Finishing cuts are used to complete a part, achieving its final dimensions within tolerance and its required surface finish. Most often an aesthetic demand and frequently a print specification, surface finish can lead to a scrapped part if requirements are not met. Meeting finish requirements in-machine has become a major point of improvement in manufacturing, as avoiding hand-finishing can significantly reduce costs and cycle times.
COMMON FINISHING PROBLEMS
FACTORS THAT INFLUENCE PART FINISH
Specific material and hardness
Cutting tool speeds & feeds
Tool design and deployment
Tool projection and deflection
Rigidity of workholding
Coolant and lubricity
Final-pass depth of cut
FINISHING PROBLEM SOLUTIONS
Tools with high helix angles and flute counts work best for finishing operations. Softer materials show great results with higher helices, while harder materials can benefit greatly from increased flute counts.
Increase your RPM and lower your IPT (Figure 2).
Ensure that tool runout is extremely minimal.
Use precision tool holders that are in good condition, are undamaged, and run true.
Opt for a climb milling machining method.
Use tooling with Variable Pitch geometry to help reduce chatter.
A proper radial depth of cut (RDOC) should be used. For finishing operations, the RDOC should be between 2 and 5 percent of the tool’s Cutter Diameter.
For long reach walls, use reduced neck tooling which help to minimize deflection (Figure 3).
Extreme contact finishing (3x cutter diameter), may require a 50% feed rate reduction.
COMMON SURFACE FINISH NOMENCLATURE
Ra = Roughness average
Rq = RMS (Root Mean Square) = Ra x 1.1
Rz = Ra x 3.1