Optimal fiber path generation method for composite part manufacturing

Abstract

A novel method designs and analyzes composite parts including optimal manufacturing strategies. The invention analyzes part design including curvatures and other surface topology to formulate an optimal strategy for material layup, number of plies, initial orientation angle, and towpath steering vectors. The method computes an optimum starting point for each fiber path and a stagger offset for each successive fiber path to as to eliminate or minimize gaps and overlaps between adjacent plies. Intermediate surfaces are generated by a polynomial discretization method which generates large computational time savings and enhances blending of adjacent zones to control surface smoothness. The method further calculates a variable steering path for the layer taking into account material parameters and limitations such that plies originating in the same location have a variable orientation angle and follow any reference curve generated by the method to maximize strength and minimize weight of the component.

Claims

1. A method for optimizing composite part manufacturing strategies so as to maximize strength, minimize material costs, and increase manufacturing speeds using a computational device, the method comprising: importing loft surface information; importing laminate information; importing material manufacturing data; executing a starting point optimizer; generating a list of optimum starting points; analyzing the list of optimum starting points for gap and overlap outcomes; and generating a list of the optimum starting points and the associated gap and overlap outcomes; sorting the list of the starting points and associated gap and overlap outcomes in accordance with user selectable parameters; displaying the list of the starting points and associated gap and overlap outcomes on a user readable device; and exporting the list to a manufacturing system.

2. A method as in claim 1 for optimizing composite part manufacturing strategies, the method further comprising: generating a mathematical description of each surface using an advanced polynomial discretization method; using the polynomial discretization method to project ply boundary curves into intermediate surfaces; using the intermediate surfaces to blend surfaces of adjacent zones together to control surface smoothness; and and exporting the information to a manufacturing system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.

(2) FIG. 1 is a flow diagram for the generating and analyzing optimum starting points for tow paths of laminate materials; and

(3) FIG. 2 is a flow diagram for the iterative method of analyzing optimum starting points to avoid and or minimize gaps and overlaps in the laminate materials.

DETAILED DESCRIPTION OF THE EMBODIMENT

(4) The Optimum Starting Point

(5) One of the most difficult challenges during fiber path generation for advanced material layup technologies hand-layup and/or automated material layup such as Fiber Placement, Tape Layer, Robotics is the location of the initial starting point necessary for the computation of fiber paths for the initial layer.

(6) The intent of this algorithm is to optimize the location of the initial starting point to prevent Gap/Overlap occurring at the same location for plies having the same orientation.

(7) A composite part is made of different layers of composite material forming a laminate. Each ply is defined by a boundary (closed curve) limiting the surface regions where the composite material will be applied, an orientation defining the material angle direction and a starting point.

(8) In order to cover plies with composite material using advanced technologies such as Fiber Placement, Tape Layer, Robotics multiple towpaths or fiber paths have to be computed.

(9) Due to a variation in surface curvature or any discontinuities such as ramps, radii, build-up, pad-up, surface tapering etc., the towpath or fiber path computed for each plies present Gap/Overlap.

(10) In fact it is not possible to compute fiber paths having a constant Gap/Overlap and same fiber orientation if the fiber paths have to cross surface regions presenting discontinuities as described above (surface curvature variation, fillet radii, ramps, build-up, surface tapering etc. . . . ).

(11) The gaps or overlaps present between towpaths or fiber paths belonging to a ply cause material fiber discontinuities plus areas of material voids (Gap) or excess (Overlap) impacting significantly the mechanical performances and part quality.

(12) The main design intent for composite parts is to prevent Gap/Overlap occurring at the same location for plies having the same orientation across the all ply stack or laminate.

(13) A common technique called ply staggering has been applied to control the position of gaps and overlaps. This technique is simply based on creating an initial starting point to compute fiber paths for the first ply or layer, and using as starting points for computation of fiber paths for all other plies included in the laminate, points that are the result of staggering or offsetting the initial starting point. Having starting points computed as an offset or stagger from a common initial starting points, is a simple way to prevent other fiber paths from belonging to different plies or layers included in the laminate have Gaps/Overlaps occurring at the same locations.

(14) Unfortunately this simple technique based on staggering or offsetting the initial starting point is not enough to prevent Gap/Overlap occurring at the same location for plies having same orientation, because the amount of offset or stagger that can be applied to the initial starting point, it is limited by the tow width or material layup band in general.

(15) Basically there is a finite number of starting points that can be computed as an offset for the initial starting point, so it is impossible to properly control Gap/Overlap distribution in a laminate using a simple offsetting or staggering technique.

(16) The innovative optimization method described hereafter, it is not solely based on a stagger or offset of the initial starting point but it uses a look-ahead to modify the fiber angle direction in order to prevent Gap/Overlap.

(17) In principle this method will allow towpaths or fiber paths to locally slightly deviate from the desired fiber direction, in accordance with design tolerance and material manufacturing limits (steering, wrinkle, bridging, compaction, angle deviation etc.) to prevent Gap/Overlap occurring at the same location across all laminates that cannot being prevented using a simple initial starting point stagger or offset.

(18) Within this method a computational loop will be launched in order to use initial starting point stagger and fiber direction look-ahead to optimize the position of the initial starting point and to define surface regions inside all laminate where the fiber direction has to be varied in accordance to design intent tolerance, to minimize the number of Gap/Overlap and to avoid Gap/Overlap occurring at the same location for plies sharing the same orientation.

(19) Basically this innovative method is shown in FIG. 1 and FIG. 2.

(20) Advanced Surface Offset

(21) One of the most difficult challenges during fiber path generation for advanced material layup technologies hand-layup and/or automated material layup such as Fiber Placement, Tape Layer, Robotics is the computation of Intermediate Surfaces representing surface topology after material layers have been applied.

(22) This Advanced Surface Offset method uses three major improvements to create Intermediate Surfaces: i. An advanced polynomial discretization method it is used to described mathematically each surface. The main benefits of the polynomial discretization method is the computational speed at which Intermediate surfaces can be computed, in fact by using a polynomial discrete approach Intermediate Surfaces can be computed extremely fast in comparison to traditional CAD systems based on NURBS. Also the polynomial discrete approach allows one to project ply boundary curves into Intermediate Surfaces extremely fast in comparison to traditional CAD systems based on NURBS. This significantly reduces the enormous time currently spent today to compute Intermediate Surfaces and ply boundary association commonly called Skin-Swap. ii. This method based on polynomial discretization allows blending surface regions representing zones at different thickness. The user can specify as input a blending radius, in order to control the surface smoothness in regions presenting ramps due to zones having different thickness. In this way the user can create an intermediate surface for design intent or for manufacturing intent where it is fundamental to have a very high continuous intermediate surface to prevent bad machine motion resulting in material layup defects (bridging, wrinkling, steering, gap/overlap, fiber deviations . . . ). iii. This method starts from the same original surface used during FEA analysis to compute the ply stacking sequences and plies area to ensure structural integrity and mechanical performance. This algorithm allows importing the FEA surface in the form of a mesh or CAD model. This surface contains all the boundaries describing for each plies the coverage area necessary to ensure structural integrity and mechanical performance. Starting from this original FEA surface, Intermediate Surfaces will be computed offsetting the original surface along its normal vectors of the proper amount defined by the material thickness and the specific number of layers. Starting from the FEA surfaces it guarantees to preserve the ply coverage area needed for structural integrity and mechanical performance and to send warnings in the case the ply coverage area is increased causing the part to be heavier or decreased causing a failure in mechanical performances.

(23) Multilayer Steering Fiber Path

(24) Traditionally composite parts are made of laminates constructed from multiple layers of fiber-reinforced material. For each layer, the fiber direction follows a design variable called orientation angle. The orientation angle is the same for the all layer or ply.

(25) Recently, it has been shown that even greater use of fiber-reinforced materials can be achieved by varying spatially throughout the layer or ply the orientation angle, generating what is called a steered fiber path increasing significantly the stiffness and overall mechanical performances.

(26) Two major limitations have prevented this technique to be successfully applied: Material Steering allowable Material allowable for part certification

(27) The innovative Multilayer Steering Fiber Path resolves the limitations above motioned, it allows one to incorporate material properties such as steering limits, material wrinkle, material bridging, material compaction during the computation of towpaths or fiber paths ensuring part manufacturability. Also within this method fiber paths belonging to different layers forming the laminates, they will be steered in a way that at any point across the entire composite laminates, if I imagine to drill a hole passing through the all laminates thickness, the angle distribution, locally to the inspection point, it will respect engineering material allowable based on a combination of 0/90/45 angular direction. Basically the fiber paths computed for each layer of the laminate can be steered or curved to follow any reference curve(s) or to interpolate any angular distribution on a layer by layer basis in order to maximize part stiffness and minimize weight, however the reference curve(s) or the angular distribution has to be computed in a way that the fiber path do not exceeds material limits in term of steering, wrinkle, bridging, angular deviation, compaction and the angular distribution across the all thickness of the laminate at each points of the laminates is a combination of 0/90/45 angles machining the angular distribution used to compute composite material allowable.

(28) The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention be limited not by this detailed description, but rather by the claims appended hereto.