WO1993000621A1

WO1993000621A1 - Integrated method for designing and manufacturing semiworked items made of composite materials and apparatus for actuating the method

Info

Publication number: WO1993000621A1
Application number: PCT/EP1992/001372
Authority: WO
Inventors: Stefano Segato
Original assignee: Ronda Europa S.P.A.
Priority date: 1991-06-25
Filing date: 1992-06-17
Publication date: 1993-01-07
Also published as: ITVI910103A0; ITVI910103A1; IT1247090B

Abstract

A method for designing and manufacturing mechanical elements α made of composite materials, generally constituted by insoluble fibrous elements embedded in a matrix of a continuous material, comprises the steps of: calculating (2) the physical and dimensional characteristics of a mechanical element, processing (3) the output data of the step so as to define the quantity, the orientation and the distribution of the fibrous elements, the spatial arrangement of the fibrous elements according to the output data of the preceding step to define a fabric, a weft or an ordered assembly β of reinforcement fibres; and forming the plastic matrix around the reinforcement β. An apparatus for actuating the method comprises a first computerized area for calculating the structural characteristics of a mechanical element and a second computerized area for producing an assembly β of fibrous reinforcement elements and for forming a matrix of plastic material around it.

Description

INTEGRATED METHOD FOR DESIGNING AND MANUFACTURING SEMIWORKED ITEMS MADE OF COMPOSITE MATERIALS AND APPARATUS FOR ACTUATING THE METHOD

The present invention relates to a method and an apparatus for designing and manufacturing mechanical elements made of composite materials.

Materials of this type are generally constituted by a plurality of insoluble elements in a filamentous state, such as fibers of synthetic materials, embedded in a matrix which is normally made of plastics. Said materials are increasingly widespread in the technology of mechanical elements and structures with marked strength and lightness characteristics combined with high anisotropy. Although composite materials are known since ancient times (consider the mud mixed with grass by the Egyptians to make bricks) , they have undergone a considerable technological development only in the last thirty years. Their application in industry has been severely limited by at least three factors: the first one consists of the fact that for many years these technologies were protected by military secret due to their use in the aerospace sector; the second one arises from the costs, which still make them scarcely competitive with other materials; and the third and last factor is represented by the considerable anisotropy, i.e. by the non-uniform distribution of the mechanical characteristics inside the items, which introduces a certain difficulty in design.

The execution of structural elements made of composite materials is furthermore subjected to at least three variables. The first one is constituted by the precision with which the directions of maximum stress of the element to be manufactured are defined; the second one consists of the actual placement of the fibers according to said directions; the third one is constituted by the amount of fiber required to ensure a desired strength.

The distribution of reinforcements orientated along selected directions according to the state of tension is a principle which is per se known in the field of mechanical elements made of composite materials. This principle is commonly applied in the manufacture of components in relatively limited series, or when the high cost associated with this process is economically justified, such as for example in the aerospace or racing-car fields. Due to these reasons, the manufacturing methods of said products are of a predominantly manual type, and therefore have the typical disadvantages of handicraft methods, i.e. limited precision and scarce repeatability of the shape and structural characteristics.

As regards the design of structures made of composite materials, several computerized calculation methods^*are commercially available: however, they are normally aimed at verifying initial choices. For example, in said known methods the orientation of the fibers is a design or tentative datum and not a final result of the calculation.

From the constructive point of view, the problem lies arranging the fibers as precisely as possible along the directions of maximum stress. In order to meet this requirement, the fibers are arranged in a relatively uniform manner even where they are not necessary, so as to produce a pseudoisotropic material. This causes a non-optimum use of the materials, leading to increases in manufacturing and raw materials costs which reduce the competitiveness of components made of composite materials with respect to those manufactured with conventional methods and materials.

It should be furthermore noted that generally only rather large corporations with significant financial resources can afford research and development departments capable of producing an adequate design and optimization of components made of composite materials, restricting small and medium corporations to the role of users of said products.

The aim of the present invention is to define a method for designing and manufacturing mechanical elements made of composite materials which allow to optimize the distribution of the reinforcements, obtaining semiworked items which are highly reliable and structurally very strong.

An object of the present invention is to provide a method and an apparatus for designing and manufacturing semiworked items made of composite materials which has particular characteristics of flexibility and precision in the formulation of the composition of the material and is capable of standardizing the manufacturing procedures and the final mechanical properties of the manufactured semiworked items. A further object of the present invention is to optimize the use of the raw materials required to manufacture semiworked items, in order to reduce production costs.

Another object of the present invention is to provide a system which allows to identify the orientation of the fibers starting from appropriate physical characteristics of the base material and of its components.

Not least object of the present invention is to provide a fully autonomous and computerized design and manufacturing center which is within the capabilities of even small production units.

This aim, these objects and others which will become apparent hereinafter are achieved by a method for designing and manufacturing mechanical elements made of composite materials of the type described in the introductory part and having the characteristics defined in the independent claim 1.

According to another aspect of the invention, an apparatus for performing the method described above comprises the characteristics defined in the independent claim 6. •

With an integrated design and manufacturing apparatus and method according to the invention it is possible to design and manufacture, with extreme accuracy, mechanical elements with particular care for the distribution and orientation of the reinforcement elements and for their type. It is furthermore possible to minimize the use of the reinforcement materials and in general of the raw materials while safeguarding structural strength and the reliability of the obtained semiworked items, so as to obtain a considerable reduction in production costs.

With these assumptions, even small companies will be able to design and manufacture, in-house, parts made of composite materials at affordable costs, increasingly diffusing the use of extremely light structures with great structural strength.

A further advantage is constituted by the great flexibility of the production method, especially in large-series productions, and simultaneously by high precision in the manufacture of the semiworked items and by standardization of the mechanical characteristics offered thereby.

Further characteristics and advantages will become apparent from the description of a preferred embodiment of a method and an apparatus according to the invention, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

Figure 1 is a schematic view of a portion of a mechanical element made of composite materials;

Figure 2 is a block diagram of a method for designing and manufacturing mechanical elements made of composi e materials;

Figure 3 is a schematic view of the main units of an apparatus for performing the method illustrated in Figure 2.

With reference to the above figures, a mechanical element made of composite material to be manufactured, generally indicated by the reference letter α, comprises a fabric, a weft or an ordered assembly β composed of a plurality of fibers F made of insoluble synthetic material embedded in a matrix M made of plastics or the like.

The method according to the invention generally comprises a first group of data programming and processing steps, followed by a second group of manufacturing steps which use the output data of the first group of steps.

In particular, there is a first step 1 of introduction of input data related to the geometry and to the diagram of the forces which act on the mechanical element to be designed and manufactured, as well as to the mechanical characteristics of the base material M and of the fibers F to be used.

The input data of step 1 are processed in the subsequent step 2 of automatic calculation with the aid of an adapted program P managed by a preprocessor of a central processing unit. In particular, the program P can be divided into a subprogram PI for defining a mathematical model which is equivalent to the physical model of the element α, into a subprogram P2 for calculating the state of tension of the mathematical model thus defined in the maximum load conditions, and into a third subprogram for seeking the most demanding load condition, so as to provide the maximum among the maximum stresses. The output data of step 2 constitute the input data for a subsequent calculation step 3, which uses an adapted calculation program Pc, installed in a post-processor of the central processing unit, which is suitable for determining the direction, distribution and type of the reinforcements to be used.

The program Pc can be associated with a program Pv for graphically displaying the numeric output data, which can be displayed on an interface 4 which can be accessed by an external operator. By means of this step it is possible to confirm or modify the numeric results obtained from the calculation, partially adapting them to particular situations.

The output data of step 3, confirmed by the operator of the interface 4, are used as input data for a first manufacturing step 5 which is intended to spatially distribute the fibrous elements F so as to define a reinforcement fabric, weft or ordered assembly β suitable for giving the necessary mechanical strength characteristics to the mechanical element α. In particular, said step can comprise the use of a program C for converting the numeric data in output from step 3 into instructions for a numeric control machine, in practice an automated loom or se- ng machine, suitable for producing the reinforcement fabric, or weft, β, possibly on a supporting layer which is identical or similar to the outer matrix. The conversion program C can be installed on a preprocessor which is associated with the machine or integrated in the central processing unit of the system.

The step 5 can furthermore have a program I for checking the actual spatial distribution of the reinforcement fibers and their amount.

The step of weaving or sewing the reinforcement β is followed by a step 6 for forming of the base material around the reinforcement so as to define the external configuration of the semiworked part which constitutes the element α.

An apparatus which allows to perform the above described method generally comprises a CAD area, generally indicated by 10, with a central computer which can comprise a preprocessor 11 for processing the subprograms PI, P2 and P3 and a post¬ processor for processing the program Pc for calculating the direction and distribution of the fibers of the reinforcement fabric, weft or assembly of fibrous elements β.

The CAD area 10 is connected to, and integrated with, a CAM area, generally indicated by 20, which can include a preprocessor 21 for converting the output data from the CΛD area into instructions I for an automatic machine 22, such as a numeric-control loom or sewing machine, to produce the reinforcement fabric or weft. The latter can be constituted by a warp of fibers with inclinations which can vary from one point to another in a continuous manner, so as to optimize the reinforcements for each semiworked item, differently from the standard distributions of the known art in which the fibers are mutually perpendicular or have discrete and fixed inclination angles, equal for example to 30°, 45° or 60°. The amount of fibers in a given region can furthermore be constant or can vary from one point to another in order to maximally economize the use of raw materials, giving the maximum structural strength to the mechanical element.

The method and apparatus according to the invention are susceptible to modifications and variations, all of which are within the scope of the inventive concept expressed in the accompanying claims.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

Claims

CLAIMS 1. Method for designing and manufacturing mechanical elements made of composite materials, wherein said materials are generally constituted by a plurality of fibrous elements (F) made of insoluble material embedded in a matrix (M) of substantially uniform base material, characterized in that it comprises at least the following steps:

— a first step (2) of computerized calculation of the state of tension of a mechanical element (α) with a preset design and base material in conditions of maximum stress, so as to obtain first output data;

— a second step (3) of computerized calculation of said first output data so as to define quantity, orientation, spatial distribution and type of a plurality of the fibrous elements (F) inside the matrix (M) of continuous material, so as to obtain second output data;

— a first manufacturing step (5) which consists in the automatic spatial distribution of appropriate amounts of fibrous elements as a function of the output data of the preceding steps, so as to define an appropriate reinforcement fabric, weft or assembly of fibrous elements (β) with preset mechanical characteristics;

— a second manufacturing step (6) which consists in forming plastics or other material around said reinforcement fabric or weft (β) so as to define, around it, a continuous matrix (M) with an external configuration which corresponds to that of said mechanical element, so as to obtain a semiworked element (α) with an optimum mechanical resistance and a minimum use of fibrous materials and matrix.

2. Method according to claim 1, characterized in that said computerized calculation steps (2, 3) are performed by means of a central processing unit (10) with the aid of adapted calculation programs (P, Pc) .

3. Method according to the preceding claims, characterized in that the calculation program (P) associated with step (2) comprises:

— a first subprogram (PI) suitable for formulating a mathematical model of the mechanical element;

— a second subprogram (P2) for calculating the state of tension of said element in maximum loading conditions;

— a third subprogram (P3) for seeking the most demanding loading condition.

4. Method according to one or more of the preceding claims, characterized in that the program (Pc) associated with step (3) consists of a calculation program which interacts with a program (Pv) for displaying and handling the numeric results obtained in the preceding steps.

5. Method according to one or more of the preceding claims, characterized in that a subprogram (C) , for converting the data in output from step (3) into instructions (I) for a numeric-control machine (22) suitable for weaving a reinforcement fabric (β) obtained from the arrangement of fibrous elements (F) along the arrangement defined by step (3) , is associated with said step (5) .

6. Apparatus for designing and manufacturing mechanical elements made of composite materials consisting of insoluble fibrous elements embedded in a matrix of continuous material, characterized in that^' it comprises a computerized design area (10) suitable for calculating the state of tension of a stressed mechanical element and for defining the optimum amounts and directions of reinforcement fibrous elements, integrated with a computerized manufacturing area (20) which is suitable for processing the data in output from said design area so as to automatically define a reinforcement fabric (β) around which a plastic matrix of continuous material (M) can be formed so as to obtain semiworked item elements (α) with optimum strength and with minimum use of materials.

7. Apparatus according to claim 6, characterized in that said design area (10) consists of a central processing unit.

8. Apparatus according to claim 7, characterized in that said central processing unit (10) comprises a first preprocessor

(11) suitable for processing, by means of appropriate programs (PI, P2, P3) initial input data (1) related to the geometry and to the loading conditions of the element to be manufactured, supplying output data related to the state of tension of said element. 1.3

9. Apparatus according to claim 8, characterized in that said central processing unit (10) furthermore comprises a post¬ processor (12) suitable for processing the output data of said preprocessor (11) to determine the optimum quantities, directions and distributions of the fibrous elements (F) , and also comprises a unit (4) for representing, displaying and handling said output data of said post-processor (12) .

10. Apparatus according to claim 9, characterized in that said computerized manufacturing area (20) comprises a preprocessor (21) on which an appropriate program (Pc) is installed for converting the numeric data in output from said first preprocessor into control instructions (C) for a numeric-control weaving machine (22) suitable for selecting and weaving a plurality of said fibrous elements (F) so as to obtain a reinforcement fabric or weft (β) around which a matrix (M) of continuous plastic material, with an external configuration which corresponds to that of the element (α) to be manufactured, is formed.