Development of precision polishing machine based on a hexapod

At a Glance

Metadata	Details
Publication Date	2017-05-29
Journal	University of Huddersfield Repository (University of Huddersfield)
Authors	Zavid Mohamed, Liam Blunt, Christian Young, Zhen Tong, Duo Li
Analysis	Full AI Review Included

Technical Documentation & Analysis: Precision Polishing for MPCVD Diamond

This document analyzes the research on hexapod-based precision polishing, connecting the demonstrated nano-scale finishing capabilities to 6CCVD’s expertise in manufacturing and finishing high-performance MPCVD diamond materials (SCD, PCD, BDD).

Executive Summary

The research validates a critical manufacturing process—precision bonnet polishing—essential for achieving the ultra-low surface roughness required by advanced materials like MPCVD diamond.

Process Validation: A novel, low-cost Bonnet Polishing (BP) machine utilizing a Hexapod (6-DOF) platform was successfully developed and tested.
Nano-Scale Achievement: The system achieved a final surface roughness (Ra) as low as 5.6 nm on P20 high hard tool steel, demonstrating the capability for nano-scale finishing.
Optimization Methodology: The Taguchi approach was effectively used to optimize polishing parameters, identifying rotational speed (1000 rpm) and tool offset (0.3 mm) as key factors for surface quality improvement.
Relevance to Optics: The process is specifically noted for its ability to reduce mid-spatial frequency errors, a critical requirement for optical-grade diamond components supplied by 6CCVD.
6CCVD Capability Match: The achieved Ra of 5.6 nm confirms the feasibility of achieving 6CCVD’s standard SCD polishing specification (Ra < 1 nm) using similar precision techniques optimized for diamond’s extreme hardness.
Material Requirement: This research confirms the necessity of highly controlled, multi-axis polishing systems for finishing ultra-hard materials, directly supporting 6CCVD’s in-house finishing services for SCD and PCD wafers.

Technical Specifications

The following hard data points were extracted from the experimental results and machine design analysis:

Parameter	Value	Unit	Context
Final Surface Roughness (Ra)	5.6	nm	Optimized result (78% improvement)
Initial Surface Roughness (Ra)	25.5 to 40.4	nm	Base line before optimization
Optimum Spindle Speed	1000	rpm	Identified via Taguchi analysis
Optimum Feed Rate	15	mm/min	Identified via Taguchi analysis
Optimum Tool Offset	0.3	mm	Identified via Taguchi analysis
Optimum Number of Passes	16	Passes	Identified via Taguchi analysis
Spindle Runout	< 1	µm	Nakanishi EMR-3008K air bearing system
Hexapod Minimum Incremental Movement	< 3	µµm	Precision movement capability in all axes
Polishing Pad Radius	10	mm	Soft rubber pad size
Slurry Particle Size	1	µm	Diamond paste abrasive
FEA Maximum Displacement	< 0.5	µm	Machine frame stiffness under load

Key Methodologies

The experiment utilized a highly controlled, optimized Bonnet Polishing (BP) process to achieve nano-scale surface finishing.

Machine Platform: A Hexapod H840.D2 (PhysikInstruments) provided 6 degrees of freedom (DOF) precision movement, mounted with an air-bearing spindle (500 rpm to 8000 rpm).
Tooling Setup: A 6 mm diameter rod with a 10 mm radius soft rubber pad and polyurethane pad was used as the polishing tool.
Workpiece Material: P20 high hard tool steel (300 HB), pre-ground to an initial surface roughness Ra of approximately 30 nm.
Abrasive Slurry: A 1 µm diamond paste slurry was used for all polishing processes.
Optimization Strategy: The Taguchi approach (L9 orthogonal array) was employed to systematically optimize four key parameters: Feed Rate, Spindle Speed, Tool Offset, and Number of Passes.
Measurement Protocol: Surface roughness (Ra) was measured using a Dektak XT stylus profiler over a 4.8 mm length, utilizing a Gaussian regression filter with a 0.8 mm cut-off to capture mid-spatial frequencies.
Optimized Recipe: The highest Signal-to-Noise ratio was achieved using 15 mm/min Feed Rate, 1000 rpm Speed, 0.3 mm Offset, and 16 Passes, resulting in the best surface finish.

6CCVD Solutions & Capabilities

The research highlights the necessity of advanced precision polishing for achieving high-performance surfaces. 6CCVD specializes in providing MPCVD diamond materials that require and benefit from this exact level of finishing control.

Applicable Materials for Precision Finishing

The ability to achieve sub-10 nm roughness is critical for optical and high-power electronic applications. 6CCVD supplies the necessary materials, pre-finished to meet or exceed the requirements demonstrated in this paper.

6CCVD Material	Application Focus	Standard Finish Specification	Relevance to Research
Optical Grade SCD	High-power optics, quantum sensing, UV/IR windows.	Ra < 1 nm	Requires the highest level of precision polishing demonstrated (sub-5.6 nm).
High-Purity PCD	Large area heat spreaders, mechanical windows.	Ra < 5 nm (Inch-size)	Requires controlled BP techniques to achieve uniform, low-roughness over large areas (up to 125 mm).
Boron-Doped Diamond (BDD)	Electrochemistry, sensors, high-frequency electronics.	Custom (dependent on doping level)	Requires precise control over surface morphology to ensure optimal electrical contact and stability.

Customization Potential & Manufacturing Synergy

The research utilized specific tooling dimensions (10 mm radius pad) and required high mechanical stiffness. 6CCVD’s in-house capabilities ensure that the final diamond product is engineered precisely for the customer’s application and subsequent processing needs.

Custom Dimensions: 6CCVD provides SCD and PCD plates/wafers in custom dimensions, including large-area PCD up to 125 mm, far exceeding the 30 mm² area tested in the paper.
Ultra-Precision Polishing: While the paper achieved 5.6 nm Ra on steel, 6CCVD routinely achieves Ra < 1 nm on Single Crystal Diamond (SCD) surfaces, validating our mastery of the precision finishing techniques required for the hardest known material.
Metalization Services: For applications requiring electrical contact or bonding (e.g., thermal management or sensor integration), 6CCVD offers internal metalization capabilities including Au, Pt, Pd, Ti, W, and Cu layers, eliminating the need for external processing steps.
Substrate Thickness: We offer SCD and PCD layers from 0.1 µm up to 500 µm, and custom substrates up to 10 mm thick, providing the necessary mechanical stability for demanding polishing processes.

Engineering Support

The use of the Taguchi approach in the paper underscores the importance of optimizing processing recipes for specific materials. 6CCVD’s in-house PhD team specializes in the material science and process engineering of MPCVD diamond.

Recipe Optimization: Our experts can assist clients in defining optimal material specifications (e.g., crystal orientation, doping level, thickness) and finishing recipes necessary to achieve performance targets for similar precision optical or thermal management projects.
Global Logistics: We ensure reliable, global delivery of finished diamond components, offering DDU (default) and DDP shipping options.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Increasing demand on mass production of high precision parts, has pushed the precision manufacturing industry to develop relatively low cost, reliable precision finishing processes to meet market requirements. A gap within the provision of low cost polishing processes has been identified; namely parts with a radius of curvature less than 10mm will be increasingly present in new mass produced products, yet such parts cannot be efficiently polished with existing bonnet polishing (BP) process due to tool head size and the tool holder being bigger than the part radius. Moreover in some applications such as optical lenses the mid-spacial frequencies errors present in the surface severely affects the optical performance of the lenses. Therefore, bonnet polishing with physical contact is more appropriate process for these types of surfaces.\nA novel low cost precision polishing machine is presented in the present paper. The machine is a form of bonnet polishing. The machine is composed of a Hexapod H840.D2 (PhysikInstruments) which allows precision movement in 6 degrees of freedom held in a machine frame. An air bearing, electrically driven spindle (speed range from 500rpm to 8000rpm) is mounted to the Hexapod to drive the polishing tool. A rubber bonnet tool with polyurethane pad is used to engage the part surface. In order to test the performance of this prototyped machine, the machine was used to polish flat surfaces of P20 steel alloy which is widely used to manufacture plastic injection moulds. All polishing processes were carried out using diamond paste with particle sizes of 3µm. Pre-polishing results showed that the feed rate of the hexapod, spindle rotating speed, tool offset and number of polishing passes are the main factors affecting the polished surface quality. Moreover, the Taguchi approach was used to investigate the four polishing parameters. The optimisation of the parameters allows the polishing machine to consistently achieve ≥10 nm surface roughness Sa.

Tech Support

Original Source

DOI: None