JP2805871B2 - Free curved surface processing method - Google Patents

Description

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

A Field of application in industry B Outline of the invention C Conventional technology (Fig. 13) D Problems to be solved by the invention (Fig. 14) E Means for solving the problems (Figs. 1 and 6) F action (FIGS. 1 and 6) G embodiment (G1) First embodiment (FIGS. 1 to 4) (G2) Second embodiment (FIGS. 5 to 11) (G3) Other Embodiments (FIG. 12) Effect of the Invention A Industrial Field of the Invention The present invention relates to a tool path determination method, for example, a CAD (compu
ter aided design), CAM (computer aided manufactur)
ing) and the like, and is suitable for producing a product die having a free-form surface shape.

SUMMARY OF THE INVENTION In the tool path determination method, the present invention creates feed rate data indicating a feed rate of a cutting tool based on path feature information obtained from temporary path data, and uses the temporary path data and the feed rate data. By determining the tool path of the cutting tool, a free-form surface can be machined on the object under optimum cutting conditions.

C Prior Art For example, when designing the shape of an object having a free-form surface using a CAD method (geometric modeling), a designer generally uses a plurality of points in a three-dimensional space through which the surface passes (this is called a node). Is specified, and a boundary curve network connecting the specified nodes is calculated by a desired vector function, thereby creating a curved surface represented by a so-called wire frame. A framework space is 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. There has been proposed a free-form surface creation method in which control edge vectors around a boundary are reset (Japanese Patent Application No. 60-277448).

For example, as shown in FIG. 13, this free-form surface creation method uses a cubic Bezier equation of a patch spanned in a quadrilateral frame space. Represented by two patches Nodes are given by the framework processing to connect Based on adjacent patches Control edge vector such that the condition of tangent plane continuity is satisfied at the shared boundary COM1 of Are set, and the internal control points are set by these control edge vectors. The principle is to set again.

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 a cubic Bezier equation Is Is expressed using parameters u and v in the u and v directions, shift operators E and F, and the control point 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 sharing boundary. For example, for each point on the sharing 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 even an object shape, which is actually difficult to design with the conventional design method, such that the curved surface shape changes smoothly as a whole as intended by the designer. A free-form surface machining method has been proposed which can create 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). .

D Problems to be Solved by the Invention By the way, conventionally, such a mold of a product having a free-form surface shape is required to be manufactured, for example, by simultaneously forming a mold as shown in FIG.
Using an NC (numerical control) milling machine 1 of an axis control system, a die 3 as a workpiece mounted on an XY table 2 is Z-rotated through a tool control unit 4 including a motor.
A tool 5 such as a pole end mill, which can be moved in the axial direction, is brought into contact with the XY table 2 and the tool 5 based on the tool path data generated by the segment height method or the like from the free-form surface data. By controlling the movement in the directions of the axis, the Y axis, and the Z axis, a mold having a free-form surface is cut.

However, in such an NC milling machine 1, cutting is performed by controlling the height of the tool 5 while cutting conditions such as a cutting speed and a feed speed are constant. Therefore, especially when machining a free-form surface, the tool 5
The length and direction of the cutting allowance portion (this is called extra thickness) that the tool 5 hits when the tool 5 moves in the X direction or the Y direction at a predetermined speed because the tool 5 always moves up or down in the Z-axis direction. Since the load of the tool 5 fluctuates due to the change of the shape, the roughness of the surface to be cut of the mold 3 fluctuates, and as a result, there is a problem that it is unavoidable that fringes are formed on the processing surface.

The present invention has been made in view of the above points, and proposes a free-form surface machining method capable of machining a higher-quality free-form surface by stabilizing a load variation when a tool is raised or lowered. It is assumed that.

Means for Solving Problem E In order to solve such a problem, the present invention provides a method of forming curved surface In the tool path determination method for determining a tool path for driving the cutting tool 21 for cutting the object to be cut 22 into a curved shape based on the curved surface shape data And, based on the tool information of the cutting tool 21, the tentative path data DT _BM of the cutting tool 21 is generated, and based on the tentative path data DT _BM , path feature information representing the feature of the moving path of the cutting tool 21
tanθ _i , K _i , and L _MAX are calculated, and the route feature information tan θ _i , K _i ,
Based on L _MAX , feed speed data F representing the optimum machining speed of the cutting tool 21 is created, and the route represented by the temporary route data DT _{BM is} moved by the feed speed represented by the feed speed data F. The tool path data for driving the cutting tool 21 is determined.

F action Route feature information tanθ _i , K _i , obtained from the temporary route data
By creating the feed speed data F indicating the feed speed of the cutting tool 21 based on L _MAX , by determining the tool path data of the cutting tool 21 using the temporary path data DT _BM and the feed rate data F, Cutting can be performed under optimal cutting conditions so as not to generate processing stripes based on fluctuations in the load on the cutting tool 21, and as a result, a high-quality processed surface can be easily realized.

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

(G1) First Embodiment The free-form surface machining method of the embodiment shown in FIGS. 1 to 4 predicts a tool movement angle based on free-form surface data representing a free-form surface to be machined, and moves the tool. By controlling the feed rate of the tool according to the change in the angle, the load applied to the tool is prevented from fluctuating.

In the case of this free-form surface machining method, the central processing unit (CPU) of the tool path data creation device uses the free-form surface data (that is, patch) created by the free-form surface creation device in advance. (Consisting of the data of FIG. 13), and executing the tool path data generation processing program in step SP1 of FIG. Based on the above, the procedure for creating the tool path data _DTBM is started.

That is, the CPU sets the free-form surface data in step SP2. Based on the tool information such as the blade shape and radius of the tool 5 (FIG. 14) used for cutting, as shown in FIG. 2, for example, the tool path is used as the temporary path data using the segment height method. The data DT _BM (in FIG. 2, the case where the Y-axis component is set to 0) is created.

Subsequently, in step SP3, the CPU sets any segment SG _i (i) on the tool path data DT _BM as tool prediction information.
= On the basis of the movement angle θ _i of the tool 5 at 0, 1, 2, ...), As described above, calculates the movement prediction information tan .theta _i consisting in X-axis direction and the Z-axis direction ratio of the moving length [Delta] X _i and [Delta] Z _i of each segment SG _i of.

Here, X _i and Z _i are the X-axis direction and Z-axis direction position data of the start point of the segment SG _{i in} the tool path data DT _BM ,
, And X _{i + 1} and Z _{i + 1} indicate the X-axis and Z-axis position data of the start point of the following segment SG _{i + 1} .

Thus the CPU, characterized in i th segment SG _i of tool path data DT _BM, grasped as the movement angle theta _i.

Subsequently, CPU in the next step SP4, the value of the movement prediction information tan .theta _i calculated in equation (6) determines whether positive or not, moves to the positive time step SP5.

In this step SP5, the CPU determines the conversion table TBL shown in FIG. 3A based on the movement angle θ _i (represented by the movement prediction information tan θ _i ) when the tool 5 rises.
Reads the feed rate coefficient K _i from _GUPX, with reference to FIG. 3 (B) to the feed speed setting value table TBL _GUP showing, the feed speed setting value F, the reference quantity the reference feed speed f [mm / min] F = K _i · f (7) is obtained by multiplying by the feed rate coefficient K _i , which is fetched into the internal register, and then proceeds to step SP7.

If a negative result is obtained in step SP4 described above with respect to this, CPU proceeds connexion to step SP6, on the basis of the movement angle theta _i of when the tool 5 is lowered, the conversion table TBL _GDNX shown in FIG. 4 (A) The feed speed coefficient _Ki is read out from the table, and the feed speed set value F is obtained by referring to the feed speed set value table TBL _GDN shown in FIG. 4 (B).

Here, in practice, the data of the conversion tables TBL _GUPX (FIG. 3 (A)) and TBL _GDNX (FIG. 4 (A)) can be input by the operator based on his / her own knowledge.

Subsequently, CPU in step SP7, after creating a new tool path data DT _BMX feed speed setting value F set in the internal register with the modification to the tool path data DT _BM at step SP5 or SP6, the following In step SP8, it is determined whether the creation of the tool path data has been completed.

If the CPU obtains a negative result in step SP8,
Proceeding to step SP3 above, steps SP4-SP5 (or S
P6) repeated -SP7 process loop, thereby gradually take corrective operation on all segments SG _i of tool path data DT _BM.

When the CPU gets a positive result in step SP8,
Moving to the next step SP9, the tool path data generation processing program ends.

Thus the CPU by supplying new tool path data DT _BMX which have been conducted under the generated tool path data generation processing program into the NC milling machine 1 (Figure 14) controls the driving the tool 5.

As described above, in the case of the free-form surface processing method of this embodiment, the free-form surface data previously created by the free-form surface creation device is used. Together to create a tool path data DT _BM, movement prediction information features in each segment of the tool path data DT _BM grasped based on the moving angle theta _i of the tool 5 tan .theta based on
_i is calculated and the new tool path data DT _BMX is created based on the feed speed set value F corresponding to the predicted movement information θ _i , so that the movement angle θ _i of the tool 5 of the NC milling machine 1 is reduced. By controlling the feed rate F of the tool 5, it is possible to prevent a load variation that may occur on the tool 5 when it changes from occurring, thereby preventing a processing stripe from being generated on a processing surface.

In the case of the tool path data creation device of this embodiment, the tool 5
The feed speed setting value table TBL _GUP or TBL _GDN created in the internal database so as to correspond to the moving angle θ _i when the ascending or descending causes, for example, a built-in table updating program (not shown) to be executed. It is possible to update the value to an arbitrary value by this. Based on the empirical knowledge information of the operator, the data can be updated according to the material of the mold 3 to be machined by the NC milling machine 1 and the rough machining shape. It may create an optimal tool path data DT _BM to the individual processing operations by updating.

In the case of tool path data generation apparatus of this embodiment, the feed speed setting value table TBL _GUP or TBL _GDN, to the extent movement prediction information tan .theta _i calculated is optional, feed speed setting value F
Thus, the interval of the variable control of the feed speed f of the tool 5 can be optimally controlled with a predetermined redundancy. Here, the corresponding range of the speed setpoint and the feed movement prediction information tan .theta _i also are adapted to be updated based on empirical knowledge information of the operator.

According to the above method, the feed speed data F of the tool is calculated according to the tool movement angle θ _i calculated from the tool path data.
While creating in addition the feed speed data F to the tool path data DT _BM create a new tool path data DT _BMX, the mold 3 as object to be cut by using the new tool path data DT _BMX By cutting into a free-form surface shape, a free-form surface can be machined under optimum cutting conditions so that the load of the tool 5 is not fluctuated as much as possible.
A free-form surface processing method that can further improve the quality of the processed surface can be realized by preventing the processing stripe from being generated on the processed surface due to the variation in load.

(G2) Second Embodiment The free-curve machining method according to the second embodiment predicts a maximum cutting depth as a feature of tool path data created based on free-form surface data representing a free-form surface to be machined. The load applied to the tool is controlled to an appropriate value by controlling the feed speed of the tool according to the maximum cutting depth of the tool.

That is, as shown in FIG. 5, a tool 21 which is, for example, a ball end mill having a radius r is fed in the X-Z plane in the X-axis direction so that a die as a workpiece 22 is formed into a target shape. When cutting to the target shape, Assuming that there is a surplus 23 with a cutting allowance δ uniformly on the surface of the tool 21, when considering the conditions for cutting this with the tool 21, the tool 21 removes the surplus 23 of the workpiece 22 with the cutting depth L. It will behave like cutting.

By the way, when the tool 21 is When cutting is performed for each segment consisting of free-form surface data, the height of the wall which is in front of the tool 21 is predicted while the tool cuts the excess portion 23 of the one segment, and according to the prediction result, If the feed rate of tool 21 is controlled by
The fluctuation of the load applied to 21 can be suppressed.

In the free-form surface machining method in the second embodiment, a free-form surface is machined by executing a tool path data generation processing program as shown in FIG. 6 based on such a method.

In this case as well, the central processing unit (CPU) of the tool data creation device stores the free-form surface data (that is, the patch) previously created by the free-form surface creation device. (Consisting of the data shown in FIG. 13) and entering the tool path data generation processing program from step SP21 in FIG. 6, and then patching in step SP22. The tool path data _DTBM is created as temporary path data based on the free-form surface data.

Subsequently, in the next step SP23, as shown in FIG. 7, the CPU 21 moves the tool 21 from the current position P ₁ (X _P , Z _P ) out of the tool path WAY (indicating the movement path of the tip of the tool 21). By moving in the positive direction along the X-axis by the distance r + δ and moving in the Z-axis direction by the height λ, the segment end position P ₃ (X _PX , Z
_PX ) to obtain the maximum height λ of the tool path WAY.

Here, considering the height at which the tool 21 hits the excess thickness 23 to be cut while the tool 21 moves from the current position P ₁ (X _P , Z _P ) to the final position P ₃ (X _PX , Z _PX ) of the segment. , Tools during this time
As the 21 cutting operation modes, three modes as shown in FIG. 8 can be considered.

The first cutting operation mode is as shown in FIG.
Target shape If There forming a horizontal plane, it becomes in this case the height Z _P of the current tool position P _1, the segment end position _{P 3 (X PX, Z PX} ) to the height Z _PX and mutually equal of, In this case, the tool 21 moves in the horizontal direction (that is, in the X-axis direction) as shown by the arrow a, and during that time, the tool 21 maintains the state of the cutting depth L corresponding to the cutting allowance δ, and To cut.

In addition, in the case of FIG. Form an inclined plane, in which case the heights Z _P and Z _{PX of the} current tool position P ₁ and the segment end position P ₃
Are different from each other, and the tool 21 has the target shape as shown by the arrow b. Segment end position from the current tool position P ₁ along the
The movement that rises linearly up to P _3.

Therefore, the cutting depth L of the tool 21 with respect to the excess 23 The cutting depth L of the tool 21 is larger than the cutting allowance δ of the surplus 23 by cutting in an oblique direction with respect to the surplus 23 having a cutting allowance δ in a direction perpendicular to the direction of the cutting.

In the case of FIG. 8 (C), the target shape In the case where There has been formed a step portion that rises abruptly to the Z axis direction with respect to the tool 21, the height position Z _P and Z _PX in this case the current tool position P ₁ and the segment end position P ₃ are differences And the desired shape Tool 21 so that it has a steep slope
Moves rapidly in the height direction in the direction along the steep slope having the steep gradient as shown by the arrow c.

Most its thickness with respect accordance connexion tool 21 is the excess thickness 23 having a tool 21 allowance sharpener in a direction orthogonal to the sharp slope δ until moving from the current tool position P ₁ in the segment end position P ₃ Large cutting depth L that crosses diagonally in the horizontal direction
Cost cutting from the state (at the current tool position P ₁ near) [delta]
Tool 21 until the smaller cutting depth extent (in the vicinity of the segment end position P ₃₎ is that the tool 21 is moved in an operation mode that varies in length which corresponds to excessive deposition 23.

By the way, in various tool movement modes as shown in FIGS. 8 (A) to 8 (C), the movement mode in which the length of the tool 21 hitting the surplus 23 is the longest is the case of FIG. 8 (C).
In this case, it is understood that the amount of cutting that the tool 21 must cut increases, and the load applied to the tool 21 increases accordingly.

By the way, in practice, when the load of the tool 21 suddenly increases, it is necessary to lower the feed speed of the tool 21 in order to maintain the roughness of the machined surface when the load is small and almost the same, so that the feed speed is always constant. It can be seen that the tool 21 should be fed at a feed rate commensurate with the maximum cutting depth L _MAX of the tool 21 for one segment in order to maintain the roughness of the processed surface at high quality.

Based on this principle, the CPU proceeds to step SP23 (6th
In FIG.), If there is a difference in the height Z _P and Z _PX between the tool 21 moves from the current tool position P ₁ to the segment end position P _3, as shown in FIG. 9, the tool 21 Has moved from the current tool position P ₁ horizontally by a distance r + δ,
That is, the intermediate position P immediately below the segment end position P _{3
2 Find} the maximum height Z _PX before moving to (X _PX , Z _P ).

Here, the way of moving the tool 21 is as shown in FIG.
After the tool 21 is moved horizontally in the X-axis direction from the current tool position P ₁ to the intermediate position P _2, staircase as rises in the Z-axis direction until the the intermediate position P ₂ in the segment end position P ₃ in the vertical direction Assuming that the tool path WAY moves, the CPU calculates the maximum depth of cut L _MAX in the following step SP24 according to the following equation: L _MAX = δ + (Z _PX −Z _P ) (8)

As can be seen from FIG. 7, the second term Z _PX -Z _P in the equation (8) is Z _PX -Z _P = λ... (9) from the current tool position P ₁ to the segment end position P _3.
Equal to the maximum height λ that can be taken when the tool is moved up, as slave connexion (8) is shown in Figure 10, the tool 21 is the current tool position _{P 1 (X P, Z P} ) intermediate from Position P ₂ (X _PX , Z _P )
Is reached, the tool 21 represents the height of the portion corresponding to the maximum height λ and the excess thickness 23 on this portion. Accordingly, the load applied to the tool 21 is the maximum in this state, and the load applied to the tool 21 does not exceed the maximum cutting depth L _{MAX with} respect to the excess thickness 23. It will not be larger than the value at L _MAX .

Therefore CPU subsequently by the said uppermost importance Komifuka of L _MAX at the step SP25 in connexion 11 feed speed conversion table shown in FIG.
Using the TBL _FSP , the feed rate F that is the optimum processing condition is determined.

Thereafter, the CPU regenerates new tool path data including the feed rate F in step SP26 and proceeds to step SP27 to determine whether or not the tool path data generation processing has been completed.

If a negative result is obtained in step SP27, this means that the segment to be processed remains, and at this time, the CPU returns to step SP23 and repeats the same processing for the subsequent segment.

On the other hand, if a positive result is obtained in step SP27, Means that the cutting for all the segments has been completed, and at this time, the CPU terminates the tool path data generation processing program in step SP28.

According to the above configuration, when the tool 21 performs cutting processing for each segment, the height of the wall in front of the tool is predicted from the free-form surface data as the maximum cutting depth L _MAX , and based on the prediction result. By controlling the feed rate of the tool 21, the feed rate of the tool 21 can be changed accordingly when the load on the tool 21 fluctuates, so that if there is a change in the roughness of the processing surface in practical use, It is possible to maintain a sufficient quality without causing processing fringes.

(G3) Other Embodiments (1) In the second embodiment, the conversion table as described above with reference to FIG. 11 is used to obtain the optimum machining feed rate F corresponding to the maximum cutting depth L _MAX . But
Instead, Alternatively, a proportional distribution may be made as shown in FIG.

As shown in FIG. 12, in equation (10), L _LIM is the limit value of the maximum cutting depth L _MAX that can be taken by the tool (for example, the length of the end mill blade), and F _MAX and F _MIN are the minimum. Indicates the optimum machining feed rate F when the important depth L _MAX is “0” and the limit value L _MIN. The optimum machining feed rate F expressed by the equation (10) is the maximum cutting depth L _MAX. machining optimum feed rate F when the change means that in one point K _F on conversion line K.

Even in this case, as in the case described above, if the height of the surplus 23 that hits the tool 21 increases, the feed speed of the tool can be reduced accordingly, so that the fluctuation of the load on the tool 21 is made uniform. obtain.

(2) In the first embodiment, tool feed speed data is created in accordance with the tool movement angle calculated from the tool route data, and the tool route data is corrected based on the tool feed speed data to obtain a new tool feed speed data. In addition to the above, a case was described in which the tool path data was created, but in addition to this, the cutting speed of the tool, that is, the rotation speed data of the tool was created according to the moving angle of the tool, and correction was performed based on the rotation speed data. New tool path data obtained may be obtained.

In this way, it is possible to realize a free-form surface machining method capable of machining a free-form surface under more suitable cutting conditions.

(3) In the above-described embodiment, the case where the die of the product having the external shape of the free-form surface represented by the cubic Bezier equation is cut, but the present invention is not limited to this. The present invention can be widely applied to the case of cutting a metal mold of a product having a free-form surface represented by the Fergason formula.

(4) In the above embodiment, the present invention is applied to the case of cutting a die, but the present invention is not limited to this, and can be widely applied to the case of directly cutting a product.

H Effects of the Invention As described above, according to the present invention, feed speed data indicating a feed speed of a cutting tool is created based on route feature information obtained from temporary route data, and the temporary route data and the feed speed data are used. By determining the tool path data of the cutting tool, it is possible to perform cutting under optimal cutting conditions so as not to generate processing stripes due to fluctuations in the load on the cutting tool, and as a result, a high-quality machining surface can be obtained. It can be easily realized.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure of an embodiment of a free-form surface machining method according to the present invention, FIG. 2 is a curve diagram for explaining tool path data, and FIGS. FIG. 5 is a diagram showing a conversion table for a feed speed set value at the time of performing, FIG. 5 is a schematic diagram for explaining a speed control method in the second embodiment, and FIG. 6 is a tool path data generation processing program in the second embodiment. 7 to 11 are schematic diagrams and charts for explaining each processing step in FIG. 6, and FIG. 12 is a curve diagram showing a method of setting an optimum machining feed rate in another embodiment. ,
FIG. 13 is a schematic diagram for explaining free-form surface data, and FIG. 14 is a front view showing an NC milling machine that is controlled based on the free-form surface data. 1 ... NC milling machine, 3 ... Mold, 5 ... Tool, DT _BM …… Tool path data, TBL _GUP , TBL _GND , TBL _FSP ……
Feed speed conversion table.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G05B 19/4093 G05B 19/416

Claims (4)

(57) [Claims] 1. A tool path determining method for determining a tool path for driving a cutting tool that cuts an object to be cut into the curved surface shape based on curved surface shape data indicating the shape of the curved surface. Generating temporary path data of the cutting tool based on the tool information of the cutting tool; calculating path characteristic information representing a feature of a moving path of the cutting tool based on the temporary path data; Based on the above, feed speed data representing the optimum machining speed of the cutting tool is created, and the path represented by the temporary path data is moved by the feed speed represented by the feed speed data to the cutting tool. Determining the tool path data for driving the tool path. 2. The method according to claim 1, wherein the path characteristic information includes moving angle information of the cutting tool, and the feed speed data is created based on the moving angle information. . 3. The path characteristic information includes moving angle information of the cutting tool, and based on the moving angle information, creates the feed speed data indicating a feed speed of the cutting tool, and includes the moving speed information in the moving angle information. Creating tool cutting speed data representing the rotation speed of the cutting tool based on the cutting speed data, and determining the tool path data for driving the cutting tool based on the tool cutting speed data together with the feed speed data. The method for determining a tool path according to claim 1, wherein: 4. The path characteristic information according to claim 1, wherein the path characteristic information includes maximum cutting depth information of the cutting tool, and the feed speed data is created based on the maximum cutting depth information. Tool path determination method.