The invention relates to a method and apparatus for the preparation of multiple gauge metal strip by a shaving operation wherein the strip is drawn through the shaving apparatus over an arced surface.
It is necessary to provide a multiple gauge thickness in a metal strip in many applications such as the production of copper strip for the formation of electrical conductors and the like. Conventional procedures such as continuous milling have been employed to produce the desired variations in gauge, however, such processes suffer from the disadvantages of being both time consuming as well as generating an unfavorable form of scrap.
An additional procedure which has been known in the art to produce multiple gauge metal strip comprises the reduction to gauge by a rolling operation. However, the rolling operation in the production of multiple gauge strip has been found to suffer from the disadvantages of being restricted to certain shapes, and furthermore tend to involve complex and costly tooling. Additionally, it has been found that the product produced by the aforesaid rolling process fails to meet commercial tolerances as well as being free from other structural defects.
A further method of producing multiple gauge metal strip is by a drawing process. However, certain complications resulted from this process. In the normal drawing process reduction of the thickness in a section results in an increase in section length so that if the thickness of a given shape varies across its width, the drawing process will result in variable changes in length causing non-uniform metal flow and stresses leading to buckling, twisting, tearing and fracture of the workpiece. Though a wide variety of drawing techniques are known, including the employment of the hydrodynamic principle, none have been suggested or would appear to alleviate the aforenoted deficiencies associated with the drawing of complex multiple gauge configurations.
The technique of shaving as a form of metal reduction has been known in the art for some time. However, its application has been generally limited to the finishing of materials of uniform cross section by the reduction of the cross sectional area of the workpiece, with the reduction being conducted along the entire surface thereof. This technique is illustrated in U.S. Pat. No. 3,055,102 to Shaw et al. wherein a shaving tool is applied against a rod or bar which reduces the cross sectional area along the entire surface thereof.
Certain problems would appear to arise if this shaving technique exemplified by Shaw et al. were to be directly applied to the production of multiple gauge strip products from rectangular stock. Specifically, the application of shaving force against only a portion of the total surface of the strip tends to magnify the problems set forth in the aforenoted patent, particularly, the inability to hold the workpiece properly centered with respect to the tool with the result that the workpiece wanders and a wavy or broken surface may result. A further difficulty which would arise and be magnified by the removal of stock from only a portion of the workpiece surface would be the excessive chattering that takes place as the strip would pass through the tool which would appear on the finished product as a torn or galled surface.
One known method of producing multiple gauge strip by draw shaving is illustrated in U.S. Pat. No. 3,992,977 to Winter et al. and assigned to the assignee of the present invention and incorporated herein by reference. The method and apparatus for producing multiple gauge metal strip in the aforesaid U.S. patent while found to be superior to previously known methods still was found to suffer from deficiencies. More particularly, the rake angle at which the tool was disposed was found to be limited to a range of 21/2.degree. to about 25.degree. and was preferably about 5.degree. to 18.degree.. Any increase in rake angle above those critical values would cause the workpiece to ride up the tool resulting in excessive strip material being removed. Thus, as a result of the limit on rake angle, the amount of volume removed per pass was also limited. Furthermore, the manner in which the tool was held in position with respect to the anvil and strip was found to produce chatter marks on the shaved portion of the multiple strip product not unlike those chatter marks encountered in the aforesaid machining operations. The chatter marks are undesirable for functional reasons as well as cosmetic reasons. Chatter marks on the metal strip impedes the bonding of semi-conductor chips to the strip as well as inhibiting the metal plating of the strip which may be necessary in the production of electrical conductors and the like. The shaved gauge variation of the strip was found to be .+-. 0.002" while variations in the transverse positioning of the cut groove were 0.005". Finally, the finished multiple gauge strip product was observed to have significant scratching on the backside thereof as a result of being drawn over the flat anvil during the shaving process. Furthermore, the shape of the final product exhibited an increase in cross-wise dish with a corresponding increase in cut depth and/or width. This cross-wise dish can be attributed to the insufficient hold-down forces of the strip against the flat anvil.