Rolling is a type of plastic processing that deforms a material by applying strong force, and is a method of forming a rod-shaped processed material with a tool called a rolling die while rotating. Rolling is a processing method developed for the processing of male threads, and the most commonly used in rolling is the male thread machining today. In addition, it is also used for the processing of mechanical element parts, which are rotationally symmetrical bodies such as splines, serrations, worms, etc.

• Comparison with cutting

merit	(1) The production speed is 5~20 times faster than cutting processing. (2) It has excellent product accuracy, finishing surface, and strength (1.5 times stronger than cutting processing). (3) No material waste, less loss (4) Low power consumption, no garbage, low noise, etc.
demerit	(1) The initial investment in die fees is high, (2) It is difficult to manage the system of parts, and (3) It is not suitable for small customers.

 

• Types of rolling processes

Method	Description
Flat Die Method	The tools are plate-shaped and called flat dies (plate dies, or rack dies). The basic principle of a typical flat die rolling machine is shown in the figure on the right. Machining is performed by fixing one of the pair of dies and reciprocating the other parallel to it. The workpiece is inserted from one end and discharged from the other. Since the rolling is completed during this stroke, the machined length is limited. Also, the distance between the dies cannot be changed during processing. A key characteristic is high productivity, but it lacks versatility in application. The main use is for the mass production of general-purpose screws.
Circular Die Method	The tools are cylindrical and called circular dies or roller dies. Machining is performed using two or three dies of the same shape, which are rotated in the same direction and at the same speed while their distance is narrowed. The rotation of the dies allows the rolling surface to be used as an infinitely extended surface, and the distance between the dies can be freely changed. These features give it excellent versatility in processing applications. It is often used for parts machining other than thread rolling.
Planetary Die Method	This method consists of an arch-shaped segment die and a circular die. The thread is formed by fixing the segment die and rotating the circular die. It has the highest productivity of the three rolling methods and is used in mass production settings. It is primarily used for bolts and cap screws.

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  Heat treatment
Heat treatment is a method of improving the perfection of a material, just like shape processing, and is a process that changes the properties of the material by heating and cooling. Heating and cooling metals to change their hardness and properties.

Type of Heat Treatment	Description
Stabilizing Treatment	The process of heating austenitic stainless steel (SUS321, 347) to 850～900℃ and then air cooling it. This is a heat treatment to form stable compounds of carbon with niobium or titanium in the steel. Purpose: Improve corrosion resistance.
Stress Relief Annealing	Annealing intended to remove residual stress from forging, casting, machining, cold working, or welding. The heating temperature and cooling method vary depending on the material and purpose. For products that have undergone quenching and tempering, the stress relief annealing temperature is generally about 20℃ below the tempering temperature.
Austempering	The process of heating above the austenitizing temperature and then quenching in a hot bath at about 350℃~400℃ to obtain a bainite structure. Austempered parts generally do not require tempering. Features: ① Improved elongation, reduction of area, impact value, and toughness compared to quenching and tempering. ② Reduced quenching distortion.
Full Annealing	The process of heating above the austenitizing temperature and then cooling in the furnace. Purpose: Soften iron or steel, adjust crystal structure, remove internal stress, and improve machinability.
Spheroidizing Annealing	The process of heating for a long time or repeatedly heating and cooling between about 700℃~800℃, followed by slow cooling in the furnace to spheroidize the cementite. Various heat treatment methods exist depending on the material and the required degree of spheroidization. Purpose: ① Pre-treatment for cold working and cold forging. ② Pre-treatment for quenching high-carbon alloy steel and tool steel. ③ Maximum softening of steel.
Induction Hardening and Tempering	The process of heating to the quenching temperature using high-frequency induction heating with a coil, etc., and then quenching in water or a water-soluble quenching medium. Tempering temperatures are generally 150℃~300℃. Quenching and tempering are performed as a pre-treatment for induction hardening. Feature: No oxide scale or decarburization occurs.
Solution Treatment	The process of heating austenitic, austenitic-ferritic, and precipitation-hardening stainless steels to about 1000℃~1200℃ and then rapidly cooling them. These dissolves carbides precipitated by forging, rolling, cold working, etc., into the alloy so they do not precipitate. It is performed as a pre-treatment for the precipitation hardening of precipitation-hardening stainless steel. It is also called solution annealing. Purpose: Improve corrosion resistance.
Sub-Zero Treatment	The process of cooling a product after quenching with dry ice (78℃ or liquid nitrogen 196℃) to transform retained austenite into martensite. Purpose: ① Prevent aging deformation. ② Increase hardness and improve mechanical properties.
Vacuum Hardening	The process of heating in a vacuum and then quench-cooling with nitrogen gas. Purpose: Hardening of products close to the finished state.
Carbonitriding and Quenching/Tempering	The process of adding several percent of ammonia gas, which contains nitrogen, to a carburizing gas, allowing carbon and nitrogen to penetrate the surface layer of the product, followed by quenching. Tempering temperatures are generally 150℃~ 200℃. Feature: A hard and wear-resistant nitride layer is obtained, and the interior has excellent toughness.
Carburizing and Quenching/Tempering	The process of heating in a carburizing atmosphere, allowing carbon to penetrate the surface layer of the product, followed by quenching. Carburizing methods include solid, liquid, and gas carburizing. Tempering temperatures are generally 150℃~ 200℃. Mainly case-hardening steel is used. Normalizing is performed as a pre-treatment. Feature: The surface is hard and wear-resistant, and the interior has excellent toughness.
Precipitation Hardening	The process of raising the hardness of precipitation-hardening stainless steel by precipitating carbides dissolved in the steel. Solution treatment is required as a pre-treatment for precipitation hardening.
Nitriding	The process of heating in a liquid or gas containing nitrogen at 500℃~ 600℃, allowing nitrogen to penetrate the product surface to form a nitrided layer and harden it. Quenching and tempering are performed as a pre-treatment for nitriding. Feature: The hardened layer is shallower but harder than carburizing and quenching, with minimal deformation.
Low-Temperature Annealing	The process of heating below the A1 transformation point and then cooling at an appropriate rate. Purpose: Decrease hardness, improve machinability, cold workability, and remove residual stress.
Softening Annealing	Annealing aimed at reducing hardness. The heating temperature and cooling rate vary depending on the material and the required hardness. Purpose: Decrease hardness, improve machinability and cold workability.
Marquenching	The process of heating above the austenitizing temperature and then quenching in a hot bath near the martensite transformation temperature. Tempering is necessary after marquenching. Features: Prevents quenching cracks and reduces quenching distortion.
Non-Oxidizing Quenching and Tempering	The process of heating in a non-oxidizing state using a reducing or inert gas, followed by quenching. Tempering is performed after quenching. Feature: No oxide scale or decarburization occurs.
Quenching and Tempering	Quenching: The process of heating steel containing a certain amount or more of carbon above the austenitizing temperature and rapidly cooling it to increase the hardness of the steel. It is very hard but brittle. Tempering: After quenching, tempering reduces the hardness but improves toughness, and mechanical properties such as tensile strength, yield strength, elongation, reduction of area, and impact are enhanced, resulting in hard and tough steel. This is the most common heat treatment for structural steel parts. Quenching and tempering are also called 'Quench and Temper' or 'QT' or 'Martensitic Heat Treatment (Mar-H)'. Feature: Improved mechanical properties (tensile strength, yield strength, elongation, reduction of area, impact).
Annealing	A general term for processes aimed at softening iron or steel, adjusting crystal structure, or removing internal stress.
Normalizing	The process of heating steel above the austenitizing temperature and then cooling naturally in air or forced-air cooling. This treatment is also called the 'Normalization' of steel, and the resulting structure is called the standard structure. It is also performed as a pre-treatment for carburizing and quenching/tempering. Normalizing is also called 'Quasi-Tempering (Yakijun)' or 'Mar-N' or 'Norma'. Purpose: ① Remove the effects of previous processing (forging, rolling, etc.), refine coarse crystal grains, and improve mechanical properties. ② Improve machinability after forging or rolling, and pre-treatment for machining.

 
Reference photo: Heat treatment plant of Taiwan CMC's cooperative factory


  Surface Treatment
Surface treatment is a type of mechanical engineering method performed to enhance the properties of the surface of a material, such as plating and painting, in fields such as mechanical engineering. It is applied with the primary purpose of improving some of these qualities, such as hardness and abrasion resistance, lubricity, corrosion resistance, oxidation resistance, heat resistance, thermal insulation, insulation, adhesion, and decorative properties and aesthetics.

Type	Description
Electroplating
Copper Plating	Copper is easily corroded by chlorinated water, so it is rarely used alone for decorative purposes. It's often used as an underlayer for nickel or nickel-chrome plating. On the other hand, industrial copper plating is widely used for its electroconductivity and uniform plating thickness characteristics.
Nickel Plating	A type of surface treatment that creates a metallic nickel film on the substrate by the reducing power of electrons from electric current in an aqueous solution. A condition for electrolytic nickel plating is that the substrate must be electrically conductive. The main purposes of electrolytic nickel plating are decoration, functional use, and electroforming.
Black Nickel Plating	Primarily used for decoration, but sometimes used as a solar selective absorbing film. The black nickel plating bath is characterized by the inclusion of zinc in addition to nickel as a metal ion. Since the zinc ions in the bath are co-deposited into the film, black nickel plating is technically a "nickel-zinc alloy plating." It is non-glossy and brittle, making it unsuitable for thick plating, with a limit of about 2μm.
Chrome Plating	Chromium provides a high degree of luster when polished, has high hardness, and offers good wear resistance, corrosion resistance, heat resistance, and adhesion, making it widely used in industry. A thin layer of chromium applied as the top layer is decorative chrome plating, and its characteristic deep color tone is used as the final finish for various parts.
Black Chrome Plating	Plating where the main chemical, chromic anhydride, is chemically reacted (oxidation reaction) to produce a black color. Similar to regular silver chrome plating, it has excellent corrosion resistance, wear resistance, heat resistance, and appearance, but it requires advanced technology as unevenness and scratches are easily noticeable. It is generally processed as a thin film with a thickness of 0.1~ 10μm.
Industrial (Hard) Plating	A representative industrial plating with many mechanical properties. It refers to plating that is relatively thick (defined as 5μm or more by JIS) and used for purposes other than decoration. The basic requirement is to apply a thick plating directly to the substrate with good adhesion. This often involves more steps before and after plating.
Zinc Plating	Zinc plating is widely used primarily for rust prevention on steel substrates. Subsequent chromate treatment on the zinc surface increases its corrosion resistance and provides an attractive appearance.
Cadmium Plating	Plating applied to steel for corrosion prevention. Compared to zinc plating for the same purpose, it has superior corrosion resistance in high-temperature, high-humidity, and chloride-containing environments, making it suitable for equipment used at sea or near the coast. However, due to drawbacks such as the high toxicity and pollution concerns of cadmium, and its tendency to cause hydrogen embrittlement in steel substrates, it has been replaced by zinc plating in most applications today, except for special uses.
Tin Plating	In recent years, the development of organic brighteners for acidic baths has made it possible to obtain bright plating with excellent luster, solderability, and corrosion resistance, leading to its attention for plating electronic components.
Gold Plating	The process of depositing a thin layer of gold onto the surface of a metal material, or the resulting coating. Traditionally used for decoration, its excellent properties such as extremely high corrosion resistance, low electrical resistance, and good solderability have led to its application in high-reliability electronic components like electrical contacts, connectors, and printed circuit boards.
Silver Plating	The process of depositing a thin layer of silver onto the surface of a metal material, or the resulting thin silver layer. Due to features like its beautiful appearance, excellent corrosion resistance, high reflectivity, high electrical conductivity, and lower cost than gold, it is widely used for plating on ornaments, reflectors, electrical/electronic equipment parts, precision machine parts, and flatware.
Electroless Plating
Electroless Nickel Plating	Unlike electroplating, it is a type of electroless plating where the metallic nickel film is deposited on the substrate by simply immersing it in the plating solution. The electrons are released by the oxidation of a reducing agent contained in the plating solution, not by an electric current. This method is also called Kanigen plating. Since it does not require electricity, it can plate non-conductive materials like plastics and ceramics. It provides a film of uniform thickness regardless of the material's shape or type.
Plastic Plating	Plastics with various properties, from general-purpose to functional, have been commercialized for a wide range of applications. Due to the rapid progress in molding technology, mass production of even complex shapes is possible, and combined with lightweighting and low cost, their applications are expanding limitlessly. While plastics can be given various appearances through surface treatments like painting, metallic finishes, and hot stamping, the optimal method to dramatically increase product value is plastic plating (Electroless Plating→Electroplating), which metalizes the plastic.
Chemical Conversion Treatment and Coloring
Chromate Treatment	Primarily applied to brass, zinc, and aluminum. By immersing the base metal in a solution containing hexavalent chromium, a self-healing passivation film is obtained, while simultaneously performing a chemical polishing action.
Antique Finishing	This process involves coloring the surface of copper/copper alloy plating, etc., to a blackish tone using sulfide treatment and then selectively removing it by buffing to give an antique or beautiful appearance. It is characterized by the harmony between the shades and blurs of black and the reddish color of the plating, creating an antique atmosphere.
Parkerizing (Phosphate Coating)	Performed to create an insoluble phosphate film on the surface to suppress the progression of corrosion. It is also applied to steel products before painting. In addition to its anti-corrosion surface protection effect, it is also used as a primer for metal soap-based lubricants during plastic working. Calcium phosphate is often used for this purpose, and the properties of the film can be changed by using additives, controlling the temperature of the phosphate solution, and adjusting the chemical conversion time.
Black Oxide Finishing	A method of protecting the interior of steel by creating a dense, black iron (II, III) oxide Fe304 film on the steel surface. Various methods exist, but the alkaline coloring method involves immersing steel parts in a treatment solution—an aqueous solution of NaOH (35-45%) with an oxidizing agent and reaction accelerator—heated to 130℃~150℃. The film thickness is about 0.2~1μｍ. Since it forms chemically from the surface inward, there is little dimensional change, making it suitable for treating precision machine parts. However, this film often develops cracks, requiring post-treatments such as chromic acid treatment or the application of rust-preventive oil.
Bright Dip	An acid pickling treatment often used for copper materials to achieve a very clean and bright surface. Typically, the material is immersed in a strong acid mixture based on nitric acid to dissolve the stained surface and expose a new, lustrous copper surface. The process is being used less frequently due to the generation of large amounts of nitrogen oxides during treatment.
Hot-Dip Plating	A method of forming a metallic coating on the surface of a material by immersing it in molten metal and then withdrawing it. It is also called immersion. Only metals with a melting point lower than the temperature at which the substrate would be damaged by heat can be plated. Aluminum, tin, zinc, and lead are used as plating metals. In particular, hot-dip zinc plating is widely used for the anti-corrosion of steel materials and is called galvanizing. Various shapes such as pipes, wires, sheets, and profiles are treated.
Painting/Coating	The purpose of painting in metal processing varies, often having multiple goals: to prevent rust by shielding the oxidizable metal from the atmosphere, to protect the surface with the elasticity of the coating film, and coloring for aesthetic appearance. The composition of the paint is divided into the main film-forming components, film-forming auxiliary components, pigments, and solvents. Pigments are insoluble fine powders added for coloring. Depending on the composition, pigments can also provide rust prevention, conductivity, and improved mechanical properties. Paint that adds functions other than aesthetics and protection to the film is specifically called functional paint. The main film-forming components, the principal constituents of paint, are shifting from natural resins/oils to various synthetic resins/oils. Film-forming auxiliary components are additives like plasticizers, dryers, and thickeners, used to complement the properties of the main components. Solvents are components used to dissolve or disperse the film-forming components to make them flow, using organic solvents or water.
Powder Coating/Lining	The process of covering metals, etc., with organic polymer materials or inorganic materials. Methods include fluidized bed immersion, spray thermal spraying, electrostatic spraying, and simple spraying. It is often performed by a single method or a combination of methods involving plastic powder (tens to hundreds of μm): ① adhesion to the metal followed by melting, ② contact with heated metal followed by melting, or ③ coating in a semi-molten state.

 

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