Patent Description:
3D printing technology refers to a device that uses 3D printing technology to produce real three-dimensional models. The basic principle is to use special consumables (glue, resin or powder, etc.) to form a 3D entity by bonding each layer of powder through the deposition of a binder according to a three-dimensional model pre-designed by a computer. At present, a variety of different 3D printing forming processes have been formed, such as Stereolithography (SLA), Laminated Object Manufacturing (LOM), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), 3D Printing (3DP), DLP 3D printing, etc. But for now, FDM and other technologies have poor precision, need to continuously melt the material filament and wait for the material to solidify, and the overall molding speed is slow. Digital Light Processing (DLP) 3D printing technology uses DLP optical machine or projector as the light source, and adopts the method of layered printing. The printing platform first rises and then descends, leaving the thickness of a slice layer with the resin tank. Layer-by-layer exposure can be completed, and the printing speed has been faster than other printing methods.

With the further increase in the production demand for DLP 3D printing technology, the layered molding method can no longer meet the market's requirements for printing speed. In recent years, a series of continuous forming technologies for DLP 3D printing have emerged. Including the continuous interface production technology (CLIP) based on oxygen-inhibited curing invented by the University of North Carolina in <NUM>. In <NUM>, Song Yanlin's team from the Institute of Chemistry, Chinese Academy of Sciences invented an ultra-low adhesion manufacturing interface inspired by the surface smoothness of Nepenthes. In <NUM>, Walker D A and others from Northwestern University in the United States invented a large-scale fast DLP 3D printing method based on liquid-liquid interface. All of the above methods can increase the speed of DLP 3D printing, but limited by the leveling speed of the photosensitive resin, the range of applicable models is limited.

In <NUM>, Liu et al. based on the ultra-low adhesion interface designed by Song Yanlin, by combining delamination with continuous printing, and proposing the key parameter of the maximum resin filling distance during continuous printing, which increases the range of model adaptation. In <NUM>, Li YD et al. based on Walker D A's liquid-liquid interface printing method, and proposed a 3D printing method combining model-guided layering and continuous. Based on the method of Liu et al. , the optimal lifting height of layered printing is proposed to reduce the layered printing time, and the method proposed by Li YD et al. can be adapted to most models. However, the parameters are determined by experiments and the efficiency is not high, which is greatly affected by the environment, and the parameters that can be optimized are limited. These have seriously affected the application of DLP 3D printing technology. The article "<NPL>et al and <CIT> disclose relevant background art.

The invention provides a method for efficient optimization and generation of rapid DLP 3D printing parameters. The liquid-liquid interface printing scene was simulated by the Volume of Fluid (VoF) method, and the flow behavior of the resin between the printed object and the fluorinated oil after printing a layer of slices was recorded. Then based on Poiseuille flow, Jacobs working curve and Lambert-Beer law are used to express resin curing time for continuous and layered printing, maximum fillable distance (MFD) for continuous printing, optimal lift distance (OLH) for layered printing and The control parameters of the printing platform lifting speed corresponding to the two methods. By adopting a proposed method for optimizing the control parameters of rapid DLP 3D printing that combines continuous and layered molding, rapid printing of any model can be achieved by obtaining the optimal control parameters.

In order to solve the above-mentioned technical problems, the embodiment of the present invention adopts the following technical solutions:
A method for efficient optimization and generation of rapid DLP 3D printing parameters, including the following steps:.

Among them, slice the three-dimensional model to be printed to obtain the slice number i. Determine the printable area of each slice, and calculate the maximum value DMAX[i] of the shortest distances from all points in the printable area of each slice to its boundary points. Step <NUM> includes:.

Among them, based on the standard solver of the open source computational fluid dynamics (CFD) software OpenFOAM. And according to the liquid-liquid two-phase flow printing scene of resin-fluorinated oil, the VoF model is used to establish a numerical simulation model. Step <NUM> includes:.

Among them, establish a Cartesian coordinate system according to the printing scene. According to the DMAX[i] obtained in step <NUM> and the numerical simulation model established in step <NUM>, the Poiseuille flow characteristic analysis is used to obtain the print mode of each slice. Step <NUM> includes:.

The origin of y is the interface between the fluorinated oil and the resin, indicating the distance from the interface. The origin of x is the interface between the fluorinated oil and the resin perpendicular to the edge of the printed object, indicating the distance of resin filling. At the same time, there is a boundary condition: <MAT> where u is the maximum speed of the resin moving in the x-axis. us is the slip speed. Hs is the height of the printing platform. <MAT> is the pressure gradient. µ<NUM> is the viscosity of the resin. The integral of formula (<NUM>) is: <MAT>.

Here C<NUM> and C<NUM> are constants. By substituting the boundary condition equation (<NUM>) into equation (<NUM>), then can get: <MAT> <MAT> <MAT>.

According to the linear slip settings of the scene, it can get: <MAT>.

Where Ds is the slip length, according to formula (<NUM>) (<NUM>) (<NUM>) can be obtained: <MAT> <MAT>.

According to formula (<NUM>), the volume flow Q between the printing model with width W and the fluorinated oil can be obtained as: <MAT>.

Then the average flow rate of the photosensitive resin is: <MAT>.

At time t<NUM> when the platform rises, there is a relationship between the resin filling distance Lr and the time variable t in one direction: <MAT> vm is the speed of the printing platform during the rising process. t<NUM> is the resin filling time when the filling distance is Lr. This is the continuous printing resin filling time;.

The boundary between continuous printing and layered printing needs to determine the maximum filling distance of the continuous printing resin. This distance needs to be less than DMAX[i]. Then the gap left after the printing platform is raised within the time <NUM>/fn of single-frame playback needs to be supplemented Completely. At the same time, it is ensured that the resin filling the gap can be completely cured before the next frame of image is played. And the printing platform rises slowly in continuous printing. The combination formula (<NUM>) has: <MAT>.

The maximum filling distance of continuous printing resin can be obtained, the corresponding DMAX[i]': <MAT>.

Therefore, if the slice's DMAX[i] > DMAX[i]', the slice is printed by layered molding. If the slice's DMAX[i] ≤ DMAX[i]', it is printed by continuous molding.

According to the slice printing mode obtained in step <NUM>, take the slices printed in continuous mode. Calculate the rising speed of the continuous forming printing platform according to the Lambert-Beer law, and write it into the printing configuration file. Step <NUM> includes:
Taking the slices of continuous molding and printing obtained in step <NUM>, according to the Lambert-Beer law: <MAT> where P(z) is the optical power at a certain depth z away from the printing interface.

The unit of depth z is µm. The unit of optical power is mW/cm<NUM>. Po is the power at the curing interface. The curing interface is the resin The interface with fluorinated oil. Therefore the critical curing energy Ec of the slice at z has: <MAT>.

Under the premise of guaranteeing curability, the relationship between the rising speed vm of the printing platform for continuous printing and the maximum curable layer thickness z is: <MAT>.

Determine the layer thickness of the slice to be printed according to the user's printing needs. Calculate the rising speed of the continuous printing platform according to formula (<NUM>). Write the rising speed of the continuous printing platform and the corresponding slice layer number into the printing configuration file.

Among them, according to the slice printing mode obtained in step <NUM>, obtain slices printed in a layered manner. Calculate the relationship between its resin leveling time and other control parameters. And according to Jacobs work curing curve to obtain the expression of layered resin curing time, and write the obtained control parameters into the printing configuration file. Step <NUM> includes:
Take the slices printed by layered molding obtained in step <NUM>. The time for the resin to flow from Lr to DMAX[i] is denoted as t<NUM>. According to formula (<NUM>), there are: <MAT>.

The time T for layered printing resin filling is recorded as: <MAT>.

According to formula (<NUM>), the slip length Ds is much smaller than the lifting height Hs of the printing platform. Therefore, it is considered that (Hs - Ds)/(Hs - 4Ds) is a constant C<NUM> greater than <NUM>. Then the relationship between the optimal lifting height of the printing platform and the resin filling time T corresponding to the minimum resin filling time of layered printing: <MAT>.

The Hs obtained at this time is the optimal lifting height for layered printing;
The resin curing time model is established according to the Jacobs working curing curve: <MAT> where Cd is the curing depth. Dp is the transmission depth. Eo is the light energy accumulated by the DLP light source at the curing interface. Ec is the critical exposure for resin curing under UV light. The unit of curing depth and transmission depth is µm. The unit of light energy is mw/cm<NUM>. The unit of critical exposure is mw/cm<NUM>. Therefore, for slices with different layer thicknesses printed in layers, the curing time t<NUM> can be expressed as: <MAT>.

Determine the layer thickness of the slice to be printed according to the user's printing needs. Calculate the optimal lifting height of the layered molding printing platform according to the formula (<NUM>). According to this, you can also obtain the printing platform rising speed. Determine the curing time of the layered molding resin according to the formula (<NUM>). Write the optimal lifting height of the printing platform, the rising speed of the printing platform, the resin curing time and the corresponding slice layer number into the printing configuration file.

Further, before printing starts, use camera monitoring to determine the printing origin, and then complete the printing step <NUM> according to the printing configuration file, including:.

A method for efficient optimization and generation of rapid DLP 3D printing parameters according to an embodiment of the present invention has the following advantages:.

Hereinafter, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that, the embodiments in the present application and the features in the embodiments may be arbitrarily combined with each other if there is no conflict.

The invention provides a method for efficient optimization and generation of rapid DLP 3D printing parameters. The liquid-liquid interface printing scene is simulated by the VoF method, and the flow behavior of the resin between the printed object and the fluorinated oil after printing a layer of slices is recorded. Then, based on Poiseuille flow, Jacobs working curve and Lambert-Beer law, it is used to express the resin curing time of continuous and layered printing, the maximum filling distance of continuous printing, the best lifting distance of layered printing, and the corresponding printing of the two methods. These control parameters of the platform lifting speed. By adopting a proposed method for optimizing the control parameters of rapid DLP 3D printing, rapid printing of any model can be achieved by obtaining the optimal control parameters.

DLP technology is considered to have the production efficiency that matches traditional manufacturing due to its faster printing speed. With the further increase in the demand for DLP 3D printing technology production. The layered printing method can no longer meet the requirements of the market for printing speed. A series of continuous forming technologies for DLP 3D printing have emerged in recent years. However, limited by the leveling speed of the photosensitive resin, the above methods are mostly used to print hollow models, and are difficult to apply to models with many large-sized solid slices. The method of the embodiment of the present invention has problems in continuous printing under the condition of ensuring model adaptation. A method for efficient optimization and generation of rapid DLP 3D printing parameters is proposed to improve printing efficiency and adaptability to model slices of any size. <FIG> is a schematic diagram of the composition of the device applying the example of the present invention, including a DLP light source <NUM>, a resin tank <NUM>, a printing platform <NUM> and a lead screw <NUM>, wherein the resin tank <NUM> is located directly above the DLP light source <NUM>, and the DLP light source and the lead screw <NUM> are respectively connected with Connect to the control host computer. The resin tank is filled with fluorinated oil <NUM> and resin <NUM> before printing starts. The DLP light source <NUM> projects a two-dimensional slice of the model to be printed onto the interface between the fluorinated oil <NUM> and the resin <NUM> in the resin tank <NUM>. The resin is induced to change from a liquid state to a solid state by ultraviolet light, and is cured into a printing object <NUM> and bonded to the printing platform <NUM>. The lead screw <NUM> drives the printing platform to move. The resin flows into the gap between the cured layer and the fluorinated oil. After that, the above steps are repeated until the curing of the printed model is finally completed.

<FIG> is a flowchart of a method for optimizing control parameters of rapid DLP 3D printing according to an embodiment of the present invention.

The embodiment of the present invention proposes a method for efficient optimization and generation of rapid DLP 3D printing parameters, including:.

Wherein, the processing step <NUM> includes:.

At time t<NUM> when the platform rises, there is a relationship between the resin filling distance Lr and the time variable t in one direction: <MAT>.

Therefore, if the slice's DMAX[i] > DMAX[i]', the slice is printed by layered molding. If the slice's DMAX[i] ≤ DMAX[i]', it is printed by continuous molding. <FIG> shows the results of the layered and continuous confirmation of the tower model, in which <NUM> is the continuous forming and printing slice layer, and <NUM> is the layered forming and printing slice layer.

Among them, continuous molding and layered molding are defined as follows:
Continuous molding, that is, the surface exposure printer continues to rise without stopping and does not fall, and it takes a short time to print one layer, which is suitable for slicing layers with small DMAX[i], Layered molding means printing a layer of images with a light source with a grayscale of <NUM>. At this time, the printing platform first rises and then falls. At this time, the photosensitive resin has been fully leveled, which is suitable for slice layers with large DMAX[i].

Sub-step <NUM>, determine the layer thickness of the slice to be printed according to the user's printing needs. Calculate the rising speed of the continuous printing platform according to formula (<NUM>). Write the rising speed of the continuous printing platform and the corresponding slice layer number into the printing configuration file.

The step <NUM> includes:
Sub-step <NUM>, take the slices printed by layered molding obtained in step <NUM>. The time for the resin to flow from Lr to DMAX[i] is denoted as t<NUM>. According to formula (<NUM>), there are: <MAT>.

The Hs obtained at this time is the optimal lifting height for layered printing.

Sub-step <NUM>, The resin curing time model is established according to the Jacobs working curing curve: <MAT> where Cd is the curing depth. Dp is the transmission depth. Eo is the light energy accumulated by the DLP light source at the curing interface. Ec is the critical exposure for resin curing under UV light. The unit of curing depth and transmission depth is µm. The unit of light energy is mw/cm<NUM>. The unit of critical exposure is mw/cm<NUM>. Therefore, for slices with different layer thicknesses printed in layers, the curing time t<NUM> can be expressed as: <MAT>.

Sub-step <NUM>, determine the layer thickness of the slice to be printed according to the user's printing needs. Calculate the optimal lifting height of the layered molding printing platform according to the formula (<NUM>). According to this, you can also obtain the printing platform rising speed. Determine the curing time of the layered molding resin according to the formula (<NUM>). Write the optimal lifting height of the printing platform, the rising speed of the printing platform, the resin curing time and the corresponding slice layer number into the printing configuration file.

Claim 1:
A method for efficient optimization and generation of rapid Digital Light Processing, 3D printing parameters, comprising the following steps
Step <NUM>: Slice a three-dimensional model to be printed to obtain a slice number i, determine a printable area of each slice, and calculate a maximum value DMAX[i] of shortest distances from all points in the printable area of each slice to its boundary points;
Step <NUM>: Based on a standard solver of an open source computational fluid dynamics (CFD) software OpenFOAM®, and according to a liquid-liquid two-phase flow printing scene of resin-fluorinated oil, a Volume of Fluid model is used to establish a numerical simulation model;
Step <NUM>: Establish a Cartesian coordinate system according to the printing scene, according to the DMAX[i] obtained in step <NUM> and the numerical simulation model established in step <NUM>, Poiseuille flow characteristic analysis is used to obtain a print mode of each slice;
Step <NUM>: according to the slice printing mode obtained in step <NUM>, obtain slices printed in a continuous manner, calculate a rising speed of the continuous forming printing platform according to Lambert-Beer law and write it into a printing configuration file;
Step <NUM>: According to the slice printing mode obtained in step <NUM>, obtain slices printed in a layered manner, calculate a relationship between its resin leveling time and other control parameters, and according to Jacobs working curve to obtain an expression of layered resin curing time, and write the obtained control parameters into the printing configuration file;
Step <NUM>: Before printing starts, use camera monitoring to determine a printing origin, and then complete the printing according to the printing configuration file.