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SARM Project

Engineering tolerance analysis is a critical aspect of designing high-speed Positive Displacement Machines, Turbine Generators and Engines. Working with the SARM Project team and Zedaxis Engineering, our focus was the tolerance analysis. Tolerance analysis involves assessing the allowable variation or deviation in the critical dimensions and characteristics of individual components and assemblies when performing at high speed, elevated temperature, and load. Analysis is essential because tolerance directly impacts performance, reliability and safety and cost of the machine.

Validation by test is a critical phase of the development providing proof of concept. Early test by the SARM Team demonstrated that at 2500 rpm that the concept is viable. The next stage is to increase this speed to 10,000 rpm.  

Here are some of the reasons why tolerance analysis is important for high speed rotating machines:

Performance Optimisation

High speed machines rely upon tight clearances between components to maximise the pressure generated and the efficiency of the system. The Positive displacement machine relies on precise aerodynamic profiles and tight clearances between components to maximise the pressure generated and minimise losses. By analysing tolerances, identification of detrimental effects on performance was carried out, these would lead to leakage or mechanical frictional wear. 

Component interchangeability

High-speed machines consist of numerous complex components that need to be manufactured and assembled with precision. Tolerance analysis helped to determine the allowable variations in dimensions, ensuring that the components can be produced within acceptable ranges without compromising their functionality. It enabled interchangeability which is important for maintenance , repairs, and component replacements during the machine's lifespan. During the analysis one of the outcomes was assessment of the complexity of the design which lead to simplification of the concept.

Manufacturing Feasibility

Cost optimisation is at the heart of the success of any new product, however reliance upon tight tolerance leads to high manufacturing cost. Controlling and understanding just the critical dimensions helps to achieve a balance between cost and performance. 

Reliability and Durability

High-speed machines can produce intense thermal loads, high forces, and vibrations that all combine to create mechanical stresses. To prevent early failures, these traits were carefully considered during the initial design phase.  Typically, thermal expansion, deflection under torsional loads as well as deflections due to vibration were all considered. 

Safety  and Risk Mitigation

High-speed machines pose potential safety risks if components fail or operate outside their intended tolerance. Tolerance analysis aids in identifying critical components, such as rotating shafts or attachments, and establishing strict tolerances to minimise the risk of failure . By understanding the effects of dimensional variation and manufacturing tolerance and performance related deflections, engineers can deign safety margins and incorporate adequate fail-safe mechanisms. 

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