MANUFACTURING TECHNOLOGY


origins in the fastening industry, so the desire to form threads was there right from the start. A wide variety of approaches to tackling


this problem can be found in publications. But most of them are hard to implement because of the complexity of the tools or the processes or the faults that developed while producing the threads. One system that became accepted


involved using clamping tools, particularly in order to produce reductions in the cross sections in the centre of components – for example, ball pins. The jaws are clamped around the thin cross section and this allows the remaining material to be compressed into a thicker cross section or moulded in the jaws. The jaws are then opened to release the component. A similar process is used when pressing


outer threads. The crucial difference is that the jaws form the thread when they close and the blank was previously forged in such a way at the points where the jaws close that no material can slip into the clamping gap of the jaws when the unit is closed. See Fig. 1.


Formed threads I


t may sound amazing, but it really is true. The idea is so simple that the question must be asked: Why did it take so long? Steel forging had its


Hall: 6 Stand: M141


Hard to believe? Well it stopped and made us think - so we asked Sieber Forming Solutions to put the case for a radically different approach to manufacturing threaded parts.


These blank cross sections illustrate


a variety of possibilities in this field. It is important to note that no material can get into the clamping points of the jaws. The diameter of the blanks is larger when pressing than when rolling – if compared to cross section forms that are then rolled. The main reason for this is that the material also flows into the relief notches when being pressed. So we recommend that the cross


section for the blank is discovered by using simulation software. The relief notch for the blank is visible


on the thread at the ends. Any weakening of the tensile strength of the cross section is almost negligible (1-2%). Fig. 2


Thread pitches can be formed just as


with tooth wheels, in order to be self- locking, they can be formed by oscillation like a spring in order to provide zero backlash or they can change their form and so change from pointed to round in order to allow screwing at an angle. The thread does not have to be cylindrical – the cross section can be a polygon, as is the case with self-tapping threads or other applications. One major difference in comparison with


rolling involves the forming of the crest of the thread. Fig. 4. The thread crests are always round and do not have any clamping marks. This means that there is no risk of people injuring themselves on unrolled profiles, the threads are very much less sensitive to impact and are better suited for coatings at the tips.


Fig. 4: Contrast between threads formed by forming and rolling.


It is possible to combine several


threads or threads with knurls or splines. When forming knurls or splines, for example, three dies, three teeth or tooth crests are used. Fig. 5.


Fig. 2: Thread forming at a jaw clamping point. It is also conceivable to deviate from


Fig. 1: Blank form when pressing threads. The cross section of the blank can


be formed from a circle with side relief notches. In this case, the outer sides of the jaws first bite into the blank. But the cross section can also be formed from three circles. In this case, the jaws immediately come into contact with almost the complete inner profile (thread profile).


the standard circular feature of the thread on a component; the thread or feature can be conical or be combined with any other shapes. This process opens up completely new design options in addition to milling, rolling or cutting. Fig. 3 illustrates some design ideas.


Fig. 5: Formed knurls. This concept is not just used


Fig. 3: Variations of formed threads. 84 Fastener + Fixing Magazine • Issue 67 January 2011


for forming outer threads on solid components, but also hollow ones. In this process, a material is pressed into the closed jaws with a mandrel. Fig. 6.


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