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Roger Street, managing partner of LMS, contacted LMT for threading expertise after receiving an enquiry for 4,000 connectors in ENIA.

Production at precision subcontractor LMS is geared to consistency and utilising the commitment and flexible working practices of the 10-man team to service its customers.

‘We are always tooling for total consistency over a batch of components and are able to predict tool changes when we are running out of hours,’ said Street.

‘Although we only run a single shift, everyone has keys to the factory and we are willing to come and go according to the priorities of the day,’ he added.

Street’s working practice is one reason for his conversion to thread rolling in preference to thread cutting, not only due to the stronger thread as a result of the cold forming process, but also the level of consistency, long tool life, minimal adjustment and the positive contribution to ‘bottom line’ costs.

Street qualifies his reasoning with a long-standing aerospace customer that specifies rolled threads on its drawings for parts in stainless steel and inconel.

He added that the level of quality and consistency provided for the customer could never be maintained by any other method of threading.

So when he received an enquiry for 4,000 connectors in ENIA from a new customer, he turned to LMT UK of Meriden, and drew on the expertise of its in-house threading specialist to help with the quotation.

They discussed screw-cutting on Street’s Citizen L20 CNC sliding head turn-mill centre with rolling the M3 thread by 10mm long, which could be carried out in under one second against almost seven seconds for the more conventional threading.

‘I reckon other suppliers quoted against screw cutting because the customer said we were so competitive and we would never have won the contract if like-for-like comparisons were made,’ said Street.

‘Once we produced initial samples the order was increased to 40,000 rather than the customer having to split source,’ he added.

LMS was also able to back up the initial quality in production.

‘The Citizen and the thread rolling was so consistent and once up and running it never stopped for a month, with the part requiring turning on the outside diameter and the thread diameter to 0.025mm and a large conical taper,’ said Street.

Two flats were milled, a cross hole drilled and deburred and the M3 thread rolled at 2,000rev/min before parting-off and being picked up by the sub-spindle to machine a spherical radius.

The thread-rolling process or ‘chipless’ cold forming is quicker to produce external threads, which can be run at up to five times the normal machining speed for thread cutting.

As the material is cold formed under mechanical pressure from the three profiled rollers, the thread is far stronger than when the fibres of the material are cut.

The resulting thread is more accurate, consistent and durable because of the burnished finish of the surface.

LMS has a portfolio of machines carefully chosen to service its covered sectors.

These include two Citizen L-Series CNC sliding-head mill-turn centres, three Nakamura TW and WT mill-turn centres, a twin-spindle, twin turret gantry loaded Takisawa TT200G lathe, one Matsuura horizontal and two vertical machining centres, the former with six pallets and 240 tools.

The most recent installations also include an Aberlink co-ordinate measuring machine, ultrasonic cleaning and an integrated MRP system.

A recent batch of 150 eye bolts in 316 stainless steel was produced on the larger capacity Citizen L32 in a single hit cycle.

Each part 12mm diameter by 70mm overall length required turning, the milling of a 30mm long flat, an 8mm-long angled flat and two shorter flats across the bolt head.

This was followed by the drilling and coning of a 5mm cross hole between the flats then the rolling of an M5 thread 30mm long at 2,200rev/min.

After parting-off, a spherical radius form was machined on the head of the bolt in the subspindle.

Once set and proven in a 4.5 min cycle, Street maintained they had total confidence to run it through the night.

In the morning, with the batch completed, the difference between the first and last part was undetectable.

The use of thread rolling was also employed in the production of high-specification eye bolts for an aerospace contract produced from 718 inconel on the Nakamura WT-150 turning centre.

The MJ6x1.0-4h thread was 28mm long with a surface finish specified at 0.8 micron CLA.

The setters throttle back cutting speeds for greater consistency and run the thread rolling head at 1,910rev/min.

‘This was still very competitive in producing the complete part within seven minutes and maintains that the inconel material rolled extremely well to meet the requirements even with soluble coolant,’ said Street.

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