Patent Application
20100083728
The present disclosure relates generally to sheet metal forming processes and, more particularly, to a die for use in sheet metal forming processes.
Automotive body panels and other similar articles of manufacture are often made by hot or warm forming a sheet metal blank using a forming press. During the hot and warm forming processes, the sheet metal blank is pressed against the surface of at least one die in the forming press in the presence of heat. After a predetermined amount of pressing time, the sheet metal blank assumes the shape of the die surface and the sheet metal blank is thereafter removed from the forming press. In some instances, the die or the sheet metal blank is coated with relatively large amounts of lubricant to reduce adhesion between the sheet metal blank and the die surface during the forming process.
As disclosed herein, a die for use in a sheet metal forming process includes a die material having a surface. A plurality of depressions is formed in a predetermined portion of the surface, where each of the plurality of depressions has a predetermined diameter and depth. Interaction of a surface of a sheet metal blank with i) the plurality of depressions, and ii) a solid forming lubricant, including particles of an average predetermined size and distribution, disposed on one of the die material surface or the sheet metal blank surface substantially reduces adhesion between the sheet metal blank surface and the die material surface during the sheet metal forming process.
Features and advantages 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.
Current metal forming processes often employ relatively large amounts of lubricant added to the die surface to reduce adhesion between the die surface and the sheet metal blank. When adhesion results, other deleterious effects (e.g., wear) to the die surface and the sheet metal blank may also result. Generally, adhesion occurs, at least in part, because of the chemical affinity between the material of the die surface and that of the sheet metal blank. Non-limiting examples of sheet metal blank materials that tend to exhibit a chemical affinity to die surface materials include pure aluminum having minimal amounts (e.g., 0.1% or less) of impurities, aluminum alloyed with at least some magnesium, other aluminum alloys, magnesium alloys, or other materials commonly produced in sheet form. When any of these materials are used for the sheet metal blank, and are subjected to heat and pressure during a sheet metal forming process, at least some adhesion may occur between the sheet metal blank and the die surface. As previously mentioned, such adhesion may cause wear and other undesirable effects, which may require the die to be subjected to additional processing in order to restore the die to production quality.
In the embodiment(s) disclosed herein, the die is advantageously configured to substantially reduce or even eliminate the adhesive effects between the sheet metal blank and the die surface during sheet metal forming processes, and especially during warm or hot forming processes. The advantageous reduction in deleterious effects is accomplished without having to apply large amounts of lubricant to the die surface. This is brought about, at least in part, by 1) modifying the surface of the die with a plurality of depressions, and 2) disposing, on either the surface of the die or a surface of the sheet metal blank, a relatively thin layer of a solid forming lubricant. The modified die surface and the lubricant together reduce the coefficient of friction between the sheet metal blank and the die surface, which reduces or even eliminates sticking of the sheet metal blank to the die surface. It is to be understood that the coefficient of friction is a relative measure obtained from a system in which two or more materials (in this case, the sheet metal blank, the die, and the lubricant) are in contact with each other under certain conditions (e.g., pressure, temperature, time, to name a few). Using the process disclosed herein, a significant reduction in the coefficient of friction (when compared to other sheet metal forming processes in which the die(s) do not have a modified surface) may be achieved. In a non-limiting example, a suitable reduction in the coefficient of friction is at least 30%. In another example, the reduction in the coefficient of friction ranges from about 40% to about 50%.
The reduced or eliminated adhesion advantageously 1) facilitates easier removal of the formed sheet metal blank (i.e., an article) from the forming press, 2) reduces the number of surface defects or blemishes of the article, 3) reduces the need for post metal finishing processes on the article due to the reduced number of surface defects or blemishes thereon, 3) extends the working life of the die, and 4) enables a higher quality of article to be formed during sheet metal forming processes.
A perspective view of an embodiment of the die 10 is generally depicted in
Without being bound to any theory, it is believed that the distance between adjacent individual depressions 14 formed in the die surface 12, as well as the surface roughness of the die surface 12 in an area where the depressions 14 are formed, affects the coefficient of friction value between the die surface 14 and a sheet metal blank (see reference numeral 102 in
The depressions 14 are formed in predetermined portion(s) of the surface 12. The predetermined portion(s), in terms of density, ranges from about 1% to about 15% of the surface 12. As such, up to 15% of the surface 12 may correspond to depressions 14, while the remainder of the surface 12 remains unmodified. While the percentage of the surface 12 that forms the depressions 14 is relatively small, the depressions 14 may be spread across the entire surface 12 in a desirable arrangement (discussed further hereinbelow).
It is to be understood that the coefficient of friction between the sheet metal blank 102 and the die surface 14 is also affected by the arrangement of the depressions 14 formed on the surface 12. Several different depression arrangements, in addition to different shapes and sizes, may be used. It is believed, however, that a substantially uniform arrangement of the depressions 14 on the die surface 12 (as shown in
It is further believed that the coefficient of friction is also affected by the dimensions (i.e., diameter and depth) of the depressions 14. For either warm or hot forming processes, the predetermined diameter of each of the depressions 14 ranges from about 240 μm to about 340 μm, and the predetermined depth of each of the depressions 14 ranges from about 15 μm to about 30 μm.
As such, the size, shape and location of the depressions 14 on the surface 12 may be altered to achieve the desirable reduction in the coefficient of friction. In one non-limiting example, when either a warm or hot forming process is utilized, the depressions 14 correspond to 5% of the die surface 12 (e.g., the entire die surface 12 is treated to form the depressions 14, but the density of the resulting depressions 14 is 5%), where the diameter of each of the depressions 14 is 320 μm and the depth of each of the depressions 14 is 20 μm. This particular combination is believed to achieve a suitable coefficient of friction in order to reduce or eliminate adhesion between the die surface 12 and the sheet metal blank 102 during metal forming.
It is to be further understood that the predetermined portion of the surface 12 which corresponds to the depressions 14 and the positioning of such depressions 14 are selected based on, at least in part, the geometry of the article to be formed from the sheet metal blank 102 during the sheet metal forming process.
In an embodiment, a layer of a solid forming lubricant is applied on the die surface 12 (depicted as reference numeral 16 in
It is to be understood that the solid forming lubricant layer 16 generally has a thickness that is smaller than the thickness of lubricant layers that are often applied in current metal forming processes. As a non-limiting example, a typical system utilizing a die without surface modifications may require lubricant applied with a thickness of 15 μm, whereas the system disclosed herein utilizing the die 10 with the modified surface 12 may include a lubricant thickness of about 8 or 9 μm. In a non-limiting example, the thickness of the solid forming lubricant layer 16 ranges from about 2 μm to about 20 μm. It is believed that the reduction in lubricant is advantageous, at least in part because the cost associated with sheet metal forming increases when more lubricant is used, the potential for more defects forming on the resulting parts increases when more lubricant is used, and more frequent cleanings are required when more lubricant is used.
A sheet metal blank 102 is placed between the upper and lower dies 10′, 10, and is supported in the forming press 100 by a support member 104 such as, for example, a clamp or other suitable support means. During the warm sheet metal forming processes, at least one of the upper or lower dies 10′, 10 is drawn toward the other of the dies 10, 10′. This movement presses the supported sheet metal blank 102 against the surfaces 12′, 12 of the dies 10′, 10 in the presence of heat. For warm forming processes, the amount of heat applied during the process ranges from about 200° C. to about 350° C.
After a predetermined period of pressing time, the sheet metal blank 102 assumes the shape of the die surfaces 12, 12′ and forms the article (not shown). Thereafter, the upper and lower dies 10′, 10 are retracted from one another (or one 10′, 10 is retracted from the other 10, 10′), and the article is released from the support member 104. The article is then removed from the forming press 100. In a non-limiting example, the predetermined pressing time for a stamping process ranges from about 1.5 seconds to about 3 seconds. In another non-limiting example, the predetermined pressing time for a quick plastic forming or superplastic forming process ranges from about 90 seconds to about 150 seconds, depending at least in part on the complexity of the part to be formed.
For hot forming processes, the temperature of the process ranges from about 400° C. to about 1200° C. Hot forming generally involves superplastic forming process in which the sheet metal blank 102 is deformed against the die cavity by the effect of blown air.
In addition, the dies 10, 10′ disclosed herein may also be used with hydroforming (cold or warm), in which the deformation on the sheet 102 is cause by pressure applied by a fluid.
While several embodiments have been described in detail, it will be apparent to those skilled in the art that the disclosed embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting.
