阅读说明：本技术 基于最大切削包角约束的型腔分区插铣刀具路径规划方法 (Cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint ) 是由 黄诺帝 巫世晶 杜航 黄茜 胡基才 李小勇 于 2019-09-27 设计创作，主要内容包括：本发明公开了一种基于最大切削包角约束的型腔分区插铣刀具路径规划方法,先生成基于同心圆的简单几何形状型腔的插铣刀具路径,用边界角代替切削包角对刀具路径规划进行约束并设定最大切削包角,根据型腔轮廓、刀具半径、加工余量及径向铣削宽度确定满足最大切削包角限制的同心圆插铣路径的圆心位置及数量,根据刀具半径、加工余量及型腔边界确定刀具可达区域,并通过修剪无效圆弧轨迹最终生成有效初始刀具路径；将基于同心圆的简单几何形状型腔划分为若干种基本模式并分别规划各有效初始刀具路径,利用切线对复杂型腔进行分解,利用基本模式对复杂型腔内部的区域进行路径规划。该方法考虑了型腔的几何特征,提高了刀具寿命和规划效率。(The invention discloses a cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint, which comprises the steps of firstly generating a plunge milling cutter path of a simple geometric cavity based on concentric circles, using a boundary angle to replace the cutting wrap angle to constrain cutter path planning and setting a maximum cutting wrap angle, determining the circle center position and the number of the concentric circle plunge milling path meeting the maximum cutting wrap angle limitation according to a cavity contour, a cutter radius, a machining allowance and a radial milling width, determining a cutter reachable area according to the cutter radius, the machining allowance and a cavity boundary, and finally generating an effective initial cutter path by trimming an invalid arc track; the method comprises the steps of dividing a simple geometric-shape cavity based on concentric circles into a plurality of basic modes, respectively planning each effective initial cutter path, decomposing the complex cavity by using a tangent line, and planning the path of an area inside the complex cavity by using the basic modes. The method considers the geometric characteristics of the cavity, and improves the service life and planning efficiency of the cutter.)

1. A cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint is characterized by comprising the following steps: comprises the steps of (a) carrying out,

s1 plunge milling cutter path generation based on the simple geometric shape cavity of the concentric circle;

s1.1, according to the relation between the cutting wrap angle and the boundary angle of the cutter, the boundary angle is used for replacing the cutting wrap angle to restrict the cutter path planning, and the allowed maximum cutting wrap angle is set;

s1.2, determining the circle center positions and the number of concentric circle plunge milling paths meeting the maximum cutting wrap angle limitation according to the profile of a cavity, the radius of a cutter, the machining allowance and the radial milling width;

s1.3, determining a reachable area of the cutter according to the radius of the cutter, the machining allowance and the boundary of the cavity, and finally generating an effective initial cutter path by trimming an invalid circular arc track;

s1.4, dividing the simple geometric-shape cavity based on the concentric circles into a plurality of basic modes, and respectively planning effective initial cutter paths of the basic modes according to the step S1.2 and the step S1.3;

s2 decomposing the complex cavity based on the maximum cutting wrap angle constraint;

s2.1, decomposing the complex cavity by utilizing a tangent line under the constraint of the maximum cutting wrap angle;

and S2.2, planning a path of each subdivided region inside the complex cavity by using the basic mode in the step S1.4.

2. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 1, wherein: in step S1.1, the wrap angle α is cut_engagePresent around the cavity boundary at a boundary angle alpha_cornerFor the angle between the tool path and the contour of the cavity, the cutting wrap angle alpha_engageAngle alpha with the boundary_cornerNegative correlation, setting maximum cutting wrap angle

3. the method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 1, wherein: in step S1.3, the tool reachable region is a region where the tool can remove material in the cavity profile under the constraint that the cutting parameters are satisfied, and the tool can be prevented from interfering with the cavity profile when the tool forcibly passes through a slender bottleneck or a sharp corner existing in the cavity; the invalid circular arc track is a circular arc which is formed by connecting two points of intersection of a concentric circular arc and a cavity boundary with a concentric circle center to generate two line segments, wherein the concentric circular arc with smaller radius is outside the two line segments relative to the concentric circular arc intersected with the boundary; the effective initial tool path is a concentric circular arc path with the invalid circular arc path deleted and constrained within the inwardly offset boundary of the cavity.

4. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 1, wherein: let line segment L ═ L (i), i ∈ [ i [, ]₀,i₁]Is a part of the boundary of an unclosed cavity with a contour of C_pocket＝c(t),t∈[t₀,t₁]Curve C_offset＝c_offset(t) is by C_pocketIs deviated towards the inside of the cavityR_tool+a_aObtained wherein R is_toolDenotes the radius of the tool, a_aDenotes a given machining allowance, P₁And P_nIs C_offsetTwo end points of (a), t₁And t_nRespectively, unit tangent vectors of two points, theta being a unit vector t₁And t_nAngle therebetween and by sin θ | | | t₁×t_n| calculation, in step S1.4, four basic patterns are divided, where sin θ > 0 in pattern i, sin θ ═ 0 in pattern ii, sin θ < 0 in pattern III and

5. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 4, wherein: the method for planning the effective initial tool path of the cavity in the mode I is to find the concentric circular arcs intersected with the line segment L, and then connect the intersection point of the concentric circular arcs and the center O of the circular arc_cAnd finally, deleting redundant arcs outside the range of the obtained line segment to obtain an effective initial tool path with constant radial milling width.

6. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 4, wherein: the effective initial tool path for the cavity in mode II is planned by cutting vector t₁Parallel to t_nLet t be_tRepresenting unit vectors perpendicular to parallel lines, t in this mode_t＝t₁If, if

7. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 6, wherein: the effective initial tool path planning method for the cavity in the mode III is that the method proposed by the mode II is firstly utilized to determine the positions of equidistant parallel lines, and the reachable area of the tool is formed by C_offsetAnd offset a by L_eThe straight line segments generated by cos α are determined, where α is the angle between L and the linear tool path, and then the effective initial tool path is determined by trimming additional line segments outside the reachable region.

8. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 6, wherein: the method for planning the effective initial cutter path of the cavity in the mode IV is that the method provided by the mode II is firstly utilized to determine the positions of equidistant parallel lines, and the accessible area of the cutter is formed by C_offsetAnd offset a by L_eThe resulting straight line segments are determined and then the effective initial tool path is determined by trimming additional line segments outside the reachable region.

9. The method for cavity partition plunge milling cutter path planning based on maximum cutting wrap angle constraint of claim 6, wherein: in step S2.1, the complex cavities include cavities whose cavity boundaries are not closed, cavities whose cavity boundaries are closed, cavities whose internal regions of the cavities are all to be processed, and cavities whose internal regions are not to be processed.

Technical Field

The invention belongs to the field of machining, and particularly relates to a cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint.

Background

In various industries such as aerospace, automation and the like, the improvement of the machining efficiency and the service life of a cutter are important targets of machining.

For a cavity with a material difficult to cut and a deep hole or a narrow channel, the traditional end milling often has the phenomena of low processing efficiency and the like caused by serious radial deformation of a cutter, quick abrasion of the cutter and low material removal rate. Plunge milling has higher axial stiffness and material removal rate than end milling, and is often considered a more efficient machining method. The plunge milling process mainly comprises the steps of horizontally moving a cutter from one position (also called a plunge milling point position) to the next position on a reference plane, wherein actual cutting is not carried out in the process, then enabling the cutter to approach a blank along the axial direction of the cutter to remove materials, and returning to the plunge milling point position on the reference plane along the axial direction after cutting is finished, wherein the process is called a single plunge milling cycle, and the process is repeated continuously to finish part machining. The tool path in the reference plane thus determines the plunge milling efficiency and the tool life.

Existing CAM software and literature research mainly generates a tool path (also called an initial tool path) on a reference plane by controlling milling parameters such as radial cut width and lateral step distance, and commonly used plunge milling strategies including profile parallelism, zig-zag and unidirectional parallelism, however, generally ignore another important index affecting the tool life-the cutting wrap angle of a tool (the cutting wrap angle converts the contact surface of a relatively complex tool and the material to be removed in an unprocessed area into an angular relationship to characterize the loaded size of the tool during machining), the size of which depends on the geometry of the tool path and the cavity profile. The greater the cutting wrap angle of the tool, the more material removed in a single plunge milling cycle, the more cutting heat is generated, resulting in reduced tool life.

From the above, in order to prolong the service life of the tool, the maximum cutting wrap angle of the tool needs to be limited within a given value, and the plunge milling path needs to be reasonably planned for different cavity forms, but the existing cavity plunge milling path planning method is either low in efficiency or does not involve consideration of geometric characteristics in a machining area.

Disclosure of Invention

The invention aims to provide a cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint, which improves the service life and planning efficiency of a cutter and considers the geometric characteristics of a cavity.

The technical scheme adopted by the invention is as follows:

a cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint comprises the following steps:

s1 plunge milling cutter path generation based on the simple geometric shape cavity of the concentric circle;

s1.1, according to the relation between the cutting wrap angle and the boundary angle of the cutter, the boundary angle is used for replacing the cutting wrap angle to restrict the cutter path planning, and the allowed maximum cutting wrap angle is set;

s1.2, determining the circle center positions and the number of concentric circle plunge milling paths meeting the maximum cutting wrap angle limitation according to the profile of a cavity, the radius of a cutter, the machining allowance and the radial milling width;

s1.3, determining a reachable area of the cutter according to the radius of the cutter, the machining allowance and the boundary of the cavity, and finally generating an effective initial cutter path by trimming an invalid circular arc track;

s1.4, dividing the simple geometric-shape cavity based on the concentric circles into a plurality of basic modes, and respectively planning effective initial cutter paths of the basic modes according to the step S1.2 and the step S1.3;

s2 decomposing the complex cavity based on the maximum cutting wrap angle constraint;

s2.1, decomposing the complex cavity by utilizing a tangent line under the constraint of the maximum cutting wrap angle;

and S2.2, planning a path of each subdivided region inside the complex cavity by using the basic mode in the step S1.4.

In step S1.1, the wrap angle α is cut_engageExist inAround the cavity boundary, boundary angle alpha_cornerFor the angle between the tool path and the contour of the cavity, the cutting wrap angle alpha_engageAngle alpha with the boundary_cornerNegative correlation, setting maximum cutting wrap angleAnd minimum boundary angle

Is composed of

The maximum cutting wrap angle is formed by utilizing the characteristic that the tangent line of a circle is vertical to the line segment from the center of the circle to a tangent point

The constraint is within 90 degrees of the total length of the steel,

in step S1.3, the tool reachable region is a region where the tool can remove material in the cavity profile under the constraint that the cutting parameters are satisfied, and the tool can be prevented from interfering with the cavity profile when the tool forcibly passes through a slender bottleneck or a sharp corner existing in the cavity; the invalid circular arc track is a circular arc which is formed by connecting two points of intersection of a concentric circular arc and a cavity boundary with a concentric circle center to generate two line segments, wherein the concentric circular arc with smaller radius is outside the two line segments relative to the concentric circular arc intersected with the boundary; the effective initial tool path is a concentric circular arc path with the invalid circular arc path deleted and constrained within the inwardly offset boundary of the cavity.

Let line segment L ═ L (i), i ∈ [ i [, ]₀,i₁]Is a part of the boundary of an unclosed cavity with a contour of C_pocket＝c(t),t∈[t₀,t₁]Curve C_offset＝c_offset(t) is by C_pocketDeviation R towards the inside of the cavity_tool+a_aObtained wherein R is_toolDenotes the radius of the tool, a_aDenotes a given machining allowance, P₁And P_nIs C_offsetTwo end points of (a), t₁And t_nRespectively, unit tangent vectors of two points, theta is singleBit vector t₁And t_nAngle therebetween and by sin θ | | | t₁×t_n| calculation, in step S1.4, four basic patterns are divided, where sin θ > 0 in pattern i, sin θ ═ 0 in pattern ii, sin θ < 0 in pattern III and

mode IV sin theta < 0 and

wherein alpha is_iI-1, 2 denotes the vector t_iAnd L.

The method for planning the effective initial tool path of the cavity in the mode I is to find the concentric circular arcs intersected with the line segment L, and then connect the intersection point of the concentric circular arcs and the center O of the circular arc_cAnd finally, deleting redundant arcs outside the range of the obtained line segment to obtain an effective initial tool path with constant radial milling width.

The effective initial tool path for the cavity in mode II is planned by cutting vector t₁Parallel to t_nLet t be_tRepresenting unit vectors perpendicular to parallel lines, t in this mode_t＝t₁If, if

Then point P_nCloser to the start of the tool path, otherwise P₁More closely, when point P is_nCloser to the starting point, P_nAnd the distance between the straight line evolved from the starting circle is R_tool-a_eSo that the positions of equidistant parallel lines are determined, and the reachable area of the cutter is C_offsetAnd offset a by L_eThe straight line segments generated by cos alpha are determined, and the effective initial tool path is determined by trimming the extra line segments outside the reachable region, where a_eAlpha is the angle between L and the linear tool path for the radial cutting width of the mill.

The method for planning the effective initial tool path of the cavity in the mode III is to firstly utilize the dieThe method provided by the formula II determines the positions of equidistant parallel lines, and the reachable area of the cutter is C_offsetAnd offset a by L_eThe straight line segments generated by cos α are determined, where α is the angle between L and the linear tool path, and then the effective initial tool path is determined by trimming additional line segments outside the reachable region.

The method for planning the effective initial cutter path of the cavity in the mode IV is that the method provided by the mode II is firstly utilized to determine the positions of equidistant parallel lines, and the accessible area of the cutter is formed by C_offsetAnd offset a by L_eThe resulting straight line segments are determined and then the effective initial tool path is determined by trimming additional line segments outside the reachable region.

In step S2.1, the complex cavities include cavities whose cavity boundaries are not closed, cavities whose cavity boundaries are closed, cavities whose internal regions of the cavities are all to be processed, and cavities whose internal regions are not to be processed.

The invention has the beneficial effects that:

the method restricts the path by the maximum cutting wrap angle, so that the service life of the cutter is prolonged; the boundary angle is used for replacing a cutting wrap angle to restrict the tool path planning, the geometric dimension of the removed material does not need to be calculated in advance, and the planning efficiency is improved; the method comprises the steps of dividing a simple geometric-shape cavity based on concentric circles into a plurality of basic modes, decomposing the complex cavity, and planning a path of each subdivided region in the complex cavity by using the basic modes, so that not only are the geometric characteristics of the cavity considered, but also the planning efficiency is improved.

Drawings

Fig. 1 is a schematic view of the geometrical angle between the tool path and the cavity.

Fig. 2 is a schematic view of two possible initial tool paths of the same simple open cavity.

Fig. 3 is a schematic diagram of concentric plunge milling paths for four different simple open cavities.

Fig. 4 is a schematic diagram of an island-free complex open cavity decomposition strategy.

Figure 5 is a schematic diagram of an exploded strategy of a complex closed cavity with an island.

Detailed Description

The technical solutions of the present invention will be further described in detail with reference to the drawings and examples, which are preferred examples and are not to be construed as limiting the present invention.

A cavity partition plunge milling cutter path planning method based on maximum cutting wrap angle constraint comprises two steps:

s1 plunge milling cutter path generation based on the simple geometric shape cavity of the concentric circle;

cutting wrap angle alpha of tool_engageRepresenting the geometrical interference between the tool and the material at each point of insertion, the cutting wrap angle alpha_engageThe larger the cutting force, the shorter the tool life. As shown in fig. 1, the cutting wrap angle α_engageThe angle existing around the cavity boundary and between the tool path and the cavity contour (i.e. the boundary angle alpha)_corner) Negative correlation due to calculation of the cutting wrap angle alpha of the plunge milling cycle_engageThe geometry of the removed material is calculated in advance, which is time-consuming, so that the boundary angle α is used_cornerInstead of cutting the wrap angle alpha_engageTo constrain the tool path planning, in this embodiment, the maximum cutting wrap angle is set

And minimum boundary angle

Is composed of

As shown in the left example of fig. 1.

Conventional plunge cutter paths typically use parallel-direction paths to generate an initial circular cutter path in a unidirectional or zig-zag manner, as shown in FIG. 2(a), with a boundary angle α_cornerMay be very small resulting in a cutting wrap angle alpha_engageToo large, to overcome this problem, an initial tool path is generated using concentric circles of constant radius increments, as shown in fig. 2 (b): let L (i) be the line segment i ∈ [ i [, ]₀,i₁]Is part of the boundary of an open cavity with a contour of C_pocket＝c(t),t∈[t₀,t₁]Default direction is counter-clockwise and tool path is clockwise, curve C_offset＝c_offset(t) is by C_pocketDeviation R towards the inside of the cavity_tool+a_aObtained wherein R is_toolDenotes the radius of the tool, a_aDenotes a given machining allowance, P₁And P_nIs C_offsetTwo end points of (a), t₁And t_nAre unit tangent vectors of two points, respectively, the center of the concentric circle being at t₁And t_nAt the intersection of the two vectors, use O_cAnd (4) showing. The smallest concentric circle becomes the starting circle with a radius of:

r₁＝d_min(O_c,L)+a_e-R_tool

wherein d is_min(O_cL) is O_cMinimum distance of point to straight line segment L, a_eThe radial cutting width of the mill, i.e. the radius increment of equidistant concentric circles.

The number of concentric circles is calculated by the following formula:

wherein d is_max(O_c,C_offset) Is O_cPoint to curve C_offsetThe maximum distance of (a) is,

represents the smallest integer not less than x.

The tool reach area is defined by curve C_offsetSum vector t₁、t_nAnd (3) trimming the concentric circular arc tracks obtained in the closed area to finally generate an effective initial tool path. For the cavity shown in FIG. 2(b), first find the concentric circular arc intersecting with the line segment L, and then connect the intersection point of the concentric circular arc and the center O of the circular arc_cThe obtained line segment is used for trimming the adjacent concentric circular arcs with smaller radius, and finally, the redundant circular arcs outside the range of the obtained line segment are deletedAn effective initial tool path with a constant radial milling width is obtained.

To apply the proposed concentric path planning method to the more general case, four basic simple geometry cavities are analyzed separately, as shown in fig. 3. Where θ is the unit vector t₁And t_nThe angle therebetween can be expressed by sin θ | | | t₁×t_nAnd calculating | l.

Mode I: sin theta > 0 and maximum cutting wrap angle

As shown in fig. 3 (a). As in fig. 2(b), the detailed effective initial tool path generation method has been described in detail, and is omitted here.

And a mode II: sin θ is 0 as shown in fig. 3 (b). At this time, the vector t is cut₁Parallel to t_nThe centers of the concentric circles being along the vector t₁At infinity, the concentric arcs evolve into a set of equidistant parallel lines perpendicular to the two vectors, and the radius of the aforementioned starting circle is no longer suitable for describing the position of the tool path and needs to be redefined. Let t_tRepresenting unit vectors perpendicular to parallel lines, t in this mode_t＝t₁If, if

Then point P_nCloser to the start of the tool path, otherwise P₁And closer. When point P_nCloser to the starting point, P_nAnd the distance between the straight line evolved from the starting circle is R_tool-a_eAnd thus the position of equidistant parallel lines is determined, this method is also applicable to mode III and mode IV. Accessible area of the tool is defined by_offsetAnd offset a by L_eThe straight line segment generated by cos α, where α is the angle between L and the linear tool path, is then used to determine the effective initial tool path by clipping additional line segments outside the reachable region.

Mode III: sin theta < 0 and

as shown in fig. 3 (c). Wherein, min (alpha)₁,α₂) Represents an angle alpha₁And alpha₂The smaller of which, α_iI-1, 2 denotes the vector t_iAnd L. Center of concentric circle is along unit vector

At infinity, the positions of equally spaced parallel lines can be determined using the method set forth in mode II. Accessible area of the tool is defined by_offsetAnd offset a by L_eThe straight line segment generated by cos α, where α is the angle between L and the linear tool path, is then used to determine the effective initial tool path by clipping additional line segments outside the reachable region.

Mode IV: sin theta < 0 and

as shown in fig. 3 (d). The center of the concentric circle is located at infinity in the vertical direction of the straight line segment L, and the generated tool path is parallel to the straight line segment L. Accessible area of the tool is defined by_offsetAnd offset a by L_eThe resulting straight line segments are determined and then the effective initial tool path can be determined by clipping additional line segments outside the reachable region.

S2 decomposing the complex cavity based on the maximum cutting wrap angle constraint;

for complex cavities, it is necessary to decompose them first under the constraint of the maximum cutting wrap angle, and then to plan the path for each subdivided region using the method proposed in step S1.

Shown in FIG. 4, is an open cavity without islands, C_pocketIs the boundary of the cavity, C_offsetIs composed of C_pocketDeviation R towards the inside of the cavity_tool+a_aObtained of O_cIs determined by the method described in step S1 and C_offsetThe center of the associated concentric circle. The decomposition standard of the open cavity is as follows:

first, using O_cP₁And O_cP₅The two control lines decompose the cavity, and the region B is cut away from the processing region;

second, from the boundary C_offsetGet a point P₂Is connected to P₂And O_cA straight line O can be determined_cP₂If O is present_cP₂And boundary C_offsetTangent and produce a new point of intersection P₃Then region C is cut away from the remaining machining region;

third, region A may generate a plunge cutter path with maximum tool cutting wrap angle constraints using the method set forth in step S1, and regions B and C will repeat this decomposition process until all subdivided regions satisfy the maximum tool cutting wrap angle constraints.

As shown in fig. 5, the closed cavity with island is a closed cavity, so that a cutting operation needs to be performed inside the closed cavity, and an optional point O is selected_cIs the starting point of plunge milling. Since the plunge milling cutter does not usually have a drilling function, drilling needs to be performed in advance or axial spiral milling needs to be used for providing a lower cutter position for plunge milling, and since the drilling and axial spiral milling technologies are relatively mature, the plunge milling cutter can be directly used for machining deep holes and is out of the scope of the patent claims, and therefore, the plunge milling cutter is not further described. The cavity is a circular island with a geometrical structure of C_islandIs shown by_pocketAnd C_islandAre all offset by R_tool+a_aThe area in which the center of the tool is located is obtained. Then the cavity decomposition is carried out according to the second decomposition standard of the open cavity, in this case, P can be found₃,P₄,P₇、P₈Four points of tangency, thereby defining a sub-region having a closed boundary curve

Region(s)

Can be dotted with O_cAnd generating a concentric circular cutter path meeting the maximum cutting wrap angle constraint for the circle center, wherein the rest sub-cavities belong to the open cavities, and subdividing by using the decomposition standard of the open cavities until all the subdivided areas meet the constraint of the maximum cutter cutting wrap angle.

It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.