Machine-Finish Surface Textures and Component Integrity

Project summary

Understanding the machined surface.

This DFA research proposal is a partnership between the University of Derby and an industrial partner.

In highly regulated sectors, the qualification and validation of new materials and manufacturing process routes that can increase safety, reliability and productivity and reduce product life-cycle cost is lengthy, and this can become the main barrier to their deployment. This EngD seeks a deeper fundamental understanding of the machined surface condition and how it affects the durable service life of the component, enabling accelerated qualification and validation of new materials and processes.

Using a fully instrumented machining test bed in a lab setting, the project will:

• develop machine-finish surfaces on nuclear heat-resisting alloys with different chattered surface textures;
• reproduce those different chattered surface textures reliably;
• measure and discern chatter surface textures from the tool feed marks;
• understand the relationship between a chattered machine-finish surface, residual stress and fatigue life;
• demonstrate an improved machine-finish protocol for a heat-resisting nuclear alloy.

The work spans experimental methods, sensors and instrumentation in manufacturing, vibration analysis, microscale vision and contact measurement, microhardness indentation testing, X-ray diffraction analysis, and quantitative and qualitative statistical methods and data analytics.

Aims and objectives

Some 80% of goods produced for highly regulated sectors such as nuclear and aerospace require a machine finish, governed by surface integrity compliance. Machining hard heat-resisting superalloys presents significant challenges through accelerated tool wear, tool chipping and a propensity to chatter vibration that increases with tool wear. While the relationship between surface roughness and fatigue endurance is well established, the underlying causes such as residual stress are still debated.

• State-of-the-art review of machining-induced surface damage and its effect on fatigue life.
• Use dynamical-frequency methods and instrumented tapping-hammer trials to identify machining parameters with a propensity to chatter.
• Conduct instrumented machining trials on a superalloy to develop repeatable chatter-textured surface conditions.
• Develop a machined-surface finish assessment method using high-magnification 3D vision optics and stylus contact measurement.
• Quantitatively investigate surface and subsurface residual stress using XRD and microhardness indentation.
• Qualitatively examine the surface and subsurface using high-magnification confocal and laser-based microscopy.
• Investigate the relationship between machine-finish surface and fatigue life through test pieces with specific chattered textures, fatigue-tested to international norms.

Deliverable: lab and factory demonstrations, documented workflow and protocols.

Alignment to STAND-UP impact targets