Question 1

What is superfinishing?

Accepted Answer

Superfinishing will be necessary to remove surface finish peaks and provide a good hardness, structure and load-bearing surface of undisturbed base metal.

Parts that require superfinishing include roller bearings, shock absorber rods, sliding vane pumps, piston pins, crankshaft journals and cam lobes. In this process, a finishing stick oscillates rapidly with a very short stroke while the workpiece rotates. As the abrasive oscillates, the workpiece rotates or oscillates under a cup or cylinder, producing microfine chips. The process removes as little as 0.5 micron (0.00002 inch) or as much as 20 microns (0.008 inch) of material. Superfinishing is also known as microfinishing, polishing, short stroke honing or superhoning (but never just “honing,” which is a separate process).

Question 2

What is superabrasive machining?

Accepted Answer

Superabrasives are diamond or CBN (cubic boron nitride) grinding wheels or mounted points. These grind extremely hard materials, with CBN working on hard steels for precise profiles and finishes, and synthetic diamond working on hard nonferrous material like tungsten carbide and cermets. Superabrasives can be used for both roughing and surface finishing, depending on the grit size involved. The core material of the wheel also has a direct influence on its performance characteristics, and should be selected to meet operation requirements.

Question 3

What are the different grinding types?

Accepted Answer

Grinding operations come in many types, with this article covering six major types and several of the subtypes within, including:
Cylindrical grinding is a common type of grinding in which both the wheel and the workpiece rotate.
Surface grinding involves grinding a plane surface by feeding the workpiece beneath a rotating grinding wheel.
Centerless grinding creates cylindrical forms at extremely close tolerances.
Creep feed grinding is a slow, one-pass operation that makes a deep cut of up to one inch in steel materials at low table speeds between 0.5 and 1 ipm.
Snagging is a rough grinding application that removes unwanted metal with little consideration of surface finish.
Cut-off operations use an abrasive wheel as an alternative to the laser, abrasive water jet, metal saw, friction saw and oxyacetylene or plasma arc torch.

Question 4

How fast should I run a grinding wheel?

Accepted Answer

Although speeds for grinding wheels are measured in sfm or smm, wheels are often rated in rpm. It is important never to operate a grinding wheel over its rpm limit — most experts recommend never mounting a wheel on a machine that can exceed the wheel’s limit.

Question 5

What interactions take place in grinding?

Accepted Answer

In all forms of grinding, three different interactions occur between the abrasive and the machined material. Cutting occurs where the abrasive grain is sufficiently exposed to penetrate the workpiece material and curl a chip, and sufficient clearance exists between the grain, bond and workpiece to flush the chip with coolant or throw it away by wheel action. Plowing takes place when the grain is unable to get enough penetration to lift a chip, instead pushing the material ahead of the abrasive edge. Sliding happens when a lack of cut depth, insufficient clearance or a grit staying on the wheel after dulling results in rubbing or creating slide marks on the workpiece surface. Grinding process control balances these three interactions to achieve the desired parameters.

Question 6

What are the major commercial grinding processes?

Accepted Answer

These interactions feed into three major commercial grinding processes: rough grinding, precision grinding and ultra-precision grinding. Rough grinding maximizes the metal removed at the cost of surface finish. It primarily sees use in cutting off billets, grinding weld beads smooth and snagging gates and risers from castings. Precision grinding is a middle-ground between metal removal and part size control, and serves as the basis for creep feed grinding, slot grinding and high-efficiency deep grinding. In ultra-precision grinding, little to no actual cutting occurs, but sliding action from very fine grains rubs the workpiece surface to a high finish. Most surface finishing processes, such as lapping and polishing, are examples of this type of grinding.

Question 7

What determines a grinding wheel's structure?

Accepted Answer

Grinding wheels have two major components: the abrasive grains and the bond. The relative percentages of grain and bond, and their spacing on the wheel, determine the wheel’s structure.

Question 8

How do I dress or true a grinding wheel?

Accepted Answer

Conventional dressing wheels do truing and dressing simultaneously with a light cut, while superabrasives require truing with a tool or roll, and separate dressing with a vitrified dressing stick. Before truing a superabrasive wheel, use a wax crayon over the wheel face — the process should eliminate all crayon marks by the end. Dressing a superabrasive will require direct application of a vitrified dressing stick (often aluminum oxide or silicon carbide, but sometimes high-performance norbide or boron carbide).

Question 9

What is grinding?

Accepted Answer

Grinding is where a machine takes a rotating tool (usually a wheel) with abrasive grains and applies it to a workpiece’s surface to remove material. Each grain is its own miniature cutting tool, and as grains dull, they tear from the tool and make new, sharp grains prominent.

Machining 101:什么是Grinding

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