Traditionally, crane main girders are manufactured manually by riveters and welders, resulting in a labour-intensive industry characterised by high costs, low efficiency and unstable quality. However, with the gradual fading of the ‘demographic dividend’ and the increasing scarcity of the labour force in today’s era, the drawbacks of this labour-intensive production model have become increasingly prominent.
In recent years, the maturation of intelligent manufacturing technology in the industrial field has made intelligent manufacturing of crane main girders an inevitable trend for industry improvement and development. In line with this, WorldHoists has invested nearly $10m and assembled a team of dozens of engineers since 2020. After two years of relentless efforts, continuous exploration, and testing, the intelligent main girder production line, featuring high efficiency, reduced labour, and stable quality, was developed in 2023.
PREREQUISITE
It is easier to realise intelligent manufacturing of box-type main girders that adopt modular design because they are highly standardised.
Presently, all 3.0-80t box girder cranes at WorldHoists utilise the crane design software called King to automatically calculate the main girder. Each girder possesses relatively stable dimensions, as its height, width, flange size, internal diaphragms, and the layout of stiffeners have been completely standardised, along with the production process. Modular standard design establishes the foundation for intelligent manufacturing of main girders, with our intelligent manufacturing exploration being based on box girders.
DEVELOPMENT PATH
‘Segmented intelligence’ is the approach to intelligent manufacturing at WorldHoists. This approach entails customising intelligent solutions for each manufacturing process and subsequently developing automation equipment accordingly.
Based on our 20-year experience in producing box girders, we first divided the manufacturing process into several stages, including:
- stiffeners’ welding
- diaphragm assembly and welding
- main girder assembly
- end carriage assembly
- pre-assembly and other processes.
We explored the feasibility of each process one by one. Ultimately, through collaboration with smart device suppliers, we jointly developed customised smart equipment.
After comprehensive trials at our new crane factory in Yangzhou city, China, the newly developed automatic spot-welding production line for stiffeners, automatic diaphragm welding robot, main girder assembly robot, main girder pre-assembly robot, end carriage assembly welding robot and other intelligent manufacturing modules have been successfully integrated into the production processes.
STIFFENER WELDING
The manufacturing of stiffeners for box girders has been standardised by integrating three angle steel materials and four position combinations. This integration provides the most effective prerequisite for intelligent manufacturing.
The biggest challenge in automatic assembly and welding of stiffeners is camber tracking. Given that each main girder has a different camber, if the automatic spot welding only follows a preset route, the stiffeners will not remain parallel to the camber, making it difficult to ensure the accurate position and height of weld beads.
The R&D engineers of WorldHoists solved the problem with a profiling tracking system. This system consists of tracking pulleys, positioning rods, and servo translation mechanisms, which allow for accurate positioning and good stability.
The automatic spot welding production line for stiffeners enables simultaneous spot welding of multiple stiffeners, increasing production efficiency by more than three times compared to traditional manual spot welding. It also reduces labour by over 80% and requires 50% less production space.
DIAPHRAGM ROBOT
WorldHoists has standardised the size and spacing of the diaphragms to facilitate intelligent manufacturing.
The automatic diaphragm welding robot includes a handling robot, a welding robot, a CNC linear rail trolley, a special material tray, and an assembly and welding support bracket. The special material tray adopts a pre-positioned modular design for easy identification by the robot. The CNC linear rail trolley is equipped with a secondary positioning mechanism for accurate material picking and precise positioning with a margin of error of 0.5mm. The robot has its own laser tracking function, which ensures precise location of welding points and high-quality welding.
The automatic diaphragm welding robot reduces labour by over 60% and doubles efficiency with its dual-station layout.
MAIN GIRDER ASSEMBLY
While the box size of box main girders has been modularised and standardised, assembling the upper cover, bottom cover, main web plate, and auxiliary web plate into a box presents a significant challenge. This task involves spot welding to create a 30-ton heavy, 40m-long, 1.0m-wide, and 2.0m-high girder, while ensuring the accuracy of the main girder’s side bend, camber and verticality.
After more than 30 node tests and dozens of trials, the WorldHoists R&D team developed the main girder assembly robot by drawing inspiration from European and US counterparts.
This robot consists of a push shoe, a compression wheel and multiple robots that achieve 11-axis linkage. The complexity of its automation process exceeds that of other crane manufacturing equipment.
The main girder assembly robot reduces labour by over 80% and doubles efficiency with its dual workstation design.
PRE-ASSEMBLY
The main girder pre-assembly robot simplifies the previously cumbersome and time-consuming process through a highprecision pre-assembly support bracket, laser measurement system, CNC fine-tuning mechanism, and welding robots. Each system replaces the work of three welders.
END CARRIAGE
The difficulty in creating the end carriage assembly and welding robot lies in automatic splicing and moulding. By optimising the process using the mortise and tenon principle, the WorldHoists design team simplified the previously challenging work, making it as simple as stacking blocks while ensuring the desired moulding size.
Once splicing and moulding are completed, the welding robot automatically tracks and welds all joints.
This robot increases efficiency by over three times.
ECONOMIC BENEFITS
The intelligent main girder manufacturing system independently developed by WorldHoists has been in operation for over six months, delivering stability, reliability, and considerable economic benefits.
An intelligent main girder production line only requires five general workers to control all robots and CNC equipment. It no longer relies on skilled riveters and welders to undertake intense work and can produce more than eight girders in a single day. In contrast, traditional manufacturing would require at least 50 people and double the space. Therefore, intelligent manufacturing not only saves labour costs but also places fewer demands on factory buildings.
Based on the past six months of operation, the intelligent system saves an average of $2m in labour costs, and the investment is expected to be fully recovered within three years.
