PROCESS AND PRODUCTION LINE FOR FORMING OBJECTS
The present invention relates to a process for forming a metal component (20), the process comprising the steps of heating a metal blank (20) coated with a protective layer; cooling said metal blank (20) in a confined space (14), said cooling involving cooling by means of a gas, the gas being cooled by heat exchange with a cooling surface of a heat sink (22) inside said confined space (14), wherein a low frequency sound wave is provided into said confined space (14) in order to improve heat exchange both between the gas and a cooling surface of the at least one heat sink (22), and between the gas and the metal component (20), wherein the heated coated blank is cooled to a temperature below the melting point of the protective layer, and forming the coated blank to a component. The invention also relates to a production line for performing the process.
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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 INVENTIONIn 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 462 374 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 INVENTIONThe 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 890° C. 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.
In the following detailed description of the invention, reference will be made to the accompanying drawings, of which
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An infra sound generator unit 50 is provided,
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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.
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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,
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 Al/AlSi coats, the temperature should preferably be below 550° C. 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.
Claims
1. A process for forming a metal component, the process comprising the steps of
- heating a metal blank coated with a protective layer;
- cooling said metal blank in a confined space, said cooling involving cooling by means of a gas, the gas being cooled by heat exchange with a cooling surface of a heat sink inside said confined space, wherein a low frequency sound wave is provided into said 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,
- wherein the heated coated blank is cooled to a temperature below the melting point of the protective layer, and
- forming the coated blank to a component.
2. The process according to claim 1, wherein the protective layer comprises zinc.
3. The process according to claim 1, wherein the protective layer comprises aluminium.
4. The process according to claim 3, wherein the protective layer further comprises silicon.
5. The process according to claim 1, wherein the heated coated component is cooled to about 550° C.
6. The process according to claim 1, wherein the forming step comprises a number of sub-forming steps up to finalised form of component.
7. The process according to claim 6, wherein the sub-forming steps also comprise cutting and/or punching of the blank.
8. The process according to claim 1, wherein the metal blank comprises a steel alloy having air hardening properties.
9. The process according to claim 1, wherein the metal blank is heated to about 890° C. in the heating step.
10. The process according to claim 1, wherein the sound wave of the cooling step has a frequency that preferably is lower than 50 Hz, more preferably lower than 20 Hz.
11. The process according to claim 1, wherein the sound wave is 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 said first end thereof.
12. The process according to claim 1, wherein components to be cooled in the confined space are conveyed from the heating step at a first end to a second end in a direction generally transversal to the direction of the sound wave and from said second end to said forming step.
13. A production line for performing the process according to claim 1, comprising a heating unit, a cooling unit and a forming unit as well as conveyors to and from said units.
Type: Application
Filed: Dec 18, 2020
Publication Date: Jan 26, 2023
Applicant: AUTOTECH ENGINEERING S.L. (Amorebieta-Etxano, Bizkaia)
Inventor: Daniel PALO (Luleå)
Application Number: 17/787,841