Case Studies: Laser Detection Prevents Damage
Italian motorcycle manufacturer Ducati (Bologna, Italy) revved up manufacturing efficiencies on its Desmodromic engines by turning to automated laser tool monitoring provided by Renishaw (Hoffman Estates, IL). Renishaw NC4 laser tool checkers were installed on two Stama vertical machining centers (VMC) dedicated to the machining of critical camshafts. The Renishaw system uses noncontact 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.
Ducati has been owned since 1996 by Texas Pacific Group of Fort Worth, TX, which has invested heavily in efficiency improvement, technology innovations and expanded production.
Great precision is required in machining the complex and costly camshafts. 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. 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.
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,” says Fulvio Abbondi, manufacturing technology specialist at Ducati’s Bologna factory. “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 and diameter, and the system takes this into account when the tool passes through the checking beam.”
The noncontact 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 correctly. Small tools can be problematic with conventional contact detection systems. 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 also is 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 the noncontact laser detection system was adopted by Ducati to replace contact devices.
“Because tools are checked for breakage automatically, one operator can easily manage both machines,” Abbondi explains. “All the operator needs to do is load the pieces and ensure that everything is running smoothly.”
Checking with LightImprovements in laser technology enable noncontact 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 millimeters (diameter) by 35 millimeters (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 millimeter. The system response time of 10 microseconds aids the accurate setting of fast rotating tools. System setup is simple, as there is no laser focal point to identify, and a visible LED mounted on top of the transmitter unit gives operators constant feedback on system status.
The Desmodromic SystemMany 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, or float, and reducing operating friction by about 30%. Theoretical speeds easily top 20,000 RPM.
However, the desmodromic system complicates engine design and manufacture. Besides the complex cam and valve train, it is 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,” notes Abbondi. “We use shims at the bottom and top and these must be adjusted with extreme precision.”
- Renishaw Inc.