Cold Pilger Rolling: Part One


Cold pilger rolling is a very well established process for efficiently and effectively controlling product quality and assisting in meeting stringent product manufacturing specifications.
Here we look at two of the most common milling techniques in VMR1 and HPTR2 which use compression rather than tension to achieve sometimes complex cross section dimensions.

One of the most important and abundant finish metallurgical products are seamless tubes. After hot rolling, a part of these tubes goes to the end-user, the other part serves as a billet to the cold pilger rolling process. The tubes, made by cold pilger rolling, are used by traditional and perspective consumers - machine-building enterprises.

As such, theses consumers make higher demand to the assortment and also the product quality. The following factors can be related with such demands: the usage of hardly-deformed materials, which have the high user’s quality and the manufacturing of the tubes with a complicated shape of cross-section – so called hollow profiles. The preciseness of the geometrical dimensions, the surface quality, the structure and mechanical characteristics of the ready tubes require under-recrystallisation temperatures for finish size deformation.

Cold pilgering is a longitudinal cold-rolling process that reduces the diameter and wall thickness of metal tubes in one process step. Depending on the material, the cold pilger process achieves cross-sectional reductions of more than 90 percent in a single working cycle.

Figure 1 shows the principle of the cold pilger process.

As mentioned above, the part of billet (hot-, cold rolled or extruded etc. tube) 1 that equals to feeding volume, gets into moving zone of working cage 2, where rolls 3 with variable dies radius are installed. The variation of dies radius is provided by specific tool calibration. In the rolling process summary deformation zone (working cone) 4 is formed at this stage. Its internal surface is formed by the mandrel 6, and the consequent deformation of the parts of billet with the low level of partial strains in working cone is the tube with finish size 5.

Considerable progress in the field of technology and pilger rolling equipment for manufacturing of precision tubes was indicated a long time ago. At that time the concepts such as cold and warm tubes rolling were formed, they had a new sense for technology and equipment improving.

Figure 1: The scheme of cold pilger rolling

The two most common ways to cold-reduce tubes by compression are VMR1 and HPTR2 cold pilgering mills. Although both VMR and HPTR dies reduce tubes via compression rather than tension, the complexity of tooling design and manufacturing varies greatly between these machine types.

The variable cross-sectional groove of a VMR die requires special expertise and equipment to be designed and built, as does the matching mandrel (conical mandrel). By contrast, the cams, cylindrical mandrels, and constant cross-sectional grooves of HPTR dies are relatively simpler to design and build. This allows the production on conventional machine tools, which gives HPTR die owners much more flexibility on sourcing tooling and modification of tool design.

Figure 2: VMR and HPTR pilgering process comparison

The cold pilgering process is suitable for all metals. Typical materials are mild steel, stainless steel, ferritic steel, low-alloy steel, copper and copper alloys, titanium alloys, zirconium alloys, and nickel alloys. Using cold pilgering to reduce precious metals is conceivable, because practically no material loss occurs. The deformation strengths of the cold pilgered tubes range from 400 N/mm2 for copper to more than 1,500 N/mm2 for special alloys.

Some applications, such as baseball bats and golf clubs, rely on cold pilgering to create the intermediate, tapered shape. Other applications are lightning poles, finned tubes, and nonround tubes with internal or external longitudinal ribs.

Table 1: Typical materials for cold pilgering







Total Materia has mechanical properties inserted for many thousands of materials and accessing them is just a click of a button away.

Covering a wide variety of property information, it is easy to find yield stress, tensile stress and elongation data for a huge number of materials within the database.

Enter the material of interest into the quick search field. You can optionally narrow your search by specifying the country/standard of choice in the designated field and click Search.

solution img

Total Materia will generate the search list for you to select the material of interest from the material list.
Click on the material of interest.

solution img

On the subgroup page, click the Mechanical Properties link to view property data for the selected material. The number of mechanical property data records is displayed in brackets next to the link.

solution img

The mechanical properties data will be then be displayed along with all selected material information for your reference.

The mechanical properties data will be displayed for all available conditions and treatments.

solution img

It is also possible to switch between metric (SI) and Anglo-Saxon units with one click depending on your preference.

solution img

For you’re a chance to take a test drive of the Total Materia database, we invite you to join a community of over 150,000 registered users through the Total Materia Free Demo.