JPH0765896B2 - How to measure the sphericity of a ball end mill - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring the sphericity of a tool used for a machine tool, particularly a ball end mill.

2. Description of the Related Art Direct measurement of the sphericity of the tip spherical edge of a ball end mill is extremely difficult in the field, and it is the actual situation that it is hardly measured other than that measured in a measuring room. The sphericity of throw-away type ball end mills is very poor, and an error of 0.1 mm or more is generally considered. However, until now, there has been no particular problem in relation to the accuracy of machines that use ball end mills such as copying machines and NC machines.

Problems to be Solved by the Invention In recent years, NC machines have become more sophisticated so that curved surfaces can be machined with high accuracy, and tool accuracy directly affects machining accuracy. It has become an important issue.

The present invention has been made in view of such a demand, and the object thereof is to easily measure the sphericity accuracy, and also to measure the mounting error in a state where the sphericity is mounted on the machine, and to easily perform tool correction. It is intended to provide a sphericity measuring method for a ball end mill that can be used.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention is a measuring element supported so as to be displaceable at right angles to the spherical blade portion of a ball end mill mounted on a spindle and an axial direction of a measuring instrument in a fixed position. Position the ball end mill at the measurement position such that the measurement disk mounted at the center of the tip and the outer circumference of the measurement disk contact each other with their axes orthogonal to each other, and coordinate of the spherical blade center at the measurement position. And the distance (R) between the center of the spherical blade and the center of the measurement disk in the non-contact state, which is obtained from the coordinates of the center of the measurement disk in the non-contact state, and the displacement of the measurement disk detected by the measuring instrument at the time of contact. The tool radius (γ) of the ball end mill at the contact point between the ball end mill and the measurement disc is calculated from ε and the previously determined radius γ ′ of the measurement disc, and this calculation is performed at each point on the surface of the ball end mill. I'll do it in It is a roar. And it is preferable to make contact while rotating the ball end mill.

Action NC The spherical edge of the ball end mill mounted on the spindle to be positioned is brought into contact with the outer circumference of the measuring disk centered on the axis with known coordinate values orthogonal to the ball end mill to displace the measuring disk and displace it. The tool radius at the contact point is calculated from the amount, the positioning coordinates of the center of the spherical edge of the ball end mill, and the coordinates of the center of the measurement disk. By rotating the ball end mill, the radius of the protruding cutting edge portion involved in cutting is measured.

Example Hereinafter, description will be given with reference to FIGS. 1 to 3. For example, in the well-known machining center 1, up and down on the column 2 (Z axis)
A ball end mill 6 is mounted on a spindle that is vertically mounted on a cross rail 3 that is positioned in the vertical direction, and a spindle head 4 that is moved and positioned in the horizontal (Y) axis direction. A measuring instrument 7 is horizontally mounted inside the side surface of the column 2.

The measuring instrument 7 uses, for example, a one-dimensional tracer head, and the probe 71 is axially inserted into the instrument body 70, and the bearing spherical surface 72 provided on the probe 71 is moved to a spherical seat 73 in the instrument body 70 so as to allow a clearance. Not supported. In this probe 71, a measuring disk 74 having a high circularity and a radius of γ ′ is fixed at the projecting tip at a right angle to the axis, a conical hole 71a is cut at the opposite end, and four springs 75 at right angles make the probe 71 It is held in a neutral state. A detector 76 is axially supported by the body 70 so as to be slidable in the axial direction coaxially with the probe 71, one end of which is formed on a spherical surface 77 and the other end of which is provided on the body 70. A core 79 located at the center of the coil portion 78 of the transformer is attached. And detector
The spherical surface 77 of 76 is always in close contact with the conical hole 71a by the spring 80. The object is achieved if the measuring disc 74 has a range of at least 90 °. The measuring instrument 7 may be a two-dimensional tracer head.

The cross rail 3 is controlled in the Z axis and the spindle head 4 is controlled in the Y axis, and the tip spherical blade portion 6a of the ball end mill 6 comes into contact with the measuring disk 74 of the measuring instrument 7 to be displaced, that is, the spherical blade center O ₁ is positioned at coordinates y, z. In FIG. 1, it is assumed that the center coordinates of the measuring disk 74 of the probe 71 before contact with the ball end mill 6 are known as y ′ and z ′. The contact point P is the center O of the measuring disc 74 and the center of the spherical cutting tool 6a of the ball end mill.
It is located on the line connecting O ₁ . By the contact of the ball end mill 6, the measuring disc 74 is displaced on the line OO ₁ and its center moves to O ′. When the angle between the axis of the ball end mill 6 and O ₁ O is θ, the spherical blade 6a at the angle position of θ
The radius γ of y is y = y′−R sinθ z = z ′ + R Cosθ where R is the length of OO ₁ . When the y position of the end mill 6 is larger than the y'position, y = y '+ RSinθ.

Since the center O ₁ of the spherical blade portion 6a of the ball end mill 6 is positioned at y, z with respect to the measurement disk center O at the coordinates y ', z', the two sides y of the right-angled triangle OO ₁ Q. ′ −y, z−
Since z'and θ are known, OO ₁ = R can be calculated in the NC unit. Then, the center O of the measuring disc 74 is displaced to O ′ in the OO ₁ direction by the contact of the end mill 6,
This displacement amount is converted into movement of the detector 76 in the axial direction, and the core 76 is moved.
The displacement amount ε is detected by the differential transformer formed by the coil 78. Based on this value of ε, the contact point P of the spherical blade 6a
The radius γ at can be obtained by γ = R + ε−γ ′. It should be noted that in the case where the measuring instrument 7 is a two-dimensional tracer head that detects the displacement in each of the Y-axis and Z-axis directions. Can be sought by.

Needless to say, it is necessary to measure the sphericity at a portion related to cutting, but if the position cannot be accurately indexed, rotate the end mill 6 (in this case, do not cut). Reverse rotation is preferable.) The maximum ε value may be used as the displacement amount.

Further, the Y-axis and Z-axis positioning positions of the end mill 6 are changed to know the values of the radius γ for various θ.

In this embodiment, the ball end mill 6 is moved, but the measuring instrument 7 can be moved and positioned freely. Moreover, it is possible to freely move and position the other party.

Effects With the above-described configuration, the present invention has the following effects.

According to the measuring method of the first aspect, the radius tolerance and the sphericity of the spherical blade of the ball end mill can be easily measured, so that the tool accuracy can be improved and the machining accuracy can be remarkably improved.

By equipping this machine with a tracer head that detects the displacement of the measuring disc, the sphericity of the spherical blade during machining can be measured, including equipment errors, and the measured values at each θ can be stored as tool correction values. By correcting the three-dimensional tool, the processing accuracy of the three-dimensional curved surface is improved and automation becomes possible.

The measuring method of claim 2 is convenient when the measuring position cannot be accurately determined, and the radius of the most protruding point involved in cutting is measured.

[Brief description of drawings]

FIG. 1 is an explanatory view of a contact state between a ball end mill and a measurement disk, FIG. 2 is an explanatory view of a one-dimensional tracer head, and FIG. 3 is an explanatory view in which a tracer head is attached to a machining center. 5 …… Spindle, 6 …… Ball end mill 7 …… Measuring instrument, 71 …… Measuring element 74 …… Measuring disk, 76 …… Sensor 78 …… Coil, 79 …… Core

Claims (2)

[Claims] 1. In an NC machine tool, a measurement mounted at the tip of a contact point which is supported so as to be displaceable at right angles to the axial direction of a spherical blade portion of a ball end mill mounted on a spindle and a measuring instrument at a fixed position. The ball end mill is positioned at the measurement position so that the disc and the disc are in contact with each other on the outer circumference of the measurement disc in a state where their axes are orthogonal to each other, and the measurement disc in the non-contact state with the coordinates of the spherical blade center at the measurement position. The distance (R) between the center of the spherical blade portion and the center of the measurement disc in the non-contact state, which is obtained from the coordinates of the center, and the displacement ε of the measurement disc detected by the measuring instrument at the time of contact, are obtained in advance. The tool radius (γ) of the ball end mill at the contact point between the ball end mill and the measurement disc is calculated from the radius γ ′ of the measurement disc, and this calculation is performed at each point on the surface of the ball end mill. Characterizing Sphericity measuring method Lumpur end mill. 2. The method for measuring the sphericity of a ball end mill according to claim 1, wherein the spherical blade portion is brought into contact with the measuring disk while rotating the ball end mill.