Grinding vs Machining: What’s the difference?
The primary purpose of any metal fabrication process is to remove excess material from the workpiece in order to get the desired object and surface finishing.
Machining processes such as cutting, drilling, turning, and milling provide high surface finish, dimensional accuracy, and close tolerance. Machining processes are used for bulk stock removal with a high MRR (material removal rate).
There is one more process of material removal that can be performed to increase the surface finish as well as dimensional accuracy. Surface finishing methods mainly include grinding, lapping, and honing. The grinding process has a low material removal rate (MRR) but high accuracy, and high finish.
Machining or the metal cutting processes shear the object using a sharp edge cutting tool. The geometry of this cutting tool is well-defined. The cutting tools used in machining processes are made from carbon, steel, CBN (Cubic boron nitride), and diamond.
The grinding process uses a circular wheel also known as a grinding wheel, made up of sharp abrasive grains. The abrasive grains bonded on the wheel with special adhesives. Grinding wheels remove material from the surface in the form of chips.
Important similarities and differences between grinding and machining are given below.
Similarities Between Grinding and Machining
- The principles of the subtractive manufacturing process are used in both grinding and machining processes (subtractive manufacturing involves the removal of material while the additive manufacturing process adds layer by layer to form a 3-D structure).
- In both processes, the cutting tool or a cutter is required for material removal.
- Material is removed in the form of solid chips in both processes.
- In both processes, excessive materials are removed in a specific order.
- Shearing is used in both processes to remove excess material (grinding involves ploughing and rubbing but they do not remove material).
- Traditional machining and grinding use mechanical energy to remove material. (non-traditional machining or NTM processes use electrical, mechanical, thermal, and chemical to remove material).
Read: Types of grinding Wheels
Differences Between Grinding and Machining
Grinding and machining both processes involve shearing and removal of excess material from the workpiece in chips form. On the basis of some important factors, below are the main differences between grinding and machining:
|
Factors |
Grinding |
Machining |
|
(Material Removal Rate) MRR Rate |
Grinding is a type of surface finishing method. It has a low MRR. |
Machining is a bulk stock removal process so has a high MRR. |
|
Tolerance & Dimensional Accuracy |
Grinding provides better dimensional accuracy and close tolerance. |
Machining tolerance and dimensional accuracy are low. |
|
Tool/Product Materials |
Grinding process needs a grinding wheel to remove material. The grinding wheels are made of sharp abrasive grains (ceramic, alumina, zirconia, silica, etc.) |
Machining process requires a cutting tool (sharp edge cutter) to remove material. This cutting tool is made of hard metal, ceramic, and diamond. |
|
Product Specification |
Abrasives have random geometry (means not well-defined or specific directions, orientation plan, the radius of nose, and edges). |
Cutting tools have pre-defined geometry (means well-defined directions, orientation plan, the radius of nose, and edges). |
|
Rake Angle |
In grinding rake angle may vary from +75° to -75° |
In machining rake angle varies from +15° to –15° |
|
Clearance Angle |
Clearance angles can be zero or negative. |
The clearance angle of the cutting tool cannot be zero or negative (usually varies from +3° to +15°). |
|
Participation Ratio |
Only 1% abrasive of the wheel participates in cutting action. |
Each cutting edge of the tool takes participates in cutting action. |
|
Shearing Process |
Grinding involves shearing, ploughing, rubbing, and scratching during the process. |
Machining mainly involves shearing during the process. |
|
Specific Energy Consumption (power required per unit MRR) |
Specific energy consumption is high (because rubbing, ploughing, scratching cause a high loss of energy. |
Specific energy consumption is low. |
|
Heat Generation |
Grinding causes high heat generation. Grinding heat passes from the surface to inside the material and can cause thermal damage. |
Cutting causes low heat generation. While machining only a few portions of heat passes from the surface to the inside of the material and the rest is carried away by chips. |
|
Material Hardness |
Cutting material toughness, hardness, and ductility do not affect the grinding efficiency. |
Materials hardness and ductility directly affect the cutting rate. |
Read: Types of Metal Cutting Tools