13 minute read
Machining superalloys
from AMT FEB/MAR 2022
by AMTIL
Superalloys have become one of the most widely used engineering materials for a long time due to their hightemperature strength and corrosion resistance. However, their poor machinability poses challenges for manufacturers.
Superalloys – metal alloys which reflect their complex alloyed structure – feature extremely high elevated temperature strength, and therefore often are referred to as high-temperature superalloys (HTSA) or heat-resistant superalloys (HRSA). The history of superalloys started with the development of gas-turbine engines that required reliable materials for high operating temperature ranges. As a result of intensive research and progress in metallurgy, modern superalloys provide a long service life for working temperatures more than 1,000 deg.C. Understandably, the largest superalloy consumers today are aerospace and marine engine producers. Superalloys are also very common in the medical industry, which effectively use them for prosthetic implants in orthopedic surgery. In addition, superalloys have become widespread in power generation and the oil & gas industries as crucial materials for essential parts of various devices. Exceptional high-temperature strength and corrosion resistance are the undeniable advantages of superalloys. However, there are two sides to the coin: superalloys are not only highly priced, but their machinability is poor, which can pose challenges to manufacturing. The specific cutting force that characterises the resistance of the material to chip removal and defines the mechanical load on a cutting tool is high for superalloys. Although the main difficulty is heat, superalloys have poor thermal conductivity. Elemental and loose chips, which are generally generated when machining superalloys, do not provide adequate heat dissipation from the cutting zone. A tendency to work hardening makes the situation worse. Manufacturers deal with various superalloy workpieces: cast, wrought, sintered, and so on. The workpiece fabrication methods also have an impact on machinability. For example, the abrasiveness of forged workpieces is higher than cast ones and substantially lower in comparison with sintered workpieces. Consequently, a cutting tool is under significant thermal and mechanical load, which dramatically reduces tool life. Therefore, in machining superalloys, the cutting speed directly connected with the heat generation during chip removal is considerably lower when compared to other common engineering materials such as steel or cast iron. The direct result of the cutting speed limitation is poor
A jet engine blisk machined with Iscar’s CutGrip systems. Superalloys are key materials for turbojet and turboprop engines of modern aircraft.
Machining a femoral knee implant component with a Multi-Master endmill and exchangeable taper barrel head.
productivity. Hence, overcoming machining difficulties and increasing productivity are the main challenges for the manufacturer of superalloy parts. According to ISO 513 standard, superalloys – together with titanium alloys – relate to the ISO S group application. Depending on the prevailing element, superalloys are divided into three types: iron (Fe), nickel (Ni) and cobalt (Co) based alloys. Machinability drops in the specified order; from the ironbased alloys, which can be compared with austenitic stainless steel, to cobalt-based alloys that represent the most hard-to-cut materials in the group. Increasing the efficiency of machining superalloys has become the focus of various scientific research and technological improvements. Their result was a significant advance in producing superalloy components. Manufacturing has effectively embraced new machining strategies and innovative methods of cutting coolant supply, such as highpressure cooling (HPC), minimum quantity lubrication (MQL) and even cryogenic cooling has successfully been introduced. This has taken the productivity of machining superalloys to a new level. However, as in the case of titanium alloys, the key element for improving the productivity of superalloy machining is a cutting tool that directly removes material layers from a workpiece that produces chips. A cutting tool features the tool material and its geometry, which determines the tool’s success or its failure. Today, coated cemented carbides are the most common materials for cutting tools for machining superalloys. The development of a carbide grade, in which strength and wear resistance will be mutually complemented is a tricky process that requires an appropriate carbide substrate, coating composition, and coating method. To the amazement of those who believe that the breakthrough possibilities in this direction are almost exhausted, cutting tool producers continue to create new effective carbide grades. Additionally, in machining superalloys, ceramics – another tool material that enables substantially increased cutting speeds – are already in active use. If tool materials are connected mostly with material sciences and metallurgy, cutting geometry is more in the tool design field. Ensuring high-performance geometry requires deep engineering knowledge and technology skills. On the one hand, to minimise heat generation and work hardening, a positive rake angle, a large enough clearance angle, and a sharp cutting edge are needed. On the other hand, such a shape weakens the cutting edge that should withstand a considerable
Iscar’s recently introduced M3M (left) and F3M (right) chipbreakers for ISO standardised turning inserts, designed specifically for ISO S and ISO M groups of application.
Milling cutters with indexable round inserts from ceramics provide considerably increased cutting speeds for higher productivity.
mechanical load. Therefore, the correct designed cutting-edge condition becomes a critical success factor. Sintered carbide inserts have the advantage of enabling complex chip forming and chip breaking shapes for insert rake faces. Today, computer modeling of chip formation and pressing processes using finite element methods provide an effective tool to optimise the shapes that are already in the design stage. In solid endmills, a variable pitch design results in improved vibration strength. Cutting edges of these endmills are produced by grinding operations, and to eliminate flaking and edge defects, strict adherence to technological process requirements is highly important. Cutting tool manufacturers such as Iscar pay a lot of attention to improving their product portfolios intended for machining superalloys. Iscar’s carbide grade IC806, which was introduced over the last few years for face grooving superalloys and austenitic stainless steel, was successfully adopted by Iscar’s threading and deep drilling lines. This grade has a hard submicron substrate and PVD TiAlN/AlTiN coating with postcoating treatment according to Iscar’s Sumo Tec technology. IC806 provides notable resistance to flaking and chipping and maintains reliable and repeatable results. In machining superalloys by solid carbide endmills and exchangeable heads, grade IC902, which combines ultra-fine grain substrate and nano-layer PVD TiAlN coating, ensures extremely high wear resistance and prolongs tool life. This grade has demonstrated very good results in producing devices for replacement knee and hip joints that are made from difficultto-cut cobalt-chrome alloys. Iscar has significantly extended the range of products for ISO S applications made from various cutting ceramics such as silicon nitride, SiAlON, and whisker-reinforced grades. The newly introduced ceramic items have replenished both indexable inserts and solid endmills. The latest rake face designs F3M and F3P for ISO standard turning inserts are intended specifically for hard-to-machine austenitic stainless steel and superalloys. Their positive rake-angle geometry reduces the cutting force and ensures smooth cutting action, while the set of deflectors on the rake face improves chip control. In ceramic double-sided inserts for turning and milling tools, Iscar has added new chamfered and combined (chamfered and rounded) cutting-edge condition options for tough applications. Iscar has enriched the range of solutions intended for high-pressure cooling by new indexable cutter bodies and tool holders. For example, thermal shrink chucks with polygonal taper shanks, which have coolant jet channels along the central bore, have been replenished by the toolholder product line. The need for increased productivity in machining superalloys is a continuous challenge for cutting tool manufacturers, and new effective tool developments are likely to come in the near future.
www.iscar.com.au
The new benchmark in production metrology.
By Alicona. That´s metrology!
µCMM is the first purely optical 3D coordinate measuring machine. As a user, you measure dimension, position, shape as well as roughness of complex components and tight tolerances with only one sensor. Length measurement deviation: E=(0.8+L/600) µm.
www.alicona.com
Available in Australia @Met Optix, Web: www.metoptix.com.au Phone: 1300 363 409
Walter presents Tiger·tec Gold for milling and drilling
Walter has released its new Tiger·tec Gold PVD grade WSP45G, a cutting tool material that it claims pushes the boundaries of coating technology in terms of application, performance and materials.
In addition to their compatibility with Xtra·tec XT, Walter BLAXX and M4000 milling cutters systems, Tiger·tec Gold PVD indexable inserts can also be used in Walter indexable insert drills such as the D4120. This now makes these tools not only suitable for ISO P steels but also difficult-to-cut materials from the ISO S and M material groups. According to Walter, the multilayer coating system is the only one of its kind in the world. The new TiAlN-Al2O3 multilayer coating makes the WSP45G hard with additional toughness and therefore tremendously resistant to abrasive wear and high temperatures. A special mechanical post-treatment process improves resistance to thermal cracks and fracture and protects the cutting edge from micro-spalling. The light gold-coloured ZrN top-coat of the multilayer system makes it easier to detect wear and therefore, improves process reliability. Unused cutting edges are reliably identified and this makes it possible to exhaust the full potential of the indexable insert. Potential fields of application for the new Tiger·tec Gold PVD grade include demanding machining tasks such as the cutting of heat-resistant alloys and materials with difficult cutting properties. The new Tiger·tec Gold PVD grade also excels in challenging conditions such as interrupted cutting. In the case of milling, the new Tiger·tec Gold PVD grade is also suitable for challenging applications such as long overhang machining or the machining of parts with delicate clamping arrangements, while indexable drilling, inclined entry and exit machining operations will benefit from the new grade. Depending on the material and application, the new Tiger·tec Gold PVD grade achieves performance improvements of up to 75% in ISO P materials and average gains of 47% in ISO P, M and S materials. Whether it is the machining of turbochargers in cast steel, fasteners and chassis parts in titanium or components in nickel-based alloys as encountered in the automotive, energy and aerospace industries, the WSP45G grade offers an impressive process improvement solution.
www.walter-tools.com
Dormer Pramet has launched a new generation of solid carbide five-flute end mills, specifically for dynamic milling in general machining and die and mould applications.
The company’s S7 assortment covers a wide range of operations in a variety of steels, cast irons and difficult-to-machine materials, including stainless steels and super-alloys. These latest additions, S770HB, S771HB, S772HB and S773HB, offer increased feed rates up to 25%, compared with four-flute cutters. All feature a positive rake angle for smooth cutting action and to reduce the risk of workhardening. An AlCrN coating provides thermal stability, reduced friction, excellent wear resistance and prolonged durability, while a small corner radius and cuttingedge design gives a stable performance and prolonged tool life. The S771HB and S773HB cutters are suitable for narrow pocketing, trochoidal slotting and profiling applications. These end mills include a chip divider to break swarf into manageable smaller pieces, helping to reduce spindle load and increase metal removal rates. This provides a 50% bigger width of cut compared to tools without a chip divider. A neck recess helps avoid contact with the wall in shoulder operations, while through coolant improves welding resistance and enables a wide range of processes, especially for difficultto-machine materials. The S770HB and S772HB are more suitable for profiling, trochoidal slotting, and semi-finishing applications, offering maximum productivity due to optimal metal removal rate and reduced machining time. Meanwhile, Dormer Pramet has added three multiapplication high-performance cutters within its S7 range for use on both CNC and conventional machine tools. The new additions – S722HB, S765HB and S768 – support most common operations, such as slotting, plunging, contour milling, ramping and copy milling in various materials, including medium strength steels, stainless steels and super alloys. These four-flute cutters have a specific tooth design for improved chip evacuation. The AlCrN and Titanium Silicon Nitride (TiSiN) coatings support longer tool life, higher cutting speeds and increased heat resistance, making them ideal for dry machining. Finally, Dormer Pramet has added a new solid carbide cutter to enhance its assortment of end mills for hardened steel above 49HRC. The S561 is specifically for high performance milling in a variety of applications, including die and mould machining. This four-flute end mill features a specific tooth design for improved chip evacuation. A sharp cutter for hardened steel (52-70HRC), the S561 offers excellent surface finishing, while a gash land design helps to improve strength and chipping resistance. www.dormerpramet.com
WIDIA launches versatile M1600 face milling platform
WIDIA has announced the release of the M1600 face mill for roughing to semifinishing operations in steel, stainless steel, cast iron and nodular iron materials.
With 16-cutting edges and a smart insert design, the M1600 performs in various machining conditions including low-power machines, unstable, non-rigid set-ups, long overhangs, weak machines or weak fixture conditions. “Face milling is one of the most common machining operations, so we designed a versatile and cost-effective solution that delivers substantial improvements in metal removal rates in steel and cast iron for our customers,” said Anna Kim, WIDIA Indexable Milling Global Portfolio Manager. “The M1600 represents a turnkey solution for general engineering, energy and automotive customers who want to reduce their face milling tooling inventory and increase their machining outputs.” The 16-edged, precision-ground insert with a positive geometry enables low cutting forces and low power consumption, resulting in higher tool life and an excellent cost per edge. The M1600 has one universal insert geometry in three versatile grades: WP35CM, WK15CM and WU20PM. The WP35CM grade targets all types of steels, while the WK15CM grade is designed for cast iron materials and performs best in dry applications but can also be used in wet conditions. The universal WU20PM grade can be used for the machining of steel, stainless steel and high-temperature alloys in both dry and wet applications. The ‘smart’ insert design features a seating surface below the cutting edge that promotes smooth chip flow and reduces cutting forces on the tool. The insert also has a curved cutting edge and is axially positive, resulting in reduced power consumption. These key design features coupled with 16 cutting edges make M1600 an economical face milling option. M1600 face mills are available in six metric diameter ranges between 50mm and 160mm. www.widia.com
FIX8 – Heavy-duty turning with eight cutting edges per insert
Kennametal has released the FIX8 heavy-duty turning system, delivering maximum metal removal rates. The FIX8 turning system increases productivity of any heavy-duty turning operation, providing the lowest cost per edge while reducing cutting forces up to 15%.
“FIX8 is designed to cover a wide range of applications, including turning and facing, smooth surfaces, interrupted, and heavily interrupted cuts,” says Matthew Fuerst, Product Manager at Kennametal. “From medium depth-of-cut to roughing in steels, cast iron, and challenging materials like stainless steel, FIX8 handles it all. Even extreme feed rates of up to 1.4mm and depths of cut up to 12mm are possible with FIX8.” The tangential design of the FIX8 insert features a rigid clamping system that pulls the insert securely into the pocket seat, offering superior stability that enables the insert to withstand large cutting forces and vibrations for optimal performance. The insert is also supported by a replaceable carbide shim, protecting the pocket against deformation and damage. The FIX8 tool holder features precision 3D coolant technology, supplying sufficient coolant precisely where needed. Three coolant nozzles are directed to the rake face, controlling temperature, chip evacuation, and supporting chip formation. Coolant exit holes in two different locations are directed toward the flank of the insert, controlling the heat in the cutting zone and prolonging tool life. FIX8 provides excellent chip control for any heavy-duty turning application while increasing tool life. The insert design reduces cutting forces and power consumption, making it ideal for any low horsepower lathe.
www.kennametal.com
