LOW-STRESS STEREOLITHOGRAPHY

Technical Field of the Invention

The invention is related to a Low-Stress Stereolithography comprising of a mobile tank that has a tilting structure that can carry out mobile laser and oscillation motion.

Known State of the Art (Prior Art)

At present two types of basic SLA methods have been presented to the market. The first one of these is the method invented by the American 3D SYSTEMS Company with the patent number US4575330A in its initially discovered state. In this method, a monomer and oligomer based, photosensitive resin contained in a tank, and a platform located inside this tank and resin, which can move sensitively at a vertical direction is present. An ultraviolet laser located at the top section of the tank freezes the photosensitive resin layer by layer and forms three-dimensional objects. After each layer, the vertically operating printing platform lowers down to the determined layer thickness and the resin is smoothed out on the surface with a scraper and the device operates again for a new layer. This method has been differentiated by using DLP based projectors instead of laser by different companies.

In the second method, a system has been conveyed that is also known as upside-down SLA, that has been revealed after the patent of 3D SYSTEMS company expired, which enables 3D printing of smaller sized parts. In this system, a photosensitive monomer and oligomer based resin with lower volume, with the bottom section being transparent is present in a tank and a platform is located on the tank, and at a distance to the layered determined from the tank. In this method, the ultraviolet light source; laser or diode, has turned into a system that provides printing in layers by operating at the bottom of the tank. The resin that is compressed between the printing platform and the bottom section of the tank is frozen via a light source and following this, the platform is elevated to the determined layer height or the tank is tilted forward in order for the previous frozen layer to be separated from the bottom of the tank and for the new layer of the new resin to be filled into this area. In this method, instead of the laser source, LCD based screens are used to provide a systematic light transition or projectors are used that utilize DLP technology. Moreover, by means of the newly developed resins, instead of ultraviolet rays, resins that are frozen with daylight have started to be used. The devices mentioned herein have a few points in common. These conditions do not affect the suggested method, however they may enable a better understanding of the method. Photosensitive resins are required for said products to be processed. In some systems, this resin is transferred from the main container automatically, where the machine adjusts the amount of the resin, however in other devices the resin is filled into the device by the user. The filling process is related to the automation of the device.

All of the mentioned devices are computer-controlled devices. In industrial type devices, the computer provided together with the device carries out layer calculation and how these layers shall be scanned by the laser and calculates the light amount to be used and the computer only requires receiving a 3 dimensional geometry file. In end-user type devices, the electronic and mechatronic infrastructure of the device does not comprise computers that can carry out these formulations and an external computer support is required in order to be able to carry out said calculations.

The movement carried out by the tank in the patent document numbered US 9452567 of the prior art, is a movement based on flexion. The movement of the tank is continuous up and down motion and this is carried by keeping one side of the tank stationary. The tank motion is a motion that enables to completely separate each layer after freezing. The tank motion has not been defined to be carried out for mixing the resin.

The movement carried out by the tank in the patent document numbered US 10201963 of the prior art, is a movement based on flexion. The motion carried out by the tank is a series of movements that comprise the flexion of the bottom surface of the tank from a single point or several points and this necessitates for the outer borders of the tank to be fixed. The bottom surface of the tank must be flexible for the mobile cylinder type removers to be able to function; however, this system is subjected to product fatigue and therefore to abrasion and wear. The tank motion is a motion that enables to separate a plurality of layers after freezing. The tank motion has not been defined to be carried out for mixing the resin. One of the most important problems among the principal problems of the upside-down SLA devices of the prior art, that are being sold in the market is that the bottom of the tank sticks to the polymer-based resin and therefore it is problematic to receive new resin.

Brief Description of the Invention and its Aims

The present invention is related to a Low-Stress Stereolithography that meets the requirements mentioned above, eliminates all of the disadvantages and brings about some new advantages.

The invention aims to solve one of the most important problems among the principal problems of the upside-down SLA devices of the prior art, that are being sold in the market which is the sticking of the polymer-based resin to the bottom of the tank which makes it difficult to receive new resin, to accelerate the printing speed by several fold and thereby to significantly shorten the total printing time.

The important topics have been listed below.

-Accelerating the printing speed by means of the suggested tank motion,

-Eliminating adhesion force formed during the transition between layers,

-Preventing the settlement of the resin mixture by continuously moving the resin used during printing,

- Eliminating the need for separating movements of the platform and the base of the tank that needs to be carried out vertically for each layer,

-Preventing the formation of entrapped air in the resin due to platform motion

The main aim of the invention is to provide a 3D printing method that is faster and more efficient and a device that can perform said printing.

Definition of the Figures of the Invention

The figures that have been prepared in order for the Low-Stress Stereolithography developed by means of this method to be better understood are described below.

Figure 1: Isometric view of the new resin tank, integrated to the upside-down SLA device. Figure 2: Top view and section line of the new resin tank, integrated to the upside-down SLA device.

Figure 3: Front view of the new resin tank, integrated to the upside-down SLA device. Figure 4: The step view of the operation of the new resin tank design integrated to the upside- down SLA device. Three tank positions have been shown. A letter has been assigned for each position and the critical motion mechanisms in said position have been enumerated next to the letters. The position titled as “Starting” where the process is started is coded with the letter “A” and the “Middle Position” where the process continues is coded with the letter “B” and the “End and Return” position where the process is ended and moved in the reverse direction is coded with the letter “C”. In these positions the “Printing Platform Lever” motion has been coded with the number “1” and the “Laser Source” motion has been coded with the number “2” and the “Tank” motion has been coded with the number “3”. Therefore the “Tank” motion described in the “Starting” motion has been shown as “3A”.

Each position has been numbered in itself.

Definitions of the parts/aspects/sections forming the invention

The parts/sections/aspects provided in the figures that have been prepared in order to further describe the Low-Stress Stereolithography developed by means of the invention have each been numbered and the references of each number has been listed below.

1 Structure

2 Printing platform rail

3 Printing platform lever

4 Printing platform

5 Tank

6 Photosensitive resin

7 Laser source

8 Laser beam

Detailed Description of the Invention

The novelty of the invention has been described with examples that shall not limit the scope of the invention and which have been intended to only clarify the subject matter of the invention. Said invention is related to Low-Stress Stereolithography.

The principal motion structure and its benefit have been shown in the section illustrated in Figure 4. The region where the section is taken and the angle of view has been shown in Figure 2. The number of the elements mentioned below in this section has shown in Figure 3. Some steps of the movement and the 3 positions that are thought to be descriptive of the phase that is reached until a printing layer is formed have been depicted in order to further describe the structure. Two steps need to be completed before reaching this said position. The first one is that the resin (6) that is required for printing should be placed inside the resin tank (5) and the second is that the object that is desired to be printed should have been delivered to the device.

In the first one of these motion steps, the printing platform (4) is positioned (1A) over the resin tank (5) in order to form the first layer. The distance between this place and the resin tank (5) is known as layer thickness.

The resin tank (5), has taken is placed at the starting position in order to form the layer. When the resin tank (5) is in this position, the resin tank (5) is rotated around the Y axis from the center and is eccentric at the X axis (3A). By means of this eccentricity and rotation, the edge of the resin tank (5) that is closest to the printing platform (4) is tangential. After this motion, the resin tank (5) shall continue its oscillation until the endpoint of the layer by centric movements (3B, 3C), accompanied by the laser beam (8).

The most important point of this oscillation motion carried out by the resin tank (5) under the printing platform (4), enables the oscillation motion to be carried out by the resin tank (5) without sliding. Therefore while this oscillation carried out by the resin tank (5) rotates around the Y axis from the point at the center in a controlled manner, it also enables the X axis to move. The laser source (7) is located under the resin tank (5), at the position (2A) where the resin tank (5) is closest to the printing platform (4). By means of this position it has taken, the laser beam (8) can perform radiation at the edge of the printing platform (4) vertical to the resin tank (5). While the laser beam (8) starts to form a layer, initially it shall scan at the Y axis and then it shall pass to the next position at the X axis. The movement amount carried out by the laser source (7) at the X axis can vary according to the diameter of the laser beam (8) and the amount of overlapping with the previous scan, however, this movement amount and the movement amount of the resin tank (5) carried out at the center (3A>3B>3C) of the X axis is the same. These series of motions shall continue during the layer forming process (2B, 2C).

If special fine-tuning is not conducted, the rest of all of the layers shall have the same thickness, therefore, the printing platform lever (3) shall lift the printing platform (4) at the end of every layer, at the Z axis, as much as the layer thickness distance. After the printing platform (4) is lifted at the Z axis to form the next layer thickness, the movements of the resin tank (5) and the laser source (7) shall continue at a reverse direction (3C>3B>3A) in order to form the next layer. When the resin tank (5) and the laser source (7) return to their starting positions, two layers will have been formed and this back and forth movement shall continue until all layers are formed.

The oscillation movements carried out by the resin tank (5) shall enable the resin (6) that is frozen to be separated from the resin tank (5) by means of a peeling motion. As this separation shall be as much as the line that is frozen at the Y axis by the laser beam (8) focal size, the separation force between the resin (6) and the resin tank (5), shall be much lower in comparison to the present upside-down SLA methods. By this means, it shall be prevented for the resin (6) to adhere strongly to the resin tank (5) and for it to come off from the printing platform (4).

The descriptions of the figures with reference to the part numbers have been listed below.

Structure (1): Structure is the main component of the SLA device. This element is a structural element to which all other elements are connected and to which the static and dynamic forces are transferred. The printing platform is coupled to the rail structure and this enables to keep the printing platform lever that moves over the rail, at a vertical angle.

Printing platform rail (2): The principal aim of the rail, is to enable the printing platform lever to move sensitively at the Z axis vertical to the resin tank. A motion transfer mechanism is used in connection with this rail. The propulsive power transmission tool used in this mechanism can be shaped according to requirements as a linear motor, trapezoid screw or ball screw. It does not have an impact on the suggested method.

Printing platform lever (3): The part between the printing platform and the carrier rail, is a carrier that reaches the mid section of the tank in order to be able to provide perpendicularity and to be able to provide positioning. One of the principal aims of this lever is to able to keep the printing platform vertical to the tank and to ensure that it has surface contact when the printing platform is lowered down onto the surface of the tank. Various precision settings are available on the printing platform lever to provide this. It is accepted that in the suggested method perpendicularity and surface contact is present.

Printing platform (4): This is the platform were the frozen photosensitive resin sticks onto. This platform, moves at the Z axis sensitively on the rail by virtue of the platform lever and enables to produce a layered structure. It is important for the base of the platform to be flat, so that the frozen resin can adhere (stick) successfully. The distance of this part to the tank base affects the time that the frozen resin needs to be subjected to laser beams and therefore the printing speed. At the same time, this distance affects the solubility of the output product and the level of surface smoothness.

Tank (5): This tank which is transparent or nearly transparent at the bottom section and whose side walls are made of various materials (Polymethyl Methacrylate (PMMA), Polycarbonate (PC), Polyethylene Terephthalate (PET), Styrene Acrylonitrile (SAN), Acrylonitrile Styrene Acrylate (ASA) etc.), forms the basis of the claimed method. The infrastructure of the proposed tank, is different from the other extant examples. The bottom of the tank has been designed to be inclined as a part of the cylinder. This bottom section is usually provided as a plane, with holes, with slits or smooth. The operation principle of the inclined surface that has been provided to overcome the high forces created due to the adhesion formed by a plane, is based on peeling motion. By means of the eccentric rotation of the cylinder part formed by the bottom section of the tank and at the same time its oscillation at the X axis, creates a cradle swinging motion for the tank and the claimed movement is established. If the bottom surface of the tank is formed of a material that is non-stick and hydrophobic (Fluorinated Ethylene Propylene (FEP), polytetrafluoroethylene (PTFE) etc.), this shall enable easy removal of the resin that is frozen between the tank base and the printing platform, from the base of the tank.

Photosensitive resin (6): The SLA resin types used in today's technology are designed to have photosensitivity between 365nm to 450nm. However, resins that are more than 405nm are called daylight resin instead of ultraviolet resin. In the claimed system, the type of resin does not affect the system.

Laser source (7): The compatibility between the laser beam and the resin used is important. As laser sources have a more limited scope in comparison to other light sources in terms of the frequency range, it is important to select the correct frequency in order to efficiently freeze the resin. The power of the laser source and the focusing on the area to be frozen plays an important role in freezing the resin. However, the laser type that is used does not play a significant role in the operation of the claimed system. An important point is to provide a controlled movement of the laser at the X and Y axes using a movement that can address the entire printing platform. The type of transfer organs that are to be used to provide a movement mechanism is not important for the claimed system.

Laser beam (8): Correct focusing and a precise focus need to be provided for the laser beam to operate efficiently. What is important for the claimed system is that the focused laser beam is vertical to the point where the bottom section of the tank is closest to the printing platform and that the laser keeps following this point and the resin freezing process is carried out at this exact location. The movement of the tank subject to the invention does not constitute flexion, thereby any kind of deformation is not present. The movement of the tank subject to the invention is a cradle swinging motion and it is bi-directional, and the tank is not fixed to any one side. The movement of the tank subject to the invention is a continuous motion that does not aim to peel off the entire layer but to peel off each frozen line. The movement of the tank subject to the invention enables to mix the resin by means of the continuous swinging motion.

The bottom surface of the tank subject to the invention is not totally flexible, it is made of rigid material and it is not subjected to friction and it will not lose its rigidity.

The movement of the tank subject to the invention is a continuous motion that aims to peel off each frozen line. The movement of the tank subject to the invention enables to mix the resin by means of the continuous swinging motion.

• The invention is a Low-Stress Stereolithography device that utilizes Photosensitive resin (6) that freezes between the tank base and the printing platform and that can be peeled off from the base of the tank following the freezing process, characterized by comprising; · A structure (1) to which all other elements are connected and to which the static and dynamic forces are transferred,

• A printing platform rail (2) that enables the printing platform lever (3) to move sensitively at the Z axis vertical to the resin tank and comprises a motion transfer mechanism attached thereto, · The part between the printing platform and the carrier rail is a carrier printing platform lever (3) that reaches inside the tank to be able to provide perpendicularity and to be able to provide positioning, • Printing platform (4) on which the photosensitive resin freezes and which enables to produce a layered structure by being moved with the platform lever on the rail, sensitively at the Z axis,

• A tank (5) that has a bottom section and side walls, and an inclined cylindrical part at the bottom section, which performs a rotation motion at the X axis under the printing platform (4) and around the Y axis located at the center by means of a mechanism and at the same time performs a swinging motion at the X axis, by virtue of its linear skid structure,

• A laser source (7) that enables the laser to move in a controlled manner at the X and Y axes in order to freeze the resin and that is positioned under the resin tank (5), at the location where the resin tank (5) is closest to the printing platform (4), and carries out irradiation by means of the laser beam (8) vertical to the resin tank (5), at the edge of the printing platform (4),

• Laser beam (8) that is vertical to the point where the bottom section of the tank is closest to the printing platform to provide the resin freezing process and that continuously follows this point in order to form a layer.

The most important point of this oscillation motion carried out by the resin tank (5) under the printing platform (4), enables the oscillation motion to be carried out by the resin tank (5) without sliding.

As this separation, shall be as much as the line that is frozen at the Y axis by the laser beam (8) focal size, the separation force between the resin (6) and the resin tank (5), shall be much lower in comparison to the present upside-down SLA methods. By this means, it shall be prevented for the resin (6) to be adhered strongly to the resin tank (5) and for it to unintentionally come off from the printing platform (4).

Operation method of the Low-Stress Stereolithography comprising the following steps;

• The resin (6) that is required for printing is placed inside the resin tank (5) and the object that is desired to be printed is delivered to the device,

• The printing platform (4) is positioned (1A) on the resin tank (5) in order to form the first layer, • The resin tank (5) is positioned at the starting position (3 A) in order to form the layer.

• The laser source (7) is located under the resin tank (5), at the position (2A) where the resin tank (5) is closest to the printing platform (4).

• While the laser beam (8) starts to form a layer, initially it shall scan at the Y axis and then it shall pass to the next position at the X axis.

• These series of motions shall continue during the layer forming process (2B, 2C)

• When the resin tank (5) is in this position, the resin tank (5) is rotated around the Y axis from the center and is eccentric at the X axis (3A).

• By means of this eccentricity and rotation, the edge of the resin tank (5) that is closest to the printing platform (4) becomes tangential and the laser beam (8) continues to scan this tangential line,

• After this motion, the resin tank (5) shall continue its oscillation until the endpoint of the layer by centric movements (3B, 3C), accompanied by the laser beam (8),

• As long as special fine-tuning is not conducted, the rest of all of the layers shall have the same thickness and the printing platform lever (3) shall lift the printing platform (4) at the end of every layer, at the Z axis, as much as the layer thickness distance,

• After the printing platform (4) is lifted at the Z axis to form the next layer thickness, the movements of the resin tank (5) and the laser source (7) shall continue at a reverse direction (3C>3B>3A) in order to form the next layer,

• When the resin tank (5) and the laser source (7) return to their starting positions, two layers will have been formed and this back and forth movement shall continue until all layers are formed.

According to a preferred embodiment of the invention, the device is a device that utilizes the above-mentioned method.

According to a preferred embodiment of the invention, the said motion transfer mechanism comprises a propulsive power transmission tool.

According to another preferred embodiment of the invention the propulsive power transmission tool used is a linear motor, trapezoid screw or ball screw. According to a preferred embodiment of the invention, the bottom section of the tank is made of transparent or nearly transparent material and its side walls are made of materials such as Polymethyl Methacrylate (PMMA), Polycarbonate (PC), Polyethylene Terephthalate (PET), Styrene Acrylonitrile (SAN), and Acrylonitrile Styrene Acrylate (ASA). According to a preferred embodiment of the invention, the bottom surface of the tank (5) is made of a material that is non-stick and hydrophobic such as Fluorinated Ethylene Propylene (FEP), and polytetrafluoroethylene (PTFE).