Grinding Tool Structuring
Tool structuring is a conditioning process for grinding wheels, where defined patterns of abrasives or of clusters of abrasives on the wheel surface are generated in order to influence the cutting performance and cutting characteristics of the wheel.
But structuring not only means that a manufactured tool is postprocessed. Manufacturing of engineered grinding tools (EGT) is also classified as generation of structured grinding tool.
Theory and Applications
The purpose of structuring is to enhance the cutting conditions on the tool surface by increasing the chip thickness per grain, thus according to Kienzle equation reducing the overall cutting forces and thereby the overall grinding efficiency. This means that heating and heat damage of the workpiece is reduced as has been shown by Rabiey (2010). Moreover, chip flow and coolant flow conditions are expected to be improved. But structured grinding wheels normally generate worse surface quality and are subject to higher wear as the number of active cutting edges is reduced.
There are in principle two methods for producing a structured wheel surface:
In the first method of structuring, hereafter referred to as the direct method, is such that the structuring of the wheel surface is part of the manufacturing process of the grinding wheel shape. This can be realized by, e.g., a segmented die/mold shape, separate abrasive segments that are applied onto the wheel body, or even single abrasive grits that are arranged in defined patterns on the wheel’s surface. The direct method is usually limited to macroscopic structuring and segmentation for multilayered wheels. For monolayered surface-set wheels, engineered grinding tools (EGT) present an approach to design specific wheel topographies on the microscale.
The second method of structuring, hereafter referred to as the indirect method, starts from a non-structured wheel of cylindrical or other shape. The surface structuring is then applied by means of a material removing process. Usually these are mechanical structuring processes utilizing a dresser. In principle, structures ranging from the macro- to the microscale are possible. However, the minimal dimensions of the generated structures are restricted to the dimensions of the dressing tool in combination with the kinematic conditions of the dressing setup.
The effect of the wheel topography and axial grooves (width 3 mm, depth 0.5 mm) on the cooling efficiency in surface grinding was studied by Okuyama et al. (1993). It was found that the heat transfer coefficient increases with the number of grooves, and it was thus concluded that coolant is accumulated and transported through the grooves. In line with these results, Lee et al. (2000) measured up to 80% lower grinding temperatures in face grinding of alumina with slotted diamond wheels.
A thermal model for grinding with slotted/segmented wheels was developed by Zheng and Gao (1994). Due to the periodic intermittent rise of the grinding temperature for slotted wheels, the heat accumulated in the grinding zone was reduced. In addition, simulation results indicate that the slotting factor (reduction of the wheel’s surface due to segmentation) has a stronger influence on the grinding temperature than the pitch of the segmentation.
Kim et al. (1997) proposed a manufacturing method for a discontinuous grinding wheel for grinding ductile metals, wherein the segments are filled with an abrasive matrix of high porosity, which wears quickly in the grinding operation and thereby results in a discontinuous cutting process.
The concept of dead-end grooves on the wheel surface, with the purpose to feed and trap coolant in the grooves, in order to reduce workpiece burning during creep feed grinding, was introduced by deGraaff (1997). A similar approach with various pattern geometries was proposed by Fischbacher and Noichl (2001).
Several researchers (Aurich et al. 2003, 2008; Burkhard et al. 2002; Pinto et al. 2008) developed brazed or electroplated monolayer EGT with defined grain patterns, applied in power honing and high-performance grinding. Some tools were designed and optimized based on kinematic process simulations. The grain rows were usually arranged in a helical pattern at a pitch angle of 15° to 30° and spacing between the grains and grain rows between 0.3 mm and 2 mm, depending on the grain size. Experimental results and simulation models led to the conclusion that grinding forces can be significantly reduced with EGT; however, even for an optimized grain pattern, the workpiece surface finish will not be better than that obtained with a conventional stochastic electroplated wheel as shown in Koshy et al. (2003).
Tawakoli et al. (Tawakoli and Rabiey 2008; Tawakoli et al. 2007) proposed a crossed helix structure (width 0.6–1.5 mm, pitch 0.8–1.9 mm, depth 0.03 mm, pitch angle 60°) on resin and vitrified bonded CBN wheels for dry grinding of hardened steel. Due to a significantly reduced wheel surface area (down to 25%) that can be achieved by this method, grinding forces and workpiece burning in dry grinding were reduced. However, an increase in workpiece roughness and radial wheel wear were the consequence.
(a) Nd:YAG laser structured.
Research work by Mohamed et al. (2013) studied the influence of circumferential grooves on the creep feed grinding performance of vitrified alumina wheels at different wheel surface areas (100%, 70%, and 50%). The grooves were produced using a single-point diamond dresser. Depending on the reduction of wheel surface area, the consumed grinding power was reduced by 30–60% compared to a non-grooved wheel. Interestingly, besides an increase of workpiece roughness, no increase in wear rate was observed for the grooved wheels.
Aurich and Kirsch (2013) demonstrated a significant improvement of the coolant supply on electroplated CBN wheels by milling slot-shaped pockets into the base body of the grinding wheel.
Guo et al. (2014) reported on grinding of optical glass by means of laser structured coarse grain electroplated diamond wheels. A nanosecond pulsed laser at 355 nm wavelength was used to ablate 10–15-μm-wide circumferential grooves into a wheel with 150 μm grain size. A higher surface roughness but less subsurface defects in the ground glass was observed when grinding with the structured wheel.
- Aurich J, Braun O, Warnecke G, Cronj¨ager L (2003) Development of a superabrasive grinding wheel with defined grain structure using kinematic simulation. CIRP Ann Manuf Technol 52(1):275–280Google Scholar
- Aurich J, Herzenstiel P, Sudermann H, Magg T (2008) High-performance dry grind¬ing using a grinding wheel with a defined grain pattern. CIRP annals -Manufacturing. Technology 57(1):357–362Google Scholar
- deGraaff WT (1997). Grinding Wheel having dead end grooves and method for grinding therewith. US patent US5611724Google Scholar
- Fischbacher M, Noichl H (2001). Grinding wheel. US patent US6283845 B1Google Scholar
- Nakayama K, Takagi J, Abe T (1977) Grinding wheel with helical grooves-an attempt to improve the grinding performance. CIRP Ann Manuf Technol 25(1):133–138Google Scholar
- Rabiey M (2010) Dry grinding with CBN wheels, the effect of structuring. PhD thesis, University of StuttgartGoogle Scholar
- Sherk HE (1936). Slotted abrasive wheel. US patent US2049874Google Scholar
- VDI 3392, Part 1 (2007) Trueing and dressing of grinding wheels -profiling and sharpening. VDI-Gesellschaft Produktionstechnik (ADB)Google Scholar
- Walter C (2014) Conditioning of hybrid bonded CBN tools with short and ultrashort pulsed lasers. PhD thesis, ETH ZurichGoogle Scholar