Metal deforming – With cutting – By composite tool
Reexamination Certificate
1999-06-25
2002-06-11
Crane, Daniel C. (Department: 3725)
Metal deforming
With cutting
By composite tool
C083S051000, C083S621000
Reexamination Certificate
active
06401510
ABSTRACT:
This application is a 371 of PCT/US99/07608, filed Apr. 7, 1999.
FIELD OF THE INVENTION
The present invention relates to a multi-layered part and a method of producing a multi-layered part having relatively rigid upper and lower layers, and a viscoelastic intermediate layer. In a particular embodiment, it relates to a method and apparatus for stamping a flat, uniformly edged part from a multi-layered strip, including a viscoelastic intermediate layer, on a mass production basis.
BACKGROUND OF THE INVENTION
Several well-known techniques are normally employed for stamping or blanking parts from sheets or strips of material. Typically, the part is sheared or cut from the strip by subjecting the strip to shear stresses at desired locations. One common blanking device includes a punch and die or similar punch press tools. The punch and die is shaped in accordance with a desired shape of the end part, and may therefore assume a number of different shapes, including circular, rectangular, etc. Generally speaking, the material strip is placed between the punch and die, and the punch is driven toward the die. During this operation, the part is sheared from the strip along fracture lines imparted by the punch and the die. Other similar shearing techniques including die cutting, fine blanking, steel rules, etc.
While blanking operations via a conventional punch press or similar technique are widely accepted, inherent limitations of these shearing techniques normally impart certain imperfections into the resulting part. For example, with the standard punch/die approach, clearance between the punch and die is a major factor in determining the shape and quality of the sheared edge of the part. During the shearing process, actual shearing normally initiates with the formation of fractures or cracks at the interface areas between the part and the punch and the part and the die. These fractures define deformation zones and eventually meet, resulting in complete separation. With this in mind, the sheared edge of the part is typically neither smooth nor perpendicular to a plane of the strip. More particularly, as clearance increases, the edge of the part becomes rougher as the zone of deformation along the part edge becomes larger. Material is pulled into the clearance area, and the edge of the sheared part becomes more and more rounded. Additionally, burrs are normally formed at the bottom surface of the part. It may be possible to better control fracture formation by incorporating a cutting edge into the punch. However, even with relatively thin strip material, uncontrolled fractures along the sheared edge of the part will still result.
Depending upon the end application for the part, the above-described defects may be of little concern. For example, stainless steel washers are typically produced via a punching operation. For most applications, it is not necessary that the washer be extremely flat or have uniform inner and outer perimeter edges. Further, where flatness and edge uniformity is of greater importance, certain additional process controls can be implemented. For example, a fine blanking operation can be employed in which a V-shaped stinger, or impingement ring, locks the material sheet or strip tightly in place so as to minimize burr formation and facilitate a more uniform shear. Alternatively, additional manufacturing steps, such as rolling, flat baking, shaving, deburring, etc. may be employed.
One particular product normally produced using a punching operation is the disk substrate material for a rotatable storage article such as a computer hard disk. Disk substrates used in computer hard disk drives are typically mass produced by blanking a properly shaped part from a sheet of aluminum. Other materials are subsequently applied to opposing surfaces of the disk, such as plated nickel and sputtered magnetic material. However, the disk substrate itself is produced by a punch and die device. It is estimated that over one billion computer hard disks are produced annually. Obviously, it is imperative that the disk substrate be flat. In this regard, current industry standards require a flatness of less than 8 microns per 96 mm (one typical hard disk substrate diameter) or 5 microns per 84 mm (another typical disk diameter). To satisfy this rigorous standard, a stinger technique is normally employed to minimize burr formation. Further, following the blanking or stamping operation, the disk substrate is typically flat baked.
The above-described techniques achieve the requisite disk substrate flatness due to the monolithic nature of the sheet material. The monolithic aluminum material facilitates successful flat baking because the imperfections imparted during stamping are relatively uniform across the disk thickness. For most end applications, a monolithic or single layered aluminum disk substrate is more than satisfactory. However, as computer hard drive technology continues to evolve, the computer hard disk is subjected to increasing demands. For example, efforts have been made to increase the rotational speed of the hard disk. Hard drives normally spin at one constant speed. Typical speeds range from 3600 to 7200 revolutions per minute (rpm). With recent improvements to hard drive designs, rotational speeds well in excess of 10,000 rpm are available. At these rotational speeds, the disk will begin to flutter or vibrate in response to air drag and/or internal hard drive harmonics. The effects of harmonic motion are greatly increased at higher rotation speeds. Because the standard computer hard disk substrate is monolithic, any resonant vibration generated at a bottom surface of the disk substrate is transferred to, or propagates to, the upper surface (and vice-versa), potentially leading to reading/writing errors.
To overcome resonant vibrational issues, recent disk substrate designs have focused on providing an internal damping mechanism. This internal damping mechanism serves to absorb or damp resonant vibrations, thereby preventing vibration propagation and resulting reading/writing errors. One such computer hard disk substrate (or similar rotatable storage article) is described in U.S. Pat. No. 5,538,774 assigned to Minnesota Mining and Manufacturing Company of St. Paul, Minn. The described disk substrate includes at least one layer comprised of a viscoelastic material. The viscoelastic layer serves to damp resonant vibrations generated during use.
Incorporating a viscoelastic material within a computer hard disk substrate is a highly viable solution to the resonant vibration issue. However, certain manufacturing concerns may arise during mass production. One technique for producing a multi-layered disk substrate, or any other product incorporating relatively rigid outer layers and a viscoelastic intermediate layer, is to prepare each of the three or more layers independently. Once cut to a proper shape and size, the three or more layers are adhered to one another. In terms of mass production, this technique may be relatively time consuming. Further, difficulties may be encountered in properly aligning the layers. Conversely, the three or more layers may be formed into a continuous strip. An individual computer hard disk substrate or other component is then stamped from the strip in accordance with previously described stamping procedures. With conventional stamping techniques, the upper rigid layer effectively cuts at least a portion of the lower rigid layer. Unlike a monolithic part, however, it is exceedingly difficult to “correct” stamping-caused defects in a multi-layered part incorporating a viscoelastic intermediate layer. Because the viscoelastic intermediate layer is soft and deformable, the rigid outer layer material will easily deform at the interface area with the viscoelastic material. This internal deformation or deflection is more prevalent along perimeter edges of the part. Because the viscoelastic interface area is internally located, it appears to be extremely difficult to correct edge deflections via an external compressive force and/or flat baking. Thus, it may
Johnson Brian D.
Morse Thomas L.
Nelson Alfred D.
3M Innovative Properties Company
Crane Daniel C.
McGeehan Lisa M.
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