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Additive Manufacturing Essentials

7.2 The Digital Thread in Design for Additive Manufacturing

Additive Manufacturing Essentials7.2 The Digital Thread in Design for Additive Manufacturing

Learning Objectives

By the end of this section, students will be able to:

  • Describe the opportunities presented by software solutions in part selection and management.
  • Understand the impact of design choices on the digital thread.

The foundational step of any 3D printing operation is the creation of a digital design file. We covered the full process of design for additive manufacturing in detail in an earlier chapter. As we break down each step of the additive manufacturing workflow, we are going to discuss how each of these parts generate digital information that can be strung together as part of a global digital thread strategy.

Digital design tools are not new for manufacturing. In fact, they have been around for the better part of several decades. What is different for AM is that they are a requirement for starting the process. A two-dimensional drawing, even if it is fully developed, will not suffice in the workflow process. Therefore, any user needs to be able to access a CAD tool to build a 3D model. This often becomes a hurdle for organizations who are building their additive manufacturing strategy because many or even most of their parts are generated for conventional manufacturing processes with 2-D drawings. Even if the part is a good business case for 3D printing (perhaps a low volume repair part or some high value component), the first step is building the model in three dimensions.

Throughout this chapter, we are going to be touching on two main aspects of how design interacts with the AM digital thread. The first is through the creation of these digital files and the types of digital tools are required to do that. The second area that we will be discussing is how the design approach influences all aspects of the 3D printing process and ways that companies are trying to build tools specifically for 3D printing modalities.

Digital Design Creation

There are many different software tools available that allow a designer or engineer to construct a part in three dimensions. Typically, these approaches live in the realm of parameter-based modeling where a solid model is developed and once it is ready for export to the 3D printer the file is converted to a triangle mesh. There are certainly other types of modeling based on scanning (point clouds) and more surface based modeling approaches that can be utilized in 3D printing, however for the most part the majority of 3D printing files start in the region of solid modeling.

An autodesk software screen with a number of three dimensional shapes, most of which resemble small columns with a textured or bumpy surface on the top. Taller columns stand to the left, and a denser cluster of shorter items is on the right. Various software menus and displays appear around the main shape.
Figure 7.3 This model was made by 3D scanning an object with an ASUS XTION depth camera, then importing the scan data into an Autodesk software where it was made into a solid and captured as an STL file. (credit: Creative Tools/Flickr, CC BY 2.0)

Because the vast majority of traditionally manufactured parts are not 3D printed, the legacy CAD and solid modeling companies have a wide range of software options that can be adapted to 3D printing. Some of the most common industry stalwarts are SolidWorks (Dassault Systemes), Onshape, PTC, Autodesk, and Siemens NX. There are also numerous free or low cost CAD software systems on the market. The primary function as it relates to 3D printing for these tools is the creation of the digital model. However, the CAD design process is actually a very small portion of the capabilities of these software tools. Most CAD systems have the ability to create complex assemblies, do different levels of part or process simulation, and manage bill of materials.

Many of the traditional CAD systems also have embedded workflows that are dedicated to specific industry applications. For instance, in the dental or medical space, imaging equipment is often used to create digital designs to assist with surgery or medical implants themselves. In these cases, point cloud data from various scanning platforms needs to be converted to STL but at the same time patient data and prescription information should be documented alongside this information. These types of workflows are where the current landscape in 3D printing is often limited because operators start to have multiple files that connect to the same patient. Manufacturers must then come up with a system to continue to manage that information as it goes into the printer and a subsequent database, ultimately landing back with the customer or patient.

Something to keep in mind as we think about the digital thread is the way in which designs are built and disseminated amongst a team. In some cases, part designs are managed by a single individual that is enabled by their own single software platform. In many other cases there tends to be a sharing of CAD or design files between numerous people in an organization. This is often one of the big reasons that individual companies will tend to have a company wide policy of only using one brand of design software as it can be challenging to move design files between different CAD platforms.

There is also a trend to deploy cloud-based CAD design tools that further enable collaboration within an organization. The principle advantage of having a cloud-based solution is that software tends to become obsolete over time without routine updates. Cloud-based systems are updated at a more regular basis, often with a subscription model for the user.

It is important to always keep in mind that 3D printing is one of many tools in the manufacturer’s toolbelt, and that the use of the technology does not always guarantee improved outcomes on every dimension. We have discussed in earlier chapters the ability of 3D printers to produce parts that are highly complex with design features like internal passageways that may not be easily replicated in conventional manufacturing. The addition of these features may allow for lightweight parts that can improve overall performance. Typically, a complex structure may only be a portion of the overall part geometry, but can still cause challenges within existing CAD files because the geometry file becomes larger. Long term, it is also a consideration as most designs are not static. Users should consider how and who might be able to edit a part in the future for improvement or including advanced features.

We have been discussing the basic tools for creating the digital files required for 3D printing. As you think about the application of the technology within an organization, a part design is not something that just materializes one day and is complete. Instead, any design file goes through numerous iterations through the prototyping process before it is finalized for production. The current STL file format does not offer an embedded iteration history in the file. A user can use an internal naming convention on the specific file to signify changes, but this is certainly a limitation of the file type. From a digital thread perspective, this does introduce potential version control issues into the process of production printing. In order for full traceability to be documented, there needs to be at minimum a process to ensure that a file is locked at a particular version signifying date and time of the last change. Not only is this important for internal organizations, but is important for organizations that are outsourcing their printing to service bureaus or contract manufacturers because there are limited controls to who can make changes to a design once they have the digital files.

Part Selection and Management

We have covered throughout this text the mechanics of designing parts for AMalong with software tools that enable that process. Up until this point, we have neglected a discussion on the ways to digitize the selection of what parts should be 3D printed. We already know that there are good and bad part choices when it comes to the technology, but as the technology becomes more improved, the hope is that the combination of geometry, materials, cost, and performance of 3D printed parts becomes more comparable to traditional technologies.

There are basic screening techniques that can be applied to help organizations decide what is a good candidate for 3D printing. Organizations must consider the digital design information such as part dimensions and features. They must also gather and assess costing and material requirements, which are critical elements of the 3D printing digital thread and ultimately help inform the pathway of production for many parts.

An engine cylinder head, which appears as a curved rectangular structure with four large openings and a number of attachment points for other components. The substructures, angles, and details reveal a complex interior structure.
Figure 7.4 An engine cylinder head cast from a 3D printed mold. Deciding on whether such a critical part could be produced through AM – even indirectly – is a complex process that can more deeply associated with digitally supported decision making. (credit: Modification of “Automotive cylinder head cast from aluminum cerium alloy in a 3D printed mold” by Oak Ridge National Laboratory/Flickr, CC BY 2.0)

At the moment, the process of selecting suitable parts and design spaces for AM components is mostly a manual process. The process is relatively slow, and requires a team with expertise in the 3D printing technology space to evaluate all the potential options. Emerging digital decision approaches have been commercialized to streamline that process. For example, Castor is an automated part screening software that informs manufacturers when it is beneficial to use additive manufacturing.

Design Implications that Impact the Digital Thread

We have emphasized the importance of contextualizing your 3D printing designs within the entire process workflow. Many of the elements involved in design approaches require a strong partnership between the user and the software tools to enable a successful thread of information. There are efforts to enhance the connection nodes between design variables with underlying file types like 3MF. However, the adoption rate of new fundamental approaches to replace files like STL will undoubtedly take time to iron out of the system.

In the meantime, users should focus on best practices to engage the operators and technicians of the equipment to leverage the most appropriate software relevant to their industry. This may sound obvious, but some organizations may not need the most expensive or advanced design tools with all the latest features because they may only use a small subset of their capabilities. As with most applied elements of the manufacturing sector, a thorough understanding of the critical workflow elements, led by those who operate the equipment, typically gleans the most insight.

The 3D printing sector should not be thought of as a static entity. There is a constant updating of processes and procedures in relation to the overall organization, facilities, and machinery. In some ways, the job of the user is never done in finding a way to optimize the process of structuring designs both for functionality in the real world but also in a digital sense to optimize the process for their construction. Part design is not only the foundation of the overarching 3D printing process, it is also the foundation upon which the 3D printing digital thread is built. The software platforms that are utilized in the beginning of the workflow to create a part underpin what decisions can be made with the digital thread later on in the process of part production.

In some cases, all design tools will reside within a single operational platform. In other cases, the software tools used to perform one aspect of the design process may be incomplete for a future step, and we need to connect that information to another software platform. These connection points are what make the digital thread so “bumpy.” We rely on operators and engineers to know what data is meaningful to keep across the timeline of the part. But the body of knowledge is not always transferable to every printing platform, new material, or design need. Many organizations go through a painful growth stage where the nuances of each machine are mapped out over a period of several months or even years to identify what signals are strong and impactful for the process.

Design factors that influence final parts and the digital thread include:

  • Software platform
  • Design approach (CAD, surface modeling, etc.)
  • Build orientation
  • Printer
  • Materials
  • Collaboration requirements
  • Intellectual property considerations

The creation of the digital file is only the first step in the printing workflow. As we build upon the subsequent steps we will continue to discuss how the data generated can influence the outcome of each 3D P\printed build but hopefully provide you with the tools to consider how best to construct your own AM digital thread that is most relevant to your industry and organization.

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