Reference no: EM133701413

Design of Machine Elements

Assessment: Welded Connection

Design Audit

Outline
Students are required to carry out a design audit on a weld group of their choosing that is subject to fatigue loading. The welded joint should be connecting steel or aluminium components (aluminium requires different SN treatment), and analysis should be possible using the techniques developed in EGB316 classes. Also, you must be able to measure all weld group and key system dimensions and approximate/calculate/determine the working loads (application location, direction, magnitude, etc.).

You can choose a welded connection from a machine you are familiar with or some other machine you have access to. The system CANNOT be akin to any of the systems analysed in the lectures (i.e. not a patient lifter or like any design workshops etc.). The main requisite is to investigate a real machine and make design decisions / engineering judgements regarding properties, forces etc. and determine if the welds are safe. This designation could be done by leaving weld size or material unknown and evaluating one or other using the analysis procedure developed in class, or you could measure/determine/estimate/research all necessary values and establish a factor of safety from the analysis procedure. Either approach will allow you to make conclusions on the safety of the existing welded arrangement, and the appropriateness of any and all loading and system assumptions you have made. The analysis must be based on fatigue loading, and the calculations will be both hand calculations and ANSYS analysis. Detailed technical drawings of the welded component are also to be produced using Solidworks or equivalent professional solid modelling package (refer to CRA).

Examples of welded system you could choose to analyse include, but are certainly not limited to:
A car towbar (normally a welded SHS type design on either side / tongue etc.).
Gym weight machines or equipment, either at home or in a commercial gym.
Machines and equipment in a workshop, mechanics shop, or industrial setting (access through existing relationships or work).
Welded tube bicycle.
Loaded components on an aluminium boat.
Cleats and members in a civil application with variable loading (like a steel walkway).
Other welded components on a car or motorbike.
Systems and components on the QUT Motorsport FSAE car (if having existing membership of, or relationship with, the team).

Report
The report for this assignment must be a concise summary of the design audit carried out. It must contain the following sections and content:

Introduction Section
This section should include a concise summary of the purpose of the design audit as it pertains to your machine, details on the system being analysed including broad function and a key photo or two (use correct figure labelling and put multiple photos side-by-side with labels to save space and enhance impact). Also include broadly what will be contained in the design audit document (section summary). It is the formal report equivalent of the "Given" section from lectures/tutorials. Recommended Length: 0.5-page 11pt font maximum including figures.

Functional Analysis Section
This should include a high-quality sketch of your welded system with dimensions of all key components and the weld group itself and an indication of load directions and magnitudes. This is the point where each possible critical loading scenario should be discussed, including force magnitudes, and directions, and time series data (i.e. is it cyclic between F and -F, or F and 0, or constant etc., at what angle is it and does that change, and what are the loading magnitudes and variations for each critical load case - use diagrams). At this point, also justify which loading scenario you are to analyze in the rest of the report. This is the formal report equivalent of the "Schematic" section from lectures/tutorials. Recommended Length: 1.5-page 11pt font maximum including figures.

Design Assumptions and Analysis Scope Section
In this section, you should state all design assumptions and decisions that are being made before the analysis, as well as the scope of the analysis, materials, weld size, mode and distribution of loadings (following on from previous section discussion), and any other choices or assumptions that are necessary including relating to load cycles based on system duty. This is the formal report equivalent of the "Assumptions" section from lectures/tutorials but requires detailed justification on each point to support why or how that assumption was made. Recommended Length: 1-page 11pt font maximum including figures.

Detailed Welded Joint Analysis Section
In this section, you must concisely summarise the whole design audit calculation. It should include:
A high quality FBD of the system with all force values determined based on the worst-case loading scenario chosen.
A reduction of that system to a single welded joint and the resultant loading at the weld group centroid.
Full hand calculation of weld stresses on the bases of worst-case loading scenarios. If the worst case is not clear, carry out test calculations for multiple cases.

Weld fatigue failure analysis using AM-Diagram approach.
Summary of resulting chosen metric (size, material, or FOS) and its comparison to actual.
ANSYS analysis of the same system including FBD showing boundary condition set-up and type of model run with full capture of all ANSYS results contours for any and all metrics of interest.
Comparison of ANSYS and hand calculations.
This is the formal report equivalent of the "Solution or Analysis" section from lectures/tutorials. Recommended Length: 15-pages 11pt font maximum including figures (should only need 10 pages but 15 is allowed for those with complicated weld groups, or multiple calculations with different materials/assumptions etc.).

Recommendations and Conclusions Section
A section summarising the findings relating to safety of the weld group. Refer to the technical drawings in Appendix A. Also include any discussion of design choices made and how they affected the results. Discuss discrepancies and errors between the critical dimensions calculated, and those of the actual weld group being analysed. IF MAJOR DISCREPANCIES WERE FOUND, RE-DO THE ANALYSIS WITH DIFFERENT OR LESS CONSERVATIVE ASSUMPTIONS. CRITERIA FOR REPEATING ANALYSIS: YOUR FOUND WELD SIZE IS ±50% OF ACTUAL WELD SIZE, MATERIAL IS UN-REALISTIC, OR FOS <1 OR >10 WITHOUT A CLEAR REASON FOR THIS
(note, some welds aren't engineered and are just over specified). Recommended Length: 1-page 11pt font maximum including figures.

Appendix A: Technical Drawings
Full technical drawing of the existing welded group and main component held by the weld, produced using Solidworks and including:
Primary Drawing: Assembly of the whole system (orthographic, shaded isometric, all view labels) with full detailed annotations on weld size (with correct weld designation arrows), notes on welding rod type, and dimensions on weld positions only. This assembly should have all welded components (i.e. plates / brackets / members). If one of the welded components is a large steel structure that continues outside of the direct loading consideration (like for example the chassis of a car that a tow-bar is connected to, or long sections of RHS that might make up a piece of gym equipment), you can draw an indicative section of that component and use break lines to indicate its continuation (see example below). The drawing should also have a BOM (Bill of Materials) and title block with appropriate details.

Secondary Drawings: You must provide at least one fully dimensioned part drawing (orthographic with dimensions plus isometric and all view labels) for a key component from your weld group. If you have several simple components, do a part drawing for each of these. These are the parts that are joined by the weld, before the welding like you would specify to a fabricator or machinist.

All drawings must be produced as a PDF from Solidworks and appended to the PDF of your report (I.E. NOT CUT AND PASTE INTO WORD, THAT PRODUCES TERRIBLE QUALITY DRAWINGS). A3 drawing size is appropriate, as when you append 2 different sized PDFs, the sizes are retained.