Electrolysis: processes – compositions used therein – and methods – Electroforming or composition therefor – Mold – mask – or masterform
Reexamination Certificate
1999-08-06
2002-06-25
Valentine, Donald R. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electroforming or composition therefor
Mold, mask, or masterform
C205S067000
Reexamination Certificate
active
06409902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a solid freeform fabrication and electroforming system, and more particularly to a solid freeform fabrication and electroforming system for use in the production of engineering tools and hollow bodies.
2. Description of the Related Art
Electroforming is the use of electrodeposition of metal onto a master to replicate the master in a reversed format to produce a metal shell. The master, which has the required shape, dimension, accuracy and roughness, is sinked into an electrolyte bath as the cathode and is deposited a required layer of metal, normally copper or nickel. If the master is nonconductive, it needs to be metalized before electroforming. The metal shell is separated from the master to form the mold cavity. Electroforming can be used to reproduce the reversed shell of a wide variety of parts and shapes, the principal limitation being that it must be possible to separate the master from the metal shell, similar to the situation that the molding part must be able to be removed from the mold cavity. Electroforming has been used for dies and molds fabrication. With the development of the electroforming technology, alloy, such as Ni—Co, can be deposited onto the master to form an alloy shell so that the strength and hardness of the mold can be largely improved.
Electroforming was invented by M. H. Jacobi of the Academy of Science of St. Petersburg, Russia in 1838. It was initially used to copy antique masterpieces in the last century. Currently, electroforming is widely used in manufacturing, electronics, aerospace, automotive, and art reproduction. Electroformed parts most commonly are made of nickel, iron, copper, or silver, and thicknesses up to 16 mm ({fraction (5/8 )}inch) have been deposited successfully. However, a variety of other types of materials have been used including other types of metals and rubber. Metals deposited by electroforming have their own distinct properties. Dimensional tolerances are very good, often up to 0.0025 mm (0.0001 inch), and surface finishes of 0.05 mm (2 microinches) can be obtained quite readily if the master is adequately smooth. The main obstacle to the development of the electroforming is the manufacturing of the master. In some less technology advanced countries, electroforming is widely used to copy the shape of an imported complex part. The copied shell is used as the mold cavity.
The emergence of the solid freeform fabrication (SFF) technology has brought about new opportunities in rapid prototyping, tooling and manufacturing. Many kinds of models can be made using available RP machines, such as Stereolithography Apparatus (SLA), Selective Laser Sintering (SLS), Three Dimensional Printing (3DP), Fused Deposition Modeling (FDP), Laminated Object Manufacturing (LOM), etc.
The use of such RP technologies has brought about new opportunities in the utilization of electroforming for making of molds, dies, EDM electrodes and hollow bodies as discussed in the present invention. Masters can be made using the mentioned RP machines. After the RP master is metalized, an electroform is made from the master with the interface layer conforms intimately to the master. However, separation of the electroform from the master may not be easy and the difficulty increases as the form complexity increases. Traditionally, the master is removed by extraction (pull-off), heat-softening, melting or chemical dissolution. Separation of RP master by mechanical pull-off has been found impractical, however, since extreme care and skills are required during the pulling off process in order not to damage the metal shell. The pulling force may break the master thus leaving some master relic in the metal shell, especially when the master is brittle and intricate in shape. Pull-off can not be used if the master is enveloped in the metal shell such as a hollow-body electroform of complex shape. Dissolving the RP master in a chemical solution to separate the metal shell by causing delamination of the interface layer may be possible but the time taken may be excessive. Melting, incineration or heat softening may be applied to wax or polymer RP masters for separating the electroform from the master. A major problem is that these materials have much higher coefficients of thermal expansion than the electroformed metal. During the process of heating up the electroformed object, the expansion of the RP master can significantly deform the metal shell. The use of thermal cycling to separate a polyurethane master from a metal shell has been attempted, but those skilled in such attempts recognize that removal of an SL master is more difficult than removal of a polyurethane part. This is due to the fact that an SL part is more brittle and tends to fracture during the removal process. Thus, an SL part is merely used as a master to create a vacuum cast mold used to produce a polyurethane master for electroforming.
Another shortage of electroforming for making complex tools is the slowness and inefficiency of the electroforming process, due in-part to the non-uniformity of the distribution of the current density between the anode and the cathode. The deposition speed is directly proportional to current density. The master areas which are closer to the anode have higher current density so more metal is plated onto these protruding areas of the master than onto the recesses. The faster deposition in these areas consequently increases the current density and thus makes the deposition rate in these areas higher and higher, and likewise the deposition rate in the recess areas lower and lower. The uneven distribution of current density results in not only uneven distribution of the electroform but also undesirable distribution of its metallic microstructure. Furthermore, dendrite or like crystalline formations tend to build up on certain localized areas for a master with complex geometry due to the non-uniformity of current density. In order to reduce these build-ups, the electroforming process is often carried out at a minimum current density. As a consequence, it may take many days for the electroformed metal layer to reach a desired thickness. However, the undesired unevenness can not be completely eliminated even at a low current density. It has thus been a common practice to interrupt the electroforming process from time to time, remove the object being electroformed from the electroforming machine, and transfer it to a cutting machine for removing dendrite and part of the metal deposited at the protruding areas to reduce the increasing current density at these areas. After each such cutting stage, the metal layer needs to be fully degreased, washed, cleaned, and then the part is returned to the electroforming machine. Since the timing for the need of such removal is generally difficult to predict, the electroforming process is often constantly monitored or interrupted from time to time in order to take the object out and observe the deposition situation. Electroforming at a higher current density accelerates the deposition rate, but it worsens the non-uniformity and increases the rate of dendrite buildup. Thus electroforming without a conformal anode is labor-intensive, time-consuming, energy-consuming, and costly. Also, it wastes chemicals and other useful resources. Conforming the shape of the anode to the shape of the work piece to be electroformed can provide a uniform distribution of current density, thus the metal can be deposited onto the work piece more uniformly. However, making of a conformal anode by machining is also expensive and time consuming.
Heat dissipation for most of molding processes such as injection molding is critical for reducing the molding cycle. The mold is a heat exchanger most of the energy (heat) added to the plastic in the mold extruder to make it soft and suitable for injection must be removed before the mold can be opened to eject the product. The common practice is to make cooling channels inside the mold. Cooling oil or water are flowing through t
Leu Ming C.
Yang Bo
Klauber & Jackson
New Jersey Institute of Technology
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