As unaccustomed as it sounds, this is the reality.
The idea is so simple that one must ask why do this now. What took so long?
Since the origin of the metal stamping industry, which initially served the fastener industry, there has always been a desire to produce formed threads in the press.
In past publications one finds evidence of failed attempts in the pursuit of thread forming. Failures were mainly attributed to the complexity of the tooling, the inability to accurately control the process and too many variables in the thread requirements. These issues contributed to this process not prevailing in the industry.
One long lasting process implementation is the use of segmented tooling to produce product such as Ball Studs. These and similar components require cross sectional reductions centrally located on the component.
The segments secure the component at the thin cross-section, this allows the remaining material to be compressed to a thicker cross-section or allow the material to flow in the developed recesses of the custom made segments.
In the forming of an outside thread, the concept is very similar to the process described above; the primary difference is that the segments are forming the thread. The blank which is being formed had recesses formed in a previous station to allow for the flow of excess material, this process step eliminates the possibility for material getting in between the segments and prohibiting proper closure of the segments. See view 1.
he blank can be a round diameter with relief notches, providing for material flow.
The required blank configuration can also be formed from a round blank. The resulting blank shape with the relief notches shown above in view 1 are required to accommodate the material flow generated during the forming process.
In the above example the segments start to compress the material at the exterior sections of the formed lobes, these are a result of forming the relief notches from a round blank.
View 1: Bank configuration prior to thread forming.
The relief notches and blank configuration can take on many variations, the key is that there is adequate room for material to flow into the relief area and not restrict the closure of the segments.
It is strongly recommended that the blank configuration be developed utilizing simulation software, this will speed up development, minimize the gap, and maximize manufacturability.
Due to the presence of the relief notches, weakening of the component tensile strength is estimated to be negligible, approximately 1% to 2%.
It is also conceivable to deviate from the standard round feature of the thread on a component; the thread or feature can be conical or have any other custom shape. The shape can also vary along the length of the feature.
This concept brings many more options to the manufacturing process than the current rolling or machining process offers.
The thread pitch can simulate a gear pitch; it can simulate a coil spring in pitch as well as transition in shape from rounded to sharp and all simultaneously on the same feature. The feature is not restricted to be cylindrical, the shape can be conical and the cross section can be a polygon as typical on self-tapping screws. Shape and feature size can be customized to your needs.
It is possible to combine multiple threads and edge features such as knurls or gear teeth on a component. By knurls and gear teeth being formed using three segments there will be a void in three places where the segments meet. View 5.
The major difference from the Formed Thread to a Rolled or Cut thread is the configuration of the thread peaks. View 4. The peaks tend to be more rounded, and do not have the sharp endings at their tip. The formed tread is less likely to cause injury from cuts due to the rounded condition of the peaks; the feature is also more forgiving to breakage from impact or shock. The rounded peak is also better suited for today’s coatings to adhere versus a sharp or pointed thread.
It is possible to combine multiple threads and edge features such as knurls or gear teeth on a component. By knurls and gear teeth being formed using three segments there will be a void in three places where the segments meet. View 5.
view 5: Formed flanges or edges.
Along with the forming of threads on solid core components it is also possible to apply this concept to thin hollow walled components.
In this application a mandrel is forced through the component after the segments have closed around the hollow component. View 6.
View 6: Thread forming on hollow components.
Unlike the requirement to provide relief notches on solid core thread forming as in view 1, there are no such requirements on hollow parts. There are advantages to be had in customizing the inside diameter of a hollow part but these need to be developed on a part-by-part basis.
Along with the forming of threads on solid core components it is also possible to apply this concept to thin hollow walled components.
In this application a mandrel is forced through the component after the segments have closed around the hollow component. View 6.
View 6: Thread forming on hollow components.
Unlike the requirement to provide relief notches on solid core thread forming as in view 1, there are no such requirements on hollow parts. There are advantages to be had in customizing the inside diameter of a hollow part but these need to be developed on a part-by-part basis.
The manufacturing of threaded hollow cored components in the press offers major cost reductions as compared to the current high cost manufacturing process. Today, due to the high manufacturing costs of threaded parts they are limited in application.
Not only does thread forming in the press eliminate a costly secondary operation it provides a completed component right off the press. Typically this component can now be made with considerable material savings versus a component machined in secondary operations.
With the ability to limit the area where the special feature gets applied it makes it possible to apply the feature where needed this enables one to use tougher materials and reduce the forming pressures.
It is not always necessary to have the threaded feature applied to the entire component; this minimizes forming pressures and provides the feature in the functional area of the part. View 8 gives examples of this application.
In view 9 is a selection of cross-sections, which can be applied to hollow thread forming. This view shows a combination of sections for both types of thread forming applications.
In view 10 you see the cross-sectional view of the thread forming process of a solid core component in action. The concept incorporates a special sleeve, which houses the segments. In order for the segments to close on the blank the sleeves motion is guided along its downward path to a solid stop. The motion is designed to limit any linear growth of the component.
The application process of the thread forming can take many variations. Below are some applications we recommend which are ideally suited for this process.
1. You have an open press station to add the thread forming.
2. Top heavy parts.
3. You require multiple features, flanges or knurls.
4. The threads must start immediately below the head or shoulder.
5. The part is thin walled and hollow.
6. The starting point of the thread has a specific orientation..
7. The thread can serve multiple functions by its shape and design,
conical, polygon, sharp, modified pitch,…
8. The point profile desired does not allow for the roll over typical to
thread rolling.
9. The relief notches are used to clean out the mating thread.
10. The relief notches are used to vent air, drain oil or other liquids.
