The shape, material and size of springs vary according to their application and environment. The shapes of materials can be roughly divided into wire and sheet, and the forming methods include hot forming, which processes materials by heating, and cold forming, which processes materials at room temperature. Cold forming is not the name of hot forming and does not involve cooling processing.
Here, we will introduce you to spring knowledge along the manufacturing process of cold forming compression helical springs. 
This is a general process. The number of steps and their sequence may vary depending on the product.
Material：
Common spring materials include piano wire, hard steel wire, stainless steel wire, oil tempered wire, phosphor bronze, etc. When designing springs, material selection is crucial to meet quality requirements and reduce costs. Each material has its own characteristics such as fatigue resistance, corrosion resistance, and non-magnetism, and there are significant price differences among them. Even if the material itself does not meet the required quality, it can be supplemented in subsequent processes, such as improving fatigue resistance through shot peening or enhancing corrosion resistance through electroplating. Besides common materials, there are also higher-strength wires developed by wire manufacturers and straightened wires. 
Winding:
Winding machines are used to form the material into a coil (helical) shape.
Heat treatment (low-temperature annealing):
The purpose of heat treatment is to stabilize the shape by eliminating harmful residual stresses caused by cold forming (the force attempting to restore the original shape). Additionally, if residual stresses remain, the spring is more prone to bending or breaking. The heat treatment methods, including temperature conditions, vary depending on the material. The size of the spring changes due to heat treatment, but the extent of the size change varies with the type of material and is not constant. After shot peening, heat treatment is performed to restore elasticity (increase fatigue strength).
End face grinding:
Generally, the end faces are ground flat to prevent load imbalance and damage to mating parts. For smaller diameter wires (fine wires), grinding can be omitted because the load bias is small and the impact on other objects is minimal. 
Shot blasting:
The purpose of shot blasting is to improve fatigue resistance. It is a surface treatment that hardens the surface layer by continuously impacting it with small metal balls at high speed. As a result, compressive residual stresses remain in the surface layer, which act to counteract repetitive loads and thereby increase fatigue strength. The hardened part is only the surface layer and does not significantly affect the tensile strength of the material itself. 
Environment：
The purpose of setting is to minimize sagging during use.
This is a process where a load greater than the maximum working stress is applied in the direction of spring use after forming and heat treatment, close to the final process, causing plastic deformation.
Depending on the usage conditions, there are also methods such as heating and solidifying the material or performing heat treatment under load. This is called heat setting.
Surface treatment：
The main purpose of surface treatment is to prevent corrosion of steel springs.
Other uses include surface treatment to improve appearance and identifiability.
In addition to simply applying anti-rust oil, there are various anti-corrosion methods such as painting, electroplating, blackening, and Parkerizing. We will provide suggestions based on your purpose and cost.
Inspection：
Inspection items include dimensions such as wire diameter, inner diameter, outer diameter, free length, pitch, as well as the number of turns, spring constant, load, appearance, and durability tests. Additionally, compression springs have perpendicularity with the spring ends, while torsion springs have winding angles.
The inspection items are determined based on the required quality, and the inspection equipment varies according to the required precision. Moreover, important components can be inspected at all points, but this naturally increases the cost.
Regarding spring defects (breakage, fatigue, deformation, etc.)：
Some spring problems occur due to aging, while others appear prematurely for some reason.
It is often assumed that early defects are caused by the manufacturer, but there are many reasons for defects. The main reasons include scratches, usage environment, design errors, etc., and sometimes multiple reasons overlap. Of course, there may be issues with the material itself or during the manufacturing process, but examples of reasons after transportation include scratches caused by improper assembly and contact with mating parts, as well as forcefully uncoiling tangled springs, which can lead to deformation. Inappropriate heat, material selection, and surface treatment for the temperature, humidity, vibration, and other usage environments.
When you hold a spring, it is easy to push or bend it, but this can cause deformation and load changes. Although it depends on the wire diameter, springs are precision components. Care must be taken when handling them.
For this reason, when investigating the cause of defects and designing, it is necessary to fully consider assembly conditions such as mating parts, how to handle them, and the usage environment.
