Clitheroe Light Engineering, a family-run contract machinist employing 35 staff, has invested £1.4 million in a second flexible manufacturing system (FMS) at its factory in Clitheroe, Lancashire, to cope with continuing high levels of business growth.
The latest installation consists of two DMG – Mori Seiki 4-axis machining centres served by a Fastems automated storage and retrieval system that houses multiple machine pallets and fixtured workpieces. Both FMS work around the clock, seven days a week, machining such diverse materials as brasses and aluminium through to steel and stainless steel.
The subcontractor is a good example of a small to medium-sized enterprise in the UK that is prepared to invest a large proportion of operating profit in developing its manufacturing plant to position itself as a world leader in lean production.
Helen Meloy, Managing Director, said "We started installing our first FMS in 2006 and completed it in 2010. By that time, the original Fastems pallet store had doubled in size and fourth and fifth machining centres had been added, bringing the total investment to £2.6 million.
"However, as fast as we upgraded the system, our customers in the mining and construction sectors gave us additional work to fill the capacity. Rather than extend the first system again, we decided to introduce resilience by adding a second, separate FMS.
"Our main customers are global players that can choose to have their price-sensitive components made anywhere, such as Eastern Europe or the Far East, so we have always placed a firm accent on automation to maintain our competitiveness."
Commissioned at the end of January 2012, the second FMS comprises a pair of DMG – Mori Seiki NH5000 twin-pallet (2APC), horizontal machining centres (HMCs) with 240-tool magazines linked by a Fastems computerised store. It holds twenty 500 mm-square machine pallets on two levels and delivers them automatically to and from the machines.
An operator fixtures components onto pallets and subsequently removes finish-machined parts at a workpiece load / unload station equipped with a rotating table. Safety is ensured by swing-out double doors and a vertically rolling shutter that isolates operators from a 3-axis CNC stacker crane running along a rail inside the store. The mast of the crane carries a load handling device that docks to a repeatability of ± 2 mm to effect pallet transfer into and out of each storage position and on and off the outer pallet of the 2APC machine tools.
Fastems MMS software oversees FMS operation. Running on a standard, Windows-based PC, its main tasks are to control the stacker crane and schedule automatic pallet transfers between the load stations, store and machines. The main window of the control displays a mimic of the entire system and uses colours and icons to advise the real-time status of all main FMS elements.
When a pallet is sent from the load station into the system, a manufacturing route defines the flow through the FMS. It ensures that the correct NC program is downloaded over a DNC link to the appropriate machine and is instigated when the job reaches the top of the queue and the pallet with components arrives.
The MMS software has information not only on the NC program to be loaded but also on the component and fixture as well as the tools needed to complete the job. If the intended machine is not available, for example because it already has work waiting on the second pallet or all the required tools are not in the magazine, the pallet is routed to the other machine, if it is available, or else into store.
To automate the often difficult and time-consuming task of managing tools, mirror images of the 240-tool magazines serving the NH5000 machining centres are held in the Fastems control, which includes data on the remaining life of each cutter. Available tools as well as those that need to be added and/or removed for any given job or series of jobs can be evaluated. Even tools stored outside the magazines are included.
Performance data and statistics of stacker crane operation are available and the production reporting interface generates information such as total machining time of a particular order. The operational modes of the machine tools are also tracked in a database, providing information covering on-line/off-line status, cycle on, feed on and errors/alarms, all of which can be interrogated remotely.
The efficiency with which a mixed schedule of work is presented to the two spindles means that small batches can be produced very economically. For example, Clitheroe Light used to machine batches of 120 manifolds for a customer that wanted 10 per month and then deliver them in 12 instalments throughout the year, absorbing the financial cost of the consignment stock. Now it is economical to run off 10 components and deliver them. Even one-offs are cost-effective.
Versatility and expandability
When Clitheroe Light installed its first two Daewoo (now Doosan) twin-pallet, 4-axis HMCs, it achieved significant reductions in labour costs and lead-times as well as improved cash flow. Parts could be set off-line, presented to the spindles more promptly, machined in a faster floor-to-floor time and invoiced more quickly. In 2004, the subcontractor moved further ahead with automation by retrofitting a 7-pallet pool to one of the machines, an HM500.
Two years later, the company embarked on its first FMS by positioning the other 2APC Daewoo, a 400 mm pallet HC400, alongside two new Mori Seiki NH5000s with 500 mm pallets. A Fastems store with two load / unload stations was purchased to feed the three HMCs automatically with pallets, 36 of which were held on three levels.
Two aspects of this installation are noteworthy. One is that not only are dis-similar makes of machine tool accommodated by the FMS, but even different sizes of pallet (400 mm and 500 mm). Components fixtured on any of 36 Wixroyd Zero Point sub-plates can be directed to either of the Mori Seiki machines, while 12 of the sub-plates are additionally able to be sent to the Daewoo.
The second point to note is the ability of such systems to be expanded as business demands dictate. In Clitheroe Light’s case, the 17 metre long Fastems store was doubled in length to house 72 machine pallets, a fourth HMC was added in 2009 and a fifth in 2010, both DMG – Mori Seiki NH5000s with 240-tool magazines. Actually, any make of 3-, 4- or 5-axis machining centre could have been added.
It is Clitheroe Light’s intention to upgrade the two FMS further with the addition of an external tool store for cutters. They will then be freely available via a gantry exchange system to any of the seven machines within the two systems. This will increase flexibility further and reduce tooling costs, as fewer cutters specific to particular machines will be needed and a reduced number of sister tools will be sufficient for unattended operation."