Bridgeport to Datron: Traditional to HSM
Manual machining is an important step into becoming a well-rounded machinist. Learning how the machine responds to the material by the feel through the handles and sound of the spindle. But although manual machining has been a crucial part of history, the industry has changed drastically with the introduction of Numerical Control (NC). Contours that would have taken hours to machine by hand can now be produced in minutes. But the industry is still evolving, with a large shift towards high-speed machining, a process with the same variables, but a very different process.
I began my milling journey in a similar way as many did, on a Bridgeport. And although I came home smelling of old coolant, with chips in my hair, and cuts on my hands, I loved taking a lump of metal and a technical drawing and creating something new. Hitting tolerances became a game and getting a great finish, a challenge. But being an engineer, we always look for more efficient methods and ways to work smarter (we’re lazy).
This is where HSM (high-speed machining) comes in. A process in which heavy, slow cuts are replaced with fast lighter cuts, in order to preserve tool life, prioritise dimensional accuracy and improve surface finish.
With the definition of HSM meaning different things to different people, we tend to say a machine operation with a spindle speed above 15k RPM would be classed as HSM. But it really ends up being a combination of things, a high speed spindle, a high feed rate and a high material removal rate. When we look at the thermodynamics of such an operation, we notice something interesting. As you can imagine, heat generated by milling is directly linked to spindle speed, and for the most part, as the spindle speed increases, so does the heat. But at a certain point, the heat begins to reduce, this is because the forces between the material and the cutter reduces due to the high spindle speed. Not only does this preserve your tools, but it also gives a superior surface finish.
Although faster operations, preserved tool life and improved dimensional accuracy sound like a no brainer, there are conditions. Attempting to machine in this style on traditional or older machines will end up in a hot mess, because they’re simply not quick enough. The load per tooth on the cutter will be too high, and you’ll end up with at least one of three things: a broken tool, a scrapped job, or worse, a wonky spindle.
So, you’ve got a fast machine and you’re ready to make some chips. Next, you’ve got to pick the right tools for the job. In all machining, whether you’re using a traditional or a CNC, vibration is your enemy, so when you’re ramping up your spindle to 40,000RPM its important you’ve taken precautions. Single flute cutters are favoured in HSM as they can spit the chips out faster than that of a multi-flute cutter.
There are variables that you need to consider before pressing the start button. What you’re cutting is an important question. For a Perspex application, a single flute and a high feed rate and RPM is perfect to get the hot chips away from the job, but for a hardened steel application, a multi-flute with a reduced RPM/feed rate is going to protect you from tool breakage and give you the best result.
When we are using traditional milling methods, we opt for larger diameter tools and deeper cuts to really chew the material away. Contrary to this, with a high speed spindle we use smaller tools. This is because we can get a higher material removal rate with smaller diameter tools without needing to subject our spindles to all those centripetal forces.
The traditional milling has its place, but we’re in an age of progressing technology, taking the process out of our hands and into the world of automation. Removing human error, cutting cycle times and increasing accuracy is the game, and Datron is on the frontline of emerging CNC technologies. If you’re thinking about developing your workshop in line with the modern standard, give one of our specialists a call today.