Grinding wheel wear

Last updated November 07, 2023

Grinding wheel wear is an important measured factor of grinding in the manufacturing process of engineered parts and tools. Grinding involves the removal process of material and modifying the surface of a workpiece to some desired finish which might otherwise be unachievable through conventional machining processes.^[1] The grinding process itself has been compared to machining operations which employ multipoint cutting tools. The abrasive grains which make up the entire geometry of wheel act as independent small cutting tools. The quality, characteristics, and rate of grinding wheel wear can be affected by contributions of the characteristics of the material of the workpiece, the temperature increase of the workpiece, and the rate of wear of the grinding wheel itself. Moderate wear rate allows for more consistent material size. Maintaining stable grinding forces is preferred rather than high wheel wear rate which can decrease the effectiveness of material removal from the workpiece.^[2]

Mechanisms of wheel wear

Industrial Grinding Gear GrindingWheel.jpg — Industrial Grinding Gear

A common attributing factor to wheel wear is grain fracture, which can be an advantage. A portion of each of the individual grains on the wheel surface breaks apart and leaves the remaining grain bonded to the wheel. The fractured grain is left with newly exposed sharp edges which attribute the self-sharpening characteristic of grinding wheels and cutting tools in general. Attritious wear or progressive wear which is typically undesirable^[3] leads to the grains dulling by developing flat spots and rounded edges on the wheel which can deteriorate the wheel’s ability to remove material. Flat spots also can lead to excessive heat generation with the added surface contact which in turn enables bond fracture, or the brittle fracture of the adhesive bonds between the grains. The removal of these worn grains from the adhesive bonds restores the wheel’s cutting ability once more.^[4] Grinding wheels can also be characterized by the grains’ increased capacity to fracture according to a level of higher value of friability . Different bonding materials are used depending on the intended use of the grinding wheel. The bonding material is classified by its individual strength called its wheel grade.^[5]

Grinding forces

Grinding Wheel Wear Curve: Diameter of wear (mm) as a function of time (td), Three stages of grinding, and dressing/tool life determined in stage II (Td). DresserWear1.jpg — Grinding Wheel Wear Curve: Diameter of wear (mm) as a function of time (td), Three stages of grinding, and dressing/tool life determined in stage II (Td).

The longevity and cutting ability of a grinding wheel can be affected by the grinding forces generated while in use. Experimental investigation has revealed a direct relationship between cutting speed, wheel geometry, chip geometry, and the grinding forces namely the resultant normal force component (F_n ), the tangential force component (F_t ), and their ratio when in contact with a workpiece.^[3]

Stage I: As a workpiece enters the grinding zone the initial contact forces are unstable and rise abruptly short period of time and a small wear spot is formed. The overall performance of a wheel during this moment of unstable rising forces can be minimized with proper dressing conditions prior to use and can help effect the high peak and steady state forces which should normally be contained within a short period of time.

Stage II: During the steady state wear stage reaction forces are constant and the flow of heat generation in both the work piece and wheel remain in equilibrium. The measurable data in this stage presents itself as a linear rate of wear as a function of the working duration of the dresser application or tool life (T_d).^[6] The tool life corresponds to the grinding wheels ability to maintain the initial shape give to it during the dressing prior to use. As the workpiece stays full contact with the grinding zone in the steady state of constant forces the flow of heat generation in the work piece and the wheel maintains equilibrium. This phase usually does not produce temperatures that would coincide with bond fracture however the material properties of the bond strength can determine the maximum applied force the wheel grit can sustain prior to fracture.^[3]

Stage III: Wear rates on the workpiece become detrimental while the rate of change in reaction forces decreases. The end of tool-life represent the initial dressing condition are no longer effective. The rate of change of forces generated in this stage are minimal and wear on the workpiece as an exponential tendency.^[7]

Effects of cutting temperature

The lifespan of the grinding wheel and final surface properties of the workpiece are directly affected by the operating cutting temperature. Heat generated during grinding penetrates the grinding wheel and the workpiece which can cause dimensional errors due to thermal expansion ^[4]

Several adverse effects of a high cutting temperature are as follows:

The addition of grinding fluids can effectively control cutting temperatures to reduce heat induced surface effects on the wheel and workpiece.^[4]

High heat flux density may result in the grinding wheel melting and consequently, increased wear. The heat flux (Φ) penetrating the grinding wheel and workpiece depends mainly on the cutting speed (v_s) and cutting force (F_c). The temperature of the grinding wheel is related to the density of heat flux (φ = dΦ/dA) generated (which also is directly proportional to the feed rate).^[8] An approximate value of the heat flux can be calculated as follows: Φ = F_c • v_s

Grinding wheel types

Grinding wheels can be made with a variety of materials depending on the desired abrasive quality required during use. Abrasive material, natural of synthetic, used in grinding include some common types of grinding wheel geometry.^[9]

Straight
Cylinder
Straight Cup
A variety of material types

Abrasive grains

The process of grinding requires an abrasive component with material properties harder than the workpiece. Most common grinders employ a rotating surface being brought in contact with a work surface. The wheel component of grinder itself is generally composed of abrasive grains held together by a bond structure which contain some amount of porosity.^[9]

Wheel speed

The grinding wheel typically operates at high rotational speeds.^[4] The wheel speed depends on several factors, some of which included the grindability of the wheel, the shape of the part, and the material of the workpiece. These properties will affect important parameters such as the surface finish, surface integrity, and wheel wear.^[1] Likewise, the grinding wheel speed will depend on which abrasive process is needed and which finishing process is desired.

Dressing

A worn grinding wheel can be dressed to restore its grinding properties. Dressing a grinding wheel causes new grains to be produced on a glazed or loaded grinding wheel. A glazed grinding wheel is the result of high attritious wear causing the grains to become dull. A loaded grinding wheel is a result of chips clogging the grains on the grinding wheel due to the grinding of soft materials, improper grinding wheel selection processing parameters. In addition to sharpening a grinding wheel dressing can also be used to true a grinding wheel that is out of round or to shape the profile of a grinding wheel to produce specific features on the workpiece.

Related Research Articles

Metalworking is the process of shaping and reshaping metals to create useful objects, parts, assemblies, and large scale structures. As a term it covers a wide and diverse range of processes, skills, and tools for producing objects on every scale: from huge ships, buildings, and bridges down to precise engine parts and delicate jewelry.

An abrasive is a material, often a mineral, that is used to shape or finish a workpiece through rubbing which leads to part of the workpiece being worn away by friction. While finishing a material often means polishing it to gain a smooth, reflective surface, the process can also involve roughening as in satin, matte or beaded finishes. In short, the ceramics which are used to cut, grind and polish other softer materials are known as abrasives.

<span class="mw-page-title-main">Grinding machine</span> Machine tool used for grinding

A grinding machine, often shortened to grinder, is a power tool used for grinding. It is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation.

<span class="mw-page-title-main">Bench grinder</span> Grinding machine

A bench grinder is a benchtop type of grinding machine used to drive abrasive wheels. A pedestal grinder is a similar or larger version of grinder that is mounted on a pedestal, which may be bolted to the floor or may sit on rubber feet. These types of grinders are commonly used to hand grind various cutting tools and perform other rough grinding.

Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and for working extremely hard materials, or materials that are difficult to machine using conventional methods. Its use is limited to electrically conductive materials. ECM can cut small or odd-shaped angles, intricate contours or cavities in hard and exotic metals, such as titanium aluminides, Inconel, Waspaloy, and high nickel, cobalt, and rhenium alloys. Both external and internal geometries can be machined.

Grinding wheels are wheels that contain abrasive compounds for grinding and abrasive machining operations. Such wheels are also used in grinding machines.

A grinding dresser or wheel dresser is a tool to dress the surface of a grinding wheel. Grinding dressers are used to return a wheel to its original round shape, to expose fresh grains for renewed cutting action, or to make a different profile on the wheel's edge. Utilizing pre-determined dressing parameters will allow the wheel to be conditioned for optimum grinding performance while truing and restoring the form simultaneously.

<span class="mw-page-title-main">End mill</span> Milling cutter designed to cut axially

An end mill is a type of milling cutter, a cutting tool used in industrial milling applications. It is distinguished from the drill bit in its application, geometry, and manufacture. While a drill bit can only cut in the axial direction, most milling bits can cut in the radial direction. Not all mills can cut axially; those designed to cut axially are known as end mills.

In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The majority of these tools are designed exclusively for metals.

Superfinishing, also known as micromachining, microfinishing, and short-stroke honing, is a metalworking process that improves surface finish and workpiece geometry. This is achieved by removing just the thin amorphous surface layer left by the last process with an abrasive stone or tape; this layer is usually about 1 μm in magnitude. Superfinishing, unlike polishing which produces a mirror finish, creates a cross-hatch pattern on the workpiece.

In machining, tool wear is the gradual failure of cutting tools due to regular operation. Tools affected include tipped tools, tool bits, and drill bits that are used with machine tools.

A diamond tool is a cutting tool with diamond grains fixed on the functional parts of the tool via a bonding material or another method. As diamond is a superhard material, diamond tools have many advantages as compared with tools made with common abrasives such as corundum and silicon carbide.

Abrasive machining is a machining process where material is removed from a workpiece using a multitude of small abrasive particles. Common examples include grinding, honing, and polishing. Abrasive processes are usually expensive, but capable of tighter tolerances and better surface finish than other machining processes

Ultrasonic machining is a subtractive manufacturing process that removes material from the surface of a part through high frequency, low amplitude vibrations of a tool against the material surface in the presence of fine abrasive particles. The tool travels vertically or orthogonal to the surface of the part at amplitudes of 0.05 to 0.125 mm. The fine abrasive grains are mixed with water to form a slurry that is distributed across the part and the tip of the tool. Typical grain sizes of the abrasive material range from 100 to 1000, where smaller grains produce smoother surface finishes.

Grinding is a type of abrasive machining process which uses a grinding wheel as cutting tool.

Honing is an abrasive machining process that produces a precision surface on a metal workpiece by scrubbing an abrasive grinding stone or grinding wheel against it along a controlled path. Honing is primarily used to improve the geometric form of a surface, but can also improve the surface finish.

Burnishing is the plastic deformation of a surface due to sliding contact with another object. It smooths the surface and makes it shinier. Burnishing may occur on any sliding surface if the contact stress locally exceeds the yield strength of the material. The phenomenon can occur both unintentionally as a failure mode, and intentionally as part of a metalworking or manufacturing process. It is a squeezing operation under cold working.

Electrochemical grinding is a process that removes electrically conductive material by grinding with a negatively charged abrasive grinding wheel, an electrolyte fluid, and a positively charged workpiece. Materials removed from the workpiece stay in the electrolyte fluid. Electrochemical grinding is similar to electrochemical machining but uses a wheel instead of a tool shaped like the contour of the workpiece.

Surface grinding is done on flat surfaces to produce a smooth finish.

Flat honing is a metalworking grinding process used to provide high quality flat surfaces. It combines the speed of grinding or honing with the precision of lapping. It has also been known under the terms high speed lapping and high precision grinding.

References

1 2 Schmid, Serope Kalpakjian, Steven (2007). Manufacturing processes for engineering materials (5th ed.). Harlow: Prentice Hall. pp. chapter 9. ISBN 978-0132272711.{{cite book}}: CS1 maint: multiple names: authors list (link)
↑ Rowe, W. Brian (2009). Principles of modern grinding technology (1st ed.). Norwich, NY: William Andrew. ISBN 0815520182.
1 2 3 Mark J. Jackson; J. Paulo Davim, eds. (2011). Machining with abrasives (1st ed.). New York: Springer. pp. 47–51. ISBN 978-1441973016.
1 2 3 4 Marinov, Valery (2012). Manufacturing Process Design (2nd ed.). Kendall Hunt Pub Co. ISBN 1465202560.
↑ Groover, Mikell P. (2010). Fundamentals of modern manufacturing : materials, processes, and systems (PDF) (4th ed.). Hoboken, NJ: J. Wiley & Sons. p. 613. ISBN 978-0470467008 . Retrieved 17 February 2016.
↑ al.], Ioan D. Marinescu ... [et (2012). Tribology of abrasive machining processes (2nd ed.). Norwich, N.Y.: William Andrew. pp. 356–359. ISBN 978-1437734676.
↑ Ioan D. Marinescu; et al. (2012). Tribology of abrasive machining processes (2nd ed.). Norwich, N.Y.: William Andrew. pp. 356–359. ISBN 978-1437734676.
↑ Kaczmarek, Jozef (2008). "The effect of abrasive cutting on the temperature of grinding wheel and its relative efficiency". Archives of Civil and Mechanical Engineering.
1 2 Fundamentals of Modern Manufacturing : Materials, Processes, and Systems (PDF). Wiley & Sons Canada, Limited, John. 2012. pp. 604–624. ISBN 978-1118393673 . Retrieved 13 February 2016.

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[:5-1] 1 2 Schmid, Serope Kalpakjian, Steven (2007). Manufacturing processes for engineering materials (5th ed.). Harlow: Prentice Hall. pp. chapter 9. ISBN 978-0132272711.{{cite book}}: CS1 maint: multiple names: authors list (link)

[2] Rowe, W. Brian (2009). Principles of modern grinding technology (1st ed.). Norwich, NY: William Andrew. ISBN 0815520182.

[:1-3] 1 2 3 Mark J. Jackson; J. Paulo Davim, eds. (2011). Machining with abrasives (1st ed.). New York: Springer. pp. 47–51. ISBN 978-1441973016.

[:3-4] 1 2 3 4 Marinov, Valery (2012). Manufacturing Process Design (2nd ed.). Kendall Hunt Pub Co. ISBN 1465202560.

[5] Groover, Mikell P. (2010). Fundamentals of modern manufacturing : materials, processes, and systems (PDF) (4th ed.). Hoboken, NJ: J. Wiley & Sons. p. 613. ISBN 978-0470467008 . Retrieved 17 February 2016.

[:2-6] .], Ioan D. Marinescu ... [et (2012). Tribology of abrasive machining processes (2nd ed.). Norwich, N.Y.: William Andrew. pp. 356–359. ISBN 978-1437734676.

[:6-7] Ioan D. Marinescu; et al. (2012). Tribology of abrasive machining processes (2nd ed.). Norwich, N.Y.: William Andrew. pp. 356–359. ISBN 978-1437734676.

[:4-8] Kaczmarek, Jozef (2008). "The effect of abrasive cutting on the temperature of grinding wheel and its relative efficiency". Archives of Civil and Mechanical Engineering.

[:0-9] 1 2 Fundamentals of Modern Manufacturing : Materials, Processes, and Systems (PDF). Wiley & Sons Canada, Limited, John. 2012. pp. 604–624. ISBN 978-1118393673 . Retrieved 13 February 2016.

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