**3D Printing and Engineering**

available to many more people, which contributes to an increase and improvement of serv‐

This book, ''3D Printing'', is divided into two parts: the first part is devoted to the relation‐ ship between 3D printing and engineering, and the second part shows the impact of 3D printing on the medical sector in general. There are five sections in the first part (sections are dedicated to stereolithography, new techniques of high-resolution 3D printing, application of 3D printers in architecture and civil engineering, the additive production with the metal components and the management of production by using previously mentioned technology

There are four chapters in the second part dedicated to medicine with the following topics: education of medical staff through surgical simulations, tissue engineering and potential ap‐

I would like to express my sincere gratitude to all the authors and coauthors for their contri‐ butions. The successful completion of the book, "3D Printing", has been the result of the cooperation of many people. I would especially like to thank the Publishing Process Manag‐

> **Dragan Cvetković** Singidunum University

Faculty of Informatics and Computing

Belgrade, Republic of Serbia

ices, systems, materials and methods of usage.

plications of 3D printing in ophthalmology and orthopedics.

er Ms. Danijela Sakić for her support during the publishing process.

in more complex ways).

VIII Preface

**Chapter 1**

**Provisional chapter**

**Stereolithography**

**Abstract**

**1. Introduction**

**Stereolithography**

Christina Schmidleithner and Deepak M. Kalaskar

Christina Schmidleithner and Deepak M. Kalaskar

SLA process and propositions to resolve these are offered.

**Keywords:** stereolithography (SLA), digital light processing (DLP), additive

manufacturing (AM), 3D printing, two-photon polymerization (TPP), continuous liquid

As the oldest additive manufacturing (AM) technology, stereolithography (SLA) was first developed by Dr. Hideo Kodama in 1981. He saw it as a fast and low-cost method of reconstructing models in 3D space as an alternative to holographic techniques [1]. The first commercially available SLA printer was patented in 1986 by Charles W. Hull, who founded 3D Systems Inc. Their aim was to facilitate rapid prototyping of plastic parts [2]. With the development of a variety of processes, SLA has far surpassed its initial applications in modeling and prototyping and can be utilized to manufacture highly complex and individually designed geometries. The material is also no longer limited to conventional polymers, but the fabrication

DOI: 10.5772/intechopen.78147

The stereolithography (SLA) process and its methods are introduced in this chapter. After establishing SLA as pertaining to the high-resolution but also high-cost spectrum of the 3D printing technologies, different classifications of SLA processes are presented. Laserbased SLA and digital light processing (DLP), as well as their specialized techniques such as two-photon polymerization (TPP) or continuous liquid interface production (CLIP) are discussed and analyzed for their advantages and shortcomings. Prerequisites of SLA resins and the most common resin compositions are discussed. Furthermore, printable materials and their applications are briefly reviewed, and insight into commercially available SLA systems is given. Finally, an outlook highlighting challenges within the

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78147

interface production (CLIP)

#### **Stereolithography Stereolithography**

Christina Schmidleithner and Deepak M. Kalaskar Christina Schmidleithner and Deepak M. Kalaskar

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.78147

#### **Abstract**

The stereolithography (SLA) process and its methods are introduced in this chapter. After establishing SLA as pertaining to the high-resolution but also high-cost spectrum of the 3D printing technologies, different classifications of SLA processes are presented. Laserbased SLA and digital light processing (DLP), as well as their specialized techniques such as two-photon polymerization (TPP) or continuous liquid interface production (CLIP) are discussed and analyzed for their advantages and shortcomings. Prerequisites of SLA resins and the most common resin compositions are discussed. Furthermore, printable materials and their applications are briefly reviewed, and insight into commercially available SLA systems is given. Finally, an outlook highlighting challenges within the SLA process and propositions to resolve these are offered.

DOI: 10.5772/intechopen.78147

**Keywords:** stereolithography (SLA), digital light processing (DLP), additive manufacturing (AM), 3D printing, two-photon polymerization (TPP), continuous liquid interface production (CLIP)

### **1. Introduction**

As the oldest additive manufacturing (AM) technology, stereolithography (SLA) was first developed by Dr. Hideo Kodama in 1981. He saw it as a fast and low-cost method of reconstructing models in 3D space as an alternative to holographic techniques [1]. The first commercially available SLA printer was patented in 1986 by Charles W. Hull, who founded 3D Systems Inc. Their aim was to facilitate rapid prototyping of plastic parts [2]. With the development of a variety of processes, SLA has far surpassed its initial applications in modeling and prototyping and can be utilized to manufacture highly complex and individually designed geometries. The material is also no longer limited to conventional polymers, but the fabrication

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


**Table 1.** Comparison of average lateral resolution and surface roughness of AM technologies for polymers and of soft lithography.

of composites [3] and even metallic [4] or ceramic [5] specimens is possible. However, to date, SLA is only being utilized to structure one material at a time, and when comparing to other additive manufacturing (AM) technologies, typical SLA processes exhibit superior resolution and better surface qualities (see **Table 1**) but at slower printing times and higher cost.

**2.1. Free and constrained surface approach**

layer [14].

In the **free surface approach**, the building platform on which the printed part grows is situated in a tank of resin and coated with a liquid resin film. Illumination of the desired crosssection, which happens from above the resin bath, cures the first layer. After each layer, the platform with the growing part (i.e. the z-stage), is lowered further into the tank, and new resin is coated on top with a mechanical sweeper. This sets the stage for the subsequent

Stereolithography

5

http://dx.doi.org/10.5772/intechopen.78147

**Figure 1.** Classification of SLA according to irradiation method (left) and direction of incident light (right).

The **constrained surface approach** or bottom-exposure approach has a building platform, which can be suspended above the resin bath. Illumination from below, through the transparent floor, cures a layer of resin between building platform and vat floor. This layer adheres to the platform, as the z-stage is raised by a defined distance. As each layer is cured, the building platform with the adhered part is elevated, and the part grows suspended from the platform downward [6]. As with the free surface setup, support structures made from the same printing material are needed in case of overhangs and undercuts to ensure adequate adhesion to the platform.

Recently, there has been a trend toward the bottom-exposure approach, as it has certain advantages [6, 15, 16]. The smooth surface, which is created with a narrowly defined layer height due to the precise movement of the z-stage at an accuracy of down to 0.1–1 μm [17, 18], is the main benefit in the constrained surface setup. Without the need for a mechanical sweeper, this layer can be created faster than in the free surface approach, reducing the printing time [15]. Another advantage, which decreases cost, is the lower amount of resin that is needed because

A main disadvantage of the bottom-exposure setup, however, is that attractive forces between printed part and vat floor need to be overcome for each layer [19]. When pulling up the z-stage, the newly cured layer needs to adhere to the layers above, and may not stick to the vat surface. Attempts to reduce this unwanted interaction include the application of hydrophobic coatings of the material tray [15, 18–20] and modification of the mechanical separation mechanism

the specimen does not have to be completely submerged in the vat [14].

with tilting steps [21] or application of shear forces [20].

While soft lithography is not an AM technology, it merits mentioning as a competing method due to its superior resolution to most SLA systems. It utilizes elastomeric stamps or molds to fabricate 3D structures and consequently does not have the characteristic advantages of 3D printing such as the ability of direct and rapid fabrication from a computer-aided design (CAD) model [12]. Nevertheless, it is often employed as an alternative to SLA in for example microfluidic applications [6].
