Abstract
Heat treatment was performed in order to improve the machinability of three lead-free extruded and drawn brasses, namely CuZn42 (CW510L), CuZn38As (CW511L), and CuZn36 (C27450), based on the concept of microstructural modification. The examined machinability criteria were the following: chip morphology, power consumption, cutting force, and surface roughness. All the above quality characteristics were studied in turning mode in “as received” and “heat treated” conditions for comparison purposes. The selected heat treatment conditions were set for CW510L (775 °C for 60 min), CW511L (850 °C for 120 min), and C27450 (850 °C for 120 min) lead-free brass alloys, according to standard specification and customer requirement criteria. The results are very promising concerning the chip breaking performance, since the heat treatment contributed to the drastic improvement of chip morphology for every studied lead-free brass. Regarding power consumption, heat treatment seems beneficial only for the CW511L brass, where a reduction by 180 W (from 1600 to 1420 W), in relation to the as-received condition, was achieved. Furthermore, heat treatment resulted in a marginal reduction by 10 N and 15 N in cutting forces for CW510L (from 540 to 530 N) and CW511L (from 446 to 431 N), respectively. Finally, surface roughness, expressed in terms of the average roughness value (Ra), seems that it is not affected by heat treatment, as it remains almost at the same order of magnitude. On the contrary, there is a significant improvement of maximum height (Rt) value of CW511L brass by 14.1 μm (from 40.1 to 26.0 μm), after heat treatment process performed at 850 °C for 120 min.
Highlights
Leaded brasses are characterized by their great corrosion resistance, electrical conductivity, superior mechanical properties, and formability, but their main industrial use exploits the excellent performance in the machinability, required for high precision and productivity manufacturing processes [1,2,3,4]
In the frame of this work, chip morphology, power consumption, cutting force, and surface roughness were assessed before and after heat treatment to highlight the influence of the modified microstructure on the evolution of machinability quality parameters
CuZn36 (C27450): 850 ◦ C for 120 min. The aim of this heat treatment process was the establishment of a microstructure with an augmented β-phase percentage, in order to assist to machinability improvement. This argument is mainly supported by the higher hardness and lower ductility demonstrated by β-phase, which contributes to the enhancement of chip fragmentation and subsequently to the improved surface roughness and lower cutting forces [27]
Summary
Leaded brasses are characterized by their great corrosion resistance, electrical conductivity, superior mechanical properties, and formability, but their main industrial use exploits the excellent performance in the machinability, required for high precision and productivity manufacturing processes [1,2,3,4]. A comparative study of leaded and lead-free brass alloys was implemented concerning the tool wear, cutting force, and surface roughness evaluation during machining in turning mode, showing positive results of substituting the leaded brass for CuZn21Si3P alloy [17]. The current project possesses a unique advantage, since it aims to improve the machinability of conventional lead-free brass alloys, without altering the material chemistry This can be regarded as an attempt to change the metallurgical condition, and, on the other hand, to comply with the product European specification limits, as far as the chemical composition and mechanical properties are concerned. In the frame of this work, chip morphology, power consumption, cutting force, and surface roughness were assessed before and after heat treatment to highlight the influence of the modified microstructure on the evolution of machinability quality parameters
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