AYA FASTENERS Guide | Bolt And Nut Manufacturing Process

Nuts and Bolts are not only commonly used fasteners but also one of the most basic components used during construction and other mechanical process. While the fastener itself may appear to be simplistic in reality there is a lot of research and development that has been necessary for the advancement of their manufacturing process. Their production is a multi-step and high-tech process that if done wrong could have significant effects on the efficiency, longevity, and quality of the final product. In this article, we will help you better understand this process while also covering some of the most important points that you need to remember when it comes to these types of fasteners.

What are nuts and bolts?

A bolt is a threaded fastener usually used to connect two or more other parts or materials. They are the external male thread which means that most often they will require to be matched with a pre-formed female thread in order for a fastening to be successful.

The nut is a threaded hole, or in other words, the pre-formed female thread that is going to be connected to the bolt. The nut is what will provide the clamping force and thus will stop any axial movement.

How do nuts and bolts work?
Nuts and bolts are some of the most common components in manufacturing, construction, and engineering. Typically most equipment and machinery are going to be using a wide variety of nuts and bolts that are selected based on the environment, material, and other needs of the process.
Nuts and their matching bolts are most commonly used for fastening together multiple different parts. While bolts are external threads they can't be used without an internal thread, such as a nut.

What needs to be decided before the bolt manufacturing process begins?
Before the start of the manufacturing process, it is necessary for one to decide on the specifications that they want the bolts to fit. This includes having the right specifications in terms of the size, shape, and material necessary. While the production process can be roughly the same regardless of the specification in basic nut and bolt manufacturing, in more precise and complex bolt design there may be steps added to fit the specifications you have determined.

What is the production process for bolts?
The production process for bolts includes seven distinct steps usually. These are important for ensuring the proper shape, specifications, strength, durability, and other qualities of the bolts you are manufacturing.
1. Wire - The first step to manufacturing requires the steel wire to be uncoiled and cut to the pre-decided length. The length needs to meet the requirement of ISO 898-1.
2. Cold Forging - The steel is then molded in the right shape. This process is completed at room temperature.
3. Bolt Head - Forming the bolt head by forcing the steel to take various shapes while at high pressure.
4. Threading - The bolt threads are created through a process of rolling and cutting.
5. Heat Treatment - Extreme Heat is used to harden the steel used.
6. Surface Treatment - Depending on the type of bolt you need; different types of plating are added to the finish of the bolt. These help add different qualities to the bolt.
7. Packing/ Stocking and Quality Control - Once the bolts have been manufactured, they need to be quality controlled before being packaged and shipped off. The quality control process helps ensure that the bolts are consistent and uniform while also fitting the international ISO standards they are supposed to abide by.

How does the production process for bolts work?

The production process for the correct bolt can have various different steps depending on how complex the bolt design needed is. In general, for steel wire to be turned into a bolt the process is as follows:

1. Cold Forging

The process begins by taking a large steel wire and uncoiling it. It is then cut into the length required by the international ISO 898-1 standard that is applicable to the type of bolt you are creating. During this process, special tools and equipment are used in order to give the wire rod the correct shape. This entire process is occurring at room temperature, rather high heat being used.
During the cold-forging process which is what gives the bolts the shape that they are going to have, high pressure Is used to give different shapes to the wire and mold it into different shapes. The tolerance requirement set during this stage can only be one-hundredth of a millimeter which showcases how high the precision requirement is.
One of the benefits of cold forging is that it can be a very speedy process that produces uniform-shaped bolts. However, when it comes to more complex bolt designs it is often the case that cold forging cannot exclusively be used for giving them the correct shape. In those cases, there are two additional processes that could be used for the development of the bolt. These are known as turning or drilling.
Turning refers to a process where bolts are rotted at a very high speed while cutting steel in order to give it the correct design and shape. Drilling on the other hand can be employed when it is necessary for holes to be drilled into the bolt. During this stage in the process, some bolts could also have washers attached.
Thread processing is the final step that is carried out while the steel is still soft as it involves a lot of rolling and cutting. Rolling as a process is extremely similar to cold forging as it also includes moving bolts through a die to form and molding the steel to have the threads required. Cutting relates to the removal of steel to form threads.

2. Heat Treatment
Once the entirety of the bolt has been shaped, from the head to the threads it is time for the heat treatment. Heat treatment is a requirement for all bolts. The process involves the exposure of bolts to extreme temperatures in order for the steel to be hardened. The heat treatment changes the steel’s characteristics making it tougher. As such, if threading was to occur during this stage of the process it would be a lot more expensive and harder to complete.
Still, there are benefits to potentially threading after the heat treatment as it could ensure that the bolt will have a better fatigue performance.
In the case of long bolts that have a length that is more than ten times the bolt diameter a straightening process is required to stop the heat treatment from restoring the steel to the shape it had during the steel wire stage.

3. Surface Treatment
The application and requirements for the bolt set by the customer are going to determine what type of surface treatment is going to be used. Generally, the most common type of surface treatment includes treatments that make the fasteners a lot more resistant to corrosion. For this galvanized coating is applied through an electrolytic treatment.
During this process, the bolt is immersed in a zinc-containing liquid and an electric current is used to force the zinc to coat the bolt. While this process is great for making bolts more resistant to corrosion, there is an added risk of hydrogen embrittlement related to it.
In cases where corrosion resistance is not a primary concern then it is also usual for phosphate to be applied during this step. This is a more cost-effective process which is why it is often selected. In more advanced bolt designs there may also be additional assembly requirements, such as brackets. Other bolts could also possibly require patching. A locking patch can help improve the grip of three threads through the application of a thick nylon layer, while a liquid patch is great for bettering the thread-forming torque.
4. Quality Control
Quality Control is the final step in the manufacturing process and it helps ensure that each of the bolts is tested for its quality before they are packaged and shipped off.

Conclusion
When it comes to the manufacturing of nuts and bolts, the process can be relatively simple, especially for standard bolts and nuts. However the more complicated and customized the bolt design gets, the more steps might need to be added to help ensure that the final fastener is going to be of the quality necessary. The customer's requirements could also affect the surface finish of the bolt in question.

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