Ever wondered what high-speed machining is? What are its benefits and is it applicable in your machine shop? Reading below will enable you to answer these questions to a great extent.
High-Speed Machining or HSM can be best defined as a machining technique that is characterized by high rotational speeds and high surface federate. If you are in search of giving a boost to your machine shop’s productivity, improving the performance of your existing machines, optimizing your tooling bills, or whatever the specific case is, employing HSM could be one of the key factors to achieving this goal.
Although to some extent the cutting techniques of high-speed machining can be applied with more standard machinery and equipment it is of high importance that devoted tools, tool holders, clamping technologies, and of course high-end rigid machines are a must for optimal results
Possibly everyone asks himself why and what makes it better compared to the conventional milling techniques. The idea and assumption that stands behind it is that with the increase of speeds and feeds 5-10 times the temperature at the cutting edge will eventually start to decrease or otherwise said the higher the relative speed between the part and workpiece the lesser the heat that is generated between them. Developing this ideology further brings with it all the rest of what characterizes HSM - high material removal rates for many materials, relatively lower cutting forces, extended and more predictable tool life, and so on. Last but not least it shall be noted that the shallow depth of cut aids for superior quality surface finish with less vibration and less stress to the part. However, in order to squeeze the maximum productivity and efficiency, there is a number of improvements that have been made throughout the years both on the machinery side and the tools and tool holding side.
Still wondering whether HSM is applicable for your shop? Let’s now look into more detail to the major aspects of it and what is needed to apply it successfully.
Materials you can machine efficiently are anything from plastics to aluminum, steel, and HRSA. The development of new materials for engineering applications, which are often very difficult to machine, has shown the importance of developing a different approach. Hardened steels like the ones used in mold making, highly abrasive materials like Inconel, grade 6 titanium alloys, and many other that are usually very tough to machine and extremely challenging to the tools are among the ones where HSM will be an excellent choice. It is also not only being a more productive technique in terms of material removal rate compared to conventional but also has the really great advantage of making tool life more predictable and thus additionally making it a more efficient and economical way to machine parts. It is also really versatile as it allows for machining literally any material from plastics, to aluminum and even the toughest steels, stainless steels, and HRSA.
Types of operations you can perform with High-Speed Machining are from roughing to semi-finishing and even finishing. This fact is caused mainly because of the light depths of cut normally employed while using HSM technique and it can machine surfaces with great surface finish and to high precision. This means even some finishing operations can be eliminated because normally surface quality free of burrs can be achieved. You can employ it for mold roughing operations, pocketing, rest machining, corner re-machining, complex 3 axis, and 5 axis operations giving it a very large range of application and versatility.
One of the greatest specifics comes in programming. From the programming point of view, the toolpaths required for HSM machining are lengthy and very complicated to be generated without the aid of CAM software. This way selecting the depths of cut and stepover (usually as a percentage of the tool diameter), entry angle for each cut, tolerances allowing the machine to avoid jerky moves and make the toolpath as smooth as possible, and many more have been made easy. Nowadays the available CAD software like Mastercam, Siemens NX, Catia, Gibbs CAM, Esprit, and many others have the possibility to employ high-speed machining strategies as they have become a substantial method for using modern toolpaths and reducing cutting times. It is also of extreme importance to simulate the program in the CAM environment or even use specialized simulating software like Vericut in order to make sure the programmed toolpath is error-free and will not cause any collision. This will save time for making this checkup at the machine, if possible at all, and this way minimize scrap. A major goal while performing HSM cuts is to preserve the chip thickness equal for all passes which ensure the exerting cutting forces to be equal as well, thus making tool life much longer and more predictable and tool wear much more even along the cutting edge.
High-Speed Machining functions
Being an obvious advantage HSM has come with some challenges for the machine tool builders as well both for the mechanics of the machine and the controller as well. Usually, the programming code consists of many more lines compared to a program for conventional milling and the CNC machine would perform many short and direction-changing moves demanding a lot in terms of stability and the machine controller, which has to process much more commands quicker than usually. This invokes the need for today’s control systems to have improved motion control, larger and faster system memory and block processing times, cutting accuracy at a higher velocity, and so on. This comes with the introduction of codes to turn on and off high-speed machining mode and many parameters controlling acceleration and deceleration, accuracy options, and many more as unlike in conventional milling where the controller is supposed to buffer a few lines ahead HSM relies on extremely quick processing. Probably you find yourself falling among the ones that one way or another will also benefit from the high surface finish and efficiency of high-speed machining. Modern controls offer additional options making you able to define what you search for - accuracy for finishing operations or speed for roughing operations. There are even more advanced options depending on how you would like the machine to react depending on your preferences for its trajectory between very close or very distant coordinate points, heaviness of the spline, control of acceleration and deceleration of the machine, and many more allowing to get the best results of your machine.
As one of the specifics of HSM is the high speed this would inevitably mean that the extremely fast rotation speed of the spindle will be highly demanding to the spindles. Higher RPMs wear off the spindle bearings much faster than usual and will result in the need for regular maintenance of the machine spindle components. Adding this to the fact that the high speed should be maintained alongside extremely small radial runouts puts even greater demand on improved machine quality and rigidity.
Tools and tool holders are another part of the equipment that comes special when we speak about HSM. These special tools have been developed to aid even more the chip thinning effect, thus lessening the heat generation. It is important to be said that about 80% of the heat generated during the cutting process is released by the chips and only about 10% goes to the tool which means it is extremely sparing as one of the key factors for built-up edge is namely the temperature. Cutting tools for HSM strategies can be both solid carbide and tool body with inserts and the optimal tool material will have to be a combination of toughness and hardness. There are already many options on the tool market that have brought a lot to the success of HSM like the ceramic tools, CBN tools, PCD tools, and the improvement of the PVD and CVD coatings to carbide tools.
When speaking about the clamping of the tool and the tool holder we have to note that rigid clamping is a key factor to the performance and tool life. With the available options for using hydraulic, power chucks, and shrink fit chucks we have the perfect solution. Having it on our side will be very important at high RPM because of the increasing centrifugal forces that disbalance the tool and not only create a much higher load to the spindle but also deteriorates tool life. Thus, the tool holder must be balanced at the right RPM so that the radial runout can be maintained.
In cases when using longer tools, especially when machining materials like steel, stainless, or HRSA the occurrence of chatter and vibration must be avoided. This has been made available with end mills with variable pitch, or tools using dampening mechanisms like the Silent Tools line by Sandvik Coromant.
Environment
If your shop is also looking for a production process causing less harm to the environment it is important to be noted that HSM is considered as eco-friendly machining. Applying coolant to modern tools having certain coatings makes the tool prone to thermal cracking when the tool is hot while cutting the material and then rapidly gets cooled down. Such tool materials ceramics and the PVD and CVD coatings of TiAlN have the so-called temperature of activation and it is against the recommendation of the tool manufacturer to use coolant even when running at very high speeds and feeds.
What could be said as a conclusion is that high-speed machining is a way of machining that deserves a lot of your attention and will boost productivity to a higher level. The initial investment will pay off quickly and prove the sustainability, productivity, and efficiency of this advanced machining technique.
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