The diversity of off-highway vehicle manufacturing makes for complex production logistics, reports Sharon Clancy

The introduction of EU Stage IIIB and US (EPA) Tier 4 emissions legislations in 2011 led to the introduction of more sophisticated powertrain systems. As is the case with many commercial vehicle manufacturing operations, to achieve the efficiencies that come with volume production, key components are often built in a single dedicated plant.

One-line, multiple cabs

Typical of this approach is Volvo Construction Equipment’s (CE) Hallsberg plant in Sweden. Volvo CE is one of the world’s leading manufacturers of construction equipment such as wheel loaders, excavators, articulated haulers, road construction machines and compact machines, with production facilities in Europe, Asia, North America and Latin America.

All Volvo Group plants comply with the Volvo Production System, a structured working method for achieving World Class Manufacturing processes, part of which is to improve the environmental performance. Volvo Group was one of the first companies in the world to have an environmental management system certified to ISO 14001. In its Project Revolution it has been working to take this further, to ensure sustainability in production by ensuring every part of the manufacturing process is performed with the minimum use of energy, materials and water. This has involved optimising processes to minimise idle running of machinery, upgrading machinery controls, using sustainable energy sources and adopting closed purification systems in areas such as the paintshop.

The Hallsberg plant is a global centre for production of off-road machinery cabs and system components such as hydraulic cylinders, oil and fuel tanks, all destined for a variety of construction machines including articulated haulers, wheel loaders, excavators and backhoe loaders. Volvo has other dedicated plants for cab manufacture but unlike truck cabs, which are fairly standard in the early stages of manufacture and thus lend themselves to linemanufacture, each construction machine type imposes its own specific requirements on the operator’s working environment and thus on its manufacture. So at Hallsberg, the production challenge was to enable the building of different cab types on the same production line. This is now possible and with a few adjustments the assembly line can be switched from excavator cab to wheel loader cab, for instance. Volvo CE says this is unique in the industry and gives it a significant competitive edge.

Hallsberg is also one of Sweden’s largest factories for heavy-duty construction machine hydraulic cylinders. Cylinders with a maximum weight of 580kg and a stroke of up to 2.6 metres are made with the help of friction welding and other techniques.

There is a specialised ultrasound and alkaline cleaning process for the production of oil and fuel tanks, which place high demands on cleanness and interior surface treatment.

The cab, tank and body paintshop are combined. The paintshop uses the very latest technology for powder-and water-based paints, and has its own fully automated filtration plant. Hallsberg factory production is sent to Volvo CE plants including Konz, Germany and Wroclaw, Poland.

Smooth and flexible

One of the perennial issues with for any manufacturing plant is that once in place, changes to manufacturing lines can be expensive to implement in terms of site works and downtime on the line. So ensuring there is sufficient flexibility to allow for product changes and additional capacity presents challenges, especially when manufacturing trucks, buses and off-highway vehicles, where components are both heavy and large.

Some plants adopt pits, chains, skillets, lift trucks and cables to manage conveyance, all of which add expensive maintenance costs. Chain-based conveyance and lift trucks are widely used in heavy vehicle manufacturing where vehicles are built to customer specifications on the production line.

A modern, more flexible and transferrable solution to assembly line design has been developed by German company Conductix-Wampfler, incorporating Inductive Power Transfer (IPT), a contactless power transfer system based on the principle of electromagnetic induction, which allows all kinds of moving machines to be supplied with electrical power.

Battery-free Automated Guided Vehicles (AGVs) on an IPT line can handle a wide variety of products and are well suited for use in large vehicle assembly, drivetrain pre-assembly lines and at the “marriage line” where subassemblies are installed in the truck or bus, and where 360° access to the line is often a requirement for delivery of JIT sub-assembled vehicle systems from tier one suppliers.

IPT solutions can increase capacity in an existing footprint and protect investment by eliminating the use of fixed vehicle conveyance methods that could limit future growth or improvements in efficiencies, says Rod Emery, vice-president of engineering at Plymouth-based SuperiorControls, the US partner of Conductix-Wampfler. “An IPT solution eliminates the requirement to physically separate and reconnect multi-track systems.,” he says. “Flexibility is designed into each customer’s IPT system from the beginning. Instead of digging new pits and adding new chains, an IPT line can be rerouted as soon as minor floor changes are made. The custom software and controls for every assembly line will easily accommodate new paths, speeds and processes.”

The US government is committed to repatriation of manufacturing jobs from overseas, and SuperiorControls says portable assembly lines can reduce the costs of doing this. “By building assembly lines that can be easily expanded, changed and relocated, it is possible to retain 90% of the assembly line investment when moved to a new location,” says Emery.

SuperiorControls has already designed and built asynchronous assembly lines for a US-based off-highway vehicle manufacturer using IPT which have delivered a 200% increase in capacity within nine months, reports Emery. The requirements included that AGVs enter from a single path, diverge into separate tracks to enter a hot test cell, exit asynchronously upon test completion, and converge into a single path for process completion. “With IPT, there is no unchaining, uncoupling, or moving with lift trucks,” points out Emery. “Instead the line uses battery-free AGVs to be deployed, eliminating the need for the routine recharging and servicing, and for spare vehicles necessary for battery-powered AGVs. The AGVs themselves contain conveyance, power and communication. The software and controls can accommodate future line changes. Power and communications connects for tools and testing can be customised.”

Because the IPT system provides both power and communication, additional efficiency was incorporated by enabling the AGVs to power the data acquisition and communication during test. Quick connect cables travel with the AGV and are used during hot test without any need for additional power. The AGVs can be customised to carry specific connections, so they can eliminate a number of outside systems. A simple installation process expedites conveyance changes and greatly reduces maintenance costs. “The installation is relatively non-invasive, requiring just two narrow, shallow floor channels to contain cables,” says Emery. “As production requirements change, line paths are readily changed and AGVs, as well as controls and programmable workstations, are easily transferrable to another line.”

SuperiorControls also offers custom-designed ergonomic tables for component handling. The battery-free AGV tables, powered by IPT, travel with the component or sub-assembly along the line, and can be adjusted to suit the height of the person working on the component and the process being performed at each station.