TECHNICAL AREA

The invention relates to a process and a production line for forming metal components, which metal components may be used as components in automobile manufacturing.

BACKGROUND OF INVENTION

In the manufacturing of components for example in the automobile industry the components are often processed in steps, from hot rolling, via a cooling step to a forming step and final cooling to ambient temperature. For best efficiency and to avoid losses of time, all steps should be performed quickly, and since the overall efficiency is governed by the slowest step, each step should be kept as efficient as possible.

Normally, the cooling step of cooling the detail prior to the forming step involves air cooling and is therefore the most time-consuming step. Therefore, if the time for the cooling step could be reduced, the overall time could be reduced by a multiple of the time reduction for the cooling step as each step of the process may be equally shortened.

As discussed above, air cooling is generally too slow for an efficient cooling, especially in a process where several steps are performed after each other. There are however methods of improving the rate of cooling in air cooling.

It is inter alia known to improve air cooling by means of the application of infra sound in order to increase heat exchange with the surrounding air. In SE 462374 B a low frequency sound generator is described. This is advantageous but has hitherto not been successfully implemented in an industrial application.

A further problem associated with cooling of hot metal components is that the hot metal from for example metal sheet production will form an outer layer of oxide scale due to exposure to oxygen. The oxide scale is unwanted since it will affect later working on the metal sheets, such as subsequent forming by pressing to different shapes, often in combination with cold hardening. The oxide scale then has to be removed before the pressing and cold hardening of the metal components. It would therefore be advantageous if the material could be cooled so rapidly that oxide scale build-up is reduced.

Another aspect with handling of metal components is when the metal blank is coated with a protective layer. This is often advantageous in many applications since the protective layer for example may increase the protection against corrosion or other effects by the environment. The protective layers often comprise zinc or aluminium or a combination of aluminium and silicone. Production-wise, it would be advantageous if the blank could be coated before the heating and forming steps. A problem in that regard is that the blanks are heated to temperatures above the melting point of the protective layer of zinc or aluminium. If the heated blanks are then placed in the forming unit at those temperatures, the materials of the protective layer will enter the grain boundaries of the steel of the blank during the forming, such as pressing and stretching, and will cause so called liquid metal embrittlement. In order to avoid this, the blank has to be left to cool between the heating and the forming step for a time period to a temperature below the melting point of the protective layer, which usually is a far too long time period from a production perspective.

BRIEF DESCRIPTION OF INVENTION

The aim of the present invention is to remedy the drawbacks of cooling of components, and in particular metal components. This aim is obtained with a process and a production line with the features of the independent patent claims. Preferable embodiments of the invention form the subject of the dependent patent claims.

According to the present application, it relates to a process for forming a metal component. The process may comprise the steps of heating a metal blank that is coated with a protective layer. A further step may be to cool the metal blank in a confined space, where the cooling involves cooling by means of a gas, and wherein the gas may be cooled by heat exchange with a cooling surface of a heat sink inside the confined space. According to a preferable solution, a low frequency sound wave may be provided into the confined space in order to improve heat exchange both between the gas and a cooling surface of the at least one heat sink, and between the gas and the metal component. Preferably the heated coated blank may be cooled to a temperature below the melting point of the protective layer, and then the coated blank may be formed to a component in a forming step.

This enables a metal blank to be coated with a protective layer before the heating and pressing steps of the process for making a component because of the addition of the rapid cooling by the low frequency sound wave which creates such turbulence and exchange between the gas of the cooling box and its at least one heat sink, which greatly reduces the cooling time and thus the cycle time for forming the component coated with a protective layer.

According to one feasible solution, the protective layer may comprise zinc, which has good properties for protection against corrosion for instance. As an alternative, the protective layer may comprise aluminium and possibly in addition with silicon. This protective layer also is highly resistant to corrosion because of the thin layer of aluminium/silicon, preventing the steel of the metal blank from oxidizing.

Preferably, the heated coated component may be cooled to about 550 ^° C. This is a temperature below the melting point of the protective layer and will enable a cooling and thereby a cold hardening in the subsequent pressing in the forming step. As an alternative, the forming step may comprise a number of sub-forming steps up to finalised form of component. This is done in order to obtain the optimum strength properties of the material of the metal blank when formed to a component coated with a protective layer. In this respect, the sub-forming steps may also comprise cutting and/or punching of the blank.

According to one important aspect of the invention, the metal blank may comprise a steel alloy having air hardening properties. The air hardening properties will enable a much shorter time period in the press as compared to hardening of the metal component during cooling when placed in the die of the press. The metal blank coated with a protective layer can then be formed when warm in the press by the die and then be removed from the die and hardened in surrounding air. This will greatly reduce the cycle time for producing a component with a protective layer, both by the rapid cooling and also by the air hardening.

Generally, the metal blank may be heated to about 890Ό in the heating step. Moreover, the sound wave of the cooling step has a frequency that preferably is lower than 50 Hz, more preferably lower than 20 Hz. Regarding the sound wave, it may be provided from a first end of the confined space so as to propagate through the confined space and away at a second end of the confined space, opposite to the first end thereof.

This may be especially beneficial if the component is a flat sheet metal blank wherein the sound wave may propagate on both sides of the blank, providing effective cooling on both sides of the blank simultaneously. In connection with this, components to be cooled in the confined space may be conveyed from a first end to a second end in a direction generally transversal to the direction of the sound wave. Here a continuous movement of components may be obtained in one direction having the standing wave propagating in the transversal direction.

According to a further aspect, a production line of provided for performing the process described above, comprising a heating unit, a cooling unit and a forming unit as well as conveyors to and from said units.

These and other aspects of, and advantages with, the present invention will become apparent from the following detailed description of the invention and from the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

In the following detailed description of the invention, reference will be made to the accompanying drawings, of which

Fig. 1 is a schematic cross-sectional view of an embodiment of an apparatus for cooling hot objects; Fig. 2 is a schematic perspective view of an alternative embodiment of an apparatus for cooling hot objects;

Figs. 3 is a schematic cross-sectional view of the cooling box shown in Fig. 2;

Fig. 4 shows a first embodiment of a pulsator to be used in the apparatus of

Figs. 1-2;

Fig. 5 shows a second embodiment of a pulsator to be used in the apparatus of Figs. 1-2;

Figs. 6-9 show a third embodiment of a pulsator in different working modes; and Fig. 10 is a schematic view of a production line.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows an apparatus 10 for cooling components, such as an automobile component 20 by means of a cooling gas, e.g. air or any other gas, with or without steam. Depending on the humidity where the apparatus is placed, the cooling gas may be dried air, which may be important in humid environments. The apparatus comprises a confined space 14 arranged inside a cooling box 16 with an opening 18 for receiving a component 20 to be cooled. Preferably, the opening is re-closable.

The cooling box 16 is preferably arranged with a plurality of heat sinks 22 inside the cooling box 16 for cooling the gas. The heat sinks 22 may be connected to cooling media via conduits 24, 26 such that a flow of cooling media is circulated through the heat sinks 22. The heat sinks 22 may also include cooling flanges 28, Fig. 3, increasing the overall cooling surface. It is obvious to a skilled person that the cooling efficiency will increase with an increased total cooling surface of the heat sink(s) 22, but that cooling will have effect also with a small cooling surface of only one heat sink 22. The apparatus 10 further includes at least one infra sound pulsator 30 and 32 arranged to provide an infra sound into said cooling box 16 to improve heat exchange between the cooling gas and a cooling surface of the at least one heat sink 22, as well as between the cooling gas and the component 20 to be cooled.

Figures 2 and 3 disclose schematically an example of an apparatus and a cooling box 16. The cooling box 16 is generally rectangular with four side walls 34, a top 36 and a bottom 38, forming a confined space 14. In one of the side walls a first opening 40’ is arranged, comprised of at least one elongate aperture, i.e. a slit shaped opening, arranged to receive a steel blank 20 or the like sideways into the confined space 10 of the cooling box 16. Also, the cooling box 16 may be provided with a second such opening 40”, where the two openings 40’, 40” preferably are arranged opposed to each other on the cooling box 16, as seen in Fig. 3, such that the object 20 to be cooled may be entered at one side of the cooling box 16 and taken out, after cooling, at the opposite side of the cooling box 16. This embodiment is hence specifically adapted to efficient cooling of blanks, such as metal sheets. The openings 40’, 40” may be provided with flexible curtains or swingable doors (not shown) arranged to cover the openings but allow entry and/or exit of metal blanks. Such curtains or doors are arranged in order to minimise sound pollution and to keep a standing wave of infra sound as intact as possible inside the confined space 14 so as to maximise the cooling effect.

As illustrated in Figs. 2 and 3, guide elements 42 may be arranged at each opening 12, to guide a component 20, such as an automobile component, between them. In the shown embodiment the guide elements 42 consist of conveyer rolls arranged to receive and guide blanks between them. As an alternative to conveyer rolls any surface which allows hot metal blanks to slide upon them may be provided, preferably combined with an apparatus for conveying said metal blanks through the confined space 14 of the cooling box 16. Also, conveyer rolls 44 or any other type of guide elements may be arranged inside the cooling box, Figs. 1 and 3. Obviously, conveyer rolls or other types of guide elements need to be arranged at even intervals at distances from each other that is smaller than the length of the component 20 to be cooled. Further, the cooling box may be arranged with stop elements 45, against which the component 20 may abut so as to stop the movement for a cooling process. When the component is cooled to the desired temperature, the stop element 45 may be moved out of contact so that the component may be conveyed to a subsequent handling station. The cooling box shown in Figs. 2 and 3 is further arranged with at least one heat sink 22 or the like cooling device. In order to increase the efficiency of the heat sink, cooling flanges 28 may be provided. As with the embodiment shown in Fig. 1 , cooling conduits 24, 26 are preferably arranged to provide a cooling fluid, e.g. water, to cool said heat sinks 22.

An infra sound generator unit 50 is provided, Figs. 1 and 2, having a first infra sound pulsator 30 connected to the cooling box 16 via a first resonator conduit 52, wherein the first infra sound pulsator 30 is arranged at a first outer end 54 of said first resonator conduit 52. The infra sound generator unit 50 is further arranged with a second infra sound pulsator 32 that is connected to the cooling box 16 via a second resonator conduit 56, said second infra sound pulsator 56 being arranged at a second outer end 58 of said second resonator conduit 56. The first and second resonator conduits 52 and 56 may be tubular as seen in Fig. 2, having substantially the same cross section along their whole length. They may however include passages of varying cross sections. A transition from one cross-sectional area to another cross-sectional area may be called a diffuser. In the shown embodiment of Fig. 1 such diffusers are arranged both at the outer ends 54 and 58, respectively, of the first and second resonator conduits 52 and 56, and at the transition 60 and 62 between the resonator conduits 52, 56 and the confined space 14 of the cooling box 16. The tubular resonators conduits 52, 56 may be bent or straight. As seen from the embodiments in figures 1 and 2 and in particular from the arrows in Fig. 2, it is apparent that the pulsed cooling air CA is moving generally transversally to the feeding direction FD of the article to be cooled and in particular over and under the article.

In Figs. 4-9 three different types of pulsators are shown. An infra sound pulsator 30, 32 may be a P-pulsator or a S-pulsator. A P-pulsator is pulsator that pumps in air pulses and a S-pulsator is a pulsator that pumps out or releases air pulses. A pulsator that alternatively pumps in or pumps out air pulses is called a PS-pulsator. Either one P-pulsator and one S-pulsator is arranged at opposite ends of the system, or a PS-pulsator is arranged at both ends. The pulsators at opposite ends need to be synchronized with each other such that the standing sound wave may be withheld between the pulsators. Normally, this synchronization is set by allowing the pulsators to swing in the natural pace governed by the standing sound wave and to enhance the movement by the addition of a force in the direction of said natural pace.

In Fig. 4, a first type of PS pulsator 30’ is shown. A piston 70 that moves back and forth inside a cylinder is arranged to act as a PS-pulsator. The shown pulsator 30’ is connected with a conduit 72 at a first outer end 54 of the first tubular resonator conduit 52. Preferably a corresponding PS-pulsator is provided at the opposite end at the second outer end 5 of the second tubular resonator conduit 7. The opposed PS- pulsators are arranged to work out of phase with each other such that one of them is at its innermost position when the other is at its outermost position. With the interaction the pulsators will be a half wavelength out of phase with respect to each other. Thereby a standing wave a half wavelength will be produced between the respective outer ends 54 and 58 of the tubular resonator conduits 52 and 56, respectively.

In Fig. 5, an alternative pulsator 30” is shown, which pulsator is connected to both the first outer end 54 of the first resonator conduit 52 via conduit 72 and the second outer end 58 of the second resonator conduit 56 via conduit 74. With this configuration the piston 70 will provide a pressure into one outer end 54, 58 of a resonator conduit and simultaneously release pressure from the outer end 58, 54 of the other resonator conduit.

In Figs. 6-9 a specific type of pulsator 30’” for producing sound waves of high intensity is shown in different modes. The pulsator 30’” includes a spring biased piston 80. The pulsator 30”’ includes an inlet chamber 82 with a valve inlet opening 84 and an outlet chamber 86 with a valve outlet opening 88. The spring biased piston 80 includes a piston port 90, which is arranged to face the valve inlet opening 84 and the valve outlet opening 88. The inlet chamber 82 is connected to a continuous pressure source (not shown) and the outlet chamber 86 is connected to a continuous negative pressure source (not shown).

As the spring biased piston 80 moves the piston port 90 alternatively connects the inlet chamber 82 via the valve inlet opening 84 to the inside of the piston 80, or the outlet chamber 86 via the valve outlet opening 88 to the inside of the piston 80. The connection between the valve inlet opening 84 and the inlet chamber 82 to the inside of the piston 80 is governed by the position of the spring biased piston 80. The openings are arranged such that only one of the valve inlet opening 84 and the valve outlet opening 88 is in line with the piston port 90 at a time.

In Fig. 6 the spring biased piston 80 is in its innermost position, in which a spring 92 that holds the spring biased piston 80 is in its most compressed state. From this position the spring 92 will act on the spring biased piston 80 so as to push it inwards to compress the air in the outer end 54 of the first resonator conduit 52 so as to create a pulse in the first resonator conduit 52, past the cooling box 16 and through the second resonator conduit 56.

In the position shown in Fig. 6 the piston port 90 is positioned in line with the valve inlet port 84 to connect inlet chamber 82 to the inside of the piston 80 so as to further increase the pressure in the resonator conduits and to build on the standing wave in said resonator conduits.

In the position shown in Fig. 7 the piston 80 has moved from its outermost position and is still accelerating in its movement inwards towards the resonator conduit so as to further compress the air in said resonator conduit. The piston port 90 is still positioned at least partly in line with the valve inlet port 84 to connect inlet chamber 82 to the inside of the piston 80 so as to further increase the pressure in the resonator conduits

In the position shown in Fig. 8 the piston 80 has moved to a position where the spring 92 has started to act outwards, i.e. in the opposite direction of the movement of the piston 80, so as to decelerate the movement of said piston 80. Further, at substantially the same position as the un-biased position of the spring is passed, the piston port 90 passes from connection to the valve inlet port 84 into connection to the valve outlet port 88, such that air will be sucked from the inside of the piston 80 via the valve outlet port 88 into the outlet chamber and on to the negative pressure source (not shown).

In the position shown in Fig. 9 the piston 80 has moved to its innermost position, from which position it will return and start moving outwards. The spring 92 is extended, acting to pull the piston 80 outwards so as to relieve the pressure in the resonator conduits and the action is enhanced in that the piston port 90 is connected to the valve outlet port 88, such that air will be sucked from the inside of the piston 80 towards the outlet chamber 86.

From the position shown in Fig. 9 the piston 80 will move reversely towards the position shown in Fig. 6 via the positions shown in Figs. 8 and 7, respectively. The pulsator 30’” is hence self-regulating in that the standing wave of half a wave-length will be produced and withheld by means of the pulsator 30’” and a corresponding pulsator at the opposite end of the resonator conduits, wherein the other pulsator will be self-regulated to lie one half-length out of phase with the first pulsator 30”’.

As illustrated in Figs. 1 and 2 the first and second resonator conduits 52 and 56 are preferably of similar lengths and a standing wave is produced from the first infra sound pulsator 30 to the second infra sound pulsator 32, wherein the first infra sound pulsator 30 is arranged to produce a standing wave of which half a wavelength corresponds to a combined length of the first and second resonator conduits 52 and 56 and the cooling box 16. Hence, the first and second pulsators 30 and 32 are out of phase with each other with half a wavelength.

The wavelength of the standing wave is, as is apparent from the above, dependent of the length of the system, i.e. the length between the first and second pulsator 30 and 32, respectively. Preferably, the frequency is 50 Hz or less, which would yield a sound with a wavelength of 6.8 metre and hence demand a length of 3.4 metre between the pulsators. The cooling effect will however increase with a lower frequency and in a specific embodiment the length between the pulsators is about 8.5 metre which will yield a sound wave of a frequency of about 20 Hz. To achieve a very high cooling efficiency the frequency could be kept at 20 Hz or below, preferably 16 Hz, and the combined length of the first and second resonator conduits 6 and 7 and the cooling box 11 should therefore be about 8.5 metre or more to obtain said very high cooling efficiency.

The infra sound cooling device may for some applications further comprise at least one inlet 100 for protective gases, Fig. 2. According to one embodiment, the inlet is placed in one or both of the resonator conduits 52, 56. The inlet 100 may be arranged as a nozzle connected to a conduit 102, which in turn is connected to a source of protective gas 104, wherein the gas may be supplied or injected into the resonator conduits 52, 56. The type of gas may preferably be inert gases that do not react chemically with their environment. One of the most used gases is nitrogen that is cost-effective and non-harmful to the environment. It is however to be understood that other gases or mixtures of gases may be used for the same purpose. For instance, there might be gasses and mixtures thereof that display increased heat transfer properties that might be beneficial for the cooling process. Further, a particle catcher 106 may be arranged to the resonator conduits 52, 56. The particle catcher 106 will ensure that any particles from the treated and cooled components inside the cooling box are prevented from entering the pulsators. The particle catcher is preferably some sort of nozzle unit connected to a vacuum source 108 via suitable conduits 110.

Figure 10 shows a production line for performing a process according to a favourable solution. The blanks have previously been coated with a protective layer such as a zinc layer or an aluminium layer, alternatively an aluminium-silicone layer. The production line comprises a heating unit 201 such as for instance a furnace provided with heating elements. The furnace is preferably provided with an inlet for the metal blanks to be heated and an outlet for the heated blanks. Typically, the metal blanks are heated to a temperature in the range 800-900Ό, preferably 890 ^° C. The blanks are then conveyed by conveying means 205 from the outlet of the furnace 201 to a cooling unit 202 having a function as described above.

In the cooling unit 202 the coated heated blanks are cooled to a temperature below the melting point of the protective coat. For Zn and AI/AISi coats, the temperature should preferably be below 550Ό in order to avoid liquid metal embrittlement at the later forming step. In that respect, the cooling unit is preferably arranged with sensors that can measure the surface temperature of the metal blanks. If needed, the cooling unit may be provided with a number of cooling boxes that are placed in succession in order to be able to cool the metal blanks to the desired temperature.

The cooled metal blanks are then conveyed by the conveyer means 205 to a forming unit 203, that in the embodiment shown may be a press having two die halves having complementary shapes. The metal blank is placed between the die halves and the die halves are pressed together during a certain time to form the finished component. During the pressing time the component is cooled and hardened.

A further advantage is obtained if the metal blank comprises a steel alloy that displays air hardening properties. The metal blank could then be cooled to certain temperature, pressed in the forming unit and removed and let to harden in surrounding air during final cooling, step 204. This is in contrast to conventional steel alloys normally used for instance in the automotive industry, which are hardened in the forming unit during cooling. The cycle time in the pressing unit is then greatly reduced in comparison to conventional steel alloys.

Regarding the pressing, the forming unit 203 may comprise a number of so called sub-units, wherein each sub-unit performs a forming that is not the end form. In this manner the blank is formed to its finished component by multi-step forming by the sub-units. These sub-units may also comprise cutting and punching tools for making cut-outs and holes in the component.

It is to be understood that the embodiment described above and shown in the drawings is to be regarded only as a non-limiting example of the invention and that it may be modified in many ways within the scope of the patent claims.