JP2775768B2 - How to create offset surface data - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial application field B Outline of the invention C Conventional technology (FIGS. 3 to 5) D Problems to be solved by the invention (FIG. 5) E Means for solving problems (FIG. 1) And FIG. 2) F action (FIGS. 1 and 2) G embodiment (FIGS. 1 and 2) H Effect of the invention A Industrial application field The present invention relates to a method for creating offset surface data, for example, CAD. (Computer aided design) or CAM (computer aided design)
It is suitable to be applied to the case of using a technique such as aided manufacturing) to create a mold for a product having a free-form surface.

B. Summary of the Invention The present invention relates to a method for creating offset surface data,
By setting the offset point based on the radius of curvature of the parting surface to be cut and the size of the tool, a highly accurate mold can be easily created.

C Prior Art For example, when designing the shape of an object having a free-form surface using a CAD method (geometric modeling), generally, a design consists of a plurality of points in a three-dimensional space through which a curved surface passes (this is called a node). Is designated, and a boundary curve network connecting the designated nodes is calculated by a desired vector function, thereby creating a curved surface represented by a so-called wire frame. Thus, a large number of framework spaces surrounded by boundary curves can be formed (this process is called a framework process).

The boundary curve network formed by such framework processing is
It itself represents the rough shape that the designer intends to design, and if the surface that can be expressed by a predetermined vector function can be interpolated using the boundary curves surrounding each framework space, the designer as a whole designed A free-form surface (which cannot be defined by a quadratic function) can be generated. Here, the curved surface formed in each frame space forms a basic element constituting the entire curved surface, and this is called a patch.

By the way, in order to give a more natural external shape to the generated free-form surface as a whole, a shared space is established between two frame spaces adjacent to each other with the shared boundary therebetween so as to satisfy the condition of continuation of the tangent plane at the shared boundary. A free-form surface creation method in which the control edge vector around the boundary is reset has been proposed (Japanese Patent Application No. 60-277448).

This free-form surface creation method is, for example, as shown in FIG. If such a method is applied to other shared boundaries COM2, COM3, and COM4, the patch will eventually end up. Can be smoothly connected to adjacent patches according to the condition of continuation of the tangential plane.

Where the vector function is used instead of the cubic Bezier equation Is Parameters u and v in the u and v directions,
Control points, expressed using shift operators E and F For the following equation 0 ≦ u ≦ 1 (4) 0 ≦ v ≦ 1 (5)

Further, the tangent plane means a plane formed by tangent vectors in the u direction and the v direction at each point of the shared boundary. For example, for each point on the shared boundary COM1 in FIG. When the tangent planes are the same, the condition of continuation of the tangent plane holds.

According to this method, it is possible to easily design an object shape in which the curved surface shape changes smoothly as a whole, which is actually difficult to design with the conventional design method, as the meaning of the design. There has been proposed an offset curved surface data creating method for creating a product having a shape intended by a designer by creating a mold based on the data of the object shape obtained as described above (Japanese Patent Application No. 63-107867).
issue).

In this method, as shown in FIG. 4, a direction vector representing the moving direction a of the mold specified by the operator is used. The normal vector on the designed free-form surface 1 Are sequentially detected at a predetermined interval, so that the outermost point spread most in the direction orthogonal to the moving direction a of the mold. Moving direction vector of mold through A ruled surface extending by a predetermined amount so as to cut the free-form surface 1 in a direction orthogonal to Forming the ruled surface The principle is that the molds 2 and 3 are cut so that becomes the parting surfaces of the molds 2 and 3 on the cavity side and the core side.

Therefore, using the method proposed in Japanese Patent Application No. 61-208551, Like the target weave surface And the position data representing the free-form surface 1, Offset surface data consisting of a surface translated in the normal direction by the amount of translation represented by And the center position of the milling machine tool (in this case, a ball end mill whose distance from the center position to the cutting edge is R) is the offset surface data. If it is controlled to move on a free-form surface represented by Is used as a parting surface, and cutting data of a die having the free-form surface 1 as an outer shape is obtained.

That is, in the mold 2 on the cavity side, the center position of the ball end mill is In the direction of movement a of the mold, The offset surface data translated in parallel by the movement amount represented by the following formula is generated, and the parting surface is cut based on the offset surface data.

Subsequently, offset curved surface data is generated for the free curved surface 1, and the ball end mill is moved based on the offset curved surface data to perform cutting.

On the other hand, in the mold 3 on the core side, contrary to the mold 2 on the cavity side, the center position of the ball end mill is
Ruled surface In the direction opposite to the mold moving direction a, The offset surface data translated in parallel by the movement amount represented by the following formula is generated, and the parting surface is cut based on the offset surface data, whereby the mold 2 on the cavity side is cut.
A parting surface having the same shape as the parting surface is formed in the mold 3 on the core side.

Subsequently, offset curved surface data is generated for the free-form surface 1 in the same manner as the mold 2 on the cavity side, whereby dies 2 and 3 having the outer shape of the free-form surface 1 are obtained.

Thus, on the parting surface, since the outer shape of the free-form surface 1 changes smoothly as a whole as intended by the designer, a curved surface that changes smoothly according to the change of the outer shape is formed. Thus, undercuts and the like can be prevented from occurring and a mold can be easily manufactured.

D Problems to be Solved by the Invention By the way, when the ball end mill is moved based on the offset curved surface data, the mold 2
In addition, there is a problem that a minute gap is formed on the parting surface of Nos. 3 and 3 and it becomes difficult to obtain a highly accurate mold.

That is, as shown in FIG. 5, when creating offset surface data, the ruled surface Dot on From the ball end mill radius R in the normal direction of the cavity side and the core side, respectively. (Hereinafter referred to as an offset point).

Offset surface Is the offset point obtained in this way. And offset point When cutting the mold 3 on the core side, the offset point on the cavity side When the center position of the ball end mill 6 is moved on a straight line L _C connecting the mold, while cutting the mold 2 on the cavity side, the offset point on the core side is required. The center position of the ball end mill 6 is moved on a straight line L _K connecting

Therefore, ruled surface In the mold 3 on the core side, the tip of the ball end mill 6 has a ruled surface. as well as Whereas the cutting by moving the core side of the upper straight line L _CP than a straight line connecting, in the mold 2 of the cavity side, cutting by moving the cavity side of the upper straight line L _KP than the straight line L _CP Become like

As a result, the core side and the cavity side in the die 2 and 3, is parting surface formed by a straight line L _CP and L _KP respectively formed, thereby the parting surface of the mold 2 and 3 of the straight line L _CP and L _KP A difference gap δ occurs.

Actually, in the case of a free-form surface designed by this kind of free-form surface creation method, it is possible to design an object shape in which a curved surface shape changes smoothly as a whole, which is difficult to actually design with a conventional design method. When a molded product having the outer shape of the free-form surface is obtained, the parting surface of the mold is also formed so as to smoothly change in accordance with the change in the outer shape.

Therefore, as shown in FIG. 5, it is inevitable that a parting surface which swells toward the cavity side or the core side is formed. There is a problem that a gap is generated on the parting surface of No. 3 and it is difficult to obtain a highly accurate mold.

Incidentally, if there is a gap between the molds 2 and 3, the resin enters the gap and burrs are generated, and the quality of the molded product is significantly deteriorated.

Therefore, in order to obtain a high-quality molded product, it is necessary to form a high-precision parting surface with a small gap, and in this case, it is necessary to perform secondary processing with a file or the like so as to eliminate the gap δ.

The present invention has been made in view of the above points, and it is an object of the present invention to propose an offset curved surface data creating method capable of easily creating a highly accurate mold.

E Means for Solving the Problems In order to solve such problems, in the present invention, a predetermined ruled surface To the normal by a predetermined amount R Multiple offset points translated in the direction In the offset curved surface data generating method for generating the data of the tool path for cutting of the dies 2 and 3 having the A plurality of offset points based on the radius of curvature r of the tool and the size R of the tool 6 for cutting the dies 2 and 3. The distance l between them is selected.

F action ruled surface Offset point based on the radius of curvature r of the tool and the size R of the tool 6 for cutting the dies 2 and 3. If the distance l between them is selected, the gap generated on the parting surface between the dies 2 and 3 can be reduced.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

In the case of this embodiment, the central processing unit (CPU) of the offset curved surface data generating device includes the data of the free curved surface (that is, the patch) created by the free curved surface creating device in advance. (Consisting of the data shown in Fig. 3) After generating (Fig. 4), the ruled surface The procedure for creating offset surface data is executed from step SP1 in FIG.

In other words, the offset surface data creating device is
In SP2, input data of an allowable gap value D (hereinafter, referred to as an allowable value) D between the molds 2 and 3 is received from a keyboard provided in a terminal of the offset curved surface data creating apparatus, and in a subsequent step SP3, The radius R of the cutting edge of the ball end mill used for cutting is input.

Subsequently, the offset surface data creating apparatus executes step SP
4 and the display device provided at the terminal of the offset curved surface data creation device And the free-form surface Along with the maximum and minimum values of the radius of curvature of the Is specified and input via the keyboard.

Subsequently, the offset surface data creating apparatus executes step SP
5 and based on the input tolerance D and the radius R of the ball end mill, Is obtained.

Actually, as shown in Fig. 2, the ruled surface Upper point At a point relative to the center of the radius of curvature r, assuming that the radius of curvature r between the two points is constant. If the angle between is 2θ, a straight line The gap δ between them is expressed by the following equation: δ = 2R (1−cos θ) (8)

Accordingly, in the equation (8), by changing the value δ to the value D, the equation (7) is obtained, whereby the equation (7) is obtained.
So that the angle θ satisfies the equation By setting the interval between the dies, cutting can be performed so that the gap δ between the dies 2 and 3 becomes the allowable value D specified and input by the operator.

Further, the offset curved surface data creating apparatus executes a calculation process of the following formula l = 2 rsin θ based on the angle θ to obtain a step length l, and obtains a step SP6.
And ends the processing procedure.

As a result, the offset surface data creating apparatus performs the following steps in the offset surface creating process. The ruled surface is set so that the interval between them becomes the step length l. To set the offset point Is set, and the data of the tool path of the ball end mill 6 is created.

Thus, in this embodiment, by setting the offset point using the equation (7) as an evaluation criterion, the mold 2 is adjusted so that the gap δ between the molds 2 and 3 becomes the allowable value D.
And 3 can be cut, whereby a highly accurate mold can be easily obtained.

In fact, it can be seen from equation (8) that the step length 1 can be reduced by using a ball end mill having a small radius R in order to reduce the gap δ between the dies 2 and 3.

In this case, if the step length 1 is shortened, the data of the tool path is maximized, whereas if the radius R of the ball end mill is reduced, the cutting surface of the mold is roughened by that amount, and a mold having a smooth cutting surface is obtained. Therefore, the data of the tool path becomes longer.

On the other hand, in this embodiment, the gap δ can be reduced in a practically sufficient range by setting the step length l to a value determined by the evaluation criterion, thereby increasing the length of the tool path data. It can be prevented beforehand.

Specifically, when machining a parting surface with a radius of curvature of 50 [mm] using a ball end mill with a radius of 1 [mm], if the allowable value D is set to 0.005 [mm], the angle θ is calculated from the equation (7). A value of 4.05226 degrees was obtained, which was (9)
It was found that the step length l should be set to 7.067 [mm] by substituting into the equation.

Thus, the parting surface was cut with the step length 1 set to 7 [mm], and a highly accurate mold having a gap of 0.005 [mm] or less could be obtained.

Incidentally, in this type of injection molding mold, if the gap δ between the molds 2 and 3 can be processed to a maximum of 20 [μm] or less, a molded product without burrs can be obtained. Thus, a highly accurate mold could be obtained.

According to the above configuration, the distance between the offset points is selected according to the radius of curvature of the parting surface to be cut and the size of the tool on the basis of the predetermined evaluation criterion, so that the gap between the parting surfaces can be set to a desired tolerance. Cutting can be performed to a value equal to or less than the value, so that a highly accurate mold can be easily formed.

In the above embodiment, the case where the distance between the offset points is selected according to the radius of curvature specified and input by the operator has been described. However, the present invention is not limited to this, and the specification input by the operator is omitted, The distance between the offset points may be selected according to the radius of curvature of the direct ruled surface.

Further, in the above-described embodiment, the case where the entire parting surface is cut by one step length l has been described. However, the present invention is not limited to this, and the step length l is partially switched as necessary. Is also good.

Further, in the above-described embodiment, the case of cutting the mold of the molded product having the external shape of the free-form surface represented by the cubic Bezier equation has been described. However, the present invention is represented by the cubic Bezier equation. Not limited to free-form surfaces, for example, Ferguson
The present invention can be widely applied to the case of cutting a mold of a molded product having a free-form surface represented by the formula (ason).

As described above, according to the present invention, the distance between the offset points is selected based on the radius of curvature of the parting surface to be cut and the size of the tool, so that the gap between the parting surfaces can be set to a desired allowable value. The processing can be carried out as follows, whereby an offset curved surface data creating method for easily creating a highly accurate mold can be obtained.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a procedure of an offset surface data creating method according to an embodiment of the present invention, FIG. 2 is a schematic diagram for explaining the operation, and FIG. 3 is a schematic line for explaining a free-form surface. FIG. 4 is a schematic diagram for explaining the generation of the parting surface, and FIG. 5 is a schematic diagram for explaining the problem. 1 ... Free-form surface, 2, 3 ... Mold, 6 ... Ball end mill,

Claims (1)

(57) [Claims] 1. A plurality of offset points translated in a normal direction by a predetermined amount with respect to a predetermined ruled surface, and the ruled surface is converted into a parting surface based on the coordinate data of the plurality of offset points. An offset curve data creating method for generating data of a tool path for cutting of a mold comprising: a radius of curvature of the ruled surface and a size of a tool for cutting the mold. A method for creating offset surface data, wherein a distance between the plurality of offset points is selected.