Abrasive machining is a material removal process that involves the use of abrasive cutting tools. There are three principle types of abrasive cutting tools according to the degree to which abrasive grains are constrained.

• Bonded abrasive tools: Abrasive grains are closely packed into different shapes, the most common is the abrasive wheel. Grain are held together by bonding material. Abrasive machining process that use bonded abrasive includes grinding, honing, super finishing.

• Coated abrasive tools: Abrasive grains are glued onto a flexible cloth, paper or resin backing. Coated abrasive are available in sheets, rolls, endless belts. Process include abrasive belt grinding, abrasive wire cutting.

• Free abrasive: Abrasive grains are not bonded or glued. Instead, they are introduced either in oil-based fluids or in water or air, or contained in semisoft binder (buffing).

Regardless the form of the abrasive tool and machining operation considered, all abrasive operations can be considered as material removal process with geometrically undefined cutting edges.

Abrasive machining can be likened to the other machining operations with multipoint cutting tools. Each abrasive grain acts like a small single cutting tool with undefined geometry but usually with high negative rake angle.

Abrasive machining involves a number of operations, used to achieve ultimate dimensional precision and surface finish. From the principal abrasive operations, grinding is covered in the present section, and some other operations are discussed in the next sections.

Grinding is a material removal process in which abrasive particles arc contained in a bonded grinding wheel that operates at very high surface speeds. The grinding wheel is usually disk shaped and is precisely for high rotational speeds.

Cutting conditions in grinding

The cutting velocity V in grinding is very high. It is related to the rotational speed of the wheel by.

V = p DN

Where D is the wheel diameter and N is the rotational speed of the grinding wheel. Depth of cut D is called infeed and is defined as the distance between the machined and work surfaces. As the operation proceeds, the grinding wheel is fed laterally across the work surface on each pass by the work part. The distance at which the wheel is fed is called a cross feed. The cross feed is actually the width of cut w.

The crossfeed multiplied by infeed determines the cross sectional area of cut, CSA:

CSA = crossfeed × infeed = wd The cross sectional area in grinding is relatively small compared to other traditional machining operations. The workpart moves past the wheel at a certain linear or rotational velocity called a feed Vw. The material removal rate, mrr is defined by mrr = VwCSA

Wheel Wear Three mechanisms are recognized as the principal causes of wear in grinding wheels:

• Grain fracture

• Attritious wear and,

• Bond fracture

Risk Management

In abrasive manufacturing, considerable amount of dust is generated. These are removed by a dust extraction system and ESP's (Electro Static Precipitators) are provided to dissipate the dust and facilitate the removal of dust. Most of the dust that is removed are non combustible abrasive dust, but the same is sometimes combined with combustible dust also. These can cause dust explosions.

To mitigate dust explosions, proper study of the dust chemistry and properties is required. Some of the properties that need close study include, dust composition, dust particle size, moisture content, dust concentration, oxygen content, temperature, pressure, dust turbulence etc. A detailed analysis of the dust explosion scenario is suggested and suitable preventive action taken.

Important

The information set out in this document constitutes a set of general guidelines and should not be construed or relied upon as specialist advice. Independent legal advice should always be sought. Therefore Risktechnik accepts no responsibility towards any person relying upon these Risk Management Guides nor any liability whatsoever for the accuracy of data supplied by another party or the consequences of reliance upon it.