Additive Manufacturing

The maturity model we propose is based on competency with a strong focus on the technical aspects of AM (e.g. uses, tools, materials, technologies). This section therefore presents definitions of technical elements that will be later found in the project results, namely, the maturity model and survey, and the integration strategy comprising the identification guide, the roadmap and the work packages.

Parts are either made by deforming material (e.g. forging), removing material (e.g. machining) or adding material. The latter is the principle guiding additive manufacturing technologies that either fuses or cures material to build a part layer by layer or by selective material deposition in the case of multiple axis processes. A digital file resulting from Computer-Aided Design software, often an STL file, is the input to AM equipment. Software specific to the AM equipment reads the digital file, performs various operations (i.e. position multiple parts in build space (nesting), generate supports if needed), then virtually slices it in multiple layers to produce code that then drives the path of the print head or energy source for each layer. The American Society for Testing and Materials (ASTM) has established in the standard on Terminology for Additive Manufacturing Technologies F2792-12a seven categories of AM processes: binder jetting, directed energy deposition, material extrusion, material jetting, powder bed fusion, sheet lamination, and vat photopolymerization. The International Organization for Standardisation (ISO, 2015) also adopted this classification of AM processes. Each process uses specific materials and materials forms (powder, filament, liquid, sheet). Materials include polymers, metals, ceramics, composites, paper, and even biological matter.

A thorough knowledge of the AM domain is required for effective AM process selection due to the large variety of AM processes, equipment and materials.

Additive Manufacturing uses 

This project is aimed towards the use of AM for industrial applications. These uses can be divided in the three following categories and sub-categories:

1) Prototyping: prototypes are physical models used to carry information during the product development process for testing the product design and set up the production process (Pfeifer et al., 1994). Specific types of prototypes will assist particular needs:
a. design models,
b. geometrical prototypes,
c. functional prototypes,
d. technical prototypes,
e. pre-production parts.

2) Production parts: also called direct part manufacturing, it refers to the use of AM to produce a part that is then sold to a customer. This category of parts can be divided in three subcategories:
a. original part (serie of one or several parts),
b. spare part,
c. repair.

3) Tooling: refers to the use of AM to produce a mold, a pattern, or a die that is then used to produce a part, also called indirect part manufacturing. Tooling can also refer to parts directly produced with AM that can be used as assembly aids, testing devices, and jigs for machining or measurement purposes. We consider both types of tooling in this project.

Part classification is adapted from Pfeifer et al. (1994) and Gebhardt (2011) for the case study domain of application.

Additive Manufacturing process flow and methodologies

This section aim is to provide definitions of AM concepts. We first present the definition, and then explain how these concepts are expressed within AM applications.

• CAD (Computer-Aided Design) software: software such as CATIA or SolidWorks used to design and represent parts in 3D;
• Support structures: when building parts layer by layer with many of the AM processes, additional material needs to be added to maintain overhanging/cantilevered features in place during part building or to anchor the part to a build platform;
• Post-processing: varies depending on AM process and includes support removal, heat treatment, curing, polishing, plating, painting, etc.;
• Design rules or design for additive manufacturing (DfAM): DfAM rules are essentially geometric guidelines allowing the manufacturability of a design by a specific AM process. Examples include: minimum wall size thickness, support structures, and powder removal design. It implies a change of paradigm to design parts by adding material compared to removing or forming material;
• 3D scanning: defining the geometry of a part by collecting data as point clouds that can be transformed in a 3D digital file of a physical part, often used in synergy with AM to copy a part;
• Topology optimization: method to optimize the distribution of material within a given design space under defined loading and boundary conditions. It is often used with AM to reduce weight of parts. Popular software include OptiStruct by Altair, Inspire by solidThinking and Within by Autodesk. AM is often seen as the only manufacturing process that can fabricate the organic and complex geometrical features resulting from topology optimization (Zegard and Paulino, 2016);
• Part slicing: the AM machine software separates the digital file into numerous slices according to the selected layer thickness, which represent the consecutive layers to be deposited, fused or cured.

The defined concepts are presented in bold in the next paragraphs.

As with traditional manufacturing processes, industries can buy equipment to fabricate parts in-house or they can outsource fabrication to service bureaus. In-house fabrication is sometimes referred to as a “Make scenario” and outsourcing as a “Buy scenario” within the industry. Since AM equipment can be expensive (Wohlers and Caffrey, 2015) and many industrials don’t yet have the necessary skills to operate AM equipment or don’t yet know how they could effectively benefit from AM, many will work with service bureaus for their AM needs. These bureaus can also assist in the design of parts for AM, the preparation for fabrication (e.g. support structures) and post-processing. Like traditional processes, design rules or Design for Additive Manufacturing (DfAM) need to be applied to obtain precise (i.e. repeatable) and accurate (i.e. within tolerances) parts. Some service bureaus can also provide 3D scanning and topology optimization services.