CNC Machining R&D Support
2026年4月24日
CASE STUDY: Achieving Ra 0.3μm Mirror Finish on AISI 1045 Steel via Turn-Mill Composite Machining
Achieved Ra 0.3μm finish on 1045 steel via turn-mill machining (replacing grinding). Precise color zinc platingcompensation ensured high-precision, high-quality delivery.
Project Overview:
This report details the manufacturing process of a high-precision bespoke stepped bolt. The component is made from AISI 1045 (45#) Carbon Steel. While the technical drawing specified a surface roughness of Ra 0.8μm, our engineering team successfully achieved a superior finish of Ra 0.3μm using advanced Turn-Mill composite technology, followed by a color zinc plating (iridescent chromate) finish.
- Technical Challenges • Extreme Surface Requirements: Achieving a Ra 0.3μm finish on medium carbon steel (AISI 1045) typically requires secondary grinding. Reaching this level of "mirror finish" solely through turning is a significant challenge for chip control and vibration management. • Complex Geometry Integration: The part requires high concentricity between the threaded end, the precision shank, and the milled flats on the head. Any re-clamping would introduce geometric errors. • Plating Allowance Management: Color zinc plating adds a layer of 5–12μm. We had to precisely calculate the pre-plating dimensions to ensure the final product met both the Ra 0.8μm requirement and the thread tolerance after coating.
- Process Innovation & Solutions To meet these stringent requirements, we utilized a CNC Turn-Mill Multi-tasking Center: • "One-Hit" Machining: By using a Turn-Mill center with C-axis indexing and live tooling, we completed the turning, threading, and milling of the head flats in a single setup. This guaranteed near-perfect concentricity and symmetry. • Advanced Tooling Strategy: ◦ Finishing: We employed Cermet (Ceramic-Metal) inserts for the final pass. Cermet has a low affinity for carbon steel, which prevents Built-Up Edge (BUE) and is the key to achieving the Ra 0.3μm "grinding-like" finish. ◦ Milling: High-performance micro-grain carbide end mills were used for the D-flats to ensure burr-free edges. • Optimized Cutting Parameters: ◦ Implemented a "High Speed, Low Feed, Micro Depth-of-Cut" strategy. ◦ Used high-pressure synthetic coolant to ensure immediate chip evacuation, preventing any micro-scratching on the finished surface.
- Quality Results & Achievements • Surface Roughness Breakthrough: Actual measurements confirmed a surface finish of Ra 0.3μm, significantly exceeding the client's Ra 0.8μm requirement. The shank exhibits a mirror-like luster, enhancing both aesthetic appeal and wear resistance. • Dimensional Precision: All critical dimensions were held within a ±0.01mm tolerance band throughout the batch. • Surface Treatment Optimization: For the Color Zinc Plating (Passivation), we pre-compensated the diameter by 6μm. Post-plating inspections confirmed that the threads remained within gauge limits and the surface finish remained well within the Ra 0.8μm threshold.
- Value Proposition
- Cost Efficiency (Eliminating Grinding): By achieving the required finish through "Hard Turning" on a composite machine, we eliminated the need for external cylindrical grinding, reducing lead times and total cost for the client.
- Superior Durability: The Ra 0.3μm base finish provides an ideal substrate for the chromate conversion coating, resulting in better plating adhesion and enhanced corrosion resistance.
- Technical Leadership: This project demonstrates our capability to push the limits of standard CNC machining to deliver "over-engineered" quality for high-end non-standard components.