Rotary transfer replaces conventional machining

Three of the latest high production, single operation rotary transfer machines for the female contacts have been so effective that the user is planning to extend its newly gained production advantage.

A product of quality has a certain feel about it - as is verified by the delicate touch of the assemblers who put together dozens of miniature contacts into electrical plugs and sockets for Lemo, a Swiss manufacturer of some 75,000 different types of high-class Unipole and Multipole electrical connectors.

Lemo's connectors are sold worldwide for applications as diverse as medical, aerospace, nuclear, satellite, defence, oil industry and even Formula One.

Lemo has four production operations in Switzerland, where it is headquartered, and recent investment in the plant at Redel, high in the hills of Sainte-Croix, has totally transformed the production processes for connector contacts, sales of which have grown by some 40% since 1998.

Indeed, the move from more traditional multiple operations for its plug and socket contacts involving cam-driven sliding head auto lathes and milling machines, to three of the latest high production, single operation rotary transfer machines for the female contacts from Mikron Machining Technology of Lugano, has been so effective that the company is now planning to extend its newly gained production advantage.

Just recently the company has placed orders for two additional Mikron machines to produce the mating male contacts and a further machine for delivery later in 2006 to produce female contacts.

It is the new method of producing the more complex bronze female contacts that has raised comments from the assembly team: they can immediately feel the difference between the new and previous process methods by the finer quality of finish gained from the rotary transfer machines.

Now, four previous individual operations of turning and three milling cycles have been combined into a single cycle ready for plating and the process integrity is so consistent, that Redel is recording a CPK of 1.67 at an overall production efficiency of better than 85%.

Abraham Ratano, a director at Redel responsible for the connector operations and spearheading the progressive installation of the Mikron Multistar CX24 rotary transfer machines, has a much stronger reaction to the new methods: "It has enabled us to cut lead times for, say, a batch of 100,000 pins from between six to eight weeks to a 'made to order' philosophy taking just 10 days.

Not only has this helped to eliminate expensive stock piles at our plants but also dramatically slashed the cost of manufacture," he says.

Redel produces three contact sizes of 1.2mm, 1.5mm and 2.2mm diameter in enormously varying lengths of between 12mm and 36mm.

In total, the company produced on its Mikron machines alone some 19.5 million female contacts in 2004, which demonstrates the potential of the return on investment generated by the method change.

But according to Ratano, further savings have been generated by the Multistars, which are rated as the fastest rotary transfer machines in the world and, depending on the component, are capable of delivering up to 240 parts per minute.

While Redel's female connector contacts are now produced nine times faster than before in a single cycle, that ensures all geometric relationships of features are maintained at a rate of 40 per minute, the new method of manufacture has also enabled a redesign to be carried out.

Incorporating a special 'super smooth' lead-in blended radius for the mating male contact as well as the introduction of a bend in the wall of the pin that, in conjunction with milled slots this forms a 'pressure spring' to maintain a constant force on the male connector when it is inserted and mated to the female.

As a result, Redel has reduced by half the force required to make a connection and indeed, this is checked 100% as part of the Mikron machining cycle.

Here production monitoring has revealed a process consistency CPK of 3, a third of the designated tolerance.

According to Ratano, the decision to change to Mikron could have been high risk due to the added complexity of the redesign, and it took some six months of internal discussions over the process to define what was required.

Three months of intensive development with Mikron then followed due to the complexity of the milling, drilling, turning and process control that was critical to the operation.

The Multistar CX24 machine is designed to accommodate larger batches of part families of complex components requiring fast changeover.

It is constructed around a central column and housing to support the 24-station rotary table which carries the location collets with separate, tailored to suit the cycle, linear cams to provide individual working strokes of the machining spindles.

Spindles can be mounted at any angle between horizontal and vertical, including for off-centre machining, when they are set on adjustable workstations.

Spindle speeds too are adjustable between 500 and 24,000 rev/min.

Although there are 24 stations to the machine, the number of collets can be doubled to provide 48 machining positions and turnover stations can be included as used at Redel for producing operations at both ends of the component in a single highly productive cycle.

Pins are bowl fed individually into the Mikron CX24 machines at Redel where the solid cable end of the contact is produced first.

It is then turned over in-cycle and the machined diameter is used as a location to produce the female end and pressure spring.

The main bore is cleaned as part of the machining process and a piezo-electric sensor finally engaged into the bore in order to measure the extraction force for the mating pin and socket before the part is unloaded.

All three Multistar CX24 machines include broken tool sensing based on a hydraphone system, real-time monitoring of production, ultra-fine two micron filtration of coolant and temperature control.

A fire extinguisher system is fitted to each machine for extended unmanned running.

All three machines are run over two shifts and are unmanned at night with four people, including a supervisor and setter that take charge of production.

Said Christopher Caretti, who is responsible for the process: "The average time lost to setting the machine is around two hours each day.

In 2004, records show they performed 146 changeovers in the 225 working days and depending on the complexity of the set up, this could take as little as 1.5 hours." Christopher Hazard, the machine setter, talks about the consistency of the process from all three machines: "We used to measure parts every hour in the inspection room using a video-based non-contact measuring machine.

This has now been extended to one measuring cycle every four hours and our SPC records confirm how consistent the process has proven to be." Indeed, with the move during 2005 to install two of the more simple LX24 Multistar machines to produce the less complex male connector contacts, Redel is still expecting further savings.

While the female contacts are produced at some 40 parts per minute, the male will be produced 50% faster.

By that time, it is expected that the assembly team at the parent company should have no reason to comment on the quality of feel between the methods of production.

Back to top