1MAT6334/MAT3334//MAT4443 Advanced Materials Manufacturing: Part 1 Process and Material Modelling L7: The individual assignment Magnus Anderson © 2020 University of Sheffield 2Plan for today L6: Introduction to DEFORM • A brief history of FEM • Key aspects of how DEFORM works • Modelling best practice L7: The individual assignment • Constructing a FEM model of turbine disc forging • Designing a turbine disc forging route to satisfy a design brief 3Individual assignment Turbine discs We are interested in creating a turbine disc forgings for aerospace applications. The component is made out of a new variant of Inconel 718. A DEFORM material file has been created for this alloy, along with a post-processor subroutine for calculating dynamic recrystallization 4Turbine disc forging Conventional disc forging is performed in two steps. The first operation is often a simple upsetting operation to make a pancake\cheese followed by a final forging operation. The tooling of the final operation is provided to you on blackboard. a) Initial billet b) Pancake c) Turbine disc forging Figure 1) An example forging disc process route 5The forging process and design constraints. Design a forging process to forge turbine discs made out the new IN718 variant alloy. The forge has an 7000tonne isothermal press and a 9000tonne hot die press available for this project and using the hot die forging press would be significantly more profitable. The isothermal press can be heated to temperatures up to 1050C, however reducing the temperature is desirable to lower costs and reduce grain growth. The hot die forging press can be heated to 850C, with an environment temperature of ~800C. Both presses can achieve uniform forging speeds varying between 1mm/s and 40mm/s. The initial billet geometry is cylindrical and has a radius of 128mm and a height of 465mm. Cylindrical upsetting tooling is available and has a radius of 750mm and a height of 210mm. Stretch target: Avoid excessive die stresses to avoid catastrophic tool failure. Stretch target: Select process conditions that reduce die stresses to improve die life. 6The forging geometry and design brief. 255 < 0 < 260 1 6 8 < 0 < 1 7 1 The tolerance for the geometry of the disc to be forged is shown in the right. The units are in mm. The area in red is the final geometry of the turbine disc to be machined from the forging. The forgings must be free of laps and folds and satisfy the geometry shown above. The recrystallization within the region highlighted in red must exceed 80%. The average grain size must be lower than 30 microns. 7Grain size and Recrystallisation calculations A user subroutine has been written for use in the post-processor for calculating the dynamic recrystallisation and grain size during the forging process. Please download the file “Dynamic_Recrystallisation.dll” from Blackboard and refer to “Tutorial_4_RX_Post_Processing” for details regarding how to implement the DRX material model. a) Example RX calculation b) Example mean grain size calculation 8Assumptions & simplifications Use suggested shear friction and heat transfer coefficients descriptive of lubricated hot forging. For the hot die forging process, the environment temperature may be better approximated by 800C rather than room temperature. Remember to apply temperature boundary conditions to the tooling to avoid them cooling to environment temperature during the simulation and account for the heating applied to maintain tool temperature. It takes between 15 to 30 seconds to move the billet from the furnace into the hot die press followed by 3-6 second dwell time. The dies are made out of a hot work tool steel with a Nickel superalloy cladding. The thermo-physical properties can be approximated by AISI H13. Assume that the yield strength of the tooling is 800MPa. 9Deliverable Write a short report describing the proposed forging route with justification, showing how the design conforms with the specification for; • The workpiece geometry • The recrystallisation and grain size targets within the regions that will form the final component. • The workpiece temperature can be in the range of 950-1050°C. Workpiece temperatures above 1100 °C need to be mitigated to reduce excessive and abnormal grain growth. Stretch target: Die stress analysis 1. Does the proposed route avoid catastrophic die failure? 2. Design the process to reduce die stress to improve die life. Stretch target: Hot die forging route 1. Will a hot die forging process with a die speed of 17mm/s, a workpiece temperature of 980C and die temperatures of 850C provide the desired microstructure? 2. Can the design brief be achieved using a hot die forging process? The report will be worth 6 credits. Marking rubric <40% 40-50% 50-60% 60-70% >70% Incorrect Major mistake Minor mistake Meets design brief Compliance clearly presented Satisfying the design brief – 40% Stretch target: Hot die forging route – 20% <50% 50-60% 60-70% >70% Major issues with model setup, with omissions of assumptions. Minor issues with model setup, with omissions of assumptions. Model setup correct, with minor omissions of assumptions. Model setup correct, with explanation of assumptions and mesh sensitivity study. <40% 40-50% 50-60% 60-70% 70-80% >80% Not investigated Major mistakes and omissions Minor mistakes and omissions Minor omissions. Parameter space explored to find most promising processing route. Clear demonstration of the understanding of the problem. Model setup – 25% Stretch target: Die stress analysis – 15% <40% 40-50% 50-60% 60-70% >70% Incorrect Major mistake Minor mistake Catastrophic failure avoided Die life optimised
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