Design and manufacturing of a new CNC gantry machine with double motion feed drive system / Seyed Reza Besharati
The CNC machine tools are spatial machines that are able to control computer. There are two types of machine tools structure, C-frame and gantry-frame. A CNC gantry machine tool is defined as a computer numerically controlled machine that is programmed and controlled through a computer. Its CNC c...
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| Summary: | The CNC machine tools are spatial machines that are able to control computer. There
are two types of machine tools structure, C-frame and gantry-frame. A CNC gantry machine
tool is defined as a computer numerically controlled machine that is programmed and
controlled through a computer. Its CNC controller offers very short setup time flexibility to
run batches of one to several thousand. Today, the CNC gantry machines are widely used
in manufacturing combined with software programs to efficiently and consistently create
different products for large companies or even single consumers. The CNC gantry machine
is used in the manufacturing sector including drilling, milling, reaming, boring and counter
boring. Parts can be grooved and threaded with CNC milling centers; they can be transformed
into CNC lathes, CNC drill and tap areas; for CNC grinding; and used in conjunction
with routers to make CNC wood engravers and letterers. The CNC gantry machine
can be used to machine small, large, short and lengthy components. Currently, there are
two types of such machines in the market. The first type has a moving worktable and fixed
gantry and the second type has a moving gantry and fixed worktable. Each type has advantages
and disadvantages. In this study, a new concept is proposed to improve the specifications
and applicability of the first type of CNC gantry machine.
In the new concept, reciprocal and simultaneous motion of the gantry and worktable is
proposed as the gantry machine’s X-axis double motion mechanism. At the beginning of
this study, the double motion mechanism is designed based on a rack and pinion system. A
new anti-backlash system is proposed to compensate for transmission error and backlash
(simultaneously) and for use in the double motion mechanism. The simulation results of the
new anti-backlash system are discussed. Due to manufacturing limitations of the rack and pinion systems, a new double motion mechanism based on a ball screw system is proposed.
Then, various designs of a new CNC gantry machine are presented. In this improvement
process the problem is solved with the new design of a completed CNC gantry machine.
The dynamic and static behavior of the final CNC gantry machine design is investigated via
modal and static structural analysis using ANSYS software. The gantry’s natural frequency
is designed to be 202 Hz in the first vibration mode, making the machine capable of working
at higher speeds of up to 11530 rpm, which is suitable not only for rough cutting but
also for finishing. The final design of the new CNC gantry machine is updated according to
the obtained results. The increase in natural frequency during gantry design modification
affects complexity, increasing the weight and manufacturing cost of the gantry. As such,
five different gantry designs are selected for comparison. Four parameters, i.e., the first
four natural frequencies, total deformation due to mechanical forces, weight and manufacturing
cost are considered performance indices. One is selected among five designs mathematically
and optimized by MOGA (multi-objective genetic algorithm) in ANSYS software.
In the optimization process, the gantry’s natural frequency is maximized, thus minimizing
the total gantry weight and deformation against mechanical forces. CNC gantry machine
documents for manufacturing are prepared, followed by modeling, casting, machining
and assembly. To evaluate and verify the design and analysis, an experimental modal
test is performed. The experimental results show less than 11% error between the dynamic
analysis and experimental test. |
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