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- Herausgeber: Hanser Publications
- Kategorie: Fachliteratur
- Sprache: Englisch
- Veröffentlichungsjahr: 2016
Oriented towards the practitioner, this book presents a clear overview of additive manufacturing, going from the basics to the properties and special aspects of industrially available machines. From the generation of data to the forming method, the complete process chain is shown in a practical light. In particular, the following additive manufacturing technologies are discussed extensively:
- Polymerization (e.g., stereolithography)
- Sintering and melting (e.g., laser sintering)
- Layer laminate method (e.g., laminated object manufacturing, LOM)
- Extrusion (e.g., fused deposition modeling, FDM)
- 3D printing
Applications for the production of models and prototypes (rapid prototyping), tools, tool inserts, and forms (rapid tooling) as well as end products (rapid manufacturing) are covered in detailed chapters with examples. Questions of efficiency are discussed from a strategic point of view, and also from an operational perspective.
This book was written to support product developers and people responsible for production who face the challenges of implementing additive manufacturing not just for prototypes or one-off parts, but for its increaingly important application in direct production of finished products. The method not only reduces the demands on industrial infrastructure, but also opens up new perspectives in terms of decentralized production and customer inclusive individualized production (customization, cyberproduction).
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Andreas Gebhardt Jan-Steffen Hötter
Additive Manufacturing
3D Printing for Prototyping and Manufacturing
The authors:
Prof. Dr.-Ing. Andreas Gebhardt, Managing Director of CP – Centrum für Prototypenbau GmbH, Erkelenz/Düsseldorf Professor, FH Aachen University of Applied Sciences Subject area: high-performance methods in production engineering and rapid prototyping
Jan-Steffen Hötter, M.Eng., Project Engineer, FH Aachen University of Applied Sciences
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© 2016 Carl Hanser Verlag, Munich
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ISBN 978-1-56990-582-1 E-Book ISBN 978-1-56990-664-4
Table of Contents
Title page
Copyright page
Table of Contents
Foreword
About the Authors
Acknowledgements
1 Basics, Definitions, and Application Levels
1.1 Systematics of Manufacturing Technologies
1.2 Systematics of Layer Technology
1.2.1 Application of Layer Technology: Additive Manufacturing and 3D Printing
1.2.2 Characteristics of Additive Manufacturing
1.3 Hierarchical Structure of Additive Manufacturing Processes
1.3.1 Rapid Prototyping
1.3.2 Rapid Manufacturing
1.3.3 Related Nonadditive Processes: Indirect or Secondary Rapid Prototyping Processes
1.3.4 Rapid Prototyping or Rapid Manufacturing?
1.3.5 Diversity of Terms
1.3.6 How Fast Is Rapid?
1.4 Integration of Additive Manufacturing in the Product Development Process
1.4.1 Additive Manufacturing and Product Development
1.4.2 Additive Manufacturing for Low-Volume and One-of-a-Kind Production
1.4.3 Additive Manufacturing for Individualized Production
1.5 Machines for Additive Manufacturing
2 Characteristics of the Additive Manufacturing Process
2.1 Basic Principles of the Additive Manufacturing Process
2.2 Generation of Layer Information
2.2.1 Description of the Geometry by a 3D Data Record
2.2.2 Generation of Geometrical Layer Information on Single Layers
2.3 Physical Principles for Layer Generation
2.3.1 Solidification of Liquid Materials
2.3.2 Generation from the Solid Phase
2.3.3 Solidification from the Gas Phase
2.3.4 Other Processes
2.4 Elements for Generating the Physical Layer
2.4.1 Moving Elements
2.4.2 Generating and Contouring Elements
2.4.3 Layer-Generating Element
2.5 Classification of Additive Manufacturing Processes
2.6 Summary Evaluation of the Theoretical Potentials of Rapid Prototyping Processes
2.6.1 Materials
2.6.2 Model Properties
2.6.3 Details
2.6.4 Accuracy
2.6.5 Surface Quality
2.6.6 Development Potential
2.6.7 Continuous 3D Model Generation
3 Machines for Rapid Prototyping, Direct Tooling, and Direct Manufacturing
3.1 Polymerization: Stereolithography (SL)
3.1.1 Machine-Specific Basis
3.1.2 Overview: Polymerization, Stereolithography
3.1.3 Stereolithography Apparatus (SLA), 3D Systems
3.1.4 STEREOS, EOS
3.1.5 Stereolithography, Fockele & Schwarze
3.1.6 Microstereolithography, microTEC
3.1.7 Solid Ground Curing, Cubital
3.1.8 Digital Light Processing, Envisiontec
3.1.9 Polymer Printing, Stratasys/Objet
3.1.10 Multijet Modeling (MJM), ProJet, 3D Systems
3.1.11 Digital Wax
3.1.12 Film Transfer Imaging, 3D Systems
3.1.13 Other Polymerization Processes
3.2 Sintering/Selective Sintering: Melting in the Powder Bed
3.2.1 Machine-Specific Basic Principles
3.2.2 Overview: Sintering and Melting
3.2.3 Selective Laser Sintering, 3D Systems/DTM
3.2.4 Laser Sintering, EOS
3.2.5 Laser Melting, Realizer GmbH
3.2.6 Laser Sintering, SLM Solutions
3.2.7 Laser Melting, Renishaw Ltd.
3.2.8 Laser Cusing, Concept Laser
3.2.9 Direct Laser Forming, TRUMPF
3.2.10 Electron Beam Melting
3.2.11 Selective Mask Sintering (SMS), Sintermask
3.2.12 Laser Sintering, Phenix
3.3 Coating: Melting with the Powder Nozzle
3.3.1 Process Principle
3.3.2 Laser-Engineered Net Shaping (LENS), Optomec
3.3.3 Direct Metal Deposition (DMD), DM3D Technology (TRUMPF)
3.4 Layer Laminate Manufacturing (LLM)
3.4.1 Overview of Layer Laminate Manufacturing
3.4.2 Machine-Specific Basics
3.4.3 Laminated Object Manufacturing (LOM), Cubic Technologies
3.4.4 Rapid Prototyping Systems (RPS), Kinergy
3.4.5 Selective Adhesive and Hot Press Process (SAHP), Kira
3.4.6 Layer Milling Process (LMP), Zimmermann
3.4.7 Stratoconception, rp2i
3.4.8 Paper 3D Printing, MCor
3.4.9 Plastic Sheet Lamination, Solido
3.4.10 Other Layer Laminate Methods
3.5 Extrusion: Fused Layer Modeling (FLM)
3.5.1 Overview of Extrusion Processes
3.5.2 Fused Deposition Modeling (FDM), Stratasys
3.5.3 Wax Printers, Solidscape
3.5.4 Multijet Modeling (MJM), ThermoJet, 3D Systems
3.6 Three-Dimensional Printing (3DP)
3.6.1 Overview: 3D Printing
3.6.2 3D Printer, 3D Systems, and Z Corporation
3.6.3 Metal and Molding Sand Printer, ExOne
3.6.4 Direct Shell Production Casting (DSPC), Soligen
3.6.5 3D Printing System, Voxeljet
3.6.6 Maskless Mesoscale Material Deposition (M3D), Optomec
3.7 Hybrid Processes
3.7.1 Controlled Metal Buildup (CMB)
3.7.2 Laminating and Ultrasonic Welding: Ultrasonic Consolidation, Solidica
3.8 Summary Evaluation of Rapid Prototyping Processes
3.8.1 Characteristic Properties of AM Processes Compared to Conventional Processes
3.8.2 Accuracy
3.8.3 Surfaces
3.8.4 Benchmark Tests and User Parts
3.9 Planning Targets
3.10 Follow-up Processes
3.10.1 Target Material: Plastics
3.10.2 Target Material: Metal
4 Rapid Prototyping
4.1 Classification and Definition
4.1.1 Properties of Prototypes
4.1.2 Characteristics of Rapid Prototyping
4.2 Strategic Aspects for the Use of Prototypes
4.2.1 Product Development Steps
4.2.2 Time to Market
4.2.3 Front Loading
4.2.4 Digital Product Model
4.2.5 The Limits of Physical Modeling
4.2.6 Communication and Motivation
4.3 Operational Aspects in the Use of Prototypes
4.3.1 Rapid Prototyping as a Tool for Fast Product Development
4.3.2 Applications of Rapid Prototyping in Industrial Product Development
4.3.3 Rapid Prototyping Models for the Visualization of 3D Data
4.3.4 Rapid Prototyping in Medicine
4.3.5 Rapid Prototyping in Art, Archaeology, and Architecture
4.3.6 Rapid Prototyping for the Evaluation of Calculation Methods
4.4 Outlook
5 Rapid Tooling
5.1 Classification and Definition of Terms
5.1.1 Direct and Indirect Methods
5.2 Properties of Additive Manufactured Tools
5.2.1 Strategic Aspects for the Use of Additive Manufactured Tools
5.2.2 Design Properties of Additive Manufactured Tools
5.3 Indirect Rapid Tooling Processes: Molding Processes and Follow-up Processes
5.3.1 Suitability of AM Processes for the Manufacture of Master Patterns for Subsequent Processes
5.3.2 Indirect Methods for the Manufacture of Tools for Plastic Components
5.3.3 Indirect Methods for the Manufacture of Metal Components
5.4 Direct Rapid Tooling Processes
5.4.1 Prototype Tooling: Tools Based on Plastic Rapid Prototyping Models and Methods
5.4.2 Metal Tools Based on Multilevel AM Processes
5.4.3 Direct Tooling: Tools Based on Metal Rapid Prototype Processes
5.5 Future Prospects
6 Direct Manufacturing: Rapid Manufacturing
6.1 Classification and Definition of Terms
6.1.1 Terms
6.1.2 From Rapid Prototyping to Rapid Manufacturing
6.1.3 Workflow for Direct Manufacturing
6.1.4 Requirements for Direct Manufacturing
6.2 Potential for Additive Manufacturing of End Products
6.2.1 Increased Design Freedom
6.2.2 Production of Traditionally Not Producible Products
6.2.3 Variation of Mass Products
6.2.4 Personalization of Mass Products
6.2.5 Realization of New Materials
6.2.6 Realization of New Manufacturing Strategies
6.2.7 Design of New Labor and Living Alternatives
6.3 Requirements on Additive Manufacturing for Production
6.3.1 Requirements on Additive Manufacturing of a Part
6.3.2 Requirements for Additive Mass Production with Current Methods
6.3.3 Future Efforts in Additive Series Production
6.4 Implementation of Rapid Manufacturing
6.4.1 Additive Manufacturing Machines as Elements of a Process Chain
6.4.2 Additive Machines for Complete Production of Products
6.5 Application Fields
6.5.1 Application Fields for Materials
6.5.2 Application Fields by Industry
6.6 Summary
7 Safety and Environmental Protection
7.1 Labor Agreements for the Operation and Production of Additive Manufacturing Machines and the Handling of the Corresponding Material
7.2 Annotations to Materials for Additive Manufacturing
7.3 Annotations for Using Additive Manufactured Components
8 Economic Aspects
8.1 Strategic Aspects
8.1.1 Strategic Aspects of the Use of AM Methods in Product Development
8.2 Operative Aspects
8.2.1 Establishing the Optimal Additive Manufacturing Process
8.2.2 Establishing the Costs of Additive Manufacturing Processes
8.2.3 Characteristics of Additive Manufacturing and Its Impacts on Economy
8.3 Make or Buy?
9 Future Rapid Prototyping Processes
9.1 Microcomponents
9.1.1 Microcomponents Made of Metal and Ceramic
9.1.2 Microcomponents Made of Metal and Ceramics by Laser Melting
9.2 Contour Crafting
9.3 D-Shape Process
9.4 Selective Inhibition of Sintering (SIS)
9.4.1 The SIS-Polymer Process
9.4.2 The SIS-Metal Process
9.5 Free Molding
9.6 Freeformer
10 Appendix
Glossary
11 Bibliography
Since the late 1980s, in fact, for more than 25 years, Additive Manufacturing (AM) has been penetrating the world of manufacturing. When the layer-based technology emerged, it was called Rapid Prototyping (RP). This was the best name for a technology that could not fabricate anything but sticky and brittle parts, which could only be used as prototypes. The process was not even “rapid,” although it allowed the making of time- and money-consuming tools to be avoided. With the creation of the first prototype by RP, a significant amount of time and money could be saved.
The initial process was called stereolithography and it was based on photo-polymerization, which first processed acrylates and then epoxies later on. In the following years, new layer-based processes were developed and an extended range of materials became qualified for AM applications, and all of them were plastics.
Around the turn of the millennium, processes for making metal parts were introduced to the market. With this development, the focus of manufacturers as well as of the users changed from just prototyping to manufacturing because of improved processes, materials, software, and control. The challenge was then to make final parts.
Today all classes of engineering materials, such as plastics, metals, ceramics, and even nontraditional materials, such as food, drugs, human tissue, and bones, can be processed using 3D printers.
There is still a long way to go, but due to vibrant activities concerning all aspects of 3D printing worldwide, this high-speed development is incomparable to the expansion of any fabrication technology in the past.
There are two main reasons for intense interesting in this technology for somebody active in the field of product development and production:
First, to stay competitive, one should be able to judge the capabilities of existing, new, and emerging AM processes in comparison to traditional manufacturing processes and process chains. The task is not just a matter of speeding up the process but to improve the way we do engineering design towards “designing for AM.” This makes completely new products possible and shifts the competition of traditional manufacturing towards a new level of lightweight design, as well as resource-saving and environmentally friendly mass production of individual parts.
Second, people begin to understand that AM is not just capable of revolutionizing our way of designing and producing parts, but able to affect many aspects of our daily lives.
AM touches upon legal aspects, such as product reliability and intellectual property rights, as compared to the digital entertainment market. AM also brings even more challenges as parts can cause significant problems like physical injuries or even death, which music and videos do not do.
Digital data, including not only technical data such as a blue print, but the exact information for creating the product, can easily be sent all over the world and encounter every imaginable hurdle, such as frontiers, embargos, custom fees, export regulations, and many more. This requires us to rethink the well-functioning world of today.
Many of the questions raised, if not the majority, need to be decided by people who are not technicians. The better that those involved understand the technical part and the more thorough their information, the better decisions they will be qualified to make.
Consequently, this book was written to support the product developers and people who are responsible for the production, as well as others who are involved in the process of realizing the enormous challenges of this technology.
Aachen in March 2016
Andreas Gebhardt
Andreas Gebhardt, born in 1953, studied mechanical engineering at the Technical University Aachen, Germany (RWTH), where he received his Engineering Diploma (Dipl-Ing). In 1986 he passed his doctoral exam (Dr-Ing) at the same university with a thesis on the “Simulation of the transient behavior of conventional power plants.”
In 1986, Mr. Gebhardt was appointed general manager of a company that specialized in engine refurbishment. In 1991, he moved to general manager at the LBBZ GmbH, a service bureau on laser material processing, where in 1992, he started working on rapid prototyping. When in 1997, the CP Center of Prototyping GmbH, an Additive Manufacturing Service Bureau was founded, he transferred there as a general manager.
With the beginning of the spring term in 2002, Mr. Gebhardt was appointed Professor for Advanced Fabrication Technology and Rapid Prototyping at the Aachen University of Applied Sciences (FH Aachen) where he established an AM Team and Lab called the GoetheLab for Additive Manufacturing. Since 2002, Mr. Gebhardt has also been a guest professor at the City College of the City University of New York (CCNY).
In 2012, Mr. Gebhardt was elected Dean of the Department of Mechanical Engineering and Mechatronics, FH Aachen. In November 2014, he was appointed extraordinary Professor at the Tshwane University of Technology (TUT), Pretoria, RSA.
Mr. Gebhardt is Chairman of the AM Research Committee (FA13) of the German Welding Association (DVS) and he heads the team of the “Aachen Center of 3D Printing,” a joint research group of FH Aachen and Fraunhofer ILT AM specialists.
Since 2004 Mr. Gebhardt has been the editor of the peer-reviewed, open access online journal on AM called the RTeJournal.
Jan-Steffen Hötter, born in 1987, received his Bachelor’s Degree (B.Eng.) and Master’s Degree in Mechanical Engineering (M.Eng.) from the Aachen University of Applied Sciences, Aachen, Germany. He established the Metal Laser Sintering Lab and Team under the umbrella of the GoetheLab, which he now is heading. He is engaged in the Aachen Center of 3D Printing and coordinates the AM work of the Institute for Tool-less Production (IWF GmbH). Mr. Hötter is a member of the VDI Committee “Additive Manufacturing,” and gives guest lectures at several German universities.
The interdisciplinary character and the enormous developmental speed of AM in general, and of the layer-based fabrication processes and machines in particular, make it almost impossible for an individual to display this discipline correctly, completely, and entirely up-to-date.
We are therefore very thankful for the enormous assistance from many people.
The practical orientation of this book mainly is backed up by the contribution of the management and the staff of the AM Service-Bureau CP-GmbH, mainly from Besima Sümer, Christoph Schwarz, and Michael Wolf.
Major help came from the GoetheLab team of the Aachen University of Applied Sciences.
First of all, a special thanks goes to the whole metal group of the Goethelab team that supported the entire process in every chapter. We want to thank Philipp Ginkel, Prasanna Rajaratnam, Simon Scheuer, Patrycja Wiezik, Alina Richter, and Niklas Kessler. A special thanks goes to Alexander Schwarz, who focused on the correct formatting of this book and supported the authors in organizational questions.
Additionally, we thank our colleagues
Miranda Fateri, who personally worked on some chapters and contributed together with her Glass- and Ceramic Team,
Laura Thurn and her Plastic and Fabber Team, and
Julia Kessler, who brought in not only professional knowledge concerning her medical research but her management skills to shape the teamwork.
As this book is based on four editions in German, our appreciation goes to all who, since the late 1990s, have helped to make and optimize the topic and who are listed in the preceding German editions.
Thanks to all members of the professional committees of the VDI, Association of German Engineers and DVS, German Welding Association (FA 13), which we are members of.
We thank countless colleagues (who must stay nameless in this content) whom we met on conferences, exhibitions, and meetings for countless discussions and suggestions. In case we forgot anyone, we sincerely apologize.
Thanks to the Hanser team and to Mrs. Monika Stüve for her support over the years.
Andreas GebhardtJan-Steffen Hötter
To understand the characteristics and the capabilities of additive manufacturing (AM), it is very helpful to take a look at the systematics of manufacturing technologies in general first.
1.1 Systematics of Manufacturing TechnologiesOrientated on the geometry only, manufacturing technology in general is divided into three fundamental clusters [Burns, 93, AMT, 14]:1
subtractive manufacturing technology,
formative manufacturing technology, and
additive manufacturing technology.
With subtractive manufacturing technology, the desired geometry is obtained by the defined removal of material, for example, by milling or turning.
Formative manufacturing means to alter the geometry in a defined way by applying external forces or heat, for example, by bending, forging, or casting. Formative manufacturing does not change the volume of the part.
Additive manufacturing creates the desired shape by adding material, preferably by staggering contoured layers on top of each other. Therefore it is also called layer (or layered) technology.
The principle of layer technology is based on the fact that any object, at least theoretically, can be sliced into layers and rebuilt using these layers, regardless of the complexity of its geometry.
Figure 1.1 underlines this principle. It shows the so-called sculpture puzzle, in which a three-dimensional (3D) object has to be assembled from more than 100 slices. Therefore the layers have to be arranged vertically in the right sequence using a supporting stick.
Figure 1.1 Principle of layer technology, example: sculpture puzzle (Source: HASBRO/MB Puzzle)
Additive manufacturing (AM) is an automated fabrication process based on layer technology. AM integrates two main subprocesses: the physical making of each single layer and the joining of subsequent layers in sequence to form the part. Both processes are done simultaneously. The AM build process just requires the 3D data of the part, commonly called the virtual product model.
It is a characteristic of AM that not only the geometry but the material properties of the part as well are generated during the build process.
1.2 Systematics of Layer TechnologyIn this section the commonly used terms in AM are addressed. The related characteristics as well as their interdependency and the hierarchical structure are discussed.
In this book the generally accepted so-called generic terms are used, and alternatively used names are mentioned.
Generic terms and brand names have to be distinguished from each other. If they are mixed, which happens quite often, this frequently leads to confusion. As brand names are important in practice, they are addressed, explained, and linked to the generic terms in Chapter 3, where the AM machines are presented.
1.2.1 Application of Layer Technology: Additive Manufacturing and 3D PrintingAdditive manufacturing is the generic term for all manufacturing technologies that automatically produce parts by physically making and joining volume elements, commonly called voxels. The volume elements are generally layers of even thickness.
Additive manufacturing is standardized in the US (ASTM F2792) and in Germany (VDI 3405), and is commonly used worldwide.
As alternative terms, additive manufacturing (technology) and additive layer manufacturing (ALM) have minor acceptance.
3D printing is about to replace all other names, including additive manufacturing, and to become the generally accepted generic term for layer technology in the near future. This is mainly because it is very easy to understand. Everyone who can operate a text editor (a word processor) and a 2D office printer easily understands that he or she will be able to print a 3D object using a 3D design program (a part processor) and a 3D printing machine, regardless of how it works.
NOTE: Additive manufacturing and 3D printing are used as equal generic terms in this book. While in Chapter 1 this is expressed by always writing additive manufacturing /3D printing (or AM/3DP). In the following chapters only additive manufacturing or AM is used in order to shorten the text volume.
Beginners should realize that 3D Printing is also the brand name of a family of powder binder processes (see Section 3.6), originally developed by MIT and licensed to Z-Corporation (now 3D Systems), Voxeljet, and others.
1.2.2 Characteristics of Additive ManufacturingLayer technologies in general and additive manufacturing in particular show special characteristics:
The geometry of each layer is obtained solely and directly from the 3D computer-aided design (CAD) data of the part (commonly called a virtual product model).
There are no product-related tools necessary and consequently no tool change.
The material properties of the part are generated during the build process.
The parts can be built in any imaginable orientation. There is no need for clamping, thus eliminating the clamping problem of subtractive manufacturing technologies. Nevertheless, some processes need support structures, and the orientation of the part influences the parts’ properties.
Today, all AM processes can be run using the same so-called STL (or AMF) data structure, thus eliminating data exchange problems with preprocessors as used in subtractive manufacturing.
Additive manufacturing/3D printing therefore ensures the direct conversion of the 3D CAD data (the virtual product model) into a physical or real part.
As scaling can be done simply in the CAD file, parts of different sizes and made from different materials can be obtained from the same data set. As an example, the towers of a chess set shown in Fig. 1.2 are based on the same data set but made with different AM machines and from different materials. The range of materials includes foundry sand, acrylic resin, starch powder, metals, and epoxy resin.
Figure 1.2 Additive manufacturing. Scaled towers of a chess set, based on the same data set but made with different AM machines and from different materials. Small towers, from left to right: PMMA (powder-binder process, Voxeljet), metal (laser sintering, EOS), acrylate, transparent (stereolithography, Envisiontec; height approx. 3 cm). Big towers, from left to right: foundry sand (powder-binder process, Voxeljet), starch powder (powder-binder process, 3D Systems; height approx. 20 cm) (Source: machine manufacturers)
One of the biggest AM parts of all is the tower shown in Fig. 1.3 with a height of approximately 2.5 m, which is higher than the general manager of the Voxeljet Company, Mr. I. Ederer.
Figure 1.3 Chess tower made from foundry sand, height approx. 2.5 m, powder-binder process (Source: Voxeljet)
By contrast, Fig. 1.4 shows a tower made by micro laser sintering. It is approximately 5 mm high.
Figure 1.4 Tower made from metal, height approx. 5 mm, micro laser sintering (Source: EOS/3D Micromac)
AM/3DP allows manufacturing of geometric details that cannot be made using subtractive or formative technologies. As an example, the towers on Fig. 1.2 contain spiral staircases and centered double-helix hand rails. The details can be seen on a cutaway model displayed in Fig. 1.5.
Figure 1.5 Internal details of the rear right tower on Fig. 1.2 (Source: 3D Systems)
Another example of geometries that cannot be manufactured using subtractive or formative technologies is shown in Fig. 2.5.
All AM/3DP processes mentioned here will be explained in detail in Chapter 3.
1.3 Hierarchical Structure of Additive Manufacturing ProcessesFor a proper definition of the terms used, it is very helpful to distinguish the technology and its application from each other. Subtractive manufacturing, for example, marks the technology level, and drilling, grinding, milling, and so on are the names for its application (or the application level).
The technology of additive manufacturing/3D printing is divided in two main application levels: rapid prototyping and rapid manufacturing. Rapid prototyping is the application of AM/3DP to make prototypes and models or mock-ups, and rapid manufacturing is the application to make final parts and products.
The manufacturing of tools, tool inserts, gauges, and so on usually is called rapid tooling. The term often is regarded as an independent hierarchical element or application level, but effectively it is not. Depending on how a tool is made, it represents a prototype or a product (Fig. 1.6).
Figure 1.6 Basic structure of additive manufacturing/3D printing technology and its subcategories rapid prototyping, rapid manufacturing, and rapid tooling
Rapid prototyping (RP) is the application of AM/3DP technology to make prototypes, models, and mock-ups, all of them being physical parts but not products. They only mimic isolated properties of the latter product in order to verify the engineering design and to allow the testing of selected product capabilities and thus to improve and speed up the product development process. The goal is to preplan a part to make it as simple as possible in order to get it quickly and cheaply. Therefore, rapid prototyping parts generally cannot be used as final products.
As prototypes differ from products, serial identical prototypes (which are not products but prototypes) do not exist, although the term is used to underline a strategy.
Rapid prototyping again is subdivided into solid imaging or concept modeling, and functional prototyping.
Solid imaging or concept modeling: If a rapid prototyping part is made mainly for 3D visualization, it is called a solid image, a concept model, a mock-up, or even a rapid mock-up. The idea behind it is to generate a 3D picture or a statue (Fig. 1.7). To highlight this aspect, the parts are also called show-and-tell models.
If a part has a single or some of the functionalities of the latter product, it can be used to verify this aspect of the engineering design. Consequently it is called a functional prototype (and the process functional prototyping accordingly).
Figure 1.7 Basic structure of the AM/3D printing technology: application levels rapid prototyping, rapid manufacturing, and rapid tooling and its subcategories
A sample of each category is displayed in Fig. 1.8. The scaled data control model of a convertible roof system (made from polyamide by laser sintering) can be regarded as a typical concept model. The air-outlet nozzle of a passenger car (made by laser stereolithography from epoxy resin) is a functional prototype that supports the testing of the car’s climate control.
Figure 1.8 Rapid prototyping: concept model or solid image (left), laser sintering (Source: CP GmbH); functional prototype (right), laser stereolithography (Source: 3D Systems)
The corresponding AM processes are presented in detail in Chapter 3.
1.3.2 Rapid ManufacturingRapid manufacturing (RM) names the application of the AM/3D printing technology to make final parts or products, often called series products, even if they are one-offs. (A deeper discussion can be found in Chapter 6.) The parts can be positives like connectors as well as negatives like cavities. Making positives or parts is called direct manufacturing, and the additive manufacturing of negatives or cavities, such as tools and tool inserts, is called direct tooling; see Fig. 1.7.
1.3.2.1 Rapid Manufacturing—Direct ManufacturingAdditive manufacturing or 3D printing of final parts or products is called direct manufacturing (DM). Frequently and for historical reasons it is also called rapid manufacturing (RM) and complies directly with the main term. Often the terms e-manufacturing, digital manufacturing, tool-less fabrication, and others are used.
Direct manufacturing is based on the same technology as rapid prototyping and, at least until today, uses the same machines. The goal is to make final products. Whether the goal can be reached or not depends on the degree of accomplishment of the required mechanical and technological properties. This again depends on the machines, processes, and materials available. Further, whether the needed accuracy can be reached and if a competitive price can be achieved are essential.
As an example of direct manufacturing, Fig. 1.9 shows a three-element dental bridge (left). The associated process chain will be shown in Chapter 3, and applications will be discussed in Chapter 6.
Figure 1.9 Rapid manufacturing: direct manufacturing of a three-element dental bridge (left) (Source: GoetheLab FH Aachen/Sokalla); direct tooling for making golf balls (right) (Source: EOS GmbH)
Additive manufacturing/3D printing of a high number tools is a rapid manufacturing process. It is called direct tooling or, to underline the character of additive manufacturing, direct rapid tooling (Fig. 1.7). Figure 1.9 (right) shows a tool for making golf balls.
Direct tooling has to be distinguished from prototype tooling. Prototype tooling is the name for processes to make tools and tool inserts from model or prototype materials, for example from stereolithography resin (see AIM, Section 5.4.1.1). Therefore, prototype tooling is basically a part of functional prototyping. Prototype tooling often is called bridge tooling as well because it bridges the gap between prototype tools and series tools, mainly for small-batch production. Prototype tooling is characterized by quickly and easily made low-volume tools.
As can be seen in Fig. 1.7, rapid tooling does not indicate a separate application level of the additive manufacturing/3D printing technology but integrates different tooling applications in the sense of a vertical structuring element.
Historically, the making of tools and tool inserts first were based on rapid prototyping and thus were realized before modern direct manufacturing was available. For marketing reasons, the new application was published as an advancement of rapid prototyping and thus was given a new name: rapid tooling. Because of this, there are still publications that structure additive manufacturing/3D printing with a separate subcategory called rapid tooling.
1.3.3 Related Nonadditive Processes: Indirect or Secondary Rapid Prototyping ProcessesThe terms indirect prototyping, indirect manufacturing, and indirect tooling do not indicate additive manufacturing/3D printing processes, although it is suggested by the names. A process is called indirect if it uses additive-manufactured masters without being an additive process itself. The best-known examples are copying processes like vacuum casting (also called room-temperature vulcanization (RTV) or reaction injection molding (RIM).
If indirect processes lead to parts (positives), the process is called indirect prototyping, if final products are the result, for example cast parts obtained from (lost) AM/3DP master models, it is called indirect manufacturing, and if tools or tool inserts (negatives) are made, it is called indirect tooling (for examples see Fig. 1.10(a)(b)).
Figure 1.10 Indirect Processes: Indirect Prototyping (left), Indirect Tooling (right)
The above-mentioned copying processes are frequently called rapid prototyping, rapid manufacturing, or rapid tooling as well; sometimes they are named a little bit more precisely as secondary rapid prototyping processes (or applications). In practice, often the adjective “rapid” is used although the processes are nonadditive. Mostly this is done to make it more attractive to customers.
The application of additive manufacturing/3DP for making rapid prototyping parts and final products is discussed in detail in Sections 4.3.2 to 4.3.6; for making tools and tool inserts it is discussed in detail in Section 5.3.
1.3.4 Rapid Prototyping or Rapid Manufacturing?Whether we talk about rapid prototyping or rapid manufacturing, it often causes intensive discussions. In fact, the same part can be a prototype or a product and consequently can be made using rapid prototyping (functional prototyping) or rapid manufacturing (direct manufacturing) processes.
A part that was designed for additive manufacturing from polyamide, is made by AM/3DP from polyamide, and that finally shows all relevant properties as designed is a product. In contrast, a part that was designed for plastic injection molding of polyamide and then is made using additive manufacturing and polyamide at best is a prototype if the geometry is exact.
In this context, the material used in AM/3DP does not play a role, as long as it is identical in engineering design and production. A part made from paper, wax, starch powder, or gypsum definitely can be a product.
1.3.5 Diversity of TermsToday, additive manufacturing and 3D printing are regarded as generic terms for layer technologies. Besides this, many other terms are in use. They change with time, and even their meaning sometimes changes with time.
With the first introduction of additive manufactured parts and processes in the late 1980s, the generic name was rapid prototyping.
At that time the term rapid prototyping was correct. First, using rapid prototyping processes, parts could be made much faster. This was mainly because for the first time parts could be made directly because tools could be avoided, thus saving time and money. Second, the parts could not be used as products but as prototypes at best. This was mainly because of the materials available and because of poor processes.
As a kind of reminiscence of rapid prototyping, even today many processes are named with the adjective “rapid,” mostly to underline their speed, even if they are nonadditive.
Besides additive manufacturing/3D printing, the most prominent term is rapid technology or rapid technologies, but additive manufacturing or, very rarely, formative manufacturing is used as well.
Another family of terms used is linked to layer-based manufacturing. Names like layer manufacturing or more often additive layer manufacturing (ALM) are used. As an equivalent to manufacturing, the terms fabrication or production are used as well.
In addition, in the literature some terms are often used that refer to a specific ability of a process. For example, solid free-form manufacturing (SFM) underlines that solids are made that are traced by free-form surfaces. Desktop manufacturing marks the manufacturing in an office environment (on the desk).
Besides the full names, three- and four-letter abbreviations are used. Often they lead to confusion rather than to precision. The most-often used ones are explained in the text or listed in the glossary.
In practice, the terms often are not properly used. Frequently, not even generic names and brand names are distinguished from each other. For example, many people call it stereolithography if they speak about AM/3DP in general.
1.3.6 How Fast Is Rapid?Many terms and definitions contain the term rapid or fast. But rapid is a relative term. It only becomes a quality term if “how fast or fast in comparison to what?” is added.
The term itself is kind of dangerous because it suggests that rapid processes are basically faster than any other manufacturing processes. This is not true and cannot be generalized. The speed depends on the geometry. If a board of 250 × 250 × 10 mm is needed, one cuts it from a semifinished bulk. No additive manufacturing/3D printing process will be faster.
Under special conditions, additive manufacturing processes are faster than nonadditive ones, for example if tools can be avoided, if a volume-independent flexible output is required, if complex geometries are needed, or if individualized parts are wanted.
But the term rapid does bear a practical advantage. It is accepted as a synonym of today’s computerized and therefore automated processes for mainly making prototypes. It is self-explanatory, which is one of the most important attributes of a term. That is why people will continue calling AM/3DP rapid prototyping, rapid tooling, and rapid manufacturing, as it is done sometimes in this book as well.
1.4 Integration of Additive Manufacturing in the Product Development ProcessAdditive manufacturing can be used not only to make parts, but due to their special abilities (see Section 1.2.2, “Characteristics of Layer Technologies”), they are suited to improve established processes, realizing new product features, and supporting new product development strategies.
1.4.1 Additive Manufacturing and Product DevelopmentIndustrial product formation involves the time period from the first product idea to the introduction of the product to the market. It includes the development of the product, the development and the fabrication of the production facility, and the production of the product itself.
The goal of all manufacturers is to keep this time span as short as possible and therefore to optimize all subprocesses. Additive manufactured parts are particularly suitable to shortening the product development process and to improving it at the same time. The biggest influence comes from the fact that expensive and time-consuming tools can be avoided with the use of additive manufacturing/3D printing.
This effect is enforced if in any phase of product development the optimal AM/3DP process is used. To identify it, it is favorable to have a correlation between the application levels of the additive manufacturing technology (as displayed on Fig. 1.7) and the phases of the product development process on Fig. 1.11. This shows an internationally accepted structure, although this particular process chain was taken from the guidelines of the German Association of Mechanical Engineers, VDI [VDI 2221].
Figure 1.11 Phases of product development in correlation to the application levels of AM/3DP (Fig. 1.7). The internationally accepted process chain following the guidelines of the German Association of Mechanical Engineers, VDI [VDI 2221] (top) and its correlation to the application levels rapid prototyping and rapid manufacturing (middle) and its subcategories concept modeling, functional prototyping, prototype tooling, direct tooling, and direct manufacturing (bottom)
Product development covers rapid prototyping and rapid manufacturing (of the production facility as well as of the product; see Fig. 1.11, middle). In detail, ideation and conception are improved by concept modeling, while the engineering design and the technical preparation are supported by functional prototyping. The fabrication of the products is done by direct manufacturing.
Rapid tooling supports the making of tools and tool inserts. In the prototyping phase, prototype tooling is applied, and in the production phase direct tooling is used (see Fig. 1.11, bottom).
A more detailed structure is discussed later in section 4.3.1. The capabilities of the models (model classes or categories, to be defined later) are linked to the AM families defined in Chapter 3.
In practice, the definitions are not as sharp as displayed here, and their transitions are smooth. In addition, depending on the product, not every phase is addressed in each product development process.
1.4.2 Additive Manufacturing for Low-Volume and One-of-a-Kind ProductionAM/3DP is done layer by layer and without product-dependent tools. It does not matter how many parts are manufactured at once in one build space (as long as they fit in) and whether they are identical or not. Therefore, AM/3DP enables a volume-independent production, even with a mixed production containing different volumes and one-offs.
1.4.3 Additive Manufacturing for Individualized ProductionAM/3DP shows not only the volume effect mentioned in Section 1.4.2, but also supports the manufacturing of individually modified products. This is the realization of the strategy of customizing, which basically cannot be done using tools.
The individualization of a product can be done by using CAD systems or by the integration of 3D scans, in so-called reverse engineering. As an example, hearing aid shells made by AM/3DP are displayed in Fig. 1.12 that show the production and the finished parts.
Besides this more professional approach, there are part libraries available, even on the Internet. Along with easy to operate (low-cost or shareware) 3D CAD systems, this provides easy access to the needed data, even for private and semiprofessional use.
Using AM, virtually everybody can be a manufacturer.
Figure 1.12 Individualized production or customizing: manufacturing of individualized hearing aid shells. Upside-down production, left; finished parts, right (Source: 3D Systems)
Today, machines for AM/3DP are called 3D printers.
Rarely, the term “fabricator” is used to indicate that the final products are made, and in contrast, the machines for making prototypes are called “prototypers.”
As indicated on Fig. 1.7, parts and machines are classified according to the application levels. They can be roughly divided into three machine classes. Machines that make
concept models are called personal 3D printers or fabbers,
functional prototypes are called professional 3D printers or office printers, and
final products are called production 3D printers.
This interrelation is displayed on Table 1.1.
Table 1.1 Classification of machines for Additive Manufacturing/3D Printing
Machine class
Designation*
Prototyper
Fabricator
Personal 3D printer
Professional 3D Printer
Production machine Production 3D printer
Fabber
Personal printer
Office printer
Production printer (Shop floor machine)
Use
Private, domestic
Semiprofessional office
Professional office or workshop
Professional, production or job shop
Usage levels (Fig. 1.7)
Prototypes Display models
X
Concept models
X
Functional prototypes
X
Final products
X
Construction material
Plastic
Plastic
Plastic
Plastic, metal, ceramic
Price level
500 to 4000 € [1 € ≈ 1.07 USD]
1000 to 10,000 €
20,000 to 70,000 €
130,000 to > 800,000 €
Example
Prusa Mendel
Dimension
Objet
Concept SLM
*The classifications are not standardized and are handled differently by different manufacturers and users. Those used here are based on the recommendation from 3D Systems and follow a system often used in practice.
The machine classes again are linked to characteristic specifications.
Personal 3D Printer
In analogy to personal computers, small, simply engineered, shareware-based, easy to operate (even on a desk), and inexpensive 3D printers are called personal 3D printers. Today they mostly use plastics, but other materials will be available in the near future.
Fabber
Personal 3D printers in private use are commonly called fabbers. Fabbers are mostly assembled by the owner and operator himself (DIY printer). The term “fabber” is an abbreviation of fabricator. The process is called fabbing. The philosophy behind it is to enable everybody to fabricate almost everything by himself. Corresponding web-based blogs and Internet communities are established (the fabbing community). They support the exchange of information regarding the construction and the operation of fabbers and propagate new kinds of cooperation, such as cloud-fabbing. Members mutually train themselves. To start with, it is sufficient to be able to operate a personal computer and to own a kitchen table as infrastructure.
Professional 3D Printer
Professional 3D printers or office printers are compact, easy to operate, and service friendly. Even semiskilled people can operate it in an office environment.
Professional 3D printers have cartridge-supported material changing systems. The parts can be taken out without contamination of the operators or the environment. Removal of the support structures and cleaning for the most part can be done automatically or semiautomatically using special washing media and devices.
Operators are trained by tutorials or by a short training session, mostly in-house. There are no special requirements concerning the infrastructure.
Production 3D Printer
Production 3D printers (or factory work floor printers) enable a continuous high-quality and high-volume output. Production 3D printers focus on productivity. Generally, they have big build chambers, material handling systems, and automated devices for postprocessing.
Production printers are heavy, have big footprints, and cause emissions that are typical for production machines. Installation, maintenance, and service require professional support. Operators need to be trained intensively, mainly supported by the machine manufacturer.
Machine Classes and Part Properties
In general, there is a correlation between the machine classes and the part properties that can be obtained. A little bit more detailed than in Table 1.1, the characteristics of parts and the capabilities of printers (machine classes) are linked as follows:
Personal 3D printers are preferred for making concept models (show-and-tell models) and less loadable parts with limited details and reduced geometric freedom. At least today, they are limited to manufacturing parts from plastics.
Professional 3D printers are preferred for making concept models and functional prototypes with good details and reasonable loading capacity. Often they are the basis for making small series of end products with the help of secondary rapid prototyping processes. Like personal 3D printers (at least today), they are limited to manufacturing parts from plastics.
Production 3D printers are used to make final products or series parts. They can be one-offs as well as series of any volume, including a mixed production of different parts and volumes. Materials are plastics, ceramics, or metals. Usually the parts need postprocessing to achieve their final properties and complexion.
But, the correlation by trend between the machine classes and the capability of the parts cannot be regarded as principles. On one hand, there are fabbers that produce plastic parts that can be used as products, for example, individually shaped clamps (Fig. 1.13). On the other hand, there are production printers that make, for example, hollow turbine blades that only can be used for cold-air testing (Fig. 1.14).
Figure 1.13 Articulated cable clamp, a final product made by laser sintering from polyamide in one piece. Closed on the left and open on the right (Source: EOS)
Figure 1.14 Cutaway model of a gas turbine blade, gypsum ceramics, made with a powder-binder process (Source: IwF-Aachen)
Endnotes
1In Germany, manufacturing technology is divided into six main categories, and each of them is subdivided into various subcategories [DIN 8580], [Witt, 06].
Additive manufacturing machines on the market today are developed at a high rate of speed. New processes that are currently in the laboratory stage or under development will break into the market while simultaneously, tried and tested systems will be upgraded within a relatively short time.
Because the equipment presently on the market will be obsolete or approaching obsolescence over a relatively short period, the physical and technological bases of the various processes are portrayed and discussed in detail in this chapter. Chapter 3, “Machines for Rapid Prototyping, Direct Tooling, and Direct Manufacturing,” then shows which industrially offered installations derive from which fundamental processes. This approach not only facilitates the assessment of the current processes, but it also supplies the basis for the assessment of future industrial processes.
This division is also intended to separate the representation of basic principles valid for a longer term from machine concepts that change more quickly. In reality, however, overlaps and repetitions are unavoidable.
2.1 Basic Principles of the Additive Manufacturing ProcessAll additive manufacturing (AM) models are built by joining single layers of equal thickness. The layer is shaped (contoured) in an x-y plane two-dimensionally. The third dimension results from single layers being stacked up on top of each other, but not as a continuous z coordinate. In the strictest sense, additive manufacturing processes are therefore 2½D processes.
The models are therefore three-dimensional forms that are very exact on the building plane (x-y direction) and owing to the described procedure are then stepped in the z direction, whereby the smaller the z step is, the more the model looks like the original. Figure 2.1 shows an example of a three-dimensional model of a plastic and the resulting shift model, which is marked by the stair-step effect.
Figure 2.1 Stepped surface as a result of the layering process. Three-dimensional solid model (left) with marked equidistant layers and the created layer model (right) (Source: FH-Aachen)
The stair-step effect is a typical characteristic of the additive manufacturing process that can never be entirely eliminated but can be reduced by decreasing the layer thickness. Figure 2.2 shows the proportions of a real model with a layer thickness of 0.125 mm.
Figure 2.2 Stair-step effect in a stereolithography component (layer thickness 0.125 mm). (Source: CP-GmbH)
Today, the layer thickness is between 0.1 and 0.05 mm. Machines that are used for macroscopic components (characteristic dimensions of several to 100 mm) have a minimum thickness of 0.016 mm, and microcomponents have layer thicknesses up into the 5 nm range. A larger layer thickness, up to around 0.2 mm, is most often used for fabbers or for reducing the building time on other additive manufacturing machines. The consequence of a large layer thickness is low precision. Layer milling processes use plates with a thickness up to 40 mm (See Section 3.4.6 “Layer Milling Process (LMP), Zimmermann”).
Depending on the type of contouring (scanning, plotting, and so on) and the chosen AM process, the object is contoured continuously in the building plane (x-y plane). If it is not, the secant effect (see also Fig. 2.12) or the stair-step effect occurs on the boundary, which develops lower in x-y direction than in the z direction. Therefore, models built by an AM process have different precisions in the x-y direction than in the z direction. As can be seen theoretically in Fig. 2.3, a drilling hole is built parallel to the x-y plane and another one perpendicular to the x-y plane. It is assumed that the circular contours in the layers are generated continuously.
Figure 2.3 Stair-step effect at a hole contingent on layer processes: (a) on layer panel; (b) perpendicular to the layer panel
Although all AM processes known today work in this way as 2½D processes, some processes (e. g., extrusion processes) are in principle 3D processes, which means they can add incremental volume elements at any chosen point of the model. This method has not been implemented to date.
The layer milling process is the only one that can be contoured continuously in the z direction (compare to Section 3.4.6 “Layer Milling Process (LMP), Zimmermann”).
The characteristic feature of additive manufacturing processes is that the physical models are produced directly from computer data. In principle, it is therefore unimportant from where the data are provided as long as they describe a 3D volume completely. Data from CAD construction, from the process of measuring and reverse engineering, or from other measurements (such as computer tomography (CT), magnetic resonance tomography (MRT), and 3D tracking systems) may be used equally as well if the relevant evaluation programs enable the preparation of the measured values in the 3D data models.
In this way, model making has become an integral part of the computer-integrated product development. From the product development aspect, additive manufacturing models can, therefore, be regarded as three-dimensional plots or facsimiles of the corresponding CAD data. The decisive advantage, in contrast to the classic manual or semiautomatic model-making processes, lies in the fact that the data remain unaltered (with the exception of the generated supports) by the model making. As a result, no data need to be taken from the model. Because the making of AM models does not alter the common database, additive manufacturing processes have become the most important elements of modern product development strategies such as simultaneous engineering. The 3D data model is used as a product model and as a basis for production at the same time.
The advantage of AM processes over nonadditive manufacturing computer-controlled processes is that the AM machines are using the same data type, the so-called STL data (STL means standard transformation language, see Section 2.2.2.1 “STL Data”). Nonadditive manufacturing numerically controlled processes, such as computer numeric control (CNC) milling, usually use a system-specific data set.
The generation of layer information is based on a purely computer-oriented CAD model (Fig. 2.4). The CAD model is cut into layers with equal thickness by mathematical methods. This layer information is used to generate the physical single layers in an AM machine; the total sum of the single layers forms the physical model. The merging of the physical layers happens during the generation of the next layer or after completing the layer. This depends on the AM process. The finished physical model can be a prototype or the final product.
Figure 2.4 Concept of additive manufacturing
With the method of layer generating it is possible to realize geometrically complex structures that are impossible or expensive to produce by conventional methods. As a result, new designs can be realized, like the mathematical compositions by George Hart (www.georgehart.com). In Fig. 2.5 a (mathematical) 4D object can be seen that consists of 120 flattened dodecahedra and 600 tetrahedra.
Figure 2.5 Complex structure of polymer printing, only additive manufacturing geometry. (Source: George Hart)
“Rapid prototyping” or “additive manufacturing processes” are classified into two fundamental process steps:
Generation of the mathematical layer information (Section 2.2)
Generation of the physical layer model (Section 2.3)
2.2 Generation of Layer InformationThe additive manufacturing process copies the virtual CAD data into a physical model, so the generation of the mathematical slice information for the production of the single layers is most important in order to produce an accurate part. It is divided into three steps:
Description of the geometry by a 3D data record (Section 2.2.1)
Generation of the geometrical information of each layer (Section 2.2.2)
Illustration of the geometrical layer information on each layer (Section 2.4)
2.2.1 Description of the Geometry by a 3D Data Record2.2.1.1 Data Flow and InterfacesThe production of models and prototypes by means of additive manufacturing processes requires that the geometry of the component is available as a 3D data record. This is achieved in most industrial applications by construction on a 3D CAD system or by other measurements. The data are produced independently of the production and need to be prepared and transferred via an interface to the machines. The data are called the digital or virtual product model.
To build the components further, process- and installation-specific calculations are necessary in addition to geometrical data and material parameters. The data are set with the help of programs called front-end software or additive manufacturing software. Front-end software is a part of AM machines and is supplied by the manufacturer. AM software is offered by a third party. The software types interface with each other (Fig. 2.6).
The STL format has been established as an industry standard (STL interface, Section 2.2.2), but other formats are also used (Sections 2.2.2.2 and 2.2.2.3).
Before starting production of an AM model, the 3D model first has to be placed on the building platform in the optimal direction by the front-end or additive manufacturing software. It is also necessary to add the process-specific data like the supports. To achieve the best use of the machine, several components are built simultaneously on the platform. In some AM processes the components are placed into and one above each other.
Figure 2.6 Data flow during additive manufacturing
Third-party software contains optional features that allow, for example, the derivation of 3D data from 2D sketches. Some of this software is just used to display the 3D model. This kind of software is trimmed of the needed features of CAD software and can transform the model into the STL format.
When the model is included with the geometrical and directional information, it is necessary to establish the machine and material parameters required for the control of the rapid prototyping process in order to proceed with the building process.
In any case, the geometrical information of the entire body, like the layer thickness and the contour data for every layer, must exist to produce the 3D model. The generation of equal layer thicknesses with mathematical methods is called slicing. Most machines slice the whole 3D model and use the layer information in the batch mode. Depending on the capacity (speed and memory) of the computers the machines generate each layer shortly before the physical generation of each previous layer. Today, the so-called adaptive slice method (“slicing on the fly”) is installed on the machines. This method allows measurement of the current geometrical height and generates the next layer depending on that value. In that way, geometrical errors in the z direction that depend on propagation errors will be reduced or avoided completely.
The data is the basis for manufacturing the AM model, and after postprocessing the model is ready for use.
In addition to this direct path, there are also alternatives in the design and production. It is possible to deliver the geometrical data in SLI/SLC (Section 2.2.2.2), PLY (Section 2.2.2.3), or AMF (Section 2.2.2.4) format instead of STL format.
Neutral interfaces are also used to transfer data. The reason is in the advantages when the construction is finished and the model has to be modified during the production process. Modification of an STL model is possible but not as straightforward as in a full-fledged CAD system.
The most important neutral interfaces that are integrated into 3D CAD systems are listed below:
IGES Initial graphic exchange specification
VDAIS Association of Automotive Manufacturers ‒ IGES interface
VDAFS Association of Automotive Manufacturers ‒ Surface interface
DXF Drawing exchange format
HPGL Hewlett-Packard graphics language
SET Standard déchange et de transfer [Standard Exchange and Transfer]
STEP Standard for the Exchange of Product Model Data.
IGES is one of the worldwide standards for geometrical interfaces. This format exhibits a lot of varieties that should be described in detail.
VDAIS is an IGES interface from the Association of Automotive Manufacturers. This interface also includes a lot of varieties, so in each particular case one must examine carefully which interface formulation the data exchange is based on.
VDAFS is specialized for freeform surfaces and therefore has importance in the automotive industry.
HPGL is a contour-oriented plotter format that is especially used in the context of direct contouring in CAD for AM processes
STEP is an interface that is becoming increasingly established after a long test phase. In addition to the geometrical information, other information can be exchanged with the STEP format. The STEP format represents an approach to exchanging the original CAD model and not only the geometry information.
2.2.1.2 Modeling 3D Bodies in a Computer by Means of 3D CADThe creation of a 3D body is the indispensable prerequisite for the production of an additive manufacturing model. Therefore, the application of AM processes is linked especially close with CAD processes. For this reason, 3D CAD processes will be looked into only as far as is absolutely necessary to understand the fundamental relationships in the production of rapid prototyping models.
Every CAD system uses certain data elements and data structures to describe a component in detail. The data record includes not only the component geometry but also the materials, the quality of the surface, the production process, and much more. The component geometry therefore comprises only one part of the information. The complete information registered in the database of a CAD system for a component is called a CAD model (the product to be made). If the geometric description of a component is 3D, then it is called a 3D CAD model or digital product model.
By choosing a certain CAD system the user commits himself to its database. The structure and the data elements decide to a high degree the quality of a CAD system and its compatibility with other systems via an interface. The CAD system also defines the type, extent, and quality of the AM process.
2.2.1.2.1 CAD Model TypesCAD models are defined by model types regardless of the kind of CAD system. As shown in Fig. 2.7, not all types that display a 3D model are suitable for an AM process; some types do not have sufficient information.
Figure 2.7 CAD elements and model types
The corner model defined by points is of less practical importance and not usable for AM processes. It is used, for example, as an intermediate model for the semiautomatic transformation of grid data or 2D CAD models into 3D CAD models.
Owing to its small amount of data, the edge model enables a fast graphic representation of 3D elements even with low-performance computers. Its importance is therefore growing again in connection with virtual reality (VR) applications and digital mock-ups (DMU). The most important disadvantage of the edge model is the missing information about the exact position of the surfaces and the volumes. For this reason it cannot be recommended as a basis for the production of AM models.
All CAD systems that process components as surface models in their geometrical databases are in principle suitable for issuing data via an additive manufacturing interface. When a component is defined by its external surface, the user is usually able to calculate the exact component volume as well. This is usually achieved by assigning and storing an additional normal vector for each surface pointing away from the inside of the component. For the complete description of a component, therefore, it is absolutely necessary that the orientation of the component volume is known.
Solids are optimal for the modeling of CAD models that (among other things) are also used for additive manufacturing. The orientation of the volume is preset exactly and need not be explicitly defined by the user.
Solids are differentiated into
basic solids,
surface determining models, and
hybrid models.
