CN102129232A - Five-axis side milling machining process parameter design method - Google Patents

Abstract

The invention discloses a five-axis side milling machining process parameter design method, belongs to the technology of numerical control (NC) machining, and solves the problem that real machining conditions cannot be reflected in cutting force calculation in the conventional process parameter design method. The method comprises the following steps of: tool path planning, cutting force calculation and process parameter optimization; in the tool path planning step, an NC code is generated by using computer-aided manufacturing (CAM) software; in the cutting force calculation step, first, a continuous tool path is generated from the NC code; then, a cutting thickness is obtained; and finally, the cutting force is calculated according to the cutting thickness; and in the process parameter optimization step, whether the calculated cutting force is not greater than a design threshold is judged; if the calculated cutting force is not greater than the design threshold, the NC code, the cutting depth and a feed rate are taken as input parameters; and otherwise, an NC code is regenerated. In the method, the real machining conditions are reflected by utilizing a tool enveloping surface analytical expression and the obtained transient cutting thickness is more accurate, so that the accuracy of the calculation of the cutting thickness and the cutting force is improved, and reliable assurance is provided for precisely and efficiently machining a spatial curved surface.

Description

Five side milling working process parameter methods for designing

Technical field

The invention belongs to CNC processing technology, relate in particular to curve five-shaft numerical control side milling job operation.

Background technology

Mill processing with respect to traditional point, five side milling working (machining) efficiencies generally decuple five points and mill processing, in five process of blade space-like curved surfaces such as aeromotor monoblock type impeller, large-scale spiral oar, particularly in roughing and the semi-finishing, five side milling processing modes mill processing than point remarkable advantages.

In five side milling processing, for efficient and Precision Machining part, at first to carry out process parameters design, comprise that cutter path planning, cutting force calculate and parameter optimization;

Cutter path planning is to generate the NC code by CAM business software or CAM free software, and the NC code comprises discrete reference point and generating tool axis vector discrete point, sees document " the practical study course of UG CAM ", (Ine U.S. writes, publishing house of Tsing-Hua University, 2003); Cutting force calculates, and generates continuous cutter path by the NC code earlier, obtains thickness of cutting by continuous cutter path, calculates cutting force according to cutting depth, feed rate and thickness of cutting again; Process parameter optimizing, be according to cutting force threshold value and the stable technological parameter of optimizing of process, see document " optimizing chosen axis " to maximizing Milling Process material removing rate under the no flutter with the radial cutting degree of depth, (Budak E.and Tekeli A., Maximizing chatter free material removal rate in milling through optimal selection of axial and radial depth of cut pairs.CIRP Annals-Manufacturing Technology, 54 (1): 353-356,2005);

Part processing precision, surface quality of workpieces and tool wear etc. all depend on the calculating of cutting force, cutting force in the calculating processing, be for the stressed design threshold that is no more than of tooling system in the process, and should guarantee the smooth change of cutting force, to reach the efficient and high precision of five side milling processing; Wherein thickness of cutting calculating is the key of calculating cutting force.

Existing five side milling transient state thickness of cutting computing method all are by discrete Tool in Cutting zone, distribute cutting load to realize, see document " the virtual five side millings processing of aircraft engine impeller, first: five side milling processing cutting force " (W.B.Ferry and Y.Altintas, 2008.Virtual Five-Axis Flank Milling of Jet Engine Impellers-Part I:Mechanics of Five Axis Flank Milling, Journal of Manufacturing Science and Engineering, Vol.130/011005:1-11), utilize cutter path and the technological parameter determined, with Tool in Cutting zone burst, calculate every feeding and thickness of cutting, and then calculate cutting force.But feeding and the thickness of cutting of this method supposition in every cutting zone fixed, do not consider in five side milling processes since the actual participation cutting that the variation of cutter path causes to load at every all be different, can not reflect real machining status, therefore five side milling transient state thicknesses of cutting and the five side milling cutting force that obtain are similar to.

The present invention is when calculating thickness of cutting, need to calculate cutter enveloping surface and instantaneous contact line, Zhu Limin etc., at document " utilizing ball family envelope theory to find the solution rotating tool scanning plane analytical expression " (Zhu, L.M.and Zhang, X.M.and Zheng, G.and Ding, H.2009, Analytical expression of the swept surface of a rotary cutter using the envelope theory of sphere congruence, Journal of Manufacturing Science and Engineering, 131/041017:1-7.2009) in the method for calculating the cutter enveloping surface is provided.Grandson family is wide etc., and the method for calculating curved surface and surfaces intersection is provided in document " computer graphics " (publishing house of Tsing-Hua University,, the 429th page-433 pages in 1998), calculates instantaneous contact line.

Summary of the invention

The invention provides a kind of five side milling working process parameter methods for designing, solve in the cutting force calculating of existing parameters design method, feeding and thickness of cutting in every cutting zone are fixed, the problem that can not reflect true machining status, with accurate calculating cutting force, for accurate, highly-efficient processing space curved surface provide reliable assurance.

Five side milling working process parameter methods for designing of the present invention, comprise cutter path planning step, cutting force calculation procedure and process parameter optimizing step, described cutter path planning step, generate the NC code by CAM business software or CAM free software, the NC code comprises discrete reference point and generating tool axis vector discrete point; Described cutting force calculation procedure generates continuous cutter path by the NC code earlier, obtains thickness of cutting by continuous cutter path, calculates cutting force according to cutting depth, feed rate and thickness of cutting again; Described process parameter optimizing step judges whether the cutting force calculate is not more than design threshold, be then with NC code, cutting depth and feed rate as input parameter, otherwise rotor tool path planning step regenerates the NC code; It is characterized in that:

Described cutting force calculation procedure comprises following substep:

(1) calculate cutter path: with the NC code, fit to continuous cutter path, cutter path is made up of reference point curve and generating tool axis vector curve;

(2) calculate the cutter enveloping surface: according to cutter path and concrete cutter geometrical calculation cutter enveloping surface, method by the calculating cutter enveloping surface analytical expression that provides in the document " utilizing ball family envelope theory to find the solution rotating tool scanning plane analytical expression ", obtain cutter enveloping surface analytical expression, described cutter is the geometric configuration and the size of cutter how much;

(3) calculate instantaneous contact line: by cutter enveloping surface analytical expression and workpiece blank how much, by the calculating curved surface and the method for surfaces intersection that provides in the document " computer graphics ", the calculating instantaneous contact line; Described workpiece blank is meant the geometric configuration and the size of workpiece blank entity for how much; Described instantaneous contact line is meant sometime, the actual contact curve of workpiece blank and cutter enveloping surface;

(4) calculate thickness of cutting: by the thickness of cutting of discrete point on the instantaneous contact line calculating osculatory, described thickness of cutting is meant that discrete point cuts the distance of corresponding intersection point on the preceding workpiece blank outline to this on the instantaneous contact line;

(5) calculate cutting force:,, calculate cutting force by the method for the calculating cutting force that provides in the document " the virtual five side millings processing of aircraft engine impeller, first: five side millings processing cutting force " by thickness of cutting, cutting depth and feed rate.

Described five side milling working process parameter methods for designing is characterized in that:

In the described substep (1), the reference point curve adopts the non-uniform rational b spline curve-fitting method, with the discrete reference point r in the NC code ₁, r ₂... r _i, r _M+1Fit to a reference point curve r (t), this curve is a nurbs curve, and wherein t is an independent variable, is time or distance;

In the described substep (1), the generating tool axis vector curve fitting process is as follows:

(1.1) find the solution hypercomplex number Q _i:

$Q_i=\sqrt{\frac{1}{2}(1+s_{\mathrm{ix}})}(\cos \mathrm{\&phi;}+l\sin \mathrm{\&phi;})(l+\frac{{\mathrm{<figure-callout\; id="1"\; label="s\; iy"\; filenames="110329111253.png"\; state="\{\{state\}\}">s</figure-callout>}}_{\mathrm{iy}}}{1+s_{\mathrm{ix}}}j+\frac{s_{\mathrm{iz}}}{1+s_{\mathrm{ix}}}k),i=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,m+1,$

Wherein, m+1 is the number of hypercomplex number, is natural number; φ is a l axle rotating freely for angles, s _iBe the generating tool axis vector discrete point in the NC code, s _Ix, s _IyAnd s _IzBe s _iThree components; L, j and k are respectively x, the vector of unit length of y and z axle:

s _i＝s _ixl+s _iyj+s _izk， $l=\left(\begin{array}{c}1\\ 0\\ 0\end{array}\right),$ $j=\left(\begin{array}{c}0\\ 1\\ 0\end{array}\right),$ $k=\left(\begin{array}{c}0\\ 0\\ 1\end{array}\right);$

(1.2) generate hypercomplex number curve Q (t):

For hypercomplex number point Q ₁, Q ₂..., Q _M+1, carry out interpolation by the method in the document " NURBS ", generate B é zier hypercomplex number curve

Wherein

Be B é zier reference mark,

Be Bornstein substrate polynomial expression;

(1.3) generate generating tool axis vector curve R (t):

Generating tool axis vector curve R (t) is expressed as:

R(t)＝Q(t)s ₁Q ^-1(t)；

In the formula, Q ^-1(t) be the contrary of Q (t), s ₁Be first generating tool axis vector discrete point in the NC code.Document " NURBS " is Piegl, and L.A.and Tiller, W. write in 1997, and (The NURBS book, Springer Verlag) become the master tool book of computer numerical control field.

1991, in the industrial products data exchange standard (STEP) of International Organization for Standardization promulgation, with the unique mathematical method of non-uniform rational b spline (NURBS, Non-Uniform Rational B-Splines) as definition industrial products geometric configuration.

Described five side milling working process parameter methods for designing is characterized in that:

Described substep (4) calculates thickness of cutting, and process is as follows:

(4.1) at first by document " infinitesimal geometry " provide etc. parametric method workpiece blank X is meshed into 9, calculate arbitrfary point p on the instantaneous contact line to the distance between each grid node, find minor increment d ₀Pairing nodes X ₀

(4.2) on workpiece blank X with nodes X ₀As initial point X _b, with d _oAs initial distance d _b, carry out process (4.3);

(4.3) calculate workpiece blank X at X _bThe section of point

To put p and project to the section

On, obtain intersection point p _b

(4.4) in the section

On get a p _B+1=X _b+ s (p _b-X _b), p will be put in constant s=0.005～0.01 _B+1Project on the workpiece blank X, obtain intersection point X _B+1, obtain a p to intersection point X _B+1Between apart from d _B+1

(4.5) judge whether | d _B+1-d _b|≤0.005mm is then with d _B+1Promptly, withdraw from calculating, otherwise turn over journey (4.6) as the thickness of cutting of arbitrfary point p;

(4.6) with X _B+1As initial point X _b, with d _B+1As initial distance d _b, turn over journey (4.3).

Document " infinitesimal geometry ": author's Mei Xiangming, Huang are respected it, and Higher Education Publishing House published in 1988.

Because the present invention has utilized the analytical expression of five side milling cutter enveloping surfaces, therefore reflected real machining status, with document " the virtual five side millings processing of aircraft engine impeller, first: five side milling processing cutting force " compare, the present invention considered actual participation cutting that the variation of cutter path causes to load at every all be different, therefore the transient state thickness of cutting that obtains is more accurate, thereby has improved the accuracy that the transient state thickness of cutting is calculated and cutting force calculates.

Description of drawings

Fig. 1 is a schematic flow sheet of the present invention;

Fig. 2 is the reference point curve;

Fig. 3 is the generating tool axis vector curve;

Fig. 4 is the discrete cutter spacing of the awl cutter of the embodiment of the invention;

Fig. 5 is five side milling enveloping surfaces of awl cutter of the embodiment of the invention;

Fig. 6 is cutter-workpiece blank instantaneous contact line;

Fig. 7 is that point on cutter-workpiece blank instantaneous contact line is to the distance of workpiece blank;

Fig. 8 be on the Tool in Cutting sword discrete point to the workpiece blank distance;

Fig. 9 is a cutting force change curve in time.

Embodiment

Below in conjunction with drawings and Examples the present invention is further described.

The workpiece blank that the embodiment of the invention adopted is No. 1050 aluminium alloys of long 200mm, wide 100mm, high 100mm, and the cutter that is adopted is commercial carbon steel four tooth millings awl cutter, and the lathe that is adopted is the Mikron600U machining center.

Embodiment of the invention flow process is seen Fig. 1, comprises the steps:

(1) cutter path planning: utilize commercial CAM software Unigraphics NX5Generate the NC code, input is: how much on cutter and surface geometry model; The cutter geological information is: four tooth millings awl cutter end diameter 6.25mm, the long 20mm of cutter, tapering 10 degree; The surface geometry model represents that with a ruled surface lead of ruled surface is made of two 3 B-spline curves, and the reference mark coordinate of two leads of ruled surface is as shown in table 1;

Two lead reference mark of table 1. ruled surface coordinate

X0, y0, z0 are respectively x, the y at base conductor reference mark, the coordinate of z direction, and x1, y1, z1 are respectively x, the y at top conductor line reference mark, the coordinate of z direction.

(2) cutting force calculates:

(2.1) calculate cutter path: CAM software output NC code; The NC code is fitted to continuous cutter path, and cutter path is made up of reference point curve and generating tool axis vector curve; The reference point curve adopts the non-uniform rational b spline curve-fitting method, with the discrete reference point r in the NC code ₁, r ₂... r _i, r _M+1Fit to a reference point curve r (t), as shown in Figure 2, indicate the Frenet coordinate of discrete reference point on the figure respectively.This curve is a nurbs curve, and wherein t is an independent variable, is time or distance; Method in the generating tool axis vector curve negotiating document " NURBS " is carried out interpolation, generates B é zier hypercomplex number curve R (t), as shown in Figure 3, indicates the Frenet coordinate of discrete generating tool axis vector reference point on the figure respectively.The reference mark coordinate of reference point curve r (t) and generating tool axis vector curve R (t) is as shown in table 2:

Table 2. reference point curve and generating tool axis vector curve controlled point coordinate

r x(mm)	r y(mm)	r z(mm)	l	j	k
						34.0682	2.3206	-0.6628	0	0	1.0000
27.8345	-7.7436	0.4715	0.1632	-0.1120	0.9802
						19.8372	-11.5360	0.6834	0.2247	-0.2610	0.9388
12.5479	-13.0996	0.1185	0.2490	-0.3939	0.8848
						4.5728	-15.4883	-0.2732	0.2813	-0.5381	0.7946
-3.6213	-21.4639	-0.8878	0.3482	-0.6540	0.6716
						-14.8317	-32.6353	0.6269	0.3897	-0.7911	0.4715

r _x, r _y, r _zBe respectively x, the y of reference point curve control point, the coordinate of z direction, l, j, k are respectively x, the y of generating tool axis vector curve control point, the coordinate of z direction.

(2.2) calculate the cutter enveloping surface: according to cutter path and concrete cutter geometrical calculation cutter enveloping surface, method by the calculating cutter enveloping surface analytical expression that provides in the document " utilizing ball family envelope theory to find the solution rotating tool scanning plane analytical expression ", obtain cutter enveloping surface analytical expression, continuous cutter path as shown in Figure 4, the cutter enveloping surface is as shown in Figure 5;

(2.3) calculate instantaneous contact line:, calculate instantaneous contact line by cutter enveloping surface analytical expression and workpiece blank how much; Instantaneous contact line as shown in Figure 6, cutter 1 is done five milling campaigns on workpiece blank 2, scanning forms enveloping surface 3, a certain moment of scanning process, cutter and workpiece blank engagement, formation instantaneous contact line 4 is shown in dot-and-dash line among the figure.

(2.4) calculate thickness of cutting: by the thickness of cutting of discrete point on the instantaneous contact line calculating osculatory, thickness of cutting as shown in Figure 7.

(2.4.1) at first by document " infinitesimal geometry " provide etc. parametric method workpiece blank X is meshed into 9, calculate arbitrfary point p on the instantaneous contact line to the distance between each grid node, find minor increment d ₀Pairing nodes X ₀

(2.4.2) on workpiece blank X with nodes X ₀As initial point X _b, with d ₀As initial distance d _b, carry out process (4.3);

(2.4.3) calculate workpiece blank X at X _bThe section of point

To put p and project to the section

On, obtain intersection point p _b

(2.4.4) in the section

On get a p _B+1=X _b+ s (p _b-X _b), p will be put in constant s=0.005～0.01 _B+1Project on the workpiece blank X, obtain intersection point X _B+1, obtain a p to intersection point X _B+1Between apart from d _B+1

(2.4.5) judge whether | d _B+1-d _b|≤0.005mm is then with d _B+1Promptly, withdraw from calculating, otherwise turn over journey (4.6) as the thickness of cutting of arbitrfary point p;

(2.4.6) with X _B+1As initial point X _b, with d _B+1As initial distance d _b, turn over journey (4.3).

Press as above step, can calculate on the cutter bar cutting edge discrete point to workpiece blank distance 5, as shown in Figure 8, the longitudinal axis is represented tool length among the figure, transverse axis is represented thickness of cutting, the distance of corresponding intersection point on the workpiece blank outline before just discrete point cuts to this on the cutting edge.

(2.5) calculate cutting force: by thickness of cutting, cutting depth and feed rate, given cutting depth is 0.02mm, and feed rate per tooth 0.01mm calculates cutting force, and change curve is as shown in Figure 9 in time for cutting force.

(3) process parameter optimizing: the cutting force and the cutting force design threshold that calculate are compared, if the cutting force that calculates is greater than the cutting force design threshold, then return and revise the NC code, if the cutting force that calculates is not more than the cutting force design threshold, then carry out side milling processing, in example of the present invention, the cutting force design threshold is 500 newton, and the maximum cutting force that calculates is 52.50 newton, less than the cutting force design threshold, therefore given NC code, cutting depth and feed rate is reasonably, can be used for actual side milling processing.

Side milling adds man-hour, carries out postposition earlier and handles: the NC code is carried out postposition handle, obtain G code, this code can be by the contained digital control system identification of Mikron600U machining center; Carry out side milling processing again: workpiece blank is installed on the anchor clamps, adopts carbon steel four tooth millings awl cutter, carry out side milling processing, obtain shaping workpiece by given G code.

Claims (3)

1. one kind five side milling working process parameter methods for designing, comprise cutter path planning step, cutting force calculation procedure and process parameter optimizing step, described cutter path planning step, generate the NC code by CAM business software or CAM free software, the NC code comprises discrete reference point and generating tool axis vector discrete point; Described cutting force calculation procedure generates continuous cutter path by the NC code earlier, obtains thickness of cutting by continuous cutter path, calculates cutting force according to cutting depth, feed rate and thickness of cutting again; Described process parameter optimizing step judges whether the cutting force calculate is not more than design threshold, be then with NC code, cutting depth and feed rate as input parameter, otherwise rotor tool path planning step regenerates the NC code; It is characterized in that:

Described cutting force calculation procedure comprises following substep:

(1) calculate cutter path: with the NC code, fit to continuous cutter path, cutter path is made up of reference point curve and generating tool axis vector curve;

(2) calculate the cutter enveloping surface: according to cutter path and concrete cutter geometrical calculation cutter enveloping surface, method by the calculating cutter enveloping surface analytical expression that provides in the document " utilizing ball family envelope theory to find the solution rotating tool scanning plane analytical expression ", obtain cutter enveloping surface analytical expression, described cutter is the geometric configuration and the size of cutter how much;

(3) calculate instantaneous contact line: by cutter enveloping surface analytical expression and workpiece blank how much, by the calculating curved surface and the method for surfaces intersection that provides in the document " computer graphics ", the calculating instantaneous contact line; Described workpiece blank is meant the geometric configuration and the size of workpiece blank entity for how much; Described instantaneous contact line is meant sometime, the actual contact curve of workpiece blank and cutter enveloping surface;

(4) calculate thickness of cutting: by the thickness of cutting of discrete point on the instantaneous contact line calculating osculatory, described thickness of cutting is meant that discrete point cuts the distance of corresponding intersection point on the preceding workpiece blank outline to this on the instantaneous contact line;

(5) calculate cutting force:,, calculate cutting force by the method for the calculating cutting force that provides in the document " the virtual five side millings processing of aircraft engine impeller, first: five side millings processing cutting force " by thickness of cutting, cutting depth and feed rate.

2. five side milling working process parameter methods for designing as claimed in claim 1 is characterized in that:

In the described substep (1), the reference point curve adopts the non-uniform rational b spline curve-fitting method, with the discrete reference point r in the NC code ₁, r ₂... r _i, r _M+1Fit to a reference point curve r (t), this curve is a nurbs curve, and wherein t is an independent variable, is time or distance;

In the described substep (1), the generating tool axis vector curve fitting process is as follows:

(1.1) find the solution hypercomplex number Q _i:

$Q_i=\sqrt{\frac{1}{2}(1+p_{\mathrm{ix}})}(\cos \mathrm{\&phi;}+l\sin \mathrm{\&phi;})(l+\frac{p_{\mathrm{iy}}}{1+p_{\mathrm{ix}}}j+\frac{p_{\mathrm{iz}}}{1+p_{\mathrm{ix}}}k),i=\mathrm{1,2},\&CenterDot;\&CenterDot;\&CenterDot;,m+1,$

Wherein, m+1 is the number of hypercomplex number, is natural number; φ is a l axle rotating freely for angles, p _iBe the generating tool axis vector discrete point in the NC code, p _Ix, p _IyAnd p _IzBe p _iThree components; L, j and k are respectively x, the vector of unit length of y and z axle:

p _i＝p _ixl+p _iyj+p _izk， $l=\left(\begin{array}{c}1\\ 0\\ 0\end{array}\right),$ $j=\left(\begin{array}{c}0\\ 1\\ 0\end{array}\right),$ $k=\left(\begin{array}{c}0\\ 0\\ 1\end{array}\right);$

(1.2) generate hypercomplex number curve Q (t): for hypercomplex number point Q ₁, Q ₂..., Q _M+1, carry out interpolation by the method in the document " NURBS ", generate B é zier hypercomplex number curve

Wherein

Be B é zier reference mark,

Be Bornstein substrate polynomial expression;

(1.3) generate generating tool axis vector curve R (t):

Generating tool axis vector curve R (t) is expressed as:

R(t)＝Q(t)p ₁Q ^-1(t)；

In the formula, Q ^-1(t) be the contrary of Q (t), p ₁Be first generating tool axis vector discrete point in the NC code.

3. five side milling working process parameter methods for designing as claimed in claim 1 is characterized in that:

Described substep (4) calculates thickness of cutting, and process is as follows:

(4.1) at first by document " infinitesimal geometry " provide etc. parametric method workpiece blank X is meshed into 9, calculate arbitrfary point p on the instantaneous contact line to the distance between each grid node, find minor increment d ₀Pairing nodes X ₀

(4.2) on workpiece blank X with nodes X ₀As initial point X _b, with d _oAs initial distance d _b, carry out process (4.3);

(4.3) calculate workpiece blank X at X _bThe section of point

To put p and project to the section On, obtain intersection point p _b

(4.4) in the section

On get a p _B+1=X _b+ s (p _b-X _b), p will be put in constant s=0.005～0.01 _B+1Project on the workpiece blank X, obtain intersection point X _B+1, obtain a p to intersection point X _B+1Between apart from d _B+1

(4.5) judge whether | d _B+1-d _b|≤0.005mm is then with d _B+1Promptly, withdraw from calculating, otherwise turn over journey (4.6) as the thickness of cutting of arbitrfary point p;

(4.6) with X _B+1As initial point X _b, with d _B+1As initial distance d _b, turn over journey (4.3).

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