Fasteners strive to achieve zero defects and improve delivery quality requirements

As customers have increased the delivery quality of fasteners, manufacturers have begun to consider special elements in mass production. Depending on the type, specification and cycle cycle of the machinery used, the productivity of modern fastener manufacturing machinery (such as cold heading machines, thread rolling machines) can reach 60 to 800 pieces per minute. The number of workpieces produced by a fastener manufacturer can reach millions of pieces per day. Therefore, special measures are required to ensure process capability. In addition, in the manufacturing process, the workpiece is loaded into the container and transported to each processing point for many times. The number of transports varies with the length of the production chain (for example: cold heading, thread rolling, cleaning, quenching and tempering, surface treatment, anti-corrosion Etc.), more than 20 times is also normal. Special measures need to be taken during transportation to prevent mechanical damage (especially sharp corner collisions) and avoid mixing.

Under the current status of production technology, the quality goal of zero defects is impossible to achieve. In order to achieve the goal of zero defects, a transitional goal was established by stipulating standards for evaluating the quality of delivered fasteners. The conditions set by this standard are based on the number of substandard products per million products and (or) the process capability value (Cpk) of the specified characteristics.

Product process influence

The measurement and tolerance requirements of certain characteristics are based on the product process used (cold forming process, metal cutting process, heat treatment process). Some examples are given below:

In the fastener manufacturing process, many production processes are realized by cold forming. The stability of tolerances depends not only on the materials used, but also many other factors; for example, the contour accuracy of free forming in the opening and closing molds is not as accurate as the contour formed in the press-fitting process. Certain cold forming processes inevitably have sharp corners. In this case, it is usually impossible to give clear tolerances or limit values.

In threaded fastener products, the thread processing method will affect the thread geometry, tolerance, surface roughness, folding on the thread, etc. These will be very different with the thread processing method.

For screws with a large ratio of length to diameter, the possibility of bending will increase (especially when the final process includes heat treatment, quenching and tempering). For individual parts and processing methods, consideration should be given to specifying corresponding tolerances.

When the anti-corrosion coating is applied to the workpiece, the phenomenon of uneven coating thickness will inevitably appear. This is related to the size of the workpiece and the coating method. The uneven thickness may affect the anti-corrosion performance of the workpiece in the salt spray test. In this case, depending on the type and geometry of the fastener, its anti-corrosion performance is largely affected by the surface condition of the fastener. It is usually impractical to insist on completing the salt spray test before delivery, because the test time often exceeds hundreds of hours. For this reason, it is necessary to adopt appropriate real-time control production management methods to ensure anti-corrosion performance. It is impossible to estimate the ppm value for the quality of this characteristic. The same applies to lubricants applied to fasteners to comply with the specified coefficient of friction. The maintenance of such a prescribed range (for example: μtotu003d0.08～0.14) can only be ensured by appropriate real-time control production management methods, and checked by random inspection.

These examples illustrate the need for close cooperation between manufacturers, distributors and users.

Problems with changing packaging

The change of packaging increases the risk of mixing miscellaneous products or other parts and causing mechanical damage.

The source of unqualified items and the method to reach the specified ppm value

There are three sources of unqualified items:

Fasteners with unqualified characteristics;

There are other parts or miscellaneous products (different fasteners);

Mixed non-fasteners (metallic or non-metallic).