THE MANUFACTURE OF MACHINED STEEL PARTS FOR CARS INVOLVES THE USE OF A CONSIDERABLE AMOUNT OF MATERIAL. EACH 100 KG OF FINISHED PART RESULTS IN MORE THAN 200 KG OF SCRAP, THIS BEING EITHER DISCHARGED AS WASTE OR RECYCLED AT DIFFERENT STAGES OF THE PROCESS WITH A HIGH ADDED VALUE. THE CONSUMPTION OF ENERGY IS ALSO HIGH. THE METAL IS HEATED BETWEEN 4 AND 7 TIMES TO TEMPERATURES VARYING FROM 500 DEGREES C TO 1400 DEGREES C DURING THE CYCLE. THE ORDER OF MAGNITUDE OF THE ENERGY CONSUMPTION FOR A GIVEN PART HAS BEEN ESTIMATED AT 800 KWH/100 KG. THE LENGTH OF THE MANUFACTURING LINE EXPLAINS THE HIGH ENERGY COST OF PARTS PRODUCED BY THIS TECHNIQUE, WHICH IS, IN ADDITION, A PROCESS OFFERING HIGH LEVELS OF PERFORMANCE AND RELIABILITY. THE AIM OF THIS RESEARCH PROJECT IS TO REDUCE THE MATERIALS AND ENERGY CONSUMPTION FOR EACH OPERATION WHILE AT THE SAME TIME MAINTAIN THE QUALITY OF THE PARTS. THE STUDY WAS DIRECTED TOWARDS ELIMINATING OR REDUCING CERTAIN PHASES OF THE PRODUCTION CYCLE OF THE PART. TWO APPROACHES HAVE BEEN STUDIED :
- SUPPRESSION OF THE ROLLING PROCESS WITH THE PARTS BEING DIRECTLY FORGED FROM CAST BARS. THE IRREGULATITIES IN THE CENTRE OF THE CAST BARS CAN BE REDUCED BY HOT WORKING. ABOUT FOUR HOT WORKING OPERATIONS ARE SUFFICIENT TO OBTAIN SATISFACTORY MECHANICAL PROPERTIES. TWO AXISYMMETRIC PARTS (WHEEL HUB, DIFFERENTIAL CROWN WHEEL) HAVE GIVEN SATISFYING RESULTS IN ENDURANCE TESTS.
- REDUCTION OR SUPPRESSION OF HEAT TREATMENT AFTER FORGING. THREE TYPES OF DIRECT TREATMENT AFTER FORGING ARE APPLIED IN THE RESPECTIVE PRODUCTION PROCESSES OF :
- ISOTHERMAL ANNEALING (FOR GEARS)
-CLASSICAL ANNEALING (E.G. FOR CRANCK ARMS)
- WATER OR OIL QUENCHING (E.G. FOR STEERING KNUCKLES).
RESEARCH WORK ENABLED THE CONTRACTORS TO DEFINE COOLING PATTERNS IN INDUSTRIAL TRIALS FOR EACH CASE ENSURING THE BEST COMPROMISE BETWEEN QUALITY (HARDNESS, STRUCTURE, ENDURANCE IMPACT STRENGTH) AND MACHINABILITY, AS WELL AS TO SPECIFY THE INDUSTRIAL EQUIPMENT NECESSARY TO CARRY OUT THESE TREATMENTS.
REGARDING DIRECT ISOTHERMAL ANNEALING, THE RELATIVELY COARSER GRAIN OBTAINED ENSURES A SUBSTANTIAL GAIN DURING MACHINING. THE FINAL QUALITY TREATMENT (CARBONITRIDING QUENCHING), ENABLES ONE TO OBTAIN THE STRUCTURE OF PRESENT MASS-PRODUCED PARTS. INDUSTRIAL PRODUCTION OF THE PARTS RESULTED IN MORE FLEXIBLE EQUIPMENT THAN FLUIDIZED BEDS, LIKE TUNNEL OVENS WITH SPECIAL HEATING/COOLING ZONES. THIS EQUIPMENT IS TO BE USED BY GEAR MANUFACTURERS.

THE PRACTICAL APPLICATION OF THESE NEW CYCLES REQUIRES CLOSE COOPERATION WITH THE FORGING SUB-CONTRACTORS OF R.N.U.R. CONTACTS HAVE BEEN MADE AND THE TECHNOLOGY OF THE NEW EQUIPMENT DEVELOPED WILL BE TRANSFERRED TO AND CONTROLLED BY THE SUB-CONTRACTORS.

USING THESE TECHNIQUES IT IS ESTIMATED THAT 20 % OF THE ENERGY CAN BE SAVED. WITH FORGED PIECES PRODUCED WITHIN THE EEC AMOUNTING TO 2 400 000 TONS/YR THIS REPRESENTS 230 000 TOE/YR.