Plastic article or earthenware shaping or treating: apparatus – Means feeding fluent stock from plural sources to common...
Reexamination Certificate
2000-06-12
2004-06-08
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means feeding fluent stock from plural sources to common...
C425S375000, C425S447000, C425S470000, C264S309000, C164S020000, C164S021000, C164S046000, C164S066100
Reexamination Certificate
active
06746225
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for the production of dies and molds and more particularly to a spray forming process for the deposition and rapid solidification of atomized molten droplets onto a pattern for manufacturing dies, molds and related tooling.
The recent explosion of interest in rapid prototyping technology is fueled in part by the restructuring of today's marketplace. Successful competition in global markets will require the ability to carry a design concept through the prototype stage to the production stage faster and at lower cost than ever before. The ability to generate plastic and wax models of prototype parts with high dimensional accuracy via selective laser sintering, stereolithography, and other approaches is now a reality. The rapid production of prototype parts from engineered materials (i.e., materials that will actually see service) is a prime goal of industry. Methodologies that can rapidly produce specialized tooling, such as molds and dies, would satisfy this goal when used with conventional manufacturing techniques such as injection molding, blow molding, compression molding, stamping and die casting.
Presently, complex molds, dies and related tooling produced by conventional machining methods are expensive and time consuming to make. Costs can easily exceed hundreds of thousands of dollars and fabrication can require months of effort to produce molds with highly accurate dimensions and tolerances within a few mils or less.
As a consequence of the various disadvantages of conventional machining methods, thermal spray forming processes have been developed for fabricating dies whereby a deposition of a metallic layer on a plaster or metal casting is used to produce the die shell. These conventional processes utilize wire or powder feedstocks and are currently limited to a maximum spray rate of approximately 15 grams per second. Conventional thermal spray processes produce relatively large droplets, generally with mass median diameters in the order of magnitude of 100 &mgr;m and with a rather broad distribution of droplet size. Due to the large droplet size, low deposition rate, and heat content associated with conventional spray processes, solidification of the deposited droplets results in relatively poor microstructure, poor mechanical properties, porous deposits and limited material choices. Most high strength metals, including low-carbon, tool, hardfacing and stainless steels have high melting temperatures, thereby limiting the choice of materials used for the pattern or requiring a protective coating on the pattern to protect the pattern from the high temperature metal if conventional spray techniques are to be used. Conventional thermal spray techniques also require feedstocks in the form of metal powders or wires which are relatively expensive and limit material choices.
It is therefore an object of this invention to provide an improved spray forming system for the manufacture of molds, dies and related tooling by controlling the in-flight a cooling of atomized droplets, thereby controlling the temperature and solidification of the droplets that are deposited on a pattern.
It is another object of this invention to provide a spray forming system for the manufacture of molds, dies and related tooling by controlling the temperature and composition of a quench gas contained within a chamber through which the atomized droplets are directed.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects, the spray forming system of the present invention provides a method for manufacturing net shape molds, dies and other tooling with excellent pattern surface finish replication by controlling the deposition conditions of droplet size, velocity, heat content, flux and flow pattern. It is also understood that the quality of the spray formed mold, die, or other tool reflects the interplay of the above mentioned properties of the spray (e.g., droplet size, velocity, liquid fraction, etc.) with the properties of the substrate (e.g., surface finish and smoothness, temperature, thermal diffusivity and thermal conductivity). Polymers are ideal to use as patterns for spray forming because they conduct heat very poorly and can be made into complex shapes with excellent surface finish. Polymers are limited however, by their maximum use temperature which is lower than many other pattern materials such as ceramics. Incoming metal droplets remain fluid longer, which in turn allows them to fuse together and better replicate the surface of the pattern. These conditions are dependent upon the relative thermophysical properties of the sprayed liquid, such as surface tension, density and viscosity, as well as the heat content and solid fraction of the atomized droplets. Droplets which form the initial layer of deposit must conform to the surface of the pattern in a controlled manner and solidify rapidly. Only small, highly undercooled droplets or droplets with low solid fraction can meet both criteria and can be produced by the technique of the present invention. A high deposition rate of these droplets helps to ensure a highly dense deposit.
In accordance with the spray forming technique of the present application, a system is provided whereby a liquid is fed or aspirated into a nozzle, through which is flowing a high temperature, high velocity gas. The liquid can be any material in liquid form, preferably however, the liquid is a molten metal or metallic alloy, or a polymer in solution or molten form. The gas atomizes the liquid into fine droplets which are then directed toward the pattern to be replicated. The atomized droplets are generally spherical and of a uniform size, typically approximately less than 50 microns. The small, uniform size of the atomized droplets permits an excellent replication of the pattern which is evidenced, for example, by the similarity in surface roughness of the deposit and pattern. The amount of heat transferred to the pattern is much less than that of the molten metal starting material due to the high convection cooling rates in the spray and at the pattern. The atomized droplets are rapidly quenched while still in-flight toward the pattern. This is accomplished by convection heat transfer to relatively cold gas within a spray chamber being entrained by the spray jet. Entrainment provides a heat sink for cooling atomized droplets, thereby allowing undercooled and partially solidified droplets to be formed in-flight. To rapidly quench the in-flight atomized droplets, the spray plume can be directed through a quenching gas having controlled temperature and composition. To further enhance the quench rate of the atomized droplets, the quenching gas can initially be in the form of a cryogenic liquid, which when it comes into contact with the spray jet becomes a gas. The quenching gas can be nitrogen, helium, argon, oxygen or air, or any combination of these gases.
Analysis of the spray formed deposit also indicates the deposited material is close to theoretical density, and has excellent mechanical properties. The present system is capable of spraying aerosols containing solid particles which are intermixed with the atomized droplets. By spraying the particles with the atomized droplets, a composite mold is formed. The composite mold formed can be a metal or polymer matrix composite.
In another embodiment of the invention, more than one kind of liquid material can be sprayed. This is accomplished by having more than one controlled feed into the nozzle, or alternatively, by having more than one nozzle. The separate liquids are each atomized and co-deposited onto the pattern to produce functionally gradient deposits and/or clad deposits.
REFERENCES:
patent: 3784152 (1974-01-01), Garner et al.
patent: 3899820 (1975-08-01), Read et al.
patent: 4066117 (1978-01-01), Clark et al.
patent: 4919853 (1990-04-01), Alvarez et
Bechtel BWTX Idaho, LLC
Dahl & Osterloth LLP
Davis Robert
Del Sole Joseph S.
LandOfFree
Rapid solidification processing system for producing molds,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rapid solidification processing system for producing molds,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rapid solidification processing system for producing molds,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3323553