Cold heading is one of the new technologies for metal forming with little or no cutting. It is a processing method that utilizes the plastic deformation of metal under the action of external force and uses a mold to redistribute and transfer the volume of metal to form required parts or blanks. The cold heading process is very suitable for producing common parts such as bolts, screws, nuts, rivets, pins, etc.
The machines commonly used in the cold heading process are special cold heading machines. If the production volume is not very large, a crank heading machine or a compression heading machine can be used instead. With the rapid development of my country's economy, the multi-station automatic machines designed and manufactured by my country's workers have reached a high level of special performance and efficiency.
The main advantages of the cold heading process
1. Cold heading is carried out at room temperature. Cold heading can improve the mechanical properties of metal parts.
2. The cold heading process can improve material utilization. Taking cold heading bolts as an example, the new process for "medium" head bolts can achieve a material utilization rate of more than 99%. In addition to the initial and final material losses, the processing is not cutting. If cutting is used, the material utilization rate is only 40%. The material utilization rate of cold heading nuts can reach 80%, while that of cutting nuts is only 54%.
3. The cold heading process can greatly improve productivity. For example, compared with the initial cutting method, the production of cold heading nuts increases by about 25 to 30 times.
4. Due to the use of multi-station cold heading machines, each process can be processed at the same time on one machine, which reduces the investment in machinery, reduces the production space occupied by machines, reduces the transportation of incomplete products between various processes, and mainly reduces labor intensity and improves the working conditions.
5. The cold heading process can improve the product finish and ensure the product accuracy. The general finish can reach V5, and the special requirements can reach V6. For large-scale production of bolts, nuts, etc., the accuracy can be fully guaranteed.
Cold heading technology has high productivity, good product quality, greatly reduced material consumption, reduced production costs, and improved working conditions. Therefore, it is widely used in machinery manufacturing, especially in the production of general-purpose parts.
Cold heading materials
Requirements for cold heading materials
1. Requires high plasticity and low toughness
Since there is tangential stress on the side surface of the blank during cold heading, longitudinal cracks often occur. Therefore, the cold heading process must use special materials with high plasticity and toughness. The surface hardness of the steel is generally required to be 75-85HRB.
2. High quality requirements
Since the cold forging process is widely used to produce common parts, these products are no longer cut, especially common parts such as screws and bolts. It is not allowed.
3. High precision requirements
To ensure the accuracy of the billet volume, the tolerance of the billet width should be very small. Taking M10×1.5 as an example, the common size and tolerance of its raw material is Φ
Cold material supply form
The materials are supplied in two forms: cold-drawn discs and cold-drawn bars. The width of the cold-drawn discs is 2~16mm, and the weight of each disc is 100~2000kg; [2]
Determining the cold head deformation rate and cold head time
How to express the cold head deformation rate and the allowable deformation rate
During cold forming, due to the effect of work hardening on the metal, the greater the cold head deformation, the greater the resistance to deformation will be. When the cold head deformation rate exceeds the maximum allowable deformation of the metal itself, cracks will form on the side surface of the part when the unit pressure of the cold head exceeds the allowable pressure of the mold, which will cause damage to the mold. Therefore, the allowable deformation rate should be:
