N. Driver

Micromachining of coarse-grained multi-phase material

Abstract The high demand of miniaturized components, coupled with geometric and material range limitations of traditional lithographic techniques has generated a strong interest in micromechanical machining. In micromachining the so-called size effect is a dominant factor. This is attributed to the fact that the unit or physical size of the material to be removed can be of the same order of magnitude as the tool edge radius or grain size. This paper explores the micro-machinability of multi-phase ferrite—pearlite steel that has a relatively large average grain size (10 μm). The investigation and cutting tests examined the effect of undeformed chip thickness, tool edge radius, and workpiece grain size on the specific cutting force, burr size, surface finish, and tool wear. The work clearly shows that micro tool edge radius and workpiece material grain size are valuable inputs in determining micromilling conditions that ensure the best surface finish and reduced burr size. Cutting conditions recommendations are also put forwards for roughing and finishing passes in micromilling of AISI 1045 tool steel.

Estimation of minimum chip thickness in micro-milling using acoustic emission:

In micro-machining, determination of the minimum chip thickness is of paramount importance, as features having dimensions below this threshold cannot be produced by the process. This study proposes a methodology to determine the value of minimum chip thickness by analysing acoustic emission (AE) signals generated in orthogonal machining experiments conducted in micro-milling. Cutting trials were performed on workpiece materials ranging from non-ferrous (copper and aluminium), ferrous (single- and multiphase steel) to difficult-to-cut (titanium and nickel) alloys. The characteristics of AErms signals and chip morphology were studied for conditions when the tool was rubbing the workpiece. This provided a foundation to contrast AE signals captured at higher feed rates. This study enabled the identification of threshold conditions for the occurrence of minimum chip thickness. The values of minimum chip thickness predicted by this new approach compare reasonably well with the published literature.

Analysis of process parameters in the micromachining of Ti-6Al-4V alloy

The demand for manufacturing technologies for micro components and features has been increasing in aerospace, biomedical, electronics, environmental, communications and automotive industries. Since titanium alloys are widely used in aerospace and biomedical applications, the development of micromachining technologies for these materials is of particular interest. This study employs statistical analysis techniques to evaluate the contributions of the different process parameters towards tool life and product quality in micro-milling in comparison with macro-milling. The establishment of key process variables would ultimately help in reducing production costs by reducing the cost of tool replacement and minimizing product rejection.

Estimation of minimum chip thickness for multi-phase steel using acoustic emission signals

The determination of minimum chip thickness is important for establishing the lower limit of the feasible process window in micro mechanical machining for a given tool and workpiece material. The minimum chip thickness is encountered in micro milling operations owing to the variation in chip load as predicted by the chip density function. This study proposes a methodology to determine the value of minimum chip thickness by analysing acoustic emission (AE) signals generated in orthogonal machining experiments conducted in micro milling. Cutting trials were performed on a near balanced ferrite/pearlite microstructure (AISI 1045 steel) with a range of undeformed chip thicknesses spanning across the tool edge radius. The characteristics of AE r.m.s signals were studied for conditions when the tool was rubbing the workpiece. This base signal signature was used to study and contrast AE signals to other machining parameters. This study enabled the identification of threshold conditions for occurrence of minimum chip thickness. The value of minimum chip thickness predicted by this new approach compares reasonably well with that existing in published literature.

Chip Morphology and Cutting Forces in High Speed End Milling of Titanium 6AI-4V Alloy

Titanium alloys pose considerable problems in manufacturing, especially when machined at high cutting speeds. Despite great advancements in cutting technology, only limited success has been achieved in improving the high-speed machinability of titanium alloys. In this paper, chip morphology, cutting forces and tool wear are studied under minimum quantity lubrication (MQL) and dry conditions in high speed milling using ball end tools. Predictive models for chip length in end milling are also revisited. For the range of speeds tested, resultant cutting forces and maximum chip lengths were found to reduce with cutting speeds. Dry machining was associated with shorter chips and lower cutting forces when compared to MQL conditions. In addition, the study also establishes a mechanism of chip segmentation in ball nose end milling of titanium at high cutting speeds.