Patent Description:
Metal spinning is a metal forming process that has traditionally been used to produce hollow, axially symmetric (axisymmetric) items or articles by forming a metal blank against the surfaces of a mandrel. The mandrel is shaped according to the design of the desired item or article and rotates with the workpiece to provide forming surfaces against which the workpiece can be shaped.

<FIG> illustrates a traditional spin forming apparatus <NUM> used for such purposes. A workpiece <NUM>, typically in the form of a metal blank, is secured to a mandrel <NUM> on a lathe <NUM>, with an inner surface <NUM> of the workpiece <NUM> facing the mandrel <NUM>. The workpiece <NUM> is gradually deformed into the desired shape by applying pressure, from a forming tool <NUM>, against an outer surface <NUM> of the rotating workpiece <NUM> and moving the forming tool <NUM> so as to trace the surfaces of the rotating mandrel <NUM>.

The forming tool <NUM> may be controlled by manual inputs from an operator or by computer numeric control (CNC). When CNC is used, the operator determines a sequence of positions through which the forming tool <NUM> should be moved to deform the workpiece <NUM> into the desired shape. For example, the sequence of positions may be determined based on a mathematical equation relating the movement of the forming tool <NUM> along an axis parallel to the axis of rotation of the workpiece <NUM> to the movement of the forming tool <NUM> along an axis perpendicular to the axis of rotation of the workpiece <NUM>. The sequence of positions provides a toolpath that the forming tool <NUM> follows to form the workpiece <NUM> against the mandrel <NUM>. Thereafter, the toolpath can be reused with further workpieces <NUM> to reproduce copies of the desired article and provide some degree of automation.

This process may, for example, be used to produce any of the axisymmetric articles shown in <FIG> and may be completed in a single pass of the forming tool <NUM> over the workpiece <NUM> (shear spinning) or by multiple passes over the workpiece <NUM> (conventional spinning).

Metal spinning is advantageous in that there is minimal springback of the finished article and the initial tooling costs are relatively low. However, a new mandrel <NUM> is required whenever the shape of the desired article changes. Accordingly, the costs associated with design variations are high.

More recently, metal spinning methods have been developed that are mandrel-free. <CIT> describes an example mandrel-free spinning apparatus <NUM> for spin forming both axisymmetric and non-axisymmetric articles. The mandrel-free spinning apparatus <NUM>, illustrated in <FIG>, includes a plurality of mobile forming tools <NUM> that are movable to engage and support or deform a rotating workpiece <NUM>. In this manner, the mobile forming tools can be moved as the workpiece <NUM> rotates to replicate the profile of a desired article and effectively replace the fully formed mandrel <NUM>.

<FIG> illustrates the principle features of a mandrel-free spinning apparatus <NUM> for gradually deforming a workpiece <NUM> into a desired shape. As shown, the mandrel-free spinning apparatus <NUM> includes: a rotatable mounting point, such as a lathe <NUM>, to which the workpiece <NUM> is secured; a first forming tool 12a arranged to act on an outer surface <NUM> of the rotating workpiece <NUM>; and a second forming tool 12b, shown proximal to the lathe <NUM>, which is arranged to act on an opposing inner surface <NUM> of the rotating workpiece <NUM>. Examples of the mandrel-free spinning apparatus <NUM> may further include one or more further forming tools, such as the third and fourth forming tools 12c, 12d, shown in <FIG>, that may be arranged to act on the inner or outer surfaces <NUM>, <NUM> of the workpiece <NUM>. For example, the third and fourth forming tools 12c, 12d may act on the workpiece <NUM> in areas of the workpiece <NUM> that are distal from the lathe <NUM>.

<FIG> illustrates an end view of the mandrel-free spinning apparatus <NUM> shown in <FIG>. In this example, the first and second forming tools 12a, 12b, are arranged to move in a first plane <NUM> aligned with a longitudinal axis <NUM> of the lathe <NUM>, whilst the third and fourth forming tools 12c, 12d are arranged to move within and outside of the first plane <NUM>. The third and fourth forming tools 12c, 12d may, for example, move symmetrically to one another about the first plane <NUM>.

<FIG> shows a practical example of the mandrel-free spinning apparatus <NUM>, as depicted in <CIT> and as illustrated conceptually in previous <FIG>. In this practical example, the positions of the first, second, third and fourth forming tools 12a-d are adjustable relative to the workpiece <NUM> by a respective set of actuators <NUM> controlled by CNC, for example.

<FIG> shows a plan view of the mandrel-free spinning apparatus <NUM> shown in <FIG>. The plan view identifies the longitudinal axis <NUM>, or axis of rotation, of the lathe <NUM> and a radial axis <NUM> which extends perpendicularly from the longitudinal axis <NUM> (in the same horizontal plane). The set of actuators <NUM> are able to adjust the positions of the first, second, third and fourth forming tools 12a-d relative to the lathe <NUM>, and hence the workpiece <NUM>, along the longitudinal axis <NUM> and the radial axis <NUM>. In this manner, the longitudinal axis <NUM> acts as a first axis of movement and the radial axis <NUM> acts as a second axis of movement for each of the forming tools 12a-d.

In <FIG>, the first forming tool 12a is shown supported at one end of a first arm member <NUM> and the second forming tool 12b is shown attached to one end of a second arm member <NUM>. The first forming tool 12a may take the form of a so-called working roller and the second forming tool 12b may take the form of a so-called blending roller. Each of the working and blending rollers may be metallic and may feature a ceramic coating that provides enhanced durability and/or minimises friction.

The angle of the first arm member <NUM> may be adjustable relative to the longitudinal axis <NUM> and the workpiece <NUM>. The angle may generally remain constant during a single spin forming process.

In use, the first and second forming tools 12a, 12b can be moved along the radial and longitudinal axes <NUM>, <NUM> to respectively engage the inner and outer surfaces <NUM>, <NUM> of the workpiece <NUM> and to deform the rotating workpiece <NUM> therebetween into the shape of the desired article. For this purpose, the second arm member <NUM> may be shaped to allow insertion/removal of the second forming tool 12b into/from an interior volume of the article as the workpiece <NUM> is deformed into a concave or tubular shape.

Hence, the mandrel-free spinning apparatus <NUM> possess sufficient mobility to deform a metal workpiece <NUM> into a variety of both axisymmetric and non-axisymmetric shapes, such as those shown in <FIG>. The absence of a fully formed mandrel also enables the production of re-entrant shapes, as illustrated by the profile in <FIG>. In addition, the spinning process can be completed in a single pass of the first forming tool 12a over the workpiece <NUM> (shear spinning) or in multiple passes over the workpiece <NUM> (conventional spinning) as practised on traditional spin forming machines. Furthermore, CNC may be used to move each of the first, second, third and fourth forming tools 12a-d according to respective toolpaths.

However, despite its potential advantages the technology is immature and the existing methods of controlling the mandrel-free spinning apparatus <NUM> have encountered various problems relating to spring-back, stretching and/or wrinkling of the workpiece <NUM> as the workpiece <NUM> is deformed into the shape of the article, i.e. the article shape.

<CIT> discloses a method and apparatus for forming an elliptical hollow cylinder, in which part of the elliptical hollow cylinder is formed into a circular hollow cylindrical shape using a two-stage spin forming process. The two-stage forming process includes: (i) a first stage, during which part of an elliptical hollow cylinder is formed into a circular hollow cylindrical shape using an inside roller; and (ii) a second stage, during which a diameter of the circular hollow cylindrical shape is then reduced using an outside roller.

The present invention has been developed to attend to at least some of the above-mentioned problems.

Aspects and embodiments of the invention provide a method of controlling a mandrel-free spinning apparatus and a controller for the mandrel-free spinning apparatus as claimed in the appended claims.

According to an aspect of the invention there is provided a method of controlling a mandrel-free spinning apparatus to produce an article, having a target geometry, from a workpiece, the mandrel-free spinning apparatus comprising: a rotatable mounting point for the workpiece; a first forming tool; and a second forming tool; the method including: whilst the workpiece rotates, moving the first forming tool so as to: engage a first surface of the workpiece; and urge the workpiece, from an initial workpiece geometry, towards and beyond the target geometry into an intermediate geometry; and whilst the workpiece rotates, moving the second forming tool so as to: engage a second surface of the workpiece, opposed to the first surface of the workpiece; and urge the workpiece from the intermediate geometry towards the target geometry. The first forming tool is moved to urge the workpiece inward, along and towards an axis of rotation of the mounting point, from the initial workpiece geometry into the intermediate geometry, and the second forming tool is moved to urge the workpiece outward, from the intermediate geometry towards the target geometry.

It shall be appreciated that the target geometry corresponds to the shape of the article.

Advantageously, the method includes two stages of spin forming. In the first stage, the first forming tool may engage an outer surface of the workpiece and urge the workpiece inwards into the intermediate geometry, which may, for example, be curved to a lesser degree than the target geometry. In the second stage, the second forming tool may engage an inner surface of the workpiece and urge the workpiece outwards and back towards the target geometry. Advantageously, the workpiece is work hardened during the first stage and deformed beyond the target geometry, i.e. deformed such that a portion of the workpiece is further along and/or closer to an axis extending through the centre of the workpiece. Consequently, the subsequent deformation of the workpiece in the second stage may be to a lesser extent, i.e. the strain on the workpiece may be less in deforming the workpiece from the intermediate geometry to the target geometry than in deforming the workpiece from the initial geometry to the intermediate geometry. In this manner, the second stage shapes the workpiece more precisely to form the surfaces of the target geometry, which may be more curved or complex.

Advantageously, the workpiece may be deformed into a tubular, or concave, shape by the first forming tool and the second forming tool may then be moved so as to indent the workpiece surfaces, increasing the curvature and concavity of the workpiece as the target geometry may require.

Optionally, the first surface of the workpiece forms an outer surface of the article and the second surface of the workpiece forms an inner surface of the article.

Optionally, in the intermediate geometry, the workpiece includes: a central hub; and a body portion extending from the central hub to a rim. Optionally, the surfaces of the workpiece in the intermediate geometry are curved to a lesser degree along the axis of rotation than is necessary to form the target geometry. Advantageously, the workpiece may be more geometrically stable in such an intermediate geometry such that the workpiece is less susceptible to stretching, wrinkling and/or other failure modes as the workpiece is deformed from the intermediate geometry to the target geometry.

Optionally, urging the workpiece from the initial workpiece geometry into the intermediate geometry comprises moving the first forming tool linearly so that, in the intermediate geometry, the body portion of the workpiece is frusto-conical. Advantageously, the frusto-conical body portion is particularly stable and provides sufficient geometric stability for the subsequent deformation into the target geometry.

Optionally, urging the workpiece from the initial workpiece geometry into the intermediate geometry comprises moving the first forming tool along a straighter trajectory than is required to form the target geometry. The straighter trajectory produces a more stable intermediate geometry and mitigates the risk of the workpiece failing.

Optionally, the first forming tool is moved between a start point and an end point along the axis of rotation of the mounting point by a distance corresponding to a length or depth of the target geometry. Advantageously, the full depth of the target geometry is produced in this motion, which minimises the number of passes in the spin forming process.

Optionally, moving the second forming tool so as to urge the workpiece outward from the intermediate geometry towards the target geometry comprises moving the second forming tool along a curve to deform the body portion of the workpiece outward. Advantageously, in this manner, the second forming tool can deform the workpiece into a curved shape with a varying profile along its length, whilst the first forming tool produces a more linear shape.

Optionally, moving the second forming tool along the curve deforms the body portion of the workpiece into a domed shape. Optionally, the target geometry is discoidal. In this manner, the method may provide a fast process for spin forming a discoidal article with enhanced surface finish compared to conventional multi-pass spinning methods.

In an example, the method may comprise supporting the workpiece distally from an axis of rotation of the mounting point relative to the second forming tool whilst moving the second forming tool so as to urge the workpiece from the intermediate geometry towards the target geometry. Supporting the workpiece in this manner may inhibit tilting of the workpiece about the mounting point. In particular, whilst the workpiece is urged towards the target geometry, the second forming tool may apply pressure to radially distal surfaces of the workpiece creating a turning moment acting to tilt the workpiece and supporting the workpiece in areas that are radially beyond the second forming tool may substantially inhibit such tilting effects. This may improve the quality of the finished article and allow for faster forming speeds.

In an example, the method may comprise supporting the workpiece at the rim of the workpiece whilst moving the second forming tool so as to urge the workpiece from the intermediate geometry towards the target geometry. Advantageously, the rim of the workpiece provides a radially outer portion of the workpiece that can be supported with minimal force.

Optionally, in the intermediate geometry, the workpiece includes a flange portion that extends around a circumference of the body portion of the intermediate geometry. The flange portion of the intermediate geometry may be formed from an unworked region of the workpiece. The flange portion may effectively extend from the rim of the intermediate geometry. The flange portion may also help to increase the circumferential stiffness of the workpiece, mitigating the likelihood of wrinkling, as the workpiece is urged towards the target geometry.

The workpiece may, for example, be oversized for the article. For example, the initial geometry of the workpiece may be circular having a radius corresponding to the net shape of the article plus an additional length corresponding to the flange portion. In this manner, the flange portion is integral with the other portions of the workpiece.

Optionally, the method comprises supporting the flange portion of the workpiece whilst moving the second forming tool so as to urge the workpiece from the intermediate geometry towards the target geometry. Supporting the workpiece in this manner may mitigate tilting effects that may otherwise occur as the workpiece is urged towards the target geometry.

The first forming tool may, for example, engage the flange portion of the workpiece to support the flange portion of the workpiece. Advantageously, the first forming tool is reused as a support for the workpiece after deforming the workpiece into the intermediate geometry.

Optionally, the flange portion of the intermediate geometry includes a flange wall that is sufficiently wide for the first forming tool to engage and thereby support the workpiece. The flange wall may be annular and the width of the flange wall may extend from an inner radius to an outer radius.

Optionally, the second forming tool is moved so as to urge the workpiece from the intermediate geometry towards the target geometry and into a formed geometry.

In the formed geometry, the workpiece may, for example, include a central hub; a body portion extending from the central hub to a rim; and a flange portion that extends around the circumference of the rim. In the formed geometry, the central hub and the body portion of the workpiece may correspond to the target geometry.

Optionally, the method comprises removing the flange portion from the workpiece after urging the workpiece into the formed geometry. This may, for example, be considered as a finishing process used to remove the excess material of the workpiece and produce the desired article.

Optionally, the movement of the first forming tool to engage the first surface of the workpiece and urge the workpiece, from the initial workpiece geometry, towards and beyond the target geometry into the intermediate geometry is controlled according to a first toolpath; and/or the movement of the second forming tool to engage the second surface of the workpiece and urge the workpiece from the intermediate geometry towards the target geometry is controlled according to a second toolpath. Advantageously, the first and second toolpaths may allow the process to be at least partially automated.

The first toolpath may, for example, be arranged to move the first forming tool along a first axis of the mandrel-free spinning apparatus and a second axis of the mandrel-free spinning apparatus. The first axis may be parallel to the axis of rotation of the mounting point and the second axis may be perpendicular to the first axis. The second toolpath may, for example, be configured to move the second forming tool along the first and second axes.

Optionally, the first toolpath is configured to move the first forming tool along a first line or trajectory arranged along the first and second axes, between a start point and an end point of the first toolpath. Optionally, the second toolpath is configured to move the second forming tool along a second line or trajectory arranged along the first and second axes, between a start point and an end point of the second toolpath.

The second line may, for example, be curved between the start and end points of the second toolpath and a maximum radius of curvature of the first line may be less than a maximum radius of curvature of the second line. This may, for example, ensure that the workpiece is more stable in the intermediate geometry than the target geometry, meaning that the workpiece is less likely to stretch, wrinkle of otherwise fail as the workpiece is deformed from the intermediate geometry towards the intermediate geometry. The first line may, for example, be straight between the start point and the end point of the first toolpath.

Optionally, the first toolpath includes: a plurality of passes, each pass of the first toolpath achieving an iterative deformation of the workpiece towards the intermediate geometry. The plurality of passes may, for example, reduce the tendency of the workpiece to fail or stretch during the forming process.

The second toolpath may, for example, include a plurality of passes, each pass of the second toolpath achieving an iterative deformation of the workpiece from the intermediate geometry towards the target geometry. The plurality of passes may allow for gradual deformation towards the target geometry with lower forces on the forming tool.

Optionally, the method further includes attaching a forming plate to the second surface of the workpiece before moving the first forming tool so as to urge the workpiece, from the initial workpiece geometry, towards and beyond the target geometry into the intermediate geometry. The forming plate may, for example, assist the transition between the initial workpiece geometry and the intermediate geometry. The forming plate may provide resistance to deformation of the workpiece in a central region of the workpiece. For example, the forming plate may support the workpiece in a region corresponding to the central hub of the target geometry and may help to guide the deformation of the workpiece around the central hub of the target geometry as the workpiece is urged away from the initial geometry. Accordingly, the forming plate may have a shape corresponding to the central hub of the target geometry.

The method may, for example, include removing the forming plate from the second surface of the workpiece before moving the second forming tool so as to engage the second surface of the workpiece and urge the workpiece from the intermediate geometry towards the target geometry.

Optionally, the target geometry is axisymmetric. Optionally, the target geometry is shallow having a diameter that is larger than a depth of the target geometry.

According to another aspect of the invention there is provided a control system for a mandrel-free spinning apparatus comprising: a rotatable mounting point for a workpiece; a first forming tool; and a second forming tool; to produce an article, having a target geometry, the control system being configured to output one or more signals to: control the rotation of the workpiece; move the first forming tool, whilst the workpiece rotates, so as to: engage a first surface of the workpiece; and urge the workpiece, from an initial workpiece geometry, towards and beyond the target geometry into an intermediate geometry; and move the second forming tool, whilst the workpiece rotates, so as to: engage a second surface of the workpiece, opposed to the first surface of the workpiece; and urge the workpiece from the intermediate geometry towards the target geometry. The first forming tool is moved to urge the workpiece inward, along and towards an axis of rotation of the mounting point, from the initial workpiece geometry into the intermediate geometry, and the second forming tool is moved to urge the workpiece outward, from the intermediate geometry towards the target geometry.

Embodiments of the present invention relate to a method of controlling a mandrel-free spinning apparatus to produce an article from a workpiece <NUM>.

The mandrel free-spinning apparatus may, for example, take the form of the example mandrel-free spinning apparatus <NUM> shown in <FIG> and <FIG>. However, the example mandrel-free spinning apparatus <NUM> is not intended to be limiting and, in other examples, the mandrel-free spinning apparatus may take any other form that includes at least: a first forming tool, such as the first forming tool 12a, arranged to engage a first surface of the workpiece <NUM>; and a second forming tool, such as the second forming tool 12b, arranged to engage an opposing second surface of the workpiece <NUM>. Such a mandrel-free spinning apparatus may, for example, include three independently controllable and movable forming tools for supporting the workpiece and a single forming tool for deforming the workpiece <NUM>.

The workpiece <NUM> may, for example, take the form of a blank sheet of ductile metal, such as aluminium, stainless steel or alloys thereof. Alternatively, the workpiece <NUM> may comprise any other similarly ductile material that is suitable for a spin forming process.

Articles formed in accordance with embodiments of the invention, from the workpiece <NUM>, may have a dish-like shape. In particular, such articles may feature a substantially flat central hub and a domed, or otherwise curved, portion that extends around the central hub to define a dished or cupped shape, terminating in an axially distal rim.

By way of example, <FIG> show an axisymmetric discoidal article <NUM> that may be formed, in accordance with an embodiment of the invention, from the workpiece <NUM>.

Being discoidal, the article <NUM> is substantially axisymmetric, having a substantially planar central region, that forms a central hub <NUM>, and a domed body portion <NUM> that extends from the central hub <NUM>, along a longitudinal axis <NUM> of the article <NUM>, to define a dome segment, which terminates in a circular rim <NUM>.

The discoidal article <NUM> is therefore hollow - having inner surfaces <NUM> of the article <NUM> effectively separated from outer surfaces <NUM> of the article <NUM> by the rim <NUM>; and shallow - having a maximum diameter that is larger than the depth of the article <NUM> between the central hub <NUM> and the rim <NUM>.

The central hub <NUM> is formed from a plate-like hub wall <NUM> that has a circular shape, in this example, extending radially from the longitudinal axis <NUM> of the article <NUM> to outline a circular crease line <NUM> on the inner and outer surfaces <NUM>, <NUM> of the article <NUM>. The hub wall <NUM> may include one or more mounting features (not shown) used to attach the workpiece <NUM> to the lathe <NUM> during the spin forming process. Such mounting features may, for example, include one or more apertures suitable for bolting the workpiece <NUM> to the lathe <NUM> so as to inhibit relative movement.

The body portion <NUM> of the article <NUM> is formed from a side wall <NUM> that extends radially from the hub wall <NUM>, around the circumference of the circular crease line <NUM>, and curves along the longitudinal axis <NUM> to define the domed segment of the body portion <NUM>. It shall be appreciated that a radial cross-section of the example article <NUM> therefore has a concave and curved profile.

The wall thickness of the article <NUM>, i.e. the thickness of the workpiece <NUM> between the inner and outer surfaces <NUM>, <NUM> of the article <NUM>, is substantially constant across the central hub <NUM> and the body portion <NUM>.

For the sake of clarity, the article <NUM> is one such example of an article <NUM> that may be formed by the method of this invention and is not intended to be limiting.

Any article produced by this method will inevitably feature a planar central hub <NUM>, where the workpiece <NUM> is mounted to the lathe <NUM>, and a body portion <NUM> that extends both radially and axially from the central hub <NUM>. However, in other examples, the central hub may not be circular and may instead be rectangular, ovalled or otherwise non-axisymmetric. Furthermore, in other examples, the body portion may not be domed, as such, but may be otherwise curved to define a generally concave dished shape.

In forming articles, such as the article <NUM>, from the workpiece <NUM>, methods in accordance with the invention may make use of, or otherwise be defined in dependence on, a target geometry that corresponds to the shape of the desired article.

Hence, in the following examples, the term target geometry <NUM> is used synonymously with the shape of the article <NUM>.

In embodiments of the present invention, the methods of controlling the mandrel-free spinning apparatus are configured to produce the dished or cup-shaped article in at least two stages.

In the first stage, the first forming tool of the mandrel-free spinning apparatus is moved, whilst the workpiece <NUM> rotates about a longitudinal axis of rotation, so as to engage a first surface of the workpiece <NUM> and to urge the workpiece <NUM> inwards, along and towards the axis of rotation, from an initial workpiece geometry into an intermediate geometry, such as a frustum shape. The intermediate geometry is characterised by the fact that the surfaces of the workpiece <NUM> in the intermediate geometry are curved to a lesser degree (along the axis of rotation) than is necessary to form the dish-shaped article.

In the second stage, a second forming tool 12b is moved so as to engage a second surface of the workpiece <NUM>, opposed to the first surface of the workpiece <NUM>, and to urge the workpiece <NUM> outwards, from the intermediate geometry, to thereby increase the curvature and concavity of the workpiece <NUM> in order to form the dish-shaped article.

Advantageously, the method is arranged to work harden the workpiece <NUM> in forming the intermediate geometry and the intermediate geometry provides stability, reducing the susceptibility of the workpiece <NUM> to wrinkling and other failure modes during the subsequent formation of the curved surfaces of the dish-shaped article. The two stage process can also offer a relatively short process time when compared to conventional multi-pass metal spinning methods.

<FIG> illustrates such a method <NUM> of controlling the mandrel-free spinning apparatus <NUM>, in accordance with an embodiment of the invention, to produce the example article <NUM> from a workpiece <NUM>. <FIG> are further provided to illustrate the various steps of the method <NUM>.

In step <NUM>, the workpiece <NUM> is mounted on the lathe <NUM> and rotated about the first axis <NUM>, as shown in <FIG>.

In step <NUM>, whilst the workpiece <NUM> rotates, the first forming tool 12a is moved so as to engage the outer surface <NUM> of the workpiece <NUM> and to urge the workpiece <NUM> towards and beyond the discoidal target geometry <NUM> into an intermediate geometry <NUM>. The target geometry <NUM> is illustrated by dashed lines <NUM> In <FIG> and the intermediate geometry <NUM> is indicated by solid lines <NUM>.

The intermediate geometry <NUM> may be shaped like a frustum with relatively straight surfaces, i.e. surfaces that are curved to a lesser degree than the target geometry <NUM>.

For this purpose, the first forming tool 12a is moved along a first trajectory <NUM>, in step <NUM>, which is relatively straight compared to the curved trajectory required to form the discoidal article <NUM>.

For example, as shown in <FIG>, the first trajectory <NUM> may move the first forming tool 12a along a straight, or substantially straight, line between a start point and an end point to deform the workpiece <NUM> into a tapered shallow dish.

The start point may be radially proximal to the first axis <NUM>, for example in a position on the first axis <NUM> corresponding to the outer surface <NUM> of the workpiece <NUM>; and a position on the second axis <NUM> corresponding to the radius of the central hub <NUM> at the outer surface <NUM> of the target geometry <NUM>. The end point may be radially distal and arranged further along the first axis <NUM>, for example in a position on the first axis <NUM> that is spaced from the start point by a distance corresponding to the depth of the article <NUM> between the central hub <NUM> and the rim <NUM>; and a position on the second axis <NUM> corresponding to the radius of the rim <NUM> at the outer surface <NUM> of the target geometry <NUM>.

As the first forming tool 12a moves between the start and end points, the workpiece <NUM> is urged inward, i.e. bent along and towards the first axis <NUM>, from an initial planar geometry to define a central hub <NUM> and a body portion <NUM> that extends, along the first axis <NUM>, from the central hub <NUM> to a rim <NUM>.

The intermediate geometry <NUM> and, in particular, the body portion <NUM> of the intermediate geometry <NUM> may take various forms in accordance with the invention, but in general the first forming tool 12a is moved as described above, so that, in the intermediate geometry <NUM>, the workpiece <NUM> features the following common features.

Firstly, the central hub <NUM> of the intermediate geometry <NUM> corresponds to the central hub <NUM> of the target geometry <NUM>. Secondly, the rim <NUM> of the intermediate geometry <NUM> corresponds to the rim <NUM> of the target geometry <NUM>. Thirdly, the distance (along the first axis <NUM>) between the central hub <NUM> and the rim <NUM> of the intermediate geometry <NUM> corresponds to the depth of the article <NUM> between the central hub <NUM> and the rim <NUM>. Lastly, and most importantly, the body portion <NUM> of the intermediate geometry <NUM> is characterised in that the surfaces of the body portion <NUM> of the intermediate geometry <NUM> are straighter, i.e. curved to a lesser degree along the first axis <NUM>, than in the body portion <NUM> of the target geometry <NUM>.

In the example shown in <FIG>, the features described above are evident in the geometry of the tapered shallow dish <NUM>, which features a frusto-conical body portion <NUM>, extending between the central hub <NUM> and the rim <NUM>, with substantially linear surfaces that have a constant, or near constant, gradient relative to the first axis <NUM>. It shall be appreciated that the surfaces of the frusto-conical body portion <NUM> of the intermediate geometry <NUM> contrast with the curved surfaces of the domed body portion <NUM> of the target geometry <NUM>.

Other intermediate geometries may be formed in accordance with the method of the invention provided that they are curved to a lesser degree than the target geometry. In particular, in each intermediate geometry <NUM>, the surfaces of the workpiece <NUM>, between the central hub <NUM> and the rim <NUM>, shall be curved to a lesser degree along the first axis <NUM> than the surfaces of the workpiece <NUM> in the discoidal target geometry <NUM>.

The body portion <NUM> of the intermediate geometry <NUM> may also be narrower than the body portion <NUM> of the target geometry <NUM> as a result of the deformation beyond the target geometry <NUM>. In particular, a given point <NUM> on the workpiece <NUM>, between the central hub <NUM> and the rim <NUM>, may be urged further along the first axis <NUM> and closer towards the first axis <NUM> in the intermediate geometry <NUM> than in the target geometry <NUM>, as shown in <FIG>.

In step <NUM>, the second forming tool 12b is moved so as to engage the inner surface <NUM> of the workpiece <NUM>, as shown in <FIG>, and to urge the workpiece <NUM> from the intermediate geometry <NUM> towards the target geometry <NUM>, as shown in <FIG>.

In particular, the second forming tool 12b is moved along a second trajectory <NUM> and pressed against the inner surface <NUM> of the workpiece <NUM> to urge the workpiece <NUM> outward. For example, the second trajectory <NUM> may be arranged to move the second forming tool 12b along a curved line between a start point and an end point to bend or otherwise press the surfaces of the workpiece <NUM> (illustrated by dashed lines <NUM> in <FIG>) into the discoidal shape of the article <NUM>.

The start point may be radially proximal to the first axis <NUM>, for example in a position on the first axis <NUM> corresponding to the inner surface <NUM> of the workpiece <NUM>; and a position on the second axis <NUM> corresponding to the radius of the central hub <NUM> at the inner surface <NUM> of the target geometry <NUM>. The end point may be radially distal and arranged further along the first axis <NUM>, for example in a position on the first axis <NUM> that is spaced from the start point by a distance corresponding to the depth of the article <NUM> between the central hub <NUM> and the rim <NUM>; and a position on the second axis <NUM> corresponding to the radius of the rim <NUM> at the inner surface <NUM> of the target geometry <NUM>.

As the second forming tool 12b moves between the start and end points, the surfaces of the workpiece <NUM>, between the central hub <NUM> and the rim <NUM>, are urged outward and into a curved and concave shape. In particular, a given point <NUM> on the workpiece <NUM>, between the central hub <NUM> and the rim <NUM> is urged backwards along the first axis <NUM> and further away from the first axis <NUM> than in the intermediate geometry <NUM>, which has the effect of increasing the concavity and the curvature of the workpiece <NUM> between the central hub <NUM> and the rim <NUM>.

Deforming the workpiece <NUM> into such a curved shape would ordinarily lead to wrinkling and/or failure of the workpiece <NUM>, particularly in radially distal regions. However, the method is advantageously arranged so that the workpiece <NUM> is work hardened and geometrically stabilised as the relatively shallow slopes of the intermediate geometry <NUM> are formed, during step <NUM>. This mitigates the tendency of the workpiece <NUM> to wrinkle and/or fail prior to forming the curved surfaces, in step <NUM>.

At the end of step <NUM>, the workpiece <NUM> may substantially match the target geometry <NUM> and the article <NUM> may be removed from the lathe <NUM>.

It is noted that the steps of the method <NUM> are merely provided as an example of the invention and the steps are not intended to limit the method of controlling the mandrel-free spinning apparatus <NUM>. Accordingly, steps may be altered, added and removed as will be appreciated by the person skilled in the art.

In particular, in another example method <NUM> of controlling the mandrel-free spinning apparatus <NUM>, the article <NUM> may be formed from an oversized workpiece <NUM> and an unworked edge region of the workpiece <NUM> may form a flange portion that extends around the circumference of the workpiece <NUM> after the workpiece <NUM> has been urged into the intermediate geometry <NUM>.

In this example, the method <NUM> is arranged to restrain or support the flange portion, for example by engagement with the first forming tool 12a, whilst the second forming tool 12b is moved so as to urge the workpiece <NUM> towards the target geometry <NUM>. As shall become clear in the description that follows, supporting the workpiece <NUM> in this manner mitigates titling effects that may otherwise occur as the workpiece <NUM> is urged towards the target geometry <NUM>. The flange portion also helps to increase the circumferential stiffness of the workpiece <NUM>, mitigating the likelihood of wrinkling, as the workpiece <NUM> is urged towards the target geometry <NUM>.

Before describing this method <NUM> in detail, it should be appreciated that workpieces for spin forming articles are traditionally net shape, or near net shape, for a desired article so that there is no, or negligible, material wastage when the article is formed. Hence, by an oversized workpiece it is intended to mean a workpiece that is larger than conventional, including additional material for forming the flange portion around the rim <NUM> of the article <NUM>. The flange portion should be large enough to be engaged, and supported, by the first forming tool 12a so as to substantially inhibit relative movement between the first forming tool 12a and the flange portion whilst the workpiece <NUM> is urged towards the target geometry <NUM>.

<FIG> illustrate such an example method <NUM> of controlling the mandrel-free spinning apparatus <NUM> in accordance with an embodiment of the invention.

In step <NUM>, the workpiece <NUM> is mounted on the lathe <NUM> and rotated about the first axis <NUM> substantially as described in step <NUM> of method <NUM>, as shown in <FIG>.

In step <NUM>, the first forming tool 12a is moved along the first trajectory <NUM> so as to engage the outer surface <NUM> of the workpiece <NUM> and to urge the workpiece <NUM> into the intermediate geometry <NUM> substantially as described in step <NUM> of method <NUM>.

It shall be appreciated that, as the first forming tool 12a moves between the start and end points, a region of the workpiece <NUM> that is radially beyond the first forming tool 12a remains unworked and extends radially around the circumference of the workpiece <NUM>.

Hence, in this example, when the first forming tool 12a reaches the end point of the first trajectory <NUM>, the oversized workpiece <NUM> includes an edge portion that remains unworked, as shown in <FIG>. The unworked portion of the workpiece <NUM> forms a flange portion <NUM> that extends radially around the circumference of the workpiece <NUM> at the end of the body portion <NUM>. It shall be appreciated that the flange portion <NUM> effectively extends around the rim of the intermediate geometry <NUM> formed at the end of step <NUM> in method <NUM>.

The flange portion <NUM> may take the form of a flange wall <NUM> that has a width extending from an inner radius, at the end of the body portion <NUM>, to an outer radius and the width may be large enough for the first forming tool 12a to engage the flange wall <NUM> and support the workpiece <NUM>.

Hence, in step <NUM>, the first forming tool 12a is held in abutting engagement with the flange portion <NUM> whilst the second forming tool 12b is moved so as to urge the workpiece <NUM> from the intermediate geometry <NUM> towards the target geometry <NUM>, as described in step <NUM> of method <NUM>.

As the workpiece <NUM> is deformed towards the target geometry <NUM>, the flange portion <NUM> serves to maintain the circumferential stiffness of the workpiece <NUM> and provides a retaining surface that bears against the first forming tool 12a, as shown in <FIG>.

This has two advantageous effects, as shall become clear in the description that follows. Firstly, by increasing the circumferential stiffness of the workpiece <NUM>, the flange portion <NUM> mitigates problems such as wrinkling as the curved surfaces of the target geometry <NUM> are formed. Secondly, using the flange portion <NUM> as a retaining surface substantially inhibits tilting of the workpiece <NUM>, relative to the lathe <NUM>, under the influence of the second forming tool 12b, which can otherwise cause the workpiece <NUM> to become warped and/or to fail.

Considered in more detail, as the second forming tool 12b moves from the start point to the end point of the second trajectory <NUM>, the second forming tool 12b applies pressure to the inner surface <NUM> of the workpiece <NUM> to bend, or otherwise deform, the workpiece <NUM> between a pair of restraining points. The first restraining point is provided at or around the first axis <NUM> by the attachment of the workpiece <NUM> to the lathe <NUM> and the second restraining point is provided at a radially distal point by the engagement between the first forming tool 12a and the flange portion <NUM>.

The second forming tool 12b applies an outward force between these radially spaced restraining points to effectively press or bend the tapered surfaces of the frusto-conical body portion <NUM> into the domed, or otherwise curved surfaces that define the domed body portion <NUM> of the target geometry <NUM>.

The force applied by the second forming tool 12b on the workpiece <NUM> is offset from the lathe <NUM> and produces a turning moment that acts to tilt the workpiece <NUM> relative to the lathe <NUM> in the absence of the first forming tool 12a. However, in this example, the first forming tool 12a applies an opposing force of resistance at the radially distal flange portion <NUM> whilst the second forming tool 12b applies pressure on the inner surface <NUM> of the workpiece <NUM>. Advantageously, the resistance of the first forming tool 12a thereby negates the turning moment that the second forming tool 12b applies about the lathe <NUM>, preventing the workpiece <NUM> from tilting relative to the lathe <NUM> in the plane of the first and second axes <NUM>, <NUM>.

With this arrangement, the workpiece <NUM> is therefore less susceptible to wrinkling or other failure modes as the curve is formed. Furthermore, the method <NUM> minimises the thinning of the workpiece <NUM>, particularly in the areas of greatest curvature, where the workpiece <NUM> may otherwise fail if deformed according to conventional forming methods.

When the second forming tool 12b reaches the end point of the second trajectory <NUM>, the workpiece <NUM> takes a formed geometry <NUM>, which substantially matches the target geometry <NUM> except that the flange portion <NUM> remains, as shown in <FIG>. Hence, in the formed geometry <NUM>, the workpiece <NUM> may be dish-shaped and correspond to the shape of the article <NUM>, further including the flange portion <NUM> around the rim <NUM> of the article <NUM>.

Thereafter, in step <NUM>, one or more finishing processes may be performed on the workpiece <NUM> to produce the article <NUM>. The finishing processes may include removing the flange portion <NUM> from the formed geometry <NUM>, for example. For example, the flange portion <NUM> may be trimmed from the end of the domed body portion <NUM> and the end of the domed body portion <NUM> may be smoothed to produce the rim <NUM> of the article <NUM>.

The formed article <NUM> can be removed from the mandrel-free spinning apparatus <NUM> upon completion of the spin forming process and the article <NUM> substantially retains its moulded shape, with minimal springback.

In order to form articles according to the above described method <NUM>, It shall be appreciated that it may also be necessary to design a blank 'oversized' workpiece for the article <NUM> that accounts for the additional flange portion <NUM>.

In this regard, a blank workpiece <NUM> may be formed in dependence on the net, or near net, shape of the article <NUM> and the width of the flange portion <NUM>. For example, the net, or near net, shape of the article <NUM> may correspond to a circular blank workpiece having a first radius, R1, so that the workpiece <NUM> may have a second radius, R2. The second radius R2 may be equal to the first radius R1 plus the width of the flange portion <NUM>. The width of the flange portion <NUM> may, for example, correspond to the size of the first forming tool 12a. For example, the width may be greater than a nose radius of the first forming tool 12a.

Methods of generating a design of a blank workpiece based on an article shape are described in method <NUM> of UK patent application no. <CIT>, for example. The skilled person shall appreciate that similar methods may be applied, mutatis mutandis, to generate the blank workpiece design for the article <NUM> with the flange portion <NUM>. However, such methods are not described in detail here so as to avoid obscuring the invention.

In another example method of controlling the mandrel-free spinning apparatus in accordance with the invention, the method may proceed substantially as described in each of the methods <NUM>, <NUM> described above, with the following exception.

Before moving the first forming tool 12a so as to urge the workpiece <NUM> towards the intermediate geometry <NUM>, for example in step <NUM> of method <NUM>, the second forming tool 12b may be moved into engagement with the inner surface <NUM> of the workpiece <NUM> whilst the first forming tool 12a is moved to urge the workpiece <NUM> into the intermediate geometry <NUM>. For example, in step <NUM> of method <NUM>, the second forming tool 12b may be moved into engagement with the inner surface <NUM> of the workpiece <NUM> at a radial position corresponding to the central hub of the article <NUM>.

Thereafter, the first forming tool 12a may be moved, as described previously, to urge the workpiece <NUM> into the intermediate geometry <NUM> and the second forming tool 12b may provide a surface against which the workpiece <NUM> is bent around.

In particular, as the workpiece <NUM> rotates, the second forming tool 12b may resist deformation at the inner surface <NUM> of the workpiece <NUM> so as to define the circular crease line <NUM> of the central hub <NUM>, whilst the first forming tool 12a deforms the workpiece <NUM> into the intermediate geometry <NUM>.

In another example method <NUM> of controlling the mandrel-free spinning apparatus in accordance with the invention, shown in <FIG>, the method <NUM> may proceed substantially as described in each of the methods <NUM>, <NUM> described above, with the following exceptions.

The method <NUM> further includes mounting a forming plate, or clamp plate, to the lathe <NUM>, in step <NUM>, after mounting the workpiece <NUM> to the lathe <NUM>, for example in step <NUM> of method <NUM>.

An example of the forming plate <NUM> is shown in <FIG>, which illustrate the method <NUM> shown in <FIG>.

The forming plate <NUM> is configured to assist the transition between the initial planar geometry of the workpiece <NUM> and the curved shape of the article <NUM>, providing resistance to deformation of the workpiece <NUM> in a central region, proximal to the first axis <NUM>. For example, the forming plate <NUM> may support the workpiece <NUM> in a region corresponding to the central hub <NUM> of the article <NUM>.

Accordingly, the forming plate <NUM> may take the form of a relatively thin plate having a shape corresponding to the central hub <NUM> of the article <NUM>. The forming plate <NUM> may have curved edges, as shown, that reduce the stress concentrations on the workpiece <NUM> as the first forming tool 12a urges the workpiece <NUM> towards the intermediate geometry <NUM>. The curved edges of the forming plate <NUM> help to define a crease line around the central hub <NUM> of the intermediate geometry <NUM> as the workpiece <NUM> is urged away from the initial planar geometry to form the intermediate geometry <NUM>.

The method <NUM> may further include removing the forming plate <NUM> from the lathe <NUM>, in step <NUM>, once the first forming tool 12a reaches the end point of the first trajectory <NUM>, for example in step <NUM> of method <NUM>.

In each of the example control methods <NUM>, <NUM>, <NUM> described above, the first forming tool 12a may be moved along the first trajectory <NUM> in accordance with a first toolpath and the second forming tool 12b may be moved along the second trajectory <NUM> in accordance with a second toolpath.

In which case, a system of devices <NUM>, shown in <FIG>, may be used to implement each method <NUM>, <NUM>, <NUM>. The system of devices <NUM> includes the mandrel-free spinning apparatus <NUM>, a control system <NUM> comprising one or more controllers for operating the mandrel-free spinning apparatus <NUM>, and a sensor system <NUM> comprising one or more sensors configured to monitor the operation of the mandrel-free spinning apparatus <NUM>.

In such examples, the mandrel-free spinning apparatus <NUM> is configured to receive control signals from the control system <NUM> to execute the steps of each method <NUM>, <NUM>, <NUM>, as will now be described in overview.

Firstly, the mandrel-free spinning apparatus <NUM> may receive control signals to rotate the workpiece <NUM> on the lathe <NUM> about the first axis <NUM>, for example in step <NUM> of method <NUM>.

Such control signals may control a rate of rotation of the workpiece <NUM> and may, for example, ensure that the workpiece <NUM> is rotated through a prescribed angle of rotation within a given interval of time.

In an example, the rotation of the workpiece <NUM> may be discretised into a plurality of time points and each time point may correspond to a particular orientation of the workpiece <NUM>, relative to a reference position. The control system <NUM> may use this arrangement to control the first and/or second forming tools 12a, 12b in accordance with the respective toolpaths.

Secondly, the mandrel-free spinning apparatus <NUM> may receive control signals to move the first forming tool 12a along the first trajectory <NUM>, in step <NUM> of method <NUM> for example, in accordance with the first toolpath. The first toolpath may take the form of computer readable instructions in the control system <NUM> that are configured, when executed, to command the set of actuators <NUM> to move the first forming tool 12a along the first trajectory <NUM> described above to urge the workpiece <NUM> from the initial geometry into the intermediate geometry <NUM>.

For example, the first toolpath may move the first forming tool 12a into engagement with the outer surface <NUM> of the workpiece <NUM> and along the first trajectory <NUM> between the start and end points, where each of the start and end points may be defined by respective co-ordinates on the first and second axes <NUM>, <NUM>.

Such movement of the first forming tool 12a may, for example, be suitable for forming the tapered surfaces of the intermediate geometry <NUM> as the workpiece <NUM> rotates.

The first toolpath may, for example, include a first set of command positions through which the first forming tool 12a is moved between the start and end points and each command position may be defined by respective co-ordinates on the first and second axes <NUM>, <NUM>. In this manner, each command position may also correspond to a respective time point so that the first forming tool 12a is moved to each command position of the first toolpath at a respective time point corresponding to an associated orientation of the workpiece <NUM>.

Thirdly, the mandrel-free spinning apparatus <NUM> may receive control signals to move the second forming tool 12b along the second trajectory <NUM>, in step <NUM> of method <NUM> for example, in accordance with the second toolpath.

The format of the second toolpath may substantially match the format of the first toolpath. For example, the second toolpath may similarly comprise computer readable instructions in the control system <NUM> that are configured, when executed, to command the set of actuators <NUM> to move the second forming tool 12b along the second trajectory <NUM> to urge the workpiece <NUM> from the intermediate geometry <NUM> towards the target geometry <NUM>.

For example, the second toolpath may move the second forming tool 12b into engagement with the inner surface <NUM> of the workpiece <NUM> and along the second trajectory <NUM> between the start and end points - where each of the start and end points are defined by respective co-ordinates on the first and second axes <NUM>, <NUM>.

Such movement of the second forming tool 12b may, for example, be suitable for pressing the tapered workpiece <NUM> into the discoidal shape of the article <NUM>.

The second toolpath may, for example, include a second set of command positions through which the second forming tool 12b is moved between the start and end points and each command position may be defined by respective co-ordinates on the first and second axes <NUM>, <NUM>.

As with the first toolpath, each command position of the second toolpath may also correspond to a respective time point so that the second forming tool 12b moves to each command position of the second toolpath at a respective time point, which corresponds to an associated orientation of the workpiece <NUM>.

Optionally, the mandrel-free spinning apparatus <NUM> may also receive control signals configured to move one or more of the third and fourth forming tools 12c, 12d in accordance with further respective toolpaths that may substantially match the first or second toolpath.

The control system <NUM> may include one or more processing devices configured to determine the computer readable instructions, described above, for generating the control signals of the first and second toolpaths. It shall be appreciated that the computer readable instructions may, for example, take the form of computer generated code that the control system <NUM> can process to determine the corresponding control signals.

The control system <NUM> may be further configured to receive inputs from a memory storage device (not shown) and/or from a user, for example through a human-machine interface device (not shown), in order to determine suitable instructions.

The sensor systems <NUM> may include one or more: accelerometers; actuation sensors; and/or force sensors; arranged to monitor the operation of the mandrel-free spinning apparatus <NUM>. The sensor system <NUM> may, for example, be configured to determine the loading on one or more of the first, second, third and fourth forming tools 12a-d and to relay such measurements back to the control system <NUM>. The control system <NUM> may adapt the operation of the mandrel-free spinning apparatus <NUM> based on feedback from the sensor system <NUM>. For example, where the loading on one of the forming tools 12a-d exceeds a predetermined threshold, the control system <NUM> may stop the movement of said forming tool 12a-d and return the forming tool 12a-d to the start point of the respective toolpath. The control system <NUM> may, for example, subsequently repeat the respective toolpath.

To control the first and second forming tools 12a, 12b according to the first and second toolpaths, each method <NUM>, <NUM>, <NUM> described above may further include or be modified to include steps of: i) receiving or determining the first toolpath; ii) receiving or determining the second toolpath; iii) controlling the first forming tool 12a in accordance with the first toolpath; and iv) controlling the second forming tool 12b in accordance with the second toolpath; as illustrated in the example method <NUM> shown in <FIG>.

In step 401a, the first toolpath may be received, or otherwise determined, at the control system <NUM>. For example, the control system <NUM> may receive the first toolpath or otherwise receive information relating to the article <NUM> for use in determining the first toolpath.

Suitable information for determining the first toolpath and, in particular the start point, the end point and the first set of command positions, may be received from the memory storage device and/or from user inputs through the human machine interface.

Such information may include one or more of: i) the co-ordinates of the start point, the end points, and/or each command position; ii) the dimensions of the article <NUM>, including the maximum radius of the central hub <NUM> of the article <NUM>, the maximum radius at the rim <NUM> of the article <NUM>, and/or the length of the article <NUM> between the central hub <NUM> and the rim <NUM>; and/or ii) a computerised representation of the article <NUM>.

In a relatively common example, the control system <NUM> may receive the co-ordinates of the start and end points from user inputs, through the human machine interface, and the control system <NUM> may be configured to determine the first set of command positions that define the first trajectory <NUM> by interpolating points along a straight line extending between the start and end points. The command positions may therefore be arranged in a linear sequence with successive command positions corresponding to successive time points or orientations of the workpiece <NUM>.

Collectively, the first set of command positions may effectively define a linear path of movement of the first forming tool 12a between the start and end points, as the workpiece <NUM> rotates.

In step 401b, the second toolpath may be received, or otherwise determined, at the control system <NUM>. For example, the control system <NUM> may receive the second toolpath or otherwise receive information relating to the article <NUM> for use in determining the second toolpath.

Suitable information for determining the second toolpath and, in particular the start point, the end point and the second set of command positions, may be received from the memory storage device and/or from user inputs through the human machine interface and may include one or more of: i) the co-ordinates of the start point, the end points, and/or one or more command positions; ii) the dimensions of the article <NUM>, including the maximum radius of the central hub <NUM> of the article <NUM>, the maximum radius at the rim <NUM> of the article <NUM>, the length of the article <NUM> between the central hub <NUM> and the rim <NUM>, and/or a mathematical equation defining a curve corresponding to the body portion <NUM> of the article <NUM>; and/or iii) a computerised representation of the article <NUM>.

In an example, the control system <NUM> may receive the co-ordinates of the start and end points of the second toolpath, as well as a mathematical equation defining a curve between the start and end points, from user inputs received through the human machine interface. In dependence on such information, the control system <NUM> may be configured to determine the second set of command positions that define the second trajectory <NUM> by discretizing the curve into a sequence of positions arranged along the curve between the start and end points. The command positions may therefore be arranged on a curved trajectory with successive command positions corresponding to successive time points or orientations of the workpiece <NUM>.

Thereafter, the method may proceed through the remaining steps of each method <NUM>, <NUM>, <NUM> described above, with the following modifications.

In step <NUM>, the workpiece <NUM> is mounted on the lathe <NUM> of the mandrel-free spinning apparatus <NUM>, as shown in <FIG>, and the control system <NUM> outputs control signals to cause the workpiece <NUM> to rotate about the first axis <NUM> on the lathe <NUM>, substantially as described in step <NUM> of method <NUM> for example.

As mentioned previously, the control system <NUM> may rotate the workpiece <NUM> at a rotational speed corresponding to the first and/or second toolpath. This may ensure that the orientation of the workpiece <NUM> corresponds to a particular time point, and hence corresponds to a respective command position of the first or second toolpaths.

In step <NUM>, the control system <NUM> outputs control signals to move the first forming tool 12a in accordance with the first toolpath so as to urge the workpiece <NUM> into the intermediate geometry <NUM>, substantially as described in step <NUM> of method <NUM> for example.

In particular, the first toolpath is configured so that the first forming tool 12a is initially moved into engagement with the outer surface <NUM> of the workpiece <NUM> at the start point of the first toolpath. Thereafter, as the workpiece <NUM> rotates, the control signals may move the first forming tool 12a through the first set of command positions, from the start point to the end point of the first toolpath, to urge the workpiece <NUM> into the intermediate geometry <NUM>.

In step <NUM>, the control system <NUM> may hold the first forming tool 12a in abutment with the flange portion <NUM> and outputs control signals to move the second forming tool 12b in accordance with the second toolpath, substantially as described in step <NUM> of method <NUM> for example.

In particular, the second toolpath is configured so that the second forming tool 12b is initially moved into engagement with the inner surface 12b of the workpiece <NUM> at the start point of the second toolpath. Thereafter, as the workpiece <NUM> rotates, the control signals may move the second forming tool 12b through the second set of command positions, from the start point to the end point of the second toolpath, to urge the workpiece <NUM> towards the target geometry <NUM>.

In step <NUM>, one or more finishing processes may be performed, as described in step <NUM> of method <NUM>, to produce the article <NUM>.

Furthermore, in another example method of controlling the mandrel-free spinning apparatus <NUM> in accordance with an embodiment of the invention, each of the first and second toolpaths may include a plurality of passes in which the respective first and second forming tools 12a, 12b are moved relative to the workpiece <NUM>.

As illustrated in <FIG>, the first toolpath may include a first, a second, a third and a fourth pass <NUM>-d and the second toolpath may include a first, a second, a third and a fourth pass 182a-d. Each pass 180a-d of the first toolpath may move the first forming tool 12a between a respective start point and a respective end point and achieve an iterative deformation of the workpiece <NUM> toward the intermediate geometry <NUM>.

Each pass 182a-d of the second toolpath may move the second forming tool 12b between a respective start point and a respective end point and achieve an iterative deformation of the workpiece <NUM> from the intermediate geometry <NUM> towards the target geometry <NUM>.

For example, as shown in <FIG>, the longitudinal positions of the end points may increase between successive passes 180a-d of the first toolpath so that the gradient of the first trajectory <NUM> increases relative to the second axis <NUM> and the workpiece <NUM> is gradually deformed into the intermediate geometry <NUM>.

Similarly, as shown in <FIG>, the radial positions of the end points, and/or the curvature of the second trajectory <NUM>, may increase between successive passes 182a-d of the second toolpath so that each pass 182a-d deforms the workpiece <NUM> closer towards the target geometry <NUM>.

Claim 1:
A method (<NUM>; <NUM>; <NUM>; <NUM>) of controlling a mandrel-free spinning apparatus (<NUM>) to produce an article, having a target geometry (<NUM>), from a workpiece (<NUM>), the mandrel-free spinning apparatus (<NUM>) comprising: a rotatable mounting point (<NUM>) for the workpiece (<NUM>); a first forming tool (12a); and a second forming tool (12b); the method including:
whilst the workpiece (<NUM>) rotates, moving the first forming tool (12a) so as to: engage a first surface (<NUM>) of the workpiece (<NUM>); and urge the workpiece (<NUM>), from an initial workpiece geometry, towards and beyond the target geometry (<NUM>) into an intermediate geometry (<NUM>); and
whilst the workpiece (<NUM>) rotates, moving the second forming tool (12b) so as to: engage a second surface (<NUM>) of the workpiece (<NUM>), opposed to the first surface (<NUM>) of the workpiece (<NUM>); and urge the workpiece (<NUM>) from the intermediate geometry (<NUM>) towards the target geometry (<NUM>);
wherein the first forming tool (12a) is moved to urge the workpiece (<NUM>) inward, along and towards an axis of rotation of the mounting point (<NUM>), from the initial workpiece geometry into the intermediate geometry (<NUM>), and the second forming tool (12b) is moved to urge the workpiece (<NUM>) outward, from the intermediate geometry (<NUM>) towards the target geometry (<NUM>).