阅读说明：本技术 一种容积驱动3d打印流涎控制方法 (Volume-driven 3D printing drooling control method ) 是由 刘利 于 2020-11-19 设计创作，主要内容包括：本发明揭示了一种容积驱动3D打印流涎控制方法,其包括设置一可上下运动的驱动滑块,所述驱动滑块只能驱动注射器活塞向下运动而不能驱动其向上运动,在喷射时间终点前提前设定时间t关闭喷头,且同时将所述驱动滑块上提d-2距离,其中,d-2为1～10mm。本发明能够有效的解决喷嘴末端的流涎问题,提高打印成型质量。(The invention discloses a volume-driven 3D printing drooling control method, which comprises the steps of arranging a driving slide block capable of moving up and down, wherein the driving slide block only can drive an injector piston to move downwards but cannot drive the injector piston to move upwards, and when the injection time is set in advance before the end point of injection timeClosing the nozzle at time t and simultaneously lifting the driving slide block up by d 2 A distance of wherein d 2 Is 1-10 mm. The invention can effectively solve the problem of drooling at the tail end of the nozzle and improve the printing and forming quality.)

1. The volume-driven 3D printing drooling control method is characterized by comprising the following steps: the injector comprises a driving sliding block which can move up and down, wherein the driving sliding block can only drive an injector piston to move down but not drive the injector piston to move up, the nozzle is closed within a set time t before the end point of the injection time, and the driving sliding block is lifted up by a distance d, wherein d is 1-10 mm.

2. The volume-driven 3D printing drooling control method of claim 1, wherein: the set time t is 10-100 ms.

3. The volume-driven 3D printing drooling control method of claim 1, wherein: the driving slide block is in split type contact connection with the injector piston.

Technical Field

The invention belongs to the technical field of printing, and particularly relates to a volume-driven 3D printing drooling control method.

Background

The drooling is one of the key problems in the material spraying/extruding process and the realization of the accurate assembly of various materials, and the quality of drooling control is a key factor for evaluating the quality of the spray head and the spraying process thereof.

Under the condition of no control, the material sections described in the sections AB and CD in fig. 1a apply pulse signals to the nozzles to spray the material, and the middle section described in the section BC in fig. 1a does not apply pulse signals to stop spraying, that is, the pulse signals received by the nozzles are shown in fig. 1b, and the obtained spraying structure is shown in fig. 1c, which has a drooling phenomenon. The drooling phenomenon can lead to the accumulation of a large amount of material at the edge and above the stent where the material is not needed to be sprayed, and the macro-pore structure is easy to be damaged. When forming a composite stent, the free tip of the nozzle can accumulate a large amount of material and accumulate on the edge of the stent during the next forming operation, which can seriously affect the final injection molding result.

The delay compensation is the most common drooling control method, and the basic thought is as follows: the nozzle is turned on at a set time/distance (on delay) before the start point a and turned off at a set time/distance (off delay) before the end point B, and it is desired to stop the ejection of the material at the end point B. FIG. 2 shows the results of scanning three material paths with respective close delay times of 0ms, 10ms, 30ms, and 60ms, showing that more material still accumulates where it is not desired to eject material; the time delay control is adopted to improve the pores on the side surface of the rear bracket to a certain extent, but the material accumulation phenomenon still exists, and the problem of drooling is not completely solved, so that the drooling problem of the volume driving spray head cannot be solved by simply adopting a method of closing the time delay.

Therefore, there is a need to provide a new method for controlling the 3D printing drooling in the volume driving process to solve the above problems.

Disclosure of Invention

The invention mainly aims to provide a volume-driven 3D printing drooling control method, which can effectively solve the drooling problem at the tail end of a nozzle and improve the printing forming quality.

The invention realizes the purpose through the following technical scheme: a driving slide block capable of moving up and down is arranged, the driving slide block can only drive an injector piston to move down but not drive the injector piston to move up, the nozzle is closed within a preset time t before the end point of the spraying time, and the driving slide block is lifted up for a distance D, wherein D is 1-10 mm.

Furthermore, the set time t is 10-100 ms.

Furthermore, the driving slide block is in split type contact connection with the injector piston.

Compared with the prior art, the volume-driven 3D printing drooling control method has the beneficial effects that: can effectively solve the problem of drooling at the tail end of the nozzle and improve the printing and forming quality.

[ description of the drawings ]

FIG. 1a is a schematic illustration of a material path for an application case of the present invention;

FIG. 1b is a schematic diagram of a showerhead pulse signal control according to an embodiment of the present invention;

FIG. 1c is a schematic diagram of the spray forming results of the application of the present invention;

FIG. 2 is a schematic diagram of the results of injection molding using delay control of 0ms, 10ms, 30ms, and 60ms, respectively;

FIG. 3 is a schematic view showing the analysis of the force applied to the liquid in the head without spraying the material according to the present invention;

FIG. 4 is a schematic view of sectional pressure gradients of the nozzle in a filament extruding state according to the present invention;

FIG. 5 is a schematic diagram of the pressure and flow rate after the piston stops depressing in the present invention;

FIG. 6 is a control schematic of the present invention;

FIG. 7 is a schematic diagram of the results of injection molding with a height of 3mm and 10mm respectively by using the control method of the present invention;

FIG. 8a is a schematic front view of a spray formed stent using the control method of the present invention;

FIG. 8b is a schematic side view of an enlarged injection molded stent according to the control method of the present invention.

[ detailed description ] embodiments

Example (b):

analyzing the reason of salivation:

fig. 3 is a stress analysis of the state that the spray head does not spray the material. The syringe piston is forced by the drive mechanism to begin its downward movement, and the pressure of the fluid in the syringe can be approximated before the material is expelled from the nozzleConstant, its magnitude can be represented by equation 1:

(formula 1)

Wherein the content of the first and second substances,is the radius of the section of the material cylinder of the injector,in order to force the drive mechanism against the syringe plunger,in order to realize the gravity of the piston,is the friction force between the piston and the inner surface of the syringe.

At the nozzle, the liquid is subjected to gravitySurface tension ofAtmospheric pressureAction, and pressure protection of the liquid itselfIn equilibrium, i.e.

					(formula 2)

WhereinIs the density of the material in the solution,is the height of the liquid, and is,is the radius of the nozzle or nozzles,is at the atmospheric pressure and is,is a coefficient of surface tension of the material,is the contact angle.

The critical condition under which the material can be extruded isFrom this, the critical pressure at which the material starts to be ejected can be calculated as:

(formula 3)

The piston continues to be depressed further, so that liquid material can be extruded onto the table to begin the material injection and forming process.

The extruded high molecular solution/suspension material belongs to viscoelastic fluid, the viscous force in the injection process can cause axial pressure loss, and the analysis of the size of the viscous force is extremely important to the extrusion process. Assuming that the flow rate of the liquid in the syringe is fastest at the center and gets smaller closer to the wall, the velocity is 0 at the wall. Viscosity per unit areaThe size of (d) can be represented by the following formula:

(formula 4)

Wherein the content of the first and second substances,is a coefficient of viscosity of the material,is the velocity gradient at the wall.

Radial velocity in straight pipeThe distribution can be calculated by:

(formula 5)

WhereinIs the pressure gradient in the axial direction and,is the radius of the straight pipe,is the radius of the location.

From equation (5), the flow rate of the injected/extruded material can be calculated：

(formula 6)

From equation (6), the calculation of the pressure gradient can be deduced:

(formula 7)

The entire showerhead can be divided into four sections as shown in FIG. 4, assuming constant pressure gradient in each straight section, the pressure loss and the pressure gradient in each section can be seenLength, lengthFlow rate ofAnd is proportional to the viscosity coefficient of the material. Because the radius difference of the four sections is large, the pressure drop of only the finest section of the nozzle can be considered. Assuming constant velocity of extruded material at the nozzle, the volume drives the flow of material in four segments of the nozzleIf the viscosity is constant, the value of the viscous force per unit area in the circular tube can be calculated by the following formulas (4), (5) and (7):

(formula 8)

At the wall surface of the round tube (at this time)) The maximum viscous force is as follows:

(formula 9)

The calculation formula of the pressure drop of the nozzle at the finest section and the actual pressure of the liquid in the spray head can also be deduced:

		(formula 10)
					(formula 11)

Wherein、Andthe jet velocity at the nozzle, the radius of the nozzle and the length of the finest segment, respectively. It can be seen that the faster the spray velocity at the nozzle, the smaller the radius and the longer the size of the narrowest section of the nozzle, and the greater the viscosity coefficient of the material, the greater the pressure drop.

Substituting the actual values into the above equations estimates their respective value ranges.Surface tension coefficient of water intake 73X 10^-3 ，Taking the density of the solvent to be 1.03 multiplied by 10³ In this example, a 20mL syringe can be used, taking the length of materialIs 0.05Atmospheric pressureTake 1X 10⁵ . The calculation results are shown in table 1, the first five-element data are common parameters, and the sixth action limit condition. It can be seen that the process of material injection/extrusion generally requires providing a pressure about 1/10 higher than the critical pressure due to the viscous forces. It can also be seen from this calculation that the pressure required to extrude the material by the volume-driven nozzle is small (typically no more than 1.3 times atmospheric pressure), and the destructive effect on the material is relatively small.

TABLE 1 volume-driven spray head mechanics calculation results

Viscosity of the oil ()	Radius of nozzle ()	Nozzle length ()	Speed of injection ()	Surface tension ()	Maximum viscous force ()	Pressure drop ()	Total pressure ()
								0.824*	0.175	0.2	10	834.3	188.3	430.5	1.0076
0.824	0.1	0.2	10	1460.0	329.6	1318.4	1.0228
								0.824	0.1	0.5	20	1460.0	659.2	6592.0	1.0755
0.824	0.1	0.2	20	1460.0	659.2	2636.8	1.0360
								6.82**	0.15	0.2	10	973.3	1818.7	4849.8	1.0532
6.82	0.1	0.5	10	1460.0	2728.0	27280.0	1.2824

PLGA (20%) concentration=9 ten thousand) viscosity at zero shear rate;

20% concentration of PLGA (=20 ten thousand) viscosity at zero shear rate.

In addition, when forming mesh stents using the MSLM process, it is also necessary to overcome the resistance of the material build-up process, the magnitude of which is related to the ejection velocity and the ejection/scanning velocity ratio. It is assumed that the pressure difference to be provided for this purpose isThe actual pressure that the syringe piston needs to provide to the liquid is then:

(formula)12）

In fact the liquid is under extrusion pressure (~) There is a slight deformation, and since the pressure is small, elastic deformation can be assumed. In formula (12)Andrespectively the modulus of elasticity and the volume strain of the liquid in the syringe.

Based on the above analysis, it can be seen that drooling is mainly due to the pressure during extrusionAnd critical pressureIs caused by the difference in (c). The liquid material in the syringe being elastically deformed and the pressure difference therein（) And speed of injectionIn proportion (equation (10)), the pressure in the piston after the piston stops pressing down is increasedCannot be released rapidly (as shown in fig. 5), but is gradually reduced by continuing to extrude the material while simultaneouslyGradually reducing the injection velocityDynamic balance is maintained. Until the pressure in the liquid drops toVelocity of jetWhen the value is reduced to 0, the salivation stops. The liquid in the syringe is driven from the pressureDown toThe total amount of liquid to be squeezed out is:

(formula 13)

In addition, as shown in fig. 5, there is a lag in the drop in pressure at the injector barrel section compared to at the nozzle, which also contributes to drooling. Overcoming resistance to the process of material accumulationThe larger the drooling problem.

Difference between liquid pressure and critical pressure in nozzle（) In relation to the speed of the extruded material, a dynamic equilibrium is spontaneously maintained during the forming process, i.e. whenWhen increasing (reduced outlet resistance or increased piston pressure), the injector will automatically increase the injection rate to reach a new equilibrium, whenWhen the pressure decreases (the outlet resistance increases or the piston pressure decreases), the injection speed also decreases accordingly.

The drooling problem is mainly caused by the fact that most of the liquid in the spray head is not released quickly when the pressure of the liquid is higher than the critical pressure.

The control method of the embodiment comprises the following steps:

based on the principle, the embodiment provides a volume-driven 3D printing drooling control method, which includes setting a driving slider capable of moving up and down, where the driving slider can only drive an injector piston to move down but not to move up, setting a time t before the end of the jetting time to close a nozzle, and simultaneously lifting the driving slider by a distance D, where D is 1-10 mm.

The set time t is 10-100 ms.

The driving slide block and the syringe piston are installed separately, and only the driving piston can descend but cannot ascend. Lifting the drive slide at the end of the material pathPressure exerted on the pistonIs removed quickly and the utility model is removed quickly,syringe piston under pressureIs moved up rapidly by the action of the pressure-reducing valve to reduce the pressure of the material in the syringe toThereafter, the ejection of the material is stopped.

The results of the spray forming by the control method of the present embodiment are shown in fig. 7-8 b, and it can be seen from the scanning experiment results shown in fig. 7 and the stent forming experiment results shown in fig. 8a and 8b that the control method of the present embodiment can better control the drooling phenomenon, and the upper and lower surfaces and the side surfaces of the formed stent can both see better through pore structures without pore blockage and redundant materials.

This embodiment is based on the flexible control principle of pressure self-release, by setting a time (closing delay) before the end point B to remove the pressure on the syringe piston, the pressure inside the liquid is reduced below the critical pressure by pressing the piston upwards, without the problem of sucking air. As can be derived from fig. 3, the requirements that the pressure self-release flexible control scheme can function are:

（）

(formula 14)

Weight of the visible pistonFriction force of piston and syringeDiameter of nozzleHeight of material in syringeThe smaller the more favorable the diameter of the syringeThe larger the more advantageous. In addition, the surface tension coefficient of the materialThere are also effects. The usable syringe of this shower nozzle mainly is disposable syringe and glass syringe, and the weight of its piston and the frictional force of syringe all are less, and this has guaranteed to a certain extent that this scheme can solve the problem of drooling of shower nozzle.

What has been described above are merely some embodiments of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the inventive concept thereof, and these changes and modifications can be made without departing from the spirit and scope of the invention.