Patent Application
20170225393
The disclosure relates to an apparatus and method for manufacturing three-dimensional objects, and more specifically, to an apparatus and method for using linear solidification and two-photon absorption to form such objects.
Three-dimensional rapid prototyping and manufacturing allows for quick and accurate production of components at high accuracy. Machining steps may be reduced or eliminated using such techniques and certain components may be functionally equivalent to their regular production counterparts depending on the materials used for production.
The components produced may range in size from small to large parts. The manufacture of parts may be based on various technologies including photo-polymer hardening using light or laser curing methods. Secondary curing may take place with exposure to, for example, ultraviolet (UV) light. A process to convert a computer aided design (CAD) data to a data model suitable for rapid manufacturing may be used to produce data suitable for constructing the component. Then, a pattern generator may be used to construct the part. An example of a pattern generator may include the use of DLP (Digital Light Processing technology) from Texas Instruments®, SXRD™ (Silicon X-tal Reflective Display), LCD (Liquid Crystal Display), LCOS (Liquid Crystal on Silicon), DMD (digital mirror device), MLA from JVC, SLM (Spatial light modulator) or any type of selective light modulation system.
Many of the foregoing devices are limited in the size of objects that they can make at high resolutions. For example, DMD devices include an array of small mirrors which vibrate to transmit light to a light hardenable solidifiable material. As the objects become bigger, each mirror (and pixel) occupies a larger area of the exposed solidifiable material surface, causing resolution to degrade. Laser based systems that use galvo mirrors typically have resolutions that are limited by the laser energy per unit area.
In most processes that involve the solidification of a photohardenable material, the photoinitiator only absorbs one photon of light at a given moment. This limits the amount of energy absorbed, and consequently, the extent of photopolymerization/cross-linking reactions that are necessary to solidify a photopolymer resin.
Two photon absorption has also been proposed. With two photon absorption, a single electron in a photoinitiator absorbs two photons simultaneously to transcend the energy gap in one excitation event. With two photon absorption, the rate of polymerization scales quadratically with light intensity, whereas with single photon absorption, the rate of polymerization scales linearly. Two photon absorption allows a comparably lower energy to be used to excite photoinitiators and monomers/oligomers/uncured or partially-cured photopolymers. Two photon absorption has a small cross-section and occurs only within the close vicinity of the laser focal point. Thus, by choosing the right combination of photoinitiators, resins, and optics, solidification occurs at small, targeted locations, thereby increasing the resolution of the three-dimensional object. In particular, femtosecond laser irradiation has been found to provide two-photon absorption effects. However, a steep intensity gradient and high intensity are required in order to ensure that two photon absorption occurs at the desired location—and not elsewhere—relative to the exposed surface of the solidifiable material.
Certain two photon systems use lenses to provide the desired gradient and targeted, localized laser light intensity. Generally, a short focal distance lens is required and the lenses tend to be wide. In order to use such systems to create three-dimensional objects by solidifying a solidifiable material, the lenses must be designed and adjusted to create a focal point beneath the exposed solidifiable material surface without causing two photon absorption between the focal point and the exposed solidifiable material surface. However, in such known lens-based systems either the lenses must move relative to the solidifiable material or the solidifiable material must move relative to the lenses. Given the required width of the lenses, moving the lenses is cumbersome and increases the complexity of the apparatus and would slow down the process of making a three-dimensional object. Moving the solidifiable material is often similarly problematic.
Thus, a need has arisen for an apparatus and method that addresses the foregoing issues.
The disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:
Like numerals refer to like parts in the drawings.
The Figures illustrate examples of an apparatus and method for manufacturing a three-dimensional object from a solidifiable material. Based on the foregoing, it is to be generally understood that the nomenclature used herein is simply for convenience and the terms used to describe the invention should be given the broadest meaning by one of ordinary skill in the art.
The apparatuses and methods described herein are generally applicable to additive manufacturing of three-dimensional objects, such as components or parts (discussed herein generally as objects), but may be used beyond that scope for alternative applications. The system and methods generally include a laser and at least one linear scanning device that applies solidification energy to a solidifiable material, such as a photohardenable resin with a photoinitiator, and optionally, a multiphoton sensitizer. The laser, the at least one linear scanning device, and the solidifiable material are configured such that solidification occurs at a focal point spaced apart from the exposed surface of the solidifiable material along a build (z) axis. Between the focal point and the exposed surface, single photon absorption occurs at an incident energy level that is insufficient to cause the solidifiable material to solidify. Thus, even in those examples in which a glass, film or glass and film substrate is used to planarize the exposed surface, the solidifiable material does not solidify in contact with that substrate, thereby obviating the need to separate the most recently solidified object surface from the substrate. By configuring the system so that solidification only occurs in regions where two photon absorption occurs, the regions of solidification also become much smaller as compared to regions in which single photon absorption is used with a corresponding intensity sufficient to cause solidification. As a result, with two-photon absorption, the resolution of the three-dimensional object increases relative to single photon absorption systems.
Referring to
When discussing a photopolymerizable, photocurable, or solidifiable material, any material is meant, possibly comprising a resin and optionally further components, which is solidifiable by means of supply of stimulating energy such as electromagnetic radiation, suitably, a material that is polymerizable and/or cross-linkable (i.e., curable) by electromagnetic radiation, including infrared (IR), ultraviolet (UV), and/or visible light. In an example, a material comprising a resin formed from at least one ethylenically unsaturated compound (including but not limited to (meth)acrylate monomers and polymers) and/or at least one epoxy group-containing compound may be used. Suitable other components of the solidifiable material include, for example, inorganic and/or organic fillers, coloring substances, viscose-controlling agents, etc., but are not limited thereto.
The solidifiable material 60 also comprises a photoinitiator. Preferred photoinitiators are those that are capable of being excited to triplet states by absorbing combined two-photon energy. The photoinitiator absorbs light and generates free radicals which start the polymerization and/or crosslinking process. In certain examples, the photoinitiator is selected to have an excitation wavelength that lies within the range of the one-half the laser 40 wavelength range. The two-photons generated in a two photon absorption process will generally have an associated wavelength that is half that of the laser 40 wavelength. Therefore, when using a laser 40 with an infrared wavelength, the photoinitiator will preferably be one that is activated by ultraviolet wavelengths, which are approximately one half of infrared wavelengths.
Suitable types of ultraviolet photoinitiators include metallocenes, 1,2 di-ketones, acylphosphine oxides, benzyldimethyl-ketals, α-amino ketones, and α-hydroxy ketones. Examples of suitable metallocenes include Bis (eta 5-2,4-cyclopenadien-1-yl) Bis [2,6-difluoro-3-(1H-pyrrol-1-yl) phenyl] titanium, such as Irgacure 784, which is supplied by Ciba Specialty chemicals. Examples of suitable 1,2 di-ketones include quinones such as camphorquinone. Examples of suitable acylphosphine oxides include bis acyl phosphine oxide (BAPO), which is supplied under the name Irgacure 819, and mono acyl phosphine oxide (MAPO) which is supplied under the name Darocur® TPO. Both Irgacure 819 and Darocur® TPO are supplied by Ciba Specialty Chemicals. Examples of suitable benzyldimethyl ketals include alpha, alpha-dimethoxy-alpha-phenylacetophenone, which is supplied under the name Irgacure 651. Suitable α-amino ketones include 2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl) phenyl]-1-butanone, which is supplied under the name Irgacure 369. Suitable α-hydroxy ketones include 1-hydroxy-cyclohexyl-phenyl-ketone, which is supplied under the name Irgacure 184 and a 50-50 (by weight) mixture of 1-hydroxy-cyclohexyl-phenyl-ketone and benzophenone, which is supplied under the name Irgacure 500.
Referring to
Solidification energy is provided by laser 40. Laser 40 is preferably selected to generate sufficient energy to cause two photon absorption in the photoinitiator(s) in the solidifiable material 60. Light from laser 40 is split in an optical fiber splitter 44 and directed to respective linear scanning devices 50a and 50b which together define a movable assembly 48. The light supplied to each linear scanning device 50a and 50b has about one half the intensity and the same wavelength as the light supplied by laser 40 to optical fiber splitter 44. Linear scanning devices 50a and 50b scan laser light received from corresponding optical fiber splitter outputs 46a and 46b in linear patterns along a scanning (y) axis. The linear scanning devices 50a and 50b are tilted at an angle θ relative to the build (z) axis so that their respective output beams 51a and 51b intersect at a focal point 62. Focal point 62 lies within solidifiable material 60 at a selected distance from exposed resin surface 63 along the build (z) axis. The focal point 62 scans along the scanning (y) axis and travels along the travel (x) axis with movable assembly 48, thereby defining a focal plane 58, which is the location of all possible points of intersection between output beams 51a and 51b in the plane perpendicular to the build (z) axis (i.e., in the x-y plane). In the region between exposed surface 63 of the solidifiable material 60 and focal plane 58, single photon absorption occurs, and the intensity is insufficient to solidify solidifiable material 60. As a result, and as best seen in
Suitable lasers 40 are those that can cause the two photon effect to occur, including UV, near IR, and IR lasers. Laser 40 is preferably a pulsed laser, with a pulse width that is preferably less than about 10−8 seconds, more preferably less than about 10−9 second, and most preferably less than about 10−11 second). Laser pulses in the femtosecond (1015 second) regime are most preferred.
In one example, laser 40 is a femtosecond laser with a wavelength ranging from about 600 nm to about 800 nm, preferably from about 680 nm to about 760 nm, and more preferably from about 700 nm to about 740 nm. At the focal point 62, two photons are generated with associated wavelengths of about one-half that of the laser 40. When the laser outputs 51a and 51b from linear scanning devices 50a and 50b recombine at focal point 62, the intensity is doubled to match that of the laser 40. Laser 40 also has an average output power that is preferably at least about 150 mW, more preferably at least about 200 mW, even more preferably at least about 500 mW, and still more preferably at least about 600 mW.
Suitable commercially available lasers for use as laser 40 include femtosecond near-infrared titanium sapphire oscillators pumped by an argon-ion laser, for example, a Coherent Mira Optima 900-F pumped by a Coherent Innova. This laser operates at 76 MHz, has a pulse width of less than 200 femtoseconds, is tunable between 700 and 980 nm, and has average power up to 1.4 Watts. Another example is a Spectra Physics “Mai Tai” Ti:sapphire laser system. This laser operates at 80 MHz, has an average power about 0.85 Watts, is tunable from 750 to 850 nm, and has a pulse width of about 100 femtoseconds. A particularly preferred laser is the Octavius Ti:Sapphire 85-M-HP oscillator with an integrated pump laser supplied by Thorlabs, Inc., which has a pulse width of less than 8 femtoseconds and an output power of greater than 600 mW. The pump laser is based on Optically Pumped Semiconductor Laser (OPSL) technology.
One skilled in the art can choose appropriate settings to use such laser systems to carry out multiphoton polymerization. For example, pulse energy per square unit of area (Ep) can vary within a wide range and factors such as pulse duration, intensity, and focus can be adjusted to achieve the desired solidification result in accordance with conventional practices. If Ep is too high, the material being solidified can be ablated or otherwise degraded. If Ep is too low, solidification may not occur or may occur too slowly.
In certain examples, each linear scanning device 50a and 50b is configured as shown in
Collimator 120 is provided between solidification energy input port 100 and cylindrical lens 122. Cylindrical lens 122 is provided between collimator 120 and rotating energy deflector 124. Collimator 120 is also a focusing lens and creates a round shaped beam. Cylindrical lens 122 stretches the round-shaped beam into a more linear form to allow the beam to decrease the area of impact against rotating energy deflector 124 and more precisely fit the beam within the dimensions of one particular facet 126(a)-(f). Thus, solidification energy received at input port 100 passes through collimator 120 first and cylindrical lens 122 second before reaching a particular facet 126(a)-(f) of rotating energy deflector 124.
In certain preferred examples where laser 40 is a femtosecond laser with a wavelength range between 600 nm and 800 nm, collimator 120 and/or cylindrical lens 122 transmit at least 90%, preferably at least 92%, and more preferably at least 95% of the incident light having a wavelength ranging from about 300 nm to about 400 nm. In one example, collimator 120 and cylindrical lens 122 transmit at least about 95% of the incident light having a wavelength of about 360 nm. Collimator 120 is preferably configured to receive incident laser light having a “butterfly” shape and convert it into a round beam for transmission to cylindrical lens 122.
In certain examples, collimator 120 has an effective focal length that ranges from about 4.0 mm to about 4.1 mm, preferably from about 4.0 mm to about 4.5 mm, and more preferably from about 4.01 mm to about 4.03 mm. In one example, collimator 120 is a molded glass aspheric collimator lens having an effective focal length of about 4.02 mm. One such collimator 120 is a Geltech′ anti-reflective coated, molded glass aspheric collimator lens supplied as part number 671TME-405 by Thorlabs, Inc. of Newton, N.J. This collimator is formed from ECO-550 glass, has an effective focal length of 4.02 mm, and has a numerical aperture of 0.60.
In certain examples, collimator 120 and/or cylindrical lens 122 are optimized based on the specific wavelength and beam divergence characteristics of laser 40. In one example, collimator 120 and/or cylindrical lens 122 are formed from a borosilicate glass such as BK-7 optical glass. In certain preferred examples, collimator 120 and/or cylindrical lens 122 are coated with an anti-reflective coating such that the coated collimator 120 and coated cylindrical lens 122 transmit at least 90%, preferably at least 92%, and more preferably at least 95% of the incident light having a wavelength ranging from about 300 nm to about 400 nm. Suitable anti-reflective coatings include magnesium difluoride (MgF2) coatings such as the ARSL0001 MgF2 coating supplied by Siltint Industries of the United Kingdom.
F-Theta lenses 128 and 140 are spaced apart from one another and from the rotating energy deflector 124 along the z-axis direction (i.e., the axis that is perpendicular to the scanning direction and the direction of movement of the linear scanning device 80). First F-Theta lens 128 is positioned between second F-Theta lens 140 and rotating energy deflector 124. Second F-Theta lens 140 is positioned between first F-Theta lens 128 and the solidifiable material 60 (as well as between first F-Theta lens 128 and a light opening in the housing, not shown in
First F-Theta lens 128 includes an incident face 130 and a transmissive face 132. Incident face 130 receives deflected solidification energy from rotating energy deflector 124. Transmissive face 132 transmits solidification energy from first F-Theta lens 128 to second F-Theta lens 140. Similarly, second F-Theta lens 140 includes incident face 144 and transmissive face 146. Incident face 144 receives solidification energy transmitted from transmissive face 132 of first F-Theta lens 128, and transmissive face 146 transmits solidification energy from second F-Theta lens 140 to a housing light opening (not shown in
In certain implementations of the linear solidification device of
As the rotating energy deflector 124 rotates, laser light will strike one of the facets 126a-126f. The rotation of rotating energy deflector 124 changes the angular orientation of the facet, which causes the deflected energy to travel through first F-theta lens 128 and second F-theta lens 140 and strike the solidifiable material in a linear pattern along the scanning (y) axis. As the next successive facet 126a-126f comes into optical communication with the laser light, a new scan line begins. Details of the operation of the linear scanning devices 50a and 50b are provided in U.S. Pat. No. 9,079,355, the entirety of which is hereby incorporated by reference.
As mentioned previously, many prior art systems use a solidification substrate such as glass 70 to planarize the surface of the solidifiable material. However, in such systems the energy incident to the resin at the solidification substrate is sufficient to cause solidification, and the solidifiable material hardens in contact with the substrate. As a result, a separation step is typically required to separate the newly formed exposed object surface 57 from the solidification substrate. However, examples of the present disclosure allow the distance between the glass 70 (and the exposed solidifiable material surface 63 on which it sits) and the focal point 62 to be set to create a non-solidification zone 61 (
The energy input to a given volume of solidifiable material is inversely proportional to the area of the incident laser light. Thus, for a circular laser spot, the incident amount of energy is inversely proportional to the square of the diameter of the spot. Two photon absorption tends to occur in relatively small volumes, which beneficially allows for greater object resolution. Thus, the spot size at focal point 62 is preferably no more than about 20 microns, more preferably no more than about 15 microns, and still more preferably no more than about 10 microns.
The energization state (ON or OFF) of laser 40 is preferably determined by data strings that includes time values at which the laser 40 is toggled on and off. Examples of such data strings are provided in FIGS. 16(d), 16(f), and 16(g) of U.S. Pat. No. 9,079,344. The linear scanning devices 50a and 50b each include a sensor 138 (
In order to solidify a line of solidifiable material along the scanning axis, the operation of the linear scanning devices 50a and 50b should be coordinated to ensure that the beams 51a and 51b intersect and are not spaced apart along the scanning (y) axis. It will not necessarily be the case that their respective solidification energy sensors 138 will be triggered at the same time due to differences in the rotation of their respective rotating energy deflectors 124.
Through experimentation, the operation of the motors used to rotate the rotating energy deflectors 124 in each linear scanning device 50a and 50b can be calibrated relative to one another to ensure that the beams 51a and 51b fully intersect. In one example, one of the sensors 138 for one of the linear scanning devices 50a and 50b may be used to toggle the laser 40 on and off. The other sensor 138 may be ignored or used to adjust the rotation of the rotating energy deflector 124 of the other linear scanning device 50a and 50b to ensure that the beams 51a and 51b intersect.
In the example of
Linear scanning devices 76a and 76b are configured similarly to linear scanning devices 50a and 50b of
During a solidification operation, the laser beams 75a and 75b are scanned along the scanning (y) axis as the movable assembly 72 travels along the travel (x) axis. The focal point 62 also scans along the scanning (y) axis. The two dimensional movement of the focal point 62 defines a focal plane 68 which is the plane that defines the locations at which linear scanning device output beams 75a and 75b may intersect. The operation of the rotating polygonal mirrors 124 in each linear scanning device 76a and 76b is preferably coordinated to ensure that the linear scanning device 76a and 76b output beams 75a and 75b intersect and are not spaced apart along the scanning (y) axis. Object data, such as data strings described previously, is used to toggle the energization state of laser 40 between ON and OFF.
The example of
A depiction of the internal components of linear scanning device 80 is provided in
In the example of
The linear scanning device 80 of
In all of the examples herein, a host computer provides object data to one or more controllers and/or microcontrollers that adjust the energization state of the laser 40, the translation of the movable assembly 48, 72 or linear scanning device 80 and the movement of the build platform 54, 64 along the build (z) axis. Also, in each example, a suitable translation assembly is provided to allow for the translation of the build platform 54, 64 along the build (z) axis and to allow for the translation of the movable assemblies 48, 72 and linear scanning device 80 along the travel (x) axis. Suitable translation assemblies may include motor-driven, pulley type assemblies of the type shown in U.S. Pat. No. 9,079,355 and allow the movable assemblies 48, 72 and scanning device 80 to travel smoothly along the travel (x) axis without allowing any movement along the scanning (y) axis or the build (z) axis. Thus, in each example, linear scan lines are formed along the scanning (y) axis as the movable assembly 48, 72 or linear scanning device 80 moves along the travel (x) axis.
Methods of using the apparatuses of
The apparatus of
A method of using the apparatus of
A method of using the apparatus of
In each of the examples described herein, the build platform 54, 64 may pause in its movement along the build (z) axis during the periods when solidification energy is being applied to the solidifiable material 60 or it may continue to move during those periods (i.e., “continuous build” processes may be used). The systems described herein are particularly well suited for continuous build processes because the obviate they need for separating a solidified object section from a solidification substrate (e.g., glass 70) after a section of the three-dimensional object is formed.
The present invention has been described with reference to certain exemplary embodiments thereof. However, it will be readily apparent to those skilled in the art that it is possible to embody the invention in specific forms other than those of the exemplary embodiments described above. This may be done without departing from the spirit of the invention. The exemplary embodiments are merely illustrative and should not be considered restrictive in any way. The scope of the invention is defined by the appended claims and their equivalents, rather than by the preceding description.
