The basics of cutting by dividing

January 2011 - Even in high-tech shop environments with the latest production-enhancing equipment, technical workers should know the basic aspects of cutting materials. For instance, what happens when workers use a wedge as a cutting tool? 

It is important to understand material cutting from the standpoint of applied physics and its use on the shop floor. First, cutting is a production process in which the shape of a solid body is changed by overcoming the cohesive force of the material at a specific point.

Dividing and cutting is going to happen with or without chip forming. Dividing consists of severing individual parts of a work piece without chip formation. Examples include knife-edge cutting with pliers, chisel cutting in the vertical position and cutting with shears.

Wedge cutting

Chipping involves removing material particles (chips) mechanically by planing or filing with tools that have precisely shaped cutters or tools with grinding cutters that do not have a precise geometrical form. Common to all cutting tools is the wedge shape. The section through the wedge has the shape of a tapering triangle. The line of intersection of both lateral wedge surfaces is known as the cutting edge. The wedge surfaces enclose the wedge angle (β).

The force exerted on the cutting tool first acts at the cutting edge. When the force is large enough, the cohesion of the material will be overcome in the moment the cutting edge penetrates the work piece. The material of the work piece distributes some of its force in the direction of least resistance, and this results in the formation of a bulge on both sides of the cutting edge. 

When the wedge penetrates further, large lateral cutting forces develop, which widen the notch and lead to crack formation. The lateral forces lead to a sudden splitting of the material. Every process of cutting with tools is a process of notching and splitting!

Resolution of forces 

The forces F exerted on the wedge resolves into two lateral forces, F sub 1 and F sub 2, when the wedge penetrates the material. These cutting forces depend on the wedge angle. The narrower the wedge is, the greater the cutting forces.

The type of material that needs to be cut greatly influences the affect of the wedge. Individual metals, including mild steels, stainless steels, aluminum and copper alloys, have different crystalline grain structure and cohesion. Additionally, the material from which the cutting wedge is made can affect its cutting ability. Cutting wedges can be made from tool steel or hardened steel, and they can have different grades of hardening applied to them. Maintenance of the wedge also can affect its ability to cut. FFJ

Udo O.J. Huff is an independent consultant with project experience in machine building, welding engineering, training and development. He holds Master of Education and Bachelor of Science in Technology degrees from Bowling Green State University. Questions or comments? E-mail uhuff@sbcglobal.net.

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