Cut Cycle Times Through an HPC and HSM Ecosystem

High-performance cutting (HPC) and high-speed machining (HSM) may not have formal standards, but in practice, these types of tools and tool paths make significant improvements to cycle times and profitability. The methods tackle different variables, with HPC referring to tools and tool paths that use heavy, aggressive cuts to increase material removal rate, while HSM refers to tools and tool paths that take fast, light movements to maintain high average feed rates and reduce non-cutting time.

Sandvik Coromant makes tooling for both ends of this high-performance dichotomy, and Sandvik Mass Production Solution Specialist Chris Monroe has experience with how job shops can use these tools to their greatest effect. Ultimately, it comes down to using the right control and CAM system; making full use of modern coatings and geometries; and picking machines with the right rigidity, spindle speed and chip clearance for your application.

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Though generally HSM tooling leaves a smoother surface finish than roughing-focused HPC tooling, Monroe says it’s not a strict divide. Tools such as Sandvik’s Plura HD end mills qualify as HPC tools under the OEM’s classification system, but still leave respectable surface finish. Images courtesy of Sandvik Coromant.

HPC vs. HSM

The greatest benefit of HPC tool paths, Monroe says, is that they encourage continuous engagement with the part. While this requires much better rigidity and fixturing on the machine, especially as programmers take heavier cuts that exert more torque on the setup, it can dramatically increase metal removal rates.

HSM tool paths, he says, show their strengths through improved motion quality and constant chip thickness. They keep radial engagement small while the cutter moves continuously, lowering cutting forces and improving tool life consistency. With this tool life, Monroe says HSM tool paths are well suited for lights-out machining. These tool paths scale well with higher RPMs, but primarily require sufficient machine acceleration and support for a significant look-ahead in the control.

CAM and Control

Monroe says CNC is a prerequisite for modern HPC and HSM tool paths, as manual operation cannot take advantage of the features of HPC and HSM tooling. A control with a large look-ahead is necessary to track the rapid movements of HSM and control acceleration so motions are smooth and free of stair-stepping or jerkiness. Adaptive controls, meanwhile, make a good fit for HPC tool paths, as they enable real-time speed and feed adjustments to prevent issues with sudden force or heat spikes.

CNC also enables the use of CAM and simulation software, which mitigate many of the difficulties with setting up advanced tool paths. Monroe points to canned cycles in CAM software being able to streamline programming of difficult features such as tight corners, which require careful speed management to prevent the tool from slamming against the part. He also says CAM software can enable adaptive tool paths in forgings or castings, adjusting slightly when workpieces for the same job have minor dimensional fluctuations before machining. Simulation features help shops control chips and monitor load, ensuring they can approach the upper limits of their tools’ productivity without clogging the work zone or damaging the spindle.

Monroe does not recommend one CAM or control brand over another, just that shops use up-to-date versions as part of their HPC or HSM workflow. Even where different types of software contain different features, they all reduce the amount of time a shop will be cutting air. By keeping torque and power usage consistent, they reduce thermal instability, improve tool life and ultimately boost productivity.

Load monitoring is vital when working with HPC tool paths, as force spikes can occur when pushing the tools too hard.

Efficient Tool Geometry

Advancements in cutting tool geometry have enabled more resilient tooling for HPC operations, with Monroe able to point to several examples in Sandvik’s lineup. The company has created tooling with conical cores, which include a taper toward the tool’s base. Monroe says these tapers improve rigidity and reduce vibrations, extending tool life and proving useful for high-feed side milling and machining of deep pockets. The tooling OEM has also started to release tooling with unequal helixes, both symmetric and asymmetric. The latter limit resonance in the cut by using helixes of different pitch angles, while the former simply pairs its helixes so no adjacent helixes use the same pitch angle. In both cases, shops experience better tool stability, which then enables them to run at more aggressive feeds and speeds to complete jobs faster.

Monroe shared an example of one customer comparing its standard tooling for roughing and finishing the surface of a steel 1030 bearing box against Sandvik’s unequal helix WhisperKut tooling. With the older tool, the shop could machine four pieces with a table feed of 214 mm/min. With Sandvik’s newer tool, the shop could produce 40 pieces with one tool at a table speed of 835 mm/min. Beyond this significant increase in tool life, Sandvik’s tooling also eliminated an additional manual post-processing surface finishing step to correct points outside tolerances.

Heat-Resistant Coatings

HSM tooling, meanwhile, has benefited from advancements in coating technology that can resist the higher heat in the cut as tool speed increases. In Sandvik’s case, these improvements do not focus on new coating formulations so much as new ways to apply and layer proven coatings for better performance. Monroe says the OEM recently developed several PVD coating processes which help the coatings stick to their substrates and generate crystalline structures in the coatings to better withstand wear and flaking.

For one customer, the coating on a Sandvik DURA tool was heat-resistant enough that the shop could use it on a 304 SS job at a table speed of 43.45 ipm compared to a competitor’s 25.12 ipm. Even at a slightly lower feed per tooth, the Sandvik tool produced 50 workpieces in 7.4 hours before needing replacement, while the competitor’s tool produced 20 parts in 5.1 hours before needing replacement. Sandvik calculated a productivity boost of 73% for the customer with a 42% cycle time reduction and a 48% cost reduction.

One of the greatest advantages of advanced tooling is controlled, constant engagement, Monroe says. By staying in the cut, shops spend more time making chips, leading to lower cycle times and greater throughput.

Advanced Tooling Requires Advanced Machine Tools

Monroe says both vertical and horizontal three- and four-axis machines are good fits for HSM tool paths, but cautions that HPC performs better with horizontal machines due to chip evacuation needs. Even then, he recommends ensuring the machine has high-pressure coolant and air systems ready to help with chips. Five-axis machines are generally compatible with both HPC and HSM tool paths, though Monroe says to pay attention to the rotary axis acceleration rate, as this can be a limiting factor if shops can’t reorient the part swiftly enough to keep up with the feed rate. Gravity also assists in chip evacuation on five-axis machines, helping shops run more aggressive feed rates as chips can be freed from pockets. This same principle applies to inverted mills and lathes, which Monroe says typically have the stability to handle both HPC and HSM tool paths.

The debuts of machines with high-RPM spindles (40,000 RPM) and sufficiently stable constructions to use the full flutes of tools under sustained load without vibration make HPC and HSM tool paths more viable, Monroe says, with improved tool life even at aggressive speeds and feeds. Many modern machines offer spindle speeds 20-40% higher than those commonly available five years ago, Monroe says, with material removal rates 100-300% higher. Together with modern tooling geometries and coatings, these enable the use of tool paths that show dramatic improvements to cycle times while extending the time between tool changes.