Robots tackle difficult finishing processes

Citation

(1998), "Robots tackle difficult finishing processes", Industrial Robot, Vol. 25 No. 4. https://doi.org/10.1108/ir.1998.04925daf.007

Robots tackle difficult finishing processes

Robots tackle difficult finishing processes

Keywords FANUC, Finishing, Polishing, Robots

Perhaps one of the most difficult polishing jobs around is artificial knee joints. On most polishing jobs one requirement dominates other features, this may be surface finish, profile accuracy or production rates.

On a knee joint all of these characteristics are equally important. One of the first "joint venture" installations following the technical liaison between FANUC ­ robots; Morrisflex ­ finishing machines; and 3M abrasive materials was an automated cell finishing cell for a major manufacturer of orthopaedic implants.

The automated cell has cut the time to finish a knee joint made of cobalt chrome to ten minutes from around 30 minutes.

The cell comprises two, two-belt linishing machines, a polishing machine, a pallet load/unload station, and a FANUC S10 Robot. All the machines are integrated with the robot controller via a PLC interface. Dust extraction is incorporated with ducts at each work station.

The load station can hold two pallets, each of which holds 42 components, 84 in all. This adds up to 14 hours operating time between loads. Pallets are loaded by forklift truck via the safety-interlocked rise and fall doors.

The cycle starts with the robot picking a component and presenting it to the first linishing machine.

There are two belts on each spindle, with two spindles this makes four belts per the machine or eight altogether. The robot progressively passes the joint through the eight belts which start as a 240 grit size and progress to a greased 600 grit size.

Each linishing machine supplied by Morrisflex is powered by a 2.2kw motor with infinitely variable speed and dynamic constant force control with 50mm of travel. A recirculating coolant system services both machines. 250mm diameter contact wheels shaped to fit the components are fitted. The grit grades for each of the eight linishing stations were determined by 3M who supplied all abrasive products for the project.

The polishing station is fitted with a double-ended spindle with 350mm diameter mops. There is an auto-feed system for solid polishing compound. After completing the finishing cycle, the robot places the joint in the pallet and picks up the next one. When the pallet is completed the system automatically indexes to the next pallet to give a total of 14 hours of unmanned production.

As well as reduced cycle time, other benefits claimed from using an automated cell included reduced scrap levels; longer abrasive life ­ as a result of dynamic force control; consistently high quality standards and, most important of all, round-the-clock working without supervision.