A General Electric survey from a few years back found that over sixty percent of all manufactured parts were not made according to the draft mainly due to
- incomplete drawings
- components that were unable to be made as drawn
- ambiguous drawings
- inability to assemble the parts as drawn
The most common trait in a practical design problem is design objects complexity. Some designs are considered complex just due to sheer size. A pressure vessel designed to withstand high pressures and thermal gradients is composed of 400 tons of steel in material alone. Thus, it is not surprising that designers are continually pressured to optimize their designs, especially in material use. Computer Aided Design helps mechanical engineers try to solve the problem with optimum efficiency.
CAG and CAA
Mechanical CAD can be seen as the combinations of Computer Aided Graphics (CAG) and Computer Aided Analysis (CAA).CAG consists of:
- 3D modelling
- preparing development of components
- the interpretation of solids
CAA consist of
- finite element modelling
- identifying forces and deformation (the objects response to the forces)
- determining the stress levels at various locations
Though CAG and CAA can be seen as two separate fields, they are intertwined in the mechanical design process. CAA depends on CAGs pre-processing and post-processing skills. Likewise, CAG needs CAAs analysis results to know how to modify the graphical design. Design and analysis in general have become dependent on each other on account of high-speed digital computers and methods (i.e., the finite element method) that relate to the structural mechanics problem.
CAD analysis
As mentioned before, optimization is essential to help keep costs and time down. But finding the most efficient procedure is no easy task, especially since most mechanical CAD systems have to handle more then ten thousand unknowns. Breaking down the design object into a set of simultaneous algebraic equations optimizes computational labor in the analysis process. Some types of analysis performed on mechanical designs and some possible characteristics they tests (according to Christopher McNulty of Creative Products Group ) are:- Finite Element Analysis: stress, deflection, modal
- Finite Difference Analysis: thermal
- Electronic Cooling Analysis: conduction, convection, radiation, airflow
- Opto-mechanical Analysis: geometric raytracing, mount induced wavefront distortions, limited error budgeting
