diameter a of the boss forming part 110 is 8 mm, the diameter b of the concave part is 5 mm, the height h of the concave part is 6 mm, and the diameter c of the screw part 121 of the screw forming part 120 is 3 mm. is there. These dimensions are examples in which a 3 mm screw hole is formed in a boss having a diameter of 5 mm, and may be appropriately changed according to the dimensions of the boss to be molded.

  Next, a method for forming a threaded boss will be described. FIG. 4 illustrates an example in which a threaded boss is formed on a magnesium alloy thin plate (AZ31B, plate thickness 1 mm) as the metal material 50 to be processed using the boss forming jig 100 shown in FIG. The metal material 50 is degreased and cleaned after machining. The degreasing cleaning is performed in order to efficiently perform friction between the surface of the metal material 50 and the processed surface 112 of the boss forming portion 110.

  First, as shown in FIG. 4A, the screw forming portion 120 rotates the boss forming portion 110 horizontally to 8,000 rpm without rotating, thereby lowering the entire boss forming jig 100. The curved arrow indicates the rotation direction of the boss forming part 110, and the straight arrow indicates the direction in which the boss forming part 110 and the screw forming part 120 descend simultaneously. In addition, the rotation direction of the boss forming part 110 may be the opposite direction to this figure.

  When the processing surface 112 of the boss forming portion 110 reaches the surface of the metal material 50 due to the lowering of the boss forming jig 100, friction is generated between the rotating processing surface 112 and the surface of the metal material 50 to generate frictional heat. To do. The metal material 50 is plastically fluidized by the generated frictional heat and flows into the concave portion 111 of the boss forming portion 110. By continuing to rotate and press downward the boss forming part 110, the fluidized metal material 50 is filled in the recess 111 following the thread formed on the wall of the recess 111 and the surface of the screw forming part 120. Go. Along with this, the boss forming jig 100 is lowered. At this time, the boss forming portion 110 rotates, and the screw forming portion 120 descends in a non-rotating state (see FIG. 4B).

  When the processed surface 112 of the boss forming part 110 reaches a depth of 0.5 mm from the surface of the metal material 50, the downward pressing is stopped. When the cooled metal is solidified after cooling down, the screw forming part 120 is pulled out while rotating. The rotation direction is rotated in the direction opposite to the screw traveling direction of the screw portion 121. As described above, the diamond-like carbon film is coated on the screw portion 121 to facilitate peeling from the metal material 50 (see FIG. 4C).

Subsequently, the boss forming part 110 is raised while rotating, and is peeled off from the metal material 50 to complete the threaded boss 51 having the screw holes 52. Here, after the screw forming portion 120 is pulled out, the boss forming portion 110 is lifted from the metal material 50 and peeled off, but these may be performed simultaneously (FIG. 4 (d)).
In this embodiment, the boss molding is performed directly without heating the metal material 50. However, the boss molding may be performed in a state where the metal material 50 is heated to approximately 200 ° C., for example. By applying heat in advance in this way, plastic fluidization is further promoted and the boss forming time is shortened.

  In the boss forming jig 100 used in the boss forming flow of FIG. 4, the screw portion 121 has a structure that penetrates the through hole 113 of the boss forming portion 110. However, as shown in FIG. 5, the screw portion 141 is the boss forming portion. The thread forming portion 140 may have a structure in which the portion extending from the gripping portion 142 passes through the through hole 114 and is provided only in the concave portion 131 of 110. By doing in this way, the gap between the boss forming part 130 rotating at the time of boss forming and the non-rotating screw forming part 140 can be reduced, and the rotational runout of the boss forming part 130 can be reduced. However, the depth of the screw hole 52 cannot be varied and becomes a constant depth.

(Example 2)
The processed surface of the boss forming jig for the metal material in Example 1 was a flat surface. The machined surface is pressed against a metal material and rotated to plastically fluidize the metal, and the fluidized metal enters a recess (the recess 111 in FIG. 3) provided in the boss forming jig to form a boss. The fluidized metal in the portion may be pressed by the boss forming jig and flow to the outside of the boss forming jig to create a “burr”. Further, when the metal below the processed surface is reduced by the flow, a dent called “sink” may be generated on the back surface of the boss-formed sheet metal.

  Example 2 is a boss forming jig for forming a threaded boss in which occurrence of such “burrs” and “sink marks” is suppressed. FIG. 6 is a view showing a structural example of the boss forming jig 200 of the second embodiment. The boss forming jig 200 includes a boss forming part 210 and a screw forming part 120. The difference from the boss forming jig 100 shown in the first embodiment is a boss forming portion 210 and the screw forming portion 120 is the same.

  The boss molded part 210 has a protruding part 213 that protrudes in a direction parallel to the central axis at the outer edge of the processed surface 212. The protrusion amount g and the radius r of the protrusion 213 are both 0.3 mm. Other dimensions (ac, h in FIG. 6) are the same as those of the boss forming jig 100 shown in FIG.

  By providing the protruding portion 213 in the boss molded portion 210, the metal fluidized under the processing surface 212 is prevented from flowing to the outside of the boss molded portion 210 and enters only the concave portion 211. FIG. 7 is a diagram for explaining a boss forming example in Example 2, and FIG. 7A shows the plastic flow of the metal during the boss forming by arrows. As indicated by the arrows in the metal material, the plastically fluidized metal flows into the recess 211 without flowing outside the boss forming part 210. FIG. 7B shows a state in which the boss processing is finished, and the protruding portion trace 53 remains, but it is the back surface of the housing, and the occurrence of “sinking” on the surface of the housing is suppressed. Incidentally, FIG. 7C shows a state where “burrs” and “sink marks” are generated. By making the boss forming jig have the structure shown in FIG. 6, the occurrence of such burrs 54 and sink marks 55 is suppressed.

  As mentioned above, although the Example of the boss | hub formation jig with a screw | thread of this invention and the boss | hub formation method was described, these are not limited to the above-mentioned content, In various aspects in the range which does not deviate from the summary of this invention. It can be implemented.

DESCRIPTION OF SYMBOLS 10 Housing parts 20 Boss 21 Boss hole 30 Boss shaping jig 31 Groove 32 Processed surface 33 Processed surface 40 Metal material 41 Boss 42 Boss hole 50 Metal material 51 Boss with screw 52 Screw hole 53 Projection part mark 54 Burr 55 Sink 100 Boss Forming jig 101 Boss forming jig 110 Boss forming part 111 Recessed part 112 Processing surface 113 Through hole 114 Through hole 120 Screw forming part 121 Screw part 122 Gripping part 130 Boss forming part 131 Recessed part 140 Screw forming part 141 Screw part 142 Gripping part 200 Boss forming jig 210 Boss forming portion 211 Concavity 212 Processing surface 213 Projection

Claims (6)

A boss that is formed by forming a cylindrical cavity that opens at the bottom of the column by aligning the column and the central axis of the cylinder, and is rotated by being pressed by the metal material to be processed using the annular surface at the edge of the column as the processing surface Molding part;
The hollow central axis of the boss molded portion has a rod-shaped screw molded portion that is disposed so as to be able to rotate and move up and down, and is screwed on the surface and coated with a low friction film. Boss forming jig characterized by The screw forming portion is rotatable in a direction opposite to the traveling direction of the tapped screw.
The boss forming jig according to claim 1. The boss forming part has a protruding part that is provided at an edge of the processed surface and protrudes in a direction parallel to the central axis.
The boss forming jig according to any one of claims 1 and 2. A cylindrical cavity that opens to the bottom surface of the cylinder is formed by aligning the center axis of the cylinder and the cylinder, and a boss-molded portion having an annular surface at the edge of the bottom surface of the cylinder as a machining surface and a substantially central axis of the cavity A boss forming jig including a cylindrical screw forming portion that is disposed on the surface and is coated with a low-friction film and is pressed against the metal material to be processed. A process of plastic fluidizing,
Flowing the plastic fluidized metal between the inside of the hollow cylinder of the boss forming portion and the screw forming portion, and forming a boss following the inner wall of the hollow cylinder and the surface of the screw forming portion; ,
A step of extracting the screw forming portion from the boss formed by rotating in the direction opposite to the traveling direction of the tapped screw;
A boss forming method characterized by comprising: The metal material is magnesium, aluminum, or an alloy mainly composed of those metals.
The boss forming method according to claim 4. The metal material is previously heated at a temperature of 200 ° C. or higher.
The boss forming method according to claim 4, wherein the boss is formed.

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