Influence of metal working fluid on chip formation and mechanical loads in orthogonal cutting

Metal working fluids are used in machining processes of many hard-to-cut materials to increase tool life and productivity. Thereby, the metal working fluids act on the thermal and on the mechanical loads of the tool. The changing mechanical loads can mostly be attributed to the changing friction between rake face and chip and changes in the chip formation, e.g., the contact length between rake face and chip. However, analyzing those effects is challenging, since a detailed look at the chip formation process is prevented by the metal working fluid. In this paper, a novel planing test rig is presented, which enables high-speed recordings of the machining process and process force measurements while using metal working fluids. Experiments reveal that process forces are reduced with increasing pressure of the metal working fluid. However, the average friction coefficient only changes slightly, which indicates that the reduced process forces are mainly the result of reduced contact lengths between rake face and chip

Identification of the process damping coefficient in dry and wet machining of steel

Flank face chamfers are an effective way to suppress vibrations and increase the productivity of milling processes. The underlying process damping mechanism is the so-called indentation effect. The effect describes the process damping as a result of an additional force due to the indentation of workpiece material under the flank face. In literature, this force is commonly modeled by the volume indented under the flank face and a process damping coefficient. To determine the process damping coefficient, various approaches with partly contradictory results exist. In this paper, a novel method to calculate the process damping coefficient based on process forces measurements in orthogonal cutting is applied for steel machining. The method considers ploughing effects of flank face chamfer and cutting edge rounding as well as plastic deformation effects. In the current investigation, the approach is applied to different cooling strategies, chamfer widths, and cutting speeds. The results show that the cutting speed has the most significant influence on the process damping coefficient. With increasing cutting speed, the process damping coefficient increases, which can be attributed to strain rate hardening effects

Production of chip breakers on cemented carbide tools using laser ablation

Chip breakers are essential for achieving reproducible and safe turning processes. In case of cemented carbide tools with standard ISO geometries, they are manufactured by form pressing before sintering. In form turning applications with individual tool geometries, chip breakers are typically avoided, because they require an additional and resource intensive grinding process. An alternative preparation strategy for chip breakers is laser ablation. In this paper, the influence of pulse fluence, areal fluence and pulse duration (pico- and nanosecond regime) on ablation mechanisms of cemented carbide tools is investigated. Different ablation mechanisms between pico- and nanosecond-lasers could be detected. Furthermore, a suitable laser ablation strategy using ns-laser is applied to create a chip breaker. Turning investigations showed distinct shorter chips when machining with modified tools. © 2020 The Authors. Published by Elsevier B.V

Tribological Effects of Metalworking Fluids in Cutting Processes

An understanding of the proper application of metalworking fluids (MWFs) is necessary for their implementation in efficient production processes. In addition, the knowledge of the process-related aspect of chip transport and the macroscopic cooling effect, the characteristics and properties of lubricant film formation, and the cooling conditions in the secondary shear zone on the chip surface, i.e., in the direct vicinity of the material separation, represent a combined fundamental scientific issue within production engineering. The aim is to transfer methods from the field of tribology of machine elements, which have already led to a considerable gain in knowledge in this discipline, to machining and to couple them with already established approaches to machining. In the case of roller bearings, the contact pressure is in the range as the pressure in the contact zone between the cutting insert and chip. Due to this, established methods might be transferred to the cutting process. In addition to classical pin-on-plate and pin-on-ring friction investigations, film thickness measurements were carried out and compared to machining tests. The coefficient of friction determined in the planing test rig is 0.48 for dry cutting, while it is 0.47 for wet cutting. These two values are much larger than the CoF with MWFs measured on the two tribometers. It is shown that the boundary friction of MWF especially influences the machining process. Thus, additives in MWF might have a high significance in machining

Evaluation of methods for measuring tool-chip contact length in wet machining using different approaches (microtextured tool, in-situ visualization and restricted contact tool)

The contact length is one of the most important factors to evaluate the chip formation process and the mechanical loads in metal cutting. Over the years, several methods to identify the contact length were developed. However, especially for wet cutting processes the determination of the contact length is still challenging. In this paper, three methods to identify the contact length for dry and wet processes in cutting of Ti6Al4V and AISI4140 + QT are presented, discussed and analyzed. The first approach uses tools with a microtextured rake face. By evaluating the microstructures on the chip, a new method to identify the contact length is established. The second approach applies high speed recordings to identify the contact length. The challenge is thereby the application of high-speed recordings under wet conditions. In the third approach, tools with restricted contact length are used. It is shown that with all three methods the contact length is reduced using metal working fluid

Increased performance in high speed turning of Inconel 718 by laser structuring of PcBN tools

In order to improve the cutting performance of PcBN tools, the cutting edge is prepared e.g. by grinding or brushing. Since PcBN is the second hardest material besides diamond, mechanical preparation of PcBN tools is associated with high wear and low productivity, which leads to high process costs. The laser preparation provides a high potential in preparing PcBN tools because of its wear free technology and its short process times. Additionally, several authors have shown that laser preparation can also lead to beneficial effects such as hardness increase or increased compressive residual stresses. Although these effects are known, they have not been linked to cutting performance of PcBN tools. This paper investigates the influence of nanosecond pulsed laser preparation of the cutting edge and the resulting surface topography on the cutting performance. Therefore, PcBN cutting tools were prepared with different laser velocities at the cutting edge and applied in high speed turning of Inconel 718. Surface integrity of the prepared tools was investigated regarding hardness, surface roughness and edge quality. Afterwards, the prepared tools are used in turning experiments, showing a decreasing flank wear of 40 % compared to reference tools. Tool life increase is linked to beneficial frictional behavior and less adhesive wear of the laser machined specimens compared to conventional tools