With the rapid expansion of the Chinese high speed rail network underway, and major levels of investment in track and rolling stock infrastructure in place, Siemens Industry Automation and Drive Technologies has worked with Halifax-based PTG Heavy Industries to help develop a new and innovative welding machine.
It is set to revolutionise welding technology and play a central role in realising the ambitious plans of a vibrant Chinese railway industry.
The Crawford Swift “Powerstir” friction stir welding (FSW) machine – developed by PTG in a joint venture with China Friction Stir Welding Centre – has already helped to manufacture China’s longest-ever single friction stir welding railway carriage panel – measured at over 15 metres in length.
It is also set to underpin future and significant levels of railway carriage manufacturing production for China, as the nation seeks to develop the world’s most comprehensive high-speed railway network that will boast 800 streamlined bullet trains by 2013.
The “Powerstir” machine offers a number of clear manufacturing benefits including welding timescales up to five times faster than seen with conventional welding techniques, as well as vastly superior joint strength and weld appearance.
These are all important factors for the production of the railway carriages that will be needed by China.
The machine specification utilises a number of Siemens products and motion control technology, including the Sinumeric 840DSL solution line with 5 axes control, Sinamics S120 drives, 1FT7 high performance, high efficiency, compact servo motors and ET200S distributed I/O.
Friction stir welding is a solid state welding process which joins materials by plasticising and consolidating the material around the joint line.
A rotating pin generates heat which creates a tubular shaft of plasticised material around the pin.
Then pressure provided by forward motion and the downward force of the tool shoulder forces the plasticised material to the back of the pin, cooling and consolidating the material.
No melting takes place and the final result is a fine-grained, hot-worked weld with no entrapped oxides of porosity.
FSW is a major advance in terms of legacy welding methodology.
With speeds of up to 2000 mm/min, the machine offers welding speeds more than five times faster than conventional techniques.
Traditional methods also suffer in a number of ways. Ranging from conventionally welded material being weakened in the heat affected zone and associated high energy consumption levels, to the creation of distortion.
This then requires secondary operations, the need for two operators per weld head and a lack of weld data records – as well as fume extraction and environmental issues.
To offset these drawbacks in the production process, FSW, through the Crawford Swift Powerstir machine, generates only low distortion levels in long welds, has excellent mechanical properties established by rigorous fatigue, tensile and bend testing and no fumes, porosity or spatter issues.
The tool is non-consumable and can operate in all positions, as well as offering measurable energy efficiency advantages. Crucially, it produces vastly superior joint strength and weld appearance with no post-weld grinding required.
The machine also contains a number of innovative and advanced technology features. These include a UK designed and built medium duty 3000 RPM 15Kw water cooled spindle, 60Kn Z axis welding force and 30Kn X & Y welding force.
In addition, an optimised front end has been developed by PTG Heavy Industries for FSW applications and employs force control in which the operator sets a welding force and the machine adapts welding parameters through closed loop control to maintain a preset welding tonnage ensuring that welding parameters are optimised.
The machine also carries state-of-the-art seam tracking and height sensing laser equipment enabling weld height and seam in the “X, Y” plane to be tracked along the curves of an aluminium panel or extrusion – an essential requirement in the welding of high speed train carriage panels and roof sections.
