JP2000024813A - Casting hole machining method, core pin used for this method, and casting to be object of this method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of machining a hole machined in a casting. SOLUTION: In this casting hole machining method, a cored hole 10h with a protruding part 10t at the center is formed using a core pin provided with a cavity part in the axial direction, and a cutting tool 4 is fed in the depth direction of the cored hole 10h to cut the protruding part 10t with the tip of the cutting tool 4. The internal wall surface of the cored hole 10h is cut in a state of holding the centering accuracy of the cutting tool 4 by starting to cut the protruding part 10t. The cutting tool 4 does not therefore follow the cored hole 10h, so that eccentricity is not generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a hole in a thick portion of a casting in which a cavity is likely to occur, a casting pin used in the method, and a casting to which the method is applied.

[0002]

2. Description of the Related Art When a molten metal injected into a mold changes from a liquid to a solid, the molten metal shrinks and its volume decreases.
For this reason, if there is no supply of the molten metal to compensate for the shrinkage, a cavity (a sinkhole) is generated in the casting. In particular, since the thick portion of the casting solidifies more slowly than the other portions, the molten metal tends to be insufficiently replenished at the time of solidification shrinkage and sink cavities tend to occur.
For this reason, as shown in FIG. 4, when the hole W is machined in the thick portion 1t of the casting 1 with the drill 4 or the like, a recess is formed in the inner wall surface Wn of the hole W due to the burrow H or the like, and the machining is defective. It may be.

[0003] In order to prevent such processing defects caused by the burrows H, a method of forming a cast hole in a casting using a cast pin has been used, as disclosed in JP-A-64-53752. By using the casting pin, the molten metal around the cast hole is cooled and solidification is accelerated, and unsolidified molten metal is supplied from the surroundings during solidification shrinkage of the molten metal,
This is because shrinkage nests H are less likely to occur. However, the positional accuracy and the shape accuracy of the cast hole formed by the cast pin are lower than the positional accuracy and the shape accuracy of the machined hole formed by the drill or the like. For this reason, usually after forming a cast hole,
A method of finishing the cast hole with a drill or the like is employed.

[0004]

However, there are the following problems when the cast hole is finished with a drill or the like. For example, as shown in FIG. 5, when the center C of the cast hole 1h of the casting 1 is deviated from the center S of the drill 4, the cut hole 1h is positioned at the tip of the drill 4 during cutting. Therefore, the drill 4 may not be able to maintain the centering accuracy, and the drill 4 may be misaligned. As a result, the center of the machined hole is the cast hole 1h.
And the accuracy of the machined hole is reduced.

[0005] Therefore, the invention according to claims 1, 2 and 3 of the present invention is intended to maintain the centering accuracy of a drilled hole when finishing the hole with a drill or the like. It is an object of the present invention to improve the accuracy of a machined hole.

[0006]

The above-mentioned problems are solved by a method for boring a casting having the following features, a cast pin used in the method, and a casting to which the method is applied. That is, in the method of forming a hole in a casting according to claim 1, a molding hole having a convex portion in the center is formed using a molding pin having a cavity in an axial direction, and a cutting tool is formed by using the molding hole. Cutting in the depth direction of the cutting tool at the tip of the cutting tool, and cutting the inner wall surface of the cast hole while maintaining the centering accuracy of the cutting tool by starting the cutting of the protrusion. I do.

For this reason, even if a force is applied to the cutting tool so as to follow the casting hole due to a positional shift between the casting hole and the cutting tool, the cutting tool cuts the convex portion of the casting hole. Since the centering accuracy of the cutting tool can be maintained by starting the cutting, the cutting tool is not misaligned following the cast hole. Therefore, a machining hole can be formed at the position of the cutting tool regardless of the position of the cast hole, and the accuracy of the machining hole can be improved.

[0008] The cast pin according to the second aspect is the first aspect.
An outer pin and an inner pin housed inside the outer pin with a clearance through which gas can pass without passing the molten metal, It has a cavity formed by the tip of the inner peripheral surface of the outer cylinder pin and the tip of the inner pin. According to the present invention, the invention of claim 1 can be carried out.
In addition, since gas accumulated at the position of the cavity during casting can be exhausted to the outside from between the outer cylinder and the internal pin, it is difficult for gas to accumulate in the cavity and the convexity of the cast hole caused by the gas is reduced. Shape defects and the like can be prevented.

A casting according to a third aspect of the present invention is a casting to be subjected to the casting hole drilling method according to the first aspect of the present invention. A corresponding convex portion is formed. Claim 1 according to the present invention
Can be implemented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for boring a casting according to one embodiment of the present invention will be described below with reference to FIGS. The method for drilling a casting according to the present embodiment relates to a method for drilling a hole in a thick part of a die-cast product, and FIG. 1 is a cross-sectional view showing the hole drilling method, and FIG. (A) and plan view (B)
FIG. 3 and FIG. 3 are longitudinal sectional views of the main parts of the die casting mold and the cast pin.

The die casting mold 20 (hereinafter referred to as the mold 20)
3), as shown in FIG. 3, includes a movable mold 22 and a fixed mold 24, and a cavity 25 which is a product molding portion is formed inside the mold 20 in a state where the mold 20 is clamped. . In addition, a cast pin 27 for forming a cast hole 10h is attached to a main portion of a cavity 25 for forming the thick portion 12 of the die cast product 10 (see FIGS. 1 and 2).

The cast pin 27 is a cylindrical outer cylinder pin 2.
7w and a cylindrical inner pin 27z housed in the outer cylinder pin 27w, and a clearance is provided between the outer cylinder pin 27w and the inner pin 27z so that the gas can pass without passing the molten metal. ing. The outer cylinder pin 27w has a tip portion serving as a product forming portion for forming the cast hole 10h, and is tapered so that the outer periphery 27k of the product forming portion is tapered. Further, a taper is provided on the inner periphery 27j of the product forming portion so that the tip is expanded. Further, the thickness of the product forming portion is set to a thickness capable of sufficiently cooling the molten metal around the cast hole 10h.

The inner pin 27z is connected to the outer cylinder pin 27.
w into the inside by the depth of the casting hole 10h from the tip surface 27f of the w, and the center of the tip of the casting pin 27 by the inner periphery 27j of the product forming portion of the outer cylinder pin 27w and the tip surface 27s of the inner pin 27z. Is formed with a hollow portion 27x.
That is, the hollow portion 27x forms a substantially cylindrical convex portion 10t having a flat tip end surface in the center of the cast hole 10h.

Next, a method of forming a die-cast product using the above-described mold 20 will be described. First, as shown in FIG. 3, the mold 20 is clamped, and molten metal is supplied into the cavity 25 of the mold 20 from an injection unit (not shown). At this time, the gas in the cavity 25 is exhausted from an exhaust passage (not shown) to the outside. Further, the gas accumulated in the hollow portion 27x of the cast pin 27 is also discharged outside through the space between the outer cylinder pin 27w and the inner pin 27z.

When the molten metal filled in the cavity 25 solidifies in this way, the mold is opened and the die cast product 10 is taken out of the mold 20. In addition, the cast pin 2
7 is provided with a taper so that the outer circumference 27k is tapered and the inner circumference 27j is expanded at the tip, so that the cast pin 2 from the die-cast product 10 is formed.
7 can be easily pulled out. As shown in FIGS. 2A and 2B, the die-cast product 10 has a cylindrical thick portion 1.
2 in the center of the thick portion 12
7 form a cast hole 10h. Further, a hollow portion 27x of the cast pin 27 is located at the center of the cast hole 10h.
A substantially cylindrical projection 10 having a flat top end surface (top end surface)
t is formed.

Here, the gas accumulated in the hollow portion 27x of the blanking pin 27 during casting is transferred to the outer pin 27w and the inner pin 27w.
Since the gas passes through the gap z and is discharged to the outside, it is possible to prevent molding defects and the like of the projection 10t due to the gas. In addition, of the molten metal that fills the cavity 25, the molten metal that forms the periphery of the casting hole 10h is cooled by the casting pin 27, so that solidification is accelerated. For this reason, when the molten metal around the cast hole 10h solidifies and contracts, unsolidified molten metal is supplied from the surroundings, and it becomes difficult to generate sinkholes and the like.

When the die-cast product 10 is molded in this way, as shown in FIG.
The cast hole 10h of 0 is finished by the drill 4. FIG. 1A shows a state of the finishing process in a state where the center C of the cast hole 10h and the center S of the drill 4 coincide with each other, and FIG. The state of the finishing process in a state where the center S of the drill 4 is shifted by the dimension L is shown. In addition, the two-dot chain line in the figure represents the portion that the drill 4 cuts. As shown in FIG. 1, when the drill 4 is fed in the axial direction with respect to the cast hole 10h, the tip of the drill 4 contacts the convex portion 10t of the cast hole 10h and cuts the convex portion 10t.

The tip of the drill 4 has a cast hole 10h.
Of the drill 4 by starting the cutting of the projection 10t of
Centering accuracy is maintained. In this way, drill 4
Finishing of the cast hole 10h is performed in a state where the centering accuracy is maintained. Therefore, as shown in FIG. 1B, the center C of the cast hole 10h and the center S of the drill 4 are formed.
Even if the drill 4 is misaligned and a force is applied to the drill 4 so as to follow the cast hole 10h, the drill 4
There is no misalignment following 0h. Therefore, the processing hole W can be formed at the position of the drill 4 irrespective of the position of the cast hole 10h, and the accuracy of the processing hole W can be improved.

As described above, according to the present embodiment, by providing the projection 10t at the center of the cast hole 10h, the drill 4 is provided.
Therefore, the accuracy of the processing hole W can be improved without significantly increasing the equipment cost. In the present embodiment, the method for improving the accuracy when processing a deep hole is described. However, the accuracy can be similarly improved when forming a through hole. Further, in the present embodiment, an example in which a cast hole is formed in a die-cast product has been described. However, the present invention is not particularly limited to a die-cast product as long as it is a casting.

[0020]

According to the present invention, since the centering accuracy of the cutting tool is maintained by the cutting tool starting cutting the convex portion of the cast hole, the cutting tool can be used regardless of the position of the cast hole. A processing hole can be formed at a position, and the accuracy of the processing hole can be improved.

[0021]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a method for boring a casting according to an embodiment of the present invention. FIG. 1A shows a state in which the center of a cast hole matches the center of a drill, and FIG. This shows a state where the center of the hole and the center of the drill are shifted.

FIG. 2 is a longitudinal sectional view of a main part of a die-cast product used in a method for drilling a casting according to one embodiment of the present invention (FIG. A).
FIG. 3 is a plan view of a main part (FIG. B).

FIG. 3 is a longitudinal sectional view of a main part of a die casting mold used in a method for boring a casting according to one embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a conventional method for boring a casting.

FIG. 5 is a cross-sectional view illustrating a conventional method for boring a casting.

[Explanation of symbols]

 Reference Signs List 4 Drill (cutting tool) 10 Die-cast product 10h Cast-out hole 10t Convex part 12 Thick part 27 Cast-out pin 27w Outer cylinder pin 27z Internal pin 27x Hollow part

Claims (3)

[Claims] 1. A casting hole having a convex portion at the center is formed by using a casting pin having a hollow portion in an axial direction, and a cutting tool is fed in a depth direction of the casting hole to cut the cutting tool. A method of drilling a casting in which the inner wall surface of a cast hole is cut while maintaining the centering accuracy of the cutting tool by cutting the protrusion at the tip of the cutting tool and starting cutting of the protrusion. 2. An extruded pin used in the method for drilling a casting according to claim 1, wherein the pin is provided inside the outer cylinder pin with a clearance through which a gas can pass without passing a molten metal. And a cavity formed by the inner peripheral end of the outer cylinder pin and the inner pin end surface. 3. A casting to which the method for drilling a casting according to claim 1 is applied, wherein a convex portion to which the tip of the cutting tool first strikes is formed in the center of the cast hole. casting.