GB2292332A

GB2292332A - Moulding process and apparatus

Info

Publication number: GB2292332A
Application number: GB9408370A
Authority: GB
Inventors: Alan Roger Harper
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-04-22
Filing date: 1994-04-22
Publication date: 1996-02-21
Anticipated expiration: 2014-04-22
Also published as: GB9408370D0; GB2292332B

Abstract

Fibre-reinforced resin is moulded by placing a pack of fibres (44) in a moulding cavity defined between a first mould member (41, 42) and a second mould member (38) in the form of an elastomeric bag which maintains a predetermined shape by virtue of a pressure difference between its inside and outside, resin is injected into the moulding cavity which has a larger volume than the final product to facilitate resin flow, the cavity is reduced to the desired volume by expanding the second mould member and the resin is allowed to polymerise and the product removed. The second mould member may initially be filled with particles and be given its shape by expanding it within a forming mould. It may then be expanded within the moulding cavity by expanding a bladder (34). Alternatively the particles may be expanded by induction or microwave heating. <IMAGE>

Description

MOULDING PROCESS AND APPARATUS THEREFOR This invention relates to a moulding process and apparatus. In particular it is concerned with a resin transfer moulding process.

The process of resin transfer moulding of resin fibre composite parts is well established. The process involves the provision of a matched pair of moulds. A pack of dry reinforcement fibre is then placed in one mould and the moulds are then juxtaposed and clamped together to provide a mould cavity enclosing the reinforcement pack. The assembled mould and the clamping can provide for pressurisation of the mould cavity. Once clamped together a thermosetting resin is injected into the mould cavity through an injection hole in one of the mould halves under a modest pressure. The injected resin mixture permeates the reinforcement fibre and eventually fills the mould cavity. The resin is then left to cure whereupon the mould is opened and the composite moulding removed.

The volume proportion of fibre used in resin transfer moulding varies according to the service requirements for the moulded product. In a general industrial moulding such as for a motor body panel the fibre volume fraction is low (between 12 and 30% by volume). However in mouldings for an advanced composite industry such as aerospace the proportion of fibre is usually at least 50% by volume. In this latter case the composites involve such a volume of fibre that a transfer moulding is more difficult to manufacture due, amongst other things, to the resistance offered by the relatively large volume of fibre reinforcement to the flow of resin during the injection step.

The present invention is concerned with providing for increased ease of moulding and speed of manufacture for high fibre volume fraction resin transfer mouldings and to improve control of the moulding process.

Accorditotg to a first aspect of the present invention there is provided a method of moulding comprising he steps of: 1 locating in a first mould member having a first mould face a pack of reinforcing fibre; 2 providing a second mould member comprising a rigid support on which is mounted an elastomeric second mould face which is conformed to a predetermined shape by maintenance of a pressure differential between the inside and the outside of the second mould member; 3 securing together the first and second mould members so that the first and second mould faces serve to define a mould cavity of a first volume in which the pack is located; 4 injecting a resin mixture into the mould cavity until the cavity is filled; 5 causing the elastomeric second mould member to expand in volume, while the injected resin mixture is not fully polymerised, by inflating the elastomeric second mould face so as to change the total volume of the mould cavity from the first volume to a second volume smaller than the first; 6 allowing the injected resin mixture to polymerise; and 7 separating the first and second mould members and removing the moulding.

According to a first preferred version of the first aspect of the present invention there is provided a method of moulding characterised in that the step of causing the elastomeric second mould member to expand in volume is achieved by means of a bladder incorporated ion the second mould member, the volume of the bladder being capable of controlled expansion from a smaller to a larger volume resulting in a corresponding increase in volume of the elastomeric second mould member.

According to a second preferred version of the present invention or the first preferred version thereof is characterised in that while the mould cavity is established at its first volume the elastomeric second mould member provides for a surface of the mould cavity at least one channel into which the pack cannot intrude, or not to any significant extent, to provide a relatively clear channel for the passage of liquid resin; and in the step of causing the elastomeric second mould member to expand in volume so as to reduce the total volume of the mould cavity from the first volume to a second volume smaller than the first the surface of the mould cavity containing the channel is caused to reform so as to eliminate the channel to a greater or lesser extent and provide for the surface to conform to a generally smooth configuration prior to the step of polymerising.

According to a second aspect of the present invention there is provided a moulded component fabricated by the method of the first aspect or any preferred version thereof.

According to a third aspect of the present invention there is provided apparatus for resin transfer moulding comprising: 1 a first mould member having a first mould face; 2 a second mould member incorporating an elastomeric mould face; 3 means for maintaining the elastomeric mould face in a predetermined shape by maintenance of a pressure differential between an inner volume of the second mould member and ambient pressure; 4 clamping together the first and second mould members to define a mould cavity of a first volume in which the pack is located; 5 a duct whereby a resin mixture can be directed into the mould; 6 providing means whereby the elastomeric second mould face can be expanded in a sense to reduce the total volume of the mould cavity from the first volume to a second volume smaller than the first at a predetermined period following injection of liquid resin material in the mould.

According to a fourth aspect of the present invention there is provided a moulded component fabricated on apparatus according to the third aspect of the present invention.

An exemplary embodiment of the present invention will now be described with reference to the accompanying drawings of a moulding operation of which: Figure 1 is a perspective view of a moulded resin transfer composite product having a large volume fraction of reinforcing fibre and Figure 1A is a detail section of a part of Figure 1; Figures 2, 3 and 4 are sectional elevations of components being used in a method of fabricating a mould tool; Figure 5 is a sectional elevation of a mould tool produced as described in connection with figures 2 to 4; Figures 6 to 8 are sectional elevations of components being used in a production method making use of the mould tool of Figure 5 to produce the component of Figure 1.

Figure 1 shows a substantially spherical composite resin transfer moulding 11 with a neck portion 12 having an aperture 13. Figure 1A shows a section of the neck portion 12 with aperture 13 framed by internal flange 15. Outer face 16 and inner face 17 of the moulding need to be maintained to close tolerances. The moulding 11 is for use in an application requiring some 50% by volume of fibre reinforcement.

The method of producing moulding 11 involves two consecutive sequences of operations namely a tool production sequence followed by a moulding sequence.

The tool production sequence is broadly described hereafter in connection with Figures 2 to 5 and provides for the creation of a mould tool which is used in two stages firstly to facilitate the passage of liquid rein into the mould a secondly to closely define the inner face 14 of the moulding.

The moulding sequence is broadly described hereafter in connection with Figures 6 to 9 and provides for the use of the tool created in the first sequence to manufacture moulding 11.

Tool production sequence Figures 2, 3 and 4 show the use of a pair of moulds 18, 19 which are shown bolted together to define a mould cavity 20 whose face 21 is adapted to serve two functions firstly to facilitate the moulding process and secondly to provide for close control of the final form and finish of inner face 17 of moulding 11 as will be described hereafter. A seal 22 located in mould 19 extends around the mould cavity 20 to provide for a pressure tight joint between the juxtaposed and clamped moulds 18, 19. A vacuum duct 23 is provided in mould half 19 to enable the pressure within the mould cavity 20 to be controlled to facilitate the moulding process.

Figure 2 shows the first step in the production of a moulding tool and involves the location of a mould bag 24 of elastomeric material in the mould cavity 20 by way of a collar 25 which provides an entry port 26 to the interior of the mould bag 24 while sealing off the mould cavity 20 between face 21 and the outside of mould bag 24.

Figure 3 shows the mould bag 24 being filled with inert particulate material 27 fed by stream 28 through entry port 26. The particulate material 27 is dry and relatively light. During the filling sub-atmospheric pressure is applied to mould cavity 20 by way of duct 23 which serves to draw the bag 24 into contact with face 21. The filling of the mould bag 24 continues until the particulate material 27 occupies virtually all the internal space of the mould bag 24 and extends part way up into the port 26 as shown in Figure 4. The face 21 can be provided with projecting regions causing the mould bag 24 in its first configuration to be provided with grooves or channels to facilitate the flow of resin when the tool is used to produce a moulding as will be described hereafter.

Figure 4 shows the closure of the entry port 26 by a cap 29 which incorporates a pressure seal 30 for seating on the collar 25 to provide pressure tight sealing of the interior of the filled mould bag 24 from the ambient atmosphere. The cap 29 incorporates a vent line 31 which can be closed by a valve 32. The cap 29 also has extending through it a flexible hollow tube 33 which serves to locate an expandable bladder 34. When required the bladder 34 can be inflated by way of tube 33 by the application of a pressurised gas.Once the cap 29 is in place a relative vacuum is applied to the interior of the filled mould bag by way of vent line 31 so as to cause the particulate material 27 to cease behaving as a mass of pourable particles and to behave thereafter as a rigidified bulk The relative pressures maintained between the inside of the filled mould bag 24 by vent line 31 and the outside of the mould bag 24 by way of duct 23 provides for the mould bag to be caused to conform very closely and to retain the form of the interior surface 21.

The mould halves 18, 19 are then separated to enable a moulding tool 38 comprising the filled and rigidified mould bag 24, collar 25 and cap 29 to be withdrawn, as shown in Figure 5, for use in the production of moulding 11.

Moulding sequence Figure 6 shows a production mould 40 (made up of two mould halves 41, 42) which serves to define a face 43 which complements the form and finish of outer face 16 of moulding 11. Figure 6 shows the mould 40 following its assembly SO as to contain mould tool 38 together with fibre reinforcement pack 44 located in mould cavity 45 lying between face 44 and the outer surface of mould tool 38. As described in connection with Figure 5 the mould tool 38 when fabricated has a volume slightly less than that of the internal volume of the moulding 11.

Consequently when the mould tool is initially loaded into the production mould 40 the volume of mould cavity 45 is somewhat larger than the final volume of the wall of the moulding 11. As a consequence the fibre reinforcement pack 44 is not so densely packed as would be the case if the volume of the mould cavity 45 was identical to that of the wall volume of the moulding 11 to be produced. In addition the initial fabrication of the mould bag 24 to conform with the face 21 can be used to provide for the provision of grooves or channels in the outer surface of the mould bag 24.

The production mould 40 is equipped with a resin supply duct 49 whereby resin is injected into the mould cavity 45 and a vent duct 50 whereby excess resin can be vented from the mould cavity 45.

Once the components are assembled as shown in Figure 6 a supply of resin is fed into the mould cavity 45 by way of supply duct 45 and maintained until the mould cavity is full (as can be evidenced by the venting of resin from the vent duct 50). The relatively uncompacted state of the fibre pack 44 facilitates the penetration of the fibre pack 44 by the incoming resin. Flow of resin can also facilitated by the provision of grooves or channels in the outer part of the mould bag 24 as described in connection with its initial fabrication earlier.

Before the injected resin has hardened, as shown in Figure 7, the bladder 33 is inflated by way of hollow tube 34 so as to cause the elastomeric mould bag 24 of the mould tool 38 to expand from its originally fabricated size so that the mould cavity 45 is reduced to its final volume, the fibre pack is compressed to its final configuration and the outside of the mould bag 24 now conforms to the required inner surface location of the finished product (this latter volume change can provide for reduction or effective removal of any grooves or channels formed to facilitate flow of resin). Any pressure change in the mould cavity can be accommodated by way of the vent line 31 in the cap 29. Thereafter polymerisation of the resin occurs resulting in the completion of the finished product 11.

Figure 8 shows the resulting product 11 following its removal from separated mould halves 41, 42. Cap 29 is removed to enable the particulate material 27 to be poured out for subsequent re-use. The bladder 33 is readily removed at the same time.

Figure 9 shows the final stage when the particulate material 27 having been poured out the now collapsed mould bag 24 is also removed leaving the finished product 11.

The moulding process of the present invention provides for the production of a compacted and consolidated product moulding which is accurately finished on both sides. The process is readily carried out at relatively low pressure differentials so providing for the use of comparatively lightweight mould sets.

The use of an elastomeric mould operating in two configurations provides for a first configuration facilitating the process of moulding by optimising the flow of resin and a second configuration providing for accuracy and good detailing and finishing of the finished product. The transition from the first to the second configuration is, in the exemplary embodiment, undertaken by the use of an expandable bladder 24. However the volume change could be undertaken in other ways such as by the use of a particulate material in the mould 18 able to expand such as by induction or microwave heating.

The exemplary embodiment shows the production of a simple bowl like moulding.

However the present invention lends itself to the production of complex and/or large finished mouldings. The use of particulate filling material in the elastomeric mould 18 provides for the ready removal of the mould 18 from a finished product.

In one example the membrane can be pierced to provide a relatively small aperture through which the particulate material can be withdrawn. Following the withdrawal the flexible elastomeric membrane can also be withdrawn if necessary.

In a second example a port is provided in the moulded component to enable the membrane to be left in place but for the particulate material to be removed by way of the port.

The exemplary embodiment shows a matched mould set of two sections. The invention is applicable to mould sets of more than two sections. In addition if necessary more than two expandable elastomeric moulds can be undertaken in which expansion of two or more elastomeric mould sections can be carried out either simultaneously or in sequence.

Claims

CLAIMS 1A method of moulding comprising the steps of: 1 locating in a first mould member having a first mould face a pack of reinforcing fibre; 2 providing a second mould member comprising a rigid support on which is mounted an elastomeric second mould face which is conformed to a predetermined shape by maintenance of a pressure differential between the inside and the outside of the second mould member; 3 securing together the first and second mould members so that the first and second mould faces serve to define a mould cavity of a first volume in which the pack is located; 4 injecting a resin mixture into the mould cavity until the cavity is filled;; 5 causing the elastomeric second mould member to expand in volume, while the injected resin mixture is not fully polymerised, by inflating the elastomeric second mould face so as to change the total volume of the mould cavity from the first volume to a second volume smaller than the first; 6 allowing the injected resin mixture to polymerise; and 7 separating the first and second mould members and removing the moulding. 2 A method of moulding as claimed in Claim 1 characterised by the step of causing the elastomeric second mould member to expand in volume is achieved by means of a bladder incorporated ion the second mould member, the volume of the bladder being capable of controlled expansion from a smaller to a larger volume resulting in a corresponding increase in volume of the elastomeric second mould member. 3 A method of moulding as claimed in Claim 1 or Claim 2 characterised in that while the mould cavity is established at its first volume the elastomeric second mould member provides for a surface of the mould cavity at least one channel into which the pack cannot intrude, or not to any significant extent, to provide a relatively clear channel for the passage of liquid resin; and in the step of causing the elastomeric second mould member to expand in volume so as to reduce the total volume of the mould cavity from the first volume to a second volume smaller than the first the surface of the mould cavity containing the channel is caused to reform so as to eliminate the channel to a greater or lesser extent and provide for the surface to conform to a generally smooth configuration prior to the step of polymerising. 4 A method of moulding as hereinbefore described with reference to and as illustrated in the accompany drawings. 5 A moulded component fabricated by the method of any preceding claim. 6 Apparatus for resin transfer moulding comprising

1 a first mould member having a first mould face;

2 a second mould member incorporating an elastomeric mould face;

3 means for maintaining the elastomeric mould face in a predetermined shape by maintenance of a pressure differential between an inner volume of the second mould member and ambient pressure;

4 clamping together the first and second mould members to define a mould cavity of a first volume in which the pack is located;

5 a duct whereby a resin mixture can be directed into the mould;

6 providing means whereby the elastomeric second mould face can be expanded in a sense to reduce the total volume of the mould cavity from the first volume to a second volume smaller than the first at a predetermined period following injection of liquid resin material in the mould.

7 Apparatus for resin transfer moulding as hereinbefore described with reference to the accompanying drawing.

8 A moulded component fabricated on apparatus the subject of Claim 6 or Claim 7.