Multiflute, solid-carbide end mills were developed especially for vibration-free HSM operations. Designs featuring a varying helix angle, variable tooth pitch, and a specially shaped chip gullet are suitable for applications such as semifinish and finish HSM, as well as roughing by a trochoidal technique.

For example, Main Manufacturing in Grand Blanc, Mich. – a family-owned business that produces hydraulic flanges and components – was experiencing short tool life and reduced productivity due to interrrupted cuts when machining high-pressure flanges from 304 stainless steel. “The severe interrupted cut was definitely affecting tool wear,” said Main Manufacturing’s plant supervisor Terry Bettinger. “We were only able to achieve about 1.5 parts per insert due to edge chippage.”

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In die- and mouldmaking, using HSM as a means of reducing production time has brought a real alternative to traditional production methods. In the aerospace industry, machining difficult-to-cut, heat-resisting superalloys using ceramic tools at high cutting speeds is now common. As for manufacturing aluminum components using HSM? These operations have become a daily reality.

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A resolution may be found in using ceramics as a tool material. Solid ceramic end mills can produce cutting speeds of up to 3,280 SFM. Using ceramic end mills in rough milling operations also has proved to decrease machining time and enable fast preshaping of a part for further finishing operations.

Since the presence of coolant, which was water in this case, can increase the thermal cracking problem, the team decided to run the application dry to see what would happen. This change doubled tool life yet again to achieve 15 parts per corner, and now the failure mode was simply due to normal abrasive flank wear.

Fig 2. Solid ceramic end mills enable cutting speeds of up to 3,280 SFM. These new end mills have a diameter range of 0.236 to 0.787 in. and are designed with three or seven flutes.

In some cases, such as when a part having complex profiles and slots is produced from a solid material, HSM provides productive, low-load roughing by trochoidal milling. Using this technique, machinists employ a rapidly rotating milling cutter that moves along a complicated trajectory, removing thin but wide layers of material. This results in shaping the part very close to its final form.

The flange starts out as a 2.25-in. by 1.5-in. rectangular plate, which is rough-faced down to a hub in the center of the part. The company was taking three passes at 0.100 in. each and a final pass at a depth of cut of 0.050 in. The job was running on a Doosan 240 CNC lathe at 300 sfm and a feedrate of 0.01 ipr.

“We initially decided to run the TM4000 using the same parameters as a competitor’s tool,” said Seco’s Miller. “But, to everyone’s surprise, TM4000 performed no better than the competitive insert.”

The result was that Main Manufacturing saved 85 percent in cost as well as reducing machining time by 52 percent. “But even more exciting,” said Main Manufacturing general manager Bob Mackey, “is that we can take what we’ve learned from this experience and apply TM4000 to hundreds, maybe even thousands, of other similar jobs that we run.”

Long-reach HSM operations are particularly tricky because they require tools with long overall length. A solid tool concept usually is not economical. However, an assembled cutter comprising a body carrying a carbide cutting head is a system that can make economic sense.

Main Manufacturing had been a long time user of tools from Seco Tools. Coincidentally, Seco had recently launched its new TM4000 Duratomic turning grades for stainless steel and was in search of a demanding interrupted-cut application. Seco’s sales and application specialists Joel Henige and Todd Miller asked if they could give the new grade a try. Seco Duratomic coatings rely on an alteration in the crystal structure at the atomic level, and have consistently provided both improved toughness and wear-resistance. In lab tests, the TM4000 construction had shown to improve resistance to crater wear and edge breakdown substantially.

Successful HSM relies on a key element chain comprising a machine tool, an effective machining strategy, proper toolholding, and a cutting tool.

The metalworking industry is always seeking ways to increase productivity when manufacturing parts from high-temperature superalloys (HTSAs), and low cutting speed is one of the existing barriers to this goal.

Andrei Petrilin is technical manager for Iscar Tools, 2100 Bristol Circle, Oakville, Ont. L6H 5R3, 905-829-9000, www.iscar.ca.

Changing technologies require new machining concepts that are more productive, more economical, and more sustainable. HSM, which already has proven itself as a method that meets today’s industrial needs, is a definite trend that no doubt, should be considered.

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However, Henige and Miller weren’t done with their analysis. Another pass under the microscope revealed that the failure was now being caused by thermal cracking. “Large differences in temperature between the cutting edge and the insert can cause cracks perpendicular to the cutting edge,” explained Henige. “Interrupted cutting applications such as this one tend to generate high heat when in the cut, causing these temperature fluctuations.”

“We were pleased,” said Main Manufacturing’s machinist Craig Bendle. “Productivity doubled relative to our original setup, and tool life jumped to seven parts per corner, which was seven times better than we were getting.”

The main advantage of MF4 is its positive cutting angle, which significantly reduces cutting forces to allow for higher cutting speeds and increased productivity. With the MF4 and the enhanced cutting data, the team was able to triple tool life and complete three parts.

New tools for HSM even integrate chip-splitting grooves in the end mill’s design. The grooves increase vibration resistance and reduce cutting forces, which improves trochoidal milling and machining performance at high overhangs. In trochoidal milling, the produced chips are thin but wide. Splitting these chips into narrower segments contributes to better chip evacuation and surface finish, which increase accuracy and effectiveness in rough HSM.

“We went from removing 3.6 to 12.483 cu-in./minute,” Bettinger said. “With our in-cut time reduced by one half, our part output increased from 17 pieces per hour to 54 pieces per hour. The improvements were beyond our expectations.”

The metalworking industry first adopted high-speed machining (HSM) in the 1990s, which then required numerous changes in tooling technology and machine tool engineering. More recently there has been significant interest in HSM that is more accurate.

“We knew that TM4000 was capable of high machining parameters,” said Henige. “So we upped the cutting speed to 650 sfm using the new MF4 chipbreaker, which is designed to provide consistent chip formation and breakage in stainless steel turning and other ISO materials.”

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In HSM, well-directed coolant significantly enhances performance. For deep pockets and cavities, chucks with precise coolant flow results can help prevent recutting, thereby improving chip evacuation and increasing tool life.

Highly accurate HSM is necessary for removing small amounts of material. Machining operations that remove a low amount of stock per pass have distinct advantages, such as lower power consumption, less heat generation, and better surface finish.

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HSM is impossible to perform without using reliable, balanced, and accurate toolholders, and thermal shrink chucks are one of the most popular types for use in HSM.

Interrupted cuts can be tough on tools. The pounding tools take during interrupted cutting frequently leads to severe edge wear that cuts short tool life. However, by carefully analyzing the tooling wear pattern and making the appropriate grade and geometry changes, the ravages of interrupted cutting can be overcome.

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Milling difficult-to-cut HTSAs using carbide tools requires that low cutting speeds (typically 65 to 130 surface feet per minute [SFM]) be used. HSM with a small radial engagement, when the width of cut is up to 10 per cent of the tool’s diameter, usually requires cutting speeds of 230 to 265 SFM.

“However, this was far from the result that we had anticipated,” Miller said. “We examined the inserts under our magnifying loupe, but couldn’t see any particular failure mode.” Then Miller and Henige decided to take a good hard look under the microscope, which provides 60 times the optical power of the loupe. This closer inspection revealed that there was an edge-chipping problem. The chip flow was eroding the back of the land on the MF4. By the wear pattern, they also noted that a larger nose radius would help increase edge strength. As a result of this analysis, they recommended that Main Manufacturing increase the feedrate to 0.016 ipr using a 0.0468-in. radius. Because they didn’t see any other heat-related problems, they left the cutting speed at 650 sfm.

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Accurate HSM requires that strict, repeatable tolerances be maintained during cutting operations. The level of necessary “strictness,” however, depends on the machining method (milling, turning, or drilling) and the type of operation (roughing, semifinishing, or finishing).

A variety of tool bodies, heads, extensions, and reducers are available. These can reduce the need for special tools. Also, replacing a worn head does not require additional tool measuring or CNC program adjustment; the insert can be replaced without withdrawing the tool from a machine spindle.

Manufacturing advances, especially in producing workpieces that are preformed, partially finished products, place a special emphasis on accurate HSM. Precise casting, metal injection moulding, and 3D printing result in workpieces that are very close to the final shape of a part, and as a result, the need to remove a high volume of material by means of rough cutting decreases.