TECHNICAL ARTICLE:

Abstract

Flexible production of a continuous range of profiles and sections using the same set of tool rolls is now possible with the world-unique FCF system. Developed by VAI, this technology was installed for the first time ever at voestalpine Krems, Austria. This paper presents the main design features of FCF technology in addition to production results and benefits.

Introduction

All downtime in tube and section mills for roll-tool changes and other operational interruptions means lost production time and reduced profit. In order to remain competitive, producers are usually required to supply a wide range of products on a just-in-time basis and are also forced to reduce their product stock for space and capital reasons.

As an answer to these demands, VAI has successfully developed and implemented a new flexible forming and sizing system for the production of cold-rolled profiles and sections (e.g., L, U and C profiles, square and rectangular sections). This technology, marketed under the name of FCF—for Flexible Cold Forming—is distinguished by the use of the same set of tools for the production of a complete product size range without the need for tool change. FCF fulfills all of the standard requirements of tolerance, corner radii and product surface quality. Because no tool changes are necessary, the standstill times for dimension changes are greatly reduced and overall productivity is considerably increased.

The innovative FCF system was first implemented at voestalpine Krems GmbH where the outlined production benefits were fully confirmed under operational conditions.

Main Design Features

FCF is the most flexible and productive solution on the market for the manufacture of products with simple cross sections such as square and rectangular sections as well as profiles (patent no. AT 344/98). During forming and sizing operations no tool change is required for the entire range of product dimensions. Product size changes are automatically carried out by means of central adjustment drives which are activated by push-button control. Adjustments in the forming and sizing section are carried out within minutes and tool settings as well as other key operational parameters are visualized by digital displays (Figure 1 and Figure 2).

Figure 1: Schematic View of the FCF System

Figure 2: Typical Operator Stand for Tool Adjustment and Line Supervision

The FCF system was developed and engineered using the most modern design techniques such as finite elements calculations, specialized software in addition to computer-aided design (CAD) to evaluate the forming process. During tool adjustment the self-supervising system assures that the adjustment drives run at the same defined speed, that the turning direction of each individual motor shaft is the same and that the sequence of value changes are within preselected limit ranges. In the event of deviations from the setpoint values, the system automatically stops and displays an error report on the system monitor. Operator errors are prevented by means of the installed control and automation system.

A typical FCF production line consists of forming, welding and sizing sections, as follows:

FCF Forming Section

For the production of square or rectangular sections the FCF forming section consists of three forming blocks where the following activities are carried out (Figure 3):

FCF Forming Block 1: The strip edges are first bent in a series of steps to an 80° inclination, forming a "near-U profile."
FCF Forming Block 2: The remaining horizontal strip is then bent in a series of steps to a 60° inclination, acquiring a "near-C-profile" shape.
FCF Forming Block 3: The C profile is then bent to a near-rectangular shape as the final forming step prior to welding.

Figure 3: Schematic Outline of FCF Forming Steps

The essential difference between FCF forming and conventional forming systems with single forming stands is the arrangement of the tool rolls as shown in Figure 4. Contrary to conventional forming stands which are characterized by the opposite arrangement of the tools on a common shaft, the tool rolls in the FCF system are alternately mounted on the left and right cantilever shafts of the forming blocks 1 and 2. The left and the right strip edges are subsequently bent as they pass the individual tool rolls. The tool roll mounted on the bottom shaft supports the strip across the entire width where strip bending takes place. The upper tool roll is installed on the top cantilever shaft using a hydraulic nut.

Figure 4: Top View of FCF Forming System

Because each pair of tool rolls is mounted on opposite, moveable frames, the production of the complete range of profile and section widths for a specific FCF line is made possible by laterally shifting the frames. This is carried out with mechanically linked adjustment spindles driven by an AC motor. In order to accommodate for different strip thicknesses, the top rolls are moved in an upward or downward direction along the bisector (of two equal angles) between the horizontal and bent strip edges. Again, all of the adjustment mechanisms are mechanically linked and centrally driven by an AC motor.

As a precaution against overload resulting from a sudden strip thickening—as is the case with a cross-welding seam—the upper rolls are protected against damage with the installed cup-spring assemblies.

In the last three forming steps of the FCF block 3 final bending and adjustment of a C profile to a profile ready for longitudinal welding is carried out by the top rolls. The top rolls are exactly positioned to match the height of the profile by means of spindle jacks. As in the FCF blocks 1 and 2, the adjustment mechanisms are mechanically linked and centrally driven by an AC motor. An overview of the FCF blocks 1–3 is seen in Figure 5.

Figure 5: FCF Blocks 1–3Figure 7—Cross Section of FCF Block 3

The strip is driven forward by pinch-roll stands with the same set of cylindrical rolls for the entire production range of the mill. The pinch roll stands are positioned in front of each of the three FCF blocks. Both the pinch rolls and the bottom rolls of the FCF blocks are driven by means of DC motors, reduction gears, distribution gears and universal joint shafts (Figure 6).

Figure 6: Front View with Pinch Roll Stands

Contrary to conventional systems, the longer profile sides are bent vertically in the FCF system. The ratio between the short and long profile sides should not exceed 2.5 because of roll-size-limitation reasons. The radius of the profile corners is determined by the slightly rounded corners of the top tool rolls. Because the tool rolls are not changed in the FCF system, the rounded corners of the FCF top rolls always have the same radius, dimensioned in accordance with the maximum strip thickness.

The FCF line also can also be used for the production of simple U and C channels. Hut profiles and Z profiles can also be produced in which case some of the equipment must be changed because of the reverse bending direction required for these profiles. Equipment change is performed with a quick-change system.

Welding Section

Welding operation is performed using a high-frequency welding system. The strip edges to be welded are squeezed with the use of two side rolls and two inclined top rolls, universally applicable for all product dimensions. In the FCF line the welding is performed centrally along the mill centerline. To assure high welding quality, the roller pressure of the side rolls can be monitored with a digital display and adjusted accordingly.

FCF Sizing Section

Following welding of the profiles, final calibration of the square and rectangular sections is carried out in the FCF sizing section which consists of four DC-motor-driven FCF sizing stands and two straightening stands (Figure 7).

Figure 7: FCF Sizing Section

The same set of universal tool rolls is used for the calibration of the final section dimensions and corner radii as well as for product-size changes carried out by the lateral and vertical shifting of the four cylindrical tool rolls (Figure 8). The top and bottom tool rolls of the FCF sizing stands are driven by means of DC motors, reduction gears, distribution gears and universal joint shafts.

Figure 8: FCF Sizing Unit

In cases where strip bulging takes place during bending, the universal roll plate of the straightening stand #2 can be replaced with a conventional plate with curved rolls to assure a straight-sided product.

An advantage of direct forming of square and rectangular sections in the FCF system is that considerably less tension is generated in the product walls compared with reshaped products (i.e., from round to rectangular). This advantage becomes apparent as shown by the reduced "caving-in tendency" of the side walls when finished products are bent for various downstream applications.

Industrial Application

Practical tests with the FCF system were first conducted at voestalpine Krems GmbH in the 1990s. Following optimization of the process and confirmation of the expected operational benefits, the world's first FCF production line went into operation at this site.

The following profiles have been manufactured at voestalpine Krems since 1999: U Channels: Width: 80–200 mm Height: 10–35 mm C Channels, Square and Rectangular Sections: Width: 30–60 mm Height: 25–80 mm Wall Thickness: 1–3 mm

Figure 9: Examples of Sections Produced at voestalpine Krems, Austria

FCF products manufactured at voestalpine Krems are used in the construction, automotive and logistics industries as well as for structural components in agricultural machines. The profiles and sections are mainly exported to Germany, France, the Scandinavian countries, the Benelux countries and increasingly to the Eastern European countries.

Figure 10: Use of Sections in the Construction Industry

In comparison with conventional profile and section lines, application of FCF technology at voestalpine Krems resulted in the following benefits:

Use of Same Set of Tools for Complete Range of Line Products
By applying universal tools for the production of the complete range of line products, time-consuming tool changes are effectively eliminated. With the application of hard-metal tools, considerably reduced wear and thus longer tool lifetimes were achieved. At voestalpine Krems this led to an impressive 80% line availability for actual production work, compared with a typical 40% production availability in conventional lines.

Reduced Tool-Adjustment Times
As a direct consequence of the automatic FCF tool-adjustment system, a drastic reduction in tool-adjustment times results. This is the basis for the decisive positive impact on operational flexibility and mill productivity.

Improved Operational Flexibility
The unique features of the FCF system allow for the economical production of small order lots in addition to intermediate product sizes—not feasible with conventional systems. This is an important factor for e-commerce applications and for the rapid, efficient and reliable fulfillment of specific customer production orders. The FCF system also makes possible realistic just-in-time production for reduced product-storage demands.

Improved Overall Productivity
As a direct consequence of its high availability, the FCF production line at voestalpine Krems is distinguished by its exceptional productivity, especially for the production of small order lots. This is the key not only for satisfying niche-product markets, but also for penetrating and succeeding in new market segments and regions.

Cost Savings
The accumulative result of all of the above outlined benefits is enormous cost saving in production, maintenance, spare-parts management and personnel expenditures. Far less capital is bound in tool inventory and product storage. Depending on the local conditions, the return on investment (ROI) for a new FCF line is estimated at 2_–3 years.

Because cost savings are equivalent to additional profit, a quantified analysis of the increased productivity and thus profitability of an FCF line is illustrated in Table 1.

Table 1: Increased Productivity and Profitability with FCF Technology

Concluding Remarks

FCF technology fulfills all quality requirements with respect to tolerances, corner radii and product surface quality. Tool rolls do not have to be changed for the complete range of profiles and sections produced by an FCF line. With the use of tungsten carbide rolls in wear-critical positions, the service life of the tool rolls can be increased by up to forty times compared with normal steel tools. This allows for many years of production without reconditioning or changing of the installed tool rolls. The main features and benefits of FCF technology are summarized as follows:

• Forming and sizing of L, U and C profiles as well as square and rectangular sections
• Use of same set of tool rolls for the complete range of line products
• Automatic product dimension change for forming and sizing within minutes
• Fulfillment of all tolerance values with respect to corner radii and surface quality
• Considerably reduced tension in the product walls as a consequence of the direct-forming process
• Highest production flexibility even for small order lots, non-standard dimensions and "just-in-time" delivery
• Significantly improved strip yield with FCF direct forming
  (smaller strip widths required for same section sizes compared with conventional systems)
• Low tool roll and product inventory
• High line availability and thus productivity
• Substantially increased profits and short return on investment

Acknowledgement

The authors would like to take this opportunity to thank Berta Haring, Marketing Manager of VAI Rolling Technology, and Dr. Lawrence Gould, VAI Corporate Communications, for their extensive support in connection with the completion of this paper and in promoting FCF technology.

Authors

Josef Pfisterer: Senior Expert for Tube and Pipe Mill Technology
Karl Steinmair: Technical Consultant Development and Design
Gerhard Schmidberger: Design Engineer