Problems in packaging modification of threaded fastener products

With the customer's demand for improved quality of fastener delivery, manufacturers begin to consider special factors in mass production. Depending on the type, specification and action cycle of the machinery used, the productivity of modern fastener manufacturing machinery (such as cold heading machines and thread rolling machines) can reach 60 to 800 pieces per minute. A fastener manufacturer can produce millions of workpieces per day. Special measures are therefore required to ensure process capacity. In addition, in the manufacturing process, the workpiece is loaded into the container many times and transported to the various processing points, the number of shipments with the production chain.
The length of the (e. g. cold heading, rolling, cleaning, quenching and tempering, surface treatment, anti-corrosion treatment, etc.), more than 20 times is normal. Special measures are required to prevent mechanical damage (especially sharp-angled collisions) and to avoid mixing during transportation.
In the current state of production technology, the quality goal of zero defects is impossible to achieve. In order to achieve the goal of zero defects, the transitional goal is established by specifying the criteria for evaluating the quality of the delivered fasteners. The conditions set in this standard are based on the number of non-conforming products per million products and/or the process capability value (Cpk) of the specified characteristics.
A.1.2 Product process impact
The measurement and tolerance requirements for 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 the tolerance depends not only on the material used, but also on many other factors; for example, the profile formed in the open and closed mold is not as accurate as the profile formed in the closed mold. Some cold forming processes inevitably have sharp corners. In this case, it is often not possible 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 depending on the thread processing method.
For large ratio of length to diameterScrewThe possibility of bending will also increase (especially when the final process includes heat treatment quenching and tempering). For individual parts and processing methods, the corresponding tolerances should be considered.
When the workpiece is coated with anti-corrosion coating, the phenomenon of uneven coating thickness is inevitable. This is related to the size of the workpiece and the coating method. The uneven thickness may affect the corrosion resistance of the workpiece in the salt spray test. In this case, depending on the type and geometry of the fastener, its anticorrosion performance is greatly 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. Therefore, it is necessary to adopt appropriate real-time control production management methods to ensure anti-corrosion performance. It is not possible to estimate the quality of this characteristic in ppm. The same applies when the fasteners are lubricated to comply with the specified coefficient of friction. The maintenance of such a specified range (e. g. μtot = 0.08~0.14) can only be guaranteed by appropriate real-time control of production management and checked by random inspection.
These examples illustrate the need for close cooperation between manufacturers, distributors and users.
A.2 Problems in packaging modification
Changing packaging increases the risk of mixing in miscellaneous products or other parts, as well as causing mechanical damage.
A.3 Sources of nonconforming items and methods for reaching the specified ppm value
There are three sources of nonconformities:
-Fasteners with non-conforming characteristics;
-There are other parts or miscellaneous items (not the same fasteners);
-Mixed non-fasteners (metallic or non-metallic).