Metal founding – Process – Shaping a forming surface
Reexamination Certificate
2001-05-29
2004-08-31
Stoner, Kiley (Department: 1725)
Metal founding
Process
Shaping a forming surface
C264S227000, C264S220000
Reexamination Certificate
active
06782940
ABSTRACT:
REFERENCES CITED
U.S. Patent Documents
2,939,199
Sep. 1960
Strivens
264/63
3,709,459
Jan. 1973
Bushrod
249/134
4,139,677
Feb. 1979
Blair, et al.
428/409
4,197,118
Apr. 1980
Wiech
264/63
4,704,079
Nov. 1987
Pluim
425/190
5,234,655
Aug. 1993
Wiech, Jr.
264/227
5,976,457
Nov. 1999
Amaya, et al.
419/36
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not Applicable.
BACKGROUND—FIELD OF INVENTION
The present invention relates to molds. More specifically, the present invention relates to an improved process for the fabrication and reproduction of molds used for the simultaneous mass-production of identical precision parts in different geographical locations.
BACKGROUND—DESCRIPTION OF PRIOR ART
With the exponential growth of technology and the globalization of markets, manufacturers of mass-produced consumer products such as watches, mobile telephones, pagers, handsets, computing, gaming and other electronic devices, etc., are challenged by an increasingly discriminating consumer population expecting innovative, technically advanced and esthetically attractive products incorporating the latest technological developments. As an example of the growth of such items, worldwide annual production of watches has skyrocketed to 1.2 billion pieces in 1999, worldwide personal computer (PC) shipments reached nearly 105 million units in 1998 and are expected to exceed 191 million by 2002, while global shipments of cellular telephones are estimated at over 500 million units for the year 2000 and are expected to reach 1 billion units by 2002.
Such products must be economically mass-produced and comply with increasingly stringent technical and environmental specifications. Accordingly, to remain competitive, manufacturers of mass-produced consumer items must be in a position to rapidly change the design of their products, not just to keep abreast of fast changes in technology, but also to maintain a steady stream of renewed products with increased functionality and enhanced esthetic appeal.
As a result of this state of things, numerous manufacturers of mass-produced consumer products relocate their manufacturing operations offshore in order to benefit from a more attractive manufacturing environment including tax holidays, employer-friendly legislation, lower cost of industrial space, water, utilities, infrastructure, labor, etc. But the conditions prevailing at such offshore locations are never constant, e.g. low labor cost countries may, within the span of a few years, turn into high labor cost countries, or change rapidly and unexpectedly due to political upheaval, culminating in manufacturing operations being curtailed or even outright suspended. To protect themselves from such contingencies and/or to be closer to specific markets, many manufacturers of mass-produced consumer articles often spread out their manufacturing operations over several countries, each having its own specific environment, language, culture, customs, rules, laws, work ethics, etc. Generally, many components of such mass-produced consumer articles are contracted out to local workshops and small businesses such as machining shops, printed circuit board assembly operations, moldmaking and molding shops and the like. In developing countries, the cheapest contractors are often small, family-run operations, unable to understand or adapt fast enough to the fast changing and increasingly sophisticated specifications of technologically advanced products. It is also essential that components made by one contractor in one location can be substituted or matched with components made by another contractor in another location. As is well known, it is virtually impossible to exactly balance and identically match cavities in a single multi-cavity molding tool, let alone in multi-cavity molding tool sets located thousands of miles away from each other.
Mold cavities are normally machined or ground as a set of carbon or copper electrodes for each mold half, and these electrodes are then used to burn a negative or female representation of the parts into the mold insert blocks, a process which is laborious, time consuming and expensive. Adding to the time and cost of fabricating molds is the detail work needed to create internal channels for heating or cooling and the fabrication of ejector pins, ejector holes and slide and wear components. Depending on the complexity and size of the tool, fabrication time can take from six weeks for a simple tool to an average of twenty-four weeks for a larger more complex one.
In addition, injection molding is extremely hard on molds. Various attempts have been made to improve the performance and economic life of molds by utilizing mold inserts or facings on the mold cavity from various materials with better wear resistance. Such attempts include the use of silicon nitride or silicon carbide mold facings as set forth, for example, in Bushrod U.S. Pat. No. 3,709,459 and Blair et al. U.S. Pat. No. 4,139,677. However, such attempts, while offering a solution to the problem of wear, run into problems of misfit and cracking as a result of the difference in the coefficient of thermal expansion between the ceramic facing and the metallic backing or body of the cavity or mold. Pluim U.S. Pat. No. 4,704,079 has attempted to solve these problems by using mold inserts formed by freeze casting particulate silicon metal and reaction bonding the thus formed inserts in nitrogen gas to generate silicon nitride. Amaya et al. U.S. Pat. No. 5,976,457 metal injection mold their mold inserts, which are subsequently machined to fit into the die pockets of multi-cavity tools.
Each of the aforementioned inventions has somewhat reduced the problems of the prior art, yet each has issues that detract from its adoption and neither methods are simple, accurate and cheap to implement. Also, they fail to address the specific issues of cost, wear and dimensional consistency raised by the simultaneous, multi-location mass-production of modern, short-lived consumer products such as watch cases, mobile telephone housings, computer enclosures, and a myriad of other mass-molded products.
Presently, the most common way of producing a watch case is by stamping a blank from of a sheet of stainless steel and machining this blank to its final configuration. Due to the complexity of the finished product, the number of machining steps involved is often large, sometimes well over one hundred, and watch manufacturers do not hesitate to capitalize on this fact in their advertising. Punching dies used for blanking usually have a very short life and may have to be replaced or repaired after as few as 500 punches. As a result of this problem, an increasing number of watch manufacturers have recently turned to plastics, metal, and ceramic injection molding technology for the fabrication of watch components such as cases, bracelet links and buckles. But as watch designs also change rapidly, the investment in tooling and its maintenance quickly becomes unaffordable.
In the case of housings for mobile telephones, the most common method of fabrication is by molding them from either filled or unfilled polymeric materials, which can be done by almost any conventional plastics molding shop. However, many molding shops find it hard to keep up with the rapid pace of change in design and materials and cannot produce the necessary molding tools fast enough. They may then have no other alternative but to raise the costs of tool making because they need more mold makers, additional or more advanced machine tools, measuring equipment, etc. This represents a substantial investment, which few mold making shops can justify. As a result, many molding contractors subcontract some of their work to other shops. All of this contributes to high tooling costs and the virtual impossibility to maintain consistent quality, tight tolerances, and high quality workmanship. To make matters worse, it is well known that mold and toolmakers are in worldwide short supply.
The total investment in tooling for mass-produced con
Billiet Romain L.
Nguyen Hanh Thi
Foley and Lardner
Stoner Kiley
Tran Len
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