JPH048204B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead screw mold.

It is known that a lead screw is used to move the head, but in the known lead screw, the side wall of the spiral groove is rectangular with the side wall falling vertically from the outer circumferential surface. With such a groove shape, when the lead screw is viewed from the front, a portion of the bottom of the groove is hidden by the outer edge of the groove, creating a so-called undercut portion. Therefore, until now, such lead screws could not be formed by plastic molding and had to be formed by cutting. Forming a spiral groove by cutting requires advanced processing technology and long processing time, resulting in high processing costs.

An object of the present invention is to provide a mold for molding a lead screw by plastic molding, and furthermore, it is possible to easily align the screw-shaped protrusions of this mold so that they are smoothly continuous. The purpose is to provide a mold.

Therefore, let us consider the helical groove 2 of the known lead screw 1 as shown in FIG. This groove 2
As shown in the second figure, the cross-sectional shape is rectangular, that is, the side wall thereof is vertically depressed with respect to the outer circumferential surface. For this reason, a portion 5 is created in which the inner edge (bottom edge) 4 is hidden by the outer edge 3 of the groove 2. This portion 5 is a so-called undercut, and due to the existence of this hidden portion 5, it has not been possible to manufacture such a lead screw 1 by plastic molding until now.

Now, if the rotation angle of the lead screw 1 is β, then the x-coordinate of the edge of the groove 2 is x=P/360β...(1) The shift P is expressed by the pitch of the groove 2.

Groove 2 when looking at lead screw 1 from the front
The y-coordinate of outer edge 3 is expressed as y=R COSβ=R COS360/Px...(2), and the y-coordinate of inner edge 4 is expressed as y=r COSβ=r COS360/Px...(3) . Here, R and r are the radii of the lead screw 1 and the bottom of the groove 2, respectively.

When the dividing angle (center angle) of the mold (90 degrees in the example shown in Figure 4) is θ, the dividing end face (θ/
2 position) and the bottom of groove 2, the distance from the x-axis of the common point y ₁
Let Xa and Xb be the x-coordinates of the outer edge 3 and inner edge 4 at the respective positions, then Xa - Xb is the undercut amount (hidden amount of the bottom of the groove 2) at that height position. Xa-Xb is expressed by the following equation, assuming that rotation angles βa and βb are rotation angles from the y-axis around the center axis of the lead screw 1.

Xa−Xb=P/360(βa−βb) …(4) On the other hand, βa and βb are βa=COS ⁻¹ y ₁ /R=COS ⁻¹ r sinθ/2/R …(5) βb=COS ⁻¹ y ₁ /r = COS ^-1 r sinθ/2/r = COS ^-1 sinθ/2 ... (6) Therefore, substituting equations (5) and (6) into equation (4) Accordingly, xa−xb=P/360{COS ^-1 r sinθ/2/R −COS ^-1 Sinθ/2} ...(7).

Therefore, in view of the above relationship (7), the lead screw 6 has a groove 7 as shown in FIG. Groove 7 has an L bottom
The shape is narrower and the side walls are slanted and depressed. The narrowing L at the bottom of the groove 7 is L≧P/360 {COS ^-1 r sinθ/2/R-COS ^-1 sinθ
/2} ...(8) is set to satisfy the following relationship. If L, P, R, r, and θ are determined to satisfy formula (8), then
Since no undercuts occur, it can be manufactured by plastic molding. In FIG. 3, 8 is a screw piece that fits into the groove 7 and is sent to the right or left by the rotation of the lead screw 6.

On the other hand, the shape of the groove 7 of the lead screw is preferably such that it does not apply much vertical force to the screw piece 8, and for this purpose, it is preferable that the side wall has a small inclination angle. Therefore, in order to be able to mold with a mold and at the same time reduce the inclination angle of the side wall, the number of divisions of the mold may be increased or the pitch P of the grooves 7 may be made smaller. However, since increasing the number of divisions complicates the mold structure, it is preferable to set the pitch P of the grooves 7 appropriately.

Furthermore, some lead screws use grooves for both forward and backward movement of the carrier, and the pitch of the grooves on the return path is increased to increase the return speed. In this case, the shape of the groove must satisfy the above formula (8) on the return path where the pitch is larger.

Therefore, as an embodiment of the present invention, FIG. 4 shows an example in which the mold is divided into four parts, and the cavity of the lead screw is constructed by four divided molds 9a, 9b, 9c, and 9d with the dividing angle θ=90 degrees. It shows. 5 to 8 show the inner surfaces of each of the split molds 9a to 9d developed and enlarged from line A. Each split type 9a~
At one end of the inner circumferential surface of the mold 9d, reference protrusions 10a to 10d for positioning the divided molds are provided so as to be continuous in a circumferential manner when the four molds are closed. Outward protrusions 11a to 11d for forming outward screw grooves of the lead screw are provided on the inner circumferential surface at positions that continue in a screw shape when the four molds are closed. Furthermore, return protrusions 12a to 12d are provided to intersect with the protrusions 11a to 11d and to form screw grooves for the return route of the lead screw at positions that continue in a screw shape when the four molds are closed. . In this example, the diameter of the lead screw to be molded is 2R = 15 mm, and the pitch of the return groove is P.
= 25.4mm/rev, and the pitch relationship of the reciprocating grooves is 1:3. For this reason, the intersection points of the reciprocating grooves are lined up on four straight lines that are out of phase by 90 degrees on the circumference, so the intersection points of the protrusions 11a to 11d and 12a to 12d are on the inner peripheral surface of each split mold. They will line up in the center. Furthermore, since the protrusions 11a to 11d and 12a to 12d in this example have narrowed widths at their tips corresponding to the grooves that satisfy the above formula (8), the narrowed width L can be adjusted as shown in FIG. The inclination angle α of the side surface of the protrusion is α=25.9 degrees. Also, protrusion 11
The pitch is changed so that it continues smoothly from both ends of the protrusions a to 11d to both ends of the protrusions 12a to 12d. Dovetail-shaped connecting protrusions 13a to 13d are provided on the outer peripheral surface of each of the divided molds 9a to 9d as shown in the fourth figure.
is formed.

The divided molds 9a to 9d formed in this way are the fourth
As shown in the figure, the connection is made by sliding the connection protrusions 13a to 13d into the respective connection grooves 14a or 15a of the fixed platen 14 or the movable platen 15 from one side. Each split type has a standard protrusion 10a.
By fixing the protrusions 11a to 11d and 12a to 12 at positions where the protrusions 11a to 10d are aligned on the circumference,
d is a continuous screw-like position. Move the movable platen 15 forward to separate the divided molds 9a as shown in the fourth figure.
-9d are joined together, synthetic resin is injected into the cavity, and after solidifying, the movable platen 15... is moved back to separate the split molds 9b-9d, and the molded lead screw is taken out.

As described above, according to the present invention, since the reference protrusion is provided on the mold, it is extremely easy to align each split mold to a position where the screw-shaped protrusion continues smoothly, and the lead screw Since it can be molded from synthetic resin, advanced processing technology is not required to manufacture lead screws, processing time can be shortened, mass production is possible, and not only can lead screws of stable high quality be provided, but processing costs can also be reduced. can be lowered.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the conventional groove shape, FIG. 2 is a cross-sectional view of the groove, FIG. 3 is a cross-sectional view showing an example of the groove shape of a lead screw formed according to the present invention, and FIG. 4 is a cross-sectional view of the groove according to the present invention. 5 to 8 are enlarged internal circumferential views of each split type developed along line A in FIG. 4,
FIG. 9 is an enlarged sectional view of the protrusion. 9a, 9b, 9c, 9d...divided type, 10a,
10b, 10c, 10d...Reference protrusion, 11a,
11b, 11c, 11d, 12a, 12b, 12
c, 12d...projection.

Claims (1)

[Claims] 1. On the inner peripheral surface of the cylindrical cavity, L≧P/360 {Cos ^-1 r/RSinθ/2-Cos ^-1 Sinθ/
2) P: Pitch of the groove R: Radius of the shaft r: Radius of the bottom of the groove θ: Dividing angle of the mold L: Protrusion for forming a screw groove that satisfies the formula for narrowing the bottom of the groove A mold for a lead screw, characterized in that: a reference protrusion is provided circumferentially at one end of the inner circumferential surface of the cavity, and the mold is divided into n parts.