COLD ROLL-FORMING – THE ROLL-FORMING MACHINES

Cold roll-forming is a process in which metal profiles are continually produced by deformation of sheet steel passing through several stations of rolls that gradually shape the product required. From the example below it is possible to see how the final product is achieved with 21 rolling stations, starting from strips of steel.

The roll-forming machine is just one of the components of the roll-forming line, which is composed of different parts connected together.
Here below there is a typical and relatively simple example:
  • Un-coiler
  • Roll-forming machine
  • Turk’s head
  • Shearing (stop or fly cut)
  • Discharge
  • Electric and hydraulic system for line automation and management ( rather complex system)
Here below there is a more common and complete example:
  • Un-coiler
  • Strip joining unit
  • Straightener
  • Feeder
  • Mechanical or hydraulic press
  • Sheet in-feed unit- Roll-forming machine
  • Turk’s head – Shearing (stop or fly cut)
  • Discharge
  • Stacking/packing
  • Electric and hydraulic system for line automation and management ( rather complex system)

The first type produces profiled rods with random lengths.

The second type produces punched/perforated profiles which are often cut to size   

Another frequent type includes a welding system to enable the production of closed section profiles. There are different kinds of welding systems: the most common is HF welding, which achieves a very fast and effective production. Alternatively laser welding can be used ( more expensive, more flexible solution with lower productivity compared to HF) or TIG welding (low cost, low versatility, and low productivity). The various components of the lines vary according to the features of the metal to be rolled:

– Galvanized steel, painted steel, stainless steel, aluminium, other

– Strip thickness

– Strip width

– Reel weight.

A critical aspect in defining a roll-forming machine is the shape of the profiles to be produced, such as: simple with few bends, complex even if open section; or closed section, either clinched, seamed or welded (HF welding or Laser/TIG welding). Roll forming machines are divided in several categories:

(A) According to the features of the main drive:

• with directly coupled gears

• with idle gears (tumbler frame type)

• with cardan shafts

(B) According to production flexibility

• with fixed or variable inter-axis distance (between upper and lower shaft)

• with fixed or mobile side supports

• with cassette system for quick and easy roll changing

• with upper shaft hydraulic control

• with fixed or mobile roll support shafts

• with or without upper roll support shaft control/adjustment system

(C) According to the product features

• with cantilever shafts

• with head and tailstock

• with a variable number of heads, approx. 6 to 36

• with roll support shafts with variable diameter of 35 to 120mm

• with or without intermediate machines

Up to this point we have presented machines which compose the roll-forming lines but not as yet dealt with the most important and complex aspect, such as the type of equipment needed in order to achieve a specific type of profile. In other words, a roll-forming line alone cannot produce any products if it is not equipped with appropriate sets of rolls and punching ( in case the profile should need to be punched or perforated).

The most complex part of the line is in fact the set or series of rolls:

  •  The first and most important operation consists in designing the rolls appropriately by expert and specialized engineers who operate with the aid of specific CAD software.
  • The rolls are then produced with numerical control machines using different types of hard materials in function to the type of metal to be rolled.
  • After this the rolls are subjected to rigorous tests entailing fine tuning operations (generally requiring only minimal adjusting) in order to achieve the profile shape required, within the tolerance limits specified in the contract. Afterwards, the automation of the line is tested in terms of productivity optimization, performance of the contract terms and compliance with the safety regulations.