FORMING PRESS OF THE PRESSURE CELL TYPE

Abstract: A forming press of the pressure cell type comprising a press stand, a pressure cell arranged in the press stand with an elastic diaphragm (23) and a tray-shaped tool-carrying member, which is insertable into the press and in which a forming tool and a work piece are located. According to the invention the pressure cell is formed from a substantially plane diaphragm (22), a substantially plane surface of the press plate, and a sealing ring (23) disposed around the periphery of the diaphragm to bridge a gap between the diaphragm and the press plate. The sealing ring (23) is U-shaped with its flanges (23a, 23b) directed inward towards the centre of the pressure cell. Inside the sealing ring (23) spring elements (30′, 32) are arranged to urge the flanges of the sealing ring outwardly to provide initial contact pressure with the diaphragm and the press plate, respectively.

Description: The invention relates to a forming press of the pressure cell type according to the precharacterising part of claim 1. Such presses are known from US-A-3 875 778, US-A-3 938 361, and US-A-3 949 583 as well as from Pamphlet AQ 30-103E, published by ASEA AB of Västeras, Sweden. Presses of the afore-mentioned kind are used to a large extent for shaping complicated sheet metal parts, for example, in the aircraft industry. A great advantage of this type of forming press is that it can be provided with a very large working surface thus enabling large sheet metal parts to be formed in a single pressing operation. The characteristic feature of a forming press of the pressure cell type is that it comprises a pressure cell with an elastic diaphragm which either directly, or usually via a thick wear-resistant forming pad, exerts a compressive force against a work piece sheet placed on a forming tool in a closed space below the diaphragm. The pressure cell, with the forming pad is arranged in a trough- or tray-shaped press plate which is attached to an upper force-absorbing member in a press with the recess of the press plate facing downwards. The forming tool is placed in a recess in a trough- or tray-shaped movable carrying member which, after insertion into the press forms a closed press space together with the press plate and its diaphragm. Owing to the high working pressure of 100 MPa and more, and the considerable stretching of the diaphragm under pressure, considerable strength and sealing problems exist. The material problems are substantial and the tool costs are high because of the size and shape of the diaphragm. This has, among other things, resulted in a limitation of the choice of materials for the diaphragm. The use of materials which are most suitable from the elastic point of view, such as crude or natural rubber, requires very expensive vulcanizing tools, with regard to both the size of the diaphragm and the shape of its attachment part. For these reasons it has been necessary to resort to the use of materials, for example polyurethane, that are capable of being cast into the required shape to allow the manufacture of diaphragms at reasonable costs. Replacement of worn diaphragms of the present design is time-consuming, which is a disadvantage. The invention aims at developing a forming press of the pressure cell type the diaphragm of which is simple to manufacture and whose attachment means for the diaphragm are such as to permit a simple and fast replacement of a damaged diaphragm. To achieve this aim the invention suggests a forming press of the pressure cell type according to the introductory part of claim 1 which is characterized by the features of the characterizing part of claim 1. Further developments of the invention are characterized by the features of the additional claims. According to the invention the diaphragm of the forming press lacks the inwardly-facing attachment flange of prior art diaphragms, which resulted in the above-mentioned difficulties in manufacture, the undesired limitation of the choice of material, or the high manufacturing costs. Instead, with the forming press according to the invention the diaphragm is substantially plane. This means that the diaphragm can be manufactured from a material such as crude rubber, which has the most favorable elastic properties for sealing, since the necessary vulcanizing tools no longer involve prohibitively high costs. The seal against the press plate, which together with the diaphragm forms the pressure cell, preferably consists of a U-shaped sealing ring. The diaphragm and the sealing ring can be simply lifted up towards the press plate and placed in the recess therein and can then be held in position by means of - with respect to the transport direction of carrying member - longitudinal side bars and transverse vertically movable beams, which seal against the end surfaces of the tool carrying member and prevent the diaphragm (or the forming pad connected to the diaphragm) from being extruded from the press during a forming operation. The diaphragm can be constructed in many different ways. A thick diaphragm consisting of one single material can be used. However, it is usually more convenient to construct the diaphragm from several different layers of different materials. A combination of two rubber qualities is thus feasible. Another possibility is to construct the diaphragm with one inner layer of crude rubber and one outer layer of nitrile rubber or polyurethane which forms the forming pad which will be pressed against the work piece sheet to be shaped. Other combinations of materials are also feasible. The sealing ring suitably has a U-shaped cross-section forming a web and two flanges and is placed with its opening between its flanges facing inwardly towards the center of the pressure cell. To obtain abutment and initial sealing when pressurizing the pressure cell, the sealing ring can be constructed so that the flanges are urged resiliently outwards apart from each other so as to obtain good contact with the underside of the press plate and with the upper side of the diaphragm, respectively. Furthermore, the sealing ring is suitably made with slots to accommodate soft O-rings to additionally secure initial sealing. To achieve a reliable and adequate seal between the flanges of a U-shaped sealing ring and the opposing parts, springs can be placed inside the sealing ring, urging the flanges of the sealing ring apart from each other. The springs suitably consist of leaf springs with a small extension in the peripheral direction of the sealing ring and these leaf springs can be connected together by means of inner and/or outer connecting layers to form continuous elongated spring elements. A number of leaf springs may suitably be cast together between rubber or plastics facing sheets. The sealing ring and the spring elements are preferably located so that they straddle the periphery of a plate or frame, thereby bestowing dimensional stability upon the sealing ring so that it can be handled in a simple manner when the diaphragm is installed in the press. The invention will now be described in greater detail with reference to the accompanying drawings showing - by way of example - in Figure 1 schematically a side view of a press plant with a forming press according to the invention, Figure 2 a much enlarged cross-section taken on the line A-A in Figure 1, Figure 3 a longitudinal section taken on the line B-B in Figure 2, Figure 4, on a further enlarged scale, part of the section shown in Figure 3, Figure 5 a section taken on the line C-C in Figure 3, Figure 6 and 7 a straight and a curved spring element, respectively, which can be inserted in the sealing ring, Figure 8 a plate which is straddled by spring elements and the sealing ring and which gives the sealing ring its required geometrical shape. In the Figures, 1 designates a press stand and 2 a pair of tray-shaped carrying members, in each of which forming tools and work pieces to be formed are placed. Each carrying member 2 is provided with transport wheels 4 running on rails 3 supported on columns 5. Each carrying member 2 is movable between a position outside the press stand 1, in which pressed work pieces are removed and new work pieces are placed on the forming tools, and a position inside the press stand 1, in which the carrying member 2 and the press stand 1 together form a closed press space for the pressing operation. For good pressing results and high accuracy of shape, high pressing pressures are required, particularly in the case of intricately-shaped sheet material. As is shown in Figure 2, the press stand 1 is then suitably constructed with a mantle 10 wound of prestressed flat wire, the mantle acting as a force-absorbing member. This mantle 10 surrounds either an upper yoke 11, a lower yoke 12 and two intermediate spacers 13 and 14, or alternatively a tube. The wire-wound mantle 10 is surrounded by a protective sheet 15. The press stand 1 rests on a support 16. The yokes 11, 12 and the spacers 13, 14, or the tube and filling pieces in the form of circular segments positioned in said tube, form a space extending through the press stand 1 and having a substantially rectangular cross-section perpendicular to the transport direction of the carrying members through the press stand 1. The upper part of the just mentioned space accommodates a press plate 20 with enlarged end wall portions 21 (see Figures 3 and 4). This plate 20 is attached to the upper yoke 11 in a manner not shown. In the space between the end wall portions 21, a diaphragm 22 is arranged which is built up of a first layer 22a and a second layer 22b united with the first layer. Layer 22a consists of a material of very good elastic and sealing properties, such as crude natural rubber or synthetic rubber, having a hardness of suitably 60 - 80 o A. Layer 22b is of wear-resistant material, such as natural rubber, nitrile rubber or polyurethane, with a hardness suitable for the pressing operation (e.g. a hardness of 90 o A). Between the diaphragm 22 and the plate 20, a sealing ring 23 is arranged with a substantially U-shaped cross-section. The plate 20, the diaphragm 22 and the sealing ring 23 form a closed pressure cell 24. The pressure cell 24 is supplied with pressure medium from a pressurized source S (shown schematically in Figure 1) through channels 25 and 29 in the plate 20. A diaphragm plate 26 extends between the flanges 23a and 23b of the sealing ring stabilizing the latter. A number of straight and curved spring elements 27 and 28, respectively, are placed in the sealing ring 23 (see Figures 6-8). Each spring element 27, 28 consists of a number of essentially U-shaped leaf springs 30 which are faced by an inner layer 31 and an outer layer 32 of a material holding together a number of individual leaf springs. Each leaf spring has a relatively small width, for example 10-20 mm, in the axial direction of the spring element. The leaf springs 30 can be adhesively secured between the facing layers 31, 32 or they can be cast in between these layers. The material of the layers 31, 32 may be rubber or plastics with a suitable elasticity. The spring elements 27, 28 are placed around the periphery of the plate 26, the sealing ring 23 is then pulled over the spring elements 27, 28, and the composite unit formed of the plate 26, the spring elements 27, 28 and the sealing ring 23, is mounted in the press stand 1. The purpose of the spring elements 27, 28 is to enlarge the sealing ring 23 somewhat so as to obtain a contact pressure which provides an initial seal against both the underside of the plate 20 and the upper layer 22a of the diaphragm 22. To ensure a good initial seal when the pressure cell 24 is first pressurized, the flanges 23a and 23b of the sealing ring 23 are formed with slots 33, 34, in which are placed O-rings 35, 36 of a soft material forming an efficient seal between the flange 23a and the plate 20 as well as between the flange 23b and the diaphragm 22 during the initial pressurization period. Thereafter, the presence of pressure medium between the flanges 23a and 23b of the sealing ring 23 will press these flanges with ever increasing force against the plate 20 and the diaphragm 22, respectively, as the pressure in the space is increased. The diaphragm 22 is fixed in the press by means of bars 40 and 41, respectively, along the long sides and by means of beams 42 along the short sides. The bars 40, 41 are fixed in the press by means of a plate 45 resting on the yoke 12. The beams 42 are vertically movably arranged and supported by lifting pistons 43 in cylinders 44 in the bars 40 and 41. During insertion and withdrawal of the carrying member 2, these pistons 43 hold the beams 42 up in the position shown in Figures 3-5, thus forming a gap 47 between the beams 42 and the end portions 6 of the carrying member 2. With a view to improving strength, the transition between the mid-portion of the plate 20 and its end portions 21 is made with a large radius. It is necessary to locate a special fill-out bar 48 in the plate 20 to allow for some vertical movement of the beam 42. During a pressing operation, the beam 42 is pressed against the end portion 6 of the carrying member 2, thus eliminating the gap 47 and preventing the extrusion of the diaphragm 22 between the end portion 21 of the plate 20 and the end portion 6 of the carrying member. At the outer corner regions of the sealing ring 23, metallic sections 50 and 51, respectively, of triangular cross-section are located, these sections preventing the sealing ring 23 from being pressed out into the gaps formed between the plate 20 and the spacers 13 and 14 and between the plate 20 and the beam 42, respectively. The gap between the plate 20 and the beam 42 arises when the beam 42 is pressed down against the end portion 6 of the carrying member 2. As will be clear from from Figures 3-5, the layer 22a of the diaphragm 22 is formed with a slot 52 near its periphery. The bars 40, 41 are formed with a bead 53, which projects into this slot 52. The beams 42 are formed with a flange 54 provided with a bead 55, which also projects into the slot 52. Together with the plate 20 and the diaphragm 22, the tray-like carrying member 2 forms a closed press space 60. The carrying member 2 is formed with detachable side walls 61 (Figure 2) in a known manner. One or more forming tool(s) 62 is/are placed on the bottom of the carrying member 2, and on this/these forming tool(s) 62 one or more sheet(s) 63 is/are placed to be formed so as to assume the shape of the forming tool 62. Around the tool 62 there may be located suitable filling pieces 64. During the pressing operation, the pressure cell 24 is pressurized by the supply of pressure medium from the source S. The lower layer 22b of the diaphragm 22 is thus pressed against the sheet 63 so that this is pressed against the tool 62 and assumes the shape of the tool 62. The invention may be varied in many ways within the scope of the following claims.

Claims: Forming press of the pressure cell type with a cylindrical press stand (1) with two opposing pressure-absorbing (11, 12) elements distanced by two spacers (13,14) between all of which an axially extending working space is formed, with a press plate (20), with means defining a recess in said press plate, with an essentially rectangular elastic diaphragm (22) mounted in a sealing manner in the recess to define an expansible pressure cell, which pressure cell has a pair or axially extending bars (40,41) supporting the underside of two parallel edge portions of the diaphragm,with a tool carrying member (2) insertable into said working space, which carrying member, in its inserted position, forms a closed press space (60) together with the press plate (20) and the diaphragm (22), and with a pressure medium source (S) for pressurization of the pressure cell to press the diaphragm against a work piece (63) on a forming tool in the carrying member (2) for forming the work piece to the desired shape, characterized in that the pressure cell is formed from a substantially plane diaphragm (22), a substantially plane surface of the press plate, and a sealing ring (23) disposed along the periphery of the diaphragm to bridge a gap between the diaphragm and the press plate, in that the sealing ring is formed with sealing surfaces making contact with the diaphragm and the press plate, in that the edges of the sealing ring and the diaphragm running perpendicular to the axis of the press stand (1) abut each to a vertically displaceable L-shaped beam (42), the horizontal part of which supports the underside of the edge portion of the diaphragm, while the upper part of the beam (42) faces the plane surface of the press plate, and in that the gap formed between the upper part of the beam (42) and the plane surface of the press plate (20) is bridged by a metallic sealing bar (50). Forming press according to claim 1, characterized in that spring elements (27, 28) are arranged in the sealing ring, said spring elements pressing the sealing surfaces of the sealing ring against the press plate and the diaphragm, respectively. Forming press according to any of the preceding claims, characterized in that the sealing ring has a substantially U-shaped cross-section exhibiting a web (23c) and two flanges (23a, 23b), and that the sealing ring is oriented with its web resting against the surrounding force-absorbing members and with its flanges making contact with the press plate and the diaphragm, respectively. Forming press according to any of the preceding claims, characterized in that the diaphragm (22) is supported in the press stand (1) by means of longitudinal bars (40, 41) fixed in the press stand supporting the diaphragm along the sides of the press stand extending in the transport direction of the tool carrying member and by means of two transverse, vertically movable beams (42) supporting the diaphragm along the sides of the press stand perpendicular to said transport direction. Forming press according to claim 4, characterized in that the transverse beams (42) rest on pistons (43) in cylinder bores provided in said longitudinal bars (40, 41), said pistons being actuable to lift the beams towards an upper position. Forming press according to any of claims 2 - 5, characterized in that the spring elements (27, 28) are arranged inside the sealing ring (23) urging the flanges (23a, 23b) of the sealing ring outwards in order to generate an initial contact pressure against the lower surface of the press plate (20) and against the upper surface of the diaphragm (22), respectively. Forming press according to claim 6, characterized in that the spring elements consist of a number of individual leaf springs (30) which are combined into a single unit. Forming press according to claim 7, characterized in that the individual leaf springs (30) are bonded to at least one layer of elastic material (31, 32). Forming press according to claim 8, characterized in that the individual leaf springs (30) are bonded to inner and outer facing layers (31, 32) of elastic material. Forming press according to any of claims 6 to 9, characterized in that a plate (26) is provided in the pressure cell, said plate being surrounded by the spring elements (27, 28) and the sealing ring, thus stabilizing the sealing ring.

Inventors: HELLGREN, KEIJO
Applicants: ASEA AB
Application year: 1986
Main classification: B30B5
IPC codes: B30B5