Pushing the Edge

The Gold-Quad F high feed mill from Ingersoll Cutting Tools.

So, you want to maximize cutting speeds and feeds to reduce cycle times? If this is your goal, there’s a series of cutting tool factors to be considered, including coatings, coolant, materials, applications, etc.

We asked industry experts if any particular applications stand out in the quest for high speeds and feeds.

“A low arc of engagement tends to lend itself to high speeds and feeds…reducing the contact area of a square shoulder tool keeps the heat low and allows us to increase feed to compensate for chip thinning that occurs at the low arc of engagement. An example of this is often called Trochoidal milling in slots but applies to any shape,” states Brian MacNeil, milling products and application specialist, Sandvik Canada. “Also Dynamic milling is a common method supported by CAM software that uses small arc of engagement with higher speeds and high feeds,” adds MacNeil.

“Almost every application lends itself to cycle time reductions,” says John Mitchell, general manager of Tungaloy Canada. “The options available to reduce cycle time are almost endless. When turning, the maximum feed rate should not exceed half of the insert nose radius, therefore use the largest nose radius possible to increase feed rates. If the part requires a good surface finish or has some corner radii restrictions, use a wiper insert.”

High Speed, High Feed

We also wanted to know what materials work best in high speed/feed operations—and what materials are best machined slowly.

“High feed milling works well in a variety of materials including, but not limited to, carbon steels, alloy steels, stainless steels, heat resistant alloys, and titanium. Cutting conditions vary depending on the type of material,” says Paul Rice, applications engineer at Kyocera Precision Tools. “For example, slower feeds and speeds are used when machining heat resistant alloys and greatly increased when machining low carbon steels.”

“Another option for finishing or semi-finishing is to use cermet,” suggests Mitchell. “Cermet is capable of running at higher speeds than carbide, produces excellent surface finish and lasts a very long time. Use CBN in hard turning applications. Some shops are still grinding their hardened parts. It is much faster to produce these parts on your CNC lathe using a CBN insert,” notes Mitchell.

“Higher than normal speeds and feeds can be applied to any material group by changing from conventional techniques,” suggests MacNeil. “Techniques allow for cutting data increases relative to material (for example, Titanium 6al4v at 250 sfm using standard toolpath can achieve 450-500 sfm with high feed side milling techniques),” he says.

Coating Solutions

Cutting tool experts were also asked about the ideal coatings for maximum speeds and feeds.

“CVD grades have a thicker coating and are better able to withstand heat in larger arcs of engagement and high speeds,” explains MacNeil. “PVD inserts are thinner and sharper which is better at low arcs of engagement. They do not withstand heat as well, but we have less heat in the process when the arc is low,” says MacNeil.

“When it comes to high speed machining, we usually like to look at ALTiN [aluminum titanium nitride] coatings, primarily because of their heat resistance and their abrasion resistance,” says Jay Ball, product manager for solid carbide endmills, NAFTA at Seco Tools “In high speed machining, there’s a lot of heat generated.”

Tool Wear

Tools wear out faster in high speed/feed operations, a fate that doesn’t unduly alarm cutting tool company officials.

“Until the process is secure and the programming suits the machine, material and fixturing, I don’t worry about wear. We can do a lot of damage before a tool wears,” says MacNeil. “To me it is the last factor left in the equation…wear is inevitable. Slow controlled wear that is predictable is the goal after we have everything else in the process secure.”

“Obviously the faster the rpm, the shorter the tool life … but tool life is really a small player in total cost,” agrees Mitchell. “I think you’re always better off running as fast as you can, within reason. If you have to go in and index your insert every three minutes on the machine [then speed is not a benefit]. You have to balance tool wear and speed,” he says.

Proper Programming

Other tips from the experts: “Programming is the key in high feed milling,” says William Fiorenza, die and mold product manager at Ingersoll Cutting Tools. “Proper programming that utilizes high speed machining techniques and programing features such as corner welding and corner smoothing promotes free and smooth cutting and constant chip load. These are all key things you need to have to effectively high feed mill.”

It’s important to note certain cutting characteristics when maximizing speed and feed.

“Typically when you deal with very, very high feed tooling, you’re also dealing with very, very light depths of cuts. So that’s the trade-off,” says Steve Geisel, senior product manager at Iscar Tools Inc.

“Unfortunately, there’s really no tools that exist that allow you to take a very, very large depth of cut and also take a very, very aggressive feedrate. Because of the heat that’s generated, you either take a big depth of cut with a light feed or a small depth of cut with a high feed…you can only generate so much heat in a cut. The minute you generate more heat than what is needed, you’re going to burn out your cutting tool.”

Coolant Conditions

Heat has the greatest impact on tool life, and speed has the greatest impact on heat. With this in mind, we asked pundits about the role of coolant in maximizing speeds and feeds.

“Because we’re talking about the heat generated, the quicker you can reduce the heat, the more aggressive you can be. Coolant is one means that you can reduce the heat in the cut. One thing we’ve developed, we call it our Jet HP line. It’s a high pressure coolant, tooling system. With our Jet HP line, people can run the coolant pumps up to 5,000 psi,” says Geisel.

“Pretty much all of our tools are designed with coolant through applications in mind,” says Cullen Morrison, business development manager at Komet of America. “We also have applications for MQL [Minimum Quantity Lubrication]…we’re looking at how can we run these components as fast and as stable as possible,” he adds.

That said, sometimes machining dry works best while trying to attain high speeds and feeds.

“When you’re running an interrupted cut in a turning situation, it’s almost always best to turn the coolant off and run dry [due to the risk of] thermal cracking,” states Mitchell.

Avoiding Chatter

A previous Canadian Metalworking story noted that on the first indication of premature tool wear, chatter or chipping, machinists will often turn down the override controlling the feedrate. In such situations, however, might it be better to boost the feedrate instead?

“I would say that’s very relative to what the process is … a low feed rate does cause increased wear. If that is the reason for the wear, then a higher feedrate would be better. If the cutting speed is too high, a higher feed rate is not going to help. If you’re talking about turning hardened steel at 60 Rc, the wear on the tool is just going to be a fact of life,” says Morrison.

Tweaking the feedrate “depends on the situation…if you’re dealing with chip thinning, then yes you really need to ramp up your feed rate. If it’s not chip thinning, I’m not sure I would agree [with increasing the feedrate],” adds Mitchell.

“Be conscious of average chip thickness,” echoes Fiorenza. “All high feed tooling has a feed rate multiplier associated with the tool that is different for almost every cutter. That multiplier allows you to compensate for chip thinning. You do have to be aware of slowing down the feed rate and possibly generating too thin of a chip in which case you end up rubbing the material … it’s a very important thing for end users of high feed milling tools to understand what their feed rate multiplier is,” he says.

High Speed/Feed Tips

Other tips: if maximizing high speeds and feeds is the goal, use a rigid machine tool—“As rigid as possible. Rigid will benefit everyone,” says Morrison.

Cutting tool companies have some new products on the market, built with high speeds and feeds in mind.

“We have a new tool we’re releasing to the US market—the Brinkhaus ToolScope machine monitoring system. It monitors load on spindle, torque forces and other key indicators of machining performance,” says Morrison.

“We have a new Plura endmill optimized for high feed side milling. This tool also incorporates new coating process technology designed to keep the coating intact at higher speeds,” says MacNeil.

“We have several new products out: Gold-Quad F and Gold-Quad XXX [high feed mills]. The first one, Gold-Quad F, is a 12-degree lead angle style tool. It does an excellent job of managing cutting forces and has up to seven different insert styles to address different milling scenarios,” says Fiorenza.

“Kyocera recently released an innovative high feed milling line-up. The MFH-Raptor and the MFH Mini high feed end mills and face mills utilize new insert grades with complex geometries that drastically reduce spindle loads and are capable of extremely high feed rates for maximum material removal,” says Rice.

“Tungaloy recently expanded its DoOcto line…this milling cutter can now take a double positive eight-edged insert or an eight-edged high feed insert. The high feed insert can be used as a conventional milling tool when the depth of cut exceeds the recommended depth for high feed,” says Mitchell.

System Approach

Of course, as most all of the experts insist, a cutting tool is only as good as its toolholder.

“I always recommend the highest quality holder you can get,” says MacNeil. “High feed and speed is used to maximize metal removal rates. Investing in a high quality machine and programming methods and not investing in quality tools and holders … is equivalent to owning a Ferrari and putting the cheapest tires you can find on it. You won’t win the race, and you may end up with damaged components.”

One final piece of wisdom: Morrison advises machinists looking to maximize speeds and feeds to take a moment to reflect before commencing work.

“We tell them, ‘look at everything as a system.’ Balance everything. You can’t put the cart in front of the horse. What are the limitations of the machine? What are its speed characteristics? You have to look at the whole system … it’s all about controlling the process,” states Morrison.