Following a management buy-out (MBO) in 2009, CastAlum — a Welshpool-based company that is one of the UK’s largest aluminium die-casters — started adding value to its products by machining some of its castings.
This development was triggered when the company won two major long-term automotive contracts for the supply of machined steering-gear housings and transmission cases. Until then, all castings had been delivered to customers in their raw state for machining further along the supply chain.
The projected production volumes from the two new contracts, which in 2015 alone will require CastAlum to machine 700,000 castings, warranted consideration of a transfer line. However, it would have been difficult to adapt such a machining system if the components change in the future. It would also have meant a substantial investment before the volumes had ramped up, which could adversely affect cash flow.
The phased purchase of twin-pallet four-axis horizontal-spindle machining centres (HMCs) was deemed to be the answer, as they could be installed progressively to suit the rising throughput — plus they are easy to reconfigure to produce almost any component.
CastAlum chairman Peter Radcliffe said: “After initial cutting trials, we chose Heller H2000 HMCs, as the supplier offered the best-value turn-key package; the company also has a reputation for good after-sales service from its Redditch head quarters in the West Midlands. This was a key requirement, as the first two HMCs — installed in quick succession during 2009 — were our first machine tools.
“Another factor that saw us favour Heller was its close working relationship with the tooling firm Mapal, whose cutting tools are used extensively throughout the automotive industry. Moreover, the company audits our tooling cabinets twice a week to ensure a continuous availability of the tooling that we use.”
Flexible manufacture
Today, 10 Heller H2000 HMCs (
www.heller.biz) are housed in the main production hall at Welshpool. Each can machine any type of steering-gear housing or transmission case in two operations, providing flexibility of manufacture.
In practice, half of them are devoted to machining steering-gear housings and the remainder to machining transmission cases. Cranes positioned between each pair of machines allow fixtures to be changed over quickly.
Castings arrive from the foundry mounted on carriers that travel on a long U-shaped Ewab chain conveyor running past all of the H2000s, creating a ‘lean manufacturing’ environment in a compact footprint. Each carrier has a chip that identifies the type of casting and the machine to which it has been allocated. Castings are automatically diverted into buffer areas on both sides of the line, allowing the operators to readily access them.
A raw casting is manually loaded into a fixture on a second machine pallet ready for Op1 after a previous fully machined part has been unloaded and a part-machined component has been relocated into another fixture for Op2.
Both operations are performed on two different components per pallet every time it ‘visits’ the spindle. This means that after a pallet index, a finish-machined casting comes off and is sent via the conveyor to the inspection department and on to dispatch.
Keith Brown, CastAlum’s managing director, said: “The Heller machining centres have an average uptime of 95%, which is very high for manually loaded twin-pallet machines. It is due to efficient presentation of material to the second pallets, which minimises change-over times. As well as being reliable, the H2000s are also accurate and repeatable machines — even the early models that have been working hard round-the-clock, six days a week, ever since they were installed in 2009.
"We easily hold tolerances down to 10µm and achieve a process capability of 1.67Cpk. Another H2000 HMC is installed in a separate area of the Welshpool factory, and a twelfth is due for delivery this quarter.”
The machine specification includes: a 40kW 16,000rev/min spindle for the productive machining of aluminium; a 630mm-cube working envelope; and 8m/sec2 acceleration to a rapid-traverse rate of 60m/min to ensure short non-cutting times.
The rotary table has a maximum speed of 40rev/min, and the pallet change time is 9sec. An installed weight of nearly 10 tonnes and glass scales for positional feedback in the three linear axes contribute to high machining accuracy.