Surface finishing of horizontally printed AM channels by a hybrid abrasive flow machining and electrochemical polishing

• Main Author: Muhammad Kurniawan Bin Ismail
• Other Authors: Sridhar Idapalapati
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Mechanical engineering::Control engineering; Engineering::Systems engineering
• Online Access: https://hdl.handle.net/10356/168074
• Institution: Nanyang Technological University

Abrasive Flow Machining (AFM) is a non-traditional polishing method that employs a semi-solid media composed of visco-elastic polymer and abrasive particles mixed in a specific proportion. This media is then extruded under pressure through or across the surface of a workpiece's internal channel to achieve the desired surface finish. Abrasive Flow Machining (AFM) is currently used to produce a nano level finish on machined components, which is a requirement of the time. However, polishing without geometrical deviation is relatively difficult, particularly in the inlet of a workpiece. Electrochemical polishing (ECP) is a finishing process that removes material from a metal or alloy using an anodic dissolution process, in which the material is removed from the workpiece surface ion by ion. Currently, Electrochemical Polishing (ECP) is used to polish without direct contact to the material's surface but over a longer period of time. Hybrid Process is a finishing process which requires a combination of ECP together with AFM to polish a surface of a workpiece. Single process of ECP or AFM has its own disadvantages and advantages. To maximise the capabilities of each process, a new methodology is proposed, which is to utilize both processes (ECP + AFM) concurrently. Horizontally printed Additively Manufactured channels result in the formation of asymmetrical surface finish which lead to two problem statements: 1. Uneven and non-symmetrical roughness distribution Results in uneven material removal during post processing causing high geometrical deviation. 2. High surface roughness with Ra value > 20 µm Results in high amount of material removal required and compounds effect geometrical deviation. By utilising the hybrid process, the main objectives of this project are as follows: 1. Achieve Ra < 1 µm with minimal pitting for down-skin surface of additively manufactured horizontal straight channels. 2. Minimise geometrical deviation up to < ± 20 µm from the original design (minimise over polishing of up-skin surface. The project is divided into three distinct processes: 1. Abrasive Flow Machining (AFM) 2. Electrochemical Polishing (ECP) 3. Hybrid (ECP + AFM) The findings are categorised into three different process and they are being compared among one another. Firstly, it is found that AFM can achieve a mirror finish on internal surfaces of workpieces with complex geometries. However, it has been noted that polishing towards the outlet of the workpiece has relatively lower surface finish compared to the inlet. This could be because the pressure at the inlet is relatively higher to that of outlet which means, there is more material removal at the inlet. Additionally, geometrical deviation can occur as the process continues, with the inlet widening over time. It has also been observed that the higher the pressure used in AFM, the shorter the time required to achieve a the desired surface finish. Conversely, low pressure will require a longer time and there will be a point where the material removal mechanism no longer exists. Overall, AFM is an ideal choice for polishing wokrpieces with complex internal geometries, regardless of length and diameter, in a reasonable amount of time. However, to polish targeted surfaces or to control the amount of polishing remains as a challenge in AFM Process. Secondly, in pure Electrochemical Polishing, it is found that while the process is capable of polishing rough surfaces, the material removal mechanism is uncontrollable, resulting in topographical fluctuations. To overcome this, a new approach has been proposed for the Hybrid Process, which involves the use of Targeted Electrochemical Polishing. In this process, a cathode is used as the negatively charged electrode to remove material from the workpiece using an electrically charged solution. Modifications to the cathode tool have allowed for the targeted polishing of specific areas within the workpiece's channel, without inadvertently affecting other areas - a problem known as masking of the AM component. This precision in material removal is crucial for achieving the desired shape or finish of the workpiece, as it allows for greater control over the material removal process in ECP. In conclusion, the Hybrid Process of ECPAFM, which combines Targeted High Intensity Electrochemical Polishing and High Intensity Abrasive Flow Machining, has proven to be a promising post-processing method for additively manufactured components. The process allows for controlled material removal in targeted areas, resulting in smoother surfaces with minimal geometrical deviation. Although further improvements can still be made, this finding is significant and could potentially unlock the full potential of additive manufacturing.