Manufacturers of medium to complex turned parts need to be aware that fitting one or more high-speed spindles, capable of milling and drilling at up to 100,000 rpm, can extend the range of applications that are possible on sliding-head lathes and solve problems on existing jobs. This is the view of Ian Baker, managing director of Emmaco UK, Hinchley Wood, the agent for sales, installation and service of high-frequency motor spindles manufactured by the Swiss company, IBAG.
Japanese sliding-head lathe supplier, Star GB, collaborated with Emmaco recently to install a lathe fitted with an 80,000 rpm IBAG spindle at a subcontractor in the North of England. The company needed to drill a 0.5 mm cross hole in a brass component, but the lathe's 8,000 rpm driven tool speed was insufficient to achieve sufficient surface speed for efficient machining.
By fitting an electrospindle capable of ten times the rpm, cutting speed was increased to around 40,000 rpm (63 m/min), resulting in better surface finish, higher productivity and reduced tool wear.
In another application cited by Mr Baker, this time in the medical sector, the cycle time for machining bone screws on a slider was reduced from seven minutes to 45 seconds by retrofitting an IBAG spindle. A further advantage was the elimination of burrs that were previously created by milling at sub-optimal speeds.
Manufacture by another company of 316 stainless steel bone screws, which required milling of a Torx drive socket, was three times faster on a slider as a result of fitting a 60,000 rpm IBAG spindle in a standard backworking tool position.
Mr Baker says that there is considerable interest at the moment from medical companies in high-speed units, especially for milling stainless steel using typically 2 mm diameter cutters. Not only are the best machining parameters attainable, but also the IBAG drive is particularly smooth, resulting in very fine component surfaces approaching a mirror finish in some instances. One US manufacturer has installed no less than 17 such spindles on one Star lathe.
As to the practicalities of fitting an IBAG spindle to a Star sliding-head lathe, either before delivery to the user or afterwards on the shop floor, Mr Baker advises that a simple, stand-alone installation could take as little as half an hour. That would involve mounting the unit in a tool position, attaching the electric and compressed air supplies and setting the speed using a potentiometer.
However, it is recommended that spindle operation is interlinked with the machine door so that rotation stops when an operator accesses the working area. Furthermore, the unit can be programmed to start and stop using spare M-codes to save energy. These additional functions increase installation time to between four and eight hours.
There is considerable flexibility on spindle location within a lathe. Clearly a live tool position is not required, as an IBAG spindle has its own power. Any non-driven tool position on a platen is ideal, either for cross, front or end working on a component. Most IBAG spindle models fit into existing tool blocks.
It is also feasible to mount an electrospindle in a turret position on sliders of that configuration, but rotary couplings are needed for the services and the extra cost normally dictates that alternatives are investigated first.
A quick-release connector allows a spindle to be exchanged as quickly as a standard tool. Apart from providing much higher speeds to reap all of the advantages described above, it is worth remembering that the spindle provides one extra driven tool and may be especially useful on machines that do not have many live positions.
There are over 60 high-speed spindles in the IBAG range suitable for fitting to sliders, including some designed specifically for mounting on the rear toolpost on Star machines. Fixed-angle and adjustable-angle units extend the machining possibilities.
IBAG products include all standard machine holder diameters: 16, 19, 20, 22, 25, 33, 35, and Imperial equivalents. As standard, they are offered grease packed up to 60,000 rpm or with oil/air lubrication up to 80,000 rpm. Higher speeds are also available.
Utilising DC brushless motor technology, the spindles are both powerful and compact enough to fit into the typical Swiss-style lathe tooling area. Up to eight spindles can be powered sequentially by the same drive under CNC command, a solution that saves the cost of extra drives but may add a little to cycle times while the switchovers occur.