What is grinding? Where is it used?
Grinding is an abrasive machining operation that removes metal using a rotating grinding wheel installed on a suitable machine.
Under one or more of the following situations, abrasive machining procedures are used:
- The material to be cut is too difficult for other machining methods to handle.
- The required surface finish is superior to what can be produced using other approaches.
- The dimensional accuracy requirements for other operations are too demanding.
The factors to be considered for the selection of the grinding wheels.
The kind of abrasive, grain size, type of bond employed, grade or strength of the bond, and the structure or packing density of the wheel are all aspects of a grinding wheel that influence how it performs in a cutting operation.
Kind of abrasive
The abrasive for a grinding wheel is selected according to the workpiece material, the amount of stock to be removed, and the required surface polish and dimensional accuracy.
Diamond has significantly greater physical qualities for grinding than other abrasives, but its application is limited due to its exorbitant cost. It is used to grind difficult materials such as ceramics, cemented carbide, glass, and stone.
When working on steel, malleable iron, and other difficult and high-tensile strength materials, aluminum oxide outperforms silicon carbide in terms of attrition resistance.
For ordinary use grinding wheels, aluminum oxide with small impurities is utilized.
Silicon carbide wheels are appropriate for cast iron, non-ferrous metals, glass, stone, rubber, leather, and other low-toughness and tensile-strength materials.
They are employed in the grinding of hardened and difficult-to-grind steels.
Coarse grains may be utilized to make heavy cuts in soft materials, whereas fine-grained wheels are preferable for hard materials since they have more cutting blades in operation at the same time.
Fine grains leave minimal scratch traces and give a smoother surface finish in general.
Fine-grained wheels allow for wheel truing to thin portions and maintain form at comers.
Thread grinding is an example where fine-grained wheels are sought to preserve the form required for thread roots.
When grinding in limited regions of contact, fine-grained wheels are also desirable.
The choice of a bond to be used for a wheel depends upon
- Operating conditions of the grinding wheel
- Grinding speed
- Pressure on the wheel
- The heat generated in the grinding zone
- Conditions of cooling.
A grinding wheel’s grade defines the strength of its bond, or how tightly the grains of the wheel is kept together by its binding substance.
A wheel’s binding substance does not entirely fill the gap between its grains.
It just covers the grains, and the binding action at the areas of contact holds the grains together. This creates cavities in the wheel, making it porous.
These open regions give space for chips and aid in the transport of cutting fluid to the cutting area.
The density of the wheel, the number of points of contact between grains, the strength of these binding connections, and the quantity of the bond all influence the grade of the wheel.
The grade is classified as either soft or hard. The grains of a soft grinding wheel is more readily broken away than the granules of a hard wheel.
A grinding wheel that is too soft for the operation loses grains before they have completed its task. A wheel that is overly firm, on the other hand, tends to hold the grains even after they have dulled.
This increases the amount of electricity required for the cut as well as the amount of heat created.
A good wheel should be firm enough to hold the grains together until they dull, yet soft enough to release them afterward to show fresh sharp grains.
A wheel that is too soft wears down quickly, resulting in material and form loss.
An out-of-shape wheel necessitates truing, resulting in production downtime and further material waste.
The structure of a grinding wheel dictates how tightly the wheel’s grains are kept together.
The spaces between the abrasive grains and the connection reflect the relationship between them.
A wheel with an open construction has more voids and cuts cooler. In softer fabrics, it may be used to remove more material with deeper incisions.
A dense wheel has fewer voids and more cutting edges per unit area than a thin wheel. It is better for tougher materials since more grains will be operating at the same time.
A dense structure also aids in the production of smoother surfaces and the preservation of wheel form. Structure and grade are linked.
For a given bond, a dense wheel is harder than an open structured wheel.
It should be noted that a wheel being overly laden with chips indicates that it is excessively dense for the particular cut.
A grinding wheel may be required for high stock removal rates, machining in hard or soft materials, achieving near dimensional accuracy, achieving a good surface finish, or some combination of these.
No one wheel can perform all of these things well. A compromise for a general-purpose wheel or a particular wheel may be considered for a manufacturing application.
Roughing and finishing procedures may need the use of separate wheels.
Proper grinding wheel selection necessitates extensive knowledge, and it may be required to consult professionals for unique applications.
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