Patent Application
20120214015
The technical field is generally joined metal panels, and more specifically, hemmed metal panels, hemming apparatuses, and hemming methods.
Roller hemming is a method used in the automotive industry to join two metal pre-formed panels. A conventional hemming process generally includes folding an outer panel over an inner panel. The two metal panels are typically joined into a unitary hollow structural unit such as a vehicle door, hood, or trunk lid. These hollow structural units are commonly referred to as closure panels.
Some vehicle closure panels are made of steel, which has desirable strength and impact absorbing properties. However, steel is heavy and it is desirable to substitute lighter materials where practical, for example, to improve fuel economy by reducing weight. Aluminum is one such lighter material with suitable strength and impact absorbing properties. The thickness of aluminum panels is generally greater than that of steel panels in order to achieve strength and stiffness that meets performance requirements. Magnesium and titanium are other structural metals lighter than steel.
Conventional hemming processes that have been developed for steel panels are generally not suitable for aluminum panels because such processes cause aluminum panels to crack or break along the hem edge. Some processes have been developed for aluminum panels that do not cause cracking along the hem edge. However, such processes are limited to lower strength alloys and/or limited in the sharpness of hem edge that can be produced. For example, such processes use aluminum sheet that has been softened or has been specially heat treated. The softening and special heat treatment avoids fracture of the aluminum sheet during the hemming process but carries a higher cost and reduces strength and other performance measures of the aluminum sheet.
A process that has been used with some aluminum panels is Retrogression Heat Treatment (RHT). The RHT process applies a local heat treatment and immediate quench to a flange area of an outer aluminum panel. This process temporarily softens the material by dissolving very fine precipitates present in the room-temperature aged material and favorably alters the deformation response of the material in hemming. Although this procedure improves hemmability, its use is generally restricted to a few lower-strength alloys that can respond to deformation at room temperature without fracture, and is not used on richer alloy compositions that rapidly re-harden at room temperature. Such richer alloy compositions include aluminum alloys that are age-hardened. Age hardening results in increased strength but decreased ductility.
The various embodiments provide higher-strength age-hardened aluminum alloy panels that are joined with a sharp hem and apparatuses and methods for hemming higher strength age-hardened aluminum alloy panels. The hemming apparatuses and methods described herein hem much stronger, thinner, less costly materials to a sharp, “jewel-effect” appearance without causing cracking at the hem edge, without the need to heat the material above a melting point, and with the need to quench the material. Since the apparatuses and methods are applicable to stronger materials, many concessions that have to be made with other methods due to material hemmability limitations are eliminated which allows many potential improvements in performance and cost.
According to an exemplary embodiment, a hemming station is configured for hemming a panel assembly with an outer panel with a hem flange defined by a hem edge. The hemming station includes a heating device configured to heat the hem edge, a roller configured to fold the hem flange, and a control unit. The control unit is configured to control the roller and the heating device such that the roller folds a hem flange when the temperature of the hem edge is in a predetermined temperature range. For example, in one exemplary embodiment, the lower limit of the temperature range is greater than room temperature and the upper limit of the temperature range is less than the melting point of the outer panel material. In another exemplary embodiment, the temperature range is 20% to 50% of the melting point of the material.
According to another exemplary embodiment, a method for hemming a panel assembly having an outer panel with a hem flange defined by a hem edge includes heating the hem edge of the hem flange and folding the hem flange while the hem edge is at a temperature in a predetermined temperature range.
The foregoing has broadly outlined some of the aspects and features of the various embodiments, which should be construed to be merely illustrative of various potential applications. Other beneficial results can be obtained by applying the disclosed information in a different manner or by combining various aspects of the disclosed embodiments. Other aspects and a more comprehensive understanding may be obtained by referring to the detailed description of the exemplary embodiments taken in conjunction with the accompanying drawings, in addition to the scope defined by the claims.
As required, detailed embodiments are disclosed herein. It must be understood that the disclosed embodiments are merely exemplary of various and alternative forms. As used herein, the word “exemplary” is used expansively to refer to embodiments that serve as illustrations, specimens, models, or patterns. The figures are not necessarily to scale and some features may be exaggerated or minimized to show details of particular components. In other instances, components, systems, materials, or methods that are known to those having ordinary skill in the art have not been described in detail in order to avoid obscuring the present disclosure. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art.
The exemplary embodiments are described with respect to higher strength age-hardened aluminum alloys. Age-hardened aluminum alloys are advantageous because of their higher yield strength as compared to other aluminum alloys. One advantage of forming outer panels out of age-hardened aluminum alloys is greater dent resistance. Further, the increased strength allows for the use of thinner gauges, which have a lower cost.
Higher-strength age-hardened aluminum alloys include 6000-series, 2000-series, and 7000-series aluminum alloys. For reference, the yield strength for 6000-series T4 alloys ranges from approximately 125 MPa to approximately 180 MPa and the yield strength for 6000-series T6 alloys ranges from approximately 240 MPa to approximately 310 MPa. For reference, the term higher-strength as used herein can refer to metals or metal alloys with yield strength that is generally in or near the range of 125 MPa to 310 MPa and ultimate strength that is above the range.
The methods and apparatuses described herein are useful for aluminum alloys that are age-hardened as they overcome the difficulty of the reduced ductility that results from age-hardening. Further, the methods and apparatuses are able to bend age-hardened aluminum alloys to a great extent to produce a sharp hem edge such as that of a “Dutch Hem” shape. It should be understood that the teachings described herein are applicable to other metals and metal alloys with similar characteristics including non age-hardened aluminum alloys such as 3000 and 5000-series alloys, magnesium sheet alloys, and titanium sheet alloys.
Referring to
The panel assembly 16 includes an outer panel 36 and an inner panel 38. The outer panel 36 includes a main panel 40 and a hem flange 42 defined by a hem edge 44. In some embodiments, the hem flange 42 and the hem edge 44 are formed during a stamping process prior to hemming the panel assembly 16 at the hemming station 10. In some embodiments, the hem flange 42 is initially stamped to be at substantially ninety degrees with respect to the main panel 40. In other embodiments, the hem flange 42 is stamped to be greater than ninety degrees, such as up to one-hundred thirty-five degrees. The inner panel 38 includes an inner edge 46 over which the hem flange 42 is folded as described in further detail below with respect to
Referring to
The exemplary illustrated roller apparatus 12 includes a heating device 20 and a roller tool 22/24 that is either configured as a prehem roller 22 or a finishing roller 24 depending on the pass. In
In still other embodiments, a roller apparatus includes multiple heating sources and/or multiple rollers to accomplish the hemming process described herein in fewer passes. For example, the two different illustrations of roller apparatus 12a/12b can be considered a single roller apparatus 12 that accomplishes the hemming method in a single pass. Alternatively, the roller apparatus 12 includes both the prehem roller 22 and the finishing roller 24.
Generally described, the roller tool 22/24 and heating device 20 are included as “end-of-arm-tooling” that is manipulated by a robot whose path is programmed to follow the perimeter of the panel assembly 16. For purposes of illustration, a robot 28 is represented by structures 29a, 29b, an actuator (e.g., motor) 30 that drives the movement of the robot 28, and a control unit 26. The control unit 26 controls the motor 30 and thus controls the speed of the robot 28.
Although a straight portion of the panel assembly 16 is illustrated, the robot 28 is configured to control or manipulate the roller tool 22/24 and the heating device 20 as a function of curvature, corners, and feature lines of a panel assembly. The axis A1 of the roller tool 22/24 is positioned at an angle A2 (see
The heating device 20 may be any suitable heating device. In one embodiment, the heating device 20 is a laser. The heating device 20 is configured to be positioned (e.g., directed) to heat a heating position P1 on the hem flange 42. The direction of the heating device 20 is controlled by one or more actuators (e.g., motors) 34a, 34b that move the heating device 20, such as around axes A4, A5. The control unit 26 controls the operation of motors 34a, 34b and thus the location of the heating location P1. In some embodiments, the control unit 26 also controls a heating temperature of the heating device 20. The heating position P1 is generally located adjacent and ahead of (downstream with respect to direction X) a folding position P2 where the roller tool 22/24 contacts the hem flange 42. The heating position P1 is ahead of the folding position P2 by a distance D1 (see
Referring to
Continuing with
One way that a bend radius R that has a jewel effect can be defined is as a function of the thickness t of the outer panel 36 or the thickness nt of the hem H. For example, a sharp hem edge has a “jewel-effect” if the outside of metal (OSM) radius (bend radius) R is about equal to the thickness t of the outer panel 36 or to half the thickness 2t of the hem H (see
Another way that a bend radius R that has a jewel effect can be defined is as a function of the current hem standard for steel panels. A typical steel panel hem has a bend radius R of about one millimeter. This bend radius R is about half of the total thickness 3t of three stacked sheets (e.g., the main panel 40, the inner panel 38, and the hem flange 42 as stacked in
As mentioned above, the control unit 26 controls the motors 30, 32, 34a, 34b and the output of the heating device 20. As such the control unit 26 controls the distance D1 associated with the heating position P1 relative to the folding position P2, the speed of the robot 28, the heat output of the heating device 20 (or the temperature increase of the material). The control unit 26 controls these parameters according to optimized values such that the hem flange 42 is folded at a time when the temperature of the hem edge 44 is in the temperature range 80. It should be understood that the values for these parameters can be alternatively determined through optimization for different applications. Optimized values, such as the speed of the robot 28, are a function of properties of the material such as the speed at which the material can be heated (which depends on, for example, the heating (e.g., laser) parameters and surface emissivity) and of the strain rate sensitivity of the outer panel at the heated temperature.
An exemplary method of hemming the panel assembly 16 is now described in further detail. To begin, the panel assembly 16 is positioned on and secured to the anvil 14. The inner panel 38 is placed on the outer panel 36 with the inner edge 46 adjacent the hem edge 44 so as to be positioned to be trapped between the hem flange 42 and the main panel 40 of the outer panel 36. In positioning the panel assembly 16 on the anvil 14, the hem edge 44 of the outer panel 36 is in some embodiments positioned along the edge 70 of the anvil 14.
During the first pass, the control unit 26 positions the roller apparatus 12 at a first end of the edge 70 and traverses the roller apparatus 12 in the direction X along the edge 70 at a predetermined speed. As the roller apparatus 12 moves along the edge 70, the control unit 26 operates the heating device 20 to heat the hem edge 44 at the distance D1 (see
For purposes of teaching, the heating and folding aspects of the method are described in further detail with respect to a single location along the length of the hem edge 44. It should be understood that the description is applicable to each location along the length of the hem edge 44.
Referring to
Referring to
As an example of application to a certain magnesium sheet alloy, the distance D1 was selected as about thirty-five millimeters, the speed was selected as about fifty-millimeters per second, and the heating device 20 generated a temperature increase of the hem flange 42 of around two-thousand degrees Celsius per second. Here, the hem flange 42 was able to be heated and folded in less than one second. The temperature 90a, 90b of the hem flange 42 was in the temperature range 80 between one-hundred and fifty degrees Celsius and three-hundred degrees Celsius when the hem flange 42 was folded. Here, the hem flange 42 was folded when the temperature 90 of the hem flange 42 was at about one-hundred and seventy degrees Celsius.
The above-described embodiments are merely implementations that are set forth for a clear understanding of principles. Variations, modifications, and combinations of the above-described embodiments may be made without departing from the scope of the claims. All such variations, modifications, and combinations are included herein by the scope of this disclosure and the following claims.
