The advancement of various industries is characterized by the machining of micro-scale complex surfaces, which is difficult to achieve using traditional finishing techniques like grinding and milling. As a result, it is imperative to develop flexible and high-precision finishing technologies, especially for surfaces with micro structures. Lately, abrasive flow machining (AFM) has been identified as a promising finishing technology. This new technique can overcome the limitations of traditional technologies as it uses semi-solid media composed mainly of hard abrasive grits and soft matrix as the cutting tools. Nevertheless, micromachining some micro structures is still a big challenge, especially those with diameters smaller than 0.1mm.
It has been established that the material removal mechanism of AFM processes is driven by micro-plastic deformation caused by abrasive grits and viscous flow. The relationships between AFM processes and key machining parameters have also been investigated. Though not fully verified, it has been hypothesized that the final machining effect could be affected by various critical machining parameters that play fundamental roles in altering the rheological properties of the media.
However, there are no studies correlating the material removal mechanism of the AFM processes with the associated rheological properties of the media. In addition, the media used in most of these studies are designated for machining macro-scale structures and may not be applicable for micro-scale structures. Various simulation models have been developed to study the flow behaviors of the media. Despite the remarkable progress, developing effective models for simulating media used in machining micro structures is still needed to define the parameters and characterize the related rheological properties.
Herein, Mr. Baocai Zhang, Ms. Yu Qiao, Ms. Nasim Khiabani and Prof. Xinchang Wang from Shanghai Jiao Tong University studied the rheological behaviors, components and structures of a typical media to provide an in-depth understanding of the material removal mechanism of AFM of micro structures. A Carreau-Yasuda model was used to simulate the AFM process to determine the relative parameters and shear viscosity by analyzing the rheological behaviors of the media. Also, a Generalized Navier slipping model was used to analyze the wall slipping behavior. Their work is currently published in the research journal, Journal of Manufacturing Processes.
The research team revealed that the plasticizer oil and the polymer melt had similar structures and compositions, which contributed to the fluidity of the media by dispersing the polymer chains to minimize the interaction force between the side chains and minimize shear viscosity. The flow of the linear side chain structures, characterized by low side groups, through the micro-holes also contributed to the fluidity and elasticity of the media. Also, the intense peak creep curve value displayed a higher viscous component value than that of the elastic component.
The authors further observed that the polymer chains remained in the desired stretched state, resulting in machining effects and uniform indentation deaths on the entire machined surfaces. This was attributed to the effects of the long media relaxation time, streamlined retraction from larger chambers into micro structures as well as the combined effects of the normal shear difference and shear stress. The micro-holes reported a flow velocity of about 1.5 m/s, a proof that the relaxation time (230s) was much longer than the retention time (2 ×10-3 s), an indication of long-distance stretched states.
In a nutshell, the authors analyzed the rheological behaviors, structures and components of a typical abrasive media to systematically investigate their influence on the material removal mechanism of AFM. The results proved that the media could remain stretched when flowing through the micro holes. The favorable and uniform machining effects were attributed to the homogenous flow state and shear stress, the correlative storage and loss moduli and the media’s ability to remain stretched. In a statement to Advances in Engineering, Professor Xinchang Wang noted that the study provided valuable insights to guide the design of media and AFM procedures for micro-structures.
Zhang, B., Qiao, Y., Khiabani, N., & Wang, X. (2022). Study on rheological behaviors of media and material removal mechanism for abrasive flow machining (AFM) micro structures and corresponding simulations. Journal of Manufacturing Processes, 73, 248-259.