Every screw fan has probably asked himself how the small threaded bolts are actually made. Screw making is easier than you think. It is important to note that there are different manufacturing processes. Of course, the type of manufacture also depends on the shape of the screw, such as thread, head shape, and tip. In FOLIV screw shop you will definitely find the right one for your next construction project from among 150,000 different screw shops.
First, let’s look at the two basic types of shaping:
- non-cutting forming (hot forming and cold forming)
These are the first two principles. In modern manufacturing processes, hot and cold forming techniques are predominantly used.
Here you have a blank like a steel rod or a piece of wire, which is shaped to fit by milling. The thread is also produced in this way. It goes without saying that the initial diameter of the steel is larger than the later screw diameter, as the material is removed.
This outdated method is usually only used for special screws that are subject to special production. Since only small numbers are produced here, this production is still worthwhile. Non-cutting forming is used for all screws that are required often and in large numbers.
However, it is not the expensive and labor-intensive manufacturing process of machining that is a major disadvantage, but also the stability of the screws. In addition to the loss of material, the removal of the material also destroys the grain. CNC milling machines or lathes are used as machines, or of course the good old handwork. Of course, we also have the right instructions for thread cutting.
Non-cutting forming is the most common way of producing screws. Here again, we differentiate between two techniques:
- Cold forming
- Cold forming is also known as cold extrusion or cold forming.
COLD FORMING (COLD FORMING
With cold forming, screws are produced in large numbers in just a few steps. Most screw manufacturers use this method because cold extrusion is very effective and inexpensive. The manufacturing process is divided into the following phases:
- To reduce
Combinations of the phases mentioned are also conceivable. It is important to choose the right forming machines, which depend on the size and strength of the degree of forming. If sharp-edged or particularly thin profiles are used for the screws, this method of manufacture is not recommended. Otherwise, you have to struggle with considerable tool wear, which is reflected in the production costs.
But we finally get to the production. As you can see in the video below, the wire of a certain steel quality comes into the production hall on large spools, some of which weigh over a ton. For production reasons, this is usually phosphate, which reduces tool wear. With large screw diameters, steel rods are used for the sake of simplicity. Now the workpiece is fed into the first machine and brought to the desired length. The pieces are literally knocked off and straightened afterward.
Now comes the compression. This is particularly interesting because it creates the head of the screw. What at first looks like a cone without a point during the pre-upsetting becomes a hexagonal head later. In the further steps of the upsetting, the complete head is created.
Now we just need a thread. To produce the thread, you can either form the thread or roll it. Here, the screw blank is pressed through two rollers, which are again driven by machines. These two rolling jaws are also called flat jaws. One of the flat jaws is firm, the other is loose. The thread is created by rolling on these jaws. With modern thread machines, almost a thousand screw threads are created per minute.
Often all the machines required are lined up in a row and the individual production stages are handled one after the other. Here again, is the short overview of the complete production by cold forming:
- Wire cut
- Intermediate upsetting
- Final upsetting
- Thread rolling
Here are the advantages of cold forming again at a glance:
- minimal material loss
- high performance and quantity
- no inaccuracies
- high strength
- gentle processing – preservation of the fibers of the metal
- favorable production costs
Hot forging is not often the first choice in screw manufacturing. But as already mentioned above, this method can be used for small quantities as well as for particularly thick or long (> M27> 30cm long) screws. Here the steel or stainless steel is heated strongly until it can be forged. Now the shape can be made. The steel is only heated where it is supposed to be shaped. The surface structure is very rough due to this type of production.
While the cold-forming by the production method rigidly corresponds to the processes, with this manufacturing variant it is possible to give the head any imaginable shape. In other words, there is significantly more scope for special head types. The thread is not created by hot forming, but, as in cold pressing, with rolling or milling.
SCREW QUALITY IN THE MANUFACTURING
There are several aspects that must be taken into account so that only the best screws reach you and are installed. In the next picture, you will find a picture that shows the testing of screws that have just been produced. These should not only be checked by hand for optics and haptics but also checked by machines. But the quality of the screws can already be influenced significantly during production.
In addition to good quality control, the choice of the right machines, clean processing and, above all, the quality of the wire determines the quality of the end product. We only work with suppliers who have their own laboratory and have been known for high-quality standards for years. Because anyone who starts a construction project with screws may not experience any nasty surprises afterward, especially with safety-relevant parts.
In order to ensure a perfect connection during processing, the challenge in the manufacture of screws is to bring the advantages and disadvantages of the material and the shape into harmony during development. You can find out which screw materials are available on our blog. In order to achieve high strength classes, the screws are subjected to additional heat treatment after cold extrusion.
After the screw has been manufactured, the screw is not quite finished. Not only does it have to be checked and packaged, but it also has to be refined if necessary. In other words, the screws are still missing a surface coating. You can also find screw coatings on our blog.