In Part 1 of this article, I drew on the notion of time travel from the 1985 movie Back to the Future to explore the accuracy of predictions made in my article from the August 2012 issue of FORGE. Without the fictional flux capacitor, which enabled time travel in the DeLorean time machine used in the movie, we will continue this analysis of the predictions regarding AM prototyping and forging and AM short-run production and forging. We will also briefly touch on die repair. We will explore how these industries will have to compete and complement each other by delivering value in the future.
AM to Compete with Forgings, Especially in Short Runs
We expect that AM will compete with conventional forging in the short-run production of new parts and replacement parts for legacy systems. Program managers of new systems have always needed parts with zero or minimal tooling costs. Supply-chain managers of legacy parts are reluctant to invest in tooling for short-run production, especially when they know tooling is obviated by AM. In either case, AM is a compelling alternative to conventional closed-die forging for short-run productions.
Although pre-dating our 2012 article by nine years, the U.S. Air Force (USAF) demonstrated the replacement of a forged aluminum component for the F-15 in 2003. The USAF summarized the results in a success story published in May 2015. Inspection of airframes revealed a forged 7075 aluminum pylon rib experienced corrosion fatigue cracking. The USAF, working with industry, transitioned from an aluminum forging to a titanium forging to address the corrosion fatigue-cracking issue. However, the lead time for closed-die forgings approached 12 months, which resulted in the increase of AOG (aircraft on ground) at Air Logistics Centers. This is something that any wing or squadron commander dreads since they potentially cannot meet mission requirements. Instead of invoking conventional forging, the part was re-engineered to accommodate additively manufactured titanium. Ultimately, approvals were granted to accept AM titanium in this application, resulting in the first structural AM part in the USAF’s fleet.
Photo 1: F-15s replaced a titanium pylon rib forging with an additively manufactured titanium part with a shorter lead time (courtesy of USAF).
More examples surfaced of AM replacing short-run productions of forgings, including spacecraft titanium propellant tanks, helicopter bellcranks and variable ballast tanks for submersibles. Case-study data is limited, but common denominators of these case studies include:
- The requirement for short-run production is clear.
- Titanium is often the AM alloy of choice.
- AM could potentially offer acquisition cost savings.
- AM could fill the gap where either tooling or even a particular supplier no longer exists.
- AM offered substantial savings in production lead time, especially with the elimination of tooling.
Digging deeper into the contemporary marketplace revealed a high-end, high-performance automotive application. In 2018, Bugatti announced the replacement of forged aluminum brake calipers with AM Ti-6Al-4V for the Chiron sports car. This approach reduced weight from 4.9 kg of aluminum to 2.9 kg of titanium. With four calipers per vehicle, weight savings multiply. Weight reduction in high-performance vehicles is valued highly, especially with respect to acceleration – less mass enables either rapid acceleration or rapid deceleration.
Matching the value of weight reduction is the tensile strength required for assured braking. Per Bugatti, the tensile strength was reportedly as high as 1,250 N/mm². In addition to the increased strength, stiffness increases through two mechanisms from forged aluminum to additively manufactured titanium. The first increase in stiffness (elastic modulus) comes from the difference in stiffness of titanium compared to aluminum. Titanium by its very nature is stiffer. The second mechanism of boosting stiffness is realized through the optimization of structural stiffness imparted by physical geometries optimized for stiffness as enabled by AM but not possible by forging. This increase in stiffness improves caliper performance in extreme braking conditions.
Photo 2: Bugatti Chiron high-performance sports car (courtesy of Bugatti)
Starting this process, Bugatti turned to Laser Zentrum Nord selective laser technology. Utilizing a solid model optimized for caliper performance and manufacture, calipers were printed using a laser-fusion/powder-bed approach. Four 400-W lasers coursed across a powder bed, melting and solidifying the powder layer by layer. Forty-five hours are required to build the part comprised of 2,213 layers and measuring 41 cm long x 21 cm wide x 13.6 cm high.
After shaking off excess powder, which is recycled, the part and its supporting structure are heat treated to enhance mechanical properties and reduce residual stresses. Final finishing operations remove the support structure and treat the surface to optimize durability. Eleven hours of additional machining is required for contact surfaces and threads. It took three months to go from “art to part,” which is a powerful case study for AM. For Bugatti, AM is enabling and game changing!
In reviewing both the F-15 pylon rib and Bugatti brake caliper, common points are noted. First, the applications enabled the performance of a highly valued system. Second, both cases invoked different AM routes to replace aluminum with titanium. Third, the parts were relatively large for their market application. Fourth, time to application or to market was highly valued.
Pivoting from replacement parts or new designs via AM, prototyping of metal parts via AM is another growing opportunity for manufacturers.
AM is a Link between a Prototype and a Forging
OEMs, Tier-1 and Tier-2 suppliers and designers are advised to identify and evaluate ways to integrate AM into the design and acquisition process.
According to George Small, chief technical officer of Moog, the company has delivered value to its customers by reducing the lead time of prove-out and supplier qualification of forged parts. A case study on Moog’s website illustrated the application of an AM 15-5 precipitation-hardened part for both development and low-rate initial production (LRIP) of flight-control actuators.
With slightly modified designs to accommodate the AM process, prototypes were printed in a week and finish-machined with the same tooling used for the incumbent forging. Additionally, AM enabled the accommodation of feature changes resulting from flight testing without investing in hard tooling. Once the design is frozen, production tooling is designed and procured to exploit the benefits for forging while amortizing tooling over the higher-volume production runs.
For short-run production of parts (e.g., 10 to 100) with small sizes or weights, AM is an attractive alternative to forging. Stepping back for a moment, short-run production is no different than producing parts for LRIP.
Photo 3: Additively manufactured brake calipers replaced forged parts, with a significant weight reduction (courtesy of Bugatti).
AM Could Assist in Tool Repair, Hard Facing and Functionally Gradient Surfaces
AM is rapidly affecting forging die repair. Multiple academic studies and industrial advances indicate the viability of cladding worn dies at potentially less cost than other traditional methods. This sea change is an opportunity for flood-welding suppliers to pivot into cladding materials such as high-entropy alloys or other alloys designed to further enhance die surfaces.
By applying select materials to tool surfaces, one could theoretically tailor a forging die with variable frictional surfaces. In other words, one could select the coefficient of friction (µ). Where resistance to flow is required, high-µ surfaces could be applied. Where less resistance to flow is required, low-µ coatings could be applied.
With affordable die-wear measurement systems and aggressive tool management, forges can track die wear more closely, pulling dies from service with minor issues requiring lighter repairs. This data-driven approach could offset the need for flood welding and extensive machining of die cavities. We know this is not what the flood-welding industry wants to hear, but technology marches toward the future.
To close this topic, readers are reminded of the February 2019 edition of FORGE, which featured DM3D Technology and die repair in which a direct-metal deposition (DMD) process is used to build, reconfigure, hard-face or repair a die.
Photo 4: Left panel: Moog flight-control actuators forged (left) and additively manufactured (right). Right panel: Actuators on a test stand (courtesy of Moog, Inc.)
In Parts 1 and 2 of this series, we have touched on the topics we believe are of most interest to forging manufacturers vis-à-vis AM. Now we direct our attention to the topic of value. Regardless of any industry, value is defined by the customer. Success for industrial salespeople will be in the ability for their clients to uncover and realize the value of your solution regardless of it being a forging or an AM component.
From a high level, the table below tallies a short list of the value realized by a customer of either the forging or the AM industries. Eventually, the customer will determine which manufacturing route delivers the value they require.
While revisiting the predictions of 2012, we can overlay concepts for both the forging and AM industries with respect to “selling” best practices. From a ValueSelling framework perspective, suppliers must facilitate their customer’s realization of the potential value a supplier can provide. In addition, a supplier must differentiate his or her solution to motivate the customer to prefer and therefore procure the supplier’s solution.
Before a technical conversation to diagnose customer problems, which a supplier can solve, it is a best practice to understand why those problems are worth solving. That best practice is to connect a client’s problems to a supplier’s differentiated solution while connecting to a measurable and timebound business metric acknowledged by the client.
Photo 5: a) S7 tool-steel blank; b) direct-metal deposition (DMD) process; c) after the DMD process; d) after DMD and final machining (courtesy of DM3D Technology)
Once these underlying client problems are identified and confirmed, a supplier can offer solutions. In effect, the conversation is reframed from price to value by differentiating a solution in the prospect’s mind.
Both the forging and AM industries offer solutions to their clients. Both industries offer metallic parts but via different paths. Some paths are faster. Some paths are more expensive. Some paths offer adequate mechanical properties, while some paths offer assured mechanical properties. Regardless, the value of the metallic manufacturing path is determined by the customer! The only thing the forger or AM maker can do is assist the customer in uncovering and realizing the value of each process path.
Ultimately, value is defined by the customer.
Looking back to 2012 from 2020, the future has arrived! AM is technically viable and both complements and competes with forging. Perhaps with a flux capacitor, which is out of stock at O’Reilly Auto Parts, we can once again go back to the future – perhaps look back at 2020 in 2030.
Peering ahead, the forging and AM companies that will survive and thrive will have to differentiate themselves from their competition. Critical to the future will be a company’s ability to uncover value for its customers. Your company does not have to wait for the future since it is here, and I would be delighted to discuss it with you today or at Forge Fair 2021!
Photo 6: Top half of control-arm forging die: a) After direct metal deposition; b) After DMD and machining (courtesy of DM3D Technology)
We are grateful for the contributions made to this two-part series by Sciaky, DM3D, NASA Marshall Space Flight Center, Schatz Bearing, Moog, the U.S. Air Force, Bugatti and MELD Manufacturing Corp.
- F-15 Pylon Rib Insertion Success Story, Distribution A: Cleared for Release Case Number 88ABW-2015-2477; 19 May 2015
- Moog article A New Way of Looking at Metal Additive Manufacturing Processes (moog.com)
- Bugatti article Bugatti - World premiere: brake caliper from 3-D printer
- ValueSelling Associates - https://www.valueselling.com/
All images supplied by Jon D. Tirpak unless otherwise indicated. Lead-in image by Natalia_80 / RB Stocker / iStock / Getty Images Plus via Getty Images; composited by FORGE art director.