Cutting values

What are Cutting Values?

Choosing the correct machining parameters is crucial for ensuring efficiency and quality in machining. Machining parameters include cutting speed, feed rate, and chip thickness, all of which directly affect the surface quality of the workpiece, tool life, and machining time. The strength and toughness of the material being machined are significant factors that influence the appropriate machining values—harder materials require slower cutting speeds. The capabilities of the machine tool often limit the selection of proper parameters; large feeds and chip thicknesses require a sturdy machine and a powerful spindle, while high cutting speeds demand higher rotational speeds. Tool type, geometry, and material, along with the use of cutting fluid, also play a role in determining optimal machining parameters. Taking these factors into account ensures productivity and the best possible results.

Key Terms in Cutting Values

• Spindle speed (n): This indicates how many revolutions per minute the rotating tool or the workpiece makes. The correct spindle speed depends on the material being machined, tool size, and cutting speed. Excessively high spindle speed can lead to faster tool wear and poor surface finish, while too low a speed can reduce efficiency and cause built-up edge on the tool.
• Cutting speed (vc): Specifies how quickly the cutting edge of the tool moves across the material’s surface during machining. Cutting speed is measured in meters per minute (m/min) and affects the efficiency of the machining process, the quality of the final product, and the tool’s lifespan.
• Feed per revolution (fn): The distance the tool moves relative to the machine tool table per one revolution.
• Table feed (vf): The distance the tool moves relative to the machine table per minute. Table feed has a direct impact on machining efficiency and quality. Higher table feed speeds up machining time, but excessive feed can reduce tool life and surface quality.
• Feed per tooth (fz): Especially important in milling; this describes the distance the cutting edge of the tool moves per one revolution. Optimal feed per tooth depends on the material being machined, tool type and material, and the width of cut.
• Material removal rate (Q): Describes how much material is removed from the workpiece in a given time. A higher material removal rate means more efficient stock removal. Optimizing material removal rate can significantly improve the economy and quality of the machining process.
• Mean chip thickness (hm): Used to determine the actual chip thickness in side milling. Optimizing mean chip thickness helps achieve efficient and economical machining, improving surface quality and tool life.

Most Commonly Used Quantities in Cutting Values

• D_c = Cutter diameter, mm
• a_p = Depth of cut, mm
• a_e = Width of cut, mm
• v_c = Cutting speed, m/min
• n = Spindle speed, 1/min
• z_c = Number of teeth, pcs
• f_n = Feed per revolution, mm/r
• f_z = Feed per tooth, mm
• v_f = Table feed, mm/min
• R_ɛ = Corner radius, mm
• h_m = Mean chip thickness, mm
• Q = Material removal rate, cm³/min
• R_a = Surface roughness average deviation, µm

Factors Affecting Cutting Values

The proper machining parameters are influenced by a wide variety of materials such as steels, cast irons, aluminum, and composites. Machine tool characteristics, use of cutting fluids, different tool tapers (SK, BT, HSK, Capto), tool geometry, tool material (such as carbide, high-speed steel, HSCo, CBN, PCD, Cermet), as well as the grade and coating of the carbide tool (CVD, PVD, TiN, TiAlN, TiCN) are all important considerations when determining machining values.

Summary

Choosing the correct machining parameters is critical for achieving efficient and high-quality machining. Various materials, machine tool characteristics, tool type, geometry and material, as well as the use of cutting fluid, all influence the determination of optimal machining parameters. Key machining values include spindle speed, cutting speed, feed, table feed, feed per tooth, material removal rate, and mean chip thickness. Optimizing these parameters can significantly improve machining efficiency and quality, reduce tool wear, and lower production costs.

To find the right machining parameters, it's important to refer to the tool manufacturer's recommendations and use machining calculators. This approach ensures the best possible results, while relying on rules of thumb can result in inaccuracies and inefficiency. Consulting an expert can also help optimize machining parameters and achieve better outcomes. This way, you can ensure that the machining process is as productive as possible and maintain high manufacturing quality.