Eventos Anais de eventos
COBEM 2023
27th International Congress of Mechanical Engineering
Machinability Evaluation of Free-Cutting Steels with Bismuth Additions by Constant Pressure Test in Drilling Process
Submission Author:
João Paulo Alves , ES
Co-Authors:
João Paulo Alves, Eduardo Sigler Junior, João Batista Ribeiro Martins , Mariane Gonçalves de Miranda, Marcelo Bertolete, Patrícia Alves Barbosa
Presenter: Marcelo Bertolete
doi://10.26678/ABCM.COBEM2023.COB2023-0944
Abstract
Free-cutting steel application in automotive industry is known to increase productivity and reduce costs compared to other steels. This grade of especial steels is defined by the element alloying additions that, alone or forming compounds, interrupt the matrix and facilitate machining, with sulphur and lead as the main elements. However, the addition of lead presents several adversities, and its use has been banned in several countries due to its toxicity to the environment and human beings. Alternatively, “friendly” free-cutting steel developments are replacing lead with non-toxic alloying elements such as bismuth without reducing the machinability. In this sense, this work aims to evaluate the machinability of three different free-cutting steels, coded as: Steel A (without Pb/Bi), Steel B (with Pb/Bi), and Steel C (with Bi). Short-duration ranking machinability test named Constant Thrust Force Test in drilling process was performed, following a 2k statistical design of experiments. A Dormer A-002 HSS drill with a diameter of 10 mm was used. Test conditions were varying in two levels: 840 and 1150 rpm for spindle speed; 5 and 10 kgf for applied load. Cutting time was kept constant at 15 s. Drilled hole length (Lf), cutting temperature, and chip characteristics were the machinability criteria evaluated. Lf results indicate that Steel C (with Bi), the grade with only Bi addition, had better machinability at a load of 10 kgf for both speeds (1150 and 840 rpm). Steel B (with Pb/Bi), the material with lead and bismuth additions, had better machinability at a load of 5 kgf for both speeds. Steel A (without Pb/Bi) presented the worst machinability under all the tested conditions. Interactions between load and speed were noted. The materials exhibited the longest drilled hole length at 1150 rpm and 10 kgf condition. Cutting temperature was mainly influenced by drill spindle speed and applied load. Statistical difference was observed in the cutting temperature results between Steel B and Steel C. In general, Free-cutting steels investigated presented conical helical chips in drilling process. Pb/Bi additions to free-cutting steel contributed to chip embrittlement. On the other hand, only the Bi addition showed tendency to longer and snarled chip formation.
Keywords
machinability, Drilling Process, free-cutting steel, bismuth, lead
