JPH02180515A - Plastic working drill - Google Patents

Abstract

PURPOSE:To enhance fatigue strength by forming both a taper surface by which a compressive load is applied to the rear end side of a boring drill to produce residual stresses and a flange part by which the circumference of a hole is flatly compression-formed, so that residual compressive stresses can be induced on the near-side periphery of the drilled hole CONSTITUTION:On the rear end of the oil hole boring drill part 8 of a plastic working drill 7, a taper surface 10 whose diameter is gradually enlarged toward the rear is formed, so that after drilling the oil hole, it is pressed against the circumference of the hole to cause cold plastic deformation corresponding to the load, and to induce residual compressive stresses. And a flange part 11 is also formed at the rear end of the taper surface 10, by which the excess thickness around the oil hole enlarged further greater than the maximum diameter, fluidized and bulged out by the cold plastic deformation due to the taper surface 10 is forcibly pressed down to assist the residual of stresses.

Description

[Detailed Description of the Invention] [Industrial Field of Application] This invention relates to a drilling drill for drilling various mechanical parts, and in particular, it applies plastic working to the hole at the same time as drilling to leave a compressive stress on the drilled part. This invention relates to plasticized nitrile that aims to improve the fatigue strength of.

[Prior art and problems to be solved by the invention] A mold is filled with a fiber-reinforced metal material, and after pouring molten metal into the mold, high pressure is applied to the mold to pour the molten metal into the fiber-reinforced metal material. Forming machine elements such as rocker arms using a high-pressure casting method (molten metal #i production method) that permeates and composes mechanical elements has the advantage of being able to form lightweight, high-strength machine elements. Fatigue cracks may also occur in oil holes, such as in rocker arms.

In other words, since the oil hole has a small diameter (approximately 28 mm) and the boss part for forming this oil hole is partially thicker than other parts, stress concentrates on the oil hole that has been drilled. This is because fatigue cracks are more likely to occur.

[Means for Solving the Problems] The present invention aims to solve the above-mentioned problems by applying a compressive load to the rear end of a drilling drill on the @ side after drilling so that compressive stress remains on the rear end side. The plasticized nitrile is formed by forming a tapered surface, and forming a flange portion on the rear end of the tapered surface to flatten compression mold around the oil hole.

[Operation] After the plasticized nitrile drills an oil hole with a dark blue diameter using the drill part at the tip, the tapered surface formed at the rear end of this drill part is further advanced toward the drilling side, and is compressed into the oil hole on the outer surface of the bearing part. Apply a load to cause cold plastic deformation. As a result, compressive stress remains in the oil hole on the outer surface of the bearing. The flange formed at the rear end of the tapered surface forcibly suppresses the portion that tends to flow and bulge toward the outer surface of the bearing during cold plastic deformation, and Keep the oil hole flat. In other words, the flange part allows the metal structure to flow in the diameter reduction direction of the tapered surface, and
The crystal grains are flattened to increase grain boundary density and promote residual stress on the outer surface of the bearing.

Therefore, by repeatedly performing cold plastic working of the oil hole formed by such plasticized nitrile,
The fatigue strength of the oil hole is further improved.

[Embodiment] A preferred embodiment of the present invention will be described below based on the accompanying drawings.

1 shown in Fig. 2 is a method in which a mold is filled with a fiber-reinforced metal material, molten metal is poured into the mold, and high pressure is applied to the mold to infiltrate the molten metal into the fiber-reinforced metal material. This is a lightweight, high-strength rocker arm formed using a composite high-pressure casting method (molten metal forging method).

In the embodiment, the rocker arm 1 has an intake or exhaust valve (
(not shown), and an adjustment screw (not shown) extending to the opposite side of this arm 2.
The force side arm 3 drives the force side arm 2 in the valve opening direction via the force point side arm 3, and these arms 2.3 are connected in the middle thereof, and are rotatably supported on a rocker arm shaft (not shown). It consists of a bearing part 4.

Now, in order to supply lubricating oil to the bearing surface 5 of the bearing part 4,
A radial oil hole 6 that penetrates from the outer surface of the bearing part 4 to the bearing surface 5 is formed in the bearing part 4 located at the lower part of the force side arm 3 by drilling.

In this embodiment, the oil hole 6 is formed by plasticized nitrile 7 having a special shape as shown in FIGS. 1 and 2.

As shown in the figure, the plasticized nitrile 7 is placed behind the drill part 8 for drilling the oil hole, and the diameter of the plasticized nitrile 7 is sequentially expanded rearward from the drill part 8, so that after drilling the oil hole 6, the plasticized nitrile 7 is placed on the outer surface side of the bearing part 4.
The oil hole 6 is cold-plastically deformed according to the load (compressive load) when pressed, and the outer surface fl1 of the bearing part 4 of the oil hole 6 is
A tapered surface 10 is formed at the rear end of the tapered surface 10 to retain compressive stress, and the outer surface of the bearing portion 4 is expanded further in diameter than the maximum diameter of the tapered surface 10 by cold plastic deformation of the tapered surface 10. The side 9 is forced to hold down the excess material around the oil 6 which is fluidized and tries to ooze out, and the bearing part 4 is
This is accomplished by forming a flange portion 11 that promotes residual stress on the outer surface side 9 of. 12 is a shank.

Therefore, the oil hole 6 formed by such plasticized nitrile 7 forms a countersunk part 13 on the outer surface IFI9 of the bearing part 5, as shown in FIG. Although there is no difference, there is an example in which the oil hole 6 is repeatedly subjected to cold plastic working using the drill 7 (dotted line) and an example in which cold plastic working is not performed (solid line) using the same materials and processing conditions. As shown in FIG. 3, which shows the test data for (2), by repeatedly performing cold plastic working, the fatigue strength of the oil hole 6 is greatly improved (about 15%). However, the material of the rocker arm is reinforced fiber metal, and the pressure of the tapered surface is test data with a load of approximately 30+r, a rotation speed of plasticized nitrile of approximately 500rl)11, and a repetition rate of plastic working of approximately 10. .

In other words, in terms of metal structure, as shown in FIGS. 4 and 5, the metal structure is fluid in the diameter reduction direction of the tapered surface 10.
(Fig. 5), the crystal grains are also flattened and the grain boundary density becomes high (Fig. 5).

Therefore, there is no need to increase the thickness of the boss portion 14 forming the oil hole 6 to improve the fatigue strength of the oil hole 6.

[Effects of the Invention] As is clear from the above explanation, the present invention exhibits the following excellent effects.

At the rear end of the drilling drill, form a tapered surface that applies a compressive load to the rear end of the hole and then leaves compressive stress at 11tlFI, and compression molds the area around the oil hole flat on the T & end of this tapered surface. Since the flange part was molded to form plasticized nitrile, compressive stress remained on the front side of the hole,
It is possible to improve the fatigue strength of drilling.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing a preferred embodiment of the present invention, Fig. 2 is a partial sectional view showing a rocker arm as an example of a drilling target, and Fig. 3 shows fatigue caused by repeated plastic working with plastic nitrile. A performance diagram showing changes in strength, FIG. 4 is a schematic diagram showing metal flow due to plastic working, and FIG. 5 is a schematic diagram showing changes in crystal grains due to plastic working. In the figure, 1 is a rocker arm, 6 is an oil hole, 7 is plasticized nitrile, 8 is a drill part, 10 is a tapered surface, and 11 is a flange part. Patent Applicant: Isuzo Jidosha Co., Ltd. Representative Patent Attorney Nobuo Kinutani 1st Figure 2

Claims (1)

[Claims] 1. At the rear end of the drilling drill, form a tapered surface that applies a compressive load to the rear end of the hole and leaves compressive stress on the rear end, and flatten the area around the oil hole at the rear end of the tapered surface. A plastic working drill characterized by a molded flange part for compression molding.