Plastic and nonmetallic article shaping or treating: processes – Stereolithographic shaping from liquid precursor
Reexamination Certificate
1999-06-14
2001-02-27
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Stereolithographic shaping from liquid precursor
C264S221000, C264S236000, C264S308000, C264S317000, C264S496000, C264S497000
Reexamination Certificate
active
06193922
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The invention is based on a method for making a three-dimensional body from a computer data model by computer-controlled layer-wise deposition of material.
2. Description of Related Art
The continued intensification of international competition with ever-decreasing product cycles calls for reduction of development time. Rapid production of prototype models yields a great cost reduction potential during all design and development phases,
Existing methods for computer controlled manufacturing of three-dimensional objects can be categorised into subtractive and additive methods. The most popular method of the first group is numerically controlled milling. Disadvantages result from geometrical restrictions even with up to five axes milling. This method is inherently expensive, especially for single pieces, and requires suitable equipment together with a trained operator.
The second group comprises newer methods like e.g. stereolithography. Here a container with liquid photopolymer resin with constant fluid level is equipped with a mechanical fixture, which allows for lowering of a submerged platform according to a desired layer thickness. In a first step, a resin film of exact thickness is being applied on the submerged platform by a wiper (doctor blade). In a subsequent step, the resin film is being cured in selected areas by radiation from a UV laser. Hereby the laser beam scans across the resin surface under computer control, exposing contour lines, solid areas, and supporting structures to UV radiation. The next step comprises lowering the platform in the resin container by one layer thickness, applying another resin layer, and repeating the radiation exposure for the desired geometry of this layer. This cycle is repeated until completion of the object. Finally the model is being removed from the resin bath, cleaned from residual uncured resin, and separated from the supporting structures.
This method is primarily limited by its high expenses for equipment, process, and consumables. Additional equipment for cleaning of the models from liquid resin is mandatory.
EP-A-0 322 257 discloses a similar method in which a photosensitive material is being exposed to radiation through a computer generated mask in a layer-wise fashion. Subsequently unexposed material is being removed and substituted by an non-photosensitive material. The process is repeated layer by layer until completion of the model.
This method requires expensive cleaning equipment for removal of unwanted material during each layer cycle, yielding a large amount of still reactive waste,
This disadvantage is avoided by methods like selective laser sintering, disclosed in U.S. Pat. No. 4,247,508. Here a thin powder layer is being applied to the building platform and selectively melted by a computer controlled scanning laser beam. Again, the cycle is repeated until completion of the model. Plastic or metal powders can be used. If designed skilfully, the loose powder can serve as supporting means. Therefore blowing off of unmelted powder after completion of the building phase is sufficient in order to get the finished model.
But this method requires expensive lasers, optics, and scanning devices as well. Furthermore, a certain degree of surface roughness of the models is caused by the granularity of the powder (ca. 50-100 micrometers average grain diameter).
A similar method, developed by the Massachusetts Institute of Technology and disclosed in EP 0 431 924 B1, applies thin powder layers on a substrate in which powder particles are bonded together according to the desired model cross-section by selectively adding small glue droplets via a printhead. The building material consists of bonded powder particles; unbonded powder acts as support and is being removed after completion of the process.
This method is used predominantly for building moulds for investment casting together with ceramics and has some disadvantages caused by the complex powder handling procedures. Moreover, the models always consist of a powder-binder composite which never achieves the bulk material density and therefore is mechanically weak,
In “Ballistic Particle Manufacturing” of the BPM company molten material is being deposited from a single nozzle which is being positioned by a five-axis unit. Supporting structures can be omitted. The method is time-consuming, because only one nozzle is used for material deposition. To save time, only hollow bodies are being made today. Another disadvantage results from uneven material distribution, which leads to a deeply grooved object surface.
WO 95/05943 is based on dosing two different materials via drop generators, where the first material generates a model cross-section, the second a support structure where needed. Upon completion of the building phase the support structure is being removed by submersion in a solvent. This step yields the finished model which consists of insoluble material.
This technique has its advantages when building subtle structures, but the process is very slow because of the two dosing steps, leading to unacceptable building times. Moreover, material properties are very limited by the current maximum temperature of 80 degrees Celsius in the dosing head.
In EP 0 500 225 B1 a method is disclosed which also uses two different materials. The first material is used for building the model by selective dosing with a dosing head. The second material, whose application method is not specified, yields a support structure.
Here, too, the disadvantage holds that the building material must be compatible with the dosing heads, reducing the choice of materials and quality. The dosing process is technically demanding, because the building material must be pre-heated. Large models are enormously time consuming for the large amount of selectively deposited material.
SUMMARY OF THE INVENTION
Considering the problems described above which are associated with current methods, it is the objective of the invention to create a method for rapidly making three-dimensional objects with low technical effort which is suited for operation in an office environment.
This objective is achieved by a method for making a three-dimensional body comprising the properties laid down in the first claim.
According to the present invention a three-dimensional body can be made in the following steps:
a) Applying a release agent in its liquid state onto selected areas of a building platform by a single-drop generator, using a pattern according to the cross-section of a thin-walled shell around the three-dimensional body, and a grid pattern across the remaining area of the building platform.
b) after completion of the pattern for the current layer, filling of the areas enclosed by the release agent with a curable resin.
c) Curing of the resin.
d) Smoothing and planing of the layer in order to expose the upper surface of the release agent.
e) Repeating of the steps a) to d) with patterns according to the current cross-section of the three-dimensional body, thereby making the body itself.
f) Removing the structures not belonging to the body by dissolving the release agent.
The method according to this invention can be realised by a device for making three-dimensional bodies directly from computer data which consists of:
A microcomputer for data processing and control of the building process,
a building platform which can be moved vertically in a stepwise fashion,
a dosing device for selective application of the release agent, comprising positioning actuators, which can be moved across the building platform under computer control so that release agent can be applied at any point,
a dosing device for uniform and rapid application of resin across the entire building platform,
a device for curing of the resin and
a device for smoothing and planing of the completed layer made up of release agent plus resin.
The advantage of the present invention in comparison with the state of the art consists of the combination of a selective material deposition, mostly in lines and a non selective, rapi
Ederer Ingo
Huang Jiawei
J. C. Patents
Tentoni Leo B.
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