The original machine cutting keys for some of the leading car and truck manufacturers had a 2.4m diameter table occupying considerable space on the production floor. It had 12 milling heads to produce the key flats, each cutting operation taking 5s, it was a highly skilled operation and time consuming. With its complex mechanical linkages and gears, routine maintenance was a very protracted task estimated to take at least 3 months to strip-down, repair and reassemble the machine.
To overcome these problems CE Marshall designed and built, in-house, a new machine which comprises a central rotating turret equipped with eight process stations on a 0.5m diameter table. The main rotary axis is controlled by a Parker Dynaserv DR1200A direct drive brushless servo system.
The motor is a gearless design fitted with a brushless resolver and high load capacity cross roller bearings. It can handle compression loads of up to 4tonne and overhung loads of up to 400Nm with very low axial and radial run-out. Maintenance free, the motor is capable of high acceleration and fast settling times and can produce a peak torque of 200Nm.
Each of the machine’s process stations handles a different aspect of key manufacture: key blank loading (by a pick-and-place unit), phase one cutting, phase two cutting, swarf removal, nibbing, brushing and key unloading. A spare station is fitted between the two cutting stations to accommodate any future process changes.
At each station the keys are held by pneumatic collets which are indexed to the key blank loading stage. The positioning operations at each station are handled by 23 frame size stepper Micromech motors, driven by Parker SD15M ministepper drives. In all there are 10 synchronised axes of motion control, each receiving its step and direction signals from one of three AT6400 four-axis PC-bus indexers, mounted in the machine’s control computer. The stepper motors are fitted with incremental encoders, with the data fed back to the AT6400s to provide position verification and stall detect functions.
In order to maximise product throughput, considerable effort went into making the key cutting machine’s control software self-adaptive. Once the code for a particular key has been defined it is automatically analysed in order to evaluate the most efficient cutting sequence; the machine then cuts all low-profile cross flats on the key blank first.
After the second cutting phase is complete, the key is transferred via the swarf removal station to the nibbing station where a profiled cutter is used to create the bevelled inserting point at the end of the key. The key is passed via a brushing stage to the unloading station, ready for the next phase to the process the fitting of a plastic finger grip in an injection moulding machine.