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Mollart Engineering has developed an 18-axis, 16-spindle gundrilling centre for an overseas customer that already has 144 spindles working in its factories.

The new machine can produce up to 16 different holes simultaneously and is capable of automatically creating up to 36,000 radial holes in a tubular die blank at the rate of almost 1,000 holes per hour, to be used in the production of wooden pellets as part of a biomass green-energy project.

The dial-type, horizontal spindle machine has a central two-axis rotary table that is also programmable for positioning in the vertical Y axis to create a rise-and-fall movement for vertically pitching each hole centre.

Around the table are four outboard wing units each carrying four independent gundrilling spindles that will produce holes between 1.6mm and 12mm in diameter up to almost a 100:1 depth-to-diameter ratio.

Each tubular die carried on the machine table can be up to 1,700mm in diameter by up to 500mm in depth and can weigh up to 250kg.

Made from heat-treated die steel, the wall thickness can be specified up to 150mm, which has to be drilled through by the gundrill tool.

John Mercer, Mollart’s technical director, said: ‘This is the first-ever deep-hole machine development that will produce up to 16 holes simultaneously, which is able to create an increase of 30 per cent in productivity over previous machine designs.

‘Through the Fanuc 30i control, it has the added flexibility of allowing the user to program any combination of spindles to be run from a single unit to the maximum of 16,’ he added.

According to Mercer, the software development team at Chessington played a key part to provide fast changeover through the programming of the control unit to suit the different combinations of die size and hole specifications.

‘Our software allows the automatic calculation of the appropriate machining cycle and creation of the program purely by inputting the diameter of the die, the tool length, the number of rows of holes required, the number of holes in each row and the appropriate pitch between each hole,’ he said.

The biomass green-energy project will make use of scrap wood that is initially shredded and mixed with sawdust and water before being pumped into the centre of the die.

It is then extruded under pressure through the wall of the die via the gundrilled holes to create pellets that are between 1.6mm and 12mm in diameter.

According to Mollart, 16 holes can be produced in less than one minute.

Also key to the process is the use of carbide tooling to achieve high orders of size consistency and surface finish in the toughened steel, which ensures that the extruded material is easy flowing and that its abrasive nature does not reduce the working life of the die.

Each of the four spindles is carried on a horizontal slide, which will feed each drill through its own guide bush for maintaining the start position of the tool and a chipbox.

High-pressure 120bar coolant passes through each gundrill, which is independently monitored for oil flow, thrust on the tip of the tool and in-service tool life.

Tool life can be calculated either from the recorded number of holes produced or the combined total depth of holes the tool has created.

The neat oil coolant, supplied from a centralised system, is filtered on the machine to 20 microns and through a flushing system introduced into each chipbox.

This ensures that there is no build-up of swarf and that the machine can run uninterrupted around the clock.

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