Classifications

• • 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
  • B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by any single one of main groups B23K1/00 - B23K28/00
  • B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by any single one of main groups B23K1/00 - B23K28/00 relating to soldering or welding
• • 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
  • B23K9/00—Arc welding or cutting
  • B23K9/10—Other electric circuits therefor; Protective circuits; Remote controls
  • B23K9/1006—Power supply
  • B23K9/1043—Power supply characterised by the electric circuit
  • B23K9/1056—Power supply characterised by the electric circuit by using digital means
  • B23K9/1062—Power supply characterised by the electric circuit by using digital means with computing means

Definitions

• the invention relates to a method for determining the shape of a liquid metal melt occurring during the implementation of a method of welding a first part and a second part.
• the direct method is to attempt to solve the problem of heat transfer in the two parts of welded structure, the melted part and the solid part. To do this, we must resolve the Navier equations Stored in the liquid, the energy conservation equations taking into account the interaction between the energy arc and the part, the interaction between the liquid part and the solid part, and the equations of the transfer of heat in the solid.
• the equivalent source method consists of giving a priori a form of the energy source and then solving a problem of nonlinear conduction of heat in the parts to be assembled.
• the parameters of this source of energy are identified by an inverse problem from the temperature measured in the solid and the macrography of the welding bath (cf ref [2] or ref [3]).
• This method provides access to the thermal loading of the welding process but:
• the present invention relates to a method for determining the shape of a melt which overcomes these disadvantages.
• This process is characterized by the following steps: a) a welding method is chosen; b) a two-dimensional or three-dimensional virtual bath shape is chosen according to the welding method chosen in step (a); c) model the shape of the virtual melt by a mathematical function that contains parameters to identify; d) calculating the temperature field in a virtual solid surrounding the melt by imposing boundary conditions; e) making a real copy of the first and second pieces; f) they are welded using the process chosen in step (a), which reveals a real melt and solid zone; g) measuring the temperature in M points of the real solid zone, M being at least equal to the number of parameters to be identified; h) comparing the temperatures measured in step (g) with the calculated temperatures at the same points in step (d) by calculating the function
• the mathematical function that contains parameters to be identified is a Bezier curve or surface.
• the mathematical function that contains parameters to be identified is a Bézier surface defined by the equation: mn TYl Tl
• step (j) the Levenberg-Marquardt algorithm is used to choose another form of virtual bath.
• step (d) the temperature field is calculated in a virtual solid surrounding the melt by solving the following equation system: dT s (x, y) r -, hp
• T (x, y) T f (x, y) eF (3)
• step (d) the temperature field is calculated in a virtual solid surrounding the melt by solving the following equation system:
• the welding process is chosen from the group comprising TIG, MIG / MAG, electron beam, plasma, laser, hybrid welding processes.
• the degree of the Bézier curve is equal to 3 or 4 in 2D and the degree of the Bézier surface is between 2x3 and 4x3 in 3D.
• Figure 1 illustrates a Bezier curve with four control points
• Figure 2 is a macrography of a non-debonding melt
• FIG. 3 is a view of a curve of
• FIG. 5 is a view of a curve of
• FIG. 6 is a diagram illustrating an example of a two-dimensional melt
• Figures 7 to 9 are three Bézier curves of degree 4 (of order 5)
• Fig. 10 is a diagram of the welding process
• FIG. 11 is a diagram of the spatial domain in 2D case
• Figure 12 is a diagram of the spatial domain in 3D case
• Figure 13 illustrates the Bezier surface of degree 3x2 with its control points
• Figure 14 illustrates the temperature field calculated in 3D case.
• the shape of the bath is parameterized with a Bézier curve of degree n (or a Bézier surface of degree m ⁇ n).
• the classical definition of Bézier curves and surfaces is based on the family of Bernstein polynomials. These polynomials were used by Bernstein for the polynomial approximation of functions. They are used in the description of the Bézier model by the definition points named also Bézier points or "points of control".
• the Bezier curve with four control points is then formulated as follows:
• This curve passes through the points Po (x0, y0) and P3 (x3, y3). Its tangent to these points is the line connecting Po (xO, yO) to Pi (xl, yl) and the connecting line
• FIG. 2 shows a macrography of the fusion front of a non-emergent weld and in FIG. 3 the parametrization of this fusion front by a Bezier curve of degree 3.
• FIG. 4 shows the macrography of the melting front of an open weld and in FIG. 5 the parametrization of this fusion front by another Bezier curve of degree 3.
• FIG. 3 shows a macrography of the melting front of an open weld and in FIG. 5 the parametrization of this fusion front by another Bezier curve of degree 3.
• FIG. 3 shows only half of the fusion front has been shown.
• FIGS. 7 to 9 show Bezier curves of order 5.
• a parametric surface is the extension of the parametric curve in which we have two parameters u and v which each vary in [0,1].
• P (u, v) passes through all points on the Bézier surface.
• P 13 is the control point
• mxn is the degree of the Bézier surface
• the surface is continuous in the convex envelope of polygon P 00 , P 0n , P m0 , P mn . "The control of the surface is global. • The Bezier surface is independent of the axis system to which it is attached.
• melts can be configured in three dimensions.
• the fusion front F is interpreted by the coordinates of the control points.
• F (P 0 , Pi ..., PN) where N is the number of parameters to identify.
• M M measuring points to identify N parameters, then M ⁇ N.
• F (P 0 , Pi ..., P N ) is known, the temperature field in the solid T (F) can be obtained by solving the heat transfer problem. It also means that the temperature field changes when we modify the shape of F (P 0 , Pi, ..., P N ).
• coefficient of sensitivity ie the derivative of the temperature in relation to the parameters to be identified
• the sensitivity matrix is defined as follows:
• T 1 T 0 + [(J (T 0) YJ (T 0) + (P 0 Q 0 Y (J (T 0) Y [YT (T 0)]
• ⁇ o is a positive scalar appointed damping parameter
• ⁇ o is a diagonal matrix
• the objective of the term ⁇ o ⁇ o is to dampen the oscillations and instabilities due to the misplaced nature of the problem.
• the damping parameter ⁇ o is chosen large at the beginning of the iterative procedure (the method is then close to the method of the steepest slope) then, is reduced when one approaches the solution (the method joins the method of Gauss).
• Example 1 two-dimensional fusion front. It is desired to weld two plates 2.4 end to end. Each of the plates has a width L y , a length 2L x and a thickness e.
• a torch 6 generates an electric arc having sufficient intensity to melt the metal and form a melt 8. It travels with a constant speed u along the x-axis on the edge of the two plates 2 and 4.
• the bath 8 melting zone is moved at the same speed as the torch 6.
• a melting zone 10 is formed behind the displacement of the melt 8.
• the objective is to find by the inverse method the shape of the bath and the temperature field in the solid region with the minimum of parameters to identify.
• the thermal field in the solid is determined by considering the temperature imposed on the liquid-solid interface, equal to the melting temperature T f .
• This curve is based on four control points Po, Pi, P2 and P3 (that is to say eight coordinates in two-dimensional case), and has the formula:
• X to identify remains limited.
• some coordinates of the control points may be constrained a priori by the physical nature of the problem.
• T (x, y) T f (x, y) eT (3)
• the temperature field T (x, y; F) in the solid is accessed for the form of the melt of step 1.
• the temperature Y m in the solid is measured in a number of M measuring points 12 at least equal to the number of parameters to be identified (3 as we have seen above).
• M 5 is chosen (ie 5 temperature measurements are made using a single thermocouple). Only one thermocouple is needed to have multiple measurement points. In quasi stationary, the different positions x m correspond to different recording times x m -uxt m , therefore, one can have several measurement points using a single thermocouple.
• Example 2 3D case opening. As in the case of the two-dimensional example, it is desired to weld two plates end to end.
• Each of the plates has a width L y , a length 2L x and a thickness e (see Figure 12).
• the problem is physically defined as follows: an electric arc of sufficient intensity moves with a constant speed along the x-axis and is applied to the edge of two metal plates. A melt is formed and moves at the same speed as the electric arc.
• the assumptions made to define this problem are as follows: • At torch speed u constant, the transfers are non-stationary in a reference linked to the plate. However, by using a reference linked to the torch, a quasi-steady state is obtained: the shape of the molten bath remains constant in this frame while the material enters and leaves the field of study. The mobile repository of the torch is therefore used for the analysis of the inverse problem.
• the shape of the liquid-solid interface F is parameterized by a Bézier surface.
• the thermal field in the solid is determined by considering the temperature imposed on the liquid-solid interface, equal to the melting temperature T f .
• Step 1
• T (x, y, z) T f in (x, y, z) eT (5)
• S is the area of the section of the room and its perimeter Adiabatic conditions (2) are considered on the edges of the computational domain without loss of generality.
• the temperature is imposed (5)
• the temperature field T (x, y, z; F) in the solid is accessed for the melt form of step 1.
• This estimated field is represented in FIG. 14.
• thermocouples the temperature Y m in the solid in a number of points M at least equal to the number of parameters to be identified (9 as has been seen above) .
• M 10 is chosen (ie 10 temperature measurements are made using a single thermocouple). Only one thermocouple is needed to have multiple measurement points. In quasi stationary, the different positions xm correspond to different recording times x m -uxt m , therefore, one can have several measurement points using a single thermocouple.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Theoretical Computer Science (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Arc Welding In General (AREA)

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• 2006
  • 2006-03-17 FR FR0650935A patent/FR2898530B1/fr not_active Expired - Fee Related
• 2007
  • 2007-03-16 EP EP07712534A patent/EP1996367A1/de not_active Withdrawn
  • 2007-03-16 WO PCT/EP2007/052488 patent/WO2007107504A1/fr not_active Ceased

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