Machining of High-Hardness Hardfacing Layers in Remanufacturing Applications

Literature Overview

This 2011 paper from the State Key Laboratory of Equipment Remanufacturing Technology at the Academy of Armored Force Engineering investigates the machining characteristics of hardfacing deposits with hardness levels of HRC30 and HRC45 using YG610 cemented carbide tools. The study employs orthogonal experimental design to evaluate the influence of cutting parameters on tool life, providing practical guidance for the machining operations required in equipment remanufacturing processes.

Experimental Design and Results

The research addresses a critical practical challenge in remanufacturing: after hardfacing repairs are applied to worn components, the overlay must be machined to achieve final dimensional accuracy and surface finish. However, hardfacing deposits are typically significantly harder than the base material, posing severe challenges for machining operations.

Cutting Parameter Influence on Tool Life

Parameter	Influence on Tool Cutting Distance	Effect Pattern
Feed rate	Largest influence	Monotonic decrease with increasing feed
Cutting speed	Moderate influence	Decreasing trend
Depth of cut	Smallest influence	Nearly negligible for high-hardness materials

Key Findings Summary

Hardness Level	Optimal Strategy
HRC30	Reduce feed rate, increase depth of cut
HRC45	Reduce feed rate, increase depth of cut (depth effect even less significant)
Tool material	YG610 cemented carbide

Technical Interpretation

The monotonic relationship between feed rate and tool failure is mechanistically explained by the increasing cutting force and thermal load imposed on the tool as feed rate increases. At higher feed rates, the chip thickness increases, generating greater frictional heating at the tool-chip interface. For YG610 grade carbide (6% Co binder), the elevated temperatures accelerate diffusion wear and chemical wear mechanisms.

The observation that depth of cut has minimal influence on tool life for high-hardness materials is particularly significant from an engineering standpoint. This finding suggests that for machining hardfacing deposits, the cutting process should be optimized by maximizing depth of cut while minimizing feed rate. This approach maximizes material removal rate while preserving tool life, which is economically critical in production remanufacturing operations.

Implications for Remanufacturing Process Planning

In a 5W2H framework applied to hardfacing deposit machining:

What: Machining of HRC30–HRC45 hardfacing deposits
Why: Dimensional restoration of repaired components
How: YG610 carbide tools with low feed and high depth of cut
What parameters: Low feed rate, moderate cutting speed, maximum practical depth of cut
When: After hardfacing overlay application, before final assembly
Where: Remanufacturing workshops with CNC turning/milling capability

Study Reflections

This paper provides valuable quantitative data for process planning in remanufacturing operations. The finding that depth of cut has negligible effect on tool life for HRC45 materials is counterintuitive and practically important. It means that rough machining passes with deep cuts are economically favorable, followed by finishing passes with reduced parameters for surface quality.

From a broader perspective, this work highlights the importance of considering post-hardfacing machining requirements during the initial process planning stage. The choice of hardfacing process and consumable should account not only for wear resistance but also for the machinability of the resulting deposit. Hardfacing deposits with hardness above HRC50 become extremely difficult to machine conventionally, often requiring grinding or abrasive processes instead.

The practical recommendation is clear: when remanufacturing specifications allow, target hardfacing deposits in the HRC30–HRC45 range where conventional machining remains feasible with appropriate tooling and parameter selection.