JP2834896B2 - Tool selection method for curved surface machining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of selecting a tool in a curved surface processing for selecting a tool when a curved surface having a desired shape is formed on the surface of a work using a milling machine.

[0002]

2. Description of the Related Art At the present time, when a curved surface is machined using a numerically controlled milling machine, a data creator selects a tool in consideration of the curvature of each part of the curved surface.

[0003]

As described above, in the method of selecting a tool according to the intuition of the data creator, the tool diameter is too large to leave a concave portion, or the tool diameter is too small to shorten the machining time. There is a problem that it becomes longer. That is, there is a demand for a method that allows an optimum tool to be selected without depending on the intuition of the data creator.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. When a curved surface is formed on a surface of a work by using a milling machine, a desired finishing accuracy can be obtained without leaving uncut portions, It is an object of the present invention to provide a method of selecting a tool in a curved surface processing, which allows a user to select a tool without increasing his or her efficiency.

[0005]

According to the present invention, in order to achieve the above object, there is provided a method for selecting a tool for forming a curved surface having a desired shape on a surface of a work by a milling machine. A curved surface is defined as a set of a number of machining points, a tool diameter row is created by arranging the diameters of the selected tools corresponding to the radius of curvature of each machining point in ascending order, and the tool is divided according to a preset division ratio. The diameter array is divided into a plurality of groups, and a set of candidate diameters corresponding to the above-described division ratios is created with the minimum value of each group as a candidate diameter. After creating a plurality of candidate diameter sets, a candidate diameter set that minimizes the number of machining points through which the tool passes when forming a curved surface using the tools constituting the set of candidate diameters in order from the larger diameter,
It is selected as a set of tools used for machining.

[0006]

According to the above method, the tool diameter is determined for each machining point on the basis of the radius of curvature of a number of machining points defining a curved surface, and then the tool diameters are arranged in order from the larger tool diameter. After that, the tool is divided into a plurality of groups according to a predetermined division ratio, and the minimum value of each group is used as a candidate for the diameter of the tool to be used, so the tool having the diameter corresponding to the portion having the smallest radius of curvature is used. Is always included, and a desired finishing accuracy can be obtained without leaving uncut portions. Also, a plurality of sets of candidate diameters are created by changing the division ratio, and a set of candidate diameters that minimizes the number of processing points through which the tool passes when forming a curved surface is a set of tools used for machining. The tool set that minimizes the machining time can be selected from among the tool sets that have the same finish accuracy, and if the tool selected in this way is used, Efficiency also increases.

[0007]

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

First, a procedure for selecting a tool will be described. The curved surface to be formed on the surface of the workpiece has many processing points Pij
(Step 100). That is, each of the lattice points when a two-dimensional square lattice having m lattice points in the u direction and n lattice points in the v direction in FIG. The processing point Pij is generated in the processing point generator 11. Here, when the lengths of the sides of the two-dimensional square lattice defining the curved surface in the u and v directions are Lu and Lv, respectively,
The number m × n of the processing points Pij is set for a constant α (= 0.01 to 0.05 mm) so as to satisfy (Lu / m ≦ α and Lv / n ≦ α). The constant α will be described later. Each processing point Pij has, as attributes, a coordinate value (x, y) in the uv plane, a coordinate value (z) in a direction orthogonal to the uv plane, and a radius of curvature (r).
The sign of the radius of curvature is set to be positive when the processing point Pij is located on a concave surface and negative when the processing point Pij is located on a convex surface.

Next, the tool allocating unit 12 associates a tool having a maximum radius not exceeding the curvature radius r of each processing point Pij among the tools prepared in advance with each processing point Pij (step 101). For example, a curvature radius of 83mm at the processing point P _33, those having a radius close to the radius of curvature of the tool that can be used, 80 m
m, if it is 85 mm, is the 80mm tool with the largest radius not exceeding the radius of curvature is associated with the working point P _33. When the processing point Pij is a point on a plane and the radius of curvature is infinite, or when the processing point Pij is a point on a convex surface
When the radius of curvature becomes a negative value, the maximum radius of the usable tools may be made to correspond, and the radius of curvature is smaller than the minimum radius of the usable tools.
In this case, a tool having a minimum radius among usable tools may be used. In this way, for each machining point Pij, an attribute table as shown in FIG. 4 in which the coordinate values (x, y, z), the radius of curvature (r), and the radius of the tool (r ₀ ) are associated is created. .

After associating the maximum diameter of a tool that can be used to machine each machining point Pij, the tool candidate selecting section 13
The radiuses of the associated tools are arranged in ascending order (step 102). That is, the tool radii R as shown in FIG. 5 are generated by sorting the radii of the tools corresponding to the respective processing points Pij in descending order. The tool candidate selection unit 13
Then, the tool diameter row R is divided into a plurality of groups according to a division ratio prepared in advance, and the minimum value of each group is set as a candidate of a radius of a tool used for machining (hereinafter, referred to as a candidate diameter) (step). 103). For example, if a curved surface is to be machined using three types of tools, the tool diameter row R may be divided into three parts, so that the tool diameter row R is divided into 8: 1: 1 and the like. Considering the diameter row R,
As shown in FIG. 6A, the set of candidate diameters is 6 mm and 5 m.
m, 3 mm. Here, a plurality of types of division ratios are prepared, and a set of candidate diameters is obtained for each division ratio. For example, in addition to the division ratio of 8: 1: 1,
7: 2: 1, 6: 2: 2, etc. are prepared, and considering the tool sequence R in FIG.
(B) As shown in (c), 10 mm, 5 mm, 3 mm
And 20 mm, 6 mm, and 3 mm. In short, by applying a plurality of division ratios to one tool diameter row R,
A plurality of sets of candidate diameters are obtained.

After obtaining a plurality of sets of candidate diameters, the tool evaluation unit 14 evaluates each set of candidate diameters (step 104) and selects a set of candidate diameters having the best machining efficiency to use for machining. A set of tools to be determined is determined (step 10
5). Here, for evaluation, a tool constant t corresponding to the radius of each tool on a one-to-one basis is introduced. As shown in FIG. 7, when the center of two circles having the same radius as the tool radius r ₀ is separated by a distance t, the tool constant t is defined as the distance between the intersection of the two circles and the common tangent of the two circles. Distance (referred to as cup height)
is a value determined by determining δ (ie, r ₀ ² = (r ₀ −δ) ² + (t / 2) ² ), and if the cup height δ is determined, the tool constant t becomes the radius of the tool. r ₀
Is uniquely determined in correspondence with For example, if the cup height δ is set to 0.01 mm, the tool constant t can be determined as follows.

Tool radius (mm) 20 10 6 5 3 Tool constant 1.26 0.89 0.69 0.63 0.49 Here, the tool constant t and the above constant α are t =
It is set so that the relationship of N · α (N is a natural number) is established. Considering that the procedure for processing a curved surface is as shown in FIG. 8, the evaluation of the set of candidate diameters is performed as follows. That is, to process a curved surface, first, FIG.
After the workpiece W is cut using the tool T ₁ having the largest radius as shown in FIG. 8, only the uncut portion D ₁ is cut with the tool T _{2 having the} next larger radius as shown in FIG. , as shown in FIG. 8 (c), the at to cut the minimum radius of the tool T ₃ only portions D ₂ uncut.
As a result, the number of machining points Pij to which each of the tools T ₁ , T ₂ , and T ₃ is applied is such that the division ratio of the tool diameter row R is c ₁ : c ₂ : c _3.
, Then (c ₁ + c ₂ + c ₃ ): (c ₂ +
c ₃ ): Set to be c ₃ . The number of working points Pij that the tool T ₁ is applied, since the total number n × m processing point Pij, the number of processing points Pij to the tool T ₂ is applied, n ×
m × (c ₂ + c ₃ ) / (c ₁ + c ₂ + c ₃ ), and the number of machining points Pij to which the tool T ₃ is applied is n × m × c ₃ /
(C ₁ + c ₂ + c ₃ ). The tool constants of the tools T ₁ , T ₂ , and T ₃ used for machining are represented by t ₁ , t ₂ , and t, respectively.
₃ (t ₁ > t ₂ > t ₃ ) and the number of machining points Pij to which each tool is applied is k ₁ , k ₂ , k ₃ (k ₁ ≧ k ₂ ≧ k ₃ ), the evaluation value S _{is, S = (k 1 / t} 1 2) + (k 2 /
t ₂ ² ) + (k ₃ / t ₃ ² ),
A set of candidate diameters that minimizes the evaluation value S is determined as a set of tools used for machining.

For example, the set of candidate diameters is shown in FIGS.
If it is determined as shown in FIG.
Evaluation value S corresponding to (a) is (10 / 0.69 ²⁾ +
(2 / 0.63 ² ) + (1 / 0.49 ² ) = 30, and similarly, 25 in FIG. 6B and 22 in FIG. 6C. Therefore, a set of candidate diameters selected as shown in FIG. 6C is selected as a set of tools used for machining. The evaluation value S is calculated based on the tool T ₁ ,
When forming a curved surface using T ₂ and T ₃ , tools T ₁ and T
_{Since 2} and T ₃ correspond to the number of processing points Pij passing, the set of candidate diameters selected to minimize the evaluation value S is determined by minimizing the number of processing points Pij passing by the tool. Become.
In other words, it is the set of tools with the highest machining efficiency among the set of obtained candidate diameters.

After a tool to be used for machining is selected, the data creation unit 15 creates numerical control data. When creating numerical control data, each tool T ₁ , T ₂ ,
Sequentially sets the movement locus of the T _3. First, among the processing point Pij, i, j is _{{1, t 1 / α,} 2t 1 / α, ......} extracts the point where the (step 106). Around the respective processing point Pij extracted, as shown in FIG. 9, it generates a spherical Sij having the same radius as the tool T _1. The point where each processing point Pij is projected on the envelope surface of the spherical surface Sij obtained in this way is set as a tool passing point Qij (step 107).
Thus the tool passing point Qij obtained such that the center of the tool T ₁ is to pass, setting the position of the tool T _1, it is the numerical control data can be created about the position of the tool T ₁ (step 108 ). The created numerical control data is output through the output unit 16 in a form corresponding to a milling machine such as a paper tape, a magnetic storage medium, and a signal. Here, the tool passing point Qij is the spherical surface S corresponding to the machining point Pij.
When it exists on ij, the machining point Pij has been machined, but when it does not exist on the spherical surface Sij corresponding to the machining point Pij, the machining point Pij is left uncut. So, to change the tool to T ₂ (step 109,11
0), Steps 106 to 108 are repeated for the machining point Pij left uncut, and the tool T
The portion that became the uncut by _2, the tool T ₃
(Steps 109 and 110), and Step 10
From step 6, step 108 is repeated.

As described above, the tools T ₁ , T ₂ , T ₃
Are sequentially reduced, and numerical control data for finishing the curved surface is created.

[0016]

As described above, according to the present invention, the tool diameter is determined for each machining point based on the radius of curvature of a number of machining points defining a curved surface, and then the tool diameters are arranged in descending order. After creating the diameter sequence, the tool is divided into a plurality of groups according to a predetermined division ratio, and the minimum value of each group is used as a candidate for the diameter of the tool to be used. Therefore, there is an advantage that a desired finishing accuracy can be obtained without forming uncut portions. Also, a plurality of sets of candidate diameters are created by changing the division ratio, and when forming a curved surface, a set of candidate diameters that minimizes the number of processing points that make up a tool when passing through the tool is used for machining. Since the tool is selected as a set of
It is possible to select a set of tools for which the machining time is almost the shortest. Use of the tool selected in this way has the effect of increasing the machining efficiency.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a procedure of an embodiment.

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

FIG. 3 is a diagram illustrating an example of a definition of a curved surface based on a processing point in an embodiment.

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

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

FIG. 6 is a diagram illustrating the concept of how to determine a candidate diameter in the embodiment.

FIG. 7 is a diagram illustrating a concept of a tool constant according to the embodiment.

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

FIG. 9 is a diagram illustrating a method of obtaining a tool path in the embodiment.

[Explanation of symbols]

Pij working point R tool径列T ₁ the tool T ₂ Tool T ₃ the tool W workpiece

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B23Q 15/00 301 G05B 19/402

Claims (1)

(57) [Claims] 1. A method for selecting a tool for forming a curved surface of a desired shape on a surface of a work by a milling machine, wherein a curved surface to be machined is defined as a set of a large number of machining points, After creating a tool diameter row by arranging the tool diameters selected according to the radius of curvature in order from the largest, the tool diameter row is divided into multiple groups according to a preset division ratio, and the minimum After creating a set of candidate diameters corresponding to the above-mentioned division ratios using the values as candidate diameters, and creating a plurality of candidate diameter sets with different division ratios for one tool diameter row, the tools that constitute the candidate diameter set are In the curved surface machining, a set of candidate diameters that minimizes the number of machining points through which a tool passes when forming a curved surface by using the larger diameter in order is selected as a set of tools used for machining. Engineering How to choose the ingredients.