Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a ...

. Implements commonly used for cutting are the

knife A knife ( : knives; from Old Norse 'knife, dirk') is a tool or weapon with a cutting edge or blade, usually attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evid ...

and saw, or in medicine and science the

scalpel A scalpel, lancet, or bistoury is a small and extremely sharp bladed instrument used for surgery, anatomical dissection, podiatry and various arts and crafts (either called a hobby knife or an X-acto knife.). Scalpels may be single-use dispos ...

and

microtome A microtome (from the Greek ''mikros'', meaning "small", and ''temnein'', meaning "to cut") is a cutting tool used to produce extremely thin slices of material known as ''sections''. Important in science, microtomes are used in microscopy, all ...

. However, any sufficiently sharp object is capable of cutting if it has a

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to localized plastic deformation induced by either mechanical indentation or abrasion. In general, different materials differ in their hardness; for example hard ...

sufficiently larger than the object being cut, and if it is applied with sufficient force. Even liquids can be used to cut things when applied with sufficient force (see water jet cutter). Cutting is a

compressive In continuum mechanics, stress is a physical quantity. It is a quantity that describes the magnitude of forces that cause deformation. Stress is defined as ''force per unit area''. When an object is pulled apart by a force it will cause elonga ...

and

shearing Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (a sheep may be said to have been "shorn" o ...

phenomenon, and occurs only when the total

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

generated by the cutting implement exceeds the ultimate strength of the material of the object being cut. The simplest applicable equation is:

\text =

\tau=\frac

The stress generated by a cutting implement is directly proportional to the force with which it is applied, and inversely proportional to the area of contact. Hence, the smaller the area (i.e., the sharper the cutting implement), the less force is needed to cut something. It is generally seen that cutting edges are thinner for cutting soft materials and thicker for harder materials. This progression is seen from

kitchen knife A kitchen knife is any knife that is intended to be used in food preparation. While much of this work can be accomplished with a few general-purpose knives – notably a large chef's knife, a tough cleaver, a small paring knife and some sort of ...

, to cleaver, to axe, and is a balance between the easy cutting action of a thin blade vs strength and edge durability of a thicker blade.

Metal cutting

Cutting has been at the core of manufacturing throughout history. For metals many methods are used and can be grouped by the physical phenomenon used. It is the process of producing a work piece by removing unwanted material from a block of metal, in the form of chips. * Chip forming (material removal processes) – sawing,

drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ...

, milling,

turning Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates. Usually the term "turning" is reserved for the generation ...

etc. *

Shearing Sheep shearing is the process by which the woollen fleece of a sheep is cut off. The person who removes the sheep's wool is called a '' shearer''. Typically each adult sheep is shorn once each year (a sheep may be said to have been "shorn" o ...

–

punching Punching is a forming process that uses a punch press to force a tool, called a ''punch'', through the workpiece to create a hole via shearing. Punching is applicable to a wide variety of materials that come in sheet form, including sheet meta ...

, stamping, scissoring, blanking * Abrasive material removal – grinding,

lapping Lapping is a machining process in which two surfaces are rubbed together with an abrasive between them, by hand movement or using a machine. Lapping often follows other subtractive processes with more aggressive material removal as a first ste ...

polishing Polishing is the process of creating a smooth and shiny surface by rubbing it or by applying a chemical treatment, leaving a clean surface with a significant specular reflection (still limited by the index of refraction of the material accordin ...

, water-jet * Heat – flame cutting, plasma cutting,

laser cutting Laser cutting is a technology that uses a laser to vaporize materials, resulting in a cut edge. While typically used for industrial manufacturing applications, it is now used by schools, small businesses, architecture, and hobbyists. Laser cut ...

* Electrochemical –

etching Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types ...

electrical discharge machining Electrical discharge machining (EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metal fabrication process whereby a desired shape is obtained by using electrical discharges (sparks). Material i ...

(EDM),

electrochemical machining Electrochemical machining (ECM) is a method of removing metal by an electrochemical process. It is normally used for mass production and is used for working extremely hard materials or materials that are difficult to machine using conventional me ...

(ECM) Every method has its limitations in accuracy, cost, and effect on the material. For example, heat may damage the quality of heat treated alloys, and laser cutting is less suitable for highly reflective materials such as aluminum. Laser cutting sheet metal produces flat parts and etches and engraves parts from complex or simple designs. It is used over other cutting options for its quick process and customizable abilities.

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*
How stuff works – Handsaws

Etching vs. traditional metal machining
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Metal cutting

See also

References

External links