Rigibore Introduces ActiveEdge Precision Boring

Kent, U.K. - The precise setting of a boring head on a machine tool has always been troublesome and time consuming because the tool cuts around its centreline and so each cutting edge must be adjusted manually to obtain the desired size. As a solution, Rigibore has created an automatic, hands-free precision adjustment system able to be applied to obtain micron tolerances on bore sizes over 16 mm diameter.

The ActiveEdge system uses wireless telemetry to enable precise adjustment of up to eight individual boring units on a single bar without any need for the tool to be touched. So precise is the ActiveEdge cartridge based system that it will react and repeat to submicron adjustment over its range of 0.6 mm on diameter. And for the user, the Rigibore system can be fitted to any type of boring bar shank without any need for modification to the spindle unit in the machine tool. Central to manufacture of the tool unit is the in-built precision within the cartridge unit that is now produced using a five-axis set up on a Fanuc Alpha T21iEL vertical machining centre from 600 Centre of Shepshed near Loughborough. This level of precision that Rigibore can now obtain at its Hayle, Cornwall, manufacturing facility has also ensured that the whole system enables total integration to a gauging station or co-ordinate measuring machine to completely close the loop between inspection, any adjustment requirements and the machining process.

When the bore is measured, the system automatically recognises when an adjustment of the tool is required and determines the appropriate offset to be applied to the tool. ActiveEdge then automatically signals using wireless transmission to the designated cartridge unit the amount of adjustment required and the tool, which draws power from a replaceable lithium battery, consequently reports back to the gauging station to qualify the adjustment has taken place.

Following a significant investment to bring ActiveEdge to market, the challenge was to source a machine tool capable of maintaining the precise tolerances required in the cartridge unit while creating a viable production method. And, with worldwide markets beckoning, Chairman Roger Bassett's challenge to machine tool suppliers was to provide a solution to faithfully reproduce the components that would create the mechanical adjustment system. These parts involved an ultra-precise blind slot in an investment cast cartridge unit that also included various drilled, tapped and milled features.

Machined out of solid, the blind slot was the real contest to the equipment suppliers. It is just 4.4 mm wide, some 26 mm long and has a depth that varies from about 6 mm where the cutter enters, up to 12 mm where there is a full radius that has to be maintained. However, the stumbling block was the tolerance: for ActiveEdge to perform as envisaged, the size and geometry of the slot had to be held within a + 3 micron band!

Following numerous discussions and trials, the machine tool order went to 600 Centre to create a turnkey project-based solution on the latest Fanuc Alpha T21i EL vertical machining centre. The Fanuc machine impressed Roger Bassett for its high speed 24,000 revs/min spindle operation, rapid traverse rates of 54 m/min and ultra-fast acceleration and deceleration. In his view the A1 contour control was a prime selling point in order to interpolate the slot in the cartridge and with the thermal displacement compensation in the new F3-31i AS control - giving an accuracy and repeatability within + 2 microns - this was just the type of solution he wanted.

600 Centre's method to drill, tap and mill the various features of the cartridge such as a grease nipple hole, a taper hole and through coolant feed holes, involved two parts per load. The machine also had to produce the mating slide made of spring steel using a multi-load fixture able to hold 16 parts at a time. For the micron demanding tolerence slot in the cartridge, the 600 Centre initially attached a high speed grinding spindle with cubic boron nitride (CBN) wheel to the Fanuc Alpha VMC to finish grind the milled slot, as 600 Centre managing director Ray Grocock recounts: "We were talking extremely tight tolerances and from our grinding experience this had to be the most effective method to accurately finish the slot. Unfortunately, the hybrid process did not give the desired consistency with so many variables in the grinding process made worse when producing batches of 1,000 parts."

At this point the decision was made to revert to milling from solid and the whole operation was re-engineered. To which Roger Bassett adds: "The 600 Centre's application engineering team then developed the process which is now running very successfully using solid carbide cutters." The five-axis Fanuc Alpha set up uses a two-axis Nikken index and rotary unit to allow in-cycle access of tools to three sides of the component. The cartridge component is machined in a slave fixture held in the taper of the Nikken unit allowing simultaneous loading of the parts while the machine is operating. In-cycle with the drilling and tapping, the set up uses a carbide ballnose cutter to rough the slot to 4 mm width using axis interpolation down the sides of the slot and around the end radius. The slot is then semi-finished milled leaving just seven micron for the final finishing pass. As Roger Bassett enthuses: "The repeatability of the Fanuc Alpha is unbelievable. The cutter is run at 10,000 revs/min and using a 90 mm/min feed rate, the machine easily maintains the slot width tolerance."

When producing the mating slide component, the same slave fixture technique is used enabling three-side machining but this time 16 parts are loaded. Between component change-over is quick with the Nikken head and all tooling is carried on the 21-position magazine for both parts. All the setter has to do is to call up the new program, use a Renishaw probe to reference the fixture and press the cycle start. A Renishaw laser system is also fitted to the machine for automatic tool measurement.

Says Roger Bassett: "The toolchange chip-to-chip is fast at under 1.8 secs so it is quicker to completely finish each part on one facet of the slave fixture incorporating tool changes, than keep indexing the fixture and continuing to use the same tool on all the parts." With production growing fast, Rigibore is now planning to add other components to the Fanuc Alpha VMC and future developments are being planned. Indeed, at IMTS in Chicago during September, Rigibore demonstrated the linking of ActiveEdge to a gauging station which drew considerable interest from visitors especially from the highly competitive automotive sector. "This system closes the loop completely without any physical adjustment of the tool in the spindle," says Roger Bassett. "Because you no longer need to gain access to the tool to make any adjustment followed by trial cuts, there's no additional lost time." Said Roger Bassett: "The level of potential business for ActiveEdge is almost unbelievable. We have certainly demonstrated an important solution to improve spindle uptime when bores are involved taking the tedium out of sizing and maintaining continuous production. With the Fanuc VMC set up, we know we can maintain the precision needed in the mechanical elements of the system to ensure quality of our production."

SOURCE: Rigibore Limited