That practice no longer fits well with today's producion processes, which have changed significantly since then, with several leading suppliers turning out 150 or more turbines a month. Industrialisation of products and automation of processes are now a key focus.
Enercon and GE were pioneers of the moving assembly line production, which they introduced in late 2006. GE's engineers at the Salzbergen assembly facility in Germany used the automotive industry and its advanced production methods as a benchmark. Car maker Toyota's experts provided support during the design, building and commissioning phases and continuous optimisation of this assembly-line process.
The Toyota Production System (TPS) aims to continually improve products and processes with a focus on preventing any form of waste. Two years after introducing the assembly-line work, a GE official reported that production on the same floor space had increased by 35-40%. He also said that further efficiency gains on the same scale were realistic.
Several other suppliers - including Nordex, Repower, Siemens and Vestas - have also introduced assembly lines, either using a discontinuous process with multiple stations or a continuous-line movement. Some, such as Nordex, have introduced robots for drilling holes in the blade root and for placing studs. Rotor-hub assembly might use electric-powered vehicles.
Bigger volume at higher speed
Gearboxes were originally produced largely in small batches of standard gearboxes. Now the focus is on large series of custom-developed products, similar to production in the automotive industry but in smaller quantities. Simultaneously, high-volume 1.5-2MW gearboxes are increasingly less specialised to produce and now originate from many international suppliers.
This market segment is characterised by strong competition and heavy price pressure. At the start of the millennium, it was not uncommon to take two to three years to produce a new gearbox design but today this is unacceptable. Time to market has become a key driver for new products, together with enhanced reliability and lower cost of energy.
Gearboxes are developed much faster by combining multiple strategies and processes. Design validation is already carried out in the factory, and by adopting product standardisation and sharing platforms to work on variants, several products can be developed at the same time.
In 2010, a spokesman from Hansen Transmissions (now ZF Wind Power) said that the wind sector was lagging behind the automotive industry in product development and use of support tools such as virtual prototyping. These tools, he said, were introduced 10-15 years earlier in the automotive industry, but were only gradually gaining ground in the wind industry.
However, the wind industry has been quicker to follow the automotive industry into the next evolution in manufacturing - digital factories. Siemens claims to be a world leader, using virtual factories for everything from product design, manufacturing, transport and logistics, maintenance, upgrades and end-of life disposal and recycling.
Erica Simmons, Siemens' global marketing manager of energy and utilities, explains that since product development and production have become increasingly digitised, demand has also grown for reliable integrated applications to manage processes and equipment control. This involves optimised hardware and software-based solutions.
Software for all occasions
Software plays a growing role in the planning, development, manufacture and service of products, known as product life cycle management (PLM). PLM software allows engineers to create their 3D-products virtually, from housing surfaces to complex inner workings, down to the smallest details. This virtual product model is available to all participants in the product life cycle, including production and service.
The digital design process means that simulation and testing of features can be done without the need for physical prototypes, explains Simmons: "The software allows digital design, not just focused on product design but also on the machines required for its manufacture and the simulation of the product during its operation."
By taking a holistic approach to the development of a product, improvements can be made throughout the process. This cuts product development cycles and reduces demand for physical prototypes - which in turn cuts cost, says Simmons.
PLM software also plays a key role in producing composite materials used for rotor blades. Siemens' acquisition of US-based specialist engineering software company Vistagy in 2011 gave it in-house capabilities for supplying the complete production chain with its software and hardware tools.
The processes range from blade product definition and development to digital composite manufacturing, project execution and service. Capabilities include composite fibre production to virtual blade layout and definition of the number of layers and layer placement, to factory automation with precision fibre cutting and fibre-matrix laying machines. The system cuts waste and improves the quality of the blades, says Siemens.
Additional software tools enable simulation of the entire manufacturing process. Digital manufacturing allows companies to plan their production environment while the product itself is still in development. By using a digitally created model and creating virtual production facilities, complete logistical processes and production output can be simulated and optimised.
This software tool is extensively used in the automotive and aerospace industries and is highly suitable for the wind industry, Simmons says. Ultimately, it saves time and money on every level, she explains. "Design time for factories from an initial concept through to assembly can be driven down by as much as 50% compared to conventional methods. In addition, throughput times are reduced by 20-60%, while material-handling costs can be cut up to 70% by optimising factory layouts during the production-planning phase."
All product and process-related information stored in a backbone system can be made available at any time, for example if a production imperfection requires a "patch" or in case of a more serious failure, she adds.
Another capability of PLM is analysis of the full operations-and-maintenance process through simulation. A virtual person can be observed moving around inside the nacelle, climbing ladders and opening latches. This aims to ensure employee health and safety while performing maintenance tasks on the turbines. Vestas has been using such a virtual reality process since 2009.
Simmons draws an interesting parallel between the challenges experienced by manufacturers of wind turbines and those of heavy trucks, despite the fact that wind industry production numbers are still substantially smaller. There is a comparable level of complexity and in both cases heavy, bulky components and systems have to be moved using heavy-duty cantilever-type devices and mobile cranes. Simulation software, used for over ten years in the automotive industry, can look at materials flow and placement inside a plant. It can also look at optimising the existing processes, or replanning a specific process for enhanced reliability, greater efficiency and reducing waste.
The process can also be used to improve the flexibility of transport logistics, for example, when a harbour being used for offshore installation is closed because of a storm warning. In such cases, simulation tools can replan the entire logistical process.
"The wind industry can still learn a lot from decades of automotive industry experience," Simmons concludes. "The increased use of robotics and investment in advanced line automation combined with full logistical support will lead to faster production automation that can deliver higher product quality with reduced costs."