Even as Citizen Machinery UK (https://is.gd/silefi) is selling those sliding-head (Citizen Cincom) and fixed-head (Miyano) models it offers with LFV in the LFV format in “almost 100%” of cases, Wilkins says that the technology is still widely misunderstood. In fact, that misunderstanding is almost total, he suggests, but appreciates that, because it is a technical subject. “People think that our technology is like everybody else’s, a CNC macro. That technology is still being introduced by others, too. I recently saw a new function promoted by a German manufacturer of CNC lathes, a macro again, but packaged in an easy format for customers to use.”
And concerning others’ macro offerings, he says: “In almost all cases, it is either turned off, not used, sold free of charge or retrofitted onto an old machine. We were doing the same thing more than 20 years ago, because customers wanted to run their machines unattended, that was the key. Machines became faster, they had sub-spindles, so we could finish a part in one hit and the only thing holding users back was chip control. So, we decided to interrupt the cut using a macro approach. Now, in some cases it worked, but where it did, in all cases tool life was lower. The end result was less productivity, not more.”
HERE’S THE RUB
This should be quite easy to understand, he says, because stopping a tool in cut will see it rub and get hot, and heat is the big tool life killer, hence the reason to apply coolant. (LFV, incidentally, sees tool life boosted, but we’ll get to that in a bit.)
So, the next step taken by Citizen Machinery was to introduce high pressure coolant (HPC) to break swarf, Wilkins continues. “HPC was developed because macro programming was not effective, and we became the best sellers of HPC, because everybody using our machines wanted to run unattended; high pressure coolant became the norm.”
Okay, so a solution was available, but with the introduction and use of exotic materials, breaking swarf became a challenge again, which saw the pressures employed getting higher and higher (and now lead is being removed from brass, making that non-chipping, Wilkins adds). “People were using huge amounts of power, the coolant oil was being ‘cooked’ and the machines were less accurate as a result, plus there were related service issues, so it was never an ideal solution,” he advises. “Even though the customers were paying £20-30-50,000 more for HPC, they were willing to do so, because the return on investment was still so high when running unattended. It offers a fantastic ROI. The volume turning business is incredibly profitable, if you can run unattended. Our customers will be paying, say, £2,500/month for the machine, but invoicing business to the value of £20,000+.”
No place for HPC anymore, then? “You might still want to make sure that the sub-spindle collet is clean, so you would have to ask whether the standard coolant pump is good enough for that. In some cases, the answer is ‘yes’, but in others it would be ‘no’,” the deputy managing director explains. “LFV doesn’t require a drill to peck anymore, but if you want to be sure that the flutes are clean of chips, it’s better to have through-tool coolant. And the smaller the hole, the higher is the back pressure, so, again, HPC may be required. Now, you could choose to peck, but our users are focused on every second and the ROI means that the investment in HPC pays off.” As it happens, Citizen Machinery UK has designed its own simple, lower cost, lower power HPC unit available in a number of pressure levels that is “more than satisfactory” for those type of requirements and which has been available for more than a year.
With this unit, no longer does the power requirement for a HPC unit outstrip the figure drawn by a whole machine, which not only meant that a higher electrical supply capability was required but that machines had to be upgraded so as to be able to isolate the coolant equipment via the machine, as required by European safety regulations, Wilkins notes. HPC also needs to be used sensibly to avoid blasting chips everywhere and should be used only where required, although it might be left on all the time, he suggests. Added to that, the vapour generated requires upgraded extraction/filtration equipment. “So, you can see where the need for LFV has come from; all these issues have existed for a very long time,” he advises.
LFV was actually designed some five or six years ago for a specific end user requirement where the demands were a huge depth of cut, zero deflection and no use of HPC. The technology is patented for use in two axes (single-axis could not be so protected) and its development required control over the machines CNC unit’s operating system, which Citizen Machinery has, while Mitsubishi took care of necessary axis and spindle drive communication. (LFV for thread-cutting is under development and the application of LFV on both main and sub-spindle simultaneously is another possible direction of future development.)
The fundamental difference between a macro and LFV is that a macro’s in-out motion is not synchronised to spindle rotation, whereas LFV is. This mean that the wavy face that results during turning sees the tool re-enter to cut off the previously produced peaks precisely. And with this in/out of cut motion, coolant gets between the normally buried tool top surface, cooling and lubricating, which leads to that longer tool life (although the coolant must be thin and tools should have ground faces and sharp edges – Arno [https://is.gd/uvuyax], for example – because a viscous coolant can actually inhibit cutting).
“We can also decide how to control the process. We can choose multiple oscillations per revolution or multiple revolutions per oscillation, depending on the application; how long you want the swarf chip,” Wilkins continues, adding: “But normally its led by the tool life. That is the real win. If you are not stopping to change tools, you get so much more efficiency – more parts per tool – so we protect to tool as much as possible. In some cases, we have extended tool life by in excess of five times.
“If the time taken to notice the need for a tool change and then making it adds up to an hour, that’s potentially five hours’ more production. And if a machine stops during an unmanned night, many hours will be lost. Most of our users are looking for 100 hours a week, so this is important. You can transform the productivity of a machine with LFV, leading to fantastic ROI.”
The cost of LFV is £10,000-£12,000, incidentally. And it is push-button technology; a page in the controller has a few variable parameters that support correct application for the circumstances, with guidance available. And the UK-written CNC Wizard programming system supports LFV, incidentally. But there is a need to educate users on, for example, surface finish. It can be better or worse, so parameter optimisation may be required. It can also look different yet still meet the technical roughness requirement.
One of the latest machines to be rolled out with LFV is a 42 mm bar diameter capacity Miyano model (BNA-42GTYLFV), the first appearance on Miyano of the technology and launched at MACH 2018 earlier this year. “This is big news. LFV is not just for sliding-heads; it’s for fixed-heads, too,” Wilkins enthuses, adding: “It has transformed the saleability of that model. It’s now one of best-selling models, as a result.” But LFV on larger bar capacity machines is not envisaged, so 64 mm. The generally larger environment and tooling mean that swarf isn’t such an issue, while with increased mass, LFV oscillation might be more problematic. But, ultimately, it’s a commercial benefit; how much would it cost versus the benefit, he concludes.