Improvement of Surface Roughness of Electroless Ni-P Plated Mold by Oblique Cutting
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-04 |
| Journal | Journal of the Japan Society for Precision Engineering |
| Authors | Tsunehiro Nakagawa, Hirofumi Suzuki, Mutsumi Okada, Akihiro Suzuki, Shinya Morita |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the use of oblique cutting to improve the surface roughness of electroless Ni-P plated molds used in ultraprecision optics manufacturing.
- Core Achievement: Successfully reduced the surface roughness (Rz) of amorphous electroless Ni-P molds from the typical 10-30 nm range down to 5-10 nm Rz (0.5-1 nm Ra) using optimized oblique cutting parameters.
- Methodology: Developed a 3-axis (X, Y, Z) controlled oblique turning method that precisely controls the tool tilt angle (oblique angle, θ) relative to the cutting direction.
- Burr Reduction: Plunge cut experiments confirmed that increasing the oblique angle significantly reduces burr height on the side opposite the tool tilt for Ni-P, Aluminum, and Brass. Ni-P exhibited the smallest initial burr height among the tested materials.
- Roughness Correlation: For amorphous materials (Ni-P) and Brass, increasing the oblique angle improved surface quality, bringing the measured roughness closer to the theoretical roughness predicted by the modified formula (Rzâ = f2 / (8 * R * cos2θ)).
- Feed Rate Dependence: The effectiveness of the oblique angle was most pronounced at smaller feed rates (f), where the measured roughness was significantly higher than the theoretical value due to burr effects.
- Material Limitation: The improvement effect was less significant in polycrystalline materials (like Oxygen-Free Copper), suggesting that material heterogeneity remains a limiting factor for surface quality improvement.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Machine Control | 4-axis (X, Y, Z, C) | N/A | Ultraprecision machine (ULG-100D) |
| Positioning Resolution | 1 | nm | X, Y, Z axes (Linear motor driven) |
| Spindle Runout | 30 | nm | C-axis (Air static pressure bearing) |
| Tool Material | Monocrystalline Diamond | N/A | Round nose tool |
| Tool Nose Radius (R) | 1 | mm | Cutting tool geometry |
| Rake Angle | 0 | ° | Cutting tool geometry |
| Relief Angle | 7 | ° | Cutting tool geometry |
| Depth of Cut | 2 | Âľm | All turning experiments |
| Oblique Angle (θ) Range | -10 to 40 | ° | Experimental variable |
| Feed Rate (F) Range | 0.5 to 10 | mm/min | Experimental variable |
| Feed (f) Range | 0.5 to 10 | Âľm/rev | Experimental variable |
| Achieved Rz (Ni-P) | 5-10 | nm | Best result using oblique cutting |
| Achieved Ra (Ni-P) | 0.5-1 | nm | Best result using oblique cutting |
| Electroless Ni-P Hardness | 565 | HV | Workpiece material property |
| Electroless Ni-P Young Modulus | 197 | GPa | Workpiece material property |
| Oxygen-Free Copper Hardness | 100 | HV | Workpiece material property |
| Aluminum Hardness | 78 | HV | Workpiece material property |
Key Methodologies
Section titled âKey MethodologiesâThe experiments utilized a linear motor driven 4-axis ultraprecision machine (ULG-100D) operating under 3-axis (X, Y, Z) control for oblique turning.
- Tool Setup: A single-crystal diamond round nose tool (R = 1 mm, 0° rake, 7° relief) was used. The toolâs cutting edge was maintained horizontally (0° rake angle).
- Oblique Angle Control: The effective oblique angle (θ) was achieved by controlling the tool movement simultaneously along the X and Y axes during scanning, allowing for precise and localized angle control (Fig. 6).
- Plunge Cut Experiment (Burr Analysis):
- Materials: Electroless Ni-P, Aluminum, and 6-4 Brass.
- Procedure: Grooves were plunge-cut into the flat surface at a depth of 1 ¾m, varying the oblique angle from -10° to 40°.
- Evaluation: Burr height on the right side of the groove was measured using a non-contact laser probe and differential interference microscopy (Nomarski micrographs).
- Flat Turning Experiment (Roughness Analysis):
- Materials: Electroless Ni-P, Oxygen-Free Copper, and 6-4 Brass.
- Procedure: Flat turning was performed at a constant depth of cut (2 ¾m), varying the oblique angle (θ = -10° to 40°) and the feed rate (f = 0.5 to 10 ¾m/rev).
- Evaluation: Surface roughness (Rz and Ra) was measured using a scanning white light interferometer.
- Theoretical Comparison: Measured Rz values were compared against the theoretical roughness (Rzâ) calculated using the modified formula incorporating the oblique angle: Rzâ = f2 / (8 * R * cos2θ).
Commercial Applications
Section titled âCommercial ApplicationsâThis technology is critical for improving the quality and efficiency of manufacturing high-precision optical components.
- Precision Optics Molds: Direct application in creating ultra-smooth electroless Ni-P molds used for injection molding plastic lenses (e.g., smartphone camera lenses, automotive sensors, pickup lenses).
- Aspheric and Freeform Surfaces: Enables high-accuracy, high-efficiency mass production of complex non-spherical optical elements by minimizing burr defects inherent in ductile material cutting.
- Ultraprecision Machining: Applicable to any ultraprecision turning process where minimizing burr formation and achieving single-digit nanometer roughness on amorphous or ductile materials is required.
- Micro-Structure Fabrication: Potential use in machining micro-structures and diffraction gratings where edge quality and surface finish are paramount.
View Original Abstract
Ultraprecision aspheric cutting process using a monocrystalline diamond tool is widely used in the manufacturing process of the optical components and their molds/dies. Plastic lenses are molded by the injection molding using an amorphous electroless Ni-P plated molds/dies and decreasing of the lens surface roughness is required. Generally, the oblique cutting is one of the methods to decrease the cutting force and the burr, and to decrease the surface roughness. In this study, the oblique cutting was applied to aspheric mold materials to decrease the surface roughness. In the experiments, plunge cut by oblique cutting was applied to the electroless Ni-P plated molds, aluminum, oxygen free copper, and brass to clarify the burr behaviors. Finally, flat surface was diamond-turned by changing the oblique angle of the tool, the cut surface was evaluated, and the effects of the oblique angle to the surface roughness were evaluated.