Alborz Shokrani

State-of-the-art cryogenic machining and processing

This article is a state-of-the-art review of the use of cryogenic cooling using liquefied gases in machining. The review is classified into two major categories, namely cryogenic processing and cryogenic machining. In cryogenic processing also known as cryo-processing, the cutting tool material is subjected to cryogenic temperatures as a part of its heat treatment process. The majority of the reported studies identify that cryo-processing can considerably increase cutting tool life especially for high speed steel tools. It also identified that, in cryogenic machining, a cryogen is used as a cooling substance during cutting operations. The cryogen can be used to freeze the workpiece material and/or cutting tool. This article concludes that cryogenic cooling has demonstrated significant improvements in machinability by changing the material properties of the cutting tool and/or workpiece material at the cutting zone, altering the coefficient of friction and reducing the cutting temperature.

Comparative investigation on using cryogenic machining in CNC milling of Ti-6Al-4V titanium alloy

ABSTRACT Ti-6Al-4V titanium alloy is one of the most important materials in industry, 80% of which is used in aerospace industry. Titanium alloys are also notoriously difficult-to-machine materials owing to their unique material properties imposing a major bottleneck in manufacturing systems. Cryogenic cooling has been acknowledged as an alternative technique in machining to improve the machinability of different materials. Although milling is considered to be the major machining operation for the manufacture of titanium components in aerospace industries, studies in cryogenic machining of titanium alloys are predominantly concentrated on turning operations. To address this gap, this article provides an investigation on the viability of cryogenic cooling in CNC end-milling of aerospace-grade Ti-6Al-4V alloy using liquid nitrogen in comparison with traditional machining environments. A series of machining experiments were conducted and surface roughness, tool life, power consumption, and specific machining energy were investigated for cryogenic milling as opposed to conventional dry and flood cooling. Analysis revealed that cryogenic machining using liquid nitrogen has the potential to significantly improve the machinability of Ti-6Al-4V alloy in CNC end-milling using solid carbide cutting tools and result in a paradigm shift in machining of titanium products. The analysis demonstrated that cryogenic cooling has resulted in almost three times increased tool life and the surface roughness was reduced by 40% in comparison with flood cooling.

Energy conscious cryogenic machining of Ti-6Al-4V titanium alloy

Manufacturing and, in particular, machining are responsible for a significant portion of global industrial energy consumption (25%). Previous research has shown that precise selection of cutting parameters can improve the energy consumption of machining processes. Cryogenic machining has attracted significant attention for improving the machinability of difficult-to-machine materials while also eliminating the environmental and health issues associated with the use of cutting fluids. Despite the advantages, there is a considerable research gap in cryogenic milling operations. This article investigates the effect of cryogenic cooling using liquid nitrogen in end milling of Ti-6Al-4V. A robust and rigorous methodology was developed and a series of machining experiments were conducted using a combination of cutting parameters repeated at dry, flood and cryogenic cooling environments. The investigations indicated that cryogenic cooling considerably reduce tool wear when compared to dry and flood cooling while allowing for using higher cutting speeds. The cutting tool used for cryogenic machining at 200 m/min cutting speed, 0.03 mm/tooth feed rate and 5 mm depth of cut showed minimum flank wear. Furthermore, the investigations demonstrated that using the machine’s coolant pump in flood cooling resulted in higher power and energy consumption than dry and cryogenic cooling. This article clearly shows that higher material removal rates are required in order to minimise specific machining energy. Therefore, since cutting speed is limited in dry machining, cryogenic machining is the most favourable as higher cutting speeds can be used. Using cryogenic machining at 200 m/min cutting speed resulted in an 88% reduction in energy consumption of the machine tool as compared to flood cooling at 30 m/min while minimum tool wear (10 µm) was detected. This clearly demonstrates the significant capabilities of cryogenic machining when compared with more conventional machining approaches.

A Surface Modification Decision Tree to Influence Design in Additive Manufacturing

Additive manufacturing (AM) presents a very different set of design challenges to traditional manufacturing. Layer-wise building brings about issues with residual stresses and support requirements which lead to failures during processing of poorly-designed parts. Additionally, there is a need for post-processing due to poor part quality, which adds another process to the chain with its own unique design limitations. This paper discusses the issues surrounding designing for AM and the subsequent post-processing. A future vision is proposed for the selection of post-processes and the relative design adjustments to accommodate the chosen techniques. A decision tree is presented as a framework for process selection based on part requirements. Although at present, the data necessary to realize this vision is incomplete, with further research into the capabilities and design constraints of different post-processes, this approach could provide a systematic method for integrating design for post-processing with AM design.

Modelling and Verification of Energy Consumption in CNC Milling

Electrical energy consumption forms 99 % of the environmental impact of machining operations. Whilst replacing existing machineries for more energy efficient ones does not deem possible in short term, process planning for machining with energy consumption in mind is a more accessible solution. The effect of cutting parameters on power consumption in CNC milling of 6082 T6 aluminum alloy was investigated in this paper. Mathematical models were developed to estimate the energy and power consumption in CNC milling machines. The analysis indicated that the two less studied parameters of axial and radial depth of cut have significant impact on the total energy consumption of machining processes. Increased axial and radial depth of cut not only increase material removal rate but also increase the portion of machine tool’s power consumption dedicated to material cutting. This study indicated that 82 % reduction in energy consumption can be achieved through precise selection of cutting parameters.

Optimal cutting conditions towards sustainable machining when slot milling aluminium alloy

Abstract Energy used in manufacturing has to be reduced in order to cut down carbon emission derived from energy generation. Optimising cutting parameters and selecting a proper cutting environment reduces energy consumption contributing to a sustainable manufacturing. The research reported herein is focused mainly on searching for an optimum combination of cutting parameters and cutting environment to minimise energy consumption when milling aluminium alloys. The selection of this workpiece material was based on its wide applications in aerospace industry basically due to its high corrosion resistance and high strength-to-weight ratio, characteristics. The experiments were conducted on a Siemens 840D Bridgeport Vertical Machining centre 610XP2. The results show that the cryogenic cutting environment is the optimal environment in terms of power consumption and surface roughness value to conduct the milling of a 6082-T6 aluminium alloy under the selected cutting parameters.

A Surface Roughness and Power Consumption Analysis When Slot Milling Austenitic Stainless Steel in a Dry Cutting Environment

Engineered components must satisfy the surface texture requirements and traditionally surface roughness (arithmetic average, Ra) has been used as one of the principles methods to assess quality. Surface roughness is a result of the cutting parameters such as: cutting speed, feed per tooth and the axial depth of cut, also the tool’s geometry, tool wear vibrations, etc. Moreover, the surface finish influences the mechanical properties such as fatigue behavior, wear, corrosion, lubrication, and electrical conductivity. The research reported herein is focused mainly on surface roughness and power consumption analysis of an austenitic stainless steel milled in a dry cutting environment. The experiments were conducted on a Siemens 840D Bridgeport Vertical Machining center 610XP2. The selection of this workpiece material was based on it’s widely applications in cutlery, hardware, surgical instruments, industrial equipment and in the automotive and aerospace industry due to its high corrosion resistance and high strength characteristics. The results show that selection of a careful combination of cutting parameters can achieve low values of surface roughness and power consumption instead of changing the cutting parameters individually.