CN112059386B - Method for controlling fuse deposition molten pool state - Google Patents

Method for controlling fuse deposition molten pool state Download PDF

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CN112059386B
CN112059386B CN202010938168.2A CN202010938168A CN112059386B CN 112059386 B CN112059386 B CN 112059386B CN 202010938168 A CN202010938168 A CN 202010938168A CN 112059386 B CN112059386 B CN 112059386B
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arc
temperature
molten pool
temperature area
winding
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CN112059386A (en
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洪波
林健
熊昊
向垂悦
刘锦
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Xiangtan University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K10/00—Welding or cutting by means of a plasma
    • B23K10/02—Plasma welding
    • B23K10/027—Welding for purposes other than joining, e.g. build-up welding

Abstract

The invention discloses a method for controlling the state of a fuse wire deposition molten pool, which can be applied to the additive manufacturing of magnetic control plasma welding, and has the advantages of improving the internal thermal circulation of the molten pool, reducing the heat accumulation in the welding process, preventing the cladding layer from collapsing, avoiding the uneven structure, ensuring the hardness andmolding quality and the like; the technical scheme is as follows: for area greater than preset minimum threshold S0The high-temperature region of (2) is classified: the high-temperature area with a regular shape directly takes the outer contour line as a path, and the arc oscillation is controlled by a magnetic field to avoid the winding of the high-temperature area; the high-temperature area with the irregular shape is segmented by adopting a fuzzy partitioning method and then is avoided winding along the non-intersecting part contour as a path; for minimum distances less than a preset minimum threshold L0The adaptive curvature radius is adopted in the plurality of high-temperature areas, and the arc transition mode is adopted to avoid winding according to the outline, so that the phenomenon that the electric arc lingers in the dense outline for a long time to cause heat accumulation is avoided.

Description

Method for controlling fuse deposition molten pool state
Technical Field
The invention relates to the field of magnetic control plasma arc fuse wire additive manufacturing, in particular to a method for controlling the state of a fuse wire deposition molten pool.
Background
Additive manufacturing is an advanced manufacturing technology developed in the middle of the 80's of the 20 th century, and the technology directly manufactures solid parts by adopting a method of material layer-by-layer accumulation according to three-dimensional model data of the parts by taking laser, electron beams, electric arcs and the like as heat sources. According to different specific forming processes, selective laser Sintering (SLM), Laser Melting Deposition (LMD), Plasma Arc Additive Manufacturing (PAAM), cold metal transition forming (CMT), selective electron beam melting (EBSM), and the like are common. Compared with the traditional machining technology, the metal additive manufacturing can reduce the working procedures, shorten the manufacturing period and save raw materials, is a new near-net-shape manufacturing method and has remarkable advantages for manufacturing complex structural parts.
In the additive manufacturing process, the control of the interlayer temperature has a crucial influence on the welding quality and the forming condition. The heat can constantly produce, spread along with the increase of the welding number of piles in welding process, and different figurative components can have different heat accumulation effects at the in-process that takes shape, after the heat accumulation to certain degree, appear that the tissue is inhomogeneous, the tissue is thick and serious composition segregation, and cladding layer edge can take place phenomenons such as collapse, can influence the manufacturing accuracy and the product quality of additive manufacturing.
Wanyuwei et al, a national energy-based wall power plant, proposes to control the magnitude of the arc welding thermal efficiency η by adjusting the welding current and the arc voltage, and at the same time, to control the welding speed and the like to control the heat input during the welding process. However, the adjustment of current and voltage may not only control the heat input but also have adverse effects on the welding quality, and may cause defects such as too narrow a melt width and insufficient melt depth, and the voltage and current cannot be modified in real time in the additive manufacturing process.
Chinese patent CN108907188 discloses a temperature control device for additive manufacturing and a control method thereof, wherein a front preheating component is arranged at the front end of a printing head, and a rear cooling component is arranged at the rear end of the printing head, so that the phenomena of uneven structure and the like of a formed part due to large temperature difference are reduced, the formed part can be rapidly cooled by cooling gas after printing is finished, and the situation that the formed part is oxidized by ambient air due to high temperature is avoided. However, the essence of the invention is that only a preheating device and a cooling part are additionally arranged, and the cooling part adopts a traditional external cooling mode of cooling by cooling gas, so that the temperature can not be adjusted from the inside, and the heat circulation in the molten pool is not improved.
Based on the defects, the invention designs the method for controlling the state of the fuse wire deposition molten pool in order to effectively solve the problems of poor heat dissipation condition of the molten pool, collapse, reduced hardness, poor molding quality and the like caused by heat accumulation in the process of additive manufacturing of the magnetic control plasma fuse wire. The method controls the swing of the magnetic field by identifying and classifying the high-temperature area of the molten pool, improves the thermal cycle of the molten pool, prevents heat accumulation and ensures the consistency of hardness and forming quality.
Disclosure of Invention
The invention provides a method for controlling the state of a fuse wire deposition molten pool, which solves the problems that a cladding layer collapses, the local structure is thick and hard, the molding quality is poor and the like due to local heat accumulation caused by uneven heat distribution in the cladding process.
The technical scheme adopted by the invention aiming at the problems is as follows: firstly, a high temperature threshold value T is set according to the welding process1And a minimum radius R of a high temperature region0The infrared scanning temperature measuring instrument carries out real-time scanning temperature measurement on the molten pool, and the temperature is higher than the temperature measured by the infrared scanning temperature measuring instrumentT1Is punctuated and noted as { A1,A2,., Ax }, automatically establishing a plane rectangular coordinate system, and projecting the scanned high-temperature region boundary into the coordinate system.
Carrying out data preprocessing on the boundary of the high-temperature area, firstly carrying out smooth processing to eliminate sharp inflection points, and secondly carrying out data preprocessing on the boundary of the high-temperature area when the curvature radius is smaller than a preset minimum value RMINThe positions and the positions with complex shapes are subjected to fuzzy processing, namely, one or more sections of circular arcs with large curvature radius are used for replacing, and the boundary curve after pretreatment is subjected to least square fitting. The high temperature region is divided into two types according to the shape: the shape is regular and approximately circular and irregular; judging the high-temperature area by least square fitting, and presetting a fitting time threshold N and a fitting minimum distance threshold L0If the fitting result is less than the fitting minimum distance threshold L0And if the fitting times are less than N, the shape is judged to be regular and approximate to a circle, and if the fitting times are more than N, the shape is judged to be irregular.
Utilizing a least square method to fit out the boundary of the high-temperature area, calculating the centroid and taking the average value R of the maximum radius and the minimum radiusXThe radius of the high temperature region is smaller than R if there is a high temperature point0Discarding the high temperature region; radius greater than R for region0Is represented by RXMake a circle O for the radiusXAnd the first point of intersection of the circle and the welding track is F, the original swing track and the winding-avoiding track of the electric arc are processed through a computer, the winding-avoiding track is converted into the frequency and the amplitude of alternating current, the frequency and the amplitude of an excitation power supply are adjusted from the point F, and the transverse magnetic field swing in the XY direction in the horizontal plane is controlled to synthesize the arc-shaped swing of the electric arc, so that the electric arc bypasses a high-temperature area.
And carrying out fuzzy partition processing on the high-temperature area with an irregular shape, selecting one or more simple regular graphs with similar shapes for substitution according to the fitting result of the Nth time, and further abandoning dead corners or small areas left after division, so that a plurality of tangent or intersected high-temperature areas with regular shapes can be obtained, controlling a magnetic field to enable the electric arc to avoid winding according to the track of the non-intersected part, and carrying out transition in a mode of circular arc transition (the minimum transition radius is preset in advance) at the tangent and intersected positions, so that the phenomenon that the electric arc lingers in the dense contour position for too long time to cause excessive heat input can be avoided, and the accuracy requirement on electric arc control is reduced.
When the distribution of a plurality of high-temperature areas is close, the minimum distance judgment is carried out along the swing track of the electric arc, and if the minimum distance is smaller than a preset value L1And determining the transition curvature radius of the arc transition according to the curvature radius of the intersection point of the contour and the swing track according to the intersection processing, and performing the transition in an arc transition mode, so that the heat input can be reduced, the swing stroke of the electric arc can be reduced, the efficiency is improved, and the requirement on the swing precision of the electric arc can be reduced. If the distance is greater than the preset value L1And performing detour according to the original contour track, and performing rounding treatment at the intersection of the contour and the swing track.
Drawings
FIG. 1 is a flow chart of bypass of a single high temperature zone
FIG. 2 is a flow chart of bypass of multiple high temperature zones
FIG. 3 is a schematic view of the outline processing of the high temperature region with regular shape
FIG. 4 is a schematic view of the outline processing of the irregularly shaped high-temperature region
FIG. 5 is a schematic diagram of a plurality of adjacent or tangent high temperature zone bypass paths
Detailed description of the preferred embodiment
The invention provides a method for controlling the state of a fuse wire deposition molten pool, which solves the problems that a cladding layer collapses, the local structure is thick and hard, the molding quality is poor and the like due to local heat accumulation caused by uneven heat distribution in the cladding process.
Example 1: referring to fig. 1 and 3, the technical solution adopted by the present invention to solve the above problems is as follows: firstly, a high temperature threshold value T is set according to the welding process1And a minimum radius R of a high temperature region0And minimum area S of high temperature regionMINAccording to the temperature measurement result of real-time scanning of the infrared scanning thermometer on the molten pool, for the temperature higher than T1Position ofPut and punctuate the analysis and mark as { A1,A2,...,AXAnd automatically establishing a plane rectangular coordinate system by the central processing unit, and projecting the scanned boundary line of the high-temperature area into the coordinate system.
Performing data preprocessing on the boundary of the high-temperature region, firstly performing smooth processing, identifying sharp inflection points by images, eliminating the sharp inflection points, and respectively spacing a distance C in a plane rectangular coordinate system0And (presetting) straight lines parallel to the X axis and the Y axis, wherein the straight lines and the contour line of the high-temperature region have intersection points, and when the number of the intersection points on each straight line is more than or equal to 3, the rest points except the first and the last points are judged to be positions with complex shapes. Presetting a minimum value R of the curvature radius according to actual process requirementsMIN，
Figure GDA0002756488140000041
S is the arc length of the fixed point on the curve, alpha is the tangential angle, K is the curvature,
for positions R with radius of curvature smaller thanMINAnd the position with a complex shape adopts a fuzzy processing method, namely, one or more sections of circular arcs with large curvature radius are used for replacing, and the boundary curve after pretreatment is fitted by adopting a curve fitting method of closed discrete points.
The fitting function is expressed as follows:
Figure GDA0002756488140000042
in the formula: a (x) ═ a1(x),a2(x),…,am(x))TIs a coefficient vector;
p(x)＝(p1(x),p2(x),…,pm(x))Tfor the basis functions, polynomial bases are typically chosen.
Linear base: p (x) ═ (1, x, y)T,m＝3
Secondary group: p (x) ═ 1, x, y, x2,xy,y2)T,m＝6
Defining an approximation functionDiscrete weighting L of2Norm is:
Figure GDA0002756488140000043
the matrix form is:
J＝(pa(x)-u)TW(x)(pa(x)-u)
in the formula: u ═ u (x)1),u(x2),…u(xN))T
Figure GDA0002756488140000044
W(x)＝diag(ω1(s),ω2(s),…,ωN(s))
Figure GDA0002756488140000045
Based on the principle of least square, the method comprises the following steps:
a(x)＝A-1(x)B(x)u
A(x)＝PTW(x)P,B(x)＝PTW(x)
the fitting process defines X between two adjacent discrete points Xi and Xi +1, takes one point (X _ val, y _ val) on a straight line passing through two points, makes X _ val equal to X, and supports the weight ω (s (X _ val) of each point in the domaini) Determined by the distance of the point to each point, and:
Figure GDA0002756488140000051
in the formula: i, j ═ 1, 2, …, N, k > 1.
Or
Figure GDA0002756488140000052
Figure GDA0002756488140000053
In the formula: α is 0.5.
The high-temperature area is divided into two types according to the shape, namely the shape is regular and approximately circular and the shape is irregular: judging the high-temperature area by using the fitting result, and presetting a fitting time threshold N and a fitting minimum distance threshold L0If the fitting result is less than the fitting minimum distance threshold L0And if the fitting times are less than N, the shape is judged to be regular and approximate to a circle, and if the fitting times are more than N, the shape is judged to be irregular.
Calculating the centroid of the boundary curve of the high temperature region and taking the average value R of the maximum radius and the minimum radiusXThe radius of the high temperature region is less than or equal to R if there is one0Discarding the high temperature region; radius greater than R for region0Is represented by RXMake a circle O for the radiusXAnd the first point of intersection of the circle and the welding track is F, the original swing track and the winding-avoiding track of the electric arc are processed through a computer, the winding-avoiding track is converted into the frequency and the amplitude of alternating current, the frequency and the amplitude of an excitation power supply are adjusted from the point F, and the XY-direction magnetic field swing in the horizontal plane is controlled to synthesize the arc-shaped swing of the electric arc, so that the electric arc bypasses the high-temperature area.
Excitation power supply output frequency
Figure GDA0002756488140000054
IINIs the pin current, and C is the pin-connected capacitance.
The specific output voltage is
Figure GDA0002756488140000061
VOUTFor outputting an analog voltage, V, of the D/A conversion chipREFS1 is the converted value of the digital frequency obtained by the cpu (range Ox 000-OxFFF),
Figure GDA0002756488140000062
Figure GDA0002756488140000063
and F is the value of the digital frequency obtained by the central processing unit.
Fy＝Isinα·cosβ
F'y＝Icosα·Bsinβ
F1＝K1Iey
Taking current I at any place of the arc, then IX，IZThe components of the magnetic field B in the transverse and axial directions, respectively, are also decomposed into BX，IZForms an angle of alpha with I, BZForming an angle beta with B. The axial force of the magnetic field received by the unit arc column is FYAnd a transverse force of FY’，K1Denotes the coefficient of restorability, eyRepresenting the length of the lateral excursion of the arc end, with an aerodynamic drag of FS
Fy+F'y＝FS+F1
Namely, it is
Figure GDA0002756488140000064
Example 2: referring to fig. 1 and 4, for a high-temperature area with an irregular shape, fuzzy partition processing is performed, one or more simple regular graphs with similar shapes are selected for substitution according to the fitting result of the Nth time, and further, some dead corners or the remaining area after segmentation is smaller than a preset value SMINThe narrow area is abandoned, so that a plurality of tangent or intersected high-temperature areas with regular shapes can be obtained, the magnetic field is controlled to enable the electric arc to avoid winding according to the track of the non-intersected part, and arc transition (the minimum transition radius is preset in advance) is adopted at the tangent and intersected positions to carry out transition, so that excessive heat input caused by overlong time when the electric arc wanders at the dense contour position can be avoided, and the accuracy requirement on electric arc control is lowered.
Example 3: referring to fig. 2 and 5, when the distribution of the high-temperature areas is similar, the minimum distance is judged along the swing track of the arc, and if the minimum distance is smaller than a preset value L0And determining the transition curvature radius of the transition arc according to the curvature radius of the intersection point of the contour and the swing track according to intersection processing, and performing transition in an arc transition mode, so that the heat input can be reduced, the swing stroke of the electric arc can be reduced, the efficiency is improved, and the requirement on the swing precision of the electric arc can be reduced. If the distance is greater than the preset value L0And performing detour according to the original contour track, and performing rounding treatment at the intersection of the contour and the swing track.
The above description is only a few specific embodiments of the present invention, and it is obvious that modifications or specific substitutions by anyone skilled in the art under the technical scheme of the present invention are included in the scope of the present invention defined by the claims.

Claims (1)

1. A method for controlling the state of a fuse wire deposition molten pool is characterized in that in the process of magnetic control plasma arc fuse wire additive manufacturing, a high-temperature area is prevented from being wound by controlling a magnetic field adaptive swing electric arc, the heat distribution is controlled, the internal heat circulation of the molten pool is improved, the defects of collapse, thick local structure and reduced hardness of the edge of a cladding layer due to heat accumulation are prevented, and the forming quality in the process of additive manufacturing is improved. The method is characterized in that the heat distribution is controlled by the magnetic field adaptive swing electric arc, an infrared scanning temperature measuring instrument carries out real-time scanning temperature measurement on a molten pool, and a temperature threshold value T is preset1For higher than T1And the position with regular shape, calculating the centroid and taking the centroid as the center of a circle, taking the average Rx of the maximum radius and the minimum radius as the radius of the circle as a high-temperature area, taking the first point of the intersection of the high-temperature area and the arc swinging track as F, controlling the magnetic field to swing transversely and longitudinally from the F point to synthesize arc-shaped swinging, so that the arc bypasses the high-temperature area, adopting a fuzzy partition method to process the high-temperature area with irregular shape, dividing the complex shape into a plurality of simple geometric figures with regular shape, and swinging the arc according to the outline of the non-overlapped part to avoid the winding. When the positions of a plurality of high-temperature areas are distributed similarly and irregularly, the electric arc is subjected toPlanning the swinging path if there is no intersection between the high temperature region circles and the shortest distance along the arc swinging direction is greater than the preset minimum value L0When the arc is not wound, arc winding is carried out in a high-temperature area according to the original swing track; if the distance between the high temperature regions is less than L0Or when the arc is intersected and tangent, avoiding winding according to the arc of the non-intersected part, and adopting arc smoothing treatment at the intersection point or tangent point to reduce excessive heat input caused by long time of wandering the arc at the dense outline position.
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