70
J. Eur. Opt. Society-Rapid Publ. 21, 37( 2025)
Table
1. Processing conditions for shape adaptive grinding.
Wheel diameter |
20 mm |
Coolant |
Water |
Point spacing |
1 mm |
Track spacing( TS) |
0.5 mm |
Tool offset |
0.15 mm |
Tool rotation |
150 rpm |
Feed rate |
300 mm / min |
Precess angle |
0 ° |
Precess direction |
90 ° |
driven wheel-workpiece interface, slipping occurs between driven and driving wheel. This makes the process completely inefficient. Therefore, the contact pressure between driven wheel and driving wheel is adjusted until there is no slipping at the interface. From the initial experiments, it could be observed that a preset load of 6 N between driving wheel and driven wheel was sufficient to balance the pressure between the driven wheel and the workpiece, and to avoid the slippage. To control the tool paths and calculate various precessions for the proposed wheel too, a new software plug-in was developed and added in the existing machine control software ZephyrCAM( Make: Zeeko).
In the SAG process, the workpiece geometry is probed using the tool itself to compensate for the workpiece geometrical errors and mounting errors in the CNC program. The probing is accomplished by reading the load variation using a load cell located behind the tool, as shown in Figure 4b and explained above. In the newly proposed tooling system, the finishing wheel is not directly in contact with the load cell, rather the wheel is pressed against the driving wheel and the driving wheel is then transferring the load to the H-axis casing. Therefore, it was necessary to check if the geometry of the workpiece could be effectively captured during probing. A total of 36 probing points were selected inside the channel, shown in Figure 4c. The residual error map of the probing is also shown. The residual error of ~ 63 lm could be observed against the designed dimensions of the channel, which is also quite close to that of the form error ~ 72 lm P-V measured by form talysurf( Make: Taylor Hobson, Model-PGI1240).
SAG processing conditions are presented in Table 1. The raster path inside the channel and tool-workpiece contact is presented in Figure 5a. Water was used as a coolant during the whole process. Tool offset was kept at 0.15 mm, as the larger offset led to quick wear and tear of abrasive pad and slipping of the wheel. Different kind of abrasive pads were used based on their removal characteristics and surface finishing capabilities. In this work, 3 lm RBD( resin bonded diamond) and 9 lm NBD( nickel bonded diamond) SAG pads were used, which are shown in Figure 5b. The surface form and surface roughness after finishing was measured using form talysurf. To capture the surface micrographs, deep focus microscope( Make: Keyence, Model-VHX7000) was utilized.
Fig
. 5.( a) Raster path inside the channel and finishing wheel and workpiece contact,( b) optical micrographs of 3 lm RBD and 9 lm NBD SAG abrasive pads.
Fig. 6. Wheel-workpiece contact during SAG finishing process.