Science, Tech, Math › Science How Cold Working Strengthens Metal Share Flipboard Email Print Novelis, Inc. Science Chemistry Chemistry In Everyday Life Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Terence Bell University of British Columbia Carleton University Terence Bell wrote about commodities investing for The Balance, and has over 10 years experience in the rare earth and minor metal industries. our editorial process Twitter Twitter LinkedIn LinkedIn Terence Bell Updated November 13, 2019 In most cases, metal is cast or forged into the desired shape after it is made malleable through the application of heat. Cold working refers to the process of strengthening metal by changing its shape without the use of heat. Subjecting the metal to this mechanical stress causes a permanent change to the metal's crystalline structure, causing an increase in strength. Metal is rolled between two rollers, or drawn through (pushed or pulled) smaller holes. As the metal is compressed, the grain size can be reduced, increasing strength (within grain size tolerances). Metal can also be sheared to form it into the desired shape. How Cold Working Strengthens Metal The process gets its name because it is conducted at temperatures below the metal's recrystallization point. Mechanical stress is used instead of heat to affect change. The most common applications for this process are steel, aluminum, and copper. When these metals are cold worked, permanent defects change their crystalline makeup. These defects reduce the ability of crystals to move within the metal structure and the metal becomes more resistant to further deformation. The resulting metal product has improved tensile strength and hardness, but less ductility (the ability to change shape without losing strength or breaking). Cold rolling and cold drawing of steel also improve surface finish. Types of Cold Working The major cold-working methods can be classified as squeezing or rolling, bending, shearing and drawing. See the table below for a summary of the various methods for cold working metal. Squeezing Bending Shearing Drawing Rolling Angle Shearing Bar wire and tube drawing Swaging Roll Slitting Wire drawing Cold Forging Roll forming Blanking Spinning Sizing Drawing Piercing Embossing Extrusion Seaming Lancing Stretch forming Riveting Flanging Perforating Shell drawing Staking Straightening Notching Ironing Coining Nibbling High-energy rate forming Peening Shaving Burnishing Trimming Die hobbing Cutoff Thread rolling Dinking Most Common Methods of Work Hardening With so many options for work hardening, how do manufacturers decide which to use? It depends on the use to which the metal will be put. Three of the most common types of work hardening are cold rolling, bending, and drawing. Cold rolling is the most common method of work hardening. This involves the metal being passed through pairs of rollers to reduce its thickness or to make the thickness uniform. As it moves through the rollers and is compressed, the metal grains are deformed. Examples of cold-rolled products include steel sheets, strips, bars, and rods. Bending of sheet metal is another process for cold working, which involves deforming metal over a work axis, thereby creating a change in the geometry of the metal. In this method, the shape changes, but the volume of the metal remains constant. An example of this bending process is simply bending of steel or aluminum parts to meet the desired curvature. Many car parts, for example, have to be bent in order to fit manufacture dimensions. Drawing essentially involves pulling the metal through a small hole or die. This reduces the diameter of a metal rod or wire while increasing the product's length. The raw metal is pushed into the die via compression force to ensure that recrystallization occurs as the metal changes shape. Products made via this process include steel bars and aluminum rods. The Modern Steel Manufacturing Process Learn About the Properties and Uses of Brass Metal The History of Steel What Is Malleability in Metal? What Happens When Metals Undergo Heat Treatment? Working Metal—The Process of Annealing The Properties and Composition of Monel 400 Metal Stress, Strain, and Fatigue The Properties, Production, and Applications of Tin An Introduction to Cryogenic Hardening of Metal History and Applications of Monel Alloys Properties and Composition of Type 201 Stainless Steel Top Steel Alloying Agents Ductility Explained: Tensile Stress and Metals What Is a Thermodynamic Process? What Are the Types and Properties of Steel?