Tool Reconditioning in Trying Times
When does it make sense to recondition metalcutting tools rather than buying new? Will cutting tools of the future eliminate reconditioning altogether?
By Bruce Morey
To recondition or buy new? That's a question any user of round tools—such as drills, end mills, and reamers—should consider. The economics of the Great Recession have spurred increased interest in reconditioning. There are many variables to consider in the equation—more than some might think. Geometry, purpose, substrate, and coating all play a part in driving the decision to recondition a tool. Other factors include the value of the part, tool life, complexity of the process, location, and the technical level of the operation. All in all, there are few hard and fast rules, though experts in the fields are willing to discuss general guidelines.
The simpler the tool the better candidate it is for reconditioning. "Carbide drills are the most commonly resharpened tools," explains Robert Goulding, technical engineering manager for Seco (Troy, MI). "They are the easiest to do. When the drill gets dull, you can re-dress the front end, or if it is chipped and has heavier damage, it can be repaired by cutting off the worn front tip of the drill and then regrinding it. Simply resharpening it is typical, as long as the back taper is not overly affected. Resharpening a drill affects its diameter less than other tools, which makes it ideal for reconditioning." Dimensional control drifts with each reconditioning. "A traditional drill you might re-use five or six times before discarding it. A drill used for making holes with tight tolerances you might use only three times."
He also notes that end mills are the next best choice for reconditioning. The tricky part with reconditioning an end mill is that reconditioning affects its diameter. Modern CNC machines with adjustable offsets make it possible to use them, and Goulding notes that many CNC machines have automatic offsets aided by toolsetting equipment.
A larger or more-expensive tool is a better candidate for resharpening. "Typically there's minimal value in regrinding solid-carbide end mills that are less than a half inch [12.7 mm] in diam," notes Bill Sebring, technical director for Niagara Cutter (Amherst, NY), a manufacturer of cutting tools such as solid-carbide end mills, drills, thread mills, end mills, slitting saws, and milling cutters. He believes cutting tools that are good candidates for regrinding are "Christmas tree cutters" and roughing end mills. Christmas tree cutters are typically used in the turbine blade industry, and have a complex and precise form. He notes that advancements in CNC grinder technology make it easier to recondition such complex cutting tools. When a solid-carbide end mill is reground at Niagara Cutter, it's referred to as "remanufactured." At Niagara Cutter, remanufactured solid-carbide end mills are completed on the same type of CNC grinder used to initially create them. Niagara Cutter also uses their own in-house PVD coating centers.
Sebring notes that coatings can also determine whether a cutting tool would be reconditioned—CVD diamond coating or diamond-like coating (DLC) typically is not economical to regrind. For cutting tools with titanium or chromium-based PVD coatings, remanufacturing is not an issue, because all functional cutting surfaces of the tool can be reground without first removing the coating. He also notes that, like many tool OEMs, standard practice at Niagara Cutter is to regrind only their own products.
Gear hobs and cutters are also expensive tools, and are almost universally reconditioned. "There are some carbide-inserted tools that are usually used in larger coarse-pitch applications for roughing," notes Tom Ware, product manager at Star SU (Farmington Hills, MI) "However, the majority of gear tools are solid HSS or carbide tools that are reconditioned." How long is tool life? According to Ware, some applications may only produce five pieces before requiring reconditioning—others may produce 10,000. Reconditioning is certainly worth it for such tools. Ware reports that reconditioning a gear-cutting tool may only cost 10–15% of the price of a new tool. He reports two significant technical developments in gear hobs and cutters that make them both last longer and easier to recondition—increased use of HSS over carbide, and newer PVD coatings. In particular, he points to increased use of aluminum chromium nitrate coating—trade named Alcrona by Oerlikon Balzers (Liechtenstein)—as advantageous for increasing high-heat cutting and reconditioning. "It is actually easier to remove Alcrona coating than the old titanium aluminum or aluminum titanium coatings," he explains. "The chemicals used to remove it don't attack the base materials, especially in the case of carbide. The chemicals used to break down TiAl also attacked the carbide substrate."
Another significant trend Ware sees is the greater outsourcing of gearcutting tool reconditioning. A combination of skilled labor, machine investment (especially in coating units), and programming expertise dedicated to reconditioning tools make in-house operations less attractive to an individual customer, according to Ware. Combining work from multiple sources allows companies like Star SU to maintain CNC machines, largely driven by the CAM programming that created the gearcutters in the first place. Full capacity utilization makes it possible to employ in-house coating tool, and then adjust the grinding program to remove only that amount of wear. As the original manufacturer of most of the gearcutters we recondition, we know how to do quality resharpening." He believes a trend to watch in the future, as more manufacturers stop reconditioning tools themselves and rely on outsourcing, is the turnaround time to get reconditioned tools back. The industry standard of two weeks may decrease as competition sets in.
Some companies emphasize reconditioning tools more than others. For example, Unimerco (Ann Arbor, MI) started its facility in North America as a reconditioning service, and later began building original tools at the request of customers. They specialize in drills, end mills, reamers, and other solid round tools, including those with PCD inserts. "While we provide custom-designed new tools to our customers, we also built a system to support reconditioning tools," explains Jim Stead, application engineering manager for Unimerco.
"Most manufacturers of tools are set up for production. To recondition tools, they have to break into their production. While we now make new tools, we continue to maintain an entire cell dedicated to reconditioning." Like other dedicated reconditioners, the company also maintains their own PVD-coating facility for faster turnaround time.
Their branded Re * New service resharpens not only Unimerco tools but many other brands of tools as well. Stead notes that some original manufacturers are not always interested in—or set up for—resharpening tools.
He notes they recondition tools for ¼ to ½ the price of new. Consistency is key. "Every Unimerco facility worldwide uses the same machinery and processes," he explains. All tools are reground according to reconditioning norms that drive tool geometry. Stead notes that every tool Unimerco makes has a unique part number that points to these norms—drawings, parameter files for fluting and clearing, and EDM profiles for PCD inserts. "For PCD tools, we go a step further and uniquely code each tool, even PCD tools made by other manufacturers." He says that reconditioning PCD tools requires special expertise that makes sense for manufacturers to outsource. "PCD damage can be so slight that a microscope is required to see it."
There are situations where it may not be worthwhile to recondition tools. Emuge (West Boylston, MA) offers a reconditioning service for its taps, end mills, and thread mills. "Taps can be resharpened, but they are geometrically a lot more complicated than other tools such as drills," remarks Alan Shepherd, technical director at Emuge. Nonuniformity between new and reconditioned tools is one situation that can be problematic. Because regrinding resizes the tap to a certain degree, that nonuniformity with other taps may cause a problem in processing. "For example, on an automotive transfer line you may have 115 spindles tapping an engine block. When it's time to swap out the tools, if some are reconditioned those tools may be shorter than the others, and the manufacturer has to adjust the spindle to compensate. That takes time, and may be more expensive than simply using new taps, especially if the tap is relatively small and inexpensive." Another example he cites is tapping holes in very expensive parts. Tapping typically occurs near the end of a machining process, meaning the part could carry a lot of value by that time. "For example, an expensive part is the outer ring of a jet engine. It might be 5' [1.5 m] in diam with 70–80 holes tapped into 6Al4V titanium. That forging is so expensive they are not going to risk putting a used tap into the metal." He goes on to note that larger parts, like blowout preventers for oilfield work with holes greater than 1" (25.4 mm), frequently use reconditioned taps.
Much depends on the customer and their process. "The big secret on reconditioning tools is knowing when to stop using them," explains Shepherd. "Everyone's situation is unique, but there was one manufacturer of automotive components that would send his taps for reconditioning after two or three thousand holes. He found he could get three uses out of each tap that way, but if he ran the tap to destruction, they might have only tapped a thousand more holes." Niagara Cutter's Sebring agrees. "Some customers will use a cutting tool and take it out of service for regrind before there's any catastrophic failure or significant cutting edge damage." He recommends this approach for any cutting tool expected to be reused. If you "pull" a tool before there is any chipping or significant wear, less material needs to be removed for the regrinding process.
Should we expect more tool reconditioning these days? "Many indexable tools are in some cases replacing a form tool," remarks Jack Lynch, rotating products manager, Sandvik Coromant (Fair Lawn, NJ). "You are justifying the higher initial purchase price because of the indexability. The customer no longer has the reconditioning expense." He points to end mills like Sandvik's CoroMill 316, which has an exchangeable head, as a tool targeted for replacing round mills.
Seco offers a drill with a Crownloc replaceable head, also designed to eliminate the need for reconditioning. "It has found quite a niche," explains Seco's Goulding. "However, there remain reasons to choose a solid-carbide drill, when high-quality holes with exceptional surface finish and high tolerance are needed." Sandvik Coromant's Lynch also agrees there is a place for solid-carbide round tools, even as he sees growth in indexable-insert or replaceable-insert tool designs. Another limiting factor of indexable solutions is the space needed for clamping. Below a certain diameter, solid tools are the only solution.
Another key element of cost that Lynch points out is the need to track and carry the extra inventory needed in the tool-reconditioning process. "It takes discipline and a degree of sophistication to manage a reconditioning process—especially in a complex, high-tech environment," he notes. First, there is the physical process of collecting the tools, packaging them up, sending them out, and receiving them back. Then, identifying their variability and either tracking or separating them properly is vital, so that they are used correctly in the machine, according to Lynch. "Especially end mills. Say you send out a 0.5" [12.7-mm] mill and it comes back 0.020 or 0.030" [0.51 or 0.76 mm] smaller in diam. The offsets in the CNC machine have to be addressed properly to get quality cuts."
This article was first published in the June 2010 edition of Manufacturing Engineering magazine.