Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to heat the... – Electrical heating
Reexamination Certificate
1999-07-14
2001-05-29
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to heat the...
Electrical heating
C137S013000, C264S308000
Reexamination Certificate
active
06238613
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION(S)
None
BACKGROUND OF THE INVENTION
This invention relates to thermoplastic extrusion technologies. More particularly, this invention relates to extrusion of thermoplastic in a predetermined spatial pattern under computer control.
Thermoplastic extrusion technologies perform rapid prototyping of three-dimensional objects by selectively extruding a molten thermoplastic from an extrusion head while moving the extrusion head in three dimensions with respect to a base. The thermoplastic is extruded in “beads” or “roads” that solidify after being deposited. Movement of the extrusion head with respect to the base is performed under computer control, in accordance with design data provided from a computer aided design (CAD) system. U.S. Pat. Nos. 5,121,329 and 5,764,521, commonly assigned to Stratasys, Inc., the assignee of the present invention, describe the rapid prototyping deposition modeling technology and are hereby incorporated by reference as if set forth fully herein.
In existing thermoplastic extrusion technologies, the configuration of the extrudate is adjustable in quantity and flow rate but not in spatial configuration. The flow rate of material out of an orifice is carefully controlled, but the spatial configuration (e.g., road width) of the flow is not readily alterable.
As the size of the element of additive material shrinks, a prototype part built with those additive elements will typically represent its CAD model parent with greater fidelity. For example, depositing layers of thermoplastic half as thick using extruded roads that are half as wide will improve the feature detail and surface finish of a model by about a factor of two. Unfortunately, with a constant deposition velocity, the time to build the model with this factor of two increase in resolution increases by about a factor of eight.
This speed/resolution conflict has been resolved in other rapid prototyping technologies by replacing vector motion of a single source with raster motion of multiple ink jets. An example is the Actua™ ink jet rapid prototyping system from 3D Systems, Inc., which forms three-dimensional models from a wax-like material. The ink jets are individually controlled so that any number of the jets will deposit the modeling material at a given time. Ink jet-based technologies are attractive for extruding discrete quantities of relatively low viscosity materials, however, ink jetting techniques have difficulty with high viscosity materials (such as thermoplastics) and particulate or fiber-filled materials. These materials tend to clog the jets. Also, in thermoplastic extrusion, “wetting” of the base by the extruded thermoplastic serves to separate the thermoplastic from the extrusion head, while ink-jetted materials break free due to the jetting momentum.
There is an unmet need for a computer-controlled extrusion apparatus suitable for dispensing thermoplastic in an extrudate configuration that may be varied quickly during deposition, in accordance with movement of the apparatus in a predetermined spatial pattern relative to a base.
BRIEF SUMMARY OF THE INVENTION
Thermoplastic is extruded in a varying extrudate configuration in synchronization with movement of a dispensing apparatus in a predetermined spatial pattern with respect to a base, by using the temperature dependent properties of the thermoplastic to valve the thermoplastic flow. A heat sink cools a valve region of a flow channel within the apparatus to a temperature below the lowest flowable temperature of the thermoplastic. A heater thermally contacting the valve region creates a thermal valve. The heater is capable of receiving heat generation signals from a control so as to selectively generate heat. A flow of thermoplastic provided to the flow channel is selectively allowed to flow through the thermal valve for extrusion in a varying extrudate configuration, by selectively heating the valve region to a temperature at which the thermoplastic is flowable in accordance with movement in the predetermined spatial pattern. A second thermal valve is optionally created by placing a second, independently controlled heater in a second valve region along the flow channel. The second thermal valve may be used to vary the pressure of the thermoplastic extrudate.
In an alternative embodiment, multiple thermal valves are integrated into compact arrays within an extrusion head of the present invention, to provide a varying extrudate configuration and high speed extrusion. The heaters associated with the various thermal valves in the array are selectively and independently controlled in accordance with the predetermined spatial pattern.
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Batchelder John Samuel
Zinniel Robert L.
Kinney & Lange , P.A.
Stratasys Inc.
Tentoni Leo B.
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