WO2012116999A1

WO2012116999A1 - A lip skin and a method and apparatus for forming a lip skin

Info

Publication number: WO2012116999A1
Application number: PCT/EP2012/053383
Authority: WO
Inventors: Michael Ludlow
Original assignee: Globally Local Solutions Limited
Priority date: 2011-02-28
Filing date: 2012-02-28
Publication date: 2012-09-07

Abstract

A method of forming a one piece annular component comprising the steps of loading a blank (19) into a forming apparatus (101), initiating an actuation means (111) to cause relative coaxial movement only between a shape forming punch (1), a draw punch assembly (3, 4) and a redraw punch assembly (5, 6). Inserting the shape forming punch (1) in an axial direction until the leading edge (21) of the shape forming punch (1) engages a surface of the blank (19), moving the draw punch assembly (3, 4) into the internal profile of the shape forming punch (1) to draw form the blank (19) whilst simultaneously maintaining the gripping force of the redraw punch assembly (5, 6) to optimally control material flow during the forming process and moving the redraw punch assembly (5, 6) axially towards the draw punch assembly (3, 4) to perform a redraw forming process.

Description

A LIP SKIN AND A METHOD AND APPARATUS FOR FORMING A LIP SKIN This invention relates to a lip skin and to a method and apparatus for forming a lip skin. A lip skin is the mechanical component surrounding the inlet opening of an aircraft nacelle. The nacelle generally has a thin, aerodynamically shaped metal skin covering the jet engine of the aircraft. The lip skin is generally comprised of a single piece or multiple sectors and the main features of the lip skin are a smooth outer trailing edge which must be free from irregularities and discontinuities to reduce drag and to avoid the creation of turbulence. An inner inlet edge which is typically shaped to attenuate noise from the engine by shielding fan noise and to guide the flow of air into the engine, and a leading edge or lip, which provides a smooth transition between the outer trailing edge and the inner inlet edge while creating a small frontal area to reduce drag.The complex three dimensional compound curvature shape of the lip skin typically requires a complex multi-stage forming process, often requiring intermediate heat treatments. Typically lip skins are produced by multiple stage deep drawings or spin forming processes, requiring complex and costly tooling and time consuming multi-step processing with intermediate heat treatments. Due to aerodynamic and noise considerations, it is particularly desirable to extend the outer trailing edge of the lip skin as far as possible, known as extended trailing edges wherein the axial length of the outer trailing edge of the lip skin can be much greater than axial length of the inner inlet edge. Standard deep drawing processes are unsuitable for the manufacture of such extended trailing edges.One object of the present invention is to provide a one piece or multiple sector lip skin and a method and apparatus for forming a one piece or multiple sector lip skin with an extended outer portion to increase the extent of laminar flow over the outer surface of the nacelle and thus remove any flow interruptions. Accordingly, the present invention provides an apparatus for forming a one piece annular component, a sector of an annular component or an arcuate component comprising a shape forming punch having a forming end with an external surface shaped to correspond to the shape of the component, a draw punch assembly for clamping a central portion of a metal blank and a redraw punch assembly for adjustably gripping a circumferential portion of the metal blank and actuation means for facilitating relative coaxial movement only between the shape forming punch, the draw punch assembly, the redraw punch assembly so that the metal blank is formed into a component in a forming process.Ideally, the apparatus comprising a flex bead formed for location between the shape forming punch and the redraw punch assembly.Preferably, the actuation means is provided for facilitating relative coaxial movement only between the shape forming punch, the draw punch assembly, the redraw punch assembly and the flex bead.Ideally, the process is a single stage process or a multistage process depending on the degrees of freedom available in the actuation means.Preferably, the flex bead is annular, part annular or arcuate. The flex bead affords an extra degree of material flow control when forming asymmetric components or dealing with anisotropic materials. The flex bead also provides a means of controlling the degree of thinning in both axis symmetric and asymmetric components through bending under tension. The latter aspect is a function of the draw radius and depth of flex bead insertion.Ideally, the metal blank is formed into an annular component such as a lip skin for an aircraft nacelle.While composite materials can be used for many parts of the nacelle, the lip skin must generally be made from a metal, such as aluminum or titanium, to be able to withstand impacts upon the leading edge or lip thereof. The titanium is also useful in view of recently legislated stringent de-icing requirements requiring higher temperatures at the nacelle leading edge. Preferably, the forming end of the shape forming punch has an annular shape.Ideally, the actuation means is capable of creating coaxial movement of the apparatus along a centerline/carriage. The centerline/carriage forms a datum for all apparatus components location and kinematics. Preferably, the shape forming punch has an external surface shaped to provide the internal profile of the finished formed lip skin.Ideally, the shape forming punch external profile is ultimately determined by the desired shape of the inlet cowl. Preferably, a clean breakpoint is provided on the shape forming punch external profile with either a coaxial or slightly tapered clearance profile from the break point to the end of the shape forming punch.Ideally, the shape forming punch internal profile is ultimately determined by the desired shape of the inlet cowl. Preferably, a clean breakpoint is provided on the shape forming punch internal profile with either a coaxial or slightly tapered clearance profile from the break point to the end of the shape forming punch.Ideally, the shape forming punch profile is designed to match that of the desired internal surface of the inlet cowl. A simple axis-symmetric component or an asymmetric profile can be used.Ideally, the external surface of the shape forming punch is optimized for springback.Preferably, the external surface of the shape forming punch has a high surface finish. Advantageously, the high surface finish value reduces friction during forming. Ideally, the actuation means is a linear actuation system. A hydraulic or electromechanical linear actuation system is aligned with the centerline.Preferably, the shape forming punch is mechanically coupled to the actuation system.Ideally, the draw punch assembly comprises a draw punch member and a counter draw punch member.Ideally, the draw punch member and a counter draw punch member are generally cylindrical block members.Preferably, the draw punch member and counter draw punch member are openable and closable to clamp the blank. The motion of both the draw punch member and the counter draw punch member is aligned with the centerline. Ideally, the draw punch member acts as a counter load system during the final re-draw/stretch forming process. Preferably, the external profile of the draw punch member is designed to match the internal profile of the shape forming punch member with a slight clearance for the blank. Ideally, the fillet radius of the draw punch member is designed to accommodate draw forming and redraw forming of the blank without causing tears or wrinkles.Preferably, the draw counter punch member acts as a counter load system during the final re-draw/stretch forming stage. Ideally, the external profile of the draw counter punch member is designed to match the external profile of the draw punch member. Preferably, the fillet radius of the draw counter punch member is optional and normally matched to the fillet radius on the draw punch.Ideally, the redraw punch assembly comprises a redraw punch member and a counter redraw punch member. Preferably, the redraw punch member and the counter redraw punch member are designed to control the flow of the metal blank during forming. Ideally, the re-draw punch assembly acts as a blank holder arrangement during the draw forming process. Preferably, the internal profile of the redraw punch member is designed to match an external profile on the shape forming punch with a slight clearance for blank thickness. Ideally, the fillet radius of the redraw punch member is optimised to match the requirements of both the initial draw forming process and the redraw forming process while avoiding tearing and wrinkling in the blank. The bending and unbending on the redraw punch when combined with redraw counter punch load serves to control the flow of material during the draw/redraw process.Preferably, the re-draw counter punch member acts as a die during the draw forming process. Ideally, the internal profile of the re-draw counter punch member is designed to match the internal profile on the redraw punch member. Preferably, the fillet radius of the re-draw counter punch member is optimised in conjunction with the flex bead. Advantageously, this matches the requirements of both the initial draw forming process and the redraw forming process while avoiding tearing and wrinkling in the blank. The optimisation process has the boundary conditions of material thickness and tool geometry. The flex bead can then be optimised through the adjustment of the flex bead profile and blank lubrication regimes within the confines of the aforementioned boundary conditions. The overall aim is to eliminate tearing and wrinkling in the blank.Ideally, the external profile of the shape forming punch is designed to match the outlet edge of the lip skin with allowance for springback where required. Preferably, the internal profile of the shape forming punch is designed to match the inlet edge of the lip skin with allowance for springback where required. Ideally, the annular draw bead is mechanically coupled to the actuation system. Preferably, a leading edge profile of the annular draw bead is optimized in conjunction with the internal profile, the blank thickness, draw depth and final thickness. These are effectively the inner boundary conditions for the optimisation.Ideally, an external profile of the annular draw bead is optimised within the constraint of an internal profile of the re-draw punch. The distance between the point of material contact on the draw bead and the outer tooling set should be minimised to near the material thickness. This is the minimum limitation on that boundary conditions.Preferably, the annular draw bead is optimised to control wrinkles and the blank thickness change through bending and unbending as the material flows from the redraw punch assembly over the shape forming punch. Ideally, the forming profile of the annular flex bead is optimized in conjunction with the external profile of the annular bead, the internal profile of the annular bead, the leading edge portion of the shape forming punch, the blank thickness, draw depth and final blank thickness. Depending upon the shape forming punch profile, the annular flex bead profile can be a complex combination of geometric shapes that provide the required control.Preferably, the external profile of the annular flex bead is optimised within the constraint of the internal profile of the redraw punch with a slight clearance for blank thickness.Ideally, the annular flex bead internal profile is optimised within the constraints of the profile of the leading edge portion of the shape forming punch and the annular flex bead profile with slight clearance for blank thickness. The annular flex bead internal profile is ultimately limited by the draw punch profile.Preferably, the blank is produced from a single sheet. Ideally, the profiled blank is typically disc shaped. Where the inlet cowl size requirements exceed a single sheet size, then tailored or profiled blanks joined using a welding process can be utilised. It is also possible to construct a basic blank that is a sector of the complete part. The sector blanks can be formed either on the complete 360° tooling system or on a sector of the complete tooling system.Accordingly, the present invention provides a method of forming a one piece annular component, a sector of an annular component or an arcuate component comprising the steps of loading a blank into a forming apparatus, initiating an actuation means to cause relative coaxial movement only between a shape forming punch, a draw punch assembly and a redraw punch assembly thereby clamping a circumferential portion of the blank in the redraw punch assembly and gripping a central portion of the blank in the draw punch assembly, inserting the shape forming punch in an axial direction until the leading edge of the shape forming punch engages a surface of the blank, moving the draw punch assembly into the internal profile of the shape forming punch to draw form the blank whilst simultaneously maintaining the gripping force of the redraw punch assembly to optimally control material flow during the forming process and moving the redraw punch assembly axially towards the draw punch assembly to perform a redraw forming process.Advantageously, the new lip skin methodology will not only allow the improved manufacture of current lip skin designs but will also accommodate the manufacture of one piece extended trailing edge lip skins which require a longer trailing edge which is an area of specific interest within the aerospace industry. Preferably, the method comprising initiating an actuation means to cause relative coaxial movement only between a shape forming punch, a flex bead, a draw punch assembly and a redraw punch assembly.Ideally, the method comprising locating the flex bead on the opposite surface of the blank between an inner profile of the redraw punch assembly and an outer profile of the shape forming punch, moving the flex bead in an axial direction only into the space between the shape forming punch and the redraw punch assembly so that the portion of the blank between the shape forming punch and the redraw punch assembly is formed over the leading edge of the shape forming punch whilst simultaneously releasing the gripping force of the redraw punch assembly to optimally control material flow during the forming process.Ideally, the blank is generally disc shaped.Preferably, the flex bead is annular.Preferably, the method comprising loading the blank into the apparatus and axially closing the draw punch member, re-draw punch member and the flex bead relative to the draw counter punch member, the shape forming punch and re-draw counter punch.Ideally, the method comprising applying a closing/clamping force between the draw punch member and draw counter punch member and applying a closing clamping force between the re-draw punch member and re-draw counter punch member.Preferably, the method comprising determining the value of the force between the draw punch member and draw counter punch member depending on the blank material and friction conditions.Ideally, the method comprising setting this value to minimise the draw from between the draw punch member and the draw counter punch member. This force becomes especially important when forming sectors as opposed to 360° parts. Preferably, the method comprising setting the re-draw force applied between the re-draw punch member and re-draw counter punch member so as to permit the material to flow from between the re-draw punch member and re-draw counter punch member without tearing, while eliminating the chance of wrinkles in the blank between the re-draw punch and re-draw counter punch.Ideally, the method comprising setting the redraw force so as to control the tension in the blank during the bending and unbending through the flex bead, thereby controlling wrinkling through this section of the draw.Ideally, the method further comprising moving the flex bead axially downwardly into the blank by a controlled displacement while maintaining the draw force and the redraw force on the draw counter punch member and re-draw counter punch member respectively.Preferably, the method further comprising maintaining the shape forming punch, draw punch and re-draw punch stationary throughout the motion of the flex bead.Ideally, the method comprising controlling the flex bead motion either through a set displacement or force, or a hybrid combination of the two.Preferably, the method comprising a draw forming stage comprising displacing the draw punch by a draw displacement, while maintaining the draw force and the redraw force on the draw counter punch and re-draw counter punch respectively. Ideally, the method comprising setting the draw and redraw forces either constant or as a function of the draw displacement. Preferably, the method comprising controlling the flex bead using a simple locked position through to a complex control mode combining force and position control as a function of the displacement during the draw forming stage.Ideally, the method further comprising maintaining the shape forming punch and re-draw punch assembly stationary throughout the draw forming stage.Ideally, the method comprising a redraw forming stage comprising increasing the redraw and draw forces sufficiently to pinch the blank preventing further flow from between the re-draw punch and re-draw counter punch, and the draw punch and draw counter punch respectively. Preferably, the redraw forming stage comprising initially disengaging the flex bead. Preferably, the redraw forming stage further comprising moving the re-draw punch assembly axially downward relative to the shape forming punch until the blank is brought into tension over the shape forming punch at which point the draw punch assembly is displaced axially upward relative to the shape forming punch. Ideally, the method comprising applying relative control of the draw punch assembly to the re-draw punch assembly either through simple relative displacement, force or a combination of the two. Preferably, the method comprising a final stretch at the end of the re-draw stage with a relative downward displacement of the draw punch assembly and counter draw punch assembly while maintaining a redraw and draw load on the blank to prevent flow from between the re-draw punch and re-draw counter punch, and the draw punch and draw counter punch respectively.The invention will now be described with reference to the accompanying drawings, which show by way of example only one embodiment of an apparatus and method for forming a one piece annular component, a sector of an annular component or an arcuate component such as a lip skin for a nacelle. In the drawings:-Figure 1 is an exploded sectional perspective view of an apparatus for forming a one piece annular component, a sector of an annular component or an arcuate component such as a lip skin for an aircraft nacelle;Figure 2 is an exploded sectional perspective view of the apparatus of Figure 1 in a pre forming position of the forming process; Figure 3 is an exploded sectional perspective view of the apparatus at a first stage of the forming process; Figure 4 is an exploded sectional perspective view of the apparatus at a second draw forming stage of the forming process; Figure 5 is an exploded sectional perspective view of the apparatus at a third redraw forming stage of the forming process;Figure 6 is a sectional perspective view of a blank in a pre formed condition;Figure 7 is a sectional perspective view of a blank in a formed condition after the first stage of the forming process;Figure 8 is a sectional perspective view of a blank in a formed condition after the second draw forming stage of the forming process; andFigure 9 is a sectional perspective view of a blank in a formed condition after the third redraw forming stage of the forming process.In the drawings, there is shown an apparatus indicated generally by the reference numeral 101 for forming a one piece annular component see Figure 9, a sector of an annular component or an arcuate component such as a lip skin for an aircraft nacelle. The apparatus 1 has a shape forming punch 1 having a forming end 21 with an external surface shaped to correspond to the shape of the annular component. The apparatus 101 also has a

draw punch assembly

5, 6 for clamping a central portion 102 of a generally circular metal blank 103 and a

redraw punch assembly

3, 4 for adjustably gripping a circumferential portion 105 of the generally circular metal blank 19. A generally annular flex bead 2 is provided formed for location between the shape forming punch 1 and the

redraw punch assembly

3, 4, An actuation arrangement 111 is provided for facilitating relative coaxial movement only between the shape forming punch 1, the

draw punch assembly

5, 6, the

redraw punch assembly

3, 4 and the generally annular flex bead 2 so that the metal blank 19 is formed into an annular component such as a lip skin in a continuous forming process having multiple stages. While the embodiment is described with reference to an annular flex bead 2 it is possible that a sectoral flex bead can be used although this design of sectoral flex bead is more likely to cause the material to wrinkle due to the non-uniform compressive circumferential stresses during the draw forming process. While composite materials can be used for many parts of the nacelle, the lip skin must generally be made from a metal, such as aluminum or titanium, to be able to withstand impacts upon the leading edge or lip thereof. The titanium is also useful in view of recently legislated stringent de-icing requirements requiring higher temperatures at the nacelle leading edge. The actuation arrangement 111 only part of which is shown in Figure 1 of the drawings is capable of creating coaxial movement of the apparatus 101 along a centerline/carriage 106. The centerline/carriage 106 forms a datum for all apparatus 101 components location and kinematics. The actuation arrangement 111 is a linear actuation system. A hydraulic or electromechanical linear actuation system is aligned with the centerline 106.The shape forming punch 1 has an external surface 10 shaped to provide the internal profile of the finished formed lip skin and the forming end 21 of the shape forming punch 1 is generally annular in shape where the shape forming punch external profile 10 is ultimately determined by the desired shape of the inlet cowl. A clean breakpoint 22 is provided on the shape forming punch external profile 10 with either a coaxial or slightly tapered clearance profile from the break point 22 to the end of the shape forming punch 1. The shape forming punch internal profile 11 is ultimately determined by the desired shape of the inlet cowl. A clean breakpoint 23 is also provided on the shape forming punch internal profile 11 with either a coaxial or slightly tapered clearance profile from the break point 23 to the end of the shape forming punch 1. The shape forming

punch profile

10, 11 is designed to match that of the desired internal surface of the inlet cowl. A simple axis-symmetric component is shown although an asymmetric profile can be used. The external surface 10 of the shape forming punch 1 can be optimized for springback and has a high surface finish. Advantageously, the high surface finish value reduces friction during forming. The shape forming punch 1 is mechanically coupled to the linear actuation system.The

draw punch assembly

5, 6 has a draw punch member 5 and a counter draw punch member 6. The draw punch member 5 and the counter draw punch member 6 are generally cylindrical block members although their profile will ultimately depend upon the punch profile. The draw punch member 5 and counter draw punch member 6 are openable and closable by the linear actuation system to clamp the blank 19. The motion of both the draw punch member 5 and the counter draw punch member 6 is aligned with the centerline 106. The draw punch member 5 acts as a counter load system during the final re-draw/stretch forming process. The external profile 13 of the draw punch member 5 is designed to match the internal profile 11 of the shape forming punch member 1 with a slight clearance for the blank 19. The fillet radius 18 of the draw punch member 5 is designed to accommodate draw forming and redraw forming of the blank 19 without causing tears or wrinkles. The draw counter punch member 6 acts as a counter load system during the final re-draw/stretch forming stage. The external profile 12 of the draw counter punch member 6 is designed to match the external profile 13 of the draw punch member 5. The fillet radius 119 of the draw counter punch member 6 is optional and normally matched to the fillet radius 18 on the draw punch member 5.The redraw

punch assembly

3, 4 has a redraw punch member 3 and a counter redraw punch member 4. The redraw punch member 3 and the counter redraw punch member 4 are designed to control the flow of the metal blank 103 during forming. The

re-draw punch assembly

3, 4 acts as a blank holder arrangement during the draw forming process. The internal profile 14 of the redraw punch member 3 is designed to match an external profile 10 on the shape forming punch 1 with a slight clearance for a blank thickness. The fillet radius 17 of the redraw punch member 3 is optimised to match the requirements of both the initial draw forming process and the redraw forming process while avoiding tearing and wrinkling in the blank 103. The re-draw counter punch member 4 acts as a die during the draw forming process. The internal profile 15 of the re-draw counter punch member 4 is designed to match the internal profile 14 on the redraw punch member 3. The fillet radius 16 of the re-draw counter punch member 4 is optimised in conjunction with the flex bead 2. The fillet radius 16 is part of the bending and unbending driven by the flex bead 2. This fillet radius 16 is critical during this initial draw phase of the process. Advantageously, this matches the requirements of both the initial draw forming process and the redraw forming process while avoiding tearing and wrinkling in the blank 103. The external profile 10 of the shape forming punch 1 is designed to match the outlet edge of the lip skin with allowance for springback where required. The internal profile of the shape forming punch 11 is designed to match the inlet edge of the lip skin with allowance for springback where required. The generally annular draw bead 2 is mechanically coupled to the actuation system. A leading edge profile 7 of the annular draw bead 2 is optimized in conjunction with its own external profile 8, internal profile 9, the preformed blank thickness, draw depth and final formed blank thickness. An external profile 8 of the annular draw bead 2 is optimised within the constraint of an internal profile 14 of the re-draw punch 3. The annular draw bead 2 is optimised to control wrinkles and the blank thickness change through bending and unbending as the material flows from the redraw

punch assembly

3, 4 over the shape forming punch 1. Depending upon the shape forming punch profile 21, the annular flex bead profile 7 can be a complex combination of geometric shapes that provide the required control. The profile 7 of the flex bead can be a complex 3D surface that varies around the axis 106 to permit the control of the material flow through bending under tension. The external profile 8 of the annular flex bead 2 is optimised within the constraints of the internal profile 14 of the redraw punch 3 with a slight clearance for a blank thickness. The annular flex bead internal profile 9 is optimised within the constraints of the profile of the leading edge portion 21 of the shape forming punch 1 and the annular flex bead profile 7 with slight clearance for a blank thickness. The annular flex bead internal profile 9 is ultimately limited by the draw punch profile 13.The blank 19 is produced from a single sheet and the profiled blank 19 is typically disc shaped although other profiles are possible. Where the inlet cowl size requirements exceed a single sheet size, then tailored blanks joined using a welding process can be utilised. It is also possible to construct a basic blank that is a sector of the complete part. The sector blanks can be formed either on the complete 360° tooling system or on a sector of the complete tooling system.Positionally, the

draw punch assembly

5, 6 is mounted centrally on the apparatus 101 and the generally annular shaped forming punch 1 is disposed radially outwardly from the

draw punch assembly

5, 6 enclosing the

draw punch assembly

5, 6. The redraw

punch assembly

3, 4 is located outermost radially on the apparatus 101 and the flex draw bead 2 is located between the shape forming punch 1 and the redraw punch assembly 3, 4.The tooling system operation is described below with reference to Figures 2 to 5. For the purposes of clarity the draw punch (5), flex bead (2) and re-draw punch (3) are illustrated under displacement control while the draw counter punch (6) and re-draw counter punch (4) are under load control. The shape forming punch 1 is considered fixed. This illustration does not discount the possibility of a mixed mode of control beyond that shown. The important aspect is the relative motion of the individual components. Although the process is shown and described in the drawings as a complete system, this does not discount the possibility of using a series of tools to achieve the same result.The blank (19) is first loaded into the apparatus 101 and then the draw punch (5), re-draw punch (3) and the flex bead (2) are closed axially relative to the draw counter punch (6), punch (1) and re-draw counter punch (4). A closing/clamping force FD is then applied between the draw punch (5) and draw counter punch (6) and a closing/clamping force FRD is applied between the re-draw punch (3) and re-draw counter punch (4). The value of FD will depend upon the blank material and friction conditions. This value is normally set to minimise the draw from between the draw punch (5) and the draw counter punch (6). This becomes especially important when forming sectors as opposed to 360° annular parts. The re-draw force FRD is designed to permit the material to flow from between the re-draw punch (3) and re-draw counter punch (4) without tearing, while eliminating the chance of wrinkles in the blank between the re-draw punch (3) and re-draw counter punch (4). The force FRD also controls the tension in the sheet during the bending and unbending through the flex bead (2), therefore controlling wrinkling through this section of the draw. The forces will be unique to each geometry and material thickness. The flex bead (2) is moved axially into the blank 19 by a controlled displacement DF while maintaining FD and FRD on the draw counter punch (6) and re-draw counter punch (4) respectively. The shape forming punch (1), draw punch (5) and re-draw punch (3) remain stationary throughout the motion of the flex bead 2. The control of the flex bead motion can be achieved either through a set displacement or force, or a hybrid combination of the two.The draw punch 5 is displaced by the draw displacement DD, while maintaining FD and FRD on the draw counter punch (6) and re-draw counter punch (4) respectively. The forces FD and FRD can be either constant or a function of the displacement DD. The flex bead (2) control can range from a simple locked position through to a complex control mode combining force and position control as a function of the displacement DD. The punch (1) and re-draw punch (3) remain stationary throughout this stage.The flex bead 2 can now be disengaged and plays no further role in the subsequent forming operations. The forces FRD and FD are increased sufficiently to pinch the blank (20) and prevent further flow from between the re-draw punch (3) and re-draw counter punch (4), and the draw punch (5) and draw counter punch (6) respectively. The re-draw punch (3) is displaced axially relative to the punch (1) until the blank is brought into tension over the shape forming punch (1) at which point the draw punch (5) is displaced axially upward relative to the shape forming punch (1). The relative control of the draw punch (5) to the re-draw punch (6) can be achieved either through simple relative displacement, force or a combination of the two. If necessary a final stretch can be introduced at the end of the re-draw with a relative downward displacement of the draw punch (5) and counter draw punch (3) while maintaining a pinch load FRD and FD on the blank (20) to prevent flow from between the re-draw punch (3) and re-draw counter punch (4), and the draw punch (5) and draw counter punch (6) respectively.The blank (19) shape changes during the main forming process as shown in Figures 6 to 9. The blank 19 shown is a full 360° part, though this does not discount the use of sectors or other profiles to aid in the forming of a complete 360° or sector part. From the initial flat blank 19 shown in Figure 6 the flex bead (2) is first inserted as to from the blank as shown in Figure 7. Next the blank (20) is drawn into the shape shown in Figure 8 before the final re-draw and stretch operation leaving the shape as shown in Figure 9. A final trim operation is then used to remove the excess material. In the preceding discussion of the invention, unless stated to the contrary, the disclosure of alternative values for the upper or lower limit of the permitted range of a parameter, coupled with an indication that one of the said values is more highly preferred than the other, is to be construed as an implied statement that each intermediate value of said parameter, lying between the more preferred and the less preferred of said alternatives, is itself preferred to said less preferred value and also to each value lying between said less preferred value and said intermediate value.The features disclosed in the foregoing description or the following drawings, expressed in their specific forms or in terms of a means for performing a disclosed function, or a method or a process of attaining the disclosed result, as appropriate, may separately, or in any combination of such features be utilised for realising the invention in diverse forms thereof as defined in the appended claims.

Claims

A method of forming a one piece annular component, a sector of an annular component or an arcuate component comprising the steps of loading a blank (19) into a forming apparatus (101), initiating an actuation means (111) to cause relative coaxial movement only between a shape forming punch (1), a draw punch assembly (3, 4) and a redraw punch assembly (5, 6) thereby clamping a circumferential portion of the blank (19) in the redraw punch assembly (5, 6) and gripping a central portion (102) of the blank (19) in the draw punch assembly (3, 4), inserting the shape forming punch (1) in an axial direction until the leading edge (21) of the shape forming punch (1) engages a surface of the blank (19), moving the draw punch assembly (3, 4) into the internal profile of the shape forming punch (1) to draw form the blank (19) whilst simultaneously maintaining the gripping force of the redraw punch assembly (5, 6) to optimally control material flow during the forming process and moving the redraw punch assembly (5, 6) axially towards the draw punch assembly (3, 4) to perform a redraw forming process.
A method as claimed in claim 1, the method comprising initiating an actuation means (111) to cause relative coaxial movement only between a shape forming punch (1), a flex bead (2), a draw punch assembly (3, 4) and a redraw punch assembly (5, 6).
A method as claimed in claim 2, comprising locating a flex bead (2) on the opposite surface of the blank (19) to the side in contact with the shape forming punch (1) between an inner profile of the redraw punch assembly (5, 6) and an outer profile of the shape forming punch (1) and moving the flex bead (2) in an axial direction only into the space between the shape forming punch (1) and the redraw punch assembly (5, 6) so that the portion of the blank (19) between the shape forming punch (1) and the redraw punch assembly (5, 6) is formed over the leading edge (21) of the shape forming punch (1) whilst simultaneously releasing the gripping force of the redraw punch assembly (5, 6) to optimally control material flow during the forming process prior to the draw forming stage.
A method as claimed in any one of the preceding claims, the method comprising applying a closing/clamping force between a draw punch member (5) and a draw counter punch member (6) and applying a closing clamping force between a re-draw punch member (3) and a re-draw counter punch member (4),
A method as claimed in claim 4, the method comprising determining the value of the force FD between the draw punch member (5) and draw counter punch member (6) depending on the blank material and friction conditions.
A method as claimed in claim 4 or claim 5, the method comprising setting this closing /clamping force FD to minimise the draw from between the draw punch member (5) and the draw counter punch member (6).
A method as claimed in any one of the preceding claims, the method comprising setting a re-draw force FRD applied between a re-draw punch member (3) and re-draw counter punch member (4) to permit the material to flow from between the re-draw punch member and re-draw counter punch member without tearing, while eliminating the chance of wrinkles in the blank between the re-draw punch member and re-draw counter punch member.
A method as claimed in any one of claims 3 to 7 when dependent on claim 2, the method comprising setting the redraw force FRD so as to control the tension in the blank (19) during the bending and unbending through the flex bead (2), thereby controlling wrinkling through this section of the draw forming process.
A method as claimed in any one of the claims 3 to 8 when dependent on claim 2, the method comprising moving the flex bead (2) axially downwardly into the blank (19) by a controlled displacement while maintaining the draw force FD and the redraw force FRD on the draw counter punch member (6) and re-draw counter punch member (4) respectively.
A method as claimed in claim 9, the method comprising maintaining the shape forming punch (1), draw punch assembly (5, 6) and re-draw punch assembly (3, 4) stationary throughout the motion of the flex bead (2).
A method as claimed in claim 9 or 10, the method comprising controlling the motion of the flex bead (2) either through a set displacement or force, or a hybrid combination of the two.
A method as claimed in any one of the preceding claims, the method comprising a draw forming stage comprising displacing the draw punch assembly (5, 5) by a draw displacement, while maintaining the draw force and the redraw force on the draw punch assembly (5, 6) and re-draw punch assembly (3, 4) respectively.
A method as claimed in claim 12, the method comprising setting the draw and redraw forces either as a constant or as a function of the draw displacement during the draw forming stage.
A method as claimed in claim 12 or 13 when dependent on claim 2, the method comprising controlling the flex bead (2) using a simple locked position through to a complex control mode combining force and position control as a function of the displacement during the draw forming stage.
A method as claimed in claims 12 or 13 or as claimed in claim 14 when dependent on claim 2, the method further comprising maintaining the shape forming punch (1) and re-draw punch assembly (3,4) stationary throughout the draw forming stage.
A method as claimed in any one of the preceding claims, the method comprising a redraw forming stage comprising increasing the redraw and draw forces sufficiently to pinch the blank (19) preventing further material flow from between the re-draw punch member (3) and re-draw counter punch member (4) , and the draw punch member (5) and draw counter punch member (6) respectively.
A method as claimed in claim 16, the method comprising the redraw forming stage further comprising moving the re-draw punch assembly (3, 4) axially downward relative to the shape forming punch (1) until the blank (19) is brought into tension over the shape forming punch (1) at which point the draw punch assembly (5, 6) is displaced axially upward relative to the shape forming punch (1).
A method as claimed in claim 17, the method comprising applying relative control of the draw punch assembly (5,6) to the re-draw punch assembly (3, 4) either through simple relative displacement, force or a combination of the two.
A method as claimed in any one of the preceding claims, the method comprising an optional final stretch at the end of the re-draw stage with a relative downward displacement of the draw punch assembly (5, 6) and counter draw punch assembly (3, 4) while maintaining a redraw and draw load on the blank (19) to prevent material flow from between the re-draw punch and re-draw counter punch, and the draw punch and draw counter punch respectively.
A method as claimed in any one of the preceding claims, the method comprising a single stage process or a multistage process depending on the degrees of freedom available in the actuation means (111).
A method as claimed in any one of the preceding claims, the method comprising forming the metal blank into a one piece annular component or a sector of an annular component or an arcuate component for a lip skin or a sector of a lipskin for an aircraft nacelle.
An apparatus (101) for forming a one piece annular component, a sector of an annular component or an arcuate component, the apparatus (101) comprising a shape forming punch (1) having a forming end (21) with an external surface shaped to correspond to the shape of the component, a draw punch assembly (5, 6) for clamping a central portion (102) of a metal blank (19) and a redraw punch assembly (3, 4) for adjustably gripping a circumferential portion of the metal blank (19), actuation means (111) for facilitating relative coaxial movement only between the shape forming punch (1), the draw punch assembly (5, 6) and the redraw punch assembly (3, 4) for forming the metal blank (19) into a one piece annular component, a sector of an annular component or an arcuate component in a forming process.
An apparatus as claimed in claim 22, wherein a flex bead (2) is located between the shape forming punch (1) and the redraw punch assembly (3, 4).
An apparatus (101) as claimed in claim 23, wherein the flex bead (2) is annular or part annular.
An apparatus (101) as claimed in any one of claims 22 to 24, wherein a clean breakpoint (22) is provided on a shape forming punch (1) external profile with either a coaxial or slightly tapered clearance profile from the break point (22) to the end of the shape forming punch (1).
An apparatus (101) as claimed in any one of claims 22 to 25, wherein a clean breakpoint (23) is provided on a shape forming punch internal profile with either a coaxial or slightly tapered clearance profile from the break point (23) to the end of the shape forming punch (1).
An apparatus (101) as claimed in any one of claims 22 to 26, wherein the shape forming punch profile has a simple axis-symmetric profile or an asymmetric profile.
An apparatus (101) as claimed in any one of claims 22 to 27, wherein an external surface of the shape forming punch (1) is optimized for springback.
An apparatus (101) as claimed in claim 28, wherein the external surface of the shape forming punch (1) has a high surface finish.
An apparatus (101) as claimed in any one claims 22 to 29, wherein the actuation means (111) is a linear hydraulic or electromechanical linear actuation system aligned with a centerline (106).
An apparatus (101) as claimed in any one of claims 23 to 30, wherein the shape forming punch (1), the draw punch assembly (5,6), the redraw punch assembly (3, 4) and the flex bead (2) are mechanically coupled to the actuation system (111).
An apparatus (101) as claimed in any one of claims 22 to 31, wherein the draw punch assembly (5, 6) comprises a draw punch member (5) and a counter draw punch member (6) openable and closable to clamp the blank (19), the draw punch member (5) and the counter draw punch member (6) acting as a counter load system during the final re-draw/stretch forming process.
An apparatus (101) as claimed in claim 32 when dependent on claim 26, wherein an external profile of a draw punch member (5) is designed to match an external profile of the draw counter punch member (6) and to match the internal profile of the shape forming punch member (1) with a slight clearance for the blank (19).
An apparatus (101) as claimed in claim 32, wherein a fillet radius (18) of the draw punch member (5) is designed to accommodate draw forming and redraw forming of the blank (19) without causing tears or wrinkles.
An apparatus (101) as claimed in claim 34, wherein the fillet radius (119) of the draw counter punch member (6) is optional and normally matched to the fillet radius on the draw punch member.
An apparatus (101) as claimed in any one of claims 22 to 35, wherein the redraw punch assembly (3, 4) comprises a redraw punch member (3) and a counter redraw punch member (4) designed to control the flow of the metal blank during forming.
An apparatus (101) as claimed in any one of claim 22 to 36, wherein the redraw punch assembly (3, 4) acts as a blank holder arrangement during the draw forming process.
An apparatus (101) as claimed in claim 36 when dependent on claim 25, wherein an internal profile of a redraw punch member (3) is designed to match an internal profile of the redraw counter punch member (4) and is designed to match the external profile on the shape forming punch (1) with a slight clearance for blank thickness.
An apparatus (101) as claimed in claim 36, wherein a fillet radius (17) of the redraw punch member (3) is optimised to match the requirements of both the initial draw forming process and the redraw forming process while avoiding tearing and wrinkling in the blank.
An apparatus (101) as claimed in claim 36, wherein the re-draw counter punch member (4) acts as a die during the draw forming process.
An apparatus (101) as claimed in claim 36 when dependent on claim 23, wherein the fillet radius (16) of the re-draw counter punch member (6) is optimised in conjunction with the flex bead (2).
An apparatus (101) as claimed in any one of claims 23 to 41, wherein a leading edge profile (7) of the annular draw bead (2) is optimized in conjunction with an internal profile (9), the blank thickness, draw depth and final thickness being the inner boundary conditions for the optimisation.
An apparatus (101) as claimed in claim 38, wherein an external profile (8) of the annular draw bead (2) is optimised within the constraint of an internal profile of the re-draw punch (3), the distance between the point of material contact on the draw bead (2) and the outer tooling set being minimised to near the material thickness which is the minimum limitation on that boundary condition.