Street Crane is probably best known in the UK as a supplier of complete factory cranes up to 200 tonnes capacity. The company manufactures and supplies both the structural elements, such as gantries and crane bridges, along with the major electromechanical sub systems such as carriages, hoists, controls and handling equipment. The UK business in complete cranes accounts for around 40% of the company’s turnover.
Internationally, the business is different. It is generally uneconomic to ship large structural elements overseas and so international trade involves supplying the major subsystems, carriages, controls, handling equipment, but principally hoists. Street Crane's overseas customers are usually other regional and national crane makers who fabricate their own structures but prefer to buy in more complex components from a competitive volume producer.
It was to satisfy this international demand that the development programme to produce a range of hoists in the high-demand 25 tonne category was launched in 2004, resulting in the ZX6-8 hoist series. Up to this point, the company had been supplying UK specification hoists that were adapted to meet different national standards and individual end-use customer needs. The overriding aim of the ZX6-8 programme was to create a competitive advantage in the international hoist market by producing a hoist that was both price-competitive and technically superior.
This gave rise to a number of goals, including the need to reduce component counts; maximise scope for parts to have multiple roles and be interchangeable, and to reduce inventory. An important aim was to make the hoist easy to ship in kit form and subsequently easy to assemble at the customer’s site. Furthermore, the hoists had to comply with different national standards and codes, and be easily customisable to meet different national and customer requirements. Meeting these goals involved a radical re-think about the design, questioning the role of each component, assessing the validity of the production technique and how each individual component contributed to the overall effectiveness of the hoist.
Software support
The design process was aided considerably by 3D modelling software (Siemens PLM Solid Edge). This allowed the product to be created in virtual reality, enabling the interaction of each component to be fully explored and designs optimised to take account of all possible component selections. One of the advantages of Solid Edge is that it integrates with many other product management lifecycle management (PLM) technologies. For example, SharePoint, a Microsoft platform that enables easy and secure sharing of data via the web, allows Street Crane to share the latest specification data on components (materials and finishes, mechanical configuration, production methods, etc) with their many supply partners in the UK, Europe and elsewhere in the world.
As the hoists were refined and component designs and sources agreed, the SharePoint integrated management system was used to document all component changes. These updates were automatically notified to supply partners so that everyone in the supply chain was aware of the latest design modification.
The company has adopted a universal design for the hoist chassis that allows many of the structural components to be standardised. Cellular construction permits assembly in a fraction of the time required for the previous hoist and allows localisation of component to meet different markets and customisation to meet end-user needs. A responsive and lean supply chain has been established to permit on-time manufacture without reliance on high stock levels of components or excessive work in progress.
One of the aims of the programme is to establish long term business relationships with suppliers and achieve buy-in to Street's design process and objectives. Most key component suppliers are in the UK or Europe, but this does not necessarily mean that any one supplier will be the sole source for a given component. Given that many hoists are destined for overseas markets, the volatility of exchange rates can have a huge impact on profitability. The information in the SharePoint database allows dual or multiple avenues of component procurement, so that the mix of components from different countries can be re-balanced if there are adverse currency movements.
In parallel with the start of production at Street's Derbyshire factory, trade partners Nanjing Hoisting Machinery General Works Company (NHM), also started manufacture of ZX6-8 hoists for the Chinese home market. NHM were included in the design and development loop and, via SharePoint, were kept fully up to date with design and production information. In an agreement signed last year, NHM already manufacture under licence the complete range of fully engineered Street Cranes in China for the local market.
Engineering design is not a static process and supply chains are complex. The use of 3D modelling enables multiple design options to be explored before proceeding to production and testing of complete prototypes. Linking this modelling with a dynamic database of components and developing open systems for sharing up-to-date information ensures that supply partners are fully engaged and reduces still further the time and costs in bringing new products to market.
Andrew Pimblett is managing director of Street Crane Company