How to make a bolt

Material selection

Carbon steel: According to the content of carbon is divided into low carbon steel (C%≤0.25%), medium carbon steel (0.25%0.45%), as well as alloy steel (adding alloying elements in general carbon steel). Low carbon steel is mainly used for 4.8 class bolts and 4 class nuts and other products without hardness requirements; Medium carbon steel is mainly used in 8 class nuts, 8.8 class bolts and other high-strength products; High carbon steel is used less in the market.
Stainless steel: mainly divided into austenite (18%Cr, 8%Ni), martensite (13%Cr) and ferritic stainless steel (18%Cr). Austenitic stainless steel has good heat resistance, corrosion resistance and weldability. Martensitic stainless steel has poor corrosion resistance, but high strength and good wear resistance; Ferritic stainless steel has better upsetting property and better corrosion resistance than martensite.
Copper: Commonly used materials for brass, zinc copper alloy, the market mainly with H62, H65, H68 copper as standard parts.

Pretreatment

Annealing treatment

For medium carbon steel and medium carbon alloy steel commonly used in high-strength fasteners, annealing treatment is an essential step.
Complete annealing: the steel is heated to a certain temperature above Ac3 (critical temperature) (such as 28℃ to 50℃), and slowly cooled after holding for a certain time to obtain a uniform and fine pearlitic structure and improve the plastic deformation capacity of the steel.
Spheroidizing annealing: the steel is heated to Ac1 (pearlite to austenite transition critical temperature) above a certain temperature (such as 20℃ to 40℃), after heat preservation slowly cooled to 450℃ below, so that the cementation spheroidization, thereby improving the cutting performance and cold heading performance of steel.

Surface cleaning and descaling

Hulling and scaling: To remove the oxidation scale on the surface of steel, the commonly used methods are mechanical scaling and chemical pickling. Mechanical descaling is suitable for low strength fasteners, while high strength fasteners may require a composite descaling method.
Cleaning: Clean the surface of the steel to ensure that there is no oil, rust and other impurities to prepare for subsequent processing.

Other pretreatment

Size adjustment: Adjust the size of the steel by cold drawing and other processes as needed to meet the requirements of subsequent processing.
Softening treatment: For some bolts with special requirements, softening treatment may also be needed to improve their processing performance and finished product quality.

 Pinching-out

Cold drawing process has two purposes: one is to change the size of raw materials; The second is to obtain basic mechanical properties of fasteners through deformation strengthening. For medium carbon steel and medium carbon alloy steel, cold drawing can also make the sheet cementite obtained after controlled cooling of the wire rod break as much as possible during the drawing process, so as to prepare for the granular cementite obtained by subsequent spheroidizing (softening) annealing.

 Combination of cold forging with warm forging

The forming of the bolt head is made of cold forging plastic processing. Compared with cutting processing, the metal fiber is continuous along the shape of the product without cutting in the middle, which improves the strength and mechanical properties of the product. The cold heading forming process includes cutting and forming, single click, double click cold heading and multi-station automatic cold heading.

Thread machining

Pre-processing preparation

Material inspection: Check the size, hardness and quality of the material to be processed to ensure that the material meets the processing requirements.
Tool preparation: According to the thread type and processing requirements, select the appropriate cutting tool, blade, rotary and other cutting tools. The commonly used tools for cutting threads are thread tools, taps, etc., when choosing tools, it is necessary to consider tool material, tool tip shape, tool Angle and other factors, and select the appropriate tool according to the diameter and pitch of the required thread.
Cutting fluid preparation: Preparing cutting fluid for cooling and lubricating tools to reduce wear and thermal deformation during cutting.

Thread processing method

Turning: threading is performed on a lathe using a forming tool or a thread cutter. The forming tool is suitable for single piece and small batch production, while the thread cutter is suitable for short thread workpiece with fine teeth in medium and large batch production.
Milling: Milling is done on a thread milling machine using a disk or comb cutter. Disc milling cutter is mainly used for milling trapezoidal external threads on screw, worm and other workpieces, and comb milling cutter is used for milling internal and external ordinary threads and cone threads.
Grinding: The precision thread of the hardened workpiece is processed on the thread grinder, which is divided into two kinds: single-line grinding wheel and multi-line grinding wheel.
Cyclone milling: Milling threads from the workpiece with a carbide forming tool mounted on a high-speed rotating cutter. This method has the advantages of slow spindle speed, high precision and good dynamic stability

Tapping and sleeve: Tapping is used to process the internal thread in the bottom hole pre-drilled on the workpiece with a tap, and the sleeve is used to cut the external thread on the bar or pipe workpiece with a die.

Thread rolling and rolling: Thread rolling is to stagger two thread plates with threaded teeth half of the pitch relative arrangement, by rolling the workpiece to make its surface plastic deformation into a thread. The rolling wire is divided into radial rolling wire, tangential rolling wire and rolling head rolling wire, of which the rolling head rolling wire is often used for processing short threads on the workpiece.
Edm: Compared with the machining method, EDM thread needs to be drilled first, and the diameter of the bottom hole should be determined according to the working condition. There are two methods of EDM thread machining, namely thread electrode rotation machining method and shaking machining method.

Process control
Machining parameter control: including cutting speed, feed speed, cutting depth and other parameters reasonable setting, to ensure the stability of the machining process and processing quality.
Processing stability control: Pay attention to maintain the stability of the processing to avoid tool jitter or vibration during the cutting process. It can be achieved by optimizing the processing path, processing mode, cutting speed, etc.
Machining surface quality control: control the roughness and flatness of the machined surface to ensure that the surface finish of the thread meets the requirements.

we have diffient of Stainless Steel Products such as Stainless Steel Ring, Stainless Steel Ring, Valve

.Heat treatment

Purpose of heat treatment

The main purpose of heat treatment is to improve the hardness, strength, toughness and wear resistance of the bolt by changing its internal structure and material properties, thus extending its service life.

Heat treatment type

The heat treatment of bolts mainly includes the following types:
Quenching: Quenching is a common method to improve the hardness and strength of bolts. In the quenching process, the bolt is heated to a suitable high temperature, and then quickly cooled to room temperature or below room temperature, so that the structure of the steel changes, obtain high hardness and high strength martensitic structure. However, the brittleness of the bolt after quenching will also increase, so subsequent tempering treatment is usually required.
Tempering: Tempering is to reheat the quenched bolt to the appropriate temperature and hold it for a period of time, then slowly cool it. Tempering can reduce the brittleness of the bolt, improve its toughness and impact resistance, while maintaining a certain hardness and strength.
Carburizing: Carburizing is a process in which the surface of a bolt is coated with a high carbon content layer. It is often used to make bolt products that require high strength and wear resistance. The carburizing process includes carbonitriding and carbonization, which can form a high-hardness carbide layer on the surface of the bolt and improve its wear resistance.
Normalizing: Normalizing is the heating of the bolt to a certain temperature (higher than annealing), so that the grain inside it is refined, thereby increasing the hardness and strength of the bolt. Normalizing is a preparation step before quenching, which can eliminate the stress inside the bolt and improve its organizational structure.

 Inspection and packing

Inspection of bolts
1. Manual inspection
Manual inspection is the most original and most commonly used method of inspection. The inspector makes a thorough inspection of the bolt by sight, hand feel and simple tools such as vernier calipers, spiral micrometers, etc. Specific steps include:
Appearance check: Check the surface of the bolt for cracks, deformation, oxidation, scratches and other defects to ensure that the surface is smooth and the thread is clear.
Dimension measurement: Use vernier caliper, screw micrometer and other tools to measure the diameter, length, pitch, thread Angle and other key dimensions of the bolt to ensure compliance with standard requirements.
Mechanical properties test: For some high-strength bolts, hardness, tension, torque and other mechanical properties test is also needed to ensure that its performance meets the requirements of use.
Surface treatment inspection: Check whether the surface treatment of bolts (such as galvanized, coated with anti-rust oil, etc.) is uniform and complete to prevent rust and corrosion.
2. Machine inspection
With the development of automation technology, machine inspection is more and more widely used in bolt inspection. Common machine inspection methods include magnetic particle inspection and so on.
Magnetic particle flaw detection: the interaction between the leakage magnetic field and magnetic powder at the defect of the bolt is used to form magnetic marks to show the location and shape of the defect. This method can efficiently detect the defects such as cracks and slag inclusion inside bolts.

Packing of bolts
1. Boxed
Boxed is a packing method suitable for a small number of bolts. It can protect the bolt from the damage of the external environment, such as dust, moisture, etc., while being easy to carry and store. But the cost of the box is relatively high, not suitable for mass production and sales.
2. Bag
The bag packing method is more flexible, suitable for different specifications of bolt packaging. Bagging not only protects bolts from damage, but also facilitates storage, sale and transportation. The cost of bags is relatively low, suitable for mass production and sales. However, it should be noted that bagged bolts should avoid extrusion and collision during transportation to avoid damage.
3. Pallet loading
Pallet packing is a packaging method suitable for large-scale production and sales. The bolt is placed on the tray and fixed with a plastic film, which can be easily transported, stored and handled. The cost of pallet loading is low, suitable for large-scale production and sales. However, pallet loading requires special equipment to carry, and pay attention to moisture and rust prevention when storing.