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Operating Strategies for Finish Machining

Any capital investment program for new production equipment requires more: ideas, insights, and tactics for selecting the best tools for carrying out the plan.

According to survey results, 25% of all metalcasting operations have indicated plans to invest in machine tools during 2019, and 24.29% indicated plans to invest in “grinding equipment", which reveals a consistent economic strategy: add value to the castings produced, and improve the performance of the casting finishing capabilities that are already in place.

But what is the operational strategy behind this: machining and grinding systems represent an entirely new process undertaking for some foundries and diecasters, and an area in need of reevaluation for others.

Specialists in machining and finishing know that the entire technology area is built on extensive and ongoing development. Operating such technology requires metalcasters to know, at the least, how to select the right tools for the processes they have – or will have once the investment is made.

For example, grinding operations demand more than a "surface" understanding of the process dynamics. Currently, there is a lively debate between proponents of different surface materials for grinding wheels. Lach Diamond Inc. emphasizes the value of “contour-profiled” diamond or CBN (cubic boron nitride) grinding wheels.

A resin-bonded grinding wheel needs several processing steps during deep grinding, while the metal-bonded contour-profiled profile grinding wheel accomplishes such works in a single time- and cost-saving step. Almost any profile type, concave or convex, is possible, and with tolerances up to 0.005 mm. Costs for abrasives and wheels could be reduced by a factor of eight, according to Lach. Tool life may be up to 25 times longer, and the “contour-profiled” wheels achieve up to 35 to 60 % time-savings through higher feed rates per work-piece.

More complex finishing operations involve more detail. In order to boost the first-stage roughing operation on automotive aluminum castings, Sandvik Coromant has introduced a new tangential milling cutter, the M5Q90.

Aluminum cylinder heads and engine blocks will be among the components to benefit, typically in foundries or Tier 1 and 2 suppliers. For example, the cubing (first machining of faces after casting) operation on a cast cylinder head involves machining the camshaft face, inlet/outlet face and combustion face. Typical cutting data using M5Q90 might include a speed of 2,500 m/min (8,202 ft/min) and feed per teeth of 0.20 mm (0.008 inch). Users also benefit from high-precision coolant channels that provide the option for either emulsion or MQL application.

Designed to complete cubing in a single operation without creating burrs, the new tool is fitted with PCD tangential inserts that provide a smooth and stable cutting action to lower power consumption and eliminate vibration. This concept ensures reliable performance, improved tool life, exceptional surface finish, high metal removal rate and an increased number of parts per insert.

“To enhance efficiency, our new M5Q90 tangential milling cutter features fully engineered cutter bodies matched with dedicated PCD insert geometries that feature a positive cutting angle to reduce cutting force and load on the machined component,” explained Emmanuel David, global automotive product manager.

M5Q90 cutter bodies are designed according to customer specifications, and therefore meet the requirements of high-productivity machining. The tool can operate in high-speed conditions in excess of 20,000 rpm. However, all cutter bodies offer the same design of tip seat, coolant channel, lead angle and rake angle. Inserts are always kept in stock.

Coating and cooling concepts are critical to the effectiveness of milling cutters. Lach developed the “dia-compact” monoblock diamond cutter for cost- and time-savings in machining of aluminum parts. More recently, it developed the “Cool Injection-Plus” concept, for direct cooling via the PCD cutting insert. The PCD monoblock milling cutter is fully mounted and balanced, and can be installed for immediate use with a holding device of choice, without adjustments.

Efficient metal-removal is a constant objective in rough machining, regardless of the material. Cutting-tool specialist Kennametal reports its new Harvi™ Ultra 8X helical milling cutter will remove more than 1,000 cm3 (61 cu.in.) of Ti-6Al-4V titanium (a very hard aerospace superalloy) in just one minute. Tim Marshall, senior global product manager for indexable milling, has tested the Harvi Ultra 8X with various customers, pushing its limits on everything from 15-5 PH to cast iron, to Aermet 100 (high strength steel), with outstanding results for each test.

“Kennametal developed the Harvi Ultra 8X to meet two distinct needs,” Marshall said. “The first came from the aerospace industry, which thanks to the large numbers of aircraft being built today requires the highest metal removal rates possible but still achieving excellent tool life. At the same time, machine-tool builders and users alike are asking for tools able to withstand higher cutting speeds but generate lower machining forces, so as to reduce wear and tear on machine components during extreme cutting conditions.”

He noted, however, that the Harvi Ultra 8X also was designed to predictably remove 20 cubic inches (328 cm3) of Ti-6Al-4V each minute while attaining 60 minutes of tool life per cutting edge. The tool combines several technology innovations:
• A double-sided yet positive rake insert that lowers the cost per edge and reduces power consumption by up to 50%.
• A AlTiN+TiN PVD coating that provides resistance to thermal fatigue.
• The Harvi Ultra 8X cutter body is constructed of a higher quality steel than competing products, to improve stiffness and rigidity under high cutting forces.
• A BTF46 (bolt taper flange) connection provides exceptional deflection resistance compared to traditional, shell mill type holders.
• The variable helix design breaks up the harmonics that lead to chatter, further improving tool life, part quality, and throughput. 

Variable-helix geometry reduces vibration significantly, and using 12-mm and 10-mm inserts also helps, as their smaller size means more inserts in the cutter body, more inserts engaged in the workpiece, and more inserts to absorb the pounding of a heavy machining operation.

Through-the-tool coolant nozzles direct cutting fluid where it’s needed most, and an enhanced flute design assures maximum chip evacuation.

Seco Tools LLC offers several new cutting tools that may benefit metalcasters: the new Double QuattroMill 22 face mill for roughing and semi-finishing offers "free cutting geometry", with innovative insert placement that reduces cutting forces, for better workpiece stability, improved tool life, and maximum productivity. Its suitable for milling a wide range of part materials, including cast steel and cast iron, 15-5 stainless steel, and superalloy like titanium and Inconel®.

The Seco Feedmax -P drill gives manufacturers the potential to boost holemaking performance beyond that of current drilling technology for ISO P (steel) and cast iron workpiece materials. The solid carbide Feedmax -P drills can increase drilling productivity by up to 35 percent while also providing longer tool life due to the combination of the drill’s new geometry and advanced TiAlN coating. Together with the drill’s strong point geometry, cutting speeds of 623 feet/min are possible in 4140 alloy steel without sacrificing tool life.

And, the redesigned Seco Perfomax indexable insert drill achieves very high productivity and longer tool life. Its higher drilling parameters as well as exceptional chip control and evacuation result from the improved helix angles and smoother chip flute exits. Seco’s engineered wave pattern minimizes contact between chips and flute surfaces.

Beyond milling and cutting, Emuge Corp. introduced a patented Punch Tap line, calling it the first tool/ technology of its kind for helical thread forming in cast and wrought aluminum alloys and similar lightweight materials. Emuge Punch Taps provide a shortened tool path process for producing internal threads in under half a second, resulting in significantly less energy consumption during the machining process and a reduction in threading time by 75% compared to cold forming and conventional tapping.

Luckily for metalcasters, cutting and grinding tool developers remain dedicated to researching identifying product improvements. The challenge is remaining in step with the changes. 

 

TAGS: Materials
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