Press and process for cold forming a starting part into a hollow body

Abstract

A press (10) which is set up for cold forming a starting part (13) into a hollow body (14), wherein the press comprises a ram (11) which is mounted to be linearly movable in a working direction (A) by means of a guide arrangement (19), wherein the press further comprises a drive (18) which is designed to move the ram (11) in the working direction (A), wherein the press further comprises a ramming tool (12) arranged on the ram (11), which is designed to transform the starting part (13) into the hollow body (14) by moving it in the working direction (A) relative to a die tool (26), characterized in that the die tool has a drawing channel (28) with at least one drawing ring (29), that the ram (11) is mounted so as to be movable in the working direction (A) along the longitudinal axis (L) by means of a guide arrangement (19), wherein the guide arrangement (19) has several separate bearings (20) arranged at a distance from each other in the working direction (A), that the ram (11) is made of an iron alloy with a coefficient of thermal expansion (α) of at most 3.0 * 10 -6 K -1 consists.

Description

[0001] The invention relates to a press and a method for cold forming a starting part into a hollow body. The formed hollow body has a cylindrical surface and is open on one axial side and closed on the opposite axial side. The closed side can, for example, form or shape a base of the hollow body. The hollow body is integrally formed and has no seams or joints. The hollow body preferably consists of a metallic alloy, for example, an aluminum alloy. The starting part consists of the same material as the hollow body to be produced and can be provided in the form of a flat, plate-like blank or in the form of a cup or bowl.

[0002] Cold forming for the production of hollow bodies using a press is known. For example, starting parts can be formed into hollow bodies by stretch forming. A device for this is known, for example, from DE 2 519 521 A1.

[0003] Besides cold forming, other presses and processes exist for manufacturing components. For example, EP 0 990 499 A2 discloses a compression mold with a lower and an upper mold part, wherein the mold forms a cavity between the two mold parts in which the component is manufactured. The component is a composite material part. Prepregs in the form of prepreg wedges are inserted into the mold, and the mold is closed. The mold is then heated via heating cartridges to melt the resin in the prepreg and bond the individual prepreg wedges together. Simultaneously, pressure is exerted on the prepreg wedges via the two mold parts. To prevent the mold from expanding when heat is applied, it can be made of a so-called "Invar" alloy.

[0004] JP S62110821 A describes a press for deep drawing a sheet metal part. The punch for forming the sheet metal part is made of an "Invar" alloy.

[0005] EP 1 347 519 A1 describes a drawing device for the production of battery housings. DE 102 61 084 A1 relates to a drawing ring for the production of hollow bodies.

[0006] A hollow cylindrical container formed from a raw part by cold forming is subject to stringent quality requirements. Wall thickness tolerances are in the micrometer range. Insufficient precision during manufacturing can lead to an undesirably high scrap rate. Therefore, the object of the present invention can be considered to be to provide an improved press or process for cold forming raw parts into hollow bodies that ensures sufficient accuracy with high productivity.

[0007] This problem is solved by a press having the features of claim 1 and a method having the features of claim 12.

[0008] The press is configured for cold forming a starting part into a hollow body. The hollow body has a closed circumferential wall, preferably circular in cross-section. The hollow body is open on one axial side and closed on the other, for example, by a bottom. The hollow body is integrally manufactured and has no seams or joints. The starting part can be made of, for example, a metallic alloy, and in particular an aluminum alloy. In the embodiment described here, the starting part has the shape of a cup or a bowl, but can alternatively be in the form of a plate-shaped blank.

[0009] The press includes a ram with a ramming tool at its free end. The ram is mounted on a guide assembly so that it can move linearly in one working direction. A drive mechanism moves the ram in working direction A and guides it through the guide assembly. In this embodiment, the guide assembly allows the ram to move in a single linear degree of freedom.

[0010] The press also features a die tool. The ram tool is movable relative to the die tool. Between the ram tool and the die tool, the initial part is formed into a hollow body, in particular by drawing and sliding.

[0011] Such presses operate at a high stroke rate. The rapid movement of the ram generates friction and heat. The invention is based on the understanding that the heating of the ram relative to its longitudinal axis is uneven, resulting in deformation of the ram so that it is no longer rotationally symmetrical about its longitudinal axis. When this asymmetrically deformed ram is accelerated to increase or decrease its speed, vibrations can be induced within the ram. These vibrations are particularly pronounced when the ram tool's end face interacts with a forming tool to shape the closed side of the hollow body, for example, to form the bottom of the hollow body. The ram vibrations typically persist for one stroke and are re-excited or amplified during the subsequent stroke.Due to the vibrations of the ram, the wall thickness of the hollow body varies, so the specified tolerance limits are frequently exceeded. The scrap rate is relatively high.

[0012] Therefore, according to the invention, the ram is to be manufactured from an iron alloy having a coefficient of thermal expansion of at most 3.0 × 10 -6 K -1 Due to its low thermal expansion, the ram's symmetry with respect to its longitudinal axis, which is aligned parallel to the working direction, is largely maintained. This minimizes vibration excitation of the ram and allows for adherence to tolerances in the manufacturing of the hollow body. Such a press can operate at high stroke rates with a low scrap rate.

[0013] It is advantageous if the iron alloy comprises at least one further major alloying element whose mass fraction in the iron alloy determines the coefficient of thermal expansion. For example, nickel and / or manganese and / or platinum and / or palladium can be included as a further major alloying element. Preferably, the iron alloy is formulated as an iron-nickel alloy. The mass fraction of nickel in the iron-nickel alloy can be 30% to 42% and preferably 35% to 36%.

[0014] It is also advantageous if the iron alloy, in addition to the at least one main alloying element, comprises a further alloying element, which may be, for example, magnesium, silicon, carbon, cobalt, or a combination of several of these elements. The mass fraction of the at least one further alloying element in the iron alloy is preferably a maximum of 10% or a maximum of 5%.

[0015] It is advantageous if the mass fraction of iron in the iron alloy is a maximum of 58% to a maximum of 70% and, in particular, a maximum of 64% to a maximum of 65%.

[0016] It is preferred if the coefficient of thermal expansion of the iron alloy is a maximum of 1.7 to 2.0 × 10 -6 K -1 Iron alloys with such a coefficient of thermal expansion are also collectively referred to as "Invar" alloys.

[0017] The press's guide assembly has several separate bearings, spaced apart from each other in the working direction. Each bearing can be designed as a sliding bearing and / or a rolling bearing.

[0018] It is also advantageous if the ramming tool is made of a material different from that of the ram itself. This allows the ramming tool to be designed according to the specific forming task. Due to the low coefficient of thermal expansion of the ram, the orientation and position of the ramming tool remain unchanged.

[0019] The press has a die tool with a drawing channel and at least one drawing ring. The forming of the starting material into a hollow body is therefore carried out by drawing sliding.

[0020] It is advantageous if the press has a hold-down device. The hold-down device has a hold-down sleeve that is movable in the working direction and is arranged coaxially to the ram. The hold-down device is designed to apply a holding force to the output part or to clamp it between the hold-down sleeve and a support surface while the ramming tool applies force to the output part and moves it into the drawing channel. During this movement of the output part into the drawing channel, the output part slides between the hold-down sleeve and the support surface.

[0021] It is also advantageous if the press has a forming tool designed to cooperate with an end face of the ramming tool to reshape the hollow body on its axially closed side, for example to form a bottom of the hollow body.

[0022] Advantageous embodiments of the method are described in the dependent claims, the description, and the drawings. Preferred embodiments of the invention are explained in detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic block diagram of an embodiment of a press, wherein the ram is in a starting position, Fig. 2 the exemplary embodiment of the press from Fig. 1, wherein the ram is in an extended position and Fig. 3 a schematic representation of a press according to the state of the art.

[0023] In the Fig. 1 and Fig. Figure 2 is an embodiment of a press according to the invention, which is configured to carry out the method according to the invention, schematically illustrated in the form of a block diagram. The press 10 has a ram 11 mounted so as to be movable in a working direction A along a longitudinal axis L. In the embodiment according to the invention, the longitudinal axis L represents the longitudinal center axis of the ram 11. A ramming tool 12, also referred to as a "punch," is arranged at a front, free end of the ram 11 and is configured to actuate an output part 13, which is, for example, cup-shaped or bowl-shaped. The output part 13 can also be referred to as a "cup." The output part 13 is integrally formed and consists, for example, of a metallic alloy. The output part 13 can be provided with a plastic coating or a paint finish on the inside and / or the outside.

[0024] In the embodiment of the press 10 described here, the cup-shaped starting part 13 is formed into a hollow body 14 by a cold forming process ( Fig. 2) reshaped. The reshaping is carried out, for example, by stretching and sliding drawing.

[0025] The hollow body 14 has a circumferential wall 14a that extends around the longitudinal axis L. The hollow body 14 is open on one axial side and closed on its opposite axial side. The starting part 13, and thus also the hollow body 14, is integrally formed. A bottom 14b of the hollow body 14 therefore joins the circumferential wall 14a without any seam or joint. In the embodiment described here, the closed axial side of the hollow body 14 is formed into a bottom 14b. Alternatively, it is also possible to form the closed axial side of the hollow body 14 into a neck region if the hollow body is to have a bottle-shaped form.

[0026] To move the ram 11 in the working direction A, the press 10 has a drive 18. The drive 18 can include a motor and a gearbox.

[0027] The ram 11 is movably mounted in the working direction A along the longitudinal axis L by means of a guide arrangement 19. The guide arrangement 19 is designed such that the ram 11 is only movable along the longitudinal axis L and movements in other spatial directions are supported. For this purpose, the guide arrangement 19 has at least one and preferably several separate bearings 20. Each bearing 20 can be designed as a sliding bearing or a rolling bearing. Hydrostatic sliding bearings are preferably used for the mounting. The drawing shows only two bearings 20 as examples. In a variation of this, more than two bearings 20 could also be present. Preferably, the ram 11 is mounted at two bearing points 21 arranged at a distance from each other in the working direction A, each supported by at least one bearing 20.

[0028] Adjacent to the guide assembly 19 is a sealing device 22 with at least one sealing element. The sealing device 22 is in contact with the outer surface or circumferential surface of the ram 11. Lubricant and / or coolant adhering to the outer surface of the ram 11 is wiped off by the sealing device 22. Coolant, lubricant, or other contaminants or particles are removed from the ram 11 by the sealing device 22 and cannot enter the bearings 20 of the guide assembly 19.

[0029] The press 10 has a die tool 26 that cooperates with the ram tool 12. The die tool 26 is, for example, arranged on a table 27 or on another suitable support of the press 10. The die tool 26 has a drawing channel 28 extending along the longitudinal axis L. The drawing channel 28 has a channel inlet 28a and a channel outlet 28b. Within the drawing channel 28, several drawing rings 29 of the die tool 26 are arranged coaxially with the longitudinal axis L. The drawing rings 29 have different inner diameters. The drawing ring 29 located closest to the channel outlet 28b has an inner diameter that corresponds to the desired outer diameter of the hollow body 14 to be produced. Starting from the channel outlet 28b, the inner diameter of the expansion rings 29 increases from expansion ring 29 to expansion ring 29 towards the channel inlet 28a.The number of forming rings 29 depends on the specific forming task and can vary.

[0030] A support surface 30 is located on the table 27 around the opening of the channel inlet 28a. The support surface 30 is designed to support the output part 13 before it is formed by a stroke of the ram 11. To press the output part 13 against the support surface 30, the press 10 has a hold-down device 31. The hold-down device 31 has a hold-down sleeve 32 arranged coaxially around the longitudinal axis L. The inner diameter of the hold-down sleeve 32 is at least as large as the outer diameter of the ram tool 12. The hold-down sleeve 32 is arranged on a sleeve carrier 33 of the hold-down device 31, which is mounted to be movable in the working direction A. For example, the sleeve carrier 33 can be guided and movable in the working direction A by at least two guide rods 34 extending in the working direction A. The sleeve carrier 33 can be moved in the working direction A via a hold-down drive 35 of the hold-down device 31.

[0031] By means of the hold-down device 31, an output part 13 can be pressed against the support surface 30 with a holding force. The hold-down sleeve 32 engages in the cup-shaped output part 13, as shown schematically in Fig. Figure 1 shows that the clamping of the output part 13 between the hold-down sleeve 32 and the contact surface 30 occurs at the latest when the ramming tool 12 comes into contact with the output part 13 during a working stroke of the ram 11. Further movement of the ram 11 draws the output part 13 into the drawing channel 28, where it is deformed by the drawing rings 29. This process is called drawing-slide drawing. The holding force with which the hold-down sleeve 31 presses the output part 13 against the contact surface 30 can be controlled or regulated during the drawing of the output part 13 into the drawing channel 28.

[0032] A forming tool 40 is arranged aligned with the longitudinal axis L and opposite the channel outlet 28b. The forming tool 40 works together with an end face 12a of the ramming tool 12 to form an area on the closed axial side of the hollow body 14, as shown in Fig. Figure 2 shows that the forming tool 40 has a forming surface 41 on the side facing the drawing channel 28. After the drawn-out starting part 13 has been moved out of the drawing channel 28, an area on the closed side of the drawn-out starting part 13 between the forming surface 41 and the end face 12a of the ram tool 12 is formed by the ram 11 moving the drawn-out starting part 13 against the forming tool 40. In the embodiment described here, this forms the bottom 14b of the hollow body 14.

[0033] Subsequently, the formed hollow body 14 is stripped from the ramming tool 12 during a return stroke of the ram 11, before entering the drawing channel 28. For this purpose, the press 10 has a stripping device 42. The stripping device 42 can be formed by mechanical stripping fingers arranged circumferentially around the channel outlet 28b, which strip the hollow body 14 from the ramming tool 12 during a return stroke of the ram 11. Additionally or alternatively, the ram 11 and the ramming tool 12 can be penetrated by at least one fluid channel that opens at the end face 12a. By pressurizing the channel with a fluid, in particular air, the formed hollow body 14 can be stripped from the ramming tool 12.

[0034] A press 10 of this type operates at very high stroke rates of up to approximately 400 strokes per minute, which necessitates high accelerations and speeds of the ram 11. The unavoidable friction between the ram 11 and the guide assembly 19 or the sealing assembly 22 generates heat. This heat generation and the resulting temperature increase of the ram 11 can be uneven. Consequently, the ram can exhibit a temperature profile that varies locally and is asymmetrical with respect to its longitudinal axis L. This is particularly true when the longitudinal axis L or the working direction A is not vertical but oriented differently from the vertical direction, e.g., horizontally. Due to the resulting gravitational force, the friction between the ram 11 and the guide assembly 19 is greater in the lower vertical regions of the guide assembly 19 than in the regions above it.

[0035] The varying temperatures of the pile driver at different points can cause it to no longer be perfectly symmetrical to its longitudinal axis L along its entire length. Deformation of the pile driver 11 due to these temperature differences is highly simplified in [reference to figure]. Fig. Figure 3 illustrates this. Due to the accelerations of the ram 11 and especially due to the impact against the forming tool 40, the ram 11, which is no longer exactly aligned along the longitudinal axis L, can be set into a vibration S, which is schematically represented by the double arrow in Figure 3. Fig. Figure 3 shows a central axis M of the ram 11, which is shown with a dashed line. Fig. Figure 3 shows that, due to the deformation of the ram 11 and the resulting vibration S, the central axis M is no longer precisely aligned with the longitudinal axis L at all times. The induced vibration S generally persists between the reversal points throughout the entire stroke of the ram 11. The accelerations of the ram 11, particularly at the reversal points during each stroke, amplify or re-induce the vibration S. This is illustrated in the schematic diagram in... Fig. Figure 3 shows that the ramming tool 12 no longer remains precisely aligned along the longitudinal axis L, causing irregularities in the wall thickness of the circumferential wall 14b of the formed hollow body 14. Since the tolerances for the wall thickness of the circumferential wall 14b are usually very tight, often in the range of a few micrometers, this can lead to a large number of rejects in the production of hollow bodies 14. The higher the stroke rate, the more heat is generated, and the larger and more frequent the tolerance deviations in the wall thickness of the produced hollow body 14 can be.

[0036] To counteract this, the ram 11 is manufactured according to the invention from an iron alloy whose coefficient of thermal expansion α is a maximum of 3.0 × 10 -6 K -1 and preferably a maximum of 2.0 × 10 -6 K -1In the embodiment described here, another major alloying element of the iron alloy is nickel, so that the ram 11 consists of an iron-nickel alloy. Preferably, the mass fraction of nickel in the iron-nickel alloy is 30% to 42%, and particularly 35% to 36%. The mass fraction of iron in the iron-nickel alloy can be in the range of 58% to 70%, and in one embodiment, 64% to 65% if it is a pure iron-nickel alloy. In other embodiments, additional alloying elements can be added, such as magnesium and / or silicon and / or carbon and / or cobalt. The total mass fraction of the at least one additional alloying element in the iron-nickel alloy is particularly at most 10% or at most 5%.

[0037] Instead of nickel, platinum, manganese or palladium can also be used as the main alloying component in the iron alloy.

[0038] Iron alloys that exhibit a local minimum in their coefficient of thermal expansion α, depending on the mass fraction of the main alloying element, are called "Invar" alloys. The ram can be manufactured from a suitable "Invar" alloy. Due to the low coefficient of thermal expansion, the symmetry and orientation of the ram 11 relative to the longitudinal axis L are maintained, as shown schematically in Fig. Figure 2 illustrates this. The tendency to vibrate due to accelerations of the ram 11, particularly upon impact with the forming tool 40 for shaping the base 14b of the hollow body 14, is reduced. This allows the wall thickness of the hollow body 14 to be produced to be maintained within the tolerance range. The production of scrap is significantly reduced.

[0039] The invention relates to a press 10 and a method for producing a hollow body 14 from a starting part 13. The press 10 has a ram 11 movable in a working direction A along a longitudinal axis L, which carries a ram tool 12. The ram tool 12 works together with a die tool 26 to form the starting part 13 into the hollow body 14. The forming is carried out as cold forming, e.g., as a drawing slide forming process. The ram 11 is mounted on a guide arrangement 19 with one or more bearings 20 so as to be movable in the working direction A and is moved by a drive 18. If uneven heating of the ram 11 leads to deformations that cause the ram 11 to no longer be exactly symmetrical to the longitudinal axis L, vibrations can occur due to accelerations of the ram 11, which lead to deviations in the wall thickness of the produced hollow body 14.To avoid this, the ram 11 is manufactured according to the invention from an iron alloy and preferably an iron-nickel alloy, which has a coefficient of thermal expansion α of a maximum of 3.0 × 10. -6 K -1 exhibits. Reference symbol list: 10 Press 11 rams 12 ramming tools 12a Front face of the ramming tool 13 Initial part 14 hollow bodies 14a Perimeter wall of the hollow body 14b Bottom of the hollow body 18 Drive 19 Leadership order 20 warehouses 21 storage location 22 Sealing device 26 die tools 27 Table 28 Squeezing channel 28a Channel inlet 28b Channel output 29 Stretching ring 30 site area 31 hold-down devices 32 Hold-down sleeve 33 shell carriers 34 Guide rod 35 Hold-down drive 40 forming tools 41 forming area 42 Scraper device α coefficient of thermal expansion A working direction L Longitudinal axis S oscillation

Claims

[1] A press (10) which is set up for cold forming a starting part (13) into a hollow body (14), wherein the press comprises a ram (11) which is mounted to be linearly movable in a working direction (A) by means of a guide arrangement (19), wherein the press further comprises a drive (18) which is designed to move the ram (11) in the working direction (A), wherein the press further comprises a ramming tool (12) arranged on the ram (11), which is designed to transform the starting part (13) into the hollow body (14) by moving it in the working direction (A) relative to a die tool (26), characterized by , that the die tool has a drawing channel (28) with at least one drawing ring (29), that the ram (11) is mounted so as to be movable in the working direction (A) along the longitudinal axis (L) by means of a guide arrangement (19), wherein the guide arrangement (19) has several separate bearings (20) arranged at a distance from each other in the working direction (A), that the ram (11) is made of an iron alloy with a coefficient of thermal expansion (α) of at most 3.0 * 10 -6 K -1 consists. [2] The press according to claim 1, characterized by , that the iron alloy has another main alloying component whose mass fraction in the iron alloy determines the coefficient of thermal expansion (α). [3] The press according to claim 2, characterized by , that the other main alloying component is nickel and that the mass fraction of nickel in the iron alloy is 30% to 42%. [4] The press according to claim 2 or 3, characterized by that the iron alloy has at least one other alloying element. [5] The press according to claim 4, characterized by , that the mass fraction of at least one other alloying element in the iron alloy is a maximum of 10%. [6] The press according to one of the preceding claims, characterized by that the mass fraction of iron in the iron alloy is a maximum of 58% to 70%. [7] The press according to one of the preceding claims, characterized by that the bearings (20) of the guide arrangement (19) are designed as sliding bearings. [8] The press according to one of the preceding claims, characterized by , that the guide arrangement (19) has several separate bearing points (21) which are arranged at a distance from each other in the working direction (A). [9] The press according to one of the preceding claims, characterized by, that a sealing device (22) with at least one sealing element is arranged adjacent to the guide arrangement (19), wherein the sealing device (22) is in contact with a circumferential surface of the ram (11). [10] The press according to any of the preceding claims, characterized by , that the longitudinal axis (L) is oriented differently from the vertical direction. [11] The press according to any of the preceding claims, characterized by , that the ramming tool (12) is made of a material that differs from the material of the ram (11). [12] The press according to any of the preceding claims, characterized by, that a hold-down device (31) is provided, wherein the hold-down device (31) has a hold-down sleeve (32) movable in the working direction (A) and arranged coaxially to the ram (11), wherein the hold-down device (31) is configured to apply a hold-down force to the exit part (13) while the ram (11) moves the exit part (13) into the drawing-off channel (28) with the ramming tool (12). [13] The press according to any of the preceding claims, characterized by , that a forming tool (40) is available, the forming tool (40) is designed to cooperate with an end face (12a) of the ramming tool (12) to reshape the hollow body (14) on its closed axial side. [14] A method for producing a hollow body (14) from a starting part (13) by cold forming using a press (10) according to any one of the preceding claims, comprising: - Arranging an output part (13) between the rammer (11) and the die tool (26), and - Moving the ram (11) with the ram tool (12) in the working direction (A) against the starting part (13) and cold forming the starting part (13) between the ram tool (12) and the die tool (26), - wherein the starting part (13) is moved for forming by the movement of the ram (11) through a drawing channel (28) with at least one drawing ring (29). [15] The method according to claim 14, characterized by , that after the initial part (13) is moved through the stretching channel (28) an area on a closed axial side of the stretched initial part (13) is formed between an end face (12a) of the ramming tool (12) and a forming tool (40).

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