Control over milling of rolled non-ferrous metal products

Abstract

This paper looks at some hot-rolled strips that were to be cold-rolled and that were machined in order to enhance the process performance. It was done, in particular, to reach an optimized topography of the machined surface that consisted of alternating high and low spots. The high surface roughness (especially in the case of soft non-ferrous metals) caused turn-to-turn friction defects during further rolling operation. A two-sided processing line was examined that comprises an unwinder, pinch rolls, a leveler, shears, machines for up-milling of the strip top and bottom and a folder. Both conventional (with 14 helical teeth) and custom-built (with 2 or 7 helical teeth) interlocking slabtype milling cutters with the diameter of ~250 mm were used. Copper strips and strips made of copper alloys (including double brass) were machined. The authors examined the effect of the cutting mode (a relationship between the feed per minute SМ and the cutter RPM n) on the formation and removal of chips, durability of the tool, quality of the cold-rolled and machined surface — in particular on the length of the low spot (L). It was calculated how much travel the strips do in a full revolution of the cutter (SО) and in one fourteenth of a full revolution per tooth (SZ). Comparing these values with the length of the low spot the number of teeth was determined responsible for one low spot (L/SZ or L/SZ). Depending on the machining mode (SМ/n ratio) and based on the earlier proposed model, the following equation was performed: L = SО(L/SZ = 14), L = SZ (L/ SZ = 1) or SZ < L < SО (1 < L`/SZ < 14). A number of different constant milling modes was compared with the new dynamic technique which allows to account for the tool wear and adjust the milling mode in relation to the initial mode by reducing SМ/n. An analytical technique is described that allows to precisely choose the initial milling mode. It is shown that due to the mode adjustment the length of the low spot L` and the number of backup teeth increase. This appears to be reasonable before the preset maximum allowable value L`critical is reached. Note that as the plasticity of a rolled non-ferrous metal product rises, the value L critical decreases. It was found that this process control technique helps extend the uptime and the overall service life of the tool and improve the process performance.