JPH04300143A - Selection method of tool for curved surface processing - Google Patents

Abstract

PURPOSE:To select a tool which leaves no rest of shaving and improves processing efficiency when a curved surface is formed on the surface of a work. CONSTITUTION:A curved surface to be processed is defined by many processing points (step 100). The diameter of a tool, selected in respouse to a curvature radius of each processing point, is arranged in order from a larger size to make a tool diameter row (step 102). The tool diameter row is divided into a plurality of groups by a division ratio which is set beforehand, and a set of proposed diameters in which the minimum values of rospective groups are proposed (step 103) diameters is created. Plurd sets of proposed diameters, whose division ratios are different from each other for one tool diameter row, are created. Next, number of the processing point which are passed by the tool are evaluated for every set of proposed points (step 104). A set of proposed diameters, whose value obtained by the evaluation is the minimum, is selected as a tool set which is used for processing.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for selecting a tool in curved surface machining for forming a curved surface of a desired shape on the surface of a workpiece using a milling machine.

0002

2. Description of the Related Art When machining a curved surface using a numerically controlled milling machine, the data creator currently selects a tool by considering the curvature of each part of the curved surface.

0003

[Problems to be solved by the invention] As mentioned above, in the method of selecting a tool based on the intuition of the data creator, the diameter of the tool is too large and the concave surface remains uncut, or the diameter of the tool is too small and the machining time is increased. The problem is that it becomes longer. In other words, there is a need for a method that allows the selection of an optimal tool without relying on the data creator's intuition.

[0004] The present invention aims to solve the above-mentioned problems, and it is possible to obtain the desired finishing accuracy without leaving any uncut parts when forming a curved surface on the surface of a workpiece using a milling machine, and to achieve the desired finishing accuracy. The purpose of this invention is to provide a tool selection method for curved surface machining that allows the selection of a tool that increases efficiency without relying on intuition.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method for selecting a tool when forming a curved surface of a desired shape on the surface of a workpiece by a milling machine, which Define a curved surface as a set of many machining points, create a tool diameter column by arranging the selected tool diameters in descending order of the radius of curvature of each machining point, and then The diameter row is divided into multiple groups, and the minimum value of each group is used as the candidate diameter to create a set of candidate diameters corresponding to the above division ratio, and a set of candidate diameters with different division ratios is created for one tool diameter row. After creating multiple sets of candidate diameters, use the tools that make up the set of candidate diameters in order from the one with the largest diameter to create a set of candidate diameters that minimizes the number of machining points that the tool passes through when forming a curved surface.
It is selected as a set of tools to be used for machining.

[0006]

[Operation] According to the above method, after determining the tool diameter for each machining point based on the radius of curvature of a large number of machining points that define a curved surface, a tool diameter array is created by arranging the tool diameters in descending order. After that, the tool is divided into multiple groups according to a predetermined division ratio, and the minimum value of each group is used as the candidate tool diameter, so the tool with the diameter corresponding to the part with the smallest radius of curvature is selected. This means that the desired finishing accuracy can be achieved without leaving any uncut parts. In addition, multiple sets of candidate diameters are created by changing the division ratio, and the set of candidate diameters that minimizes the number of machining points that the tool passes when forming a curved surface is selected as the set of tools used for machining. Therefore, it is possible to select a set of tools that will shorten the machining time among the set of tools that have the same finishing accuracy.If you use the tools selected in this way, you can It also increases efficiency.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a process for creating numerical control data according to the present invention, and FIG. 2 shows a schematic block diagram. The process of creating numerical control data is the process of selecting tools (
Steps 100 to 105) and a process of determining the position of the tool during machining (Steps 106 to 110).

First, the procedure for selecting a tool will be explained. The curved surface to be formed on the surface of the workpiece has many processing points Pi.
j (step 100). That is, when a two-dimensional square lattice having m lattice points in the u direction and n lattice points in the v direction in FIG. 3 is brought into close contact along the curved surface to be machined, each lattice point is defined as a processing point Pij. A machining point Pij is generated in a machining point generation section 11. Here, when the lengths of the sides in the u direction and v direction of the two-dimensional square lattice that define the curved surface are Lu and Lv, respectively, so that (Lu/m≦α and Lv/n≦α) are satisfied. , the number m×n of machining points Pij is set for a constant α (=0.01 to 0.05 mm). The constant α will be described later. Each processing point Pij has as attributes a coordinate value (x, y) within the UV plane, a coordinate value (z) in a direction orthogonal to the UV plane, and a radius of curvature (r). Further, the sign of the radius of curvature is set so that it is positive when the processing point Pij is located on a concave surface, and negative when it is located on a convex surface.

Next, in the tool allocation section 12, among the tools prepared in advance, a tool having a maximum radius that does not exceed the radius of curvature r of each machining point Pij is assigned to each machining point Pij.
(Step 101). For example, processing point P
The radius of curvature at 33 is 83 mm, and among the usable tools, those with a radius close to this radius of curvature are:
If they are 80 mm and 85 mm, the 80 mm tool having the maximum radius that does not exceed the radius of curvature is associated with the machining point P33. When the machining point Pij is a point on a plane and the radius of curvature is infinite, it is sufficient to use the tool with the maximum radius among the usable tools, and
If the radius of curvature is smaller than the minimum radius of the tools that can be used, or if the machining point Pij is on a convex surface and the radius of curvature is a negative value, use the tool with the minimum radius of the tools that can be used. That's fine. In this way, each processing point Pi
For j, coordinate values (x, y, z) and radius of curvature (r)
An attribute table as shown in FIG. 4 is created in which the tool radius (r0) is associated with the radius (r0) of the tool.

After associating the maximum diameters of tools that can be used to machine each machining point Pij, the tool candidate selection section 13 arranges the radii of the associated tools in descending order (step 102). That is, the radii of the tools corresponding to each machining point Pij are sorted in descending order, and
A tool radius sequence R is generated as follows. In addition, the tool candidate selection unit 13 divides the tool radius row R into a plurality of groups according to a predetermined division ratio, and uses the minimum value of each group as a candidate radius of the tool to be used for machining (hereinafter referred to as candidate radius). (step 103). For example, 3
If a curved surface is to be machined using different types of tools, the tool radius row R can be divided into three parts, so it is divided into 8:1:1, etc. In this case, the tool diameter row R shown in FIG. As shown in Fig. 6(a), the set of candidate diameters is 6mm, 5mm.
mm, it becomes 3 mm. Here, a plurality of types of division ratios are prepared, and a set of candidate diameters is determined for each division ratio. For example, in addition to the split ratio of 8:1:1,
7:2:1, 6:2:2, etc. are prepared, and considering the tool series R in Fig. 5, the candidate diameter sets are respectively shown in Fig. 6 (
b) As shown in (c), the lengths are 10mm, 5mm, 3mm, and 20mm, 6mm, and 3mm. In short, for one tool diameter row R, a plurality of division ratios are applied to obtain a plurality of sets of candidate diameters.

After determining a plurality of sets of candidate diameters, the tool evaluation unit 14 evaluates each set of candidate diameters (step 104), selects the set of candidate diameters with the highest machining efficiency, and uses the set for machining. (Step 105)
). Here, for evaluation purposes, a tool constant t is introduced that corresponds one-to-one to the radius of each tool. As shown in Fig. 7, the tool constant t is the distance between the intersection of two circles and the common tangent of both circles when the centers of two circles having the same radius as the tool radius r0 are separated by a distance t. (referred to as cup height amount)
is the value determined by determining δ (i.e., r0 2 = (r0 − δ) 2 + (t/2) 2 )
, the cup height amount δ is determined, the tool constant t is uniquely determined corresponding to the radius r0 of the tool. For example, if the cup height amount δ is set to 0.01 mm, the tool constant t can be determined as follows.

Tool radius (mm) 20 1
0 6 5
3 Tool constant 1.26
0.89 0.69 0.63 0.49 Here, the tool constant t and the constant α mentioned above are t=N
- It is set so that the relationship α (N is a natural number) holds true. Considering that the procedure for machining a curved surface is as shown in FIG. 8, a set of candidate diameters is evaluated as follows. That is, to process a curved surface, first, as shown in FIG. 8(a), the workpiece W is cut using the tool T1 with the largest radius, and then, as shown in FIG. 8(b), the uncut portion D1 is cut. Cutting with the next largest radius tool T2,
Furthermore, as shown in FIG. 8(c), only the uncut portion D2 is cut using the tool T3 having the smallest radius. As a result, the number of machining points Pij to which each tool T1, T2, T3 is applied is determined by the division ratio of the tool diameter row R being c1:
When c2 :c3, (c1 +c2 +c3
):(c2 +c3):c3. Since the number of machining points Pij to which tool T1 is applied is the total number of machining points Pij n x m, the number of machining points Pij to which tool T2 is applied is n x m x (c2 + c3
)/(c1 +c2 +c3), and the number of machining points Pij to which tool T3 is applied is n×m×c3/(c
1 +c2 +c3). Each tool T used for processing
The tool constants of 1, T2, and T3 are t1 and t, respectively.
2, t3 (t1 > t2 > t3), and the number of machining points Pij to which each tool is applied is k1, k2, k3
If (k1 ≧k2 ≧k3), the evaluation value S is
S=(k1/t1 2 )+(k2/t2 2 )
+(k3/t3 2 ), and a set of candidate diameters that minimizes this evaluation value S is determined as a set of tools used for machining.

For example, a set of candidate diameters is shown in FIGS.
If it is determined as shown in (c), then the
) is the evaluation value S corresponding to (10/0.692)+(
2/0.632)+(1/0.492)=30, and similarly, it becomes 25 in FIG. 6(b) and 22 in FIG. 6(c). Therefore, the set of candidate diameters selected as shown in FIG. 6(c) is selected as the set of tools used for machining. The above evaluation value S is the tool T1, T
2, when forming a curved surface using tool T3, tool T1
, T2, and T3 correspond to the number of machining points Pij that the tool passes through, so the set of candidate diameters selected to minimize the evaluation value S is the one that minimizes the number of machining points Pij that the tool passes through. Become. In other words, this is the set of tools with the highest machining efficiency among the sets of candidate diameters obtained.

After the tool used for machining is selected, numerical control data is created in the data creation section 15. When creating numerical control data, each tool T1, T2
, T3 are sequentially set. First, processing point P
Among ij, i, j are {1, t1 /α, 2t1 /
} are extracted (step 106). As shown in FIG. 9, a spherical surface Sij having the same radius as the tool T1 is generated around each extracted processing point Pij. A point obtained by projecting each machining point Pij onto the envelope surface of the spherical surface Sij obtained in this way is set as a tool passing point Qij (step 107). The tool passing point Qij obtained in this way is defined as the tool T1
By setting the position of the tool T1 so that the center of the tool T1 passes through, numerical control data regarding the position of the tool T1 can be created (step 108). The created numerical control data is outputted through the output unit 16 in a form compatible with the milling machine, such as paper tape, magnetic storage medium, signal, etc. Here, when the tool passing point Qij exists on the spherical surface Sij corresponding to the machining point Pij, the machining point P
ij has been processed, but if it does not exist on the spherical surface Sij corresponding to the processing point Pij, then the processing point Pij
will remain uncut. Therefore, the tool was changed to T2 (steps 109 and 110), and the machining point Pi, which remained uncut, was
Steps 106 to 108 are repeated for j, and then the tool is changed to T3 for the part left uncut by tool T2 (step 109).
, 110) and repeat steps 106 to 108.

As described above, the tools T1, T2,
Numerical control data for finishing the curved surface is created by successively decreasing T3.

[0016]

Effects of the Invention As described above, the present invention determines the diameter of the tool for each machining point based on the radius of curvature of a large number of machining points that define a curved surface, and then arranges the tool diameters in descending order of diameter. After creating a diameter array, the tool is divided into multiple groups according to a predetermined division ratio, and the minimum value of each group is used as a candidate tool diameter, so the diameter corresponding to the part with the smallest radius of curvature is selected. This means that the tool always includes a tool having the following characteristics, which has the advantage that the desired finishing accuracy can be obtained without leaving uncut parts. In addition, multiple sets of candidate diameters are created by changing the division ratio, and the set of candidate diameters that minimizes the number of machining points that the tool passes through when forming a curved surface is selected for the tool used for machining. Since it is selected as a set of tools, among the sets of tools that have the same finishing accuracy,
It is possible to select a set of tools that will substantially shorten the machining time, and using the tools selected in this way has the effect of increasing machining efficiency.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the procedure of an example.

FIG. 2 is a block diagram of an apparatus used in the example.

FIG. 3 is a diagram showing an example of defining a curved surface using processing points in the embodiment.

FIG. 4 is a diagram showing an attribute table for machining points in the embodiment.

FIG. 5 is a diagram showing an example of a tool diameter array in the embodiment.

FIG. 6 is a diagram showing a concept of how to obtain a candidate diameter in an embodiment.

FIG. 7 is a diagram showing the concept of tool constants in the embodiment.

FIG. 8 is a diagram showing a process of machining a curved surface using a tool selected in the example.

FIG. 9 is a diagram illustrating how to obtain a tool trajectory in the example.

[Explanation of symbols]

Pij processing point R Tool diameter row T1 Tool T2 Tool T3 Tool W Work

Claims (1)

[Claims] Claim 1: A method for selecting a tool when forming a curved surface of a desired shape on the surface of a workpiece using a milling machine, the curved surface to be machined being defined as a set of many machining points, and each machining point being After creating a tool diameter column by arranging the diameters of the selected tools in descending order of radius of curvature, the tool diameter column is divided into multiple groups according to a preset division ratio, and the minimum diameter for each group is Create a set of candidate diameters corresponding to the above division ratio with the values as candidate diameters, create multiple sets of candidate diameters with different division ratios for one tool diameter column, and then select the tools that make up the set of candidate diameters. Select a set of candidate diameters that minimize the number of machining points that the tool passes when forming a curved surface by using them in order from the largest diameter.
A method for selecting tools in curved surface machining, characterized by selecting a set of tools to be used for machining.