The article describes the effects of wear upon the axial profile of a grinding wheel in the axial cylindrical grinding processes. This mechanism was used to develop a grinding wheel with zone diversified structure made of microcrystalline sintered corundum abrasive grains and vitrifies bond. Such a grinding wheel is characterized by the conical rough grinding zone that is made by grains of a relatively large size, and a cylindrical finish grinding zone with grains of a smaller size and can be used in the single-pass grinding processes. Investigative tests conducted using newly-developed grinding wheels were described. Investigations were operated in the single-pass internal cylindrical grinding process of 100Cr6 steel. A comparison of results obtained using a zone diversified structure grinding wheel, with reference to a grinding wheel with grains of one size, were given. The analysis provides the roughness of the grinded surface, the grinding power, as well as chosen indicators of grinding efficiency. Experimental results obtained with use of a zone-diversified grinding wheel, built from relatively cheap grains of microcrystalline sintered corundum, showed that it is possible to obtain large material removal rate ^{3}/s and high quality of machined surface (

Grinding is a method of producing technical surfaces with great precision and fineness using tools made from thousands of little grains of a hard material (aloxite, silicon carbide) or a very hard material (diamond, cubic boron nitride), bonded appropriately [

Procedures for designing modernized grinding tools with specified types of modifications.

Of the many issues surrounding the decision-making processes in the area of technological developments, one is particularly important and concerns how to rationally manage or how to use owned resources to get the maximum effect

More specifically this task can be shown by writing: find the minimum grinding cost function

To solve this task, a system approach was used. It focuses on the investigation of optimal solutions through a logical analysis of the structure of the system. The next steps of this analysis are given in a concise form in Figure

To obtain the final result it was required to make significant changes in the analyzed operation system. These changes were written as a modification:

One of the possible ways to observe the wear of the axial profile of the grinding wheel is the formation of a conical zone. During the grinding, the grinding wheel cuts into the material of the workpiece with one of its front edges. The simple wear model assumes that there is a formation of diagonal wear in the attacking part. In reality, the shape is curvilinear (Figure

The effects of wear upon the axial profile of a grinding wheel [

There are two phases to the wear described. Firstly, in a short time, a slant is formed on the front part of the grinding wheel active surface (GWAS) along its entire width

The described wear of the grinding wheel mechanism causes the taking over of the main work of removing the allowance from the conic zone; however, the cylindrical zone removes the unevenness from the ground surface. This means that with the increase of wear of the grinding wheel, the smoothing area decreases, which has a negative effect on the quality of the workpiece surface.

Such a characteristic of the profile wear of the GWAS was used to work on a grinding wheel with a conic chamfer. Such grinding wheels are intentionally characterized by their chamfer with an adequately chosen angle

As already presented, the essence of single-pass grinding is the complete removal of machining allowance in one passing of the grinding wheel, whilst maintaining the desired quality of the surface of the workpiece [

In such processes grinding wheels with super-hard grains are mainly used, like Cubic Boron Nitride (CBN) grains. In addition, the methods of single-pass grinding with the use of conventional grinding wheels are also developed [

Single-pass grinding processes carried out using grinding wheels with conic chamfer.

In the first group of single-pass grinding processes (Peel grinding, High-Speed Peel grinding), CBN grinding wheels with conic chamfers are used. Such grinding wheels are narrow (usually a few millimeters) with a diameter of 300–400 mm. They are characterized by division into two basic zones: a rough grinding zone 2 to 5 mm wide and a finish machining zone 2 mm wide [

Grinding wheels with a zone-diversified structure [

Grinding wheel active surface load in the single-pass internal cylindrical grinding process (a) and microscopic images of chips produced in the rough grinding zone (b) and finish grinding zone (c) of the zonediversified structure grinding wheel [

In grinding wheels shaped in such a way, there is also a conic chamfer with an angle

An important influence on the grinding process is the wearing of the grinding wheel. The complete edge wear

Forms of the grinding wheel active surface edge wear occurring in the course of single-pass grinding using grinding wheels with a conic chamfer [

The parallel wear influences the shortening of the effective width of the finish grinding surface, which leads to the decreasing of the number of active grains, which in turn increases the roughness of the worked surface. The angular wear, however, causes the decrease of the angle of the conic chamfer which means the extension of the rough grinding zone. In such a case there is an increase in the number of active grains in the worked zone, which leads to the decrease of their individual load and decrease in the intensity of their wear [

Additional benefits of the exploitation of the grinding wheels may be provided by the use of different types of grains in the rough and finish grinding zones. In the rough grinding zone, these should be grains made from monocrystals or poly-crystals, with very sharp vertexes, mechanical resilience with good cutting ability, and the aptitude to self sharpen. In the finish grinding zone, however, the grains should have microcrystalline structure with large numbers of microvertexes which can carry out the process of microsparking out and smoothing machined surfaces [

Prototypes of such grinding wheels were mainly made with grains from cubic boron nitride (CBN), with ceramic binding. The progress of tests of the described processes and the optimization of the structure of the grinding wheel has allowed for the replacing of CBN grains with much cheaper grains of microcrystalline sintered corundum SG [

The carrying out of a wide range of simulation research tests helped determine the most beneficial conditions for implementing the processes of single-pass internal cylindrical grinding with new grinding wheels. The structure of the zone-diversified grinding wheel was also optimized taking into account the type and size of the abrasive grains in each of the zones, the whole height of the grinding wheel

Presented below are the test results of the influence of depth of grinding

In tests a zone-diversified grinding wheel was used with the most beneficial characteristics (marked 46/80–30%)—Figure

Grinding wheel with zone-diversified structure made of microcrystalline sintered corundum abrasive grains SG size 46 and 80: (a) construction scheme of grinding wheel with zone-diversified structure; (b) construction scheme of reference grinding wheel built of SG grains size 46; (c) microscopic view of SG grains size 46; (d) microscopic view of SG grains size 80; (e) microscopic view of the GWAS in conical zone of rough grinding; (f) microscopic view of the GWAS in cylindrical zone of finish grinding; (g) microgeometric axial profile of the grinding wheel active surface with an exposed conic chamfer.

In these grinding wheels, a special glass-crystalline bond was used. It distinguishes itself by the mechanism of the fatigue cracking of binder bridges, which is comparable to the fatigue crumble of microcrystalline vertexes of SG abrasive grains because these are materials of similar brittleness [

In Tables

Breakdown of mathematical models describing the changes in the surface roughness of a workpiece

Breakdown of mathematical models describing the grinding power gain

The differences in the obtained values of the arithmetic average deviation of the roughness of the surface workpiece

Along with the rise of material removal rate, the differences in achieving a roughness of the workpiece surface visibly declined. Along with the increase of

Comparing the results of the grinding power gain

Comparison of changes in the arithmetic mean roughness

Microscopic view of the GWAS after grinding: (a) wear land of SG abrasive grain; (b) smear of workpiece chips on the abrasive grain vertex; (c) crack of the vitrified bond bridge; (d) spherical chips of machined material on the abrasive grain vertex.

Experimental tests allowed the capture of a series of microscopic images of the GWAS after grinding (Figure

A relatively large load in the rough grinding zone of the GWAS locally caused fatigue wear and cracking of vitrified bond bridges (Figure

In addition, the efficiency of the implementation of the described process with the two subject grinding wheels was tested. Among the many grinding judgement criteria described in the literature, four basic indicators were selected:

quality indicator:

indicator of the course of grinding:

grinding power

appropriate grinding power

synthetic indicator:

The stated indicators include, in the most, normalized criteria (

Percentage value breakdown of the grinding performance evaluation criteria for grinding wheels with the best results (46/80–30%) with regard to grinding wheel 46–100% is presented in Figure

Percentage value setting up of the grinding efficiency evaluation criteria for a grinding wheel of zone-diversified structure (46/80–30%) with reference to a 46–100% grinding wheel.

This means that the processes used in single-pass internal cylindrical grinding with grinding wheels with a zone-diversified structure allowed for the significant increase in efficiency of the process through the decrease of the roughness of the surface of the machined workpiece and the increase of the waste effectiveness.

During the grinding process, many of the wear processes affect the GWAS, such as abrasive wear, adhesive wear, thermal wear and fatigue wear. All these phenomena occur at the microscale of contacts between the components of the GWAS (abrasive grains, bond) and the machined material. Their intensity depends primarily on the grinding parameters. In the case of single-pass grinding, it depends on machining allowance

A naturally formed axial profile of the grinding wheel was the basis for the development of a grinding wheel with conic chamfer. The developments of this concept lead to the creation of a grinding wheel with a zone-diversified structure. In such tools, it is necessary to optimize the type and size of the abrasive grains in each zone as well as the whole height of the grinding wheel

The use of such grinding wheels built from relatively cheap grains of microcrystalline sintered corundum SG allowed for the achievement of effective grinding at the level ^{3}/s. At the same time, beneficial values of parameters describing the roughness of the worked surfaces were attained, which depending on the process parameters changed in the range:

The tests carried out pointed to the significant increase in the efficiency of the process of single-pass internal cylindrical grinding achieved by the use of grinding wheels with a zone-diversified structure, in relation to grinding wheels entirely constructed from grains of one size.

Grinding wheel active surface

Working engagement, mm

Efficient working engagement, mm

Total working engagement, mm

Feed engagement, mm

Conic chamfer breadth, mm

Grinding wheel diameter, mm

Workpiece diameter, mm

Grinding wheel outside diameter, mm

Grinding wheel inside diameter, mm

Synthetic indicator of the grinding efficiency, mm^{2}/W·s

Grinding wheel rotational frequency, rpm

Workpiece rotational frequency, rpm

Cutting (grinding) power, W

Proper cutting power, W·s/mm^{3}

Speed ratio (

Coolant flow rate, L/min

Material removal rate, mm^{3}/s

Effective proper material removal rate, mm^{2}/s

Multidimensional correlated coefficient of mathematical model

Arithmetic mean deviation of the assessed profile,

Maximum height of the profile within a sampling length,

Shape of the grinding wheel active surface in axial direction after grinding time

Grinding time, s

Grinding wheel total height in axial direction, mm

Grinding wheel rough grinding zone height in axial direction, mm

Grinding wheel finish grinding zone height in axial direction, mm

Axial table feed speed, mm/s

Grinding wheel peripheral speed, m/s

Workpiece peripheral speed, m/s

Conic chamfer angle,°

Final conic chamfer angle,°

Initial conic chamfer angle,°

Conic chamfer parallel wear, mm

Conic chamfer total wear, mm

Conic chamfer angular wear,°

Increase of grinding wheel spindle current power, W.