A steel roll mill takes a roll of steel "strap" and passes it through a series of rollers which progressively shape the cross section of the strap and form a channel, tube or other shape.  As the material is rolled, pieces are cut to length while the material is moving.

Roll mills typically produce large quantities of identical peices of the finished product as quickly as possible.

Our client wanted to produce batches of rolled steel in which each piece was a different length, and included holes punched in the sides of the finished product at varying locations for each piece. 

This presented several problems:

• Varying length parts mean that the process control is more complicated, and the description of the production requirement is quite complicated.
• The holes in the sides of the finished product must be punched before the material is rolled, however the material cannot be cut until it is rolled.
• The production requirement included standard batches of identical pieces, and mixtures of varying lengths with varying hole locations.
• Vary part details, mean that the parts must be produced in the correct order, otherwise later production stages are slowed by having to sort the pieces.
• In order to roll different shapes, the rollers must be a changeable module.  The guillotine must also change in order to cut different shapes.  Some cross sections require a guillotine which "wastes" some of the material causing a loss of material each time it is cut.
• The punch tool must be changeable for different hole requirements. 
• Different material shapes and thicknesses require different drive gear ratios making material measurement more difficult.
• Material cut length and hole locations must be accurate (1mm).

This was a significant departure from previous roll mill projects, where production speed is the highest priority, and roll mills typically only even roll one size of product.

Extensive investigation and research were the first parts of this project.  Feasibility was established, and the scope of the project was established.  This roll mill would be much slower than traditional roll mills.  The design for a production batch would be stored as an access database.  The design would be developed using the production software (without the mill), then emailed to the mill and produced.

Firstly the mechanical components of the roll mill were built and tested.  An SEW servo drive was used to power the mill.  An external movement encoder is used so that the drive gear ratio can be changed as required.  The drive was programmed to allow control button operation of inching when loading material.  The hydraulic power pack, punch and guillotine are controlled by the drive, so that no cutting operations are possible while the material is moving.

A PC was connected to the SEW Drive unit via a serial port.  Initially a simple HMI control panel on the PC was used to control and test the drive and hydraulic units.

While the mechanical components were being built and tested, the software to design and edit the production packs was developed. This allows you to specify a "pack" of "sticks".  Each stick has a length, a hole location list, and a count.  The sequence of the sticks in the pack is the production sequence.  A graphical display of the pack provides a simple check of the design against the intended function.

The roll mill software was then connected to the SEW Drive unit and we began developing the machine control software.  Initially manual control was implemented.  This allows the user to specify a series of "move", "punch" and "cut" operations.  The list can be edited, saved to a file, and executed on the roll mill.  Then the ability to repeat a control list was added, making it possible to automatically produce batches of idential sticks.  The safety controls and pause or cancel production functions were implemented and tested.

Next the ability to read a pack design database and convert it to a move, punch, cut sequence was developed and tested.

The mill "raft" which carries all the rollers are identified by number, and the software will produce a move, punch, cut sequence suited to which raft is fitted.  All the hydraulic controls and manual overrides are implemented on the control screen.

This mill has now been in production for over 12 months.