TECHTIP #3
SELECTING THE PROPER HELIX AND RAKE ANGLES FOR YOUR APPLICATION
The Helix and rake angles on carbide EndMills affect the cutting forces, chip evacuation, tool deflection, and overall performance of your spindle and work holding. Selecting the appropriate angles for your application and material can help optimize the milling process, improve surface finishes, and extend tool life.
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Helix Angle The helix angle is the angle between the cutting edge and the axis of the tool. It influences the cutting forces, chip evacuation, and tool deflection.
Low helix angles (30°-35°) These angles generate less axial force on the spindle and work holding, resulting in reduced tool deflection. However, they produce a more aggressive cutting action, which can lead to chatter and poor surface finishes, especially in long-reach applications. High helix angles (40°-50°): These angles generate greater axial force on the spindle and work holding, which can lead to increased tool deflection. However, they provide better chip evacuation and smoother cutting action, resulting in improved surface finishes and reduced chatter, especially in materials like aluminum and non-ferrous alloys.
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A.
HELIX ANGLE - EFFECTS ON CUTTING FORCE By increasing the Helix Angle:
- Axial Force F z , increase (and the ratio F_ AX /F_ TAN ) - Cutting forces in the XY plane decrease - The delay between the cutting edge “slices” engaged increase. - Reduction of the Torque
B.
HELIX ANGLE - EFFECTS ON CHIP EVACUATION By increasing the Helix Angle: - The flute section effective for chip evacuation decreases in surface - The direction of chip evacuation changes: ▪ Chips are pulled up more with a “Corkscrew Effect”
45•/
HELIX ANGLE - SQUARE SHOULDER END MILLS 30• C. ▪ Wide chip flutes
▪ Small axial forces (reduced risk of pull out from the holder
50•
45•/
▪ Wide chip flutes ▪ Small axial forces (reduced risk of pull out from the holder
60•
▪ Good surface finish (finishing/super finishing) ▪ Smallest possible tool deflection
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Rake Angle The rake angle is the angle between the cutting edge of the tool and a perpendicular line to the workpiece. It affects cutting forces, chip formation, and tool life.
Effect on cutting process
- Has a direct impact on: ▪ Yielding angle of the chip and plastic strain ▪ Max Temperature and temperature distribution on the rake face. ▪ Strength/Toughness of the cutting edge - Positive/Negative Rake Angle
Positive rake angles: These angles reduce the cutting forces on the spindle and work holding, making it easier to shear the material. This leads to reduced power consumption, lower heat generation, and improved tool life. Positive rake angles are suitable for materials like
aluminum, brass, and plastics. Negative rake angles:
These angles increase the cutting forces on the spindle and work holding, providing a stronger cutting edge and improved edge retention. However, they require more power to cut and can generate more heat. Negative rake angles are typically used for hard materials like cast iron, hardened steels, and stainless steel.
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E VALUATION Assessing the EndMill performance and suitability for a specific application. N EEDS Understanding the specific requirementsof the material and application to select the right EndMill. D IAMETER The width of the cutting edge of the EndMill, which impacts the material removalrate and tool stability. M ATERIAL Considering the compatibility of the EndMill with the workpiece material, such as hardness and machinability I NSERTS In some EndMill, replaceable cutting edges that can improve tool life and performance. L IFETIME The overall service life of the EndMill which is influenced by factors like tool material, coatings and maintenance. L UBRICATION Ensuring proper cooling and lubrication to minimize heat buildup and extend tool life during machining.
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