Good rotations

The star of the exhibition was the launch of the new Citizen D25 sliding headstock turn-mill centre. This latest machine comes with Citizen’s next generation advanced CNC system featuring touchscreen and qwerty keyboard.

The machine tool’s flexibility is increased for complex cycles by incorporating two gang vertical toolposts each with X-, Y- and Z-axes and one with a B-axis capable of both front and back machining. In addition, there is a back toolpost and opposite toolpost.

The machine on show at the open house was a prototype Cincom D25 with production machines ready to be delivered in April 2018. The sliding head machine has a capacity up to 59 tools with the added advantage of removable guide bush for more economic material use on shorter components.

The Cincom D25 is configured as a 10-axis machine which includes the 0 to 135° swivelling B-axis. This swivel axis is incorporated within the first (X1, Y1, Z1) axis gang toolpost capable of holding four double-sided driven spindles to service both the main and sub-spindles. In addition, the second gang toolpost (X2, Y2, Z2) is able to work independently or simultaneously with the (X1, Y1, Z1) toolpost to overlap for instance, rough or finish turning operations or apply in unison, drilling or milling based cycles.

Adding to the flexibility of the tooling applications there is a further (Y3) back toolpost axis with one fixed or three driven tools having 90° adjustment for face, radial or angle machining. The opposite toolpost is positioned alongside the sub-spindle (X3, Z3) which provides a further two fixed tool positions.

The power of the main spindle is 5.5kW and 3.7kW for the back spindle with both having a maximum speed of 10,000rpm. The gang driven tools are powered by drives of 2.2kW with maximum speeds of 9,000rpm and the back driven tool speeds are 6,000rpm. Rapid traverse rates are 32m/minute with 24m/minute available on the Z2 gang toolpost.

Darren Wilkins, deputy managing director at Citizen UK, explains: “This design is a completely new concept based on twin platens which can perform balanced turning. A unique feature is that one of the platens moves in three axes, which means we can control the distance between the two tools, during balanced turning. This allows you to optimise cutting with two tools on the same part. This also helps stability and chip control.

“Another advance is that this machine’s new CNC platform means it is the first lathe in the world to have true 5-axis control. True 5-axis control, as opposed to 4+1-axis, is not often needed on sliding head machines but in certain instances there are components that benefit both in tool life and process speed. It allows you to machine elaborate features and contours on very small workpieces. We can now demonstrate that for certain components it is possible to machine them rather than using other methods such as casting because conventional cutting tools and CNC machines would be unable to do the job.”

Citizen’s main focus is to help its end users improve productivity by making it machines easier to use and able to run longer unattended.

Mr Wilkins continues: “Our end users have to be as competitive as possible. They are looking for machines that increase productivity – but that’s not just about speed – it’s also about how many components they can produce with their current skills set. There is a continuing need to de-skill machines. We also have to maximise speed, reliability, stability and tool life, and have the ability to maximise productivity by running unattended. This is where our development resources are being further directed.”

Citizen’s Low Frequency Vibration (LFV) technology introduced to its machines last year is also intended to enable cutting more reliably, reducing the need for operator intervention.

“For any high-speed lathe, the amount of swarf generated becomes a challenge,” Mr Wilkins comments. “This why the majority of our machines are sold with the ability to add high pressure coolant in an attempt to break swarf into pieces and reduce it wrapping round spindles and other parts of the machine. Any stoppage you have due to swarf problems immediately counters any efficiencies you may have gained by faster cutting.”

He concludes: “We are rolling out LFV across our range. This programmable chip control system, completely changes the way we cut metal. During machining the servo axes are vibrated in the axial direction and cutting is performed while synchronising this vibration with the rotation of the spindle.

“Because air cutting takes place during cutting, this leads to the intermittent expulsion of chips. Through further rotations we remove high spots and then lastly lightly cut the workpiece with a superior finish, reducing or removing the need for high pressure coolant and increasing tool life. We have used it on every material with many different machining operations: stainless steel, aluminium Hastelloy, copper, even nylon, and have had a 100% success rate.”

A video of the Citizen open house is available: https://www.pesmedia.com/citizen-machinery-uk-transforming-turning-technology/

CITIZEN www.citizenmachinery.co.uk