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.