Grinding (abrasive cutting)

Grinding Processes

• Grinding is a type of abrasive machining process that uses a grinding wheel as a cutting tool.
• It can produce very fine finishes and accurate dimensions.
• Grinding is better suited for machining very hard materials.
• It is usually used to take shallow cuts.
• Lapping and sanding are subsets of grinding.

Types of Grinding

• Creep-feed grinding (CFG) was invented in Germany in the late 1950s.
• CFG is used for high rates of material removal.
• It has a grinding depth of up to 6mm.
• Surfaces with a softer-grade resin bond are used for improved surface finish.
• CFG can remove 1 inch of material in 117 seconds.
• Cylindrical grinding is used to grind cylindrical surfaces and shoulders of the workpiece.
• The five types of cylindrical grinding are outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep feed grinding, and centerless grinding.
• Tolerances for cylindrical grinding are held within ±0.0005 inches for diameter and ±0.0001 inches for roundness.
• Surface finishes can range from 2 microinches to 125 microinches.
• Surface grinding uses a rotating abrasive wheel to create a flat surface.
• Tolerances achieved with grinding are ±2×10 inches for grinding a flat material and ±3×10 inches for a parallel surface.
• The surface grinder is composed of an abrasive wheel and a workholding device known as a chuck.
• Grinding is commonly used on cast iron and various types of steel.
• Materials like aluminum, stainless steel, brass, and plastics can also be ground with special techniques.
• Centerless grinding supports the workpiece with a blade instead of centers or chucks.
• Two wheels are used in centerless grinding.
• Electrochemical grinding erodes a positively charged workpiece with a negatively charged grinding wheel.
• Through-feed grinding, in-feed/plunge grinding, and internal centerless grinding are types of centerless grinding.
• Ultra-high speed grinding is still in the research and development stage.

Grinding Wheel

• Grinding wheel is an expendable wheel used for various grinding and abrasive machining operations.
• It is generally made from a matrix of coarse abrasive particles pressed and bonded together to form a solid, circular shape.
• Various profiles and cross sections are available depending on the intended usage for the wheel.
• Grinding wheels may also be made from a solid steel or aluminum disc with particles bonded to the surface.

Lubrication

• The use of fluids in a grinding process is often necessary to cool and lubricate the wheel and workpiece.
• Common grinding fluids include water-soluble chemical fluids, water-soluble oils, synthetic oils, and petroleum-based oils.
• The fluid needs to be applied directly to the cutting area to prevent it from being blown away due to the wheel's rapid rotation.
• The workpiece is manually clamped to a lathe dog, powered by the faceplate, that holds the piece in between two centers and rotates it.
• Special drive centers may be used to allow the edges of the workpiece to be ground.

Workpiece Materials and Geometry

• Typical workpiece materials include aluminum, brass, plastics, cast iron, mild steel, and stainless steel.
• Aluminum, brass, and plastics may have poor to fair machinability characteristics for cylindrical grinding.
• Cast iron and mild steel have very good characteristics for cylindrical grinding.
• Stainless steel is difficult to grind due to its toughness and ability to work harden, but it can be worked with the right grade of grinding wheels.
• The final shape of a workpiece is the mirror image of the grinding wheel used.
• Cylindrical wheels create cylindrical pieces, while formed wheels create formed pieces.
• Typical sizes of workpieces range from 0.75in to 20in in diameter and 0.80in to 75in in length.
• Pieces from 0.25in to 60in in diameter and 0.30in to 100in in length can also be ground.
• Resulting shapes can be straight cylinders, straight-edged conical shapes, or crankshafts for engines with low torque.

Effects of Grinding on Workpiece Materials

• Grinding can cause changes in the chemical, mechanical, and physical properties of the workpiece materials.
• High surface stress during grinding can increase the susceptibility to corrosion.
• Stresses put on the part during grinding can lead to the formation of a thin martensitic layer, reducing material strength.
• Ferromagnetic materials may lose their magnetic properties due to grinding.
• Overall, grinding can have significant effects on the properties of the workpiece materials.

Grinding (abrasive cutting) Data Sources