Process Modeling

Process Modeling

Process Modeling • Learning Activities • View Slides; • Read Notes, • Listen to lecture • Do on-line workbook • Lesson Objectives • When you finish this lesson you will understand: • The various modeling techniques listed below Keywords Electro-thermal Modeling, Thermo-mechanical Modeling, Electrode Modeling, Surface Contact Modeling, Solidification Modeling, Process Control Modeling, Law of Thermal Similarity, Machine Characteristics Modeling

Modeling Efforts • Electrothermal Modeling • Nugget Growth • Electrode Design • Expulsion • Thermomechanical Modeling • Stress Analysis • Electrode Modeling • Electrode Life • Electrode Misalignment • Surface Contact • Solidification • Process Control • Law of Thermal Similarity • Machine Characteristics

Resistive Current Path “Breakdown” Model Liang, “Foundational Study of Contact Behavior..”, OSU Dissertation, 2000

Liang, “Foundational Study of Contact Behavior..”, OSU Dissertation, 2000

Model for Heat Generation - Electrode Face IRW Tech Catalog, Rel #2, Jan 1999

Electrode Design - Heat Generation Alcan A-Nose IRW Tech Catalog, Rel #2, Jan 1999

A Model For Expulsion Prediction IRW Tech Catalog, Rel #2, Jan 1999

Model of stress IRW Tech Catalog, Rel #2, Jan 1999

Model of Heating for Electrode Misalignment IRW Tech Catalog, Rel #2, Jan 1999

Modeling Efforts • Electrothermal Modeling • Nugget Growth • Electrode Design • Expulsion • Thermomechanical Modeling • Stress Analysis • Electrode Modeling • Electrode Life • Electrode Misalignment • Surface Contact • Melting &Solidification • Process Control • Law of Thermal Similarity • Machine Characteristics

Heat Balance A heat balance problem is set up when welding Steel to Aluminum Using a Transition Material of Roll Bonded Al to Steel Sheet. Steel Steel-Al Transition Aluminum Move to Next Slide to See Nugget Growth

Two Cycles Three Cycles Four Cycles Five Cycles Eight Cycles Six Cycles Seven Cycles Nine Cycles Ten Cycles Eleven Cycles Twelve Cycles Results and Discussion(nugget development model) One Cycle Steel Al

Law of Thermal Similarity 0.1 Sec 10 sec Temp at x0 at t0 = Temp at n*x0 at n2*t0 Temp at 1mm, 0.1 sec = Temp at 10 mm, 10 sec Okuda, T. Law of Thermal Similarity, Mitsubishi Electric 1973

Law of Thermal Similarity “For the case where the plate thickness and the diameter of the electrodes are magnified by n times, if we also change the current density by 1/n times (which is current by n times), and heating time by n2 times, the new temperature distribution becomes similar to the original one” Okuda, T. Law of Thermal Similarity, Mitsubishi Electric 1973

n=6 n2 = 36 8 * 36 = 288 Okuda, T. Law of Thermal Similarity, Mitsubishi Electric 1973

Measurement of melted and partially melted thicknesses using picral etch Melted & solidified weld nugget Thickness not melted Nugget Partially melted zone Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Measurement of Heat affected(HAZ) and non-heat affected (N-HAZ) melted thicknesses using Nital etch Non-recrystallized thickness (N-HAZ) Recrystallized thickness (HAZ) Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Law of Thermal Similarity Applied to Stacks of Mild Steel Sheet Thinnest Outer Sheet Sum of All Thickness

Optimum Weld Time Example Optimum weld time for 1.25 sheet welded to itself = 8 cycles Total thickness welded with this combination = 2.5 mm Optimum weld time for different thickness combinations can be derived from the following equation: *optimum weld time for the experimental thickness = weld time for new thickness Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Calculate Time Constant for unit thickness 1mm to 1mm(for 1.25mm – 1.25mm = 8 cycles) *optimum weld time for the experimental thickness = weld time for new thickness Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Thick/thin and multi-sheet welding Combination 1 2.5 mm sheet welded to 1.25 mm sheet Combination 2 3 sheets of 1.25 mm thickness each welded together Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Verification – Thin-Thick sheet • Total thickness welded for combination 1 = 3.75 • mm • Weld time for combination 1 = (3.75/2.5)2*8 = 18 cycles • Weld time for any single welding pulse can not exceed 8 cycles; cooling times need to be added and pulsed welding done to keep thin sheet from overheating • Weld schedule = 7 cycles weld + 4 cycles cool + 7 cycles weld (total time = 18 cycles) • Note: weld time reduced from 8 cycles to 7 cycles for each pulse to fit in within the total weld time. Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Verification – Thin-Thick sheet Weld nugget is evenly distributed in the thick/thin sheets Thin sheet is not overheated and the nugget is symmetrical with the two outer surfaces Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Verification – 3 Sheet Combination • Total thickness welded for combination 2 = 3.75 mm • Weld time for combination 1 = (3.75/2.5)2*8 = 18 cycles • Weld time for any single welding pulse can not exceed 8 cycles; cooling times need to added and pulsed welding needs to be done • Weld schedule = 7 cycles weld + 4 cycles cool + 7 cycles weld (total time = 18 cycles) • Note: weld time reduced from 8 cycles to 7 cycles for each pulse to fit in within the total weld time. Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Verification – 3 Sheet Combination Weld nugget is evenly distributed in the 3 sheet combination as well Good sized nugget without overheating surfaces Fong & Tsang “Law of Thermal Similarity” Senior Project, OSU, 2000

Machine Characteristics - Regions to Model IRW Tech Catalog, Rel #2, Jan 1999

Mechanical Models to Characterize Machine Model 2 Bouncing Region Model 3 Welding Region IRW Tech Catalog, Rel #2, Jan 1999

Ball Test Results to Confirm Bouncing Region Model After the first bounce, the model prediction in brown fits well to the experimental data in black. IRW Tech Catalog, Rel #2, Jan 1999

Process Modeling