The Case For Resharpenable, Insert-Type Form Tools
Users explain the advantages of these tools over solid and throwaway-insert-type form tools.
Historically, form tools for multi-spindle screw machines were ground from a solid chunk of metal, usually high speed steel. Today, they are still predominantly machined from the solid, although they are more likely to be produced by wire EDMing than by the grinding process.
Machining form tools from the solid is no longer the only way to go, however; technology has given us other ways to make them. Years ago, the growing popularity of insert-type cutting tools gave rise to the throwaway-insert-type form tool, consisting of a holder that accepts replaceable cutting tool inserts custom designed and machined for the size and shape of the part to be produced. When the insert becomes dull, the operator removes it from the machine; discards it; installs a new, sharp insert; and resumes operation.
The insert can be replaced faster than the larger, solid tool, reducing the amount of time that the machine stands idle. It seats in its holder with such repeatability that, unless the operator changed the position of the tool to compensate for dulling, no adjustment must be made to go from one insert to the next, which helps the operator get the machine up and running again quickly.
More recently, another insert-type form tool has become available that uses resharpenable inserts instead of throwaway inserts. Just as with its predecessor, the resharpenable, insert-type form tool has an insert that can be replaced quickly, easily and accurately when it dulls, to minimize machine downtime. However, just as is the case with the solid form tool, the resharpenable-insert can be repeatedly sharpened, making its useful life many times greater than that for the throwaway insert, with a corresponding cost savings.
Users Weigh In
Good as it is, the resharpenable, insert-type form tool is not about to make the solid form tool or the throwaway-insert-type form tool obsolete. Each of the three types of tools offers unique advantages, and two Chicago area firms that are using the resharpenable, insert-type form tool were willing to discuss the advantages of that tool for their operations.
American Couplings Co. (Westmont, Illinois) manufactures brass, low-pressure, hose couplings. It produces barbs, stems and other hose coupling components on Acme Gridley multi-spindle automatics ranging in bar capacity from 9/16 inch to 2 inches. The firm has a large product line and carefully manages its finished goods inventory, producing many of its part numbers in short-run quantities.
Uptime Is Key
The company keeps its multi-spindle automatics busy. It cannot afford to dedicate production machines to one part or a family of parts and allow them to remain idle when those parts are not being run. Each machine must run a full shift, every shift. "Uptime is the key to productivity," notes operations manager Jim Jablonsky. "Thus we're constantly looking for ways to reduce all machine downtime, not just setup time."
American Couplings buys its screw machine tooling from outside sources. Most of the form tooling that it buys is solid rather than insert-type tooling. "A solid form tool costs us $250 to $350, which is less expensive than an insert-type tool," Mr. Jablonsky explains. "And it's ideal for our short runs. About the time the tool starts to dull, the run is finished, so there's usually no need to make an adjustment or replace the tool because of wear. At the end of the job the solid form tool is returned to the tool crib where it is resharpened for the next time that the job runs."
The firm's part production is not limited to short runs, however. Some products sell at a rate of about 100,000 units per month and dictate part runs that last for days or weeks. The solid form tools frequently dull in mid-run, and the machines must be stopped for tool changes. That's a problem. "We cannot afford machine downtime," Mr. Jablonsky emphasizes. "There are times when the machines are idle for reasons beyond our control, for example when the operators load fresh bars into the stock tubes, but we were not willing to put up with downtime caused by having to replace dull or worn tooling."
Bill Swier, American Couplings' foreman, explains that replacing a solid form tool in mid-run can be very time consuming. The operator must remove the worn tool, take it over to a grinder, sharpen it and reinstall it in the machine—the process can take up to 20 minutes. To eliminate the downtime associated with resharpening worn tools, the shop tried replacing the worn solid form tools with "duplicate" form tools, however the replacement tools differed enough from the originals that more time was lost adjusting the machine to the new tool than for grinding the original.
Never Needs Resetting
American Couplings needed an alternative to solid form tooling that would permit faster tool changes and minimize time-consuming adjustments to the machine. It found what it was looking for in the Resharpenable Quick-Change (RQC), insert-type form tool system made by Somma Tool Co., Waterbury, Connecticut. The RQC system consists of a holder and a relatively thick (5/16- or 3/8-inch) insert that is made of micrograin carbide or high speed steel and machined to produce the desired form in the bar. The insert can be resharpened by grinding material from its top surface and reused without resetting.
Even though material is removed from the insert with each sharpening, the insert returns to the original center setting because it is clamped with upward pressure against the locating shoulder in the holder. According to the manufacturer, once the insert is set to the centerline and to the proper diameter, it never needs to be reset. The form insert can be replaced in about a minute, and production can resume. Best of all, the insert can be resharpened 20 to 30 times, making it very economical in the long run.
"Where a conventional form tool might last for about 1 year, we can get the equivalent production from the RQC system with two or three sharpenings of the insert and still have 25 or so sharpenings left," explains Mr. Swier. "The resharpenable insert tool, with holder, can cost twice as much as a conventional form tool; however, it lasts many times longer, making it more economical in the long run."
Mr. Swier also notes that crashes are less costly with the resharpenable insert tool: "If the machine crashes and wipes out a conventional form tool, we're out the $250 to $350 that it would cost to replace the tool, but if we're using the resharpenable insert tool, we're just out the cost of the insert."
The resharpenable insert form tool provides the fast setup and tool change times that American Couplings needs to keep machine uptime high for long-run jobs—at a very economical price. Because tool changes can be made so quickly with the quick-change system, Mr. Swier credits it with boosting throughput of a long-run job on a multi-spindle as much as 10 to 15 percent.
Camcraft, an engineering and manufacturing company in Hanover Park, Illinois, also uses the RQC system, with some interesting variations. But first some background. As is the case with many other shops, Camcraft makes its own solid form tools for its multi-spindle automatics. In the past, the shop made its form tools by the grinding process. Most toolmakers agree that grinding produces a quality tool capable of achieving fine surface finishes unobtainable by any other method. Grinding provides a more uniform cutting edge that holds up longer between sharpenings, and it can also provide the clearances behind the cutting edge that make the tool freer running.
However, grinding a solid form tool by hand is demanding work and takes a lot of time. Skilled toolmakers capable of handling the task are getting scarce. The industry has had to find a more automated, less labor- and skill-intensive process for making form tools, and so for the last dozen years or so, Camcraft, like many of its competitors, has made its form tools by the wire EDM process.
Form tools cut from the solid by the wire EDM process are great for short runs of parts made from free-cutting material. They are relatively inexpensive, resharpenable and the tool most commonly specified for a job, particularly if the initial run is small and there is no assurance that it will repeat. However, when solid form tools are used for long runs, they eventually dull and must be replaced. The screw machine must be stopped, sometimes for as long as 20 minutes, to replace the dull tool.
"Originally, we made our solid form tools in pairs, expecting that we would be able to minimize downtime by quickly swapping out the worn tool," explains Marc Bossert, Camcraft's engineering manager. "But our operators would install the back-up tool and get the machine back into production only to find that the parts were no longer within specs. It sometimes took so much time to adjust the back-up tool to get the parts back within tolerances that it became faster and easier to stop the machine, remove the dull tool, sharpen it, return it to the machine and resume production.
"The problem was not that we couldn't produce identical tools," Mr. Bossert adds. "The wire EDM process is very repeatable. However it was difficult to precisely locate the back-up tool in the machine, and even when we located the back-up tool properly, we might not tighten it down with the same pressure and get different results."
Solid form tools were dragging down Camcraft's productivity on large runs. The shop needed a tooling system that would enable it to set up quickly for large runs and permit fast replacement of dull tools to minimize machine downtime. It found what it was looking for in an insert-type form tool system that consists of a throwaway insert machined by the tool manufacturer to the precise shape and size required for the part, along with a mating holder. The throwaway-insert-type form tool system offered another important advantage: The profiles are ground in the inserts, which makes for form tools capable of producing fine surface finishes on difficult-to-machine materials.
Wanted: Resharpenable Inserts
Camcraft has used the throwaway-insert-type form tool system successfully for the last several years, particularly for relatively large runs of parts made from free-machining materials. However, on large jobs involving relatively difficult materials that really chew up tooling, the throwaway inserts dulled faster and had to be changed more frequently, resulting in significantly higher tool costs. The shop had come to rely on the advantages of the insert-type form tooling, but it also wanted to be able to resharpen the inserts, just as it had for years resharpened its solid form tools, in order to better control tooling costs.
Camcraft found the combination of features it was looking for in the RQC form tool system with resharpenable inserts. However, instead of buying the inserts from the manufacturer already machined to the desired size and shape, Camcraft purchases resharpenable insert blanks and cuts them to the desired form in-house on its wire EDM machine.
John Kopkowski, tool room supervisor for Camcraft, explains some of the advantages of the quick-change system for the shop: "The resharpenable-insert system offers all of the rapid setup and tool-change features of the throwaway-insert system," he begins. "That's paramount because machine uptime is a high priority for us. However, where the throwaway-insert system is based on discarding the insert when it dulls, the RQC system uses a thicker insert that can be resharpened and reused 20 or more times over its useful life, making for a substantial savings in tool costs.
"The ability to EDM our resharpenable inserts in house enables us to fill our form tool requirements much faster, which enables us to be more responsive to our customers' emergency needs when they arise," Mr. Kopkowski continues. "Delivery of throwaway inserts cut to shape from the manufacturer takes from 2 to 4 weeks depending on whether they are a repeat order or a new tool. By contrast, we can produce a resharpenable-insert-type form tool in house in a matter of hours. With the throwaway-insert-type form tool, the insert and insert holder are designed for a specific part and provided as a matched set. With the resharpenable-insert-type form tool, however, the holder is more universal. Inserts for a new job can be used with an appropriate holder purchased for a previous job, helping to hold down the number of components required for the job and the tooling costs."
At Camcraft, the resharpenable-insert form tool is designed in 30 minutes in the engineering department on the shop's CAD/CAM system. Programming takes another 15 to 30 minutes depending on the difficulty (number of characteristics) of the tool. Finally, an operator loads a stack of three resharpenable-insert blanks in a fixture on the shop's wire EDM machine (photo on page 33) and hits the go button. The wire EDM machine cuts the required form in the blanks in 45 minutes to 3 hours depending on the amount of surface area to be cut. The machine runs largely unattended during that period, freeing the operator to perform other tasks away from the machine. When the EDMed form tool inserts are removed from the machine, they are ready for use without additional processing.
Also, after one set of inserts is cut, the wire EDM machine can be set up in minutes to cut a different set of inserts. The machine does not need a breather before it moves to the next job.
Camcraft's Mr. Kopkowski is pleased with the ease and speed with which form tool inserts can be produced on the shop's wire EDM machine. He notes the shop's multi-spindle machines can achieve finishes down to 32 RMS on some materials with the wire EDMed tools. He hastens to add, however, that the wire EDMed resharpenable inserts produced in-house cannot meet the surface finish requirements for all jobs; the throwaway-insert type tooling, with its ground edges, is usually used for jobs with more demanding finish requirements. (The ground throwaway inserts are also usually coated as they come from the manufacturer, increasing their performance and longevity.)
However, Camcraft has found a way to use the resharpenable inserts without running afoul of part finish requirements. The shop uses the resharpenable insert form tool system for roughing applications only, so that it not only achieves the fast tool setup and replacement times it needs to maintain high uptimes but it also keeps tooling costs at competitive levels. A shaving tool is used to achieve the required finish, and the shop is still able to save hundreds of dollars on overall tooling costs for the job.