FR3017473A1 - ESTIMATION OF A SIZE RELATING TO A PROCESS FOR MANUFACTURING A PIECE BY INJECTING MATERIAL - Google Patents

Abstract

The invention relates to a method for estimating a quantity relating to a method for manufacturing a part by injecting material from an injection point, the quantity to be estimated being chosen from an injection time and a pressure. injection. This method comprises a step of obtaining (30) a geometrical representation of the part by a mesh defined by points having first geometric coordinates associated with a first reference, followed by a step of converting (36) the first coordinates. geometric coordinates in second coordinates relative to the quantity to be estimated, associated with a second reference frame, as a function of local physical characteristics associated with said mesh. Then, a calculation (38), in the second frame of reference, using a shorter path algorithm, of the maximum distance between the second coordinate corresponding to the injection point and a second coordinate corresponding to another point of the part, and an estimate (40) as a function of the calculated maximum distance, of said quantity to be estimated are implemented. It also relates to a method of selecting a method for manufacturing a part by injection of material from an injection point, among at least two such separate manufacturing processes.

Description

The present invention relates to a method for estimating a quantity relating to a process for manufacturing a part by injecting material from a point. injection.

It is located in the field of the manufacture of composite material parts comprising an injection of material. The invention applies in particular in the field of the manufacture of parts made of fiber-reinforced composite material, for example glass or carbon, by resin injection, known by the acronym RTM (for Resin Transfer Molding). It can also be used for other resin injection processes. The composite material parts are used increasingly in various industrial fields, because they have good mechanical properties while being lighter, with equivalent properties, as steel or aluminum parts for example.

In particular, in the field of the automotive industry, it is particularly advantageous to use such parts which have mechanical properties comparable to those of steel while being much lighter, which ultimately makes it possible to produce lighter vehicles with reduced consumption and reduced emissions.

For the mass production of such composite parts, it is important to optimize production to meet industrial constraints, while ensuring mechanical properties meeting a given specification. In order to reduce the manufacturing cost in terms of the quantity of material used, it is known to use anisotropic fold stacks, each ply having a given thickness and possibly comprising reinforcing fibers arranged in a given pattern, the pattern being potentially different between two successive fibers in the stack. Such a stack introduces a large number of degrees of freedom, and different mechanical properties. In addition, different injection manufacturing times are obtained for different stacks.

The manufacturing process of such parts has many variables, for example the number of folds, the materials used for each fold, the geometry of the piece. It is therefore necessary to develop methods for optimizing the manufacture of parts made of composite material with stacked folds.

There are methods for determining a set of manufacturing parameters of a part, meeting specifications including mechanical constraints to be respected by the manufactured part. Once this set of parameters meets the specifications defined, a simulation of the manufacturing process by injection of material, for example resin, is performed, and if it turns out that the manufacturing does not meet the constraints of feasibility another set of parameters is determined. Such a method requires a particularly long simulation time. Also known are methods for performing a complete simulation of the manufacturing process for each set of manufacturing parameters defining a part envisaged, and selecting, after an iterative comparison process, the set of parameters that optimizes a predetermined global criterion. However, in this case too, the time taken for optimization is particularly long. In particular, the Applicant has noted that the complete simulation time of the manufacturing process of a composite part defined by a set of parameters is particularly long. There are also known methods offering quick and simplified calculations but by their simplification do not take into account the local characteristics of the room. Thus these methods will not be applicable for more complex parts as used in the automotive industry.

The object of the invention is to overcome the above-mentioned problems by proposing a method of estimating a quantity relative to a process for manufacturing a part by injection that is faster and requires less computation, which makes it possible to save money. time and computing resources. For this purpose, the invention proposes, according to a first aspect, a method for estimating a quantity relative to a process for manufacturing a part by injecting material from an injection point, the magnitude to be estimated being selected from an injection time and an injection pressure. This method comprises the following steps: obtaining a geometrical representation of the part by a mesh defined by points having first geometrical coordinates associated with a first reference, -conversion of the first geometrical coordinates into second coordinates relating to the magnitude to be estimated associated with a second repository, based on local physical characteristics associated with said mesh, - calculating, in the second repository, using a shorter path algorithm, the maximum distance between the second coordinate corresponding to the point d injection and a second coordinate corresponding to another point of the part, and - estimate according to the calculated maximum distance, said magnitude to be estimated. Advantageously, the invention makes it possible to take into account local physical characteristics of a part to be manufactured in order to obtain, by a simplified calculation, an estimate of a physical quantity relative to the manufacturing process of the part. The method for estimating a quantity relative to a process for manufacturing a part by injection according to the invention may have one or more of the following characteristics, taken independently or in combination, in any technically acceptable combination: mesh points are connected by edges forming mesh elements, said local physical characteristics include porosity and permeability characteristics, and said local physical characteristics are homogeneous within each element of the mesh; said local physical characteristics depend on a stacking sequence of folds containing fibers of material; when the quantity to be estimated is the injection time, the injection pressure is constant or constant in steps; when the quantity to be estimated is the injection pressure, the injection flow rate is constant or constant in steps; the conversion of the first geometrical coordinates into second coordinates relative to the quantity to be estimated uses a calculation formula obtained for a linear modeling of the flow of material injected between the injection point and a mesh point; the conversion of the first geometric coordinates into second coordinates relative to the quantity to be estimated uses a calculation formula obtained for a radial modeling of the flow of material injected from the injection point. According to a second aspect, the invention proposes a method of selecting a method for manufacturing a part by injecting material from an injection point, among at least two such distinct manufacturing processes, comprising steps of: for each of the manufacturing processes, estimating a quantity relative to said process for manufacturing a part by injection of material from an injection point, the quantity to be estimated being chosen from an injection time and a pressure of injection, by an estimation method as briefly described above, and calculation of a performance score as a function of the estimated quantity, -selection of the manufacturing process from among said at least two distinct manufacturing processes as a function of the calculated performance score. The method of selecting a method for manufacturing a part by injecting material from an injection point, among at least two such distinct manufacturing processes according to the invention may have one or more of the following characteristics, taken independently or in combination, according to any technically acceptable combination: each distinct manufacturing process being defined by a stacking sequence of folds for the manufacture of said part, and the method further comprises a step of determining a sequence of stacking for each of said manufacturing methods; the determining step comprises determining a number of successive folds, a thickness of each fold and at least one fiber orientation per fold of the stack; it furthermore comprises, for each manufacturing method, a step of mechanical simulation of the mechanical performances of the part to be manufactured according to the stacking sequence; the calculation of a performance score implements a cost function expressed as a weighted sum of several cost values.

According to a third aspect, the invention relates to a device for estimating a quantity relative to a method for manufacturing a part by injecting material from an injection point, the quantity to be estimated being chosen from a time of injection and injection pressure. The device comprises units adapted to: obtaining a geometrical representation of the part by a mesh defined by points having first geometrical coordinates associated with a first reference, -converting the first geometrical coordinates into second coordinates relative to the quantity to be estimated, associated with a second repository, as a function of local physical characteristics associated with said mesh, - calculating, in the second frame of reference, using a shorter path algorithm, the maximum distance between the second coordinate corresponding to the injection point and a second coordinate corresponding to another point of the part, and - estimating according to the calculated maximum distance, said magnitude to be estimated. According to a fourth aspect, the invention relates to a device for selecting a method for manufacturing a part by injection of material from an injection point, among at least two such distinct manufacturing processes, comprising units adapted to for each of the manufacturing processes, estimating a quantity relative to said method of manufacturing a part by injecting material from an injection point, the quantity to be estimated being chosen from an injection time and a pressure of injection, by an estimation device as briefly described above, and calculating a performance score as a function of the estimated relative magnitude, - selecting a manufacturing method from among said at least two distinct manufacturing processes according to the score of calculated performance.

Other features and advantages of the invention will emerge from the description which is given below, by way of indication and in no way limitative, with reference to the appended figures, among which: FIG. 1 represents a block diagram of a device programmable to implement the methods of the invention; FIG. 2 is a block diagram of a method for estimating a physical quantity relating to a manufacturing method according to one embodiment of the invention; FIG. 3 is a schematic example of representation of a part in a first reference frame and in a second reference frame; - Figure 4 schematically illustrates a linear flow modeling; FIG. 5 schematically illustrates two-dimensional radial flow modeling; FIG. 6 is a block diagram of a method for comparing two methods of manufacturing and selecting a manufacturing method according to one embodiment of the invention; - Figure 7 is a block diagram of a method of manufacturing a part according to an embodiment of the invention. The invention will be described in detail hereinafter in the particular case of the manufacture of parts made of composite material reinforced with resin injection fibers (RTM).

However, the invention is not limited to this application case and applies to any method of manufacturing parts by injection of material. The methods of the invention are implemented by programmable devices. FIG. 1 illustrates the main blocks of a programmable device able to implement the method for estimating a quantity relating to a process for manufacturing a part by injection or the method of selection, among at least two methods of separate manufacturing, an optimal process according to a given performance score.

A programmable device 10 capable of implementing the invention, typically a computer, comprises a screen 12, a means 14 for inputting commands from an operator, for example a keyboard, optionally an additional pointing means 16, such as a mouse , for selecting graphic elements displayed on the screen 12, a central processing unit 18, or CPU, able to execute computer program instructions when the device 10 is powered up. The device 10 also comprises information storage means 20, for example registers, capable of storing executable code instructions allowing the implementation of programs comprising code instructions able to implement the method according to the invention. . The various functional blocks of the device 10 described above are connected via a communication bus 22. FIG. 2 illustrates the main steps of a method for estimating a quantity relating to a process for manufacturing a part by injection according to one embodiment of the invention, implemented by a central processing unit 18 of a programmable device 10. In this embodiment, an anisotropic piece of composite material is to be manufactured, the part being defined by its geometric shape. and having to respect a specification of mechanical constraints. In a first step 30, a geometrical representation of the piece is obtained in the form of a mesh, defined by points or nodes connected by edges, the edges defining elements of mesh, for example triangles or quadrilaterals. This is a representation of the part in a first repository, which is a geometric reference. A set of manufacturing parameters, in particular a stacking sequence defining the stack of plies containing fibers, is obtained during a step 32 of obtaining the manufacturing parameters of the part. Indeed, a large variety of stacking sequences can be used to manufacture a given piece, each stacking sequence defining the number of successive folds, and for each of these folds, the thickness of the fold, the direction or orientations of the fibers.

For each element of the mesh, and for each point of the mesh, a set of physical characteristics, associated with the injection manufacturing process and / or associated with the mechanical calculation, is calculated during a step 34 of local characterization of the elements of the mesh. In particular, for each element of the mesh, values of permeability, porosity and fiber volume fraction are calculated and stored. Thus, the local characteristics of the geometrical structure defining the part to be produced by injection are stored.

Next, the method comprises a step 36 of converting the first coordinates of the points of the mesh in the first frame into second coordinates in a second frame of reference, the second coordinates being relative to a physical quantity of the injection manufacturing process among an injection time. and an injection pressure. The point of injection of material during the implementation of the manufacturing process is predefined, and this point is the origin point of the second frame of reference. When the second frame of reference is relative to the injection time, the injection pressure is assumed to be constant during the total duration of the injection or constant in steps. In this case, the physical quantity relative to the manufacturing process to be estimated is the injection time. When the second reference is relative to the injection pressure, the other physical quantity considered is assumed to be constant, or constant in steps. The other physical quantity considered is in this case the injection rate, which is directly correlated to the injection time. The injection pressure is to be estimated at a constant injection rate during the entire injection manufacturing or constant stepwise during the injection. The applied conversion depends on the first coordinates in the first frame of reference and the local physical characteristics associated with the previously calculated injection manufacturing method, as described in detail below.

After step 36 of converting the first coordinates into second coordinates, the method comprises a step 38 for calculating a maximum distance between the injection point and another point of the part, this other point being the furthest point the injection point according to the mesh in the second frame, by implementing an algorithm of shorter path passing through the points of the mesh in the second frame. In the preferred embodiment, the Dijkstra algorithm is applied to the mesh nodes in the second repository, the distance between two successive nodes being the distance in this second repository. The maximum distance is equal to the maximum of the shortest path distances calculated by the Dijkstra algorithm for each node of the mesh. The Dijkstra shortest path calculation algorithm is well known and will not be described in more detail here. As a variant, any other known algorithm for calculating the shortest path between two points of a mesh can be used.

Finally, during a step 40 for estimating the physical quantity characteristic of the injection manufacturing process, this quantity is calculated as a function of the previously calculated maximum distance and path segments, corresponding to the edges of the mesh, obtained by the search algorithm of shorter path. FIG. 3 schematically illustrates a first representation R1 of a workpiece P in the first geometric reference, and a second representation R2 of the same workpiece P in the second reference associated with the magnitude of the manufacturing process to be estimated, by example the injection time. The workpiece P is composed of three zones Z1, Z2 and Z3 of respective permeabilities K1, K2, K3 with K1> K2> K3.

The geometric mesh of the part is schematically represented also, and comprises points or nodes 42, connected by edges 44 and forming mesh elements 46. The injection point 48 is the initial point of injection of material in the manufacture of the room.

The step 36 of converting the first coordinates into second coordinates is based on an application of Darcy's law to define a filtration rate of a fluid: upK-VP (Eq 1) Where up is the filtration rate of Darcy , K the permeability, it the viscosity and VP the pressure gradient. The flow velocity is related to the Darcy filtration rate by: UD v = - = VP (Eq 2) 0 of - 0 Where 0 is the porosity. The equation (Eq 2) above can be solved in a one-dimensional domain (1D), considering a linear flow, or in a two-dimensional domain (2D), considering a radial flow. FIG. 4 schematically illustrates a one-dimensional linear modeling of the flow, along a flow line 50 between the injection line 52 comprising an injection point 54, and the external limit 56 of the part to be manufactured, over the entire length xL of the piece. In the example shown diagrammatically in FIG. 4, the part comprises zones of permeability K1 and zones of permeability K2. In the case 1 D, the pressure gradient is defined by: OP Pin; Pvent (Eq 3) where Pm is the pressure at the injection nozzle and Pvent is the pressure at the extreme point of the flow line, and x is the spatial coordinate of the flow front in the first repository.

The flow velocity is also equal to the derivation of x in the time t: K P1Pvent dx v = = (Eq 4), c1 - 0 x dt Assuming Pvent 0 and a constant injection pressure during the total duration of trot injection for a total length xL starting from the injection point, the total injection time is calculated as follows: trot (Eq 5) - 2.K - Puy 0 - it- The equation (Eq 5) above implies permeability values K, porosity 0 and constant viscosity for the length x L of the flow line. However, in practice, the property of homogeneity of permeability values K, porosity 0 and viscosity it is verified for mesh elements, which are segments in modeling 1D, of length d, in the 1D modeling. Thus, for an element of length d, between the coordinate points xt_i and xt, and respective initial and final pressures / 1, the injection duration t, is expressed as follows: 0. it - da (Eq 6 ) 2K - (111- 11) When the line segment [, xi] is the last segment of the part, the final pressure / 1 Pvent ° The injection time or total injection time trot is calculated as the sum of the times of injection by segment: L trot = ti (Eq 7) In the more general case of a mesh of points, for a segment i formed by two successive points of length di, of permeability Ki and of porosity 0, the formula (Eq 6) above can be used to calculate the injection time t,. The pressure is obtained by applying the principle of conservation of the mass of the fluid. The filtration rate of Darcy is constant for each considered point of the mesh: By applying this property, we obtain: ## EQU1 ## KP -P n-1 n-1 n-2 On dn 1 On-1 dn-1 n-1 And therefore; 1 Kn ± Kn-1 P -2 (Eq 9) Pn-i = Kn + K n_i dn - On P nd n_i - 0 n_i n dn- On d n_i- 0 n_i This expression is also written as: (Eq 8) 1 1 1 Pn an, 1in a n-1.1in Pn-1 1 1 year Jin a n-1.1in Pn-2 (Eq 10) - with an lin = dn On (Eq 11) Kn By setting b njin = bn-1, lin + an lin (Eq 12) and bo, iin = 0 (Eq 13), we get Pin '(Eq 14) with the boundary condition: P = O.

The pressure gradient is expressed by: vp _ Pi - Pinj 0i (Eq 15) to di K b di'Oi Finally, we obtain an iterative equation, which makes it possible to compute, for each point of first spatial coordinate xi, a second coordinate ti representative of the injection time, in the second representative representative of the injection time: bai Jin Pi-1 = P Pin. = - b + aib i-1, lin ± ai K. -1 Jin + di 'di - Oi (11 ft bi_uindi + (Eq 16) 2 in. Ki) In the linear case described, it is easy to calculate a total injection time by a sum of the injection times: trot - (Eq 17) i = 0 According to a second variant, a 2D radial flow starting from a central injection point is envisaged. As schematically illustrated in FIG. 5, a flow line 60 is considered, between the injection point 62 and the outer limit 64 of the part, over the entire radius R = xL of the part. In the example shown diagrammatically in FIG. 5, the part comprises zones of permeability K1 and zones of permeability K2. Analogously to what has been described above for the case 1D, for a radial flow, an injection time t, corresponding to an x-ray, of a piece of total radius xL is obtained ((d, 2 -d2 (((t + - (d, do) 'd + C1,2-2 - ln -1 + d2 pd)))) (Eq 18) 21) -1 rad,, + (Eq 19), bo , rad (Eq 20), ai, rad (Eq i Ki xi (di Oi-di- With bi 'd = Et x, = dn (Eq 22), do being a local injection radius, corresponding to a n = 1 scaling of the element of the global injection radius Ro In practice, for a mesh of a part to be manufactured, the first coordinates of the points of the mesh are transformed into second coordinates representative of the injection time according to the invention. one of the formulas (Eq 16) and (Eq 18) above in the conversion step 36, the local physical characteristics of porosity and permeability, being homogeneous within each element of the mesh.

The choice of one or the other of the formulas, or a combination of both, is determined beforehand according to considerations of geometric shape of the part to be manufactured. The choice of a combination of the two formulas is made by an operator. Thus, in one embodiment, each point i of the first coordinate x, of the geometric mesh has, after application of the conversion, an injection time value t, associated, therefore a second coordinate in the second frame of reference, each element of the mesh having associated values of permeability K, and of porosity 0, calculated during the step 34 of local characterization of the elements of the mesh.

Next, the application of a shorter path algorithm in step 38 makes it possible to obtain a path whose length in the second reference frame is equal to the total injection time trot = t, estimated for the part to be manufactured . = 0 Advantageously, the computation comprises for each point of the mesh, an analytical computation is carried out for the application of the conversion formula, and then the application of the Dijkstra algorithm for the computation of the shortest paths for each point of the mesh and for determining the path corresponding to the maximum distance between the injection point and another point of the mesh. The method for estimating a quantity relative to an injection manufacturing process can be used in a method for comparing two or more processes for manufacturing a composite part meeting a specification, and then selecting the manufacturing method. the most efficient according to a given criterion. The criterion can be a simple criterion, such as the manufacturing time of a part, or a complex criterion, taking into account several simple criteria, for example the weight of the part, the manufacturing time and the mechanical strength.

Figure 6 schematically illustrates the main steps of a method for comparing two manufacturing methods, Proc A and Proc B, according to an embodiment of the invention. Each of Proc A and Proc_B manufacturing processes is defined by a set of manufacturing parameters of a part P, including inter alia parameters determining physical characteristics of the part, such as the stacking sequence, the injected material. The respective steps implemented for each of the processes Proc A and Proc_B compared are either performed successively for each of the processes, or performed substantially in parallel.

A step 70A, 70B for estimating a selected quantity relative to the manufacturing method Proc A, Proc_B is carried out, according to the method described above. At the output of respective steps 70A, 70B, a magnitude value V A, V_B relative to each of Proc A, Proc_B manufacturing processes is obtained.

Next, a simulation 72A, 72B of the mechanical performances of a part obtained respectively by Proc A, Proc_B manufacturing processes is implemented. This simulation step, which is optional, makes it possible to verify that the piece thus manufactured meets the specifications imposed for the part to be manufactured. Then, during a score calculation step 74A, 74B, a performance score SC A, SC_B is calculated for each of the manufacturing processes Proc A, Proc B, taking into account the estimated quantity VA, V_B for each of the processes. . A simple score is based only on the calculated values V A, V_B. In this case, SC A = V A and SC B = V B. A complex score calculated as a weighted sum of several cost functions can be used. A same performance score calculation formula is applied in each of the score calculation steps 74A, 74B, and a respective performance score SC A, SC_B is obtained for each manufacturing method. These Proc A, Proc_B manufacturing methods are then compared in a comparison step 76, and the most efficient method according to the calculated performance score is selected as a result of the comparison. Thus, the invention makes it possible to compare two processes for manufacturing a part by injection of material and to select the most efficient of the two according to a criterion evaluated by a performance score. Advantageously, the estimation of a magnitude V A, V_B relative to each of the manufacturing processes is effective from a computational point of view. FIG. 7 illustrates the application of a comparison method according to the invention in a method for determining a set of stacking parameters or stacking sequence defining a process for manufacturing a part by optimized injection according to a given criterion.

During an initialization step 80, an initial stacking sequence is chosen as the current stacking sequence. Such a stacking sequence is defined by a number of successive folds, and for each fold, by its thickness and by the orientation or orientations of the fibers of the fold. The geometric shape of the part to be manufactured, and the mesh of the part are predefined in this embodiment.

Preferably, the stacking sequence is symmetrical with respect to the central layer, and each fold is symmetrical with respect to an axis of symmetry of the part to be manufactured. Preferably, the thickness of a fold is selected from a discrete set of predetermined values, for example from the following values: [0.125mm; 0.25 mm; 0.50 mm]. Preferably, the orientations of the fibers are selected from a discrete set of possible orientations, for example: [0 °; 90 °; -22.5 °; 22.5 °, -45 °; 45 °; -67.5 °; 67, 5 °].

Thus, the space defining the possible stacking sequences is discretized, and the combinatorics in this space is reduced, which makes it possible to limit the number of stacking sequences to be tested and to reduce the calculation time. For the current stack, a step 82 for estimating a quantity relative to the manufacturing process is carried out.

This step 82 comprises substeps 84 to 90. The first optional substep 84 consists in testing whether the current stacking sequence is not defined by multiples of a stacking sequence already tested, in which case it it would be useless to evaluate their performance. If the result of the test is positive, the substep 84 is followed by the step 92 of selecting a new stacking sequence to be tested. If the result of the test is negative, the substep 84 is followed by an optional substep 86 for testing the respect of the initial constraints, for example a maximum weight constraint of the part to be manufactured. In case of non-compliance with the initial constraints, the substep 86 is followed by the step 92 of selecting a new stacking sequence to be tested. If the initial constraints are respected, the sub-step 86 is followed by an optional sub-step 88 for testing the respect of rules for modeling the part, for example symmetry rules, defined by the designer. If the modeling rules are not respected, the substep 88 is followed by the step 92 of selecting a new stacking sequence to be tested. If the modeling rules are respected, the sub-step 88 is followed by a substep 90 of implementing the method for estimating the quantity relative to the manufacturing process of the part, chosen from the injection time and the injection pressure as described above.

An estimated value of the selected quantity is provided at the end of step 82.

Then, during a mechanical simulation step 94, the mechanical performances of interest of the part to be produced according to the current stacking sequence are tested. In one embodiment, an available simulation software, such as the LS-Dyna (registered trademark) software, is used in this mechanical simulation step 94. This mechanical simulation makes it possible to validate the fact that the part manufactured according to the stacking sequence current meets the specifications, for example in terms of weight and resistance to mechanical traction in a direction of stress.

In case of non-compliance with the specifications, the mechanical simulation step 94 is followed by the step 92 of selecting a new stacking sequence to be tested. In the case of compliance with the specifications, the mechanical simulation step 94 is followed by a step 96 for calculating a performance score SC implementing a cost function.

For example, a complex cost function is expressed as follows: SC (x) = f (x) = 1 -1 co, * f (x) (Eq 23) With weighting factors CD,, with coI, = 1, and simple cost functions fi (x): - - ft (x) 0.5 2 x, xmax x min (Eq 24) 2. (x.-xmm) Where xi is the value reached, and xi.n and xmax are respectively the minimum and maximum bounds that can be taken by this value. The cost function above is given for the example, any other cost function being applicable. Next, in the embodiment of FIG. 7, a CMAES ("covariance matrix adaptation evolutionary strategy") optimization algorithm, known in the field of numerical optimization, is implemented at step 98 to determine a new stacking sequence that can optimize the performance score calculated in step 96. As a variant, any other optimization algorithm is applicable.

The performance score SC calculated in step 98 is stored at each iteration for a current stacking sequence being tested, and the stacking sequence 100 retained is the sequence that obtains an optimal performance score SC.

Thus, the method makes it possible, after a number of iterations, to obtain a stacking sequence that optimizes the evaluated criterion. The method described with reference to FIG. 7 was tested for the selection of a stacking sequence for the fabrication of a piece modeled by a mesh with 22085 points or nodes, comprising 21697 elements of mesh of type Quad-4 ( quadrilaterals), on a 2.4 GHz processor with 4 Giga Bytes of RAM. The calculation time for estimating a quantity relative to the manufacturing method according to the invention at each iteration is of the order of 1 minute, whereas a complete simulation of the manufacturing method with commercial software such as PAM-RTM (registered trademark) would take about 25 minutes. Advantageously, the total time of the method of selecting an optimized stacking sequence is greatly reduced thanks to the implementation of the invention.

Claims (14)

CLAIMS 1. A method for estimating a quantity relating to a method for manufacturing a part by injecting material from an injection point, the quantity to be estimated being chosen from an injection time and a pressure of injection, characterized in that it comprises the steps of: -obinding (30) of a geometrical representation of the part by a mesh defined by points having first geometric coordinates associated with a first reference, -conversion (36) of the first geometrical coordinates in second coordinates relative to the quantity to be estimated, associated with a second repository, as a function of local physical characteristics associated with said mesh, - computation (38), in the second repository, using an algorithm of more the shortest distance between the second coordinate corresponding to the injection point and a second coordinate corresponding to another the piece, and - estimating (40) as a function of the maximum calculated distance, of said quantity to be estimated. 2. Method according to claim 1, wherein the points of the mesh are connected by edges forming mesh elements, characterized in that said local physical characteristics comprise porosity and permeability characteristics, and in that said physical characteristics localities are homogeneous within each element of the mesh. 3.- Method according to one of claims 1 or 2, characterized in that said local physical characteristics depend on a stack stack sequence containing fiber material. 4. A process according to any one of claims 1 to 3, characterized in that when the magnitude to be estimated is the injection time, the injection pressure is constant or constant increments. 5. A process according to any one of claims 1 to 3, characterized in that when the magnitude to be estimated is the injection pressure, the injection rate is constant or constant increments. 6. A process according to any one of claims 1 to 5, characterized in that the conversion (38) of the first geometric coordinates into second coordinates relative to the magnitude to be estimated implements a calculation formula obtained for a linear modeling of the flow of injected material between the injection point and a mesh point. 7.- Method according to any one of claims 1 to 6, characterized in that the conversion (38) of the first geometric coordinates into second coordinates relative to the magnitude to be estimated uses a calculation formula obtained for a radial modeling of the flow of material injected from the injection point. 8. A method for selecting a method for manufacturing a part by injecting material from an injection point, among at least two such separate manufacturing processes, comprising steps of: for each of the manufacturing processes , estimating (70A, 70B, 90) a magnitude relative to said method of manufacturing a workpiece by injection of material from an injection point, the magnitude to be estimated being selected from an injection time and a pressure of injection, by an estimation method according to one of claims 1 to 7, and calculation (74A, 74B, 94) of a performance score as a function of the estimated quantity, -selection (76, 96) of the method of said at least two distinct manufacturing processes based on the calculated performance score. 9. A method for selecting a method for manufacturing a part according to claim 8, characterized in that each of said distinct manufacturing processes is defined by a stacking sequence of folds for the manufacture of said part, and the method further comprises a step of determining a stacking sequence for each of said manufacturing methods. 10. A method for selecting a manufacturing method of a part according to claim 9, characterized in that the determining step comprises the determination of a number of successive folds, a thickness of each fold and at least one fiber orientation per fold of the stack. 11. A method for selecting a manufacturing method of a part according to any one of claims 9 or 10, characterized in that it further comprises, for each manufacturing method, a mechanical simulation step (72A, 72B, 94) mechanical performance of the part to be manufactured according to the stacking sequence. 12. A method for selecting a method for manufacturing a part by injection of material from an injection point according to any one of claims 8 to 11, characterized in that the calculation (96) of a performance score implements a cost function expressed as a weighted sum of several cost values. 13. A device for estimating a quantity relative to a method for manufacturing a part by injecting material from an injection point, the quantity to be estimated being chosen from an injection time and a pressure of injection, characterized in that it comprises units adapted to: -obtaining a geometrical representation of the part by a mesh defined by points having first geometric coordinates associated with a first reference, -converting the first geometrical coordinates into second relative coordinates at the magnitude to be estimated, associated with a second reference frame, as a function of local physical characteristics associated with said mesh, - calculating, in the second frame of reference, using a shorter path algorithm, the maximum distance between the second coordinate corresponding to the injection point and a second coordinate corresponding to another point of the part, and - estimating according to the calculated maximum distance, said magnitude to be estimated. 14. A device for selecting a method for manufacturing a part by injecting material from an injection point, among at least two such distinct manufacturing processes, comprising units adapted to: for each of the processes of manufacturing, estimating a quantity relative to said method of manufacturing a part by injection of material from an injection point, the quantity to be estimated being chosen from an injection time and an injection pressure, by a device of estimation according to claim 13, and calculating a performance score as a function of the estimated relative magnitude, - selecting a manufacturing method from among said at least two distinct manufacturing processes according to the calculated performance score.