LIMIT VALUES OF MAXIMAL LOGARITHMICS STRAIN IN MULTI-STAGE COLD FORMING OPERATIONS
In the project phase of one multi-stage metal forming process special attention should be placed on maximal logarithmic strain φmax which can be achieved in one operation. Value of this strain has direct impact on number of needed operations (forming steps), number of heat treatments between certain steps, duration of the whole process, quality of the workpiece and on the die life. Amount of φmax in one forming process can be determined theoretically, based upon the stress state analysis, and by experiment. Experimental investigation within this paper have shown that stability of one multi – stage process like ironing, depends to great extent on re-distribution of strain values between the single dies. Improper distribution can lead to the cracks at the workpieces and other production failures.