November 29, 2001
This article discusses three main criteria that govern tube mill tooling—design, materials used in their construction, and alignment of tooling on the mill. Discusses advancements in design due to CAD technology; experimental use of ceramic and plastic materials for making tooling; and the use of subplates and interchangeable components to ease tube mill alignment.
One of the most important lessons any successful tube mill producer learns is that high-quality tooling is mandatory to achieving and sustaining top-grade production values. To put it simply, tooling is to a tube mill as an engine is to an automobile: You can't get where you need to go without it.
Tooling that stands up to the harsh demands of a tube mill that runs two or even three shifts a day is absolutely necessary.
Although each tube mill is custom-built to fit manufacturers' needs, all tooling shares common characteristics. These similarities are:
In the past few years the use of computer-aided design (CAD) programs has helped design engineers to establish higher tooling standards. Before a block of hardened steel is ever turned on a lathe, software programs allow engineers to check their work in three dimensions to see how it holds up under the stress of production conditions.
These programs also play an important role in turning design into reality. The actual production of the tooling is an eight-step process — soft turning, keying, stamping, heat treating, flat grinding, hard turning, boring, and polishing — that turns tool steel into a complete set of forming and sizing rolls.
Precision components are developed through the latest interfacing between computer and production equipment under the guidance of the design and production engineers. CNC lathes and grinders help toolmakers to manufacture finished tooling consistently.
Refurbished tooling can be turned even more quickly in an emergency, especially with the use of CAD programs that compare worn rolls with their original condition.
Equally important, CAD programs can generate drawings for optical comparators so inspectors can check rolls to determine if they need to be reconditioned or replaced. They are also useful for checking concentricity, total indicator runout (TIR), and bore wear.
Such inspections allow manufacturers to hold their tooling to the tight tolerances necessary to manufacture thin-walled products made from aluminum or other malleable metals.
A continual concern for many manufacturers is producing tubing that is unblemished. The answer lies in using materials in the tooling that are not abrasive enough to mar the finished product.
Using different coatings on the tooling also can save product appearance and improve the efficiency of dies and blades.
Most sizing and forming rolls are turned from D2 hardened steel, but recent advances show that carbides and ceramics have a place in the manufacturing of sizing rolls. Researchers are making big strides in the use of ceramic materials, which were once thought too brittle to stand up to daily use. Improved plastics also show potential for tooling applications.
Coatings serve two purposes: They protect the product and increase the life of the tooling. Coatings such as titanium nitrate increase the hardness and the lubricity of tooling, cutoff guides, and blades.
After the tooling is manufactured and passes quality inspection, the last step is to align it properly.
For welded seam tube mills, the tooling commonly is mounted to interchangeable subplate systems. These systems allow the operators to reconfigure the mill to run different tube shapes and materials.
Improved performance means fewer subplates can be used in the production line of the tube mill, shortening not only the size of the tube mill but the changeover time as well. A typical mini-mill has 10 stations, while larger tube mills have up to 20 stations.
Aligning these systems is critical, and one way to ensure constant alignment is to build them with interchangeable parts. Interchangeable parts play a role in the upkeep of quick-change tooling plates, which have been in use for more than a decade and continue to be improved with better tooling components.
Besides periodic inspections of the tooling, users must check to see that the alignment of the system falls within authorized specifications. Adjustable stock guides facilitate mill alignments when adjustments are necessary.
Design, materials, and alignment are three of the important considerations in tube mill operations. A fourth component, maintenance, is crucial after the tooling is installed.
Not limited to roll tooling, a maintenance program can include inspections of roll stands, weld boxes, dies, and blades. Keeping the tooling rolls clean also helps to improve mill operations.