FMS makes short production runs profitable

Citation

(2005), "FMS makes short production runs profitable", Assembly Automation, Vol. 25 No. 1. https://doi.org/10.1108/aa.2005.03325aaf.003

FMS makes short production runs profitable

FMS makes short production runs profitable

Keywords: Flexible manufacturing systems

A 4,500 m² factory, due to be extended to 7,000 m² by mid-2004, has been built in Brownhills, Birmingham, by automotive subcontractor, CMC Speedwell, to house a new, flexible manufacturing system (FMS) which became operational in August 2003.

Comprising a Fastems automated storage and retrieval system for machine pallets and raw casting stillages, it currently links three Toyoda FH55S horizontal machining centres. However, the system has space for an additional machining centre which will be delivered in June 2004, and a Fastems robotic deburring cell which will be delivered at a later date. When the FMS is completed, the total cost will be £1.7 million.

The reason behind the investment, according to CMC Speedwell's Managing Director, Mark Lewis, is for the cost effective manufacture of components with a high machining content in relatively low batch sizes of between 30 and 140 per week.

He said, “Our main production runs are typically 500 up to 10,000 per week. We machine a wide variety of cast iron chassis parts, brackets, engine and gearbox components, manifolds and exhaust systems for cars and commercial vehicles. However, most components have variants which need to be run off in much smaller batches of, say, 30 per week. Companies do not allow their suppliers to cherry-pick jobs, so the less economical short batches have to be done to secure the main production volumes. Added to this, there are certain contracts that require only limited runs of, for example, parts for buses, military vehicles and ships.”

“The problem has always been to find a way of making money on these smaller jobs. So we tended in the past to produce larger batches to achieve economies of scale, and store the undelivered parts in our factory. Occasionally we were caught out when components became obsolete before they could be delivered, leaving us with wasted stock worth several thousands of pounds. It also costs money to hold these buffer stocks.”

Now CMC Speedwell's production is split between the Brownhills FMS for small batch runs and the original Lichfield site where ten Toyoda horizontal machining centres, two with a radial facing slide for U-axis contouring, handle much of the volume production. It was fortunate that the subcontractor's rapid growth, with the £7 million turnover in 2002/ 2003 set to increase by 50 per cent in the current financial year, has enabled investment in the FMS while the capacity at Lichfield has been filled by the increase in high volumes being ordered by car companies. This now includes machining of 5,000 aluminium castings per week for Toyota – a side of the subcontractor's business that is growing strongly.

Continued Mark Lewis, “Automotive manufacturers are notoriously demanding and you have to be able to react quickly to their just-in-time delivery requirements. It is not unusual for a schedule to change twice during the week. The FMS allows us to respond promptly without contingency stocks, or if we do have buffers, they are a fraction of what we were holding before. We simply key in the customer's requirements at the start of the week, insert any changes subsequently received, and the Fastems manufacturing management system software takes over, scheduling and prioritising the work in real time and co-ordinating all aspects of the FMS.”

The store is a modular, two-level system designed to hold thirty-six 550 × 550 mm pallets used in the Toyoda FH55S 2APC machining centres. There is the same number of storage positions for stillages of free- issue castings (Plate 3). Capacity is high for the footprint, allowing efficient utilisation of floor space. There are two load-unload stations with a rotating pallet table where the operator removes machined parts and fixtures new castings. Adjacent material stations with input conveyors allows stillages of raw castings to enter the system for storage and to be retrieved when needed. Material movement within the store is by three-axis CMC, rail-guided stacker crane fitted with telescopic forks for pallet handling.

Plate 3 One of the load/unload stations, showing a new part being fixtured before entering system

Controlling production in the FMS is Fastems' Windows-based manufacturing management system (MMS) software. Its core tasks are scheduling of automatic pallet transfers between the loading station and the machine tools, input and output of raw castings as required, and control of the stacker crane. When a pallet is sent from a loading station into the system, a route is assigned to it and the system automatically controls the defined sequence of steps and ensures that the correct NC programs are downloaded over DNC links and instigated when the pallet reaches a machine. Should the next machine not be available for any reason, for example it already contains a pallet or all requisite tooling is not in place, the pallet is taken to its storage position until the destination becomes available.

The main window in the control displays a mimic of the system and uses colours and icons to advise the real-time status of the all FMS elements. Parts data, manufacturing routes and NC programs are entered and maintained in the basic data window. The phase of the pallet within the system can be checked at any time.

Job scheduling is based on the first- in/first-out principle which can be over-ridden by the operator. The software uses an algorithm to schedule pallet transfers so that idle time of the Toyoda machines is minimised by transferring pallets to them whenever it is possible. The MMS log lists all events, warnings and alarms and there is a modem connection for remote diagnostics. Online help is embedded in the user interface. In addition, the system guides the user to solve error situations.

Capacity simulation enables short term “what-if” production planning and scheduling. Actual manufacturing orders within the system create the basis for this simulation. The operator is able to test different scenarios by adding test orders and/or modifying the existing ones. The results of the calculation are displayed by a bar graph and a Gantt chart.

A tool management module creates a mirror image of the actual tool magazine data including the lifetime and condition of the tools. It is possible to check whether the next pallet in the queue can be machined or not and to determine the tools required to manufacture all jobs queuing in the system. A Kelch tool pre- setter is integrated so that presetting lists can be received and measured values sent back.

Each Toyoda FH55S machine, described by Mark Lewis as “the best horizontal on the market and super- reliable”, is of high specification.

Having a working envelope of 750 ×750 × 600 mm, it includes a 30 kW(22 cont) spindle drive, BT50 taper, full 4th axis NC rotary table, Fanuc 16JMB control, Renishaw touch sensor plus tool breakage detection, 120 tool magazine and Balluff tool identification with unique tool storage in specified pockets.

Apart from their reliability, other reasons cited by CMC Speedwell for opting for Toyoda machines were competitive price, historically good level of service provided from the UK subsidiary's Coventry office, and the supplier's all-round programming and project management capabilities.

Concluded Mr Lewis, “Although our FMS has yet to be completed with the fourth machining centre and deburring robot, it is already clear that spindle utilisation is higher within the system than on our stand-alone machines. Moreover, for every shift we need only one operator for two machines in the FMS, whereas each stand-alone machine needs a full-time operator, so there is a significant labour saving.”

“The combined effect of higher efficiency machining and leaner manning together with faster response to our customers' low-volume parts orders has made a significant difference to our profitability in what used to be a difficult sector of the business.”

For further information contact: Robert Humphreys, Sales Manager (UK). Fastems Division, Helvar Limited, Hawley Mill, Hawley Road, Dartford, Kent, DA2 7SY. Tel: 01322 282276; Fax: 01322 282250; E-mail: robert.humphrevs@fastems.com; Web site: www.fastems.com