**2. The principle of EFD jet deposition 3D printing**

#### **2.1. The basic principle**

(embedded electronic products, flexible electronics, and wearable devices) has been proposing wide scientific and practical engineering requirements for the multi-material and multiscale manufacturing technique. However, the existing manufacturing technologies are facing enormous challenges in the field of multi-material and multi-scale structure manufacturing

3D printing has shown great potential and broad engineering application prospect in the field of multi-material and multi-scale 3D structure manufacturing due to its advantages including (1) the shape complexity; (2) the material complexity; (3) the function complexity and so on. In recent years, in order to achieve the goal of functional driven integrated manufacturing of "material-structure-devices," 3D printing technology has been developed from traditional controlling shape to controlling properties, from printing single homogeneous material to printing multi-material or functional gradient material, from macro-scale to micro-scale or multi-scale including macro/micro/nanoscale. The functional structure electronics, as one kind of typical multi-material and multi-scale 3D printing product, which is composed of structural materials (plastics, polymers, ceramics, metals, etc.), conductive materials (the conductive silver paste, the nanosilver conductive ink, etc.), dielectric materials (various insulating materials), and semiconductor materials. The feature size of printed structure includes multi-scale (macro/micro/nanoscale) [4–10]. However, most of the existing 3D printing technologies are limited to print single material, and it is difficult to achieve the multi-scale (macro/micro/nanoscale) heterogeneous

Compared with other 3D printing processes, the 3D printing technologies (inkjet printing and electrohydrodynamic jet printing) based on materials' jet deposition have shown outstanding advantages for multi-material and multi-scale structure manufacturing. However, the inkjet printing is limited by the viscosity of printing material, which is usually less than 30cp. And the resolution of the current printed patterns is generally not more than 20 μm of line width. The electrohydrodynamic (EHD) jet printing [11, 12], which has been proposed and developed by Park and Rogers, has much higher resolution because of the Taylor cone induced by electric field. However, there are still many shortcomings and limitations as follows: (1) The height limitation of the printed structure, it is also difficult to achieve macro/ micro scale integrated printing due to the limitation of 3 mm for the distance between nozzle and substrate; (2) The insulating substrate and its thickness limitation [13]. (3) The big challenging for the conformal printing on the surface of an existing object, especially on the

In order to solve the problems of complex 3D structure manufacturing with multi-material and multi-scale, and to achieve the integrated manufacturing with heterogeneous multimaterial in macro/micro multi-scale. A novel high-resolution 3D printing, named as highresolution electric-field-driven jet 3D printing, which is based on the induced electric field and EHD cone-jetting behavior, has been developed to provide a feasible approach to implement additive manufacturing with multi-scale and multi-material at low cost. This chapter will introduce the principle, the simulation, the experiments, and the applications of EFD jet

[1–3].

24 3D Printing

3D structure manufacturing.

inclined and curved surfaces [14].

deposition 3D printing technology.

The electric-field-driven (EFD) jet 3D printing system is mainly composed of a printhead, a three-axis translation stage, a high-voltage power supply, a signal generator, and a material feeding unit. **Figure 1** shows the setup schematic of the EFD jet deposition 3D printing system. The nozzle of the printhead is directly connected to the anode of the high-voltage pulse power supply for inducing an electric field. The three-axis translation stage can be programmed to provide the planar movement of the target substrate for printing patterns and up-and-down movement of the nozzle for changing the intensity of the induced electric filed. Liquid materials are delivered to the printhead by the material feeding unit, which consists of a pneumatic control system and a material reservoir. The pneumatic control system can adjust the flow rate to optimize the shape of the pendent meniscus at the nozzle by changing the gas pressure. A signal generator is used to produce the modulated voltage command signal with desired frequency and duration to trigger the output of high-voltage power supply. The printing process can be recorded by a CCD camera.

Differing from the traditional pressure-driven 3D printing and the existing EHD jet printing, the proposed technique is a liquid ejection and deposition printing based on the electrostatic induction and EHD cone-jetting. The fundamental principle of the EFD jet 3D printing is illustrated in **Figure 2**. The printing process can be described as follows:


**Figure 1.** Schematic of system setup for the EFD jet deposition 3D printing.

coupling effect of the electric field force, surface tension, viscous force, and gas pressure, the meniscus will be elongated gradually to form a Taylor-cone.


**1.** In the pulsed cone-jet mode, the printing is a drop-on-demand process based on a pulsed voltage. When a pulsed voltage is applied, the meniscus will be deformed into Taylor-cone, and a micro-size jet is extracted to produce a micro-droplet. Then, the meniscus will be returned to the original position to produce a consistent and repeatable jet at the next pulse voltage. The printing material is deposited onto the substrate or the printed objects in the form of dots. The size of the printed dots is determined by process parameters involving the applied voltage, pulse duration time, and gas pressure, etc. The dots' spacing is mainly

High-Resolution Electric-Field-Driven Jet 3D Printing and Applications

http://dx.doi.org/10.5772/intechopen.78143

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**2.** In the continuous cone-jet mode, the DC-voltage is applied to drive and maintain the ejection behavior. The continuous liquid with a constant flow rate is rapidly pulled from the nozzle by the electric field force. Therefore, the printing material can be deposited on the substrate or the printed object in the form of lines (similar to FDM, but the dominant driving force is still the electric field force). Moreover, the line width is related to process parameters such as the voltage, the gas pressure, and the stage velocity, etc. The continuous cone-jet mode, based on continuous printing, possesses the ability of manufacturing largearea patterns and macro/micro-scale structures compared to the pulsed cone-jet mode.

Therefore, the proposed EFD jet deposition 3D printing possesses the following advantages: (1) suitable for both conductive and non-conductive (or insulating) substrates; (2) breaking through the height limitation of printed structures of traditional EHD jet printing; (3) it can be widely used for various printing materials with large range of viscosity; and (4) it also can be

In order to further reveal the injection molding mechanism and influencing rules of the processing parameters for EFD jet deposition 3D printing technology, this part will be focused on the investigation of printing performance under different conditions by means of numerical simulation and experimental verification. For the numerical simulation, the properties of substrate (or the printed layers), the printing height, and the variety of printing materials have been studied by the finite element simulation software (COMSOL MULTIPHYSICS), and the

simulation results are verified by experiments. The results can be seen as follows.

used to print on the uneven surface and the conformal surface.

**3. The numerical simulation and experiments verification**

determined by the pulse interval time and the moving speed of the X-Y stage.

**Figure 3.** Two working modes (a) pulsed cone-jet mode; (b) continuous cone-jet mode.

**5.** Regarding the first layer as the target substrate, then moving up the nozzle to keep the constant distance between the first layer and nozzle, a stable electric field will be reformed between the nozzle and the printed object, ensuring the stability and reliability of the process mentioned above. The thickness of the printing layer must be appropriately controlled to maintain a constant distance between the nozzle and the printed object. This process will be repeated until forming a desired 3D object.

#### **2.2. The two working modes**

Unlike the traditional macro-scale 3D printing and micro-scale 3D printing, the macro/ micro-scale 3D printing should take into account both the printing accuracy and the printing efficiency in the printing process [15, 16]. To ensure the capability of integrated printing of multi-scale complex 3D structure, and to better meet the requirements of the practical engineering of 3D printing. We proposed two kinds of working modes for this new technique, including the pulsed cone-jet mode and continuous cone-jet mode, to achieve both high precision and high efficiency during the printing process, as shown in **Figure 3**.

**Figure 2.** Schematic principle of the EFD jet deposition 3D printing: (a) the electrostatic induction between the nozzle and substrate; (b) stresses acting on the meniscus.

**Figure 3.** Two working modes (a) pulsed cone-jet mode; (b) continuous cone-jet mode.

coupling effect of the electric field force, surface tension, viscous force, and gas pressure,

**3.** When the tangential electric stress exceeds the surface tension during a single pulse, a droplet or fine jet from the apex of the cone will be produced. The droplet diameter and jet size are significantly smaller than nozzle size, indicating the EFD jet printing can overcome

**4.** The simultaneous control of the ejection and movement of the printhead or substrate allows precise deposition of materials on the substrate, forming the first layer of printing

**5.** Regarding the first layer as the target substrate, then moving up the nozzle to keep the constant distance between the first layer and nozzle, a stable electric field will be reformed between the nozzle and the printed object, ensuring the stability and reliability of the process mentioned above. The thickness of the printing layer must be appropriately controlled to maintain a constant distance between the nozzle and the printed object. This process

Unlike the traditional macro-scale 3D printing and micro-scale 3D printing, the macro/ micro-scale 3D printing should take into account both the printing accuracy and the printing efficiency in the printing process [15, 16]. To ensure the capability of integrated printing of multi-scale complex 3D structure, and to better meet the requirements of the practical engineering of 3D printing. We proposed two kinds of working modes for this new technique, including the pulsed cone-jet mode and continuous cone-jet mode, to achieve both high preci-

**Figure 2.** Schematic principle of the EFD jet deposition 3D printing: (a) the electrostatic induction between the nozzle

sion and high efficiency during the printing process, as shown in **Figure 3**.

the meniscus will be elongated gradually to form a Taylor-cone.

the resolution limitation from the nozzle size.

will be repeated until forming a desired 3D object.

object.

26 3D Printing

**2.2. The two working modes**

and substrate; (b) stresses acting on the meniscus.


Therefore, the proposed EFD jet deposition 3D printing possesses the following advantages: (1) suitable for both conductive and non-conductive (or insulating) substrates; (2) breaking through the height limitation of printed structures of traditional EHD jet printing; (3) it can be widely used for various printing materials with large range of viscosity; and (4) it also can be used to print on the uneven surface and the conformal surface.
