Application 11
Application 11
Application No.11 - Clad Welding Machine
Application No.11 - Clad Welding Machine
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We were approached by a local company looking to develop the next generation of clad welding machines for their business. The company specialises in the supply of corrosion resistant weld overlay cladding and high quality fabrications for the oil & gas, nuclear, renewable energy, water & wastewater and naval industries. They were looking for the basis of these machines to be plc control.
The plan was to build a prototype machine, thoroughly test it in a production environment, then build eleven production machines. PJC Systems were to be part of the development process.
Please scroll down to see more detail of the application
The key components of the system were: Mitsubishi Q series processor, Mitsubishi GOT screens connected via Ethernet, axis control, and serial comms to Nord drives via CC-Link & Can-bus.
The aim of the project was to design a rig which is capable of running every type of job, instead of having a number of machines which would only do specific work. It meant that the control "pendant" became quite a complex item. It was also considered necessary for the operator (welder) to be able to monitor the key parameters in real time. Bearing in mind the nature of the environment, it was important that the pendant was "rugged"; a touch screen hmi would not be a suitable interface. For this reason, it was decided to use 22mm lamps, switches, joysticks & pushbuttons, and to have a simple display, protected by a perspex cover. In the end, however, it was a lot more versatile (and cost effective!) to use a small GOT, (Graphic Operator Terminal) fundamentally as a display, although we did end up with a number of pages, most of which were for maintenance purposes.
The main slides (the aluminium ones) are driven by Nord Inverters. This was the customer's choice, as they have used them satisfactorily for a number of years. It is possible to communicate with these over a network, but using CANbus. Unfortunately a Q series processor cannot talk directly via CANbus, so we had to use a signal interface to convert CC-Link to CANbus. We used encoder feedback into the inverters so that a certain amount of the positioning control can be handled by the inverter itself.The smaller slides (the black ones) were controlled via axis control directly from the plc. Again, the encoder feedback connects back to the drives. These smaller slides are used to accurately control the distance between the weld head and the item being welded.
A fifth drive (inverter) is used to control the feed of the wire into the process. This uses encoder feedback to verify the actual speed, but is not needed for positioning.
The item being welded is secured to a turntable, constantly rotating it as it is being welded. There a several types and sizes of turntable, all with their own inverter control. The plc communicates directly with this via a plug and socket, so that it can accurately control the speed of rotation.
What the Plant does
What the Plant does
The component being welded is being completely clad with the weld. It is, therefore, essential to maintain a constant quality of weld throughout the process. The machine has to maintain:
a constant voltage across the weld head - this will ensure a constant arc
a steady feed of wire into the weld
a constant linear speed of welding
Each time the table completes a revolution, the welding head will step out by a preset distance. This clearly changes the diameter at which the system is now working. Consequently, the speed is reduced accordingly to maintain the same linear speed
The panel was split into two sections: Power (at the bottom) & Control (at the top).
Control System
Control System
The basis of the control system was a Mitsubishi Q-series PLC (Programmable Logic Controller). It controls/monitors all discrete i/o (both digital and analogue), communicates with the inverters (via CC-Link/CANbus) and axis controllers, and communicates with two hmis (via ethernet) and a data station (via RS232).
Datalogging
Datalogging
We also developed some datalogging for the machine.
It was a requirement to be able to log all the process parameters during a whole weld job.
Some of these jobs can last several days, so we split the logging into three logs, rather than clog the system with lots of repetitive data.
Job set-up - details for the job which are only logged when something changes
Logging set-up - set-up of the required logging rate etc
Parameters - data logged at the rate set up by the operator
This is initially logged to a compact flash card in a Red Lion Data Station, saved as a .CSV file.. The Data Station communicates directly with the Q-series plc via RS232. It can be accessed via ethernet.
The data being logged can also be viewed in real time using the Data Station's Web Server function.
The main control panel has a Mitsubishi GT2000 colour touch screen operator interface
This panel is well away from the welding, so the screen is not likely to be damaged. All the information displayed to the operator via the pendant station is also displayed on here.
In addition there are a number of set-up screens which are only used at the start of the job so do not need regular access by the operator.
The original idea was to have fixed displays on the pendant as it was felt that an hmi would be too vulnerable.
After a great deal of consideration, it was decided that the number of displays required would make the pendant far too big.
We came up with the idea of this very small and compact Mitsubishi GOT which is not only of a suitable size, but is also significantly cheaper than the number of displays we were considering,
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