Method for increasing the plastic deformability of a workpiece using an absorption agent

Abstract

A method for at least locally increasing the plasticity of a metal workpiece, which contains in particular an aluminum alloy, wherein the workpiece is irradiated in order to increase its temperature, and an associated production device, is provided. In order to be able to more quickly and thoroughly heat specific regions of a metal workpiece than other regions in a targeted manner, wherein it is possible to heat these regions more quickly and thoroughly with the same radiation output, while the surface of the workpiece remains largely unaffected, it is proposed that an absorbent be applied at least locally to the workpiece prior to irradiation thereof, wherein the degree of absorption of the absorbent for the radiation is greater than the degree of absorption of the workpiece for the radiation.

Claims

1. A method for at least locally increasing the plasticity of a metal workpiece, which contains an aluminum alloy, wherein the workpiece is irradiated in order to increase its temperature, an absorbent is applied to a first region of the workpiece prior to irradiation, the absorbent is not applied to a second region of the workpiece, the absorbent includes graphite and the degree of absorption of the absorbent for the radiation is greater than the degree of absorption of the workpiece for the radiation, wherein the absorbent adheres to where it is applied to the workpiece during irradiation of the workpiece even when the workpiece is shaken or moved, and further including shaping only the first region of the workpiece which includes the absorbent applied thereto after irradiation.

2. The method according to claim 1, wherein the absorbent is applied to at least two sides of the metal workpiece.

3. The method according to claim 1, wherein the absorbent contains grey and/or black components.

4. The method according to claim 1, wherein the absorbent at least partially evaporates after application to the workpiece and prior to irradiation.

5. The method according to claim 1, wherein the absorbent includes a carrier medium, the carrier medium includes at least one of a hydrocarbon and an alcohol, and wherein the absorbent is powdered.

6. The method according to claim 1, wherein the absorbent is sprayed onto the workpiece by a nozzle.

7. The method according to claim 1, wherein the absorbent is applied to the workpiece by at least one applicator roller, and the workpiece is guided between at least one pair of opposing stripping elements.

8. The method according to claim 1, wherein at least a portion of the absorbent is stripped from the workpiece by at least one stripping roller after irradiating the workpiece, and/or at least a portion of the absorbent is removed from the workpiece by applying a cleaning agent which contains liquid and/or gaseous components to the absorbent after irradiating the workpiece.

9. The method according to claim 8, wherein the cleaning agent is sprayed under pressure onto the workpiece, and the workpiece is spray-cleaned.

10. The method according to claim 1, wherein the aluminum alloy of the workpiece includes copper and magnesium.

11. The method according to claim 1, wherein the shaping includes bending or pressing regions of the workpiece where the absorbent was applied, the bending or pressing being conducted after the irradiation.

12. The method according to claim 1 including irradiating the workpiece in an infrared oven at a temperature of 250° C. to 500° C. after applying the absorbent to the workpiece.

13. The method according to claim 1, wherein the graphite has a grain size of less than 10 μm.

14. The method according to claim 13, wherein the aluminum alloy of the workpiece includes copper and magnesium, the method further includes irradiating the workpiece in an infrared oven at a temperature of 250° C. to 500° C. after applying the absorbent to the workpiece, and the shaping includes bending or pressing regions of the workpiece where the absorbent was applied, the bending or pressing being conducted after the irradiation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

(2) FIG. 1 shows a schematic illustration of a first exemplary embodiment of a production device according to the invention.

(3) FIG. 2 shows a schematic illustration of a second exemplary embodiment of a production device according to the invention,

(4) FIG. 3 shows a schematic illustration of an embodiment of a cleaning station with a cleaning nozzle,

(5) FIG. 4 shows a schematic illustration of an alternative embodiment of a coating station, and

(6) FIG. 5 shows a diagram, in which the course of the temperature increase over the period of irradiation is shown for surfaces of a metal workpiece to which an absorbent has been applied in comparison with surfaces of the same metal workpiece to which no absorbent has been applied.

DETAILED DESCRIPTION OF THE ENABLING EMBODIMENT

(7) Identical reference symbols shall be used for identical or corresponding features of the invention in the various figures.

(8) FIG. 1 shows a production device according to the invention, which has an irradiation station in the form of an infrared oven 1, and a coating station 2, by means of which an absorbent can be applied to metal workpieces 5. Instead of an infrared oven, other ovens can also be used.

(9) The metal workpieces are thin, flat plates made of an aluminum alloy that can be hardened through precipitation in the exemplary embodiment shown therein. The use of workpieces of a different shape, e.g. having a round or polygonal shape, or more massive workpieces, is also conceivable. Furthermore, the production device has a cleaning station 3, by means of which an absorbent can be removed from metal workpieces. The production device also has an infeed station 4, in which individual workpieces are removed from a first stack 6 and supplied to the production device, and a stacking station 7, in which individual workpieces are stacked on a second stack 8 after passing through the production device.

(10) Conveyors in the form of conveyor rollers 9 are located between and/or in the individual stations, which convey the individual workpieces 5 from one station to the next, and convey the workpieces through the stations. The conveyance of the workpieces from one station to the next can alternatively be achieved with grippers, e.g. robot grippers, or manually. The conveyor rollers 9 can be disk rollers. In particular when the surface of the workpiece 5 that comes in contact with the rollers is also coated with an absorbent 10, the disk rollers are suitable for maintaining the positioning of the absorbent intact during the conveyance.

(11) Before passing through the coating station 2, there is no surface coating on the workpieces 5 that would affect the degree of absorption. After passing through the coating station 2, while passing through the infrared oven 1, and prior to passing through the cleaning station 3, the locally applied absorbent 10 is located on a limited area of the workpieces 5. Where no absorbent 10 has been applied to the surface of the workpiece 5, there are regions 11 of the workpiece that have no absorbent 10. Alternatively, it is likewise conceivable to coat the entire surface of the workpiece with an absorbent, in order to obtain a higher absorption of radiation, and thus a uniform, greater heating over the entire surface.

(12) FIG. 2 shows an alternative embodiment of a production device according to the invention, in which the cleaning station 3 is located downstream of an oiling station 12, by means of which the workpieces are coated with a film of oil after the absorbent 10 has been removed, in order to prepare the workpieces for the subsequent shaping process. For this, after the workpieces 5 have been cleaned and oiled, they are not placed on a second stack, but instead are conveyed to a press 13 in which the subsequent shaping takes place.

(13) The schematically illustrated coating station 2 has a nozzle 14, by means of which the absorbent 10 can be sprayed locally onto the workpiece 5. The absorbent 10 is stored in a reservoir 15, and conducted to the nozzle 14 by means of a hose. The cleaning station has two pairs of opposing stripping rollers 17, between which the workpiece 5 passes after it has been irradiated, such that the absorbent 10 is stripped off of the workpiece 5 through contact with the stripping rollers 17, and is thus removed therefrom.

(14) There are numerous disk rollers 24 in front of, inside and behind the infrared oven 1, each of which is mounted on an axle, which improve conveyance of the workpiece from the conveyor belt 23 into the oven, inside the oven, and into the cleaning station 3.

(15) FIG. 3 shows a schematic illustration of an exemplary embodiment of a cleaning station 3. After passing through the oven 1, the metal workpiece 5 rests on a subsurface 18. The surface of the workpiece 5 is coated locally with an absorbent 10. The cleaning station 3 has a cleaning nozzle 19, to which a cleaning agent 21 is conducted from a cleaning agent reservoir 22 by means of a cleaning hose 20. The cleaning agent 21 can be sprayed under pressure onto the workpiece 5 through the cleaning nozzle 19, thus resulting in a jet spray cleaning of the surface of the workpiece 5.

(16) The method according to the invention is primarily suited for metal substances, in which a change in the mechanical properties takes place as a result of heating the metal. This is the case in particular with aluminum alloys that can be hardened through precipitation, which are formed, for example, with copper and magnesium alloy elements. The metal substance can be, by way of example, one of the aluminum alloys EN AW-5882, EN AW-6016 and EN AW-7021, or some other aluminum alloy of a similar composition.

(17) Depending on the subsequent treatment, e.g. bending or pressing, the regions of the workpiece requiring a specific increase in plasticity as a result of local heating are selected. The workpiece is then conveyed to a coating station, in which the absorbent is applied to those regions in which plasticity is to be increased in a targeted manner.

(18) The workpiece that has been pre-treated in the coating station is then subjected to radiation, which is absorbed in part on the surfaces of the pre-treated workpiece. This radiation can be a heat radiation or infrared radiation, for example, wherein the irradiation station can be an oven known in the field, i.e. an infrared oven, as in the first exemplary embodiment. The temperatures reached at least in sections of the workpiece are advantageously approx. 250° C. to 500° C. The temperature in the oven typically fluctuates within a range of approx. 1000° C.

(19) Through the increased degree of absorption of the absorbent, a larger portion of the radiation striking the surface is absorbed than in the untreated surface of the workpiece. As a result, the absorbent heats up locally more than the other surfaces of the workpiece, and reaches a higher temperature more quickly. Because the absorbent is in contact with the underlying surface of the workpiece, the quick heating of the absorbent leads to a likewise more quickly resulting temperature increase in the underlying surface section of the workpiece in contact with the absorbent. This results in the desired effect that the regions of the workpiece coated with absorbent reach a higher temperature with the same radiation output than those regions of the workpiece that are not coated.

(20) Two-phase mixtures composed of a liquid carrier medium and a powdered absorbent are particularly suitable as absorbents. The carrier medium can primarily be a flowing or workable medium, such that the absorbent can be applied evenly in the coating station, such that it thoroughly covers all of the targeted regions of the workpiece. The absorbent should also exhibit the highest possible degree of absorption, and adhere well to the surface of the workpiece.

(21) Graphite with a grain size of less than 10 μm is suitable for the absorbent, by way of example. Graphite has a high degree of absorption for visible light, heat and infrared radiation, due to its black surface, and due to the specified grain size, it can be applied to the workpiece in a thin and thorough coating, and adheres well to the aluminum surface. In alternative embodiments, other black powders or substances that have a high degree of absorption can also be used. These should be heat resistant, such that they change very little or not at all when applied to the workpiece and/or when irradiated, in particular regarding their aggregate state, and with hardly any chemical reaction.

(22) By way of example, liquid hydrocarbons or alcohols are suitable as the carrier medium, which form a suspension with the absorbent, wherein the carrier medium can be applied in liquid form to the workpiece, thus distributing the powdered absorbent suspended therein on the surface. The carrier medium can be selected such that it quickly and thoroughly evaporates at room temperature into the atmosphere, such that only the absorbent remains on the surface of the workpiece after the evaporation thereof. As a result, the absorbent is unable to flow further on the surface of the workpiece, such that only the desired regions of the workpiece remain coated with the absorbent and are accordingly heated more than the other regions of the workpiece. The carrier medium should likewise be as heat resistant as the absorbent. During evaporation, it should be ensured that the carrier medium does not ignite when exposed to the atmosphere or a surrounding gas. Components of the carrier medium remaining on the workpiece during irradiation should remain chemically stable at the high temperatures in the oven.

(23) After heating the workpiece in the irradiation station, the absorbent is removed form the workpiece in a cleaning station in the illustrated embodiments. As shown in FIG. 2, this can take place using stripping rollers that come in contact with the workpiece such that the absorbent is stripped from the surface of the workpiece. Two pairs of opposing stripping rollers 17 are shown in FIG. 2, wherein the workpiece passes between the two stripping rollers forming a pair, and comes in contact with both stripping rollers simultaneously.

(24) The embodiment of a cleaning station shown in FIG. 3 is based on a different active principle. In this embodiment, a cleaning agent 21 composed of liquid or gaseous components, is sprayed at high pressure onto the surface of the workpiece 5. As a result, the absorbent is released from the surface of the workpiece 5 and removed.

(25) In alternative embodiments, the principles for removing the absorbent, schematically shown in FIGS. 2 and 3, can also be combined or carried out successively in order to obtain a good cleaning result.

(26) FIG. 4 shows an alternative embodiment of a coating station 2. The workpiece 5 moves in a direction of movement 27 between two applicator rollers 25, which have the absorbent on sections of their surfaces, and which roll in the rotational direction 26 over the workpiece 5. The workpiece 5 is a plate with two opposing parallel planar surfaces, each of which comes in contact with an applicator roller 25.

(27) The absorbent 10 adheres to the workpiece 5 through the surface contact between the applicator rollers 25 and the workpiece 5, and is transferred from the applicator rollers 25 to the workpiece 5 thereby. The active principle of this arrangement is similar to the offset printing methods known from printing technology. Instead of two opposing applicator rollers 25, a single applicator roller with a rigid counter-resistance can be used, or only one of the applicator rollers may be provided with absorbent, such that absorbent is only applied to one side of the workpiece. Instead of a plate, this method can also be applied to workpieces of different shapes, which have more than two surfaces.

(28) FIG. 5 shows two graphs plotting the temperature curves in the surface of an aluminum plate in a radiation oven, wherein it can be clearly seen that those surface regions that are coated with an absorbent reach a higher temperature substantially more quickly than those surface regions that are not coated with an absorbent. Both surfaces are subjected to the same radiation output. It is clear from the diagram that with equal radiation periods of 12 seconds, the surfaces with absorbent reach an end temperature of 300° C., that is three times as high as those surfaces without absorbent, which only reach 100° C. Similarly, this shows that the end temperature of 100° C. is reached in the regions without absorbent in 6 seconds, while the regions with an absorbent reach this temperature in 2 seconds, thus reaching this temperature in one third of the time.