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Development of face milling cutters for the automotive industry

Nov 05, 2018

Improvement of geometric angle of milling cutter

    According to the experience of NPP, when the machine power is insufficient, the geometric angle of the tool can be correctly selected, and the production capacity of the low-power machine tool can also be expanded. For example, conventionally, cast iron milling cutters have negative axial and radial rake angles (double negative angle milling cutters). This negative geometric angle makes the cutting edge relatively strong. On the contrary, the positive and negative angle milling cutters (axial positive rake angle, radial negative rake angle) cut smoothly, which also reduces the machine power requirements and makes it easier to use advanced tool materials.

   Depending on the grade and use of the insert, the cutting edge of the cutter insert can be sharp or it can be ground with a chamfer of 0.013 to 0.076 mm. For the Kyon 3500 ceramic insert, a 20° chamfer is ground and the chamfer width is 0.2mm to prevent the cutting edge from being damaged by the chip at high speed.

    Kennametal's Fix-Perfect system is a product line that combines different positive and negative angles. It is characterized in that the positive radial rake angle and the negative axial rake angle of the insert have shearing action opposite to the positive and negative angle milling cutters (axial positive rake angle, radial negative rake angle). Due to the vertical type of the blade, the lower part of the blade has a strong physical support, which increases the strength of the blade. The negative axial rake angle forces the cutting force towards the spindle and the milling cutter works stably. Moreover, the negative axial rake angle allows the "impact point" that is first cut into the workpiece to leave the tip and protect the tip.

    The Fix-perfect cutter has a scraping blade for roughing and finishing. The surface roughness is up to 32 (contour root mean square deviation), which reduces one finishing and reduces cycle time.

    The tool should adapt to the changes of various parts of the car.

    Due to the toughness of cast iron and its high compressive strength, and its ability to be cast into very complex shapes, it has been used in the manufacture of automotive engine casings and other parts. Later, under the promotion of CAFE (Corporate-average-fuel-efficiency), the use of heavy alloys was reduced on light vehicles. In 1980, according to the American Foundry Association, household cars were controlled at 600 pounds of cast iron. By 1999, the average had dropped by nearly half to 325 pounds and is expected to drop to 230 pounds in 2006. On the other hand, the aluminum industry analysis predicts that the application of automotive aluminum parts will rise by 50% in five years, from 250 pounds per vehicle in 2000 to 380 pounds per vehicle in 2005.

    The processing of aluminum parts in mass production requires the use of polycrystalline diamond (PCD) tools. The chips generated during machining are the main cause of damage to the PCD tool.

    To maintain the integrity of the cutting edge of the PCD tool, it is best to distribute the cutting load evenly to each milling cutter. Therefore, precision adjustment (especially axial) is an important means to extend the life of PCD milling cutters. For example, the Flex-Lok insert of the Ingersoll cutter allows fine adjustment of the vertical insert and then secures the insert with a barrel screw. In this way, the load on each insert on the milling cutter is balanced, resulting in the longest tool life.

    The processing of aluminum alloys has special requirements on the geometrical angle of the tool. Aluminum alloys for the aerospace industry should use large positive rake angle cutters because of their high viscosity and low silicon content. For cast aluminum alloys with high silicon content in the automotive industry, It is not necessary to use a sharp front angle, but should be stable and durable. Therefore, most automotive manufacturers use aluminum alloys with small axial and radial positive rake angles.

    In addition, some automotive parts are now hardened to increase productivity and reduce costs. For machining hardened ferrous metals, milling cutters with CBN or ceramic inserts are available.