Cutting edge compensation

When a leading engine manufacturer looked at reducing both, it turned to Rigibore and its fully automated boring tool compensation system, Zenith.

Rigibore’s Zenith system was selected for its ability to make cutting edge compensations automatically from measurement data to an accuracy of 1µm on diameter. Maintaining much closer machining tolerances on crankshaft bearing journals not only enhances the quality of the finished component, but has a direct impact on engine efficiency and emissions.

Rigibore’s solution was to produce line boring bars with five semi-finish cartridges set 0.1mm below nominal to allow five ActiveEdge finish cartridges to machine all journals in a single pass. The ActiveEdge line bars were automatically compensated to nominal from data provided by offline gauging that was transferred to the machine control as part of Rigibore’s Zenith closed-loop system.

Prior to installing the ActiveEdge tools into the production line the customer carried out verification checks to confirm Rigibore’s confidence that each cartridge could be independently adjusted in increments of 0.001mm on diameter. With this ability confirmed an extended live cutting trial was instigated.

The trial took place on a twin-spindle machining centre, with each spindle machining 946 crankshaft bores over the 24-hour period of the trial, so 1,892 in total. Over that 24-hour period not a single bore was out of tolerance thanks to ActiveEdge’s intervention. The finished bores had a mean diameter of 52.965mm with a tolerance of ±0.015mm, within the test period bore sizes were maintained within a variance of just 2µm.

Before installing the Rigibore tooling, the manufacturer’s operation had two line bars running on a multi-spindle CNC. Adjustments were made by the operator entering the machine with a dial indicator and adjusting each individual cutting edge manually. Once adjustments were completed on all ten cutting edges, these parts were machined, measured with a bore gauge and checked for size. Often several cartridges will need further tweaking to reach the desired tolerance.

The tool setting process was very time consuming, requiring skilled operators to make adjustments based on a trial and error approach. The process of ensuring nominal size before the production run was taking on average 45 minutes. Rigibore’s Zenith allows automatic, individual cutting edge compensations to be made with the tool located anywhere in the machine, completing the setting process after an insert change within a matter of minutes.

“ActiveEdge, along with the totally autonomous Zenith boring bar adjustment system, has been developed over many years to deliver efficient management of fine boring applications that reduce machine downtime and eliminate scrap resulting from variance in bore sizes,” says Rigibore’s chairman Roger Bassett. “At present Rigibore is the only company capable of making fully automatic adjustments to multiple cutting edges on the same boring bar to one micron on diameter.”

The Zenith solution has made significant and measurable contributions to the engine manufacturer’s machining process, both in terms of part quality and production efficiency. Rigibore macros set a pre-defined upper and lower warning limit on bore sizes to ensure a tighter, more consistent tolerance.

If bore sizes reach this warning limit an automatic compensation request is initiated, adjusting to ensure then next machined bore is returned to nominal size. By holding closer tolerances there are substantial benefits in subsequent operations and processes, reducing time on honing after the finish bores have been completed.

Rigibore www.rigibore.com