Ducati revved up manufacturing efficiencies on its unique high-revving desmodromic engines by turning to automated laser tool monitoring. Renishaw NC4 laser tool checkers were installed on two Stama vertical machining centers dedicated to machining of critical camshafts. The innovative Renishaw system uses non-contact laser technology to provide detection against tool breakage that can damage the valuable cams.
Desmodromic valves, standard on all Ducati two-cylinder motorcycles since 1972, require a unique camshaft design with special lobes that provide positive mechanical actuation to open and close both intake and exhaust valves. The race-proven design avoids the valve "float" that can occur at high revolutions with conventional spring-return valves, a key factor in Ducati's long, successful competition record.
The famous Italian motorcycle maker has been owned since 1996 by Texas Pacific Group of Fort Worth, Texas, which has invested heavily in efficiency improvement, technology innovations and expanded production.
Great precision is required in machining the complex and costly camshafts, according to Fulvio Abbondi, manufacturing technology specialist at Ducati's Bologna, Italy factory. Forged from a special steel alloy, then hardened and tempered, a camshaft already represents a significant investment as a rough-turned blank when it reaches a machining center, he noted. The Stama VMCs are configured for four-axis machining with a rotary fixture. Four cam workpieces are mounted on the fixture at a time for batch processing.
Between the toughness of the cam steel and volume production requirements, there is constant risk of a chipped or broken tool being picked up from the magazine, leading to serious damage and costs, he noted. A tool breakage that goes undetected can force the scrapping of the expensive components or costly re-machining, along with wasted time. At worst case, it can damage the machine tool spindle at great cost — potentially thousands of Euros — between repairs and lost production, he said.
Ducati aims to keep the cam machining centers working non-stop producing camshafts for all its different engines.
“It is essential that control checks be carried out on the work performed by the machines," said Abbondi. "The NC4 systems are installed so that a tool loaded in the spindle immediately crosses the laser beam at a set height. If the cutting tip is broken, for example 97 millimeters long instead of 100 millimeters, the laser system triggers an alarm. Each tool has its own length, diameter, etc., and the system takes this into account when the tool passes through the checking beam.”
The non-contact system is particularly effective at checking small tools used to make keys and other reference points on the cam, vital if the engine is to operate properly. Small tools can be problematic with conventional contact detection systems, he explained. The tool must activate a button or rod, so the touch must be done at low speed, which slows down the process and lengthens cycle times. Contact systems tend to jam and present poor reliability. There is also the danger that the contact action can break or damage a small tool. Contact systems must often be fitted inside the operating area, occupying valuable space and causing possible collision risks. For all those reasons, according to Abbondi, the non-contact laser detection system was adopted to replace contact devices.
"Since tools are checked for breakage automatically, one operator can easily manage both machines," said Abbondi. "All the operator needs to do is load the pieces and ensure that everything is running smoothly.”
Checking with light
Improvements in laser technology enable non-contact detection of ever smaller tools. A laser beam runs between a transmitter and a receiver and is broken when the tool enters the beam, generating a trigger pulse. If no reduction in light is detected, the system emits a tool-broken signal. The NC4 transmitter and receiver units measure just 30 mm (diameter) by 35 mm (height), less than 1.5 inches in each dimension, for space-savings and installation flexibility, while providing separation distance and beam length of up to 5 meters. Depending on separation distances, breakage detection can be carried out on tools as small as 0.1 mm. System response time of 10µs aids the accurate setting of fast rotating tools. System set-up is simple, as there is no laser focal point to identify, and a visible LED mounted on top of the transmitter unit gives users constant feedback on system status.
The desmodromic system
The vast majority of the world’s motor manufacturers use return springs in their engines to close exhaust and inlet valves. Ducati's desmodromic system offers greater engine reliability at high speeds by solving the problem of spring inertia — "float" — and reducing operating friction by about 30 percent. Theoretical speeds easily top 20,000 revolutions per minute. However, the desmodromic system complicates engine design and manufacture. Besides the complex cam and valve train, it’s not possible to take up the slack as with hydraulic tappets.
"The clearance between the stem and the cam is adjusted by hand during assembly and is a critical operation," said Abbondi. "We use shims at the bottom and top and these must be adjusted with extreme precision.”
The desmodromic camshaft is not conventional. Special lifting ramps provide positive mechanical action to precisely open and close exhaust and inlet valves at very high engine speeds.
The Renishaw NC4 system is used to prevent damage by broken tools to very expensive cam parts – eliminating resultant scrap, re-machining and wasted time.
Fulvio Abbondi, manufacturing technology specialist, shows three different desmodromic camshaft configurations awaiting machining.
The desmodromic cam system has been used on Ducati engines since 1972 to give great reliability at high speeds. The race-proven design avoids the valve "float" that can occur at high revolutions with conventional spring-return valves, a key factor in Ducati's long, successful competition record.