JPS6161924B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for machining a three-dimensional curved surface using a multi-axis controlled NC milling machine having three or more axes. When machining curved surfaces with a multi-axis control NC milling machine, especially a three-axis control NC milling machine, a cutter such as a radius end mill or a ball end mill is usually used. In these milling machines, the workpiece position is sequence-controlled or numerically controlled in the X and Y directions, and the cutter position is copy-controlled or numerically controlled in the Z-axis direction, or the workpiece is fixed.
There are tools in which the tool position is controlled on three axes, and
In addition to the three axes XYZ that can be controlled simultaneously, only two axes (XY, YZ, or XZ) can be controlled simultaneously, but the remaining one axis can also be controlled in a non-simultaneous sequence control or tracing control separately from the above two axes. , and or NC
There are things that are controlled. These multi-axis mills usually do not have a tool shift function, and machining in each block is usually linear interpolation or circular interpolation. In addition, the curved surface to be machined is usually given as several cross-sectional figures, but each cross-section is not necessarily parallel;
They are often inclined to each other, and it is required to create a curved surface that connects them smoothly. Further, machining is usually divided into several steps of rough machining and one step of finishing. Therefore, problems in this type of curved surface machining are the machining method such as copy machining or numerical control, and the selection of tools, and machining errors due to uncut parts in the cutting direction of the curved surface and the pick feed direction of the tool, etc. It is. In addition, in the case of numerical control (NC control), consideration should be given to the time required for program creation and machining, and the difficulty and time required for manual work such as removing cutter marks and inspecting the shape after machining. Therefore, the conventional method of creating a program for an NC device is to first select a ball end mill, etc. with an appropriate diameter for the machining process, taking into account the shape of the workpiece to be machined, the required accuracy, the material quality, etc. , determine the machining method, that is, the starting point of the cutter path, the cutting direction, and the pick feed direction, and further calculate the pick feed amount and cutting length per block so that the machining is performed within the given tolerances in the cutting direction and pick feed direction. By inputting these along with other initial set data into an appropriate computer, the data necessary for processing to create a smooth curved surface and perform fairing processing is obtained, and finally punched out as an NC tape. . Now, if the cutter radius of a radius end mill, ball end mill, etc. is r, the radius of curvature of the workpiece in the cutting direction is R, the pick feed amount is P, and the cutting length per block is S, then the cutter radius and The height V of the uncut peak caused by the pick feed and the error U when processing a curved surface approximately by interpolating the linear feed are expressed by the following equations. V=P ² /8·r ...(1) U=S ² /8·R ...(2) Therefore, equation (1) shows the problem of this milling process. That is, the value of U in equation (2) is 0.03~
It is easy to make it 0.05mm or less,
Furthermore, even if the value of U is made smaller, the number of tape blocks in the NC tape increases and the length of the NC tape becomes longer, but the cutter path does not become longer, so there is no particular problem, but (1)
Regarding V in the formula, the permissible value is normally 0.1 to 0.4 mm, and if you try to reduce V to less than this, you will have to reduce the pick feed amount, which will only increase the number of tape blocks in the NC tape. Since the cutting path itself is lengthened dramatically, the time required for machining is also lengthened proportionally. Therefore, problems arise in that the tool is used for a long time, its life is shortened due to wear, and a good machined surface cannot be obtained. In other words, even if the pick feed is made smaller and the cutter path is lengthened, if the machining depth of the machined surface to be created is sufficiently deeper than the radius of the cutter diameter, heavy cutting must be performed on the entire front surface in the cutting direction. Some parts still exist, and while this part requires considerable heavy cutting, in other cutting parts the pick feed decreases and the depth of cut in the pick feed direction becomes too small. This makes rational selection of tools difficult and leads to redundant working time. Also, in order to reduce this V, it seems best to use a cutter with the largest possible diameter, but
When using a large-diameter cutter, the above-mentioned problems become even more serious, and in addition, the tool rotational speed is restricted as the cutter diameter increases, and the amount of material that can be machined near the chisel point is relatively reduced. This will shorten tool life. In addition, not only does cutting resistance increase during machining, but the curved surface to be machined is essentially machined only with the chisel edge, which has an extremely slow cutting speed, making it impossible to obtain a good machined surface. occurs. The present invention has been made based on the above-mentioned viewpoint, and uses a radius end mill or a ball end mill as a cutter, and uses a multi-axis control NC milling machine to form a three-dimensional curved surface on a workpiece that is sufficiently deeper than the radius of the end mill. In curved surface machining that creates
A rough cutting process in which the desired curved surface is machined with a coarse cutter pass, with a value P ₀ within a range of less than 100%, and a cutter that is the same or different from this rough cutting process, without considering uncut areas, The desired curved surface is obtained by setting the pick feed amount as P ₀ , which is the same as the pick feed amount in the rough cutting process, and setting a positive integer N ₁ , and shifting the cut pass in the rough cutting process by P ₀ /N ₁ in the pick feed direction. Continue processing,
In the first finishing step for removing uncut parts, the same or different cutter is used for this rough cutting step or the first finishing step, and the pick feed amount is the same as the above P ₀ ,
Then, a positive integer N ₂ is determined, and the desired curved surface machining is continued using a cutter pass that is shifted by P/N ₁ N ₂ in the pick feed direction with respect to the cutter pass in the rough cutting process or the first finishing process, and uncut parts are further removed. Furthermore, if necessary, positive integers N ₃ , N ₄ , etc. are sequentially determined, and in particular, when all of these positive integers N ₁ , N ₂ , N ₃ , N ₄ , etc. are 2, The curved surface is processed by a series of finishing steps that are sequentially continued in the same manner as described above. By this curved surface machining, if the machining depth of the machined curved surface to be created is sufficiently deeper than the radius of the cutter diameter, the time required for machining can be significantly shortened, and furthermore, during a series of machining, fluctuations in machining load can be avoided. As a result, the most suitable tool for each process can be selected for the machining purpose, and the machining can be performed under the optimal cutting conditions for the material and tool from beginning to end, resulting in a good machined surface. Ta. Hereinafter, the method of the present invention will be explained in detail with reference to the drawings in comparison with a conventional processing method. FIG. 1 is a perspective view showing an example of a conventional processing method;
FIG. 2 is an XY plan view showing another example, and FIG. 3 is a diagram illustrating the steps of the method of the present invention. In the following explanation, in order to simplify the drawings and explanation, the workpiece is fixed, the tool is controlled in three axes, the tool rotation is parallel to the Z axis, and the cross section to be machined is The shape is given for the XZ cross section and the YZ cross section, and furthermore, the tool position is controlled simultaneously in the X and Z directions, cutting is performed in the It is assumed that a constant amount P ₀ is applied in the axial direction. Furthermore, although machining is normally performed in several steps, including rough machining and a final finishing process, the following explanation assumes that the machining is performed all at once. However, these limitations
It will be clear from the following description that the essence of the invention is not altered in any way.
Therefore, W in Fig. 1 is the workpiece being processed,
Curves Czx and Cyz indicate the cross-sectional shape to be machined, t ₀ , t ₁ , t ₂ , t ₃ and t ₄ are the cutter centers on the plane X=0, and t ₃ and t ₄ are the cutter centers.
This is the profile of a ball end mill, which is a cutter corresponding to t ₃ and t ₄ . Therefore, one cutting surface parallel to the XZ plane,
For example, on the plane Y=0, cutting is performed by linear interpolation or circular interpolation between the tool height Z and the feed in the X-axis direction in order to create a curve along the curve Czx, and on the plane X=0 , the envelope of the ball end mill profile is the curve Cyz
Control is performed to match the . Therefore, in the X-axis direction and the Y-axis direction,
Although uncut parts U and V occur, the problem here is the uncut part V in the Y-axis direction. This uncut portion V is given by the above-mentioned equation (1). For example, the relationship between the uncut V and the pick feed P when machining with a ball end mill with a radius of 10 mm is as shown in the following table.

[Table] Therefore, in order to reduce the value of this uncut V, it is necessary to use a cutter with a large r or to reduce the pick feed P, but in either case there is a problem. be. In other words, when using a thick cutter (ball end mill) with a large r, it may be difficult to process small corner radiuses, etc., but the biggest problem is that with thick cutters, the number of revolutions of the cutter is usually inversely proportional to the cutter diameter. need to be lowered. However,
Although it depends on the inclination angle of the machined surface, the machined surface is often machined mainly with the cutting edge near the center of the cutter, that is, near the chisel point. In any case, as shown in Figures 1 and 2, when the depth of the curved surface machined using the conventional method is sufficiently deeper than the radius of the cutter diameter, the cutting speed is extremely slow, resulting in good cutting. The surface is cut by the chisel edge of the cutter, which is not the blade, but the thicker the cutter, the lower the rotation speed, so it is difficult to obtain a good machined surface, and the cutting continues near the chisen point. The lifespan of the katsuta itself is also shortened. Further, if the pick feed P is made smaller, the cutter path is lengthened, and on the other hand, it is difficult to increase the cutting speed, so the time required for machining ends up being extended. In addition, when the cutter path is, for example, shown by abcd...mnop in Fig. 2, in the sections abc, fgh, klm, etc., the cutting part covers the entire surface of the cutter in the direction of movement of the cutter, resulting in heavy cutting. On the other hand, in other sections, the depth of cut in that direction becomes shallower as the pick feed is made smaller, so the cutting resistance becomes lighter. Therefore, even though the machining load fluctuates greatly, it is not desirable to cut these workpieces W with a single cutter at the same rotation speed and the same feed rate. . The method of the present invention will be explained below with reference to FIG. 3 and 3 are explanatory diagrams (YZ sectional views) showing the rough cutting step, which is the first step in the processing method of the present invention, and the subsequent first finishing step and second finishing step, respectively. FIG. 3 is an XY plan view showing a cutlet path. In each step constituting the processing method of the present invention, processing is performed using a pick feed P ₀ selected within a range of at least twice the radius of the tip of the ball end mill of the cutter used. That is, in the rough cutting method, cutting is performed along _the cutter path P ₁ shown as a thin line in FIG. Finishing is performed using the indicated P ₃ and the two-dot chain line P ⁴ as cutting passes. In these cutter passes, the pick feed amount is all the same value P ₀ , and P ₂ is at a position shifted by P ₀ /2 in the Y-axis direction with respect to P ₁ , and P ₃ and P 4 are different from P ₁ or P ₄ . It is located at a position shifted by P ₀ /4 from P ₂ in the Y-axis direction. Then, if necessary, a similar finishing process is performed using a cutter pass that passes between P ₁ and P ₃ , between P ₂ and P ₃ , etc., and where the pick feed amount is P ₀ . The following description assumes that the processing is completed at the stages shown. Therefore, in Fig. 3, W is the workpiece, T' ₁ , T' ₂ ,
T′ ₃ and T′ ₄ are ball end mills, and Cyz is a curve showing the _YZ cross-sectional shape of the curved surface to be created. Upon completion, at first glance, the same curved surface can be obtained as when processing using the conventional method with a pick feed amount of P ₀ /4. However, when using the processing method of the present invention,
It becomes possible to significantly shorten the processing time, and moreover, it is possible to obtain a better finished surface than before. The reason for this will be explained below. In addition, in order to carry out the processing method of the present invention most effectively, it is necessary to set the pick feed amount P ₀ to 80% of the cutter diameter.
It is recommended to select within the range of ~90%, so in the following explanation, P ₀ is 80 to 90% of the cutter diameter 2r.
shall be. If you increase the amount of pick feed like this,
During the rough cutting process, which is the first step, heavy cutting is performed on the workpiece on almost the entire surface of the cutter in the cutting direction, but this load is at the same level as the heaviest cutting load in the conventional method. Moreover, since it is constant during the rough cutting process, the cutting conditions such as the number of rotations of the cutter, the depth of cut, and the cutting speed can be made the same as or more severe than those of the conventional method. In other words, this process does not include light cutting, and only heavy cutting is performed from start to finish, so tools and cutting conditions can be selected that suit only the specific purpose, and the tool Regarding the shape, etc., there is no need to take much consideration to the shape, height, etc. of the uncut mountain. The total length of the cutter pass in this process is approximately one-fourth of the length of the cutter pass when processing with the same tolerance using conventional methods, but 90 to 99% of the amount of metal that should normally be removed is removed in this one process. It is something that will be done. In the subsequent finishing process, the cutter is usually replaced and the cutting conditions are changed to those suitable for light cutting. That is, even if the profile of the cutter used as a milling cutter is the same as that used for rough machining, a cutter with a thin web and thinning suitable for the purpose of finishing is used. Furthermore, the cutter rotational speed and cutting speed are usually much higher than those used during rough machining. As a result, the time required for this finishing process, which accounts for about three-quarters of the total cutter pass, is significantly reduced, and tool life is also extended. In addition, the curved surface that is created is now cut with the cutting blade of a cutter that rotates at high speed, so the curved surface itself is finished well, and the occurrence of burrs on the tops of uncut peaks is reduced. The final finishing process by hand or other means is also extremely easy compared to conventional processing methods. In the present invention, the pick feed amount is equal to the cutter diameter.
The reason why it is limited to 50 to 100%, and more preferably the meaning of limiting it to 80 to 90% of the diameter of the cutter, will be obvious from the above explanation. Also, depending on the inclination angle and curvature of the surface to be machined, in this series of finishing processes, it is not necessary to use cutters with the same profile as those used for rough finishing, and the shape of the surface to be machined is Depending on the inclination, for example, a ball end mill, radius end mill, cone end mill, etc. can be used freely, and in that case, the effects of the present invention will be even more remarkable. In addition, in the above explanation, Katsutapas mainly refers to
Although we have shown an example of processing in which the material is folded back and forth in a zigzag manner, it is obvious that it can also be applied to curved surface processing by running the processing surface in a lightning bolt shape, maze shape, spiral shape, twill shape, etc. In addition, in the above example, the cutter pass shift amount during finishing machining is set to 1/1 of the pick feed amount during rough machining.
2, 1/4 (= 1/2 x 1/2), but each of these is 1/4
3. 1/9 (= 1/3 x 1/3) or 1/2, 1/6
(=1/2×1/3) is also possible. The present invention can also be applied to multi-axis controlled milling with four or more axes. Since the present invention is constructed as described above, it is possible to significantly improve the operating efficiency of an extremely expensive multi-axis control NC milling machine, and the tool can also last for a long time, and a good machined surface can be obtained. is obtained.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional processing method, FIG. 2 is an XY plan view showing another example, and FIG. 3 is a process explanatory diagram of the method of the present invention. W, W', W...workpiece, Czx, Cyz...cross-sectional curve showing the curved surface to be created, T ₃ , T ₄ , T _b , T _e , T
_n , T _p , T' ₁ , T' ₂ , T' ₃ , T' ₄ ...Ball end mill.

Claims (1)

[Claims] 1. Using a radius end mill or ball end mill as a cutter, using a multi-axis control milling machine,
The above multi-axis control characterized in that the curved surface machining method for creating a three-dimensional curved surface sufficiently deeper than the radius of the end mill diameter on the workpiece includes the steps described in a) to b) below. Curved surface machining method using NC milling machine. a Set the pick feed amount P to 50% or more of the cutter diameter.
A rough cutting process in which the desired curved surface is machined using a rough cutting path, with P ₀ within a range of less than 100%, without considering uncut areas. b Use the same or different cutter as in the above roughing process, set the pick feed amount to P ₀ , which is the same as the pick feed amount in the above rough removal process, and set it to a positive integer.
A first finishing step in which the desired curved surface machining is continued using a cutter pass in which _N1 is determined and the cutter pass of the rough cutting step is shifted in the pick feed direction by _P0 / _N1 , and uncut portions are removed. c Using the same or different cutter as in the rough cutting process or the first finishing process, adjust the pick feed amount to the above P ₀
and continuing the desired curved surface machining by a cutter pass that is the same as that and a positive integer _N2 , and is shifted in _the pick feed direction by _P0 / _N1N2 with respect to the cutter pass in the rough cutting process or the first finishing process, A second finishing process to further remove uncut parts. d) A series of finishing steps in which positive integers N ₃ , N _{4 .} . . are sequentially determined as necessary and continued in the same manner as above. 2. A machining method using a multi-axis controlled NC milling machine according to claim 1, wherein the positive integers N ₁ , N ₂ , N ₃ , N _{4 .} . . are all 2. ”