In modern manufacturing, bolts, as a vital component of fasteners, rely heavily on the quality of their head formation process for overall product quality and performance. This article will provide a detailed analysis of the cold forging process, an advanced technique widely used in the formation of bolt heads.
I. The Advantages of Cold Forging Process
Compared to traditional cutting processes, the cold forging process offers significant advantages. It involves cold heading plastic processing, which allows metal fibers (metal lines) to distribute continuously along the product shape without any interruptions, thus greatly enhancing the product's strength, especially its excellent mechanical properties.
The cold forging process primarily includes two steps: cutting and forming, which can be further divided into single-station single hit, double hit cold heading, and multi-station automatic cold heading. Let's delve into the specific implementation points of this process.
II. Key Implementation Points of the Cold Forging Process
Selection and Use of Cutting Tools
In the cold forging process, using semi-closed cutting tools for blank cutting is the simplest method. Sleeve-style cutting tools are favored for their convenience. It is important to note that the cutting angle should be controlled within 3 degrees. If an open-style cutting tool is used, the oblique angle of the cut can reach 5-7 degrees.
Blank Flipping and Precision Enhancement
During the transfer of short-length blanks, achieving a 180-degree flip is crucial. This operation helps maximize the potential of automatic cold heading machines, allowing for the processing of complexly structured fasteners and thus improving part precision.
Punch Ejection Device and Die Sleeve Ejection Device
To ensure smooth production, each forming station should be equipped with a punch ejection device, and the dies should have a sleeve-style ejection device.
Rational Configuration of Forming Stations
Generally, the number of forming stations (excluding cutting stations) should be 3-4, and can be increased to 5 or more in special cases.
Stability of Main Slider Guide Rails and Process Components
Within the effective service life, the structure of the main slider guide rails and process components should guarantee the positioning accuracy of the punch and die.
Control of Heading Force and Wire Ovality Requirements
When manufacturing high-strength fasteners on automatic cold heading machines, it is essential to strictly control the heading force. The ovality of the wire should be within the diameter tolerance range, and for precision fasteners, the ovality should be limited to half the diameter tolerance range. Wire diameter that does not meet specifications can lead to issues such as cracks and burrs in the head of the part.
Forming Precision and Die Surface Roughness
The precision achievable in cold heading is related to the choice of forming method, process steps, equipment structure, and process characteristics. The surface roughness of high-alloy steel and carbide dies should not exceed Ra=0.2μm, with the optimal roughness being Ra=0.025-0.050μm, which corresponds to the highest die life.
Through the above analysis, you now have a deeper understanding of the cold forging process. The application of this advanced process will help improve the quality and performance of fasteners like bolts, contributing to the development of China's manufacturing industry.
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