Sequential success

A rule-based software tool employed in tractor production delivers a manageable workload to the final assembly lines.

As the complexity of tractors has increased in recent years, so has the problem of scheduling production. To avoid bottlenecks on the final assembly line, it is necessary to sequence production orders, a computer process designed to match the workload against available capacity and logistics to achieve an optimum throughput from the factory.

AGCO’s Massey Ferguson tractor factory in Coventry, produces about 60 tractors a day, most of which are different. Every machine is built to order and customers can choose from a wide range of features and options covering engine size, drive transmission, cab equipment and functional accessories.

There are two main product platforms, the 200 Series is the utility workhorse and the more sophisticated 4300 series. A large proportion of the output from the factory is shipped to customers overseas. Delivery arrangements have to be co-ordinated with transportation and must therefore be reliable. Sequencing the production line has become a crucial process. It reduces the order cycle time and helps to secure the maximum return on investment from the factory by supporting a strategy of lean manufacturing with just-in-time deliveries for high value components.

A Sequence Generation and Management System (SGMS) updates the production schedule every week to sequence the release of a week’s worth of orders. Every machine entering the final assembly line is given a sequence identity number.

An important by-product of the sequencing process is the production of delivery schedules for key components supplied just-in-time. Previously these schedules were accessed by the suppliers using PC Anywhere software. This information is now being updated several times a day and posted as web JIT schedules, allowing key component suppliers the maximum time to respond to changes in the requirements.

The previous Sequencer tool had been installed five years earlier with the introduction of the 4200 Series, the precursor to the 4300 series of models. This was superseding the 300 series and AGCO were faced with a situation where it was going to be running three different model platforms for a time.

‘Whilst this system fulfiled our initial requirement it was very monolithic and it became difficult to support. It also lacked capability and we were unable to make any improvements ourselves,’ explained Henry Filipiuk, AGCO’s manufacturing and engineering systems manager. ‘We regard sequencing as crucial to our production process and we wanted to have more control over our own destiny’.

‘The solution came with the development by Tecnomatix Technologies of a replacement sequencing processor module as part of its eM-Power range of manufacturing process management tools. The SGMS application runs on a high specification PC that communicates with the company’s mainframe business management database via the local area network.’

‘We now have the best of both worlds. The functionality we created around the Tecnomatix Sequencer was developed in Microsoft Access 2002 and used Access tables on the PC. As a result we have a future proof system which we are able to support and update to meet new requirements.’

Additional functionality provided by the SGMS includes an interface for the production of assembly documentation. Other features include calendar displays related to shift times; tractor commitment recording as the machine enters the assembly line; and gap analysis to detail the reasons for drop outs, the exceptions usually caused by a major supply shortage. This information can then be used to provide feedback for remedial action.

The Tecnomatix eM-Plant software generates the sequence by following specific criteria and parameters governing the engineering content, features and line capacity as standard hours. Processing starts with a list of orders of all the tractors scheduled for delivery within a given week. From this the software calculates a sensible starting position and then it runs through different scenarios trying out different sequences until it comes up with an optimum throughput for the factory.

Effectively each tractor order is weighted according to its complexity and then sequenced to ensure the line is supplied with a manageable workload. This is determined by a list of features, defining the build specification. Every feature, or possible variation in equipment fit is assigned a priority ranking number enabling a total value for complexity to be calculated.

Processing has been improved with the introduction of a genetic algorithm. This continues to search for an optimum solution for as long as it is allowed to run, whereas previously the system would stop after it had reached a result that agreed with pre-defined rules. For additional flexibility, rules can be applied to bias the throughput of particular orders, for instance a batch of export orders being made available by a specific date for transportation and sea freight arrangements.

On a day-to-day basis the SGMS supports a busy communications activity dealing with numerous enquiries relating to programme management and component deliveries.Orders are imported into the SGMS database and a new sequence generated after a weekly production-planning meeting. Updates from the shop floor confirm the launch of each new build in the sequence.

If for some reason, the tractor order cannot proceed to final assembly, the order line can be removed from the sequence and parked on the bottom of the screen where it can be seen. Once the problem has been resolved the order is simply re-inserted back into sequence.

‘I have more information available for handling enquiries and updating the production status, ‘ said senior product scheduler Bill Solloway. ‘I can call up the complete bill of materials for a tractor order at each level and then drill down through each of the engineering group units that make up the specification.’

The database includes a summary of all the features for a given range of tractors. From this the user can select a group and obtain a count of features and the timing and standard hours allowed. This feature is useful for assessing the impact of changes to the programme.

System utilities enable the user to create and maintain features. Data such as a list of features can be attached to specific orders and this will be flagged up when the order is imported into the system. Maintenance of features is used to keep track of design changes and add specific information, such as tools or particular assembly requirements for each feature.

New build starts with the assembly of rear axle and gearbox combinations, which are then held in a buffer store. These are dispatched to the main assembly hall, by sequence against a tractor order, as all the necessary component parts are confirmed as available. Engines and front axles are added to form a chassis, which then progresses on to the chassis paint process. After painting the line splits into two final assembly tracks, the primary line handles the larger more sophisticated models and the second line provides an alternate track for the smaller less complicated machines.

Whilst the new system has improved the efficiency on the shop floor the full impact is still being felt with component suppliers. AGCO operates a lean manufacturing strategy with high value items delivered just-in-time to meet the production schedule.

AGCO has suppliers all around the world. Engines are manufactured in the UK but several long lead-time items such as axles, are currently being imported from Italy and Turkey which is up to three days away for transit by road.