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Grinding (abrasive cutting)

technology Maturity 11-13 Next article →

Grinding is a specialized abrasive machining process used to shape and finish materials. It uses a grinding wheel as a cutting tool to remove material with great precision.

2 الحداد
2 الحداد

This process is essential in manufacturing because it can produce extremely fine surface finishes. It can also remove large volumes of metal quite rapidly in mass production settings. Grinding is particularly effective for machining very hard materials. Until recent decades, it was the only practical way to machine hardened steels. While it is a true metal-cutting process, many professionals categorize it separately from macroscopic cutting operations like milling or drilling.

The mechanism of grinding relies on microscopic action. A grinding wheel is made of a matrix of coarse abrasive particles bonded together.

Unbestimmte Schneide
Unbestimmte Schneide

Each individual grain acts as a microscopic single-point cutting edge. As the wheel rotates against a workpiece, these grains shear off tiny chips. These chips are analogous to the larger chips produced in conventional turning or milling. Because the cuts are so small, grinding is often used for very shallow tasks. For example, it can reduce a shaft's diameter by only half a thousandth of an inch, or 12.7 μm.

Different types of grinding are chosen based on the desired shape and production rate. Creep-feed grinding (CFG) was invented in Germany in the late 1950s by Edmund and Gerhard Lang. While normal grinding focuses on finishing surfaces, CFG is used for high rates of material removal. It can achieve a grinding depth of up to 6 mm. To keep temperatures low, CFG uses surfaces with a softer-grade resin bond. In the 1970s, continuous-dress creep-feed grinding (CDCF) was developed to keep the wheel sharp. This advancement increased productivity significantly, reducing removal time to just 17 seconds.

Machinists grinding workpieces on a bench grinder.
Machinists grinding workpieces on a bench grinder.

Other advanced methods include high-efficiency deep grinding (HEDG) and peel grinding. HEDG uses plated superabrasive wheels that do not require dressing. This process can remove material in 83 seconds and works well on long parts. Peel grinding was patented in 1985 by Erwin Junker Maschinenfabrik, GmbH in Nordrach, Germany. It uses a thin superabrasive disk that operates similarly to a lathe turning tool. There is also ultra-high speed grinding (UHSG), which can run at speeds higher than 40,000 fpm or 200 m/s. Currently, UHSG remains in the research and development stage.

Cylindrical grinding is used to shape the cylindrical surfaces and shoulders of a workpiece. The part is typically mounted on centers and rotated by a device called a lathe dog.

Centerless grinding schematic
Centerless grinding schematic

The abrasive wheel and the workpiece are rotated by separate motors at different speeds. There are five main types: outside diameter (OD) grinding, inside diameter (ID) grinding, plunge grinding, creep-feed grinding, and centerless grinding. Precision in this process is very high. Tolerances for diameter and roundness can reach as high as ±0.00001 inches. Surface finishes produced by these machines can range from 0.1 to 16 μm.

Surface grinding is another common method used to create flat surfaces. It utilizes a rotating abrasive wheel and a reciprocating table. The machine often includes a workholding device called a chuck, which can be electromagnetic or vacuum. This method is frequently used on cast iron and various types of steel. These materials are ideal because they can be held by magnetic chucks and do not melt into the wheel. Other materials like aluminum, brass, and plastics are harder to grind because they tend to clog the wheel. They require special techniques to prevent the wheel from becoming blocked.

Specialized technologies like electrochemical grinding and ELID grinding offer even more precision. In electrochemical grinding, a negatively-charged wheel erodes a positively-charged workpiece in a conductive fluid. This process actually dissolves the pieces of the workpiece into the fluid.

ELID Basic
ELID Basic

Electrolytic in-process dressing (ELID) grinding is an ultra-precision technology. It uses a metal-bonded wheel that is dressed electrochemically during the process. A nozzle injects an alkaline electrolyte into the gap between the wheel and an electrode. This maintains a gap of approximately 0.1 mm to 0.3 mm and keeps new sharp grits protruding.

Fitting and Turning students on a bench grinder at Tshwane South College, South Africa
Fitting and Turning students on a bench grinder at Tshwane South College, South Africa

Lubrication is a critical part of the grinding process to manage heat and debris. Fluids are applied directly to the cutting area to ensure they are not blown away by the rapid rotation.

Different materials require different fluids. For instance, cast iron often uses heavy-duty emulsifiable oil. Aluminum and brass typically use light-duty oils or waxes. The choice of fluid helps cool the wheel and the workpiece while removing the tiny chips produced during the cut. This ensures the machinery remains efficient and the parts remain accurate.

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🖼️ Images & Media (6)
File:2 الحداد.jpg
2 الحداد.jpg
File:Unbestimmte Schneide.svg
Unbestimmte Schneide.svg
File:Machinists grinding workpieces on a bench grinder..jpg
Machinists grinding workpieces on a bench...
File:Centerless grinding schematic.svg
Centerless grinding schematic.svg
File:ELID_Basic.JPG
ELID_Basic.JPG
File:Fitting and Turning students on a bench grinder at Tshwane South College, South Africa.jpg
Fitting and Turning students on a bench...
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