|
Modern cutting machines and techniques in shipbuilding industry
Cutting machines should provide constant cut quality, giving the user the confidence to start secondary processes without correction, says Klaus Decker.
Modern cutting machines are equipped with one or two plasma bevel heads. The heads enable the customer to perform straight cuts or bevel cuts. The torches are equipped with anti-collision devices, which protect them from crashes.
In addition to the cutting operation, the marking of plates plays an important role at shipyards. For many cutting installations, the time spent for the marking operation equals the time spent for the cutting operation.
A system of long standing is powder marking, which uses a special powder through an oxy-fuel burner. The system permits line speed of up to 20 m/min, depending on circumstances. Its drawback is that the powder absorbs moisture from the air and that the system demands maintenance and upkeep. In spite of good upkeep, the line thickness tends to vary.
One recent development in the marking process is "Arc Marker." This system produces an etched line, but, unlike powder marking, the "Arc Marker" system breaks the paint coating and penetrates slightly into the plate surface. This feature is not always desirable. Both systems produce only lines and only in one line thickness. Other types of marking systems also create an opportunity for production directions, by using different line characteristics or by marking with letters and signs, for logistical purposes. But, these systems were not available before the introduction of ink-jet marking.
Surface cleaning
To cut welded plates (16-20 m) for further production of exact measurement, there are panel line machines, which have a span of up to 25 m. These machines are used for cutting the edges for weld preparation and to mark the positions at which the stiffeners should be placed.
For shipbuilders, the manufacture of vessels from shop-primed material is a must. However, other steel fabricators also have to face certain production problems from today's protective paint systems. In particular, the use of zinc-based paints gives the difficulties associated with subsequent welding. If the paint is not removed, the zinc content will reduce the welding speed and, in some cases, will produce porosity.
There are various views to the solutions to these problems. One way has been to integrate shot-blasting equipment in the cutting installation and thus obtain more or less clean metal surfaces, where webs and stiffeners are to be welded at a later stage.
The latest development in this field has been the introduction of special grinding tools integrated in a cutting installation. The grinding tool permits a dramatic speed improvement. The surface cleanliness is also much improved.
New controller generation for cutting machines
The Windows NT-based cutting machine controller is the only "Open CMC" available in the cutting machine market. This powerful control features a Pentium-based PS running Windows NT workstation.
This means that nesting programs, post processors, productivity, production scheduling or remote monitoring software can be run straight on the control. Windows NT provides a stable, open architecture operating system that the customer can use to run any Windows or DOS programs. Some key features of the Vision NT include a familiar Windows graphical user interface, network and Internet connectivity, kerf-on-the-fly with kerf override, programmable cutting parameters, user-definable macro keys and enhanced shape library features.
Programmable cutting parameters
Programmable cutting parameters allow process times and parameters, along with feed rate and kerf values, to be recorded in a file that can be recalled later. A cutting parameter file can be created for each type of material a customer cuts, so that the repetitive, critical task of adjusting timers and parameters can be automated. The operator can manually select a parameter file or the files can be called from within a part program, thus automatically setting the same values every time. The operator can also correct these files himself and can store them.
The newly developed "Adaptive Process Control" provides a higher level of process automation and quality improvement. All the necessary process parameters can be programmed and are repeated during the cutting process with a very high level of accuracy. Some parameters are: Cutting Speed, Arc Voltage, Pierce Time, Gas Flow and preheat Time.
The machines must also be equipped with control functions such as proportional solenoid valves, pressure sensors, flow controls, speed measurements and so on.
Operator calling system
Cutting machines with the latest open CMC controllers can be run without any or with very limited personnel. Connected telephone links to the controller permit status reports for the machine or the cutting process to be sent to the user of the machine. With such a system, one operator can supervise a number of machines, without any problem.
Internet connectivity
This feature enables that the machine can be operated over long distances and can be directly monitored from the machine supplier's service center. The following are some of the applications possible due to the Internet connectivity:
* Direct access to the machine from the service centre
* The software department can trace all functions of machine on line
* Scope function can be transferred to the service center
* Service center can directly install software updates
* Machine parameters can be checked via specific software
* Cutting programs can be downloaded from the cutting machine and checked at the factory
In particular, intermittent errors, which occur at only one time of the day or week, can be detected with Internet connectivity. The service centre can write (store) all activities of the selected machine, including push-button pressing, the cutting program, drive system operation and so on. If an error occurs, the service department can check all functions that were executed at that particular time to diagnose the cause of the error.
(The author is MD, Esab Cutting Systems GmBH, Germany. The article has been reproduced from Svetsaren, a welding review published by Esab.)
Modern cutting machines and techniques in shipbuilding industry
|
