Mills Made-to-Order

What to consider when ordering engineered, application-specific milling tools.

Applying “off-the-shelf,” standard milling tools to get the job done provides several benefits: the tools are readily available and usually from numerous suppliers, their prices are competitive and the results are predictable. Nonetheless, even with a multitude of standard tools available for nearly every milling application, parts manufacturers often require specials engineered for a specific application. “As an example, there is not an off-the-shelf, industry standard cutter for machining crankshafts,” said Donald R. Hughes, application engineer/project development for Greenleaf Corp., Saegertown, Pa. “Crankshaft cutters are custom engineered for a specific part and machine tool.”

Courtesy of Greenleaf

When working with an experienced cutting tool supplier, successfully implementing special or application-specific tools does not have to be a challenging task.

A similar scenario exists for the compressor screw business. “Every cutter is an engineered special and they are form cutters,” said Ken Accavallo, milling product specialist for Sandvik Coromant Co., Fair Lawn, N.J.

Accavallo noted that those milling tools enable end users to create the male and female forms where two screws join together and force air through a compressor without having to take multiple tool passes.

Satisfying Specifications

Regardless of the industry being served, engineered specials are also needed when a standard milling tool can’t achieve the required cycle time. And the cycle time requirement might change if, for example, a customer changes a production order. Duane Drape, national sales manager for HORN USA Inc., Franklin, Tenn., described a hypothetical situation in which a manufacturer was able to produce the annually required 20,000 parts on one machine fully dedicated to the job using a standard milling tool but the order increased to 25,000 components. “Now the manufacturer has a choice: tie up another machine to make those additional 5,000 components or find a way of improving the process on the machine he’s currently on so he can machine the 25,000 components without making a capital investment,” Drape said. He added that the appropriate special might not only allow all the parts to be produced on one machine but free up time on that machine for other jobs.

Customizing a tool to enhance productivity and metal-removal rates doesn’t always involve extensive engineering. “Productivity gains can sometimes be realized by simply increasing the effective number of inserts or by positioning inserts within a special tool to perform multiple operations and save machining passes,” Hughes said.

Drape concurred that a custom tool may only require slight alterations to an existing standard one, such as adding a chamfer or radius to minimize or eliminate manual deburring.

An end user might also need a custom cutter to satisfy tight tolerance and fine surface finish requirements. Drape gave the example of milling a 0.200 “-wide groove when the closest standard tool offering without going oversize is 0.156 ” wide. “If he uses the 0.156 ” tool, he has to take two passes, which requires more cycle time and creates the potential for a small overlap that the surface finish requirement will not allow,” he said, “so he has to take it in one pass.”

MultiMill

Toolmakers often design specials for performing multiple operations with one tool. One reason is to reduce cycle time by eliminating the time to change tools. Another is there may be no remaining stations in a toolchanger and an additional operation is needed. “You have 50 tools in the chain and there is one more operation. Where can you get it?” Accavallo asked. “You add it to one of the drills or one of the mills. Then a special tool comes in as a necessity.”

Hughes noted one example when Greenleaf engineered a special cutter with inserts positioned in eight different axial and radial locations to machine an unusual contour that saved the customer eight passes with multiple standard cutters.

When a multiple-function tool is not a necessity, end users generally prefer to apply a tool created to perform one operation the best it can, according to Ross Wegryn-Jones, national sales manager for TMFM LLC, Lake Bluff, Ill., which focuses exclusively on making application-specific carbide spline and form milling tools. “Mainly what we push is just our tool as it is and rely on the toolchanger for the rest,” he said. “The drill/thread mill isn’t all that it’s cracked up to be, and people get upset when the tool life of the drill isn’t the same as the thread mill.”

Hughes noted that an end user may want to consider redesigning a special tool to improve upon an existing special. “All special tools are not created equal,” he said. “This is where an experienced cutting tool supplier can help.”

In addition to improving upon an existing design, specials are sometimes reengineered when there’s a workpiece change or some other alteration to the application. “We would consider that a new special even if it’s just a slight modification,” Drape said, noting that about 40 percent of the company’s business is in engineered specials. “If it’s small change, we would maintain the same part number and change the dimension. However, a slight modification may result in a superior tool.”

Whatever the goal is for a special, it’s rare to apply one for small runs because the initial cost of the tool is almost always higher—sometimes significantly higher—than a standard tool. However, high-volume production is a moving target. “Large volume doesn’t have to be millions of components,” Drape said. “Large volume could be 50 components if you’re in the aerospace industry making very large components where the operation gets repeated over and over. You may go through 10 inserts for one component and you’re thrilled with that vs. the previous process.”

Machine’s Role

In other situations, a special is reengineered to boost productivity by switching tool materials. An example is when an end user is applying a HSS hob or form tool and wants to run faster by switching to carbide. However, replacing HSS with carbide won’t necessarily allow a shop to increase its cutting speed.

Courtesy of TMFM

A special spline mill engages the workpiece. TMFM custom made the inserts to match the form at hand.