Tolerance design and processes for fabricated jet engine components

Abstract: Understanding the causes and effects of dimensional and geometric variation
is a major concern in the design and manufacturing of products. Geometry
assurance is a generic name for different activities with the aim to secure
the quality of the company’s geometry definition and verification process,
which includes both virtual and physical processes. Methodology and support
for a robust design, simulation and visualization of variation is important
to be able to make the product as insensitive to manufacturing variation as
possible. It is important to have an internal overall picture of the
geometry process to become more effective and achieve higher quality on the
products and an efficient manufacturing process.
To be more competitive in the market Volvo Aero has launched the concept of
Make it light. This design objective is partly met by fabrication, i.e.
designing products with an increased number of subparts. Fabrication leads
to new/increased demands on the ability to break down geometrical
requirements to subparts and to be able to sum up the expected variation
from subparts to a top level to assess producibility/quality. It is
important to be able to take control of geometrical variation in an early
stage of product development, and this requires new tools and working
methods. Volvo Aero is currently developing several products that will
enter into service in the near future, and several other product
development projects are in the planning. When this happens, and production
volume increase, the number of deviations might increase many times
compared to the present levels according to internal estimations. This will
result in increased cost of poor quality (non-conformance handling, tied up
material and scrap).
This thesis work has through analysis, of Volvos GDP (Global Development
Process) and Geometry Assurance processes in the automotive industry,
worked towards a description on how this method can be used at Volvo Aero.
An interview study was made to be able to form a description of how the
Geometry Assurance process could be visualized today. Suggestions of
improvements of today’s Geometry Assurance process was discussed and
visualized through a future Geometry Assurance process, which shows the
possibilities for what Volvo Aero could achieve. Through the studies and
the interviews it became quite clear that improvements regarding handling
and visualizing variation is something that is needed at Volvo Aero. A case
was used to show the possibilities of improvements with a method to analyze
and visualize stability, contribution of locating points, variation
envelope and stack-ups, this all in 3D environment, which could be
implemented early into the design process.
The recommendations are that Volvo Aero should implement the suggested
Geometry Assurance process, because it is a good way of visualizing the
working process and highlights problem/improvement areas for further
discussions. The process is in line with Volvo Aero’s current strategy
regarding producibility and fabrication. A 3D visualization stability and
variation simulation tool should be acquired since it shows a lot of
potential of minimizing deviations and creating a better connection between
tolerance chains and the 3D model. The tool is also most likely to improve
the efficiency of the Product Development process, because of the few hours
it takes to perform the analysis. If the Geometry assurance process and a
3D visualization tool are implemented at Volvo Aero, future work is needed
regarding easy access and search ability of capability data and Geometry
Assurance process support for the projects etc.