Toolmaker's Material 'Tough as Nails'
You've heard the phrase, "Tough as nails." There's a good reason for the "tough" reputation. There was a time when premature tool wear would limit nail production for customers of Pyramid Machine of Whiteville, Tennessee. But no longer--the tool and die shop pulled opportunity from the jaws of dissatisfaction to become the supplier of choice for many nail producers.
Each high speed, heavy duty, wire nail press at one of Pyramid's customers, chattering like a heavy machine gun, was pounding out up to 900 nails per minute. The severity and frequency of the machines' blows, combined with the cold working, raised havoc with the tooling.
The grippers and cutters used in the nail presses were made from AISI Type D2 tool steel. They wore so badly that the nail presses had to be stopped after eight hours for a one-hour tool changeover. Cracking and crevice formation at stress points also contributed to making the tools useless.
To improve customer's nail production rates, Pyramid switched to Micro-Melt M-4 alloy, a powder high speed tool steel made by Carpenter Technology Corp., of Reading, PA.
Now, Pyramid's grippers and cutters can be run continuously for up to 100 hours--more than 12 times longer than the D2 tools--before wear requires a change. Cracking and splitting problems have been eliminated.
The tools made from M-4 powder high speed steel permit this Pyramid customer to recover all the production lost previously during tool changeover, as well as the labor cost for that function.
Production increased extensively for the nail manufacturer. Before the material change, each press, spitting out nails at rates of up to 900 a minute, was unable to produce 54,000 nails during each hour of downtime. Since presses using D2 tool steel had to be idled every eight hours for tool changeover, they were down at least 12 times during the same 100 hours of service provided by the M-4 alloy before a single changeover was necessary. Thus, the total production recovered was 648,000 nails (54,000 nails x 12 downtimes) at each machine during the powder high speed steel's uninterrupted service cycle.
Another nail manufacturer had an even more disappointing experience with A-18 tool steel cutters on a high speed press chewing up 250,000 pounds of nail wire a day.
Those cutting tools, heat treated to HRC 60 maximum, wore out every four to six hours. Each time that happened, the machine had to be shut down one hour for tool changeover, with significant loss in production before it could resume operation.
The manufacturer eventually installed a set of cutters that Pyramid made from M-4 powder high speed steel. These cutters showed no wear after 46 hours of continuous operation, and still no sign of wear after an additional 27 hours of running time!
The M-4 alloy tools, at last count, had lasted 12 to 18 times longer than the original A-18 tool steel dies, and were still going strong. When the manufacturer considered the productivity gained and downtime eliminated for tool change, the company realized it had more than paid for the upgraded tools after 18 hours of press time, and was getting free use of the tools thereafter.
Nail makers have used Pyramid's tools to make a wide assortment of nails ranging in diameter from 0.027 to 0.205 inch, and in length from 0.255 to 5.511 inches.
Pyramid fabricates its grippers and cutters from M-4 alloy flat bar stock of various sizes. The tools, weighing from less than one pound to more than six pounds, are made in 18 different sizes.
Each tool is shaped by sawing, using a bi-metal blade, and milling with carbide cutters. It is then commercially heat treated in a salt bath or vacuum furnace to HRC 62-63. Then it is ground on a surface grinder, using a special grit wheel, to produce a mirror finish. The fine finish is to avoid the possibility of tools marking the nails.
In production, high speed presses push the 1010 or 1015 alloy steel wire through the machine, two grippers seize it, two cutting tools cut off the wire to desired nail length and form a point, and an M2 tool steel header upsets the head. The nail-forming operations occur almost simultaneously.
The M-4 alloy is a molybdenum-tungsten bearing material containing high carbon and vanadium. Production of the material starts with pre-alloyed metal powder. The powder is blended, filled into mild steel canisters, hot isostatically pressed to 100 percent density, then hot worked to produce mill forms for further processing into finished products.
The resulting material has very high wear resistance and strength. Additional advantages include ease of grinding, improved toughness, and more uniform structure.
Its improved grindability results in reduced tooling wear and increased manufacturing productivity. Grinding operations also produce a smoother cutting edge on the finished tool.
Increased toughness translates to a greater resistance to tool breakage, especially in intermittent cutting operations. Increased toughness also permits a tool to be heat treated to a higher hardness for a desired toughness level, resulting in either longer life or higher cutting speeds.
The material's less out-of-round distortion after heat treating increases the predictability for scheduling tool changes. This results in less down time for unscheduled retooling and more efficient usage of tools in multi-spindle machines, where failure of a single cutter usually requires changing all the cutters, including those that are still good.
The uniformity of size also permits a more predictable heat treat envelope, which, in turn, permits tool manufacturers to machine annealed tool blanks closer to finished size. This reduces the amount of final grinding required after heat treatment.
The unique properties in the Micro-Melt M-4 alloy, Carpenter notes, are the direct result of how this powder high speed steel is processed. Stock so processed has refined microstructure--smaller, more uniformly distributed carbide particles, and finer grain size. The refined microstructure and lack of segregation result from the significantly higher quench rate attained in the as-atomized metal powder particles, compared with the slow cooling rate that occurs in conventionally cast ingots.
As explained by Pyramid owner Jack Green, "The alloy has a very fine grain structure because it is made through powder metallurgy. That means we don't have the problem of finding and working with the grain.
"And the M-4 tool steel can take a lot of abuse," he continued. "It gives you no stress points for the potential formation of cracks and crevices. We can also get two to four more Rockwell points harder with the powder M-4 steel than with a conventional tool steel. That gives us sufficient hardness to resist the abrasiveness in nail manufacture."
When tool wear and cracking were problems, some manufacturers tried to make their own tools--without much success--because there were long delays in receiving replacement tooling from the nail press manufacturers overseas.
When they turned to Pyramid for help, they found the answer to their problem wasn't so tough.
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