Machining Operations by Ed Red Objectives Introduce machining operations terminology

Ideal roughness,

Ri = f2/(32 NR)

where NR = tool nose radius

• Actual roughness,
• Ra = rai Ri (about 2 x Ri )
• because of edge effects, chip interactions, surface tearing, etc.

• Machinability is a measure of machining success or ease of machining.
• Suitable criteria:
• tool life or tool speed
• level of forces
• surface finish
• ease of chip disposal

• Machinability

• What is a free machining steel?
• http://www.sandmeyersteel.com/303.html#1

• Problem statement:
• A series of tool life tests is conducted on two work materials under identical cutting conditions, varying only speed in the test procedure. The first material, defined as the base material, yields the Taylor tool life equation
• v T0.28 = 1050
• and the other material (test material) yields the Taylor equation
• v T0.27 = 1320
• Determine the machinability rating of the test material using the cutting speed that provides a 60 min. tool life as the basis of comparison. This speed is denoted by v60.

• Machinability - example

• Solution:
• The base material has a machinability rating = 1.0. Its v60 value can be determined from the Taylor tool life equation as follows:
• v60 = 1050/600.28 = 334 ft/min
• The cutting speed at a 60 min. tool life for the test material is determined similarly:
• v60 = 1320/600.27 = 437 ft/min
• Accordingly, the machinability rating can be calculated as
• MR (for the test material) = 437/374 = 1.31 (or 131%)

• Machinability - example

• Optimized machining

• Cutting speed can be chosen to maximize the production rate or minimize the cost per part (or unit) produced. This is referred to as optimized machining because more than one production variable contributes to the production rate and costs.
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