by Vuyisile L. Dube

TITANIUM alloy Ti6Al4V is among the most demanding materials in modern manufacturing. 

Prized for its exceptional strength-to-weight ratio and corrosion resistance, it is the metal of choice for aircraft engines, medical implants, and defence components. 

But machining it is notoriously energy-intensive, and understanding exactly where that energy goes has long posed a challenge to engineers. 

New research published in the Zimbabwe Journal of Science and Technology (ZJST) by Dr Nicholas Tayisepi of NUST's Department of Industrial and Manufacturing Engineering offers a practical and accessible answer, one that lies in the shape of the chips.

The study investigated whether the physical features of chips produced during the CNC turning of Ti6Al4V could serve as a reliable, macroscopic indicator of how efficiently energy is being used in the machining process. 

Rather than relying on continuous online energy measurements or complex instrumentation, the research proposes that engineers could simply observe the chips coming off the machine and draw meaningful conclusions about process efficiency.

To test the concept, Dr Tayisepi ran eighteen carefully planned cutting experiments on a CNC lathe, adjusting how fast the tool moved and how deeply it fed into the metal with each pass. 

Every time the tool cut, it produced small metallic fragments, the chips, which were collected, set in resin, polished smooth, and placed under an optical microscope for detailed examination. 

What the microscope revealed was not random debris but highly structured, saw-toothed fragments whose shape changed in measurable and predictable ways depending on how the machine had been set up. 

Seven distinct geometric features of these chips were recorded and compared against how much energy the machine consumed per unit of material removed. 

The findings revealed a consistent and significant relationship between chip geometry and energy use, meaning the shape of the chip and the efficiency of the machine were telling the same story, just in different languages.

“Results established the correlation between the seven analysed chip morphology attributes changes with specific energy use minimisation up to some point beyond which the reduction trend changes direction towards energy consumption increase,” said Dr Tayisepi.

In practical terms, this means there is a sweet spot in the chip morphology profile at which specific cutting energy reaches its lowest point. 

Operating beyond or below this optimum range, whether through chip segmentation angles that are too shallow or too steep, or through chip thicknesses and pitches that fall outside the efficient zone, results in higher energy consumption per unit of material removed.

The research also found that higher material removal rates, achieved through increased cutting speed and feed rate, generally corresponded with more favourable chip morphology and lower specific energy use. 

The connection between cutting conditions, chip shape, and energy consumption is not merely correlational; it reflects the underlying thermo-mechanical behaviour of the titanium alloy as it deforms and segments under the cutting tool.

“The profiles of the chip morphology versus specific cutting energy plot suggest the subsistence of an energy use optimum point during the cutting of Ti6Al4V,” said Dr Tayisepi.

The possible implications of this finding could extend well beyond the laboratory. 

For production engineers and machining process planners working with titanium, it means that energy efficiency monitoring need not depend on sophisticated real-time power measurement infrastructure. 

By establishing what the optimal chip profile looks like for a given operation, floor-level technicians can use visual or microscopic observation of chip features to assess whether the process is running efficiently.

Below is the abstract of the research and a link to the paper.

Abstract

During mechanical cutting of aircraft grade titanium alloy, Ti6Al4V, chip morphology features observation relay fundamental intelligence towards understanding the machining activity energy efficiency management. In the present study, the effect of chip formation, on specific energy use, was experimentally investigated. Design of experiments was used to plan the 18 machining experiments iteration set in Minitab 22 software. The input cutting parameters were varied and the segmented chip morphological variation was studied in order to understand its effect on the energy efficiency, which is reflected through specific energy use. Key, Ti6Al4V material chip formation feature attributes, were examined and characterised as regards how the chip profile features correlate with specific energy use during cylindrical billet exterior cutting on the CNC turning machine tool. The research, aimed to generate insight into the energy efficient machining of the Ti6Al4V, as mirrored through the chip morphology system. Furthermore, the intention was to get a macroscopic insight about the energy use from observing the chip profile trends during machining of the high-grade titanium alloy. Results established the correlation between the seven analysed chip morphology attributes changes with specific energy use minimisation up to some point beyond which the reduction trend changes direction towards energy consumption increase. The profiles of the chip morphology versus specific cutting energy plot suggest the subsistence of an energy use optimum point during the cutting of Ti6Al4V. The study findings provide important reliable guidance to the machining industry stakeholders who could apply this knowledge to monitor the process efficiency of their operations by macroscopically monitoring the features of the cutting chips produced. Conclusion reached is that it is feasible to observe the specific energy use trend, of the machining process, through observing the chip morphology system. Future work related to establishing the optimum operating parameters from the chip morphology models.

Keywords: Energy efficiency, chip morphology, specific cutting energy, machining process, titanium alloy

The paper is accessible at: https://journals.nust.ac.zw/index.php/zjst/article/view/315