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Bolts, a basic component of construction and engineering, are produced in a high-tech, multi-step process. Learn how steel is turned into metal tools that are highly precise and spec'd out.
Bolts come in many different shapes and sizes, but their basic production process is the same. The process begins with cold forging the steel wire to the desired shape. Heat treatment is then applied to increase strength, and surface treatment to improve durability. For more complex bolt designs, however, the process can be extended by several additional steps.
The production process
Cold forging begins with large steel rods that are uncoiled, then cut to size. Steel grades are standardized in the industry according to ISO 898-1. The wire is cold-forged using special tooling. The steel is molded at room temperature by pushing it through dies under high pressure. Tooling can contain up to 200 parts, with tolerances as small as a hundredth of a millimeter. Cold forging is a process that can produce bolts quickly, in high volumes and with a high degree of uniformity.
Turning or drilling is sometimes required to contour more complex designs that cannot be contoured by cold forging alone. The bolt is turned by spinning it at high speeds while the steel is removed to create the desired design. To make holes in the bolt, drilling can be used. Some bolts can have washers added at this point if required.
All bolts are subjected to heat treatment, which is the standard procedure. The bolt is exposed to high temperatures to harden its steel. When the steel is soft, threading is applied by either rolling or cutting. The process of rolling is similar to cold forging and involves passing the bolt through dies in order to form and mold threads. By cutting and removing the steel, threads are formed.
Threading before heat treatment is more cost-effective and easier because it will make the steel harder. Threading after heat-treatment will result in better fatigue performance.
Heat treatment may cause the steel to revert back to its original round shape for long bolts. A process of straightening is often required.
Surface treatment depends on the application of the bolt and customer requirements. Fasteners are often chosen for their corrosion resistance. A zinc-plated surface, applied by electrolytic treatment, is the most common solution. The bolt is immersed in a zinc-containing liquid and then an electric current is used to coat the bolt with zinc. Electrolytic treatment comes with an increased risk of hydrogen embrittlement. Zinc flakes are another option, but they come at a higher cost.
If corrosion resistance isn't an issue, such as in an engine or application that is exposed to oil regularly, phosphate can be a cost-effective solution. Standard bolts can be packaged once the surface treatment is applied. Some more complex designs, like brackets, may require additional assembly. Some bolts may also need some type of patching. This could be a locking patch, or a liquid one. A locking patch is a layer of nylon over the threads that helps to improve grip. A liquid patch can improve the thread-forming torque.
The bolt is now finished. All that is left to do now is to perform some sort of quality control in order for the bolts be uniform and consistent before they can be packaged and sent.
Wire - Uncoiled and straightened, then cut to desired length.
Cold forging - Forming steel at room temperature into the desired shape.
Bolt Head- Forming steel by pressing it into dies under high pressure.
Threading_ Threads can be formed by cutting or rolling.
Heat Treatment_ The bolt is exposed at extreme temperatures to harden the steel.
Surface Treatment- It varies depending on the application. It is common for zinc-plating to be used as a corrosion resistant coating.
Stocking/Packing_ After quality control, to ensure consistency and uniformity, the bolts will be packaged.
Panda Fasteners has over 20 years of experience in bolt manufacturing, establishing itself as a leader in the industry through exceptional technology and extensive knowledge. We operate more than 80 advanced cold heading machines to ensure high precision and efficiency in our production process. Additionally, we have three heat treatment lines to enhance the strength and durability of our bolts, along with a modern surface treatment line to meet diverse customer requirements for surface quality and performance.
Our products are widely used in various fields such as automotive, machinery, and construction, earning trust and praise from customers. Panda Fasteners is committed to delivering high-quality products to our clients while continuously pursuing innovation and excellence. We welcome all customers to discuss business opportunities with us and look forward to creating a bright future together!
