Adopting new technologies generally involves lots of experimentation coupled with low expectations. Sloppiness, imprecise results, or outright failure are fine learning experiences when evaluating a novel system’s potential but completely unacceptable outcomes for production systems.
With additive manufacturing (AM) moving from prototyping and design labs into serial production, users demand higher levels of quality, repeatability, traceability, and output. And while 3D printer makers and other AM technology providers continue to improve their equipment, a new, advanced supply chain has emerged.
Just as traditional job shops work with a network of machine tool manufacturers, cutting tool makers, software vendors, and materials suppliers, AM users are learning that it takes a network of manufacturing technology providers to create a finished part.
An early dream of AM was direct print-to-use components – imagining a 3D part using digital design software, sending it to a 3D printer, and getting a finished, usable part within a few hours of ideation. While possible in some situations, users have found that building semi-finished parts and going through post-processing improves cost, quality, and productivity.
In the pages of the 2019 AM/3D Target Guide, several technology experts discuss where post-processing techniques fit into the maturing AM ecosystem. Experts highlight heat-treatment systems for thermoplastic AM parts, finishing fluids used in cleaning post-processes, and using AM to develop custom tooling. There’s also coverage of cutting-edge developments in AM systems and use cases showing how manufacturers can benefit from new equipment.
AM is still a cool, gee-whiz, sky’s-the-limit technology capable of revolutionizing any industry it touches. The growth of support industries and post-processing shows that it’s also maturing, making it more capable of producing complex parts quickly, cost effectively, and most importantly, reliably.
— Elizabeth, Robert, Eric, & Michelle
Finishing fluids for 3D-printed parts
Features - 2019 AM/3D Target Guide
Choosing the proper post-processing fluid can save time, energy, and improve plastic and metal parts.
3D printing (3DP), a subset of additive manufacturing (AM), is gaining widespread acceptance for functional applications within the aerospace manufacturing industry. With the advancement of technologies and materials, 3DP is now regarded as a viable alternative to more conventional large-scale production methods, such as subtractive manufacturing or injection molding, and in some instances, eliminates the need for machining altogether.
Ideal for producing parts with complex geometries, 3D printing can maximize production by creating parts in hours rather than days, which otherwise would be too expensive or time-consuming to make using lathing or turning. Instead of being restricted to prototyping samples and low production runs, 3DP is used to make high-volume, fully finished, machine-grade parts.
More than 80% of 3D-printed parts are made using thermoplastic or thermoset polymers, with metals, ceramics, and other composite materials comprising the other 20%. 3DP parts are manufactured using 3D printing methods including fused-filament fabrication (FFF), digital light processing (DLP), selective laser melting (SLM), electron-beam melting (EBM), or material jetting processes. Parts are created from a computer aided design (CAD) file and are fabricated using a polymer or metallic construction material that is powder-deposited or extruded through a nozzle in progressive layers until parts reach their final shape.
Items made using 3DP require minimal post-processing and have excellent dimensional repeatability. Building parts is just the beginning of the 3DP process – choosing the correct post-processing fluids also plays a key role in the successful construction of the 3DP components.
Fluid finishing for plastic parts
The layered 3DP process leaves some plastic printed parts with a tiered or stepped surface, requiring smoothing to get a finished part. Traditional smoothing methods – such as sandblasting, buffing, or grinding – are manual, time-consuming, and often leave particles behind. A more efficient method is fluid finishing. In this method, unfinished parts are immersed in a fast-evaporating fluid inside a vapor degreaser that slightly melts the parts’ plastic surface – levelling out irregularities, removing the tiers, and leaving a smooth finish without any leftover particles or damage to the finished parts. The quality is comparable to parts made by injection molding.
For effective smoothing, it is necessary to understand the chemical composition of polymer parts. ABS, acrylic, polycarbonate, and highly basic materials with a pH of 10 or more have the potential for softening and swelling. Thus, the selected smoothing fluid should have enough solvency to effectively level parts but not be so strong that it damages them or compromises structural integrity.
In addition to smoothing parts, the fluid must be able to remove soils or particles left behind from other manufacturing processes. The fluid, when used in a modern vapor degreaser, can be used to dissolve and clean various oils, greases, and waxes. Dust or shavings typically will not dissolve in the cleaning fluid. Therefore, particles must be removed using displacement cleaning, where cleaning fluid gets under the particulate matter, dissipates any static charge, and lifts it off the surface. The key to effective displacement cleaning is to use a dense, heavy fluid that floats particles off the substrate surfaces. Today’s fluids are typically 20% heavier than water and 50% heavier than alcohol, making them suitable for displacement cleaning of 3DP polymer parts.
An added advantage of fluid smoothing and cleaning is that they dry quickly and completely, leave no residue on parts, and are cool after they exit the vapor degreaser. This allows parts to be packaged or post-processed immediately, speeding production and overall throughput.
In addition, 3DP post-processing fluids are nonflammable and safe for use in cold operations, heated machines, or in ambient temperatures. They also are formulated without n-propyl bromide, methyl pyrrolidone, polyethylene glycol, heptane, or trichloethylene, all of which can create groundwater and air quality issues.
3DP finishing is reliably and consistently achieved using a vapor degreaser. (Photo courtesy of MicroCare)
Metal debinding fluids
Until recently, metal 3DP was only used for prototyping or low-volume runs since it was too expensive and too slow for mass production and overly complex for wide-scale use. However, as the technology advances, metal 3DP is making its way to the manufacturing floor for higher production runs of end-use parts.
Metal 3DP uses the same layered-build process as plastic 3DP but employs fine metal powders and a binding agent, typically paraffin wax, carnauba wax, or specialty polyethylene waxes, to create green-state parts. The binders are critical in forming the metal powder into a specific shape. However, they must be selectively removed before the green parts can be exposed to the high heat required for the next step of sintering.
Fluid extraction of the binders is accomplished with a vapor degreaser. The debinding may be performed in either the vapor or liquid phase, depending on the metals used and the binders being removed. Both phases rely on the debinder fluid penetrating the parts efficiently to dissolve the wax from the part’s interior.
The wax binders are progressively removed to avoid deformation and cracking during sintering while also allowing parts to maintain their dimensional accuracy, compress uniformly, and sinter evenly. Debinding is a balance of selectively eliminating some, but not all, of the binders in the shortest time and with the least amount of damage to the parts’ structure, because as the binders are removed, the parts become fragile. This is why the debinding fluid’s physical properties are important and the fluid should be chosen carefully.
Complex metal parts are made using fine metal powders and binding agents.
The debinding fluid should have good materials compatibility with metal powders and binders to safeguard the integrity of the formed parts. It should also feature low viscosity, low surface tension, and high liquid density to allow the debinding fluid to flow over, around, and into the internal pores of the parts to remove and wash away the binders more easily. The debinding fluid should be aggressive enough to selectively remove the soluble binders but still maintain part integrity. Too much binder left behind could result in cracking, deformation, or part expansion during sintering.
Energy, time savings
A low-boiling debinding fluid melts the wax binders and additives but also allows the vapor degreaser to run more efficiently, saving energy costs. The low boiling point also prevents damage to non-soluble components. Debinding fluids with a low boiling point and low latent heat of evaporation also dry more quickly, enabling faster production times.
Safety
Nonflammable debinding fluids are safer for workers and do not require specialty fire or explosion-proof equipment. When used in a vapor degreaser, they can be distilled and reused to minimize waste. Additionally, some debinding fluids can be shipped as not hazardous, not regulated, even by air.
Finding a partner
Companies seeking help in determining the correct smoothing or debinding fluids or method should consult with a cleaning partner who specializes in vapor degreaser smoothing and debinding to ensure 3DP post-finishing success.
Additive manufacturing (AM) needs tools to manage data to ensure quality, repeatability, traceability, and reliability, especially in the heavily regulated aviation and medical industries.
Throughput Consulting’s Bluestreak | Bright AM™ management execution system (MES)/quality management system (QMS) solution manages AM production and can interface with existing systems to share data. The Bluestreak software portfolio is dedicated to manufacturing process control, work order management, QA/QC, and industry specification adherence.
“Our MES/QMS solution is a unified system contained within an all-encompassing MS SQL Server database that is equipped to manage data and give real-time visibility into the production environment, and it eliminates confusing paper trails and disparate silos of redundant data,” says Todd Wenzel, President and CTO, Throughput Consulting Inc.
The software supports:
Unique serialization for build traceability throughout a product’s life cycle, even if multiple parts with different serial numbers are printed on the same build plate.
Advanced dispositioning to manage nonconformances, scrap disposition, and the ability to allow parts to go down different processing paths without breaking the audit trail.
Ron Beltz, Director of Strategic Accounts, says AM “machines have gotten faster and more predictable; materials have gotten better; design and prototype software solutions have advanced. But one of the remaining hurdles – and one that individual companies are often working out for themselves – is standardization. How do you ensure predictable parts in a process that has so many parameters?”
The U.S. Air Force Research Laboratory, Boeing, and Thermwood partner on a low-cost responsive tooling program using large-scale, polymer-based additive manufacturing.
Boeing responded with a submission on ManTech’s Open broad-agency announcement (BAA) to evaluate the current state of additive manufacturing (AM) technology with respect to fabricating low-cost, autoclave-capable tools. The initial demo tool is for an AFRL concept aircraft fuselage skin.
Boeing contracted Thermwood to demonstrate its large-scale additive manufacturing (LSAM) machine with vertical lay print (VLP) capability. VLP AM reduces costs by increasing the size that components can be printed, reducing assembly cost for large tools.
Mid-scale tool 3D printing on large-scale additive manufacturing (LSAM).
To validate the LSAM VLP process using high-temperature autoclave-capable materials, Boeing and AFRL chose to 3D print a section of the large tool. The mid-scale tool was printed on Thermwood’s LSAM AM demonstration machine in Indiana using a 40mm print core running 25% carbon fiber-reinforced polyethersulfone (PESU).
The initial test tool has the same width, height, and bead path as the final mold and incorporates all major features of the final mold – but was compressed in length to 4ft. The final tool will be more than 10ft. The mid-scale tool was the first high-temperature tool printed using the VLP system.
The mid-scale tool required 5 hours, 15 minutes to print and weighed 367 lb. After final machining, the tool passed room temperature vacuum testing and achieved dimensional surface profile tolerances.
The next step in the program is for production of a full-size 1,400 lb tool that will required 18 hours to print.
Boeing and the Air Force are carefully documenting all operational parameters with hopes of transitioning the technology to production programs. AM autoclave tooling offers significant advantages over traditional production methods – primarily lower cost and fabrication in days or weeks rather than months.
AFRL is very interested in tooling approaches for the Low-Cost Attritable Technology (LCAAT) program, which targets breaking the cost growth curve to field new systems faster.
AFRL Program Manager Andrea Helbach says, “We are interested in additively manufactured tooling’s ability to reduce the cost and time to procure autoclave-capable tooling. Additionally, AM tooling supports changes in vehicle design with minimal non-recurring expenses.”
“Future fielded low-cost, but capable unmanned aerial vehicles (UAVs) will need a responsive materials and manufacturing processes strategy,” says Craig Neslen, LCAAT initiative manufacturing lead. “Additive manufactured composite tooling is one of many technologies being evaluated to ensure the industrial base can handle future manufacturing surge requirements as well as accommodate periodic system tech refresh activities which could necessitate minor vehicle design changes at an acceptable cost.”
