JPS6261370B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming holes with high accuracy in a plate material. Conventionally, holes have been formed in plate materials by cutting or punching using a press. However, although the cutting method can machine holes with high precision, it has the disadvantage that it is troublesome to dispose of chips and the machining time is long, making it unsuitable for mass production. In addition, punching using a press is excellent for mass production, but since regular punching requires a large clearance between the punch and die, a fractured surface occurs in addition to the sheared surface, making it impossible to form holes with good cylindricity. . Therefore, it is not suitable when it is necessary to insert or press fit a shaft or pin into a punched hole perpendicular to the plate surface. On the other hand, if precision punching is performed, it is possible to machine a hole with excellent cylindricity and a 100% sheared surface without sacrificing mass productivity, but it is expensive due to its high precision and ability to apply plate holding pressure and counter pressure. In addition to requiring a special press, the life of the punching tool is a fraction of that of conventional punching, and the cost of the tool is high. In order to eliminate the drawbacks of the prior art described above, the present invention inserts a core metal having the same size and shape as the pilot hole into a pilot hole formed by punching a plate material,
With the cored metal inserted, the inner material of the plate is compressed by applying pressure only in the thickness direction of the surface of the pilot hole with a surface pressing part having a pressure surface substantially parallel to the surface of the plate. By causing the flow to flow in the direction of the core metal, the accuracy of punching holes is improved. The present invention will be explained below with reference to embodiments shown in FIGS. 1 to 3. FIG. 1 shows the longitudinal cross-sectional shape of a hole punched out of a plate 1 having a thickness H=6 mm (hot-rolled steel plate) using a conventional press and a die having the dimensions shown in the table.

[Table] The clearance in the table is the dimension that is generally said to have the minimum shear load, that is, approximately 20 mm of the plate thickness.
%, and was determined to extend the life of the tool. As shown in Fig. 1, the inner surface of the hole punched in this way consists of a sheared surface section 2 with a length of approximately H ₁ = 1.5 mm and a tapered fracture surface section 3 with a length of approximately 4.5 mm following this.
It is formed from D ₀ = 19.2φ, D = 20.2φ
Its cylindricity is extremely poor. FIG. 2 is a diagram showing a method for improving the cylindricity of the inner surface of the round hole punched with the ordinary press shown in FIG. In Fig. 2, 4 is a punch, 6 is a surface pressing part that presses the peripheral part of the hole, and 5 is a core metal provided at the tip of the punch 4, and the outer diameter of the core metal 5 is equal to that of the hole punch. At the tip, it is easy to insert into the hole, and by adjusting the amount of surface stamping of the plate material, the cylindricity after forming can be arbitrarily determined according to the purpose of use (details are shown in Figure 3). A corner radius is provided so that the Next, the operation will be explained. A plate material 1 with a hole punched therein is placed on a die 7, a core metal 5 of a punch 4 is inserted into the hole, and then a surface pressing portion 6 of the punch 4 is pressed around the hole. In this way, the material flows, and the fractured surface 3 of the hole shrinks inward, approaching the inner diameter of the sheared surface 2, thereby improving the cylindricity of the hole. FIG. 3 shows the embodiment shown in FIG. 2 (D ₁ =29.8φ,
D ₂ = 19.17φ, D ₃ = 17φ, h ₁ = 5, h ₂ = 2.5), the relationship between the amount of surface press on the top surface of the plate material (H = 6) and the cylindricity of the hole is shown. In this case, if the top surface of the plate is compressed by about 0.43 mm, the cylindricity becomes 0 and a highly accurate hole can be obtained. If it is better for the fractured surface 3 to be slightly larger than the sheared surface 2 (for example, in the case of a hole for inserting a pin), select the amount of surface pressing to be 0.43 mm or less, and conversely, the lower part of the fractured surface 3 should be slightly smaller than the sheared surface 2. If it is better (for example, in the case of a hole into which a pin is press-fitted), the surface pressing amount is set to 0.43 mm or more to allow a part of the material to escape into the corner radius of the core bar 5. In this way, the amount of surface pressing may be appropriately selected depending on the intended use of the hole. Note that the relationship between the amount of surface stamping and cylindricity shown in Figure 3 varies depending on the material of the plate material, the processing specifications of the punched hole, the area of the surface stamping, the shape of the surface stamping part, etc., so it must be determined in advance during processing. It is necessary to keep it. In this embodiment, the diameter of the core metal 5 is set to be the same as the outer diameter of the hole punch, but the same effect can be obtained even if the core metal 5 is slightly larger or smaller. The corner radius at the tip of the core bar 5 may not be provided depending on the processing conditions (for example, when the positioning accuracy of the plate is good and a hole for inserting a pin is to be processed). Alternatively, the core metal 5 may be made longer, a hole may be bored on the die 7 side, and the tip of the core metal 5 may be inserted into the hole. In this way, since the core metal contacts the entire length of the hole, a hole having a smooth surface over the entire length can be obtained. In addition, if a V-shaped (or semicircular) protrusion is formed in the die 7 in a ring shape (concentric with the hole in the periphery of the hole in the plate material 1), when the plate material 1 is pressed by the surface pressing part 6, the fractured surface 3 This has the effect of promoting the flow of the material toward the core metal. Although the core metal 5 is provided on the punch 4 in this embodiment, it may also be provided on the die 7. Further, although the hole has been described as being round, the present invention can also be applied to machining a hole having a shape other than round, such as a long hole. As explained in detail above, according to the present invention, a core metal having the same dimensions and shape as the pilot hole is inserted into a pilot hole formed in a plate material by punching, and the core metal is inserted into the pilot hole. Since the surface pressing section having a machined surface substantially parallel to the surface of the plate material presses and compresses the peripheral part of the surface of the prepared hole only in the thickness direction of the plate material, the material is positively and effectively applied to the inner surface of the hole. This has the effect of improving the dimensional accuracy of the punched hole with a small amount of compression. As a result of this effect, it is possible to mass-produce holes with high accuracy by progressive machining using a normal press machine, and the tool life is several times longer than that of precision punching. The next effect is created.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing a hole made by conventional punching, Fig. 2 is an explanatory view showing an embodiment of the present invention, and Fig. 3 is a surface of the embodiment shown in Fig. 2. It is a figure which shows the relationship between the amount of presses and cylindricity. 1: Plate material, 2: Sheared surface of hole, 3: Fractured surface of hole, 5: Core bar.

Claims (1)

[Claims] 1. Insert a core metal having the same size and shape as the pilot hole into a prepared hole formed by punching in a plate material, and with the core metal inserted, pressurize the surface approximately parallel to the surface of the plate material. Pressurizing and compressing the surface peripheral part of the prepared hole only in the plate thickness direction with a surface pressing part having
A method for improving the precision of a punched hole, characterized by improving the dimensional precision of the pilot hole.