Bland, Richard (Unit 21F, Brunel Road Saltash Industrial Estat, Saltash Cornwall PL12 6LF, GB)
Williams, Stephen Leonard (Unit 21F, Brunel Road Saltash Industrial Estat, Saltash Cornwall PL12 6LF, GB)
Gouldthorpe, Martin (Unit 3, Focus 4 Fourth Avenue, Letchworth SG6 2TU, GB)
Bland, Richard (Unit 21F, Brunel Road Saltash Industrial Estat, Saltash Cornwall PL12 6LF, GB)
Williams, Stephen Leonard (Unit 21F, Brunel Road Saltash Industrial Estat, Saltash Cornwall PL12 6LF, GB)
| 1. | A method of moulding a helmet shell having a return curve or undercut comprising the steps of: providing a mould cavity between a substantially nondeformable male mould component and a female mould component; introducing mould material into the cavity; after a predetermined time period, releasing the female mould component; and removing the helmet shell from the male mould component by expanding the shell. |
| 2. | The method of claim 1 wherein the removal step comprises expanding the shell by pressurising it internally. |
| 3. | The method of claim 1 or 2 wherein the removal step is performed by introducing air under pressure into the shell. |
| 4. | The method of any preceding claim comprising the step of providing a reinforcing material on the male mould component prior to the mould material introduction step. |
| 5. | The method of any preceding claim wherein the reinforcing material is a dry fibre pack. |
| 6. | The method of claim 5 wherein the fibre pack is made from fibreglass or carbon/aramid fibre. |
| 7. | The method of any preceding claim wherein the mould material is thermosetting resin. |
| 8. | The method of any preceding claim wherein the mould material is introduced into the cavity via an injection port on the male mould component. |
| 9. | The method of claim 8 wherein the removal step is performed by introducing air under pressure to the shell via the injection port. |
| 10. | The method of any preceding claim wherein the male mould component and/or the female mould component is heatable to aid in curing the resin during the predetermined time period. |
| 11. | The method of claim 10 wherein the predetermined time period is about 3 to 4 minutes. |
| 12. | The method of any preceding claim wherein the cavity is configured such that the shell has an opening which extends in three dimensions such that the shell is expandable by deflection in a first direction of a portion thereof which is peripheral to the opening to permit removal of the shell from the male mould component in a second direction. |
| 13. | Apparatus for moulding a helmet shell having a return curve or undercut, the apparatus comprising: a substantially nondeformable male mould component and a female mould component defining a mould cavity therebetween; a port for introducing mould material into the cavity; and means for removing the helmet shell from the male component, wherein the removing means comprises means for expanding the shell. |
| 14. | The apparatus of claim 13 wherein the expanding means comprises means for internally pressurising the shell. |
| 15. | The apparatus of claim 13 or 14 wherein the removing means comprises an air injection port for injecting air into the shell to release it from the male mould component. |
| 16. | The apparatus of claim 15 wherein the air injection port is the introduction port. |
| 17. | The apparatus of any of claims 13 to 16 wherein the introduction port is on the male mould component. |
| 18. | The apparatus of any of claims 13 to 17 wherein the cavity is configured such that the shell has an opening which extends in three dimensions such that the shell is expandable by deflection in a first direction of a portion thereof which is peripheral to the opening to permit removal of the shell from the male mould component in a second direction. |
| 19. | A moulding method or moulding apparatus substantially as herein described with reference to the accompanying drawings. |
| 20. | A helmet shell produced by a moulding method or moulding apparatus substantially as herein described with reference to the accompanying drawings. |
TECHNICAL FIELD
The present invention relates to moulding methods and apparatus and in particular to injection moulding methods and apparatus for forming helmet shells with a return curve or undercut.
BACKGROUND ART
Injection moulding processes are well known for producing articles, such as polymeric articles. Such processes typically involve injecting mould material into a cavity provided between a male mould component and a female mould component, where the female mould component is typically in two pieces for easier assembly and removal. Once the mould material has cured, the female mould component is removed, and the article removed from the male mould component.
Difficulties in injection moulding processes occur when the article has a return curve, or undercut. One solution for moulding articles with a return curve is to mould the article in two parts for subsequent joining when removed from the mould. Articles formed from this process typically have areas of weakness at or near the join of the two parts.
Another solution for moulding articles with a return curve is to use a collapsible male mould component. For example, the male mould component may be a rubber inflatable bag which is deflated when the article is cured. This solution has problems when used in resin transfer moulding processes.. For example, in the resin transfer moulding of helmet shells, a dry fibre pack may be used with the resin to reinforce the strength of the helmet shell. In
this process, the fibre pack in a roughly rounded cup shape is placed in the female mould cavity and the deflated male mould component inserted into the fibre pack. The male mould component is then inflated and thermosetting resin introduced into the cavity such that it fills the cavity and envelops the fibre pack. The resin is then cured, prior to removing the female mould component, deflating the male mould component and removing the helmet shell. This process has several shortcomings. For example, the male mould component has a limited working life compared to the female mould component.
Due to the elastic nature of the male mould component, the interior of the helmet shell is manufactured with poor tolerance levels. Also, due to the flexibility of the fibre pack, it is time consuming to prepare the mould cavity with fibre pack in place.
It is an object of the invention to overcome or ameliorate at least one of the deficiencies of the prior art, or at least to provide a suitable alternative thereto.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a method of moulding a helmet shell having a return curve or undercut comprising the steps of: providing a mould cavity between a substantially non-deformable male mould component and a female mould component; introducing mould material into the cavity; after a predetermined time period, releasing the female mould component; and removing the helmet shell from the male mould component by expanding the shell.
Advantageously, it is possible with the invention to mould helmet shells with a return curve in a one piece construction. Also, the substantially non- deformable male component may be manufactured from material with a longer operational life than the inflatable bag of the prior art, for example. It also allows for the use of matched tooling of the mould components, which means the helmet shell can be manufactured to closer tolerances compared to the prior art.
Preferably the removal step comprises expanding the shell by pressurising it internally, preferably by introducing air under pressure into the shell. This may be achieved by introducing air under pressure between the male component and the shell. The pressure of the introduced air is preferably 60- 100psi and more preferably 90psi.
Preferably the method comprises the step of providing a reinforcing material on the male mould component prior to the mould material introduction step. Advantageously, because the male mould component is substantially non- deformable, the fibre pack can be positioned on the male mould component prior to positioning in the female mould component. This allows for an improvement in both quality of the shell and throughput of shell production.
Preferably the reinforcing material is a dry fibre pack, wherein the fibre pack is preferably made from fibreglass or carbon/aramid fibre.
Preferably the mould material is thermosetting resin and is introduced into the cavity via an injection port on the male mould component. Preferably the removal step is performed by introducing air under pressure to the shell via the injection port. The thermosetting resin may be selected from the group of polyester, vinylester and epoxy.
Preferably the male mould component and/or the female mould component is
heatable to aid in curing the resin during the predetermined time period. The predetermined time period is preferably about 3 to 4 minutes.
Preferably the cavity is configured such that the helmet shell has an opening which extends in three dimensions such that the shell is expandable by deflection in a first direction of a portion thereof which is peripheral to the opening to permit removal of the shell from the male mould component in a second direction.
According to another aspect of the invention there is provided apparatus for moulding a helmet shell having a return curve or undercut, the apparatus comprising: a substantially non-deformable male mould component and a female mould component defining a mould cavity therebetween; a port for introducing mould material into the cavity; and means for removing the helmet shell from the male component, wherein the removing means comprises means for expanding the shell.
Preferably the cavity is configured such that the shell has an opening which extends in three dimensions such that the shell is expandable by deflection in a first direction of a portion thereof which is peripheral to the opening to permit removal of the shell from the male mould component in a second direction.
According to another aspect of the invention there is provided a helmet shell formed by the above described method aspect of the present invention.
According to another aspect of the invention there is provided a male mould component being substantially non-deformable and configured to define a mould cavity with a female mould component such that a helmet shell formed within the cavity has a return curve or undercut, the male mould component
comprising a port for introducing mould material into the cavity and for introducing air into the shell to expand and release the shell from the male mould component.
Preferably the male mould component further comprises heating means for aiding in curing the mould material introduced into the cavity.
As will be understood by the skilled addressee, the term "helmet shell" refers to the outer, hard, impact resistant component of a helmet and not to a cushioning helmet "liner", typically formed from polystyrene beads into a relatively thicker helmet component.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 illustrates a side view of a male mould component for use with an embodiment of the present invention;
Figures 2a and 2b illustrate side and end views of a female mould component for use with an embodiment of the present invention;
Figure 3 to 5 illustrate alternative embodiments of the male mould component in the female mould component;
Figures 6 and 7 illustrate several incremental steps in an embodiment of the present invention; and
Figures 8 and 9 illustrate a helmet shell produced by an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to Figures 1 to 6 and 9, a preferred embodiment of the present invention is an apparatus for moulding a helmet shell 20 having a cross- sectional thickness of 1.5-4. Omm, and preferably 2.0-2.5mm. The apparatus comprises a substantially non-deformable male mould component 22 and a female mould component 24. The female mould component 24 is in first and second adjoinable parts 24a and 24b, which when adjoined form an internal space 26. The male and female components constitute matched tool components. As illustrated in Figure 3, the male mould component 22 is configured to be placed in the internal space 26 of the female mould component 24 to form a mould cavity 28 therebetween. The male and female components 22, 24 are matched tooling components allowing for closer dimensional tolerances in manufacture compared to prior art processes. For example, helmet shells 20 manufactured by the preferred apparatus can be manufactured to have a cross-sectional thickness of 2.0mm in side regions of the helmet and 2.5mm in a centre region within a tolerance of 0.2mm.
As illustrated in Figure 1 , the male mould component 22 has an injection port 30 which has the dual purposes of being a port for the introduction of mould material into the cavity 28, and for the introduction of relatively high pressure air to remove the helmet shell from the male mould component 22 at the end of the manufacturing process. The injection port 30 is positioned centrally of the male mould component 22.
Figures 4 and 5 illustrate two alternative embodiments for hingedly connecting the male mould component 22 to the female mould component 24. In the embodiment illustrated in Figure 4, the rotational axis 32 of the male mould component 22 is at the second part 24b of the female mould component 24, whereas in the embodiment illustrated in Figure 5, the rotational axis 32' of the male mould component 22 is spaced from the
second part 24b of the female mould component 24. The latter hinge embodiment allows for easier placement of the male mould component 22 in the internal space 26 of the female mould component 24.
Both the male mould component 22 and the female mould component 24 are preferably made from tool steel, though may be made from any other suitable material for moulding. In an alternative embodiment, the male mould component 24 and/or the female mould component 24 are made from a substantially non-deformable polymer.
Referring to the Figures, another preferred embodiment of the invention is a method of moulding a helmet shell using an injection moulding process. In this embodiment, the injection moulding process is a resin transfer moulding process, and will be described with reference to moulding a helmet shell 20 using the apparatus described above. The helmet shell 20 is used in forming a helmet in the form of a hard-hat, bicycle helmet, motorcycle helmet, pilot helmet, etc.
Firstly, reinforcing material in the form of a dry carbon/aramid fibre pack 34 is placed over the male mould component 22, as illustrated by arrow 36 in
Figure 6. Alternatively, the reinforcing material may be fibreglass. The first female mould component part 24a is moved away from the second female mould component part 24b. The male mould component 22 with fibre pack
34 thereon is then rotated in the direction of arrow 38 to be positioned in the internal space 26. The first female mould component part 24a is then lowered onto the second female mould component part 24b and the two female mould components clamped together. Mould material in the form of a thermosetting resin, in this embodiment polyester, is injected in liquid form into the mould cavity 28 through the injection port 30, and envelops the fibre pack 34. Metering equipment is used to control the amount of resin injected into the cavity 28 to ensure it is appropriately filled. Once a required amount
of resin is injected into the cavity 28, the injection port is closed to the cavity 28 and flushed with solvent, eg acetone, and then flushed with air at room temperature to remove the solvent. The male mould component 22 is heated to 30-70 0 C and the resin allowed to cure for a predetermined time period.
In this embodiment, the predetermined curing time period is about 3-4 minutes. In alternative embodiments, the female mould component 24 is heated, or both the male mould component 22 and the female mould component 24 are heated to improve and to decrease the time of the resin curing process. Also, since the male mould component 22 is made from tool steel, it is possible to use resin which requires a higher curing temperature, e.g. 100 0 C. Once the predetermined time period has passed, the first female mould component part 24a is removed from the second female mould component part 24b and the male mould component 22 rotated out of the second female mould component part 24b.
The male mould component with a helmet shell blank 20' thereon is illustrated in Figure 7. The helmet shell blank 20' has a return curve, or undercut, due to its neck portion 40 being narrower than its widest portion 42. To remove the blank 20' from the male mould component 22, compressed air is injected at 90psi through the injection port 30 such that the helmet shell blank 20' is expanded at its neck portion 40 and blown off the male mould component 22 without the blank 20' being damaged. This is in part achieved by the flexibility of the blank 20', particularly about the neck portion 40 and ear covering portions 44 peripheral to the shell's opening 45. Also, since the opening 45 extends in three dimensions, the expansion is achievable by the deflection of the ear covering portions 44 in a first direction outwardly with respect to the blank 20', to permit removal of the blank 20' from the male mould component 22 in a second direction.
To increase the working life of the male mould component 22, it is preferably
hardened, particularly at its neck 40' and widest 42' portions where the neck 40 and ear covering 44 portions of the helmet shell expand and flex over the male mould component 22 when being removed therefrom.
Flashing from the moulding process is then removed from the helmet shell blank 20' to produce the helmet shell 20, as illustrated in Figure 8. Figure 9 illustrates a helmet 46 on a user's head 48, the helmet 46 including the helmet shell 20.
The embodiments of the present invention have clear advantages with respect to prior art moulding processes. For example, in the prior art described above where the male mould component is an inflatable bag, the curing temperature must be kept below 75°C, or the bag will be heat damaged. This both slows down the curing step and limits the type of resin which can be used. Also, since the male mould component 22 of the present invention is substantially non-deformable, resin can be injected into the cavity 28 at a higher pressure and therefore the cavity can be filled at a faster rate compared with using the prior art inflatable bag. Injection pressure is limited when using inflatable bags due to risk of bag deformation and thus cavity shape alteration. Throughput of this prior art method is therefore typically limited to about three helmet shells per hour. By comparison, using the preferred embodiment of the present invention, throughput is about ten to twelve helmet shells per hour. This increased throughput greatly decreases labour costs per helmet shell and results in cheaper overall manufacturing costs per helmet. Furthermore, the prior art inflatable male mould component has a reduced working life compared with the male mould component of the present invention, which adds to the relative manufacturing costs per helmet when using the prior art process.
The central positioning of the injection port 30 on the male mould component 22 allows for a more efficient spread of mould material through the cavity 28,
and is the preferred location for the introduction of air to force the helmet shell from the male mould component. However, as will be apparent, it is not essential that the air be introduced either through the same port as the mould material is introduced, nor into the centre of the shell. For example, the air may be introduced at an edge of an open end of the shell, such on the edge of the neck portion 40 in the above example of manufacturing a helmet shell 20.
While the invention has been described with reference to its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made to the invention without departing from its scope as defined by the appended claims.
The text of the abstract filed herewith is repeated here as part of the specification.
A method and apparatus for moulding a helmet shell having a return curve or undercut comprises providing a mould cavity between a substantially non- deformable male mould component and a female mould component. Mould material is introduced into the cavity and cured therein. After a predetermined time period, the female mould component is released and the shell removed from the male mould component by expanding the shell, preferably by pressuring it internally.