Navigating Material Complexities
This article explores various advancements and techniques in the machining and metalworking industry, focusing on the development of cutting tools for drilling, milling, and threading in challenging materials such as composites, high-temperature alloys, and stainless steels. Key topics include the optimization of cutting tool geometries through 3D printing, the adaptation of drills for versatile applications across different metals, innovative thread milling approaches for tough materials, and the introduction of specialized end mills for efficient machining practices. The discussion also highlights the strategic use of CAD/CAM technologies to enhance tool performance and the importance of continuous innovation in tooling to meet the evolving demands of the aerospace and medical industries.
The drive for invention and innovation can be sparked by need and chance, including unexpected situations. For instance, during the recent slowdown caused by the COVID-19 pandemic, numerous innovative cutting tool companies took advantage of this period to experiment with and launch new products. Meanwhile, some have transformed apparent geographical setbacks into tactical advantages.
Consider the modern advanced high-strength materials that have historically complicated manufacturing processes, particularly in the aerospace sector. The latest advancements in cutting tools are equipped to tackle these challenges, whether dealing with composites, titanium, Inconel, or Hastalloy.
Achieving High-Speed Drilling in Composites
Sharon-Cutwell Co., under the leadership of President Jeff Prom, exemplifies innovation, benefiting from its secluded location in Belgium, Wisconsin, which Prom suggests provides the tranquility necessary for contemplation. However, Prom emphasizes that despite their remote location, Cutwell actively maintains strong global connections with both customers and technology collaborators.
The company’s recent breakthrough involves a family of solid-carbide drills coated with CVD diamond, named “Wave-Point.” This patented design boasts a unique cutting edge with multiple radii that alternate along its length, enhancing its drilling capabilities. According to Prom, these drills excel in high-speed penetration and maintaining tight tolerances while minimizing exit delamination in materials like carbon fiber.
Cutwell has developed variations of this drill to cater to different materials, including carbon-fiber-reinforced polymers (CFRP), aluminum stacks with CFRP, CFRP titanium stacks, and even hard metals like titanium, Inconel, and Hastalloy. Prom advises that choosing a drill optimized for the most frequently machined material can allow for versatile use across various materials without the need for frequent tool changes.
Prom’s claims are substantiated by impressive performance metrics. Testing of the 1/4" Wave-Point drill shows it can achieve a feed rate of 70 IPM in carbon fiber, drilling at 600 SFM with an 8,500 rpm speed while maintaining extremely tight diameter tolerances and minimal delamination, over a length of more than 1,200 inches.
Cutwell’s rigorous testing protocol, which employs the Spike force sensing unit from Pro-Micron, allows for precise monitoring of drilling forces. This data-driven approach enables continuous refinement and optimization of their tools.
Prom shares a notable success story with Boeing, where Cutwell’s Wave-Point significantly outperformed previous drills. Initially struggling with chipping at low feed rates, Boeing, upon switching to Wave-Point, achieved a feed rate of 64 IPM and extended tool life to over 800 holes – a marked improvement in both efficiency and durability for drilling fuselage sections of the 787 plane. This enhancement resulted in significant time savings, equivalent to an entire shift per fuselage joint, underscoring the profound impact of Cutwell’s innovation.
Optimizing Composite Drilling for Aerospace
Jeff Prom outlines the demanding requirements for Boeing’s 777X, its newest and largest aircraft, needing drills with diameters up to 1 inch for fastening and 1.4 inches for access holes, all achievable with Cutwell’s Wave-Point technology.
The challenge escalates with so-called stacked composites. For a 1/4 inch drill, Cutwell recommends starting speeds of 500 SFM and feeds of 0.008 IPR for composites, with a slight adjustment for aluminum at 400 SFM and the same feed rate. Impressively, they’ve achieved over 800 inches of tool life in these materials. For stacks combining carbon fiber reinforced polymer (CFRP) and titanium, the recommended speeds and feeds adjust accordingly to accommodate the varied hardness and abrasiveness of each layer.
Prom highlights the complexity of drilling through a stack of composite, titanium, and aluminum, which necessitates perfect execution through dissimilar materials in a single operation. This task demands precision programming and highly automated equipment due to the different drilling speeds and feeds required for each material layer, posing one of the most challenging tasks in aerospace assembly.
Despite these challenges, Cutwell’s 0.393-inch diameter drill boasts a tool life of 150 inches when drilling through a 1.25-inch thick CF/Ti/Al/Ti stack, a testament to its performance and durability that has been consistent for six years in production.
For drilling aluminum, Cutwell adopts a peck drilling method to minimize chip size and prevent composite damage. In a groundbreaking advancement, Cutwell collaborates with Mitis for micro pecking, introducing vibration-assisted drilling (VAD) that oscillates the drill slightly for efficient chip formation and faster drilling. This innovation reduces drilling time from twelve seconds per hole to just three seconds, significantly enhancing productivity without compromising tool longevity. Prom’s insights underscore Cutwell’s commitment to overcoming the intricate challenges of aerospace manufacturing with inventive solutions.
Enhancing PCD Drilling Tools through Additive Manufacturing
Jeff Prom observes that while polycrystalline-diamond (PCD) drills were traditionally favored for composite materials, the advent of diamond-coated carbide drills has now claimed supremacy in many high-performance applications. This shift is attributed to the latter’s ability to combine refined geometries with a diamond coating, yielding both superior cutting capabilities and extended tool life.
However, Sandvik Coromant has initiated a breakthrough by employing 3D printing to enhance the functionality and cost-effectiveness of PCD drills. This innovative approach not only reduces the cost per hole but also presents a formidable challenge to the reigning carbide and diamond-coated alternatives.
Traditionally crafted through a meticulous process that combines PCD with carbide, the manufacturing of PCD drills involved grinding and sintering diamond grit into precisely shaped carbide pieces, followed by brazing these components onto a carbide shank. This method, while effective, necessitated excessive use of carbide and PCD, driving up costs due to the complex shaping required for the drill’s flutes.
David DenBoer, an aerospace specialist with Sandvik Coromant, explains that the traditional method also imposes limitations on tool geometry, as the flutes could not be designed to follow an optimal path due to the constraints of the grinding process. This resulted in shorter nibs and thus limited the effective length and design flexibility of the PCD drills.
3D printing, conversely, offers the capability to place diamond material exactly where needed, allowing for longer nibs that closely follow the flute path, optimizing material use and extending the tool’s lifespan. This not only makes the tool more economical by reducing the material wastage but also enhances its performance and allows for up to 10 times re-sharpening, drastically lowering the overall cost per hole. With the promise of lasting through 9,000 holes, Sandvik Coromant’s innovation in applying 3D printing to PCD tool production marks a significant advancement in drilling technology, particularly showcased in their 85 and 86 series drills with diameters ranging from 0.190 to 0.376 inches.
“Soft-Serve Ice Cream” Inspired Flute Geometry for Cutting Unidirectional CFRP
David DenBoer of Sandvik Coromant acknowledges that while PCD drills might be the preferred choice for conventional composite materials used in aircraft manufacturing by companies like Boeing and Airbus, these drills often fall short in preventing delamination in unidirectional materials. To address this, Sandvik Coromant has introduced a novel diamond-coated carbide drill known as TNT, which boasts an innovative flute geometry reminiscent of a soft-serve ice cream cone.
This TNT drill operates through a slicing motion, utilizing a longer and curved edge compared to the shorter cutting face of standard PCD drills, effectively mitigating delamination typically observed upon exit. DenBoer explains that the design’s unique force can occasionally cause delamination at the entry on the opposite side due to its powerful lifting action – a unique challenge that highlights the drill’s exceptional capabilities.
During a demonstration, a three-flute CVD diamond-coated TNT drill with a 1/4 inch diameter was tested on woven CFRP without coolant at 5,000 RPM and a feed of 0.008 IPR, achieving a velocity of 327 SFM. The tool impressively maintained stringent hole diameter tolerances over 3,000 holes, with minimal delamination observed. The test was prematurely concluded due to a mishap at hole 3,303, but until then, the drill displayed no wear.
The TNT drill also played a pivotal role in eliminating the need for protective taping against delamination in unidirectional composite sections of the F-35 fighter jet, a process previously deemed necessary by a leading manufacturer. This change is set to streamline production processes significantly.
Moreover, the TNT tool’s design ensures low operating temperatures, crucial for preventing the melting of CFRP materials during drilling. While the TNT drill, available in diameters ranging from 0.190 to 0.685 inches, is priced lower than its PCD counterparts, its diamond coating primarily wears at the cutting edge, rendering it non-regrindable. Despite this, its longer lifespan positions PCD tools as the better choice for unidirectional materials, according to DenBoer.
Versatile Drill Adapts to Various Metals
During the quiet period induced by the pandemic, Emuge-Franken USA, based in West Boylston, Massachusetts, embarked on extensive testing of its InoxDrill across a broad spectrum of materials, as shared by Marlon Blandon, the product manager for drills and thread mills. The outcome is a detailed speeds-and-feeds chart, meticulously crafted to cater to the diverse materials prevalent in the medical and aerospace sectors. This chart empowers the InoxDrill to proficiently penetrate an array of stainless steels – including the ferritic martensitic 440, austenitic ferric, heat-resistant super duplex, alongside nickel alloys such as Inconel 718 and 625, Incoloy 901 and 903, Waspaloy, and various forms of pure and alloy titanium.
The InoxDrill series, featuring two flutes in either 3xD or 5xD sizes, is enhanced with a unique monolayer PVD coating that extends across all these materials, according to Blandon. This self-centering drill eliminates the need for a spot drill or any piloting tool beforehand.
Equipped with a K-Land-style cutting edge and further refined with an additional hone post-grinding, the InoxDrill is engineered to thrive under substantial load. Blandon points out that, in comparison to competitor drills, the InoxDrill can handle feed rates significantly higher, recommending feed rates of seven and a half to eight thousandths per revolution for materials where others might suggest six thousandths.
Originally designed with high-temperature alloys in mind, the InoxDrill features a single margin to ensure stability by having only one side of the flute marginated. This design detail makes the InoxDrill especially suitable for materials prone to heat hardening, such as Inconel, which often forms a protective layer when machined, posing challenges for subsequent tooling operations like threading.
Innovations in Milling and Thread Milling
Thread milling stands out as the method of choice for crafting internal and external threads in various challenging materials, primarily due to their propensity to wear down cutting edges quickly. Blandon from Emuge-Franken USA elucidates that traditional high-speed steel tools may not be effective for certain high-temperature alloys or stainless steels rich in nickel and vanadium, as well as softer nickel alloys, which can be difficult to tap or cut continuously. Thus, thread milling emerges as the superior strategy for these applications.
Emuge prides itself on offering exceptional thread mills, such as the THRILLER-AERO and THRILLER-MAX. These tools are ingeniously designed to drill and thread simultaneously, especially in difficult materials. The THRILLER-AERO is optimal for working with high-temperature alloys, stainless steel, titanium, and nickel, whereas the THRILLER-MAX is recommended for materials exceeding hardness levels of 46 to 50.
Blandon stresses the importance of the correct CAM strategies, noting that these specialized tools require a left-hand spindle rotation and a corkscrew motion for optimal use.
Dan Doiron, milling product manager at Emuge-Franken USA, highlights a general underutilization of advanced CAD/CAM toolpaths like trochoidal machining in the industry. He advocates for the more strategic use of even general-purpose end mills, which can significantly improve performance and tool life through proper programming techniques.
Emuge has developed Trochoidal End Mills specifically for trochoidal machining, designed for light radial passes and featuring chip breakers along the flutes to facilitate easier chip evacuation and produce smooth finishes. Additionally, Emuge is introducing six- and seven-flute end mills tailored for faster speeds despite reduced horsepower in modern machines, emphasizing lighter radial passes at higher feed rates.
Looking forward, Doiron is excited about Emuge’s upcoming Hard-Cut End Mill line, engineered for materials reaching hardness levels close to 70 Rockwell, promising significant advancements in speeds and feeds based on current testing.
The key takeaway is the continuous innovation in cutting tools. With regular advancements in geometry, coating, and design, Emuge encourages users to stay in touch with their suppliers to leverage the latest in tooling technology for enhanced efficiency and performance.
In conclusion
The article showcases the machining industry’s relentless pursuit of innovation, particularly in the development of cutting tools and machining strategies to address the complex challenges of working with advanced materials. Through examples such as the optimization of cutting tools for composite materials, the creation of versatile drills capable of handling diverse metals, and the refinement of thread milling techniques, the conversation highlights the industry’s commitment to improving efficiency, precision, and cost-effectiveness in manufacturing. The emphasis on leveraging CAD/CAM technologies and the strategic importance of staying engaged with the latest advancements in tooling further underline the dynamic nature of the field. This ongoing evolution in machining practices and tool development not only meets the current demands of sectors like aerospace and medical manufacturing but also anticipates future challenges, ensuring the industry remains at the forefront of technological progress.
