Over the last two decades, the world has seen a significant advancement in metalworking and the same has been adopted very nicely. There is more emphasis on productivity improvement, cut-down in operation costs and quality and most importantly, reliability.
Cutting tools are in a rapid revolution with the different cutting tool materials, grades, geometries and coatings to extract the maximum hardness, strength and wear resistance. We are witnessing a significant increase in verity of workpiece materials, like super alloys (Ti- & Ni-based), cobalt based materials, composites, high strength aluminium & special alloy steels. The ‘machinability’ depends not only on hardness but on many other physical and mechanical properties, such as thermal conductivity, strain hardening, chemical reactions, etc. All the aspects related to the surface integrity and quality are of paramount importance, especially in aerospace, defence & medical segments.
As new manufacturing methods emerged and established is the Near Net shape machining from the casting or forging with a common goal to enhance the productivity and reduce the operation cost, it has further drilled the importance of cutting tools.
In view of the above points, the use of solid carbide tooling is getting more momentum. One can get the multifold advantages when using the application-based tooling for that specific material & application and that is very well supported by the latest available softwares.
The use of solid carbide can be seen in all the segments, like general engineering, die & mould, aerospace, medical, electronics and power generation, and that too in all kinds of workpiece materials. Depending upon the complexity of the operation and the shape of the component, we can use different strategies to extract the full milage from solid carbide end mills. The strategies can be like high-speed machining, high feed machining, high performance machining, machining with miniature toolings, etc. This covers all the operations, like face milling, slot milling, side milling, copy milling with methods, like ramping, helical interpolation ramping, trochoidal milling, push-pull method, plunge milling, Z-level milling, advance roughing, etc.
High-Speed Machining (HSM): HSM is a machining strategy where a combination of small radial depth of cut & high cutting speed and table feeds are used. This strategy possess low cutting forces, less heat build-up in tool & work piece, less burr formation and high dimensional accuracy on the workpiece. These HSM solid carbide tools have a thick core which provides the stability in the tool and have a well-formed chip space for good chip evacuation.
High Feed Machining (HFM): This is a strategy where high feed rates can be reached with large radial engagement in combination with a small axial depth of cut. With HFM, we can achieve high metal removal rates and/or surface finish by using a much higher table feed compared to general machining. HFM end mills have specially developed front tooth and very short cutting length.
High Performance Machining (HPM): HPM is a machining strategy where very high material removal rates can be achieved. For this strategy, radial engagement is 1 times of cutter diameter and axial depth of cut is 1 to 1.5 times of cutter diameter, depending on the workpiece material. We can achieve extremely high metal removal rate by using a much higher chip load then in general machining. End mills for HPM having specially developed chip formers in the flute, tip protection, special formed chip space. The application areas for HPM are where operation in a mass production, production time/lead time is of great importance or on products, where high metal removal rate is required.
Advance roughing strategy: This is a well-defined tool path with a constant arc of contact for reliable roughing of simple and complex shapes. The large axial depth and small radial depth of cut combined with high feed per tooth and cutting speeds result in high productivity. When reducing the arc of contact, the amount of heat generated during roughing operation is reduced. As the radial depth of cut decreases, so does a cutter’s arc of contact. A smaller amount of contact results in less friction and therefore, less heat between the cutting-edges and the workpiece. These lower machining temperatures, and in turn, allow for increased cutting speed & shorter cycle times.
Machining difficult to cut materials: Depending on challenges in new difficulties to cut material coming in, the geometries on solid carbide tools take a new height. The formula is simple – to cut the material with ease without compromising on cut time and maintaining the quality requirements. Titanium, nickel alloys and stainless steel, steel alloys are the dominant materials in aeroengine designs. This type of material possesses high specific strength, corrosion resistance, mechanical strength and creep resistance. These are difficult to machine due to high cutting forces, high cutting temperatures, long chipping, abrasiveness & work hardening. Application security and the reliability are the major challenges while machining these super alloys. The use of solid carbide on these materials are increasing and require a special feature on tools. Thick core, special geometries, optimised helix angle, modified grain size and low friction coatings with the optimised machining techniques are the key to handle HRSA materials.
Carbon fiber-reinforced plastic (CFRP): CFRP composite is one of the most sought-after materials owing to its superior physical and mechanical properties, such as high durability and high strength-to-weight ratio. CFRP composites are often used by stacking up with titanium (Ti) to form multilayered material stacks for applications involving extreme mechanical loads, such as in aerospace and automotive industries. Several problems arise during the machining process due to the non-homogeneous structure and anisotropic & abrasive properties of composites. Traditional methods of micro-machining the CFRP stacks result in several issues, including high-cutting force and high tool wear, composite delamination, large groove depth in composites and poor surface quality. A lot of R&D has gone through to overcome these issues and develop the end mills which results in trouble-free effective machining for CFRPs. For example, two-in-one geometry solution designed for machining hybrid stacked material combinations, such as CFRP-Ti and CFRP-Alu. Due to its left-hand helix & right-hand helix, this tool prevents delamination, fibre pull-out & chip marks from damaging the workpiece surface and gives a perfect surface finish & prevents chip pollution between the two stack layers.
Ceramic end mills: Another development is to achieve revolutionary speeds in superalloys with ceramic end mills. SiAlON ceramics, high strength geometries and reinforced frontal tooth are some of the main features of these highly optimised tools and allow full utilisation of high-speed, highperformance machining tools. The tools can operate at a cutting speed of up to 1200 m/min and can offer a significant productivity increase when compared to standard solid carbide solutions.
Barrel tools: Barrel tools are another example of the developments in solid carbides and the productivity can be multifold as compared to the normal solid carbide tools. The main trust is to improve the process in machining to reduce the machining time, improve the surface integrity and the reliability. For the fastest, most reliable finishing operations, new barrel-shaped tools use an innovative ‘taper’ or ‘drop’ geometry with a 10° rake and 20° helix angle to enable large increases in stepover. This is possible through the use of advanced CAD/CAM systems or new plugins built for the uses of these tools. Using 5-axis machine movement, the tool’s cutting profile can always remain engaged with the surface of the part at the proper angle. Finishing tough materials, such as titanium, precipitation-hardened steels and stainless steel can require slow cutting speeds and multiple tool geometry variations that lead to long cycle times. Speed up these time-consuming processes without speeding up the spindle using new barrel solid end mills. With a 5-axis machine, these innovative, circle-segment end mill geometries allow for big stepovers to finish the same parts up to 80% faster than conventional ball-nose end mills.