Advanced edge preps, coatings, geometries lead the way
Solid-carbide round tools have seemingly been around forever; before them, high-speed steel (HSS) tools ruled the roost, and after them a growing selection of alternative processes like indexables, EDM, waterjet and now additive manufacturing emerged as competition.
Solid-carbide round tools cover a wide range of applications, including drilling, milling, as well as reaming and threading. The newest product innovations, however, are opening eyes in job shops and production shops to their capabilities in finish machining. New end mill and drill product lines are coming out almost daily that improve machining processes for the more mundane applications in cast iron and steel to the increasingly complex demands of titanium, stainless steel and heat-resistant superalloys (HRSA). Following are suggested approaches by leading suppliers to finding the right tooling match for a variety of applications.
Higher Precision Key to Higher Performance
Edwin Tonne, training and technical specialist for Horn USA Inc., Franklin, Tenn, puts a little bit of a different twist on the evolution of solid-carbide round tools and looks into the background of machine technology to determine “which came first, improved tools or improved machines. Better precision of all components, more sophisticated electronics and control systems have produced superior machine technology,” said Tonne. “Advanced machining centers with the required acceleration and deceleration in combination with advanced CAM programming have set the stage for serious improvements in solid-carbide round tools. End mills, for example, are able to be designed with more flutes, as many as 16, and with chip gullets to facilitate chip removal.”
Advanced CAM programming enables milling strategies that include high-speed milling, high-efficiency milling, optimized roughing and proprietary CAM software. “In the past, for a pocketing application you might use a two- or three-flute end mill. Now you can use a high-performance drill to start the hole and trochoidal milling to complete the pocket. You couldn’t do that before the control system and CAM were up to snuff,” Tonne explained.
Horn’s multi-flute end mills for machining titanium, Inconel, stainless and other high-temperature resistant metals benefit from high-speed and high-efficiency strategies. The highest MRR possible in high-speed machining with multi-flute tools happens when the process engages the full flute length of the tool. “The more flutes, the larger the core diameter of the tool needs to be for rigidity,” he said.
Horn’s DSFT end mills—part of the DS line of high-DOC, low-radial-engagement tools—are designed for the consistent chip thinning required to get the maximum advantage out of these strategies. “With an end mill, you are normally looking at radial chip thinning, unless it’s a ball nose where you have radial chip thinning and an approach angle,” said Tonne. “Radial chip thinning requires a very accurate system or you’ll lose your advantage and chip or destroy the tool. There’s a balance between how many flutes you put on a tool, how fast you need to go, and the volume of chips that are going to reside in that flute. Typical for a half-inch mill, you would look for a five-flute end mill for trochoidal milling of gummy materials.”
Three flutes are optimal for slotting and five flutes and up for more advanced processes like trochoidal strategies. For finishing operations, tools may have up to 16 flutes or more, according to Tonne.
“The real limitation in machining efficiency is that when you produce a chip it has to go someplace,” he said. “If the volume of the chip is more than the flute can handle, pressure will build behind the cutting edge and breakage or crashes can result.”
Micrograin carbides continue to be a key element of the tools. They represent the best way to achieve the middle ground between a tough, coarse carbide grade with lower cutting speed or a higher speed but brittle cutting grade. “A coarse-grain end mill can take more abuse without chipping but its speed and productivity are lower. You can have a tough carbide grade or a higher-speed carbide grade or something in the middle. Our grade is durable with higher speed capability,” Tonne said.
Determine the Shop’s Main Driver
Before you can pick the right tool, you need to first determine what it will be used for. “In order to select the correct solid-carbide round tool for a given milling application, we must understand the end user’s main driver,” said Matt Clynch, national product specialist-milling at Iscar USA, Arlington, Texas.
What are the main drivers in milling? “That is the first question we ask and one that has multiple answers,” he said. “Machining costs (productivity), tooling costs (cost per edge), and tool change costs (tool life) are three considerations for determining the impact that a cutting tool can have on cost per unit (CPU) in a manufacturing environment. We simply inform the end user to pick two of the three drivers because achieving all three simultaneously is practically impossible. Once we know the drivers that the end user needs, we choose specific tooling from three product areas: high-performance; standard (or legacy type, standard flute/helix design); and a newly introduced general-purpose product.”
Iscar’s high-performance line is tailored with specific geometries for various material groups like stainless steel, titanium, and 4000 series alloys. “One of the secrets to high-performance capability is found in the geometries that can be produced with new advanced grinding technology and software,” said Clynch. “If you can imagine a cutting edge geometry, today’s advanced machines and software can grind edge geometry and improve chip gullet designs for ejecting or evacuating chips out of the cutting zone.
“You can’t walk into an aerospace shop without seeing titanium and stainless steel everywhere,” Clynch continued. “Our new carbide grades allow us to run much faster for machining those material types. For example, the Ti-Turbo end mill machines titanium at 250-300 sfm, compared to normal cutting speeds of 140-160 sfm. Heat is a critical consideration when machining with carbide. When we engineer new carbide substrates, we’re looking for ways to remove as much cobalt content as possible within the substrate because cobalt melts at high temperatures and studies have shown that wear rates increase as cobalt content is increased.”
Trend Toward Drilling Harder Materials
Today’s advanced solid-carbide drills feature modern carbide substrates, coatings, edge preps and updated software for grinding machine capability that allows putting different styles of grinds on the drills, according to Patrick Cline, national holemaking product manager, Iscar USA. “The trend with solid-carbide drills is to machine materials in the hardened rather than in the soft state before heat treating,” he said.
Iscar’s IC903 coated grade solid carbide, with an AH grind special edge prep, drills materials with hardnesses from 55 to 70 Rc. “In the past, you would have to put the holes in the part while in a soft state, which may not be optimal, but your only other option would be to ram EDM the hole which is a slower process,” said Cline.
Chip evacuation is a major limiting factor in drilling that is being addressed by twisted coolant-through holes, according to Cline. “The twisted coolant holes allow for deep chip gullets with plenty of room to evacuate chips while maintaining a very large and strong core,” he said. “The rigidity of solid carbide allows increasing the length-to-diameter ratios of solid-carbide tools to 20, 30, 40 and even 50 times diameter—ratios unimagined in the past. You wouldn’t see this in the past because if the carbide was tough, it had no wear resistance and if it had wear resistance it was so brittle that it would deflect and break.
“With longer drills the designs are changing,” Cline continued. “For our 20×D, we’ll have four margins down on the bottom. When the first part of the drill is engaged, it has four margins and two of the margins will drop off as you go up the drill body and it’ll be a double-margin drill. Also, you’ll see designs where the gullets have been increased due to the strength of the substrates. The helix ratios will change and the core diameters will change when drilling really deep (20×D). The chips come up the body and we’ll alter the inside diameter of the core to facilitate ejecting them.”
According to Cline, a drill can be produced with a larger gullet area without sacrificing the strength and integrity of the tool. “In the past, if you wanted to make a drill with a large gullet, you would either make it stubby or sacrifice some of the penetration rate since you would run slower to reduce force,” he said. “For faster drilling, we have a line of three-flute solid-carbide drills for a higher penetration rate in order to reduce cycle times.”
Two Tools for Aerospace Machining
GWS Tool Group, Tavares, Fla., has introduced a new Ti Feed mill specifically for machining titanium. Not yet released but coming in the fall is a combination solid-carbide tool with brazed ceramic milling head for high-feed milling of high-temperature alloys like Inconel 718, according to Drew Strauchen, executive vice president.
Both tools are designed for machining aerospace engine components for the substantial backlog of aircraft engines, which is challenging to the supply chain. According to Strauchen, it’s critical for the supply chain to be able to increase throughput and reduce cycle times. “Engine and engine component manufacturers place a significant premium on productivity,” he said. “With backlogs being what they are, the value of time trumps tool cost and tool life every time.
“Like many industries, the aircraft industry has transitioned to using more five-axis machining centers to produce parts like turbine blades,” Strauchen continued. “The combination of five-axis machines and fixturing is often not conducive to certain types of roughing, where you would traditionally take the whole length of the cut of the tool and use a trochoidal milling path to rough out the material. That’s a very efficient way to rough but a lot of machining environments, especially five-axis, don’t permit that style of machining and require Z-level machining tool paths instead.”
Ti Feed end mills are available in coolant-through and solid configurations in 3/8-1" (9.53-25.4 mm) sizes with the most popular being ½" (12.7 mm). “Z-level processing engine parts with the Ti Feed mill taking a lot of light cuts doesn’t produce a lot of torque or load on the workpiece,” Strauchen said. “Ti Feed end mills take advantage of radial chip thinning, wherein higher feed rates can be realized with lighter depths of cut to rough parts to near net shape. The optional coolant-through capability dramatically improves thermal resistance, which is critical in machining titanium alloys.”
The brazed ceramic tip end mill is capable of machining five to 10 times faster than a carbide tool when machining heat-resistant superalloys like Inconel 718. For example, while a solid-carbide tool might reach 100 to 150 sfm, the new brazed tip tool can reach speeds of 400 to 900 sfm. “Of course because it’s a brazed tip rather than solid ceramic, the cost of the tool is much lower,” Strauchen pointed out.
Drill Right to Avoid Tapping Problems
Having trouble with your tapping process? If so, Bill Minhas, applications engineer-II for OSG USA Inc., Irving, Texas, advises checking the drilled hole for straightness and other defects that can destroy hole quality. “When I’m called into a shop that is having trouble with their tapping process, I usually find that most of the time it isn’t the tap, it’s the drilling process. If the drill is dull and not drilling straight, there are a number of defects that can destroy hole quality. I suggest checking the hole with a pin gage and replacing the drill with a new one.”
There are three features of OSG’s AE-H ball nose end mills that make them ideal for machining hardened steels and die/mold applications, according to Minhas. “The first feature is the high precision radius tolerance of two-tenths that is very important for surface finish and reduces polishing time. The second feature is its unequal index, which reduces vibration. And the third feature is the variable rake angle, meaning that it’s not the same rake angle from the tip to the main diameter.”
Minhas explained the advantage of having the variable rake angle on the AE-H end mill: “Ball end mills always start cutting at the tip, which is not rotating. The variable rake angle is very strong at the tip to avoid chipping. Then, as you go further up to the diameter of the tool, it’s sharper so that you can cut the material lightly.”
The AE-H ball nose end mill has OSG’s Durorey multi-layer coating on the substrate. Coatings are super heat resistant with an ultrafine nano structure and a special strength medium for long life, fine finish, and process stability, according to Minhas.
Also new from OSG is the 1 to 2-mm ADO microdrill for medical and dental applications, available in 2×D to 3×D lengths. “The ADO micro features coolant-through for good chip evacuation and, though it’s small, has a double margin that is important for stability in the hole,” said Minhas.
OSG’s ADO SUS drills for titanium and stainless feature the company’s proprietary WXL coating; specially shaped coolant holes for 33 percent more coolant flow to the cutting edge; and cutting forces that are always 90º to the cutting edge. With a wavy cutting edge, there isn’t a large cutting force going in one direction, which minimizes heat producing friction—an important feature in stainless steel and titanium machining.
Finishing Holes with Deburring
Deburring drilled holes and bores in production quantities represents a challenge to companies in virtually every industry. To deal with these challenges, deburring products and processes from Heule Tool Corp., Loveland, Ohio, are being used by manufacturers in aerospace, automotive, heavy equipment, energy, medical and precision machining for their finishing operations.
“The biggest challenges our customers face are location and part variation, which can occur for a variety of reasons, including tool and process failure, uneven surfaces or drilling difficult configurations or drilling at angles,” said Gary Brown, president of Heule Tool. “The majority of our tools are compensation tools, meaning they are spring loaded or activated by centrifugal force. They perform processes like back boring, back machining, back chamfering, compensating, counter sinking and combination drilling. Products are available to handle all types of materials, including nickel-alloys all the way down to brass, bronze and composites.”
Heule’s products are used for new materials and processes such as dry machining or minimum mist, as well as drilling holes in small motors and medical applications. “Our products are used anywhere holes are drilled that have burrs that have to be removed. They eliminate a lot of manual operations, making it possible to manufacture products from beginning to end without touching them or with minimal manual intervention.”