CIRP Encyclopedia of Production Engineering

Living Edition
| Editors: The International Academy for Production Engineering, Sami Chatti, Tullio Tolio

Grinding Wheel

  • Jan C. AurichEmail author
  • Benjamin Kirsch
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-35950-7_6429-4

Keywords

Material Removal Rate Basic Body High Surface Roughness Synthetic Resin High Removal Rate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Synonyms

Definition

A grinding wheel is an axisymmetric tool, consisting of the basic body and the abrasive body. It is used for most grinding processes (surface grinding, cylindrical grinding, screw grinding, gear grinding, profile grinding, etc.) with very few exceptions (e.g., belt grinding or other special grinding processes).

Theory and Application

Introduction

In general, grinding wheels are distinguished in conventional and high-performance wheels. While conventional grinding wheels are completely made of abrasive body, high-performance grinding wheels consist of a basic body covered with an abrasive body. For both types, the abrasive body consists of the abrasive grains and the bond (See Fig. 1).
Fig. 1

High-performance grinding wheel and a close-up of an abrasive body

As indicated by their names, conventional grinding wheels are commonly used for conventional grinding processes with low material removal rates and grinding wheel speeds. High-performance grinding wheels are used with the primary goal to achieve high removal rates. High removal rates require high grinding wheel speeds which conventional grinding wheels cannot withstand. Because of the high grinding wheel speeds and material removal rates, the basic body has to provide high mechanical stability, good damping, and thermal conductivity. Materials used for the basic body of high-performance grinding wheels are:
  • Metal (aluminum, steel, bronze)

  • Synthetic resin (with metallic and nonmetallic filler)

  • Fiber-reinforced synthetic resin

  • Ceramics

Commonly, aluminum or steel is used for the basic body of high-performance grinding wheels. They provide sufficiently high mechanical stability and thermal conductivity, thereby overcompensating their poor damping.

The geometry of grinding wheels ranges from plain cylindrical to complex grooved profiles (DIN ISO 525 2015). The materials of the bond and the abrasive grains for both grinding wheel types will be outlined in detail below.

Bond

The bond is responsible for the retention of the abrasive grains until they are blunt. Blunt grains should ideally break out of the bond to allow subsequent sharp grains to participate in the material removal process. The bond has to provide room for chips and cooling lubricant (either by pores or by space between grains). There are three types of bond that are commonly used for grinding wheels:
  • Synthetic resin

  • Elastic

  • Ceramic

  • Metal (also galvanic)

The ideal bond would provide the following properties (Yegenoglu and Thurnbichler 1995):
  • Good dimensional stability

  • High toughness

  • Good thermal conductivity

  • Good damping

  • Good temperature stability

  • Potentiality to be profiled

None of the available bond types provides all these properties. Figure 2 shows the different types of bonds and their properties. While, for example, synthetic resin bond is easy to profile and provides good damping, its temperature stability is low, and it provides poor thermal conductivity. Wheels with metal bond possess excellent temperature stability and thermal conductivity but only low damping and are hard to profile, or, in the case of galvanic bond, they cannot be profiled at all.
Fig. 2

Properties of bond (Zitt 1999)

The bond is chosen depending on the intended application: the material to be removed, the required quality, and the grinding parameters (cutting speed, depth of cut, feed rate). Synthetic resin bond is commonly used for conventional grinding processes and is the most economical bond. Elastic includes bond like rubber, being a very soft bond. This is favorable for, e.g., polishing of gears. Ceramic bond is used for thermally critical processes and high removal rates. Its porosity can be adjusted, which offers the possibility to generate large pores for grinding fluid delivery and chip transport. The main advantage of metal bond compared to the aforementioned, specifically galvanic and brazed bonds, is their extreme high grain retention force. This enables material removal rates of 50–300 mm3/(mms) in industrial applications (Tawakoli 1990). Grinding wheels with metal bond provide high grain protrusion heights and do not need dressing, while conventional grinding wheels have to be dressed regularly.

Abrasive Grains

The abrasive grains are the cutting edges of the grinding wheel, embedded in the bond, that perform the actual material removal. They have to provide (Klocke and König 2005; Yegenoglu and Thurnbichler 1995):
  • High hardness and toughness

  • High thermal conductivity and thermal (alternating) resistance

  • High chemical resistance

The abrasive grains used for grinding wheels today are synthetic. Natural abrasives are rarely used because they provide low stability, except for diamond; natural diamonds of small size or with flaws are used for grinding wheels and dressing tools (Klocke and König 2005). Similar to the grinding wheel itself, the abrasive grains can be subdivided into:
  • Conventional abrasive grains (silicon carbide (SiC), aluminum oxide or corundum (Al2O3), sol-gel corundum)

  • High-performance abrasive grains (diamond, cubic boron nitride (cBN))

As indicated by their names, conventional abrasive grains are commonly used for conventional grinding wheels and high-performance abrasive grains for high-performance grinding wheels. This is due to the fact that diamond and cBN are much harder and much more wear resistant than conventional abrasive grains. The physical properties of the abrasive grains are depicted in Table 1.
Table 1

Physical properties of abrasives (Zitt 1999)

 

Al2O3

Sol-Gel

SiC

cBN

Diamond

Density (g/cm3)

3.96

3.87

3.15

3.48

3.52

Hardness (HK01)

1850–2000

1900–2400

2450–5000

4500–5000

5000–7000

Hardness (HV01)

2100

2500

6000

Not specified in reference

Modulus of elasticity (GPa)

400

400

680

890

Poisson’s ratio

0.20

0.17

0.17

0.20

Coefficient of friction

0.34

0.34

0.19

0.05–0.15

Melting point (°C)

2050

2300

2730

3700

Temperature stability (°C)

1750

2000

1500

1200

900

Coefficient of thermal expansion (10−6/K)

7.4 (<500 °C)7.5–8.5 (>500 °C)

4.7

3.6

0.8 (RT) 1.5–4.8 (>500 °C)

Thermal conductivity (W/mK)

30 (RT) 14 (400 °C)

30 (RT) 14 (400 °C)

110 (RT) 55 (600 °C)

200 (400 °C)

600–2000 (RT)

Heat capacity (J/gK)

1.08 (400 °C)

1.08 (400 °C)

1.1 (500 °C)

1.57 (400 °C)

6.19 (RT)

Besides the type of abrasive grains used for a grinding wheel, the grain size and grain concentration significantly influence the grinding process and the workpiece quality. Generally, higher grain sizes lead to a smaller grain concentration, resulting in increased surface roughness of the ground surface. This can be attributed to the higher undeformed chip thickness, because the same amount of material has to be removed by a smaller number of grains. Therefore, in ultra-precision grinding, very small grain sizes and high grain concentrations are applied to generate high surface finish.

When using a specific grain size, the grain concentration itself can be increased or decreased. Decreasing the grain concentration can bring advantages concerning the material removal behavior (Aurich et al. 2008; Tawakoli et al. 2007). This is realized by lowering the number of stochastically placed grains. For high-performance grinding wheels, this can also be realized by structuring the grinding wheel or by using defined grain patterns. A lower grain concentration when using a specific grain size leads to:
  • Higher chip space

  • Less number of rubbing and plowing grains

  • Higher undeformed chip thickness

  • Smaller grinding forces and power, resulting in smaller thermal loads of the ground workpiece

  • Higher grain wear, resulting in a higher grinding wheel wear

  • Higher surface roughness

The surface roughness of ground surfaces is also influenced by the sharpness of the grinding wheel, specifically the sharpness of the grains. Sharper grains lead to higher surface roughness. While blunt grains lead to a lower surface roughness, they also result in higher friction and hence in higher thermal impact of the workpiece. The sharpness of grinding wheels is influenced by the dressing conditions.

A coding system for conventional wheels specifies abrasive grain type, grain size, wheel grade (wheel grade specifies grain retention forces), grain spacing (grain concentration), and wheel bond. This coding is internationally normed in ISO 525. It helps to identify and select grinding wheels. The specification of grain sizes requires careful handling, as it differs much in dependence of the country of production (a comparison of grain size codings can be found in Marinescu et al. 2007). Similar coding is used for superabrasive wheels, as, e.g., defined by the American National Standards Institute (ANSI) (Marinescu et al. 2007). However, especially in the case of superabrasive grinding wheels, many manufacturers do not comply with this coding, hampering identification of grinding wheel properties.

Cross-References

References

  1. Aurich JC, Herzenstiel P, Sudermann H, Magg T (2008) High-performance dry grinding using a grinding wheel with a defined grain pattern. CIRP Ann Manuf Technol 57(1):357–362CrossRefGoogle Scholar
  2. DIN ISO 525 (2015) Schleifkörper aus gebundenem Schleifmittel-Allgemeine Anforderungen [Bonded Abrasive Products-General Requirements]. Beuth, BerlinGoogle Scholar
  3. Klocke F, König W (2005) Fertigungsverfahren 2: schleifen, honen, läppen. [Production Methods 2: Grinding, Honing, Lapping], 4th edn. Springer, Berlin (in German)Google Scholar
  4. Marinescu ID, Hitchiner M, Uhlmann E, Rowe WB, Inasaki I (2007) Handbook of machining with grinding wheels. CRC Press, Boca RatonGoogle Scholar
  5. Tawakoli T (1990) Hochleistungs-flachschleifen – technologie, verfahrensplanung und wirtschaftlicher einsatz [ High performance surface grinding – Technology, Process Design and economic application]. VDI Verlag, Düsseldorf (in German)Google Scholar
  6. Tawakoli T, Westkämper E, Rabiey M (2007) Dry grinding by special conditioning. Int J Adv Manuf Technol 33:419–424CrossRefGoogle Scholar
  7. Yegenoglu K, Thurnbichler M (1995) Hochleistungsschleifen: CBN-schleifscheiben als wichtige systemkomponenten beim hochleistungsschleifen [High Performance Grinding: CBN Grinding Wheels as important system components in high-efficiency grinding]. wt-produktion und management 85:517–522 (in German)Google Scholar
  8. Zitt UR (1999) Modellierung und Simulation von Hochleistungsschleifprozessen [Modelling and Simulation of High Performance Grinding]. FBK Produktionstechnische Berichte 34. Dissertation, TU Kaiserslautern (in German)Google Scholar

Copyright information

© CIRP 2016

Authors and Affiliations

  1. 1.FBK – Institute for Manufacturing Technology and Production SystemsUniversity of KaiserslauternKaiserslauternGermany

Section editors and affiliations

  • Konrad Wegener
    • 1
  1. 1.Institut für Werkzeugmaschinen und Fertigung (IWF)ETH ZürichZürichSwitzerland