BENEFITS OF A FIVE-AXIS MACHINING CENTRE COMBINE WITH THOSE OF A MILL-TURN LATHE

There are a number of purpose-built 5-axis / 5-sided machining centre designs on the market, including types with a rotary table and either a trunnion support or a swivelling B-axis head to provide the fifth CNC axis. A number of companies including Hurco supply such machines, but neither configuration suited Brunswick Tooling, Brighouse, a manufacturer of reamers and special cutting tools, both solid carbide and indexable-insert.

Instead, it asked Hurco to supply an alternative 5-axis configuration based on a 3-axis VMX30m machining centre fitted with a 2-axis NC tilting rotary table. Many regard such a solution as inferior to a custom-made 5-axis machine, sometimes referring disparagingly to a lack of rigidity with 'bolt-on attachments'. However, for producing Brunswick Tooling's products, which are essentially rotational components, the arrangement has proved to be optimal.

The rigidity issue was tackled at the outset by selection of a Kitagawa TT182 hydraulic, 2-axis table with -35 / +110 tilt angle and a 360-degree table rotation. According to Brunswick Tooling's managing director, Paul Briggs, the attachment is so robust that machining performance is just as good as that of purpose-built, 5-axis machines.

Indexing accuracies of 20 and 60 seconds of arc respectively for table rotation and tilt, with 4 seconds of arc repeatability, ensure top precision metalcutting when combined with Hurco's ± 0.005 mm linear positioning accuracy and ± 0.0025 mm repeatability.

The real advantage of the set-up is that Brunswick Tooling is able to clamp the rotary table in its vertical position and fit a tailstock to the left hand side of the machine bed. In this way, the tools it manufactures can be positioned between centres and clamped securely for prismatic machining operations to be carried out, such as milling of indexable insert pockets.

The first Hurco machine installed, in March 2010, has been operated in this mode for a large part of the time. However, for certain jobs the tailstock is removed and the Kitagawa table is inclined upwards to position the component at a compound angle for 3-axis machining of complex features on some tooling products. Both rotary axes are currently used in this way, ie indexed and clamped, but they could be interpolated with the linear axes in future, if desired, as the Hurco Max CNC system is able to control full 5-axis cycles.

It was the flexibility of being able to use the machine either in turn-mill mode or as a 5-sided or 5-axis machining centre that convinced Mr Briggs to choose the Hurco / Kitagawa option. The merits of the decision were underlined by the purchase of a second, identically equipped VMX30m one year after the first. Even the tools in the magazines are identical. Programs are stored on the factory server, allowing any job to be downloaded to, and produced on, either Hurco machine, with certainty that the most up-to-date cutting cycle is being used.

Mr Briggs said that there is a particular functionality within Hurco's WinMax conversational programming software that lends itself well to 5-sided machining applications, during which the part is tilted upwards at an angle. It is called 'transform plane' and is used in a rotary program to re-establish part zero to any plane for non-rotary 3-axis milling or drilling. This facilitates machining of repeating features on several sides of a component, as the tool automatically moves so that it is always perpendicular to the transformed plane.

Essentially, whatever angle the part is at in one or two rotary planes, the Hurco software always knows where the datum is, which has allowed us to increase productivity on complex, high added value products, confirmed Mr Briggs.

His lead machine tool programmer, Andrew Bell, also commented on the software: With WinMax, it is easy to program a part without any need for an expensive 5-axis CAM system.

We take the DXF file from the 3D model we create in Autodesk Inventor and load it directly into WinMax. The data is then used to generate the cutter paths using conversational routines, quickly and accurately, without the risk of introducing G-code errors.

The software is years ahead of its time and always has been, even the earlier, non-Windows version, Ultimax.

Mr Bell, who uses WinMax software daily, also likes the way a graphic of the part being programmed is generated concurrently in background. He said it allows any potential mistakes in component geometry to be spotted quickly, this being especially useful when programming a cylindrical part, which is difficult to visualise from a 2D drawing.

Brunswick Tooling manufactures reamers in batches of up to 300-off for world markets, but its special cutting tools are normally produced in ones and twos, for which WinMax software is ideal. Often, the company is asked by firms to design and produce a tool from scratch from a CAD drawing of the end component. Customers include Ford, JCB, Airbus, AgustaWestland and BAE Systems, from which it recently received the Chairman's Silver Award for reducing lead-time for a Joint Strike Fighter titanium machining operation from three days to five minutes.

Mr Briggs concluded, The Hurco machines are good value for money and have a large working area for the factory space they take up.

Their accuracy is fantastic – we easily hold 50 microns on indexable insert pocket dimensions and position, despite sometimes machining a long component held at one end.

We still operate a number of universal, 4-axis toolroom machines, which have a manually tilting table and require longhand G-code programming. They will continue to have their place for manufacturing reamers and some repeat special tools.

But for particularly complex tooling designs, which are becoming more and more frequent, the Hurco / Kitagawa configuration is the future for our business and the avoidance of expenditure on CAM software, and an operator to use it, is an added bonus.