Accelerating Manufacturing Operations with High-Strength Plastic 3D Printing
3D printing in a factory 3D printing encompasses a family of processes that involve building up a plastic or metal part in an incremental layer-by-layer fashion.
3D printing offers manufacturers attractive capabilities by enabling them to produce geometrically complex parts with minimal operator input and no machine supervision. Additionally, there is no specialized high-skill machine operating knowledge required as in computer numerical control (CNC) machining: 3D printing quickly provides engineers with a powerful extra resource to solve problems without adding to their workload.
BUSINESS CHALLENGES AND PROCESS IMPROVEMENTS FIRST
3D printing fundamentally offers a lower-effort path to producing a physical part, so many manufacturers initially approach it with a ‘parts-first’ mentality: attempting to shoehorn 3D printing in to replace an existing component without first considering the larger picture. A common focus is evaluating two elements: 1) whether a 3D printed version of an existing design (with minimal changes) can be used as a drop-in replacement and 2) what the direct cost and lead time will be for the 3D printed part. While this approach is not without merit, it often fails to address the root cause of these manufacturers’ challenges and takes a short-sighted approach that misses much more valuable opportunities for process-level improvements.
Manufacturers should instead consider the underlying operational challenges in their business, focusing on tackling the sources of excessive cost and production risk in their processes. Common challenges in manufacturing that high-strength 3D printing can impact are:
- Unplanned downtime mitigation and avoidance
- Supply chain risk from outsourced tooling and assembly fixtures to critical manufacturing, repair and operations parts
- Yield and scrap issues, especially those due to out-of-control processes
- Excessive cycle times, especially in robotic automation
For example, if a machine component frequently fails due to physical impact during production and causes a line-down scenario, it’s often more valuable to solve the process issue causing the part to fail in the first place rather than to reduce the cost and lead time of the actual component itself. To solve the issue, manufacturers could consider 3D printing a fixture to more gently control movement of product through the manufacturing line or an impact-resistant bumper to shield the at-risk component. In either case, addressing the root cause can solve a downtime issue costing thousands of dollars, rather than providing an ongoing temporary fix at a reduced cost.
A RANGE OF TECHNOLOGIES FOR A RANGE OF APPLICATIONS
There are three primary plastic 3D printing technologies that can offer capabilities that meet the unique needs of manufacturers, especially in the valve industry. These three technologies are:
- fused filament fabrication (FFF) and continuous filament fabrication (CFF)
- stereolithography (SLA) of photopolymers
- powder bed fusion (PBF) technologies such as selective laser sintering (SLS) or multi jet fusion (MJF)
FUSED FILAMENT FABRICATION AND CONTINUOUS FILAMENT FABRICATION
Fused filament fabrication is the most widespread 3D printing technology. At its core, FFF involves melting a thermoplastic plastic filament and extruding it through a nozzle, producing a fine path of plastic. Multiple paths are laid down to trace out the cross-sectional area of a part, called a layer and successive layers are built on top of each other to form a part. The suitability of FFF parts for manufacturing purposes is largely determined by the material being printed, with high-toughness materials like nylon, thermoplastic polyurethanes (TPUs) and high-temperature materials like PEEK and Ultem being of particular interest.
Continuous filament fabrication is a reinforced 3D printing process that can be used during the nylon FFF process to add significant strength and stiffness. It is the only process to truly offer ‘high-strength’ plastic 3D printing. FFF+CFF parts provide the highest strength and toughness across the plastic 3D printing landscape. In the CFF process, continuous strands of high-performance composite materials like carbon fiber, Kevlar and fiberglass are incorporated into a part at strategic locations during FFF printing to create strong, lightweight parts suitable for replacing traditionally machined engineering materials like aluminum 6061, Delrin, nylon and ultra high molecular weight (UHMW) polyethylene. CFF is not a standalone technology and can be used only as a reinforcement to strengthen parts during the FFF process.
FFF and FFF+CFF 3D printing have many advantages: the technologies are easy to use, can produce parts that are both strong and tough, require minimal operator effort to process parts post-print and present few, if any, environmental health and safety (EHS) challenges.
FFF and FFF+CFF fall short when confronted with small, intricate parts and struggle to properly produce features smaller than 0.02 in. (0.5mm). In some cases, this may simply require some post-print machining to rectify. Because of these limitations, FFF and FFF+CFF parts made from a combination of tough and strong engineering materials are typically implemented in manufacturing line components, assembly fixtures and other tools for manufacturing with feature sizes larger than this effective limit.
Stereolithography is a 3D printing process that involves the layer-by-layer curing of thermoset photopolymers via a UV source, usually either a laser or through digital light projection (DLP). A typical SLA printer contains a bath of photopolymer resin with a UV-transparent window on the bottom through which the light source passes. Either a laser traces an extremely fine point-source curing path that defines a layer of the print or, in the case of DLP, a projector cures an entire high-resolution layer at once. Layers are printed one after another and the part is printed upside down and slowly drawn out of the resin bath. After printing, parts are usually washed clean of resin with isopropyl alcohol and then finish-cured in a UV chamber to achieve final mechanical properties.
SLA printers typically use light sources with resolutions that are significantly smaller than the nozzle diameter of an FFF printer and are known for producing parts with extremely fine surface finish with intricate features. Valve designers and manufacturers may find these capabilities useful in product R&D: when testing new valve body geometries, flow chambers and more where the surface finish of a part is critical.
Material properties and process requirements are potentially key limitations of SLA printers. While there is a range of materials available, including ones with appropriate toughness or high elasticity, many photopolymers have limited ultimate tensile strength and are brittle. Additionally, while photopolymers are cured with UV, light can also degrade them over time and result in extremely brittle parts that are susceptible to physical impact. From a process standpoint, the post-print processing required for SLA parts requires additional equipment beyond the 3D printer and the large quantity of isopropyl alcohol involved can present EHS challenges for some facilities.
POWDER BED FUSION
The final set of 3D printing technologies relevant to manufacturers is the PBF family, in which parts are made by selectively fusing together successive layers of plastic powder. During PBF processes, a thin layer of powder is spread uniformly over the preceding layer before a heat source is applied to the areas of the layer to be fused. PBF technologies are unique among the previously discussed 3D printing processes as they’re suitable for higher volume manufacturing of parts. The bed of powder composing the PBF print volume is also self-supporting and does not require the same amount of printed support material necessary in FFF or SLA processes to successfully produce overhanging features.
PBF processes are more optimized for higher volume production than any of the other 3D printing technologies and can produce parts with complex geometries while requiring the least amount of specialized design expertise. PBF parts have some of the most isotropic (equal in all directions) mechanical properties across the 3D printing landscape and are often excellent for producing beta or pre-production runs of parts, such as electronics enclosures, that will eventually be injection molded during high-volume production.
PBF technologies have two main limitations: the somewhat low impact resistance of the parts and system costs. While PBF processes produce parts in high-toughness materials such as nylon, the powder-based process itself often leads to microscopic porosities through the part that act as stress concentrators under load. Physical impacts, like those present in a manufacturing environment, can initiate cracks that propagate through the part and cause premature part failure. PBF technologies can also be expensive, especially if run at lower duty cycles and include high equipment costs, extensive EHS requirements to handle loose powders and substantial training for equipment operators. Fortunately, there are plenty of third-party service bureaus running PBF technologies at reasonable prices, presenting an easier option to manufacturers looking to explore these parts.
It’s important to remember that 3D printed part performance is a combination of the materials involved and the properties imparted by the process itself. Parts made from manufacturing processes like machining or casting are usually solid (although castings often have a low level of porosity) and have generally isotropic material properties. This is not necessarily the case when printing the same part and for many 3D printing processes the parts will be extremely anisotropic with a hollow, honeycombed interior. You can view these properties as characteristics that should be considered in design, similar to how you might design a machined part to take into account an end mill cutter’s radius.
Strength is only one of the metrics manufacturers should focus on when they are evaluating 3D printing technologies. Materials on the plant floor often require both high-strength and high-toughness, as physical impact occurs daily. Compare the impact strength of the 3D printing materials under your consideration. For context, think about the fixtures in your own operations that are made from engineering plastics like Delrin or UHMW. Few, if any, of these tools are ever going to be loaded to their ultimate tensile strength (you probably would have made them from metal if they were), but they will be dropped and have tools dropped on them, as well as other kinds of physical impact every day.
High-performance 3D printable engineering plastics include:
- thermoplastic polyurethanes (TPUs)
In addition, for true high-strength 3D printing that can replace or substitute for aluminum-strength parts, manufacturers can utilize CFF processes to reinforce nylon FFF parts with high-performance composite fibers such as:
- carbon fiber
SUCCESS IN MANUFACTURING
Thousands of manufacturers across the world have already driven success in their manufacturing operations by adopting high-performance 3D printing capabilities. Here are two examples.
The first is a U.S-based manufacturer of hose fittings, valves and other fluid transfer accessories. Throughout its existence, this company has invested in new technologies that can accelerate operations, most recently in high-strength 3D printing. The advanced manufacturing engineering (AME) team uses this technology to rapidly iterate and build production tooling, including more effective end-of-arm tools (EOATs) for their industrial robots. 3D printing eliminates scrap due to misplaced components, minimizes line changeover times and planned downtime with quick-change machine components and creates other production tooling applications. This has meant hundreds of thousands of dollars in savings and allowed rapid response to new challenges that arise in the company’s plants.
The second company is an industrial control manufacturer that makes a wide variety of products used in process industries, from chemicals and pharmaceuticals to semiconductors and tank storage. The company prioritizes ongoing engineering improvement, with a focus on enabling and empowering its tooling engineers, designers and machinists. The company originally invested in high-strength 3D printing technology to reduce the burden on its machine shop when creating EOATs for their industrial robots. The EOATs are required with every new product launch and as part of their ongoing manufacturing, repair and operations efforts. The engineers and machinists found that they could produce high-strength 3D parts with less effort, freeing them to pursue other higher-value tasks.. The company has since begun printing fixtures that allow parts to be loaded into multiple different machining centers without re-fixturing. This reduces potential yield problems due to operator error and accelerates the pace of production.
BEST PRACTICES IN DESIGN
Every family of 3D printing processes has different capabilities and limitations, so each specific process has unique design guidelines. Rather than cover all of these in a single article, we’ll focus on a design workflow that’s broadly relevant to the 3D printing technologies already discussed, with a specific focus on FFF and FFF+CFF printing, as these processes have the widest potential for application in the valve manufacturing industry.
Design best practices for high-strength 3D printing involve the following workflow:
- Investigate the root cause of the underlying problem, not just the most immediate challenge.
- Estimate the business case and ensure 3D printing is a viable solution. The technology typically excels at low-volume, high-mix production and becomes less viable the more production volumes increase.
- Identify the functional requirements of the application in question. Understand the required loading and environmental conditions as well as any interactions the part will have with other components or equipment. Ensure that the 3D printing process and materials being considered are compatible with these functional requirements.
- Create an initial design from which to iterate. Generally speaking, a good starting point is to design a part that is roughly similar to something that could be machined or cast and fits within the 3D printer’s build envelope.
- Adjust the design to take into account the part’s functional requirements. There’s no need for perfection at this stage, just take steps toward addressing what’s needed. At this point it’s a good idea to consider the characteristics imparted by the 3D printing process and adjust the design around any limitations.
- Fail fast and iterate quickly and often. 3D printing requires no operator supervision and minimal setup time, so an engineer can design the next revision of a part, send it to the printer and continue on with other work while the printing occurs.
HOW TO GET STARTED
The bottom line is that valve manufacturers can take advantage of 3D printing technology to meet the challenges of increased competition. As momentum builds for 3D printing, manufacturers are learning where to use 3D printed solutions for maximum business impact.
Start by thinking about the biggest inefficiencies and bottlenecks in your operation where a high-strength, high-toughness, 3D printed tool, fixture or manufacturing line component could accelerate production, improve quality and reduce cost.
Nick Sondej is senior application engineer at Markforged.
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