Grinding Wheels

Grinding wheels are made up of thousands of minute abrasive grains that are bonded together. Every abrasive grain acts as a cutting edge.  The abrasive grains are made of very hard materials. The diamond grinding wheels features the hardest material known to man. The grain cuts a small chip to leave a smooth and perfect surface as it passes over the work piece. As each abrasive grain becomes dull, it breaks away from the bonding material to expose sharper grains.

The abrasive grains used for grinding wheels are differentiated between natural and manufactured. These days, the natural abrasives have largely been replaced by manufactured abrasives. The diamond tools are the last of the grinding wheels that use natural material. And even then, the natural diamonds are starting to get replaced by synthetic diamonds.

Manufactured abrasives are easier and more affordable to produce than natural abrasive materials that need to be mined and then processed. Manufactured abrasives also offer more consistent cutting quality due to the controlled conditions of the manufacturing process. The most widely used abrasives for grinding wheels are aluminum oxide, cubic boron nitride, diamond, and cubic boron nitride.

There are few remaining grinding wheels that use natural abrasives today. Most of these tools are able to subsist because of traditions. An example is in sword making wherein the inconsistency of natural abrasives give the blade a unique and attractive patterns.  

Graphite and Electrodes

Electrical discharge machining or EDM is a process used for cutting intricate shapes, cavities and contours in pre-hardened steel. There is no heat treatment required. Compared to other machining methods, EDM involves less processes as there is no need to soften and then re-harden the steel. One of the key components for EDM are the electrodes. Rapid recurring current discharges between two electrodes remove the material from the work piece.

There are different types of electrodes used for EDM. Graphite electrodes is one of the most widely used. There are several reasons why graphite is preferred by many. It is fast and easy to produce. It is also resistant to thermal shock. Thermal shock happens when different parts of an object to expand by different amounts. This differential expansion can causes stress on the material. At some point, this stress can exceed the strength of the material, causing a crack to form.

Graphite electrode does not melt. It goes directly from solid to gaseous state. Graphite removes material better than copper or copper-tungsten while wearing slower. The wear rate tends to diminish as the discharge increases, unlike copper, whose wear increases at higher currents. This makes graphite more suited for machining of large electrodes since working with a high current intensity provides decreased roughing time.

Although graphite is prone to abnormal discharge, this can be eliminated through quality flushing, and lowering the intensity of discharge during negative polarity machining. However, since graphite is a ceramic, it is sensitive to mechanical shock. It must be handled and machined with care.