Knowledge of the cold heading process of fasteners

Cold heading forming process is widely used in aerospace, automobile, and other industrial sectors, mainly used for #bolts , #studs, #screws , #nuts, and other fasteners processing technology, with stable work, high precision, and high production rate, and easy-to-realize automation process characteristics.

Today, we will take a comprehensive look at the cold-heading forming process of #fasteners.

The forming of any fastener can be achieved not only by #coldheading deformation. In addition to upsetting deformation, the cold heading process is accompanied by various deformation methods such as forward and reverse extrusion, composite extrusion, punching and cutting, and rolling. Therefore, a cold heading is just familiar.

The advantages of cold heading (cold extrusion) are many, mainly in the following aspects:

Save raw materials

Cold extrusion uses the plastic deformation of metal to make parts of the desired shape, significantly reducing cutting processing and improving material utilization. The material utilization rate of cold extrusion can generally reach more than 80%.

Increase labor productivity

Using a cold extrusion process instead of cutting to manufacture parts can increase productivity by several times, dozens of times, or even hundreds of times.

Parts achieve ideal surface roughness and dimensional accuracy

The accuracy of the details can reach IT7~IT8, and the surface roughness can reach R0.2~R0.6. Therefore, #parts processed by cold extrusion are rarely re-cut and must be finely ground in particularly demanding places.

Improve the mechanical properties of parts

The cold work hardening of the metal after cold extrusion, as well as the formation of a reasonable fiber streamline distribution inside the part, make the strength of the part much higher than the strength of the raw material. In addition, a reasonable cold extrusion process can improve the fatiue strength by forming compressive stress on the surface of the part. Therefore, some parts that originally needed heat treatment and strengthening can be eliminated after the cold extrusion process, and some parts originally need to be made of steel with high strength, and can be replaced with steel with lower strength after the cold extrusion process.

It can machine parts with complex shapes that are difficult to cut

Such as special-shaped sections, complex inner cavities, internal teeth and invisible inner grooves on the surface.

Reduce parts costs

Because the cold extrusion process has the advantages of saving raw materials, improving productivity, reducing the amount of cutting and processing of parts, and replacing high-quality materials with poor materials, the cost of parts is significantly reduced.

Positive extrusion

When extruded, the flow direction of the metal coincides with the law of movement of the punch. Positive extrusion is divided into positive extrusion of solid parts and positive extrusion of hollow parts. The positive extrusion method can manufacture reliable and open parts of various shapes, such as screws, mandrels, tubes, and cartridge cases.

Anti-extrusion

When extruded, the flow direction of the gold chip is opposite to the punch's movement direction. The anti-extrusion method can manufacture cup-shaped parts of various cross-sectional shapes, such as instrument shells, universal joint bearing sleeves, etc.

Composite extrusion

When extruded, the flow direction of a part for the blank metal is the same as the movement direction of the punch. In contrast, the flow direction of the other part of the gold chip is opposite to the movement direction of the point, and the composite extrusion method can manufacture double cup parts, cup rod parts, and rod parts.

Reducer extrusion

A metamorphosis positive extrusion method with a small degree of deformation and the blank section is only slightly reduced. It is mainly used to manufacture stepped shaft parts with little difference in diameter and as a dressing process for deep-hole cups.

The common feature of the above extrusions is that the flow direction of gold chips is parallel to the convex and horizontal axis. Therefore, it can be collectively referred to as the axial extrusion method. In addition, there are radial extrusion and upsetting processes.

Next, let's talk about the difficulties in applying cold extrusion technology.

High requirements for molds

During cold extrusion, the blank is subjected to three-way compressive stress in the #mold , and the deformation resistance is significantly increased, which makes the pressure of the mold much larger than that of the general stamping die. The stress of the mold is often up to 2000MPa~2500MPa when cold extrusion steel. In addition to high strength, the mold must have sufficient impact toughness and wear resistance. In addition, the solid plastic deformation of the metal blank in the mold will increase the mold temperature to about 250 °C ~ 300 °C. Therefore, the mold material needs specific tempering stability. Due to the above situation, the life of cold extrusion dies is much lower than that of stamping dies.

Presses of large tonnage are required.

Due to the significant deformation resistance of the blank during cold extrusion, hundreds or even thousands of tons of presses are required.

Only suitable for high-volume production of parts

Due to the high cost of cold extrusion molds, it is generally only suitable for the high-volume production of parts. The minimum batch size ideal for it is 5.1 million pieces.

The blank needs to be surface treated before extrusion

The blank needs to be surface treated before extrusion, which increases the process, occupies a large production area and makes it challenging to automate production.

It is not suitable for high-strength material processing.

The plasticity and impact toughness of cold extruded parts are poor

The plasticity and impact toughness of cold extruded parts deteriorate, and the residual stress of the components is significant, which will cause the deformation of the features and the reduction of corrosion resistance (stress corrosion). Finally, let's look at the development trend of cold extrusion technology.

1. With the increasingly severe energy crisis, people will pay more attention to environmental quality, coupled with the increasingly intensified market competition, promoting the production of forgings to high efficiency, high quality, refinement, energy saving, and material saving direction. Therefore, it will significantly develop the output of refined forgings produced by extrusion forming and other technological means in the market competition.

?2. The development of automobiles in the direction of lightweight, high speed, and stability puts forward high requirements for dimensional accuracy, weight accuracy, and mechanical properties of forgings. For example, in addition to the error between the head size, the weight error of each piece is not more than eight grams. The high requirements for new products will promote the development of refined production processes.

?3. Specialized and large-scale organizational production is still the development direction and trend of cold extrusion production. In France, the professional manufacturers who produce forgings by extrusion forming process from 1991 to 1994, that is, the output and output value of extruded parts per person, are higher than those of generic manufacturers of die forgings or free forgings. Taking 1994 as an example, the per capita output of extruded parts of professional manufacturers was 51024KG, with an output value of 775688 francs. In the same period, the per capita output of manufacturers of the general production of die forgings was only 39344KG, and the output value was 592384 francs, equivalent to 77.1% and 76.37% of professional manufacturers of extrusions. Free forging production plants are lower in comparison.

?4. Extrusion of particular aircraft will become a development trend. With the development of refined production of small and medium-sized forgings and the promotion and application of cold extrusion and warm extrusion processes, multi-station cold extrusion presses, fine presses, and unique opportunities for the design and manufacture of specific forgings have been vigorously developed.

?Well, about the fastener cold heading process, let's talk about it today. If you want to know more about the cold pier process, you can leave a message in the comment area!