Design optimization of a CNC machine bed
Background
This case pertains to a top manufacturer and exporter of CNC machines worldwide, located in Peenya, Bengaluru. Sometime in 2004, their CEO randomly reached out to me, seeking to know if I could achieve around a 100 kg reduction in mass of their machine beds. These beds, that were iron castings, supported all their CNC machine systems: tooling heads, electricals, oil tank, etc. Though skeptical at first, as this was a near 10% reduction in mass of their (then) ~1000 kg beds, I anyway agreed to give it a try.
In 2003, what started as a casual effort to build GENSIZ, a demo tool for optimization of thin- walled structural forms, went on to yield great solutions for the above case. This incidentally, was the first consultancy project in my career.
Property Groups
The machine bed was partitioned into 50 distinct property zones, many of which are seen in the pic below, in distinct colors. Of these, 41 zones were open to re- sizing by GENSIZ. The other 9 zones were non- mutable, in order to preserve integration compatibility with third- party subsystems.
From hope to reality!
GENSIZ was employed with an objective to maximize ratio of Euclidean norm of the lowest few modal frequencies, relative to a norm of the bed's mass. After some three months of runs on just a humble Intel P4 machine together with select validations from a high- precision finite element simulations on a workstation, it was a pleasant surprise to discover a near three- fold potential for mass reduction, that is about 300 kg! The convergence graph of population average fitness vs. generations, is seen above, with about 36- 38% improvement in just about 20 generations.
Frequencies and Mass Compared
The table below lists the lowest 15 modal frequencies and structural mass for the top 5 near- optimum designs designated D1 thru D5, along with the existing baseline design. DSM refers to Design Structural Mass while the norm (RMS) of lowest five modal frequencies is referred to as RMS-I in the table. From the table, we can see that D2 has a significantly higher fundamental frequency of 22.29 Hz than the 14.61 Hz of the baseline's, while corresponding structural mass of 769.63 kg is significantly less (~ 24%) than the 1007 kg of the latter.
