Additive manufacturing of metal-bonded grinding tools

At a Glance

Metadata	Details
Publication Date	2020-03-01
Journal	The International Journal of Advanced Manufacturing Technology
Authors	Berend Denkena, Alexander Krödel, Jan Harmes, Fabian Leander Kempf, Tjorben Griemsmann
Institutions	Laser Zentrum Hannover, Leibniz University Hannover
Citations	33
Analysis	Full AI Review Included

Executive Summary

This research validates the use of Laser Powder Bed Fusion (LPBF) for manufacturing high-performance, metal-bonded diamond grinding tools using a Nickel-Titanium (NiTi) matrix.

Core Value Proposition: LPBF enables the creation of porous metallic bonds, addressing the primary drawback of conventional metal bonds (low porosity) by allowing engineered cavities for improved coolant/chip transport.
Material Suitability: NiTi (Nitinol) is confirmed as a highly promising bonding material, offering high grain retention and potential for enhanced wear resistance due to its inherent ductility and work hardening affinity.
Process Optimization: Pre-alloyed NiTi powder (Powder #2) demonstrated superior results (smoother surfaces, homogeneous element distribution) compared to elemental Ni/Ti mixtures, minimizing crack formation.
Abrasive Performance: Scratch tests performed on cemented carbide (KXF) confirmed the abrasive capability of the LPBF-manufactured segments. The bond exhibited high grain retention forces, with no diamond breakout observed.
LPBF Parameters: The optimal energy density (E_l) for composite fabrication was found to be lower (0.23 J/mm) than that required for manufacturing pure NiTi components, indicating that diamonds significantly influence the laser process.
Tool Preparation: A successful dressing process using vitrified white corundum achieved an average grain protrusion (S_pk) of 8.27 µm, sufficient for effective material removal during scratch testing.

Technical Specifications

Parameter	Value	Unit	Context
Matrix Material (Powder #2)	Ni 55.5 / Ti 44.5	wt%	Pre-alloyed gas atomized NiTi
Diamond Concentration (Powder #2)	28	v%	Abrasive content (D46 FMD60)
Diamond Grain Size	19	µm	Diameter
LPBF Laser Wavelength	1070	nm	Fiber laser source
LPBF Slice Height	50	µm	Layer thickness
Optimal Relative Density (Pure NiTi)	99.09	%	Achieved at P_L=50 W, v=110 mm/s, d=50 µm
Optimal Energy Density (E_l) for Composite	0.23	J/mm	Parameter Set 4 (P_L=25 W, v=110 mm/s)
Dressing Cutting Speed (v_c)	10	m/s	Machining white corundum
Dressing Feed Rate (v_f)	600	mm/min	Machining white corundum
Dressing Infeed (a_e)	15	µm	Material removal per pass
Average Grain Protrusion (S_pk)	8.27	µm	Measured after dressing
Scratch Test Material	KXF (10% Co, 0.7 µm)	-	Cemented carbide workpiece
Scratch Test Cutting Speed (v_c)	20	m/s	Machining cemented carbide
Scratch Test Infeed (a_e)	10	µm	Cutting depth

Key Methodologies

The experimental procedure involved a two-step process development: feasibility testing followed by parameter adaptation for cuboid samples and abrasive testing.

Powder Selection and Mixing:
- Two matrix materials were tested: elemental Nickel/Titanium mixture (Powder #1) and pre-alloyed NiTi (Powder #2).
- Diamonds (D46 FMD60) were dispersed in the powder mixtures (25 v% or 28 v%).
LPBF Feasibility Trials (Line Scans/T-Structures):
- Initial structures were built directly on a NiTi sheet substrate using a laboratory LPBF machine (50 W fiber laser).
- Analysis showed that Powder #2 (pre-alloyed) resulted in more homogeneous element distribution and fewer cracks than Powder #1, leading to its selection for subsequent tests.
Pure NiTi Parameter Optimization:
- A parameter study was conducted on pure NiTi (Powder #2, no diamonds) to maximize relative density.
- The highest density (99.09%) was achieved at P_L = 50 W, v = 110 mm/s, and hatch distance (d) = 50 µm.
Composite Sample Fabrication:
- Cuboid specimens (4.95 mm x 4.95 mm x 3 mm) were built using Powder #2 and diamonds, testing four parameter sets based on energy density (E_l = P_L/v).
- Parameter Set 4 (E_l = 0.23 J/mm) was selected for abrasive testing due to minimal cracking and no tarnish, indicating better process stability.
Material Characterization:
- X-ray Diffraction (XRD) confirmed the presence of cubic and martensitic NiTi phases in the bond.
- SEM/EDX mapping was used to analyze diamond dispersion and element distribution within the metallic matrix.
Dressing Process:
- Printed segments were bonded to metal pins and dressed using vitrified white corundum.
- The process parameters (v_c = 10 m/s, v_f = 600 mm/min, a_e = 15 µm) were chosen to profile the segment and sharpen the diamonds, achieving an average protrusion of 8.27 µm.
Scratch Testing:
- Tests were performed on a flat grinding machine using tungsten carbide (KXF) as the workpiece.
- Process parameters: v_c = 20 m/s, v_f = 200 mm/min, and a_e = 10 µm.
- Laser profilometry confirmed that scratch paths remained stable and unchanged over the workpiece length, validating high grain retention.

Commercial Applications

This LPBF methodology for NiTi-diamond composites is highly relevant for industries requiring precision grinding of hard materials and customized tool geometries.

High-Performance Grinding: Manufacturing superabrasive grinding wheels for machining difficult materials like cemented carbide, hardened steels, and ceramics.
Tool Prototyping and Small-Lot Production: Enables rapid construction of fully functional grinding tools and prototypes without the long lead times and high costs associated with traditional sintering or brazing.
Advanced Tool Design: Allows for the integration of engineered internal cavities and topology-optimized structures within the metallic bond layer to maximize coolant flow and chip evacuation, improving grinding efficiency.
Aerospace and Medical Tooling: NiTi’s inherent properties (shape memory, superelasticity, high wear resistance) make it suitable for specialized tools used in high-stress or precision environments.
Additive Manufacturing Services: Expansion of LPBF capabilities to include metal-diamond composite fabrication, broadening the scope of AM in the tooling sector.

Tech Support

Original Source

DOI: https://doi.org/10.1007/s00170-020-05199-9

References

2017 - 7. WGP-Jahreskongress Aachen, 5.-6. Oktober 2017
2017 - Additive Manufacturing Quantifiziert: Visionäre Anwendungen und Stand der Technik
2017 - Additive Manufacturing Quantifiziert: Visionäre Anwendungen und Stand der Technik [Crossref]