Comparison of Different Manufacturing Processes of AISI 4140 Steel with Regard to Surface Modification and Its Influencing Depth

Abstract

<jats:p>The surface and subsurface conditions of components are significant for their functional properties. Every manufacturing process step changes the surface condition due to its mechanical, chemical and/or thermal impact. The depth of the affected zone varies for different machining operations, and is predetermined by the process parameters and characteristics. Furthermore, the initial state has a decisive influence on the interactions that lead to the final surface conditions. The aim of the investigation presented here is to compare the influence of the load characteristics over the depth applied to manufactured components by several different machining operations and to determine the causing mechanisms. In order to ensure better comparability between the surface modifications caused by different machining operations, the same material was used (AISI 4140; German steel grade 42CrMo4 acc. to DIN EN 10083-3) and annealed to a ferritic-pearlitic microstructure. Based on interdisciplinary cooperation within the collaborative research center CRC/Transregio 136 “Process Signatures”, seven different manufacturing processes, i.e., grinding, turning, deep rolling, laser processing, inductive heat treatment, electrical discharge machining (EDM) and electrochemical machining (ECM), were used, and the resulting surface zones were investigated by highly specialized analysis techniques. This work presents the results of X-ray measurements, hardness measurements and electron microscopic investigations. As a result, the characteristics and depths of the material modifications, as well as their underlying mechanisms and causes, were studied. Mechanisms occurring within 42CrMo4 steel due to thermal, mechanical, chemical or mixed impacts were identified as phase transformation, solidification and strengthening due to dislocation generation and accumulation, continuum dynamic recrystallization and dynamic recovery, as well as chemical reactions.</jats:p>

Wire Tool Electrode Behavior and Wear under Discharge Pulses

“…Volumetric wear rate R v was 1.22 ± 0.04 mm 3 •s −1 at roughing and 0.52 ± 0.002 mm 3 •s −1 at finishing; mass wear rate R m -9.6 × 10 −3 ± 0.01 g•s −1 and 4.0 × 10 −3 ± 0.008 g•s −1 , respectively. 41 ÷ 62% of the tool subjected wear under discharge impulses at roughing during electrical discharge machining of anti-corrosion steel when summarized lateral wear exceed front wear by 29.17%.…”

“…where ∆V is volumetric wear, mm 3 , ∆m is a worn mass, g, and t is the wire length wear time; for a thickness of 20 mm, t = 0.343 ± 0.005 s. The discharge gap is calculated by the following equation:…”

“…The subject of electrical discharge machining (EDM) and wear of a wire tool electrode is not new, but the physical processes that occur during processing are still not sufficiently studied [1][2][3][4]. It is related to the absence of the possibility of visual control over the processes occurring in the discharge gap during EDM especially for large workpieces [5,6].…”

Modelling of Grain Size Evolution with Different Approaches via FEM When Hard Machining of AISI 4140

“…According to the detailed literature review by Jawahir et al [5] and the recent research of Borchers et al [6] about Surface Integrity in machining, the functionality and fatigue life of a machined part is strongly related to its topographical, metallurgical and mechanical properties in the rim zone. Hard turning is known for the induced thermo-mechanical loads that lead to altered microstructures, hardness, residual stresses, dislocation densities and grain sizes at the surface layers.…”

Cutting force based surface integrity soft-sensor when hard machining AISI 4140

“…High thermo-mechanical loads that are generated during the hard turning process have a great influence on the functionality of a machined part [1,2]. These loads are responsible for microstructural alterations, modification of hardness, residual stress state, mechanical properties, chemical composition and corrosion resistance in the workpiece rim zone [3].…”