Amir Mir

Deterministic manufacturing of ultra-precision structured/freeform surfaces on Si and SiC

Project aims & objectives

The project aim is to develop single diamond turning process for ultra-precision structured/freeform surfaces on silicon (Si) and silicon carbide (SiC). This will be achieved by improving the machinability of Si/SiC. Since brittle fracture of work-piece materials along with tool wear aggressively deteriorates the surface finish, the focus is on the improvement of single point diamond turning process by avoiding brittle fracture of work-piece and catastrophic diamond tool wear.

Parallel simulation study combined with experimental study will provide good understanding of silicon and silicon carbide machining behaviour against different tool geometry and different cutting conditions. Recently developed surface defect machining method will be adopted to verify the effect of defect generation on silicon and silicon carbide. Freeform/structured surfaces will be generated using fast tool servo on Si/SiC materials to validate the improvement in machining.

Background

Silicon and silicon carbide are two important materials of great interest in many technical and engineering fields. Surface quality with nano-metric finish is crucial to attain the product performance with high efficiency. Due to the high hardness and high brittleness of these materials, it is difficult to achieve ductile mode machining consistently and for longer cutting distances. Brittle fracture of work-piece materials and rapid tool wear are the two major challenges in ultra-precision turning.

With these machining challenges, it is quite difficult to manufacture structured or freeform surfaces on these materials. For structured or freeform surfaces, surface finish of sub-nanometer level is desirable. This surface finish can’t be achieved without rectifying the two drawbacks of the machining process.

Approach

All manufacturing processes are endowed with some pros and endure some limitations that make them inappropriate for machining structured/freeform surfaces. Although, single point diamond turning also suffer from some limitations, it has the ability to generate required surface finish on these materials in one single step without the need of subsequent polishing or any other process.

Experiments have been performed to find the effect of diamond tool geometry on ductile mode machining of silicon material as well as on the life of diamond tool. Additional experiments will be performed to verify the results combine with finite element simulation study for silicon. Further experimental study will explore the performance of recently developed surface defect machining on silicon and silicon carbide. Finite element simulation technique will be developed to optimise the machining simulation for silicon and silicon carbide.

Progress

Experimental study verifies that certain negative rake angles of diamond tools perform better and can undergo longer cutting distance with longer ductile mode machining of silicon. Experimental study also explored that cutting edges of the tool play a significant role in optimising the machined surface quality as well as reduction in tool wear.

Impact

Due to the superior qualities of silicon and silicon carbide, their importance has widely been accepted and adopted in many advanced ultra-precision engineering applications. The use of silicon in micro-electromechanical systems (MEMS), solar application, optics, semiconductor industry and bio-medical imaging application has been widely recognised. The importance of SiC is known in quantum computing, laser devices, vacuum ultra-violet telescopes and satellites, in thermal protection system development for defence applications and many other applications.

In many of the applications of silicon and silicon carbide, the surface quality is the functional candidate in optimal performance of the product. Development of single point diamond turning process will significantly help in the production of optical quality products of silicon and silicon carbide in less time, with lesser steps and resources and improved structured quality of the machined surface.

Next steps

In the next step, surface defects method will be tested for silicon and silicon carbide to see the improvements in the machinability of two materials. This will be done by experimental along with simulation based study.