Four-axis HMC doubles machining capacity

Subcontract aerospace parts supplier researched the market for a 4-axis HMC with rotary table to machine multiple components and to double machining capacity overnight.

Subcontract aerospace parts supplier researched the market for a 4-axis HMC with rotary table to machine multiple components and to double machining capacity overnight.

One of the first horizontal machining centres (HMC) on the Isle of Wight is a Japanese-built MA-50HB, installed by UK agent, NCMT, in August 2004 at the Freshwater works of Patrick Engineering.

Aerospace work accounts for 95 per cent of turnover, the remainder being mainly in offshore work.

Operations Manager, Kieron Fry, says that the GBP 250,000 investment including tooling and training follows an agreement reached with their main customer, GKN Aerostructures in East Cowes, guaranteeing engine nacelle component production for four turbo-prop aircraft programmes until 2008.

As ever, cost-down formed part of the deal.

Four old vertical machining centres (VMC) on site - inherited from GKN Aerostructures when it closed its machine shop in 2001 - could not produce many of the nacelle components sufficiently economically to make a profit at the new prices.

Commented Fry, "We carried out a reappraisal of our manufacturing processes and identified that to achieve the required economies in unit production, we needed a rigid machine to ensure long cutter life and so minimise tooling costs and downtime for replacement, plus fast axis speeds, high spindle up-time and lights-out capability.

"So we researched the market for a 4-axis HMC with rotary table in order that multiple components could be fixtured and left to run unattended.

In addition, we opted for a twin pallet changer so that load/unload did not disrupt production and to double machining capacity overnight.

"We evaluated HMC's from three suppliers, opting for the Okuma as its specification exactly met our requirements.

We were also impressed with NCMTs willingness to take one of our VMC programs, convert it and prove out the component on a horizontal-spindle machine at their Middlemarch technical centre, all without any commitment from us." The first parts to be produced on the machine at Freshwater were engine mounting structure (EMS) nacelle components, four of which are fixtured on a cube on each pallet.

The titanium components, which require three set-ups, were for the Dash 8 400 turbo-prop and are required in aircraft sets of four, there being 22 aircraft orders for 2004 with options on 24 more for 2005.

By the end of 2004, the machine will have produced 20 different aircraft components and the intention is that eventually, this number will rise to 70.

As each part is brought across from the VMCs to the HMC, the existing programs are translated through 90 degrees.

At the same time, a certain amount of re-engineering is carried out to take advantage of the higher spindle speeds and heavier roughing cuts that the MA-50HB is capable of.

In addition, finishing cycles are now included in the programs owing to the machines superior accuracy.

Another early component produced on the HMC was for an EMS forward nacelle for Bombardier-Shorts.

The component requires four set-ups and the fixturing on each cube is arranged so that a different operation is performed on every face.

In this way, a complete component comes off the machine after one revolution of the rotary table, facilitating rapid delivery to the customer and minimising the risk of having to scrap several components rather than one.

A high grade stainless steel billet measuring 250 x 240 x 63mm thick is roughed out using a 125mm diameter button mill during the first operation, then rough milled on the reverse in the second operation.

Ops three and four involve finish machining the first side followed by finishing the reverse and milling the external profile.

Cycle time has been reduced from three hours on one of the VMCs to two hours owing to faster speeds and deeper cuts on the Okuma.

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