Case Study: Burnishing a Bore for a Space Exploration Application

THE CHALLENGE

An aerospace manufacturer needed to meet a finish requirement of 0.4µm Ra (16µ” Ra) in a stainless steel bore. 
Material: Nitronic 60 – Austenitic Stainless Steel
Machine: CNC mill
Part: Housing
Finish Required: 0.4µm Ra (16µ” Ra)
Part preparation: Pre-bored to a 2.0/3.0µm Ra (80-120µ” Ra) finish with 0.35-0.45mm (0.014”-0.018”) stock allowance

OUR SOLUTION

We recommended the customer use a long reach ID multi-roll burnishing tool made by Elliott Tool Technologies. Here is the data for the burnishing operation which allowed customer to eliminate a honing operation:
Speed: 196RPM
Feed: 1.9mm/rev (0.075”/rev)
Bore achieved: Diameter within 0.020mm (0.0008”)
ID multi roller burnishing tool used in a aerospace application

FINAL RESULTS & PRODUCT SUPPPORT

After several hundred parts the surface finish had increased up to 0.3µm Ra (12µ” Ra) and the customer noticed a slight dark discoloration on the front 1/3 of the rolls.
Although the discoloration toward the lead of the roll is normal after several cycles, we suggested the customer check the stock allowance and surface finish from the pre-burnishing operation.
What they found was the surface finish before burnishing had increased up to 4.5-5.0µm Ra (180-200µ” Ra), so they indexed the cutting insert and took the surface finish and stock allowance back to our recommendations.
That did the trick! The bores were back to below 0.2µm Ra (8µ” Ra) finish and no changes were required to the burnishing tool.
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