Contract CNC Programming Services: Intro To High-Speed Machining

High-speed contract CNC machining is generally associated with spindle speeds that are greater than 15K RPM or greater. There is more to it than just a fast spindle for CNC machining parts. First let’s look at what our process intent, are we using the HSM as a function of rough machining the workpieces or finishing as well. Is the tooling we will be using large in diameter or small in diameter for a job.

HSM machining has grown along with Contract CNC Programming Services and its uses & capabilities just like any other facet of machining over the years. The capabilities have grown due to problem solving & engineering.

Let’s look at the machine tool. The newer equipment for HSM processing has had the problems solved by engineering creating improvements for a better machine tool for the HSM process.  The ultimate machines for taking advantage of all the different HSM strategies will have high RPM spindles, direct drive spindles with ceramic bearing & chillers. Spindles of this type are ideal for HSM creating accurate high metal removal rates with little vibration. The control in the machine will look ahead many blocks of code & calculate for compensation of motion during the execution of the programmed geometry. Creating accurately machined features, fast. The traverse axis will also have chillers to compensate for thermal growth during long cycle times at high speed. These chillers make a big difference when finishing tight tolerance workpieces. These machines usually have a different architecture than traditional CNC machine tools too; the machine bases are made of materials other than just cast iron. The bases on the ultimate machines are made of vibration dampening materials. These are great solutions to the issues created when the HSM strategies were in development & use. However, those solutions were created by identifying the problems encountered while performing different HSM strategies. Having the ultimate machine is great. However, they are expensive & are not always needed depending on the HSM process intent.

Contract CNC Programming Operations

Let’s take a quick look at some of the HSM operations related to machine tools. Using HSM as a roughing process can be completed on some older equipment that may not have all the capabilities of the newer equipment available. If we are performing a roughing process, we don't need to have chillers on our table traverse axis. Because we are roughing & will leave material for the finishing.  We don’t need to worry about the effect of thermal growth as much in a rough process. The limitation to rough processing using HSM strategies on older machines is the processing capabilities of the machines control, RPM, and vibration. The processing capabilities for HSM generally require a look ahead in the controls processing capability of the programmed code. The machines control should have this option if you intend to get the most out of HSM. However, it depends on your program code & process too; you just might be able to get by without that much or any look ahead at all, depending on your data points in the program. The less data points needed to be processed in the time it takes to perform a toolpath the less coded the control must process to make the necessary compensations to the machines travel during execution. In the case of an older machine with less processing power, a high-feed mill may be a better solution for HSM then tri cordial, or other HSM is roughing strategies. The high feed mill can use the same style of tool path as traditional tool paths employed in CNC machining, however at a much less depth of cut & at accelerated feed rates. This is due to the engineering in high-feed mills. High feed mills have different tool geometries that allow the high feed rates to be achieved. The tools usually have lead angles & a radius at the business end of the tool. These geometries are slight, however, transfer the usual radial tool pressure into axial tool pressure. Picture the tool pressure during conventional rough milling; it is perpendicular to the tools axis. So, when the load is too great, it breaks. The High feed mill geometry creates axial pressure that is sent parallel to the tools axis. This creates the ability to achieve higher feeds with the high feed mill. Looking at this as a possible HSM strategy for older machines works well because even know the feeds are higher, the data points are less then tri cordial, or other cam dependent strategies. The machine will probably be able to keep up the tool path. It is like running your regular tool path 100 times faster & ten or more times less depth of cut. This strategy has a place as a tool for higher metal removal rates than compared to roughing with regular milling tools in some cases. Obviously, if you have the ultimate machine for HSM, you will be able to process faster & more accurately with less vibration, opening most if not all the HSM strategies up for use.

Contract CNC Programming Tooling

The type of tooling used for the HSM process plays an important part. We want to use balanced, near zero runouts, vibration dampening tool holders. Why do we want this type of tool holder you say? If we us this type of tooling in all our processes, not just HSM you will see the benefit of longer tool life. However, in HSM it is a bit more important because of the higher spindle speeds usually associated with HSM. Between the spindle & the business end of the cutting tool is the tool holder. If we use tooling that is out of balance, we will have spindle issues & vibration. If we use a tool holder with run out, we will have lower tool life & vibration. What does run out have to do with it? If we have a 1/32 tool running out .003 the cutting forces will be focused on the flute that has the most radial runout. Causing a premature failure of that tool. Along with the focus of force being on one flute, it causes vibration & vibration kills tools. During troubleshooting a tool failure, I have brought this up to machinists with the symptomatic issue. Some have said .003 is not much (usually used to performing processes with larger tooling) & I say now picture a 1” diameter end mill running out .100. How long do you think that tool would last? When I say near zero runouts I mean near zero.

Another side to look at is, the other side of the contract programming services is the workpiece and  how stable is the work holding set up. If the setup is weak or unstable, you may encounter vibration too. It is important that the setup of the tooling be ridged & accurate. HSM has been around for quite some time, the speed of the metal removal rate is relative, to the setup. If you do not have the Ultimate machine, you can still achieve varied results with different HSM strategies. Focus on the process intent, within your machine environment. Design the process around your environments capabilities. If you have an older machine get a couple of vibration dampening, balanced, tool holders that will interface with your machine. Pick up a high-feed mill or multi-fluted mill and start machining. You will encounter problems & create solutions to the problems, just like the engineers did to create the tooling & machine tools that perform so well in HSM. With the variety of tooling, tool holders, etc. you can incrementally work towards the confidence to purchase that ultimate machine & get a return on your investment as you go.