A method of manufacturing a shell element provided with an undercut and a shell element manufactured by said method

Abstract: A method of manufacturing a shell element (13) for an electronic device, said shell element (13) having a front (5) and at least one part that is angled in relation to said front (5). The shell element (13) further comprises a formed sheet (6) that constitutes at least a part of the outer surface of said front (5) and at least a part of said part that is angled in relation to the front of the shell element (13). The method comprises the steps of first forming a sheet (1) to a desired shape including a part that is angled in relation to a front part (5) and then injection moulding a plastics material on the back of the formed sheet (6). At least one area of the angled part of the formed sheet (6) is provided with an undercut (7) at the latest during injection moulding of the plastics material on the back of the formed sheet (6). A shell element manufactured by this method is also disclosed.

Description: The invention relates to a method of manufacturing a shell element for an electronic device, said shell element having a front and at least one part that is angled in relation to said front, said shell element further comprising a formed sheet that constitutes at least a part of the outer surface of said front and at least a part of said part that is angled in relation to the front of the shell element, said method comprising the steps of: forming said sheet to a desired shape including a part that is angled in relation to a front part, injection moulding a plastics material on the back of the formed sheet. WO 81/00654 discloses such a method. The invention further relates to a shell element manufactured by this method. The term electronic device includes portable radio communication equipment which includes all equipment such as mobile telephones, pagers, communicators, i.e. electronic organizers, smartphones or the like. Another example of an electronic device is a Personal Digital Assistant (PDA). In order to produce electronic equipment such as mobile phones with varying outer appearances, a number of different techniques have been developed. One of these techniques is the one described above in which a sheet of e.g. PC (polycarbonate) is provided with a decoration in terms of a print. The sheet is then formed into a desired shape by first heating the sheet, e.g. in an infra-red oven, and then use any conventionally known technique to form the heated sheet, e.g. by high pressure forming, hydro forming or vacuum forming. The heated sheet may also be positioned in a press mould with mould parts that form the sheet into the desired shape. When the sheet is cooled, it is removed from the press mould or male form part. In relation to the present invention, the formed sheet is provided with at least one part - preferably a circumferential flange - that is angled in relation to the front of the formed sheet. Usually, the edges of the formed sheet are trimmed and openings for e.g. keys and a display are provided in the front of the formed sheet. The openings may be made by punching or cutting. The formed sheet is then positioned in an injection mould in which one mould part has an inner shape that is complementary to the outer shape of the formed sheet and of the finished shell element. The mould part is provided with protrusions that extend into the openings of the formed sheet. The protrusions of the mould part abut the other mould part when the injection mould is closed. A plastics material, such as PC or ABS, is injected into the closed injection mould onto the back of the formed sheet. Due to the above-mentioned protrusions the finished shell element is provided with openings corresponding to the openings in the formed sheet. When the plastics material is cooled, the finished shell element is removed from the injection mould. The shell element needs no further trimming. By using the above-described method, varying outer appearances of e.g. mobile phones may be accomplished by varying only the printed decoration on the sheet, i.e. the method of manufacturing remains unchanged. This technique has therefore been found to be economically beneficial if it is desired to vary the outer appearances of a shell element for electronic devices. JP patent abstract No. 59-152,834 discloses a method of manufacturing a plastics injection moulded item with openings and an injection mould therefore. The injection mould is provided with stamping pins that punch the openings in a preformed and decorated sheet when the injection mould is closed. The plastics material is then injection moulded directly on the back of the preformed sheet to form a finished shell element. According to the prior art, shell elements of the type described above are manufactured with openings in the front part and with an angled part, e.g. a circumferential flange, extending from the front of the shell. It is only known to manufacture shell elements of this type in which the angled part forms an obtuse angle with the front, i.e. the formed sheet is provided with an obtuse angle between the front and the angled part and this formed sheet is positioned in a female injection mould part having an inner shape that is complementary to the outer shape of the formed sheet. If an electronic device comprising a shell element is to be provided with some kind of gripping means at the angled part, e.g. in form of recesses, these gripping means must be provided in the shell element after it has been ejected from the injection mould. It is an object of the invention to provide a method of manufacturing a shell element of the above-mentioned type, said shell element being provided with means that at least partly constitute gripping means for the electronic device in which the shell element is applied. This object is achieved by providing at least one area of the angled part of the formed sheet mentioned in the opening paragraph with an undercut at the latest during injection moulding of the plastics material on the back of the formed sheet. Thereby the shell element is provided with means that at least partly constitute gripping means, said means being provided without need for any later trimming of the shell element. The edges of the formed sheet are preferably trimmed and openings in the front part of the formed sheet, if any, are preferably provided before the plastics material is injection moulded on the back of the formed sheet. Thereby no further trimming of the finished shell element after injection moulding is necessary. Preferably the undercut is provided during forming of the sheet to the desired shape, i.e. only one process is applied for forming the sheet. Furthermore, the formed sheet provided with at least one undercut in the angled part can be more safely retained in the injection mould than the known formed sheets, since the injection mould has an inner shape that is complementary to the outer shape of the formed sheet, i.e. with protrusions that engage the undercut areas of the formed sheet. The injection mould may be provided with at least one protrusion that extends into at least one area provided with an undercut when the formed sheet is positioned in the injection mould for injection moulding a plastics material on the back of the formed sheet, or it may be provided with at least one displaceable member that is displaced into at least one area provided with an undercut when the formed sheet is positioned in the injection mould. If the injection mould is provided with protrusions, the injection mould can be made relatively simple. This structure requires, however, that the formed sheet as well as the finished shell element is sufficiently flexible in order to flex into and out of the injection mould part that has these protrusions. A more complex structure of the injection mould is achieved if it is provided with displaceable members. However, if the material used is relatively unflexible, this may be a preferred injection mould structure since the formed sheet can be positioned directly in the injection mould without flexing, and the finished shell element can be removed from the injection mould without flexing. In an alternative method according to the invention the undercut is provided in the formed sheet by means of protrusions provided in the injection mould and under influence of an injection moulding pressure when the plastics material is injected into the injection mould. In this method the undercut is provided during the injection moulding process, i.e. forming of the formed sheet with an undercut is avoided. The formed sheet may preferably cover the entire front of the shell element while the angled part comprises a circumferential flange that extends from the front of the shell element. Thereby the outlook of the shell element is determined solely by the appearance of the formed sheet. The plastics material that is injection moulded onto the back of the formed sheet can therefore be of any kind that fulfils the physical requirements to the material regardless of colour and appearance. In a preferred embodiment the sheet is a plastics material, such as polycarbonate (PC), and the material that is injection moulded on the back of the formed sheet is also a plastics material, such as PC or ABS. Such plastics materials can be easily formed to the desired shape and are very suitable for injection moulding and calls for good chemical bonding between the formed sheet and the backing. The electronic device, which the shell element is intended for, is preferably a mobile radio station, such as a mobile telephone. It shall be emphasised that the term "comprise/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps components or groups thereof. The invention will be described in detail in the following with reference to the drawings in which Fig. 1 stepwise shows the manufacturing of a shell element according to the invention, Figs. 2a and 2b each shows a cross-section of an injection mould in a first embodiment for use in the method of manufacturing according to the invention, and Fig. 3 shows a cross-section of an injection mould in a second embodiment for use in the method of manufacturing according to the invention. Fig. 1 shows the manufacturing process for a shell element having undercuts in side parts that are angled in relation to the front of the shell element. The starting material is a sheet 1 of a plastics material, such as polycarbonate (PC). The sheet 1 is provided with a print 2 which may comprise more than one colour or pattern as shown. The print may be provided at one or either side of the sheet 1 or it may be provided between two layers of a laminated sheet 1. The sheet 1 is heated, e.g. in an infra-red oven 3 as schematically illustrated, and is then formed into a desired shape by any known process, such as high pressure forming, vacuum forming, hydro forming or in a press tool. These forming processes are well-known in the art and are not shown in details. The preferred process is the high pressure forming process in which the sheet is positioned over a male form having undercuts and pressurized air is applied to the outer side of the heated sheet. After forming, the formed sheet 6 is provided with a circumferential flange 8 that is angled in relation to the front 5 of the formed sheet 6. The angulation may in a preferred embodiment be about 90° as shown, i.e. the flange 8 extends in a substantially right angle in relation to the front 5 of the formed sheet 6. The angled part, i.e. the flange 8, is provided with undercuts 7 at its two long sides. After forming the formed sheet 6, the edge of the sheet 1 is trimmed by cutting, and openings 4 are punched or cut in the front 5. At this point in the manufacturing process the formed and trimmed sheet 6 has achieved the desired shape and no further trimming is needed. The formed sheet 6 is positioned in a lower mould part 9a of an injection mould. This lower mould part 9a is provided with a recess 10 having a shape that is complementary to the outer shape of the formed sheet 6, i.e. the formed sheet 6 fits snugly into the recess 10. The recess 10 is provided with raised portions 11 that fit into the openings 4 provided in the formed sheet 6. The raised portions 11, 12 are abutted by the upper mould part 9b when the mould is closed, thereby forming cores for moulding openings in the finished shell element 13. The recess 10 is further provided with protrusions 12 that fit snugly into the undercuts 7 of the formed sheet 6 when it is positioned in the lower injection mould part 9a. The upper mould part 9b is provided with a sprue cup 14 through which the plastics material, such as PC or ABS, is injected after the injection mould has been closed. The injected plastics material spreads throughout the injection mould, forming a backing for the formed sheet 6 by adhering to the back of it and creating openings defined by the raised portions 11 of the injection mould. When cooled, the finished shell element 13 is ejected from the injection mould and is ready to be furnished with components extending through the openings 4, i.e. no further trimming is necessary. Figs. 2a and 2b show schematically a cross-section through an opened and a closed injection mould corresponding to the injection mould disclosed in Fig. 1. The injection mould comprises a lower injection mould part 9a and an upper injection mould part 9b. The lower injection mould part 9a is provided with raised portions 11 and protrusions 12 that protrude from the inner sidewall into the recess 10. A formed sheet 6 is positioned in the recess 10, ready for injection moulding of a plastics material on the back of it. The formed sheet 6 is relatively thin and flexible and it can usually be pressed readily into the shown position having the raised portions 11 extending through the openings 4 of the formed sheet 6 and the protrusions 12 engaging the undercuts 7. Since the raised portions 11 and the protrusions 12 extend in different directions, the formed sheet 6 is securely retained in the recess 10 when it is positioned as shown. Thus, provision of undercuts in the angled part or flange 8 and of openings 4 in the front 5 of the formed sheet 6 calls for good retaining of the formed sheet 6 in the injection mould recess 10 which has a complementary shape. After the formed sheet 6 is positioned in the recess 10, the injection mould is closed as shown in Fig. 2b. The upper injection mould part 9b is provided with a male part 15 that fits into the recess 10, abutting on the raised portions 11. When a plastics material is injected through the sprue cup 14, it spreads throughout the injection mould, adhering to the back of the formed sheet 6 and creating openings defined by the raised portions 11 abutting the male part 15. When the plastics material is cooled, the injection mould is opened and the finished shell element 13 is ejected. In order to eject the finished shell element 13, the flange 8 is pressed inwards to release the opening 7 from the raised portion 12. Fig. 3 shows a cross-section of an injection mould in a second embodiment for use in the method of manufacturing according to the invention. This injection mould corresponds to the injection mould shown in Figs. 2a and 2b except that the protrusions 12 have been replaced by displaceable members 22 that can be brought into engagement with the undercuts 7 of the formed sheet 6. This means that, when the members 22 are retracted, the finished shell element 13 can be ejected from the injection mould without deforming the flange 8, which is otherwise the case when the protrusions 12 are fixed as shown in Figs. 2a and 2b. An injection mould having displaceable members 22 may also advantageously be applied if the formed sheet 6 is made of a relatively unflexible material that cannot be deformed so as to snap over any fixed protrusions like the protrusions 12 shown in Figs. 2a and 2b. A preferred embodiment for a method of manufacturing a shell element according to the invention has been described above with reference to the drawings. In an alternative method of manufacturing a shell element according to the invention, the formed sheet 6 is not initially provided with undercuts 7. In this alternative method, the undercuts are provided during the injection moulding process, i.e. the formed sheet is provided with a smooth flange 8 when it is positioned in the injection mould part 9a that is provided with protrusions 12, 22. When the plastics material is injected into the closed injection mould, the injection moulding pressure forces the formed sheet against the outer wall of the injection mould to form around the protrusions, thereby forming the undercuts 7 in the finished shell element. It should also be realized, that the shell element may have other forms than the one shown. For instance, the formed sheet could constitute only a part of the surface of the front of the shell element, whereas the injection moulded plastics material constitutes a backing for the formed sheet as well as a part of the outer surface of the front of the shell element. According to the invention, however, at least a part of the formed sheet is angled in relation to the front of the shell element, said angled part being provided with at least one undercut.

Claims: A method of manufacturing a shell element (13) for an electronic device, said shell element (13) having a front (5) and at least one part that is angled in relation to said front (5), said shell element (13) further comprising a formed sheet (6) that constitutes at least a part of the outer surface of said front (5) and at least a part of said part that is angled in relation to the front of the shell element (13), said method comprising the steps of: forming a sheet (6) to a desired shape including a part that is angled in relation to a front part, injection moulding a plastics material on the back of the formed sheet (6), characterised in providing at least one area of the angled part of the formed sheet (6) with an undercut (7) at the latest during injection moulding of the plastics material on the back of the formed sheet (6). A method according to claim 1, characterised in trimming the edges of the formed sheet (6) before the plastics material is injection moulded on the back of the formed sheet (6). A method according to claims 1 or 2, characterised in providing at least one opening (4) in the front part of the formed sheet (6) before the plastics material is injection moulded on the back of the formed sheet (6). A method according to any one of claims 1-3, characterised in that the undercut (7) is provided during forming of the sheet (1) to the desired shape. A method according to claim 4, characterised in that the injection mould (9a, 9b) is provided with at least one protrusion (12) that extends into the at least one area provided with an undercut (7) when the formed sheet (6) is positioned in the injection mould (9a, 9b) for injection moulding a plastics material on the back of the formed sheet (6). A method according to claims 4 or 5, characterised in that the injection mould (9a, 9b) is provided with at least one displaceable member (22) that is displaced into the at least one area provided with an undercut (7) when the formed sheet (6) is positioned in the injection mould (9a, 9b) for injection moulding a plastics material on the back of the formed sheet (6). A method according to any one of claims 1-3, characterised in that the undercut (7) is provided in the formed sheet (6) by means of protrusions (12, 22) provided in the injection mould and under influence of an injection moulding pressure when the plastics material is injected into the injection mould (9a, 9b). A method according to any one of claims 1-7, characterised in that the formed sheet (6) covers the entire front (5) of the shell element (13) and that the angled part comprises a circumferential flange (8) that extends from the front (5) of the shell element (13). A method according to any one of claims 1-8, characterised in that the sheet (1) is a plastics material, such as polycarbonate (PC). A method according to any one of claims 1-9, characterised in that the material that is injection moulded on the back of the formed sheet (6) is a plastics material, such as PC or ABS. A method according to any one of claims 1-10, characterised in that the electronic device is a mobile radio station, such as a mobile telephone. A shell element (13) for an electronic device, said shell element (13) having a front (5) and at least one part that is angled in relation to said front (5), said shell element (13) comprising a formed sheet (6) that constitutes at least a part of an outer surface of said front (5) and at least a part of said part that is angled in relation to the front (5) of the shell element (13), a backing that is injection moulded on the back of the formed sheet (6), characterised in that at least one undercut (7) is provided in the part of the shell element (13) that is angled in relation to the front (5) of the shell element (13). A shell element according to claim 12, characterised in that the formed sheet (6) covers the entire front (5) of the shell element (13) and that the angled part comprises a circumferential flange (8) that extends from the front (5) of the shell element (13). A shell element according to claims 12 or 13, characterised in that at least one opening (4) is provided in the front (5) of the shell element (13). A shell element according to any one of claims 12-14, characterised in that the sheet (1) is a plastics material, such as polycarbonate (PC). A shell element according to any one of claims 12-15, characterised in that the material that is injection moulded on the back of the formed sheet (6) is a plastics material, such as PC or ABS. A shell element according to any one of claims 12-16, characterised in that the electronic device is a mobile radio station, such as a mobile telephone.

Inventors: NILSSON GERT, PERSSON MICHAEL, NILSSON, GERT, PERSSON, MICHAEL
Applicants: ERICSSON TELEFON AB L M, TELEFONAKTIEBOLAGET L M ERICSSON (PUBL)
Application year: 2000
Main classification: B29C45
IPC codes: B29C51, H04M1, B29C45