It’s as unusual as it sounds.
The idea is so simple that one must ask; “What took so long for this to happen”.
     
There are commonly known procedures in the industry to produce spirals. Procedures such as rolling, spinning, turning and twisting can produce a spiraled part.
In the process of making blanks for Hammer Drills, the blanks are typically cold headed and then the spiral is created in a secondary operation. It would only make sense to complete the blank and spiral in the same cold heading operation.
In utilizing Sieber’s experience with segmented tooling in progressive cold forming presses and in particular with our success in forming threads on parts in the header with our applied for patented process, then it was only a natural progression to implement this expertise in the making of spiral parts in the cold header as well.
The die segments with the desired spiral configuration are closed onto the blank and then with an extrusion like action the blank is forced through the segments thus creating the spiral. (See view 1) At the completion of the stroke the segments are opened to allow removal of the part.

                               



The tooling segments are relatively short as compared to the part, the tooling only starts the initial revolutions and the spiral is generated as the blank flows through the segment. The entire contour does not need to be generated since the spiral is created in the initial shape of the segment.
It is not an issue if there are multiple steps in the spiral, but it is preferred that the spiral has the same pitch at the various steps on the outside diameter. This maintains a constant speed of material flow. Variations in the blank design influence the material flow of the spiral. In view 2 there are several illustrations of blank configurations. Example “B” has a balanced flow and uniform forming pressure. It also requires less pressure than example “A” or “C”.


It is also possible to produce profiles with a straight head. This allows for a better surface to fasten the cutting blade to the drill blank. In this scenario the desired pre-form is created in previous operations and thereby the blade and spiral combination can be formed. The flat bladed preform needs to be long enough to extend beyond the spiral shape of the tooling insert, this way it stays straight after forming of the spiral. (View 3)

There is a significant difference in a rolled profile as compared to an extruded profile. In the extruded profile you can control the edge condition, unlike the folded over edge condition as in view 4.
gepresst | gerollt

Shapes that were not capable of being produced with conventional methods are now possible to be made with the cold heading process.
In comparison to machined spirals, where we have chip removal in the process, we can save time and material by cold forming the part. This is especially true when the spirals have a very short pitch.
The technical boundaries for the process are set by the formability of the blank material, and the size and tonnage of the available equipment to produce the part. The tooling life is also a factor and is affected by the material and size of the part being produced.
The focus of this article has been for the manufacture of Masonry and Hammer Drills, but we are confident that the process can be applied to other parts requiring a spiral shape.

Sieber has applied for a patent for this process.

SIEBER Forming Solutions GmbH, Tiedenkamp 1,
24558 Henstedt-Ulzburg,
Tel.: 49 41 93 90 07 55, FAX: 49 41 93 90 07 48,
E-mail: info@sieber-fs.com, www.sieber-fs.com