Additive-manufacturing (AM) technologies have drawn a lot of attention and investment from the manufacturing community in recent years. This article presents an overview of AM processes, including their economic and operational advantages and constraints.
The origins of the AM industry (also called the 3D-printing industry) date back to the 1980s, when the technology set of processes that produced parts additively – one layer at a time – were referred to as “rapid prototyping.” For more than a decade, additive technology was focused only on processing polymer materials, in various forms, with the exception of the Laminated Object Manufacturing (LOM) process, which utilized paper materials. As the technology set inevitably improved in capabilities and processes exceeded certain operating temperatures, new materials emerged as candidates for AM processes, most notably metals.
During the last decade and a half, the growth of the AM sector has been strong and steady, with increasing uptake and adoption of plastic/polymer and metal processes across many industrial sectors for prototyping (form, fit and function); tooling; and, more recently, final production applications. At the forefront is the aerospace sector, but other strong indicators can also be seen in the automotive, medical and engineering sectors.
Progressive and innovative developments of the direct-metal AM subsector in particular are generating significant growth in terms of the sector’s value and applications development. Indeed, for direct-metal AM, the 2016 Wohlers Report (most recent) indicates a year-on-year increase of global sales of metal AM hardware systems, specifically a 75.8% increase in 2013, 54.7% increase in 2014 and 46.9% increase in 2015.
Market indicators are many and varied – system sales, new market entrants and share prices to name a few – but perhaps the most significant to date came in September 2016 when GE announced its intent to acquire two European metal AM hardware vendors (Arcam in Sweden and Concept Laser in Germany). The combined deal is stated to be worth in the region of $1.4 billion.
Beyond the headline figures, however, these acquisitions ensure GE has access to two dominant industrial metal AM processes: electron-beam melting (EBM) and selective laser melting (SLM). GE’s evolution from a user of AM technologies to a user and service provider (internal and external through the previous acquisition of Morris Technologies) to a user, service provider and vendor of hardware and metal materials singularly highlights the current capabilities of direct-metal AM processes and points to its future potential.
It is easy to understand the many unique and well-documented benefits of metal AM technologies, namely: greatly increased design for manufacture (DfM) freedoms; production of complex and functional parts without assembly requirements; production of stronger, lighter-weight structures; reduced material consumption; and the cost and time savings associated with tool-less production.
Overview of AM Processes
There are, in fact, a number of different metal AM processes commercially available and suitable for a wide range of industrial applications. A brief overview of these processes is provided here.
The dominant commercial process for metal AM is powder-bed fusion (PBF). This process employs a bed of powdered-metal materials and utilizes a heat source (either a laser or electron beam) to melt and fuse layers of material powder together to produce fully-dense metal parts. PBF is synonymous with many other terms that are either used as brand names or generically to distinguish differences in techniques such as “direct metal laser sintering (DMLS),” “electron-beam melting (EBM),” “selective laser melting (SLM)” and “selective laser sintering (SLS).”
Directed Energy Deposition
The directed energy deposition (DED) process, also called direct-metal deposition (DMD) or 3D laser cladding/welding, is generally considered to be an important subsector of the metal AM industry. However, it is not a process that is conducive to “manufacturing” new/original parts. Rather, it is a complex additive process that is commonly used to repair existing components by adding new metal materials to the original part.
The binder-jetting process utilizes two materials during the build process: usually a powder material (metal) and a liquid binder. The binder material in this process can have a significant impact on the material characteristics of the final part, meaning that this process can be unsuitable for structural parts. Furthermore, this process demands additional post-processing procedures that can add significant time to the overall process.
Direct Material Jetting
Material jetting creates objects by directly jetting material onto a build platform using either a continuous or drop-on-demand (DOD) approach. A suspension material is required For the direct jetting of metal materials.
Another growing subsector of the metal AM industry is visible in the commercialization of hybrid additive and subtractive manufacturing processes, with single hardware systems that combine additive PBF processes with CNC milling capabilities.
Existing Barriers to Adoption
Despite the increased focus on metal AM for manufacturing and production, as well as specific application development, there are still numerous constraints and barriers to mainstream adoption for this tech sector.
The most fundamental issues include (relatively) slow build speeds, low production volumes, costs (both capital and running), limited build sizes, limited material palette and lack of certification/QA procedures. The latter issue is particularly pertinent for highly regulated industries such as aerospace, automotive and medical. Safety is also an issue, although not generally considered a barrier to adoption. The raw metal powders for PBF systems are identified as a particular risk since they have multiple safety issues associated with them in terms of skin contact and respiratory concerns.
However, commercial vendors of metal AM hardware systems and materials – both incumbent and new entrants – are attacking these adoption issues from multiple angles. Investment into R&D is widespread to develop significant improvements for in-process variables that increase metal material options and improve handling issues and for supply chain and in-process monitoring capabilities to achieve full traceability. Process monitoring and process feedback control in existing metal AM systems is currently limited, but it is a significant area of research that will likely bring quantifiable results over the next few years.
Metal AM System Parameters and Constraints
Due to the process parameters, AM is typically suitable for the production of small- or medium-sized parts in low to medium volumes. Part size is typically limited, particularly with powder-bed fusion processes where the part size is constrained by the powder-bed size. Vendor companies offer average build volumes around 250 mm x 250 mm x 250 mm (XYZ), which accommodate a wide variety of suitable small and micro applications (medical/dental/jewelry, etc.).
Industrial-focused system developers have also scaled up AM systems to 1 meter in the X axis, with further notable developments still in the R&D phase. Furthermore, part sizes can be greater with the directed-energy deposition and binder-jetting processes, but the trade-off here is the structural integrity of the part. Parts produced with additive manufacturing tend to show anisotropy in the Z axis, and while densities of 99.9% can be achieved with PBF and DED processes, residual internal porosity can be an issue along with residual stress, delamination, cracking and swelling.
Setting and monitoring of process parameters such as operating temperature, feedstock, build-chamber atmosphere and laser quality all contribute to the quality of the final part. Overlooking these parameters can result in an increased occurrence of defects.
And then there is accessibility to the technology. Here accessibility refers to both costs (capital expenditure and running/consumables) and democratization. Manufacturing of metal prototypes and production parts is essentially an industrial discipline due to the operational and safety complexities involved in handling systems day to day. However, access to these systems is often cost-prohibitive for all but the largest OEMs or specialist service bureaus. Therein lies the best access route to date for smaller companies that want to take advantage of the capabilities and output of metal AM – through contracts with service bureaus.
New options are emerging for accessibility to direct-metal AM. One company in particular has identified the need for a smart, fully capable metal 3D-printing system at an accessible price point. Considerable market research demonstrated that metal AM had tremendous potential for small and medium-sized enterprises (SMEs), particularly in the jewelry, dentistry and medical sectors, as well as for smaller engineering firms and laboratories.
German machine manufacturer OR Laser has a 19-year history in the field of lasers and machine production and can demonstrate a reputation for quality and performance hardware together with a new software approach. Following the successful commercialization of DMD equipment, OR Laser most recently designed and developed a direct-metal AM system, the ORLAS CREATOR, specifically to provide access to metal 3D printing for SMEs with a very competitive price point that amounts to half the cost of comparable machines on the market. A trend is likely to follow, with numerous start-up companies already following suit.
What is certain is that the metal additive-manufacturing sector is on an upward trajectory that looks set to continue for the foreseeable future. This growth is across an increasing spectrum of industry sectors and increasing number of applications for prototyping and production.