The usage of Friction Stir Welding in the Chinese shipbuilding industry.
Selected parts of the article.
There are many types of aluminium alloy ships, ranging from 5m long rigid inflatable boats, 50m long military patrol boats to more than 200m long luxury cruise ships. Therefore, the shipbuilding industry needs aluminium panels of different shapes and sizes. In 2003, China FSW Center (CFSWT) in Beijing designed and fabricated its first FSW industrial product-line for a small company in Chang Zhou ( Fig.21). This PLC controlled equipment can weld 2600 x 1100mm panels from 6mm thick aluminium extrusions for use in various sectors of the transport industry.
The first industrial FSW production facility in China Fig.21. The first industrial FSW production facility in China
China FSW Center designed and produced the first large FSW machine for wide ship-panels in China in 2006 after considering production, weight and transport aspects. This FSW machine ( Fig.22) is designed in separate modular parts. The main frame is separated from the hydraulic clamping system. The clamping forces, which are needed to keep the parts in position, do not influence its working precision. The CNC system, which can be used to set and adjust the welding parameters, is also developed as an independent unit. The system provides two integrated control methods and can be used either in closed-loop position or closed-loop pressure control mode according to different parts and their structure. This machine can weld aluminium alloy sheets and extrusions from 2 to 6mm thickness. The largest size panel produced so far was 60m 2 (12m x 5m, Fig.23).
Fig.22. CFSWT's first 12m long FSW machine for wide Al panels Fig.23. FSW of 5 x 12m large aluminium ship panels at CFSWT
CFSWT's first 12m long FSW machine for wide Al panels FSW of 5 x 12m large aluminium ship panels at CFSWT
The CFSWT machine can be used for batch production of wide stiffened panels, which are used in high-speed aluminium alloy ships. Since the introduction of FSW panels, a new era started for the Chinese aluminium shipbuilding industry. First of all, batch production of panels by FSW helps to resolve on-site welding problems significantly. This technology has also simplified the design of ships. And most importantly naval architects have now more options, when they design new structures regarding material selection:
* FSW can join extruded AA 6082 to corrosion resistant AA 5083.
* Forged or stamped parts can be welded to castings.
* Thin sheets can be welded to thick sheets or plates.
* MIG welds can cross over friction stir welds, e.g. when joining FSW panels to girders ( Fig.24).
Crossover of MIG and FSW Fig.24. Crossover of MIG and FSW
Batch production by FSW also reduces the welding workload in shipyards. Shipbuilding changes from manual fieldwork to standardised production lines. Production efficiency of shipbuilding is therefore greatly improved. And finally, the residual stresses of friction stir welded aluminium alloy panels are very low and distortion is very small. Parts of ships can therefore be assembled more accurately, and the precision of ship modules and the final shape of ships can be significantly improved. Nowadays, the concept of using prefabricated FSW panels for shipbuilding is popular at shipyards in Dalian, Shanghai, Wuhan, Guangxi and Guangzhou. These wide panels have successfully been used in many shipbuilding projects, including ships designed and fabricated in China for export to Vietnam and Micronesia ( Fig.25).
FSW used on Chinese aluminium alloy ships for various export markets Fig.25. FSW used on Chinese aluminium alloy ships for various export markets
The Type 022 Houbei Class is the Chinese People's Liberation Army Navy's new-generation stealth missile fast attack craft (FAC). The boat features a unique high-speed, wave-piercing catamaran hull with evident radar cross-section reduction design features ( Fig.26). A number of Chinese shipyards across the country have been involved in the construction of the boat and it has been reported that FSW aluminium alloy panels have been used to produce this very advanced navy vessel in China. The futuristic design of this vessel has been admired internationally. This military stealth catamaran is believed to be equipped with 4 anti-ship missiles, 12 surface-to-air missiles and a 30mm gun. It has great stealth capability, and can move very quickly in various sea conditions.
The Chinese Friction Stir Welding Centre was founded in 2002, after an agreement was signed by TWI and Beijing FSW Technology Ltd, which is an offshoot of BAMTRI - Beijing Aeronautical Manufacturing Technology Research Institute. The Centre has made remarkable progress in the last five years, employing over 30 people and building a number of different machines for customers. TWI now has 22 FSW licensees in China, most of them as a direct result of the collaboration with BAMTRI. So far the following Chinese companies have been licensed to use the patented FSW process:
Table 3. TWI and BAMTRI have issued 22 licenses to Chinese companies to use the patented FSW process
* Beijing FSW Technology Co. Ltd
* Beijing Xinfeng Mechanism Factory
* Capital Aerospace Machinery Company
* Changzhou Railcar Propulsion Eng. R&D Centre
* China Aerospace Science & Industry Nanjing Group
* East China Shipbuilding Institute
* Gansu Polytechnical University
* Harbin Institute of Technology
* Hongyang Machinery Factory
* Institute of Metal Research Chinese Academy of Science
* Jilin 3305 Machinery Works
* Lanzhou University
* Nanchang Institute of Aeronautical Technology
* Northwestern Polytechnical University
* Qing Hua University
* School of Industry Senior Mechanic Hunan
* Shanghai Aerospace Equipment Manufactory
* Tianjin University
* Tsinghua University
* University of Science & Technology Beijing
* UT Alloy Works Corporation
* Xi'an Gu Ben Technology Corporation
TWI recently opened an office in the Baliqiaobei Chaoyang District of Beijing. The role of TWI in China is to assist TWI experts in communicating with the Chinese market and to identify co-operation opportunities.
