Path planning of mechanical polishing process for freeform surface with a small polishing tool
Lin et al. Robotics and Biomimetics
Path planning of mechanical polishing process for freeform surface with a small polishing tool
Weiyang Lin 0 1 2
Peng Xu 0 3
Bing Li 0
Xiaojun Yang 0
0 Shenzhen Graduate School, Harbin Institute of Technology, Shenzhen University Town , Xili, 518055 Shenzhen , China
1 Mechanical Automation of Engineering, the Chinese University of Hong Kong , NT Road, 999077 Shatin , Hong Kong
2 School of Astronautics, Harbin Institute of Technology , Xidazhi Street, 150001 Harbin , China
3 Department of Industrial and Systems Engineering, the Hong Kong Polytechnic University , Yuk Choi Road, 999077 Kowloon , Hong Kong
Products with freeform surface are widely applied in industries, and the surface quality plays an important role in order to fulfill the targeted functions. As polishing path of small polishing tool affects the polishing removal function considerably, it is highly necessary to study the polishing path of freeform surface for obtaining good polishing efficiency and well-proportioned surface quality. By combining the Preston polishing removal function, the material removal model of small polishing tool under the control of constant polishing force and pressure is established. Based on this model, the material removal functions of scan line, Archimedean spiral, and Hilbert fractal polishing path are derived. The simulation results show that the Hilbert fractal polishing path has the best comprehensive performance. By using the projection relation of differential geometry, the optimal path generation algorithm of the Bézier surface based on Hilbert fractal polishing path is established. The polishing experiments are conducted on a self-developed polishing machine which is based on a parallel manipulator. The experimental results demonstrate that the surface roughness is improved from level 9 to level 11.
Mechanical polishing; Small polishing tool; Freeform surface; Polishing path; Removal function
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Background
Product structure can be optimized by using freeform
surfaces, which opens the door for solutions with
improved performance, reduced complexity, lower mass,
and smaller size. However, due to the geometric
particularity, freeform surfaces face more challenges and
difficulties in precision manufacturing. Polishing is usually one of
the final processing steps of precision manufacturing, and
the results directly affect the appearance and longevity
of parts [1]. It is fundamentally different from other
precision manufacturing technologies. Removal of polishing
does not only depend on the position of the tool
orthogonal to the workpiece, as for grinding and cutting processes
but also proportional to the product of local pressure and
relative-speed between tool and workpiece and the dwell
time. In recent years, there were efforts to develop
versatile polishing processes in order to achieve high accuracy.
The current polishing methods mainly include
electrochemical polishing [2], magnetorheological fluid polishing
[3,4], plasma polishing [5,6], ultrasonic polishing [7,8] and
computer-controlled mechanical polishing [9,10].
Nowadays, a lot of freeform components are still produced by
final manual polishing. It not only heavily relies on the
know-how and experience of technicians but also needs
much attention for processing and testing. To achieve a
given level of precision with high efficiency and
reliability, process automation is clearly the way forward. As the
computer-controlled mechanical polishing has high
efficiency and can be controlled easily [11], it is the focus of
this study. The mechanical polishing is a statistical
‘rubbing’ process that the microscopic loose-abrasive particles
in the polishing liquid which is driven by high-speed
rotational polishing tool could produce friction with the part
surface. Protruding portions of the surface are removed
to meet the roughness requirement. However, due to the
various factors, the polishing process heavily relies on trial
and experience, which leads to a slow development in the
mechanical polishing process.
Compared with the large polishing tool, the small
polishing tool used in this study has many advantages [12].
The small tool can follow the freeform surface with
relatively large curvature, while large tool cannot polish the
freeform surface with curvature smaller than its radius.
The small tool can redress the error of local surface, while
a large tool may polish the nearby surface when it polishes
a local surface. The small can also operate at greater
pressure and velocity than a large tool; therefore, it can remove
the material in a rapid manner. In the case of
manufacturing one single piece, small polishing tool has a higher
polishing efficiency.
As the polishing surface is highly nondeterministic, one
of the reasons is that the polishing path of the tool affects
the removal considerably. A basic requirement for
polishing paths is that the surface can be completely and
uniformly covered during a polishing cycle (...truncated)