Patent Application
20120279271
The present disclosure relates generally to a clinching method and a tool for performing the same.
Materials may be secured together using many different methods including, for example, pre-heated hot clinching and friction stir spot welding. Pre-heated hot clinching techniques often result in the thermal expansion of the materials. For example, in one form of pre-heated hot clinching, after the punch and/or the die are continuously heated by resistance heaters, the sheets are placed in the die where they draw heat from the pre-heated tools. When the sheets reach a desired temperature, the punch advances to form the clinch joint in the die. Friction stir spot welding often results in brittle phase formation when joining different materials (e.g., aluminum and magnesium). Other clinching techniques may require the precise alignment of the clinching tool with particular features of the materials to be clinched and/or may result in the splitting or cracking of the clinch button.
A method of clinching a first layer and a second layer includes establishing a first layer on a second layer and disposing an induction coil within induction proximity to the second layer. The induction coil is electrically energized thereby heating the second layer. A die having a die cavity is translated from a first location spaced substantially beyond an induction heating distance from the induction coil to a clamping location adjacent the second layer such that the induction coil surrounds a predetermined location on an external surface of the die. The die is heated by induction between the induction coil and the die while the die is translated toward the clamping location until the die reaches a predetermined die temperature. The induction coil is de-energized after the die has reached the predetermined die temperature. The first layer and the second layer are clamped between a binder and the die.
Features and advantages of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear.
Examples of the method disclosed herein advantageously enable the formation of a lap joint between layers of material. For example, the method may clinch overlapping sheets of material. The layers to be joined may be of similar materials, or may be of different materials. In one example, aluminum alloy sheet metal may be joined to magnesium alloy sheet metal using an example of the disclosed clinching method.
Further, examples of the present disclosure include a clinching method and a tool utilized in the clinching method. The tool uses the same induction heating coil to apply induction heating to the second layer and then to the die after the layers have been loaded into the clinching tool. It is believed that the arrangement of the induction heating coil in the clinching tool, along with the position control of the die, gives reduced overall cycle time compared to resistance or conduction-heated clinching. It is further believed that the disclosed method and tool achieve a more uniform heating of the second layer and the die compared to the uniformity of heating that would be achieved if both the second layer and the die were induction heated simultaneously. Still further, it is believed that the disclosed method and tool avoid overheating of the die, thereby extending a usable life of the die.
Referring now to
The method further includes establishing the first layer 20 on the second layer 30 in a stack 48. It is to be understood that the first layer 20 and the second layer 30 may be loaded together into a clinching tool 10, or the first layer 20 and the second layer 30 may be loaded separately (e.g., one layer at a time) into the clinching tool 10.
An example of the clinching tool 10 includes a retractable punch 60, and a clinching die 50. The clinching die 50 includes a die cavity 52 defined in the clinching die 50. The die cavity 52 has an aperture 56 and a reaction surface 58 opposed to the punch 60. The die cavity 52 further includes an annular recess 54 with an outer diameter 84 substantially equal to a largest diameter 83 of the die cavity 52. It is to be understood that the term “substantially equal” as used herein means the dimensions are exactly equal, or they differ by less than about 5 percent of the larger diameter. The recess 54 surrounds the reaction surface 58 and extends axially deeper into the clinching die 50 than the reaction surface 58. A support surface 62 circumscribes the aperture 56 and is configured to receive the first layer 20 overlapping the second layer 30.
The die 50 may be formed from steel alloys or more refractory alloys. For example, the die 50 may be formed from molybdenum-based alloys such as TZM, or nickel-based alloys such as the family of austenitic nickel-chromium-based superalloys known as INCONEL® (INCONEL® is a registered trademark of Special Metals Corporation.) Because of the lower maximum die temperatures experienced by the die 50 of the present disclosure, the die 50 may be formed from less expensive alloys than those listed above. For example, the die 50 may be formed from tool steels, including e.g. H13 and P20. Clinching tool 10 may further include a binder 90 having an aperture 92 defined therein and configured to clamp the first layer 20 overlapping the second layer 30 to the support surface 62 while the punch 60 is advanced toward the die 50, and as the punch 60 is retracted.
The clinching tool 10 includes an induction coil 40 disposed within induction proximity to the second layer 30. It is to be understood that “induction proximity” refers to a distance between a workpiece and the induction coil 40 that is small enough to allow efficient inductive heating of the workpiece by the induction coil 40. It is to be understood that “workpiece” refers to a piece to be heated, e.g., the second layer 30 or the die 50. As such, the distance associated with induction proximity depends, at least in part, on the workpiece material and an inductive power of the induction coil 40. In an example, a 1 mm thick sheet of Mg alloy disposed between about 1 mm and about 5 mm from a 5 kW induction coil would be within induction proximity. Correlatively, the 1 mm thick sheet of Mg alloy in the example disposed about 20 mm or more from the 5 kW induction coil would experience insignificant inductive heating. The induction coil 40 may have a coil aperture 41 sized to circumscribe the clinching die 50. The induction coil 40 is disposed in the clinching tool 10 on a die-side 44 of the stack 48 as shown in
Referring now to
It is to be understood that the target temperature for a particular thickness of a particular material will be the temperature at which the material has sufficiently reduced yield strength and sufficiently increased ductility. Sufficiently reduced yield strength and sufficiently increased ductility may be determined empirically with the apparatus presently included in the clinching tool 10. The combination of process parameters that produce an acceptable clinch joint may be determined by systematically varying induction power, time of heating of the second layer 30, and time of heating of the die 50. Alternatively, tensile tests could be conducted on specimens of the second material 36 at various temperatures. From the tensile tests, the temperature at which the strength of the specimen drops sufficiently (and the ductility increases sufficiently) to allow a desired level of formability may be determined. In yet another alternative, published data may exist for the particular material. Heating of the second layer 30 by the induction coil 40 may be controlled in a closed loop system that senses the temperature of the second layer 30. Alternatively, the time to reach the target temperature may be established empirically, and process timing may thereby be used to control the temperature of the second layer 40 in a form of open-loop control.
Since the first layer 20 is in contact with the second layer 30, the first layer 20 may be heated by conduction from the second layer 30. However, because the temperature change of the second layer 30 occurs rapidly from induction, the first layer 20 is not significantly heated. Not significantly heated means that the strength and ductility of the first layer 20 are not significantly changed. In an example where the second layer 30 is heated to 300° C., the first layer would remain below about 100° C.
As depicted in
Heating is identified by reference numeral 46 in
Without being bound to any theory, it is believed that after the layers 20, 30 are clamped together, the first layer 20 draws heat from the second layer 30. The energy lost to the first layer 20 may be compensated by heat from the die 50. The amount of heat which the first layer 20 draws from the second layer 30 depends on the thicknesses of both layers 20, 30, their thermal properties, and the duration and pressure of punch/die clamping. These factors, in turn, determine how much heat/temperature from the die 50 will keep the second layer 30 at about the target temperature.
It is to be understood that the position of the die 50 within the induction coil 40 (as shown in
Referring now to
As depicted in
It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range. For example, a range from about 250° C. to about 300° C. should be interpreted to include not only the explicitly recited limits of about 250° C. to about 300° C., but also to include individual values, such as 250° C., 260° C., 265° C., 290° C., etc., and sub-ranges, such as from about 250° C. to about 265° C., from about 260° C. to about 290° C., etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/−10%) from the stated value.
While several examples have been described in detail, it will be apparent to those skilled in the art that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.
