Some was under control and the cutting efficiency

      Some
authors strongly focused in ISF (Incremental sheet forming process), which
depends strongly on the forming tool path that in?uences greatly the part
geometry and sheet thickness distribution (Figure
3). A regular thickness distribution requires an accurate optimization of
the parameter settings and an optimal parameterization of the forming strategy (Liu, et al., 2013). Among previous
research, single steepest ascending tool path is the most efficient tool path,
which means the cutting machines a strip on the surface along the path and its
neighboring sides at maximum rate. This is the new principle for 3-axis tool
path planning (Suresh, et al., 2013).

                                                                               
Fig 3: Process variants in ISF

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  Due to their strength and
simplicity, ISO-planar zig-zag toolpaths have been created. The generated tool
paths were submitted to a certain tolerance and surface ?nish speci?ed on the
surface. Tool holder collision detection has been done to help selecting the correct
tool. The input is a solid model of the surface in SAT format while the output
is a text ?le containing the machine code (Selvaraj & Radhakrishnan,
2006).

 
  Many tool path generation methods
of plunge milling have been proposed, but almost none of them has taken into
consideration the radial depth during the milling processes, which has great
influence on the cutting force and cutter life. Cutting radial depth was under control
and the cutting efficiency and cutter life were improved (Huang, 2014).
Meanwhile, a new method was discussed to create constant engagement tool path
generation such that it can be operated to any kind of contour geometry
containing convex and concave arcs. And given the planner curve representing
the geometry of the final contour to be machined, the objective of the proposed
algorithm is to modify an original contour parallel tool path such that the
cutting engagement angle is regulated at the given required level throughout
the path that compared to contour parallel path, the variation in cutting force
is drastically bring down when the modified tool path generated by the proposed
algorithm is applied (P.K., 2011).

  
On the other hand, another analysis with the term “backward tool path
modification” is comprehended in the sense that, for a given final tool path
and the required engagement angle to be regulated along the final path. The
proposed algorithm aims to modify the previous tool path in backward direction.
It must be highlighted that the backward path modification algorithm focuses on
the finishing process by using a straight end mill. In the machining of
three-dimensional (3D) geometry, the finish path is in many cases implemented
with a ball or filleted end-mill (Chung, et al., 2011).

 

2.3 Challenges and
future development of tool path generation

        Further investigations could be
conducted to improve the surface quality of the part by shrinking the amount of
?uctuations studied over the sheet surface after optimization. Additional optimization
techniques will be verified such as the genetic algorithm and simplex search
method. Finally, as full-scale ?nite element calculations of the process are
time-consuming, simpli?ed process models could be developed to allow for a
faster evaluation of the outcome of a given multistep forming strategy (Mohamed
Azaouzia, 2012).

         Another researcher predicted a further program
of work is required to supply complimentary data. ASTM D143-09 standard test
procedures for three points bending and longitudinal shear will be implemented
to indicate wood strength across and along the grain respectively. Regression
analysis will establish a relationship between the collected cutting force data
and the obtained mechanical properties such as fracture stress and elastic
modulus (Naylor, et al., 2011).

        Further
developing multiple implemented tool path planning strategies should be applied
in future. It is selected based on a part geometry analysis feature detection
and its part subdivision will be needed for this function. Finally, it will be
possible to create a tree of solutions and with that purpose it would make
sense to run a developed path planning system on a cluster or cloud where each
node processes an independent list of strategies used for tool path planning.
Development of all illustrated features will immediately make it possible to
replace a human engineer completely and reduce manufacturing the time and cost significantly
(Konobrytskyi, 2013).

 

3.0 Geometric
error fundamentals

 

         High accuracy CNC milling machines are
required in many manufacturing industries because of demand of precision
components and consistency of quality are growing. The most important factor of
precision components is the accuracy of machine tools. Mainly, position errors
are originated from geometry, cutting force, dynamic loading so forth (Pashaki & Pouya, 2016).

        Various sources of geometric errors were
usually encountered on machine tools and the methods of error compensation
employed in machines. Previous research has developed geometric error models.
Geometric error is an important source of inaccuracy of CNC milling machine.
They measured 21 geometric error components and compensated the systematic
errors in CNC milling machines (R.Ramesh, 2011).

       Some authors presented a method to build a
general error model of a multi axis machine of random configuration. It is
based on assumption of strict body motion and utilizes regular transformation matrices.
whereas, another researcher claimed source of general volumetric error model,
which synthesized both geometric and thermal of vertical milling machine using regular
transformation matrices of slide axis (Ehmann, 2012) (A.C. Okfor, 2011).

      Geometric
errors are primarily related with errors in the structure elements of the
machine tools. These errors affect the machine repeatability and kinematic
accuracy, which are inherent in the machine tool. For 3-axis milling machine, there
are 21 errors component namely: 3 linear position errors, 6 straightness
errors, 9 angular errors and 3 squareness errors. Angular errors such as pitch,
roll and yaw errors are common causes of positioning errors. Also, a small
angular of spindle can cause a major effect at the tool tip. Straightness
errors seriously degrade machine tool performance and have a direct influence
on machine tool path accuracy. These errors can be the result of wear in
machine tool guide ways. Also, they can be due to mistake which may have
damaged the machine tool structure in some way, or poor machine foundation that
are causing a bowing effect on whole machine tool. Straightness errors have
direct effect on positioning and contouring accuracy a machine tool. Axes of
machine tools should be perpendicular to each other along their length. Out of
squareness between axes can seriously lower machine tool performance by
producing dimensional errors in produced parts. The squareness errors between
the axes are calculate by slopes of two sets of straightness error profiles (Soori, et
al., 2014).

 

 

 

3.1 Problems and
methods of geometric error

 

       Major
cause of inaccuracy in CNC milling machine is due to cutting force. The error
is workpiece caused either by excessive deformation at the tool and workpiece
interface due to cutting action or by deformation of machine tool structure. A
new method that is a theoretical
model was introduced to predict cutting forces and machining error of convex and
concave surfaces in ball-end milling. The machining errors resulted from force
induced tool deflections were calculated at various parts of machined surface (H.F.F.
castro, 2012).

       Several research
papers proved that due to shorter product life cycles, demand of displaying
novel options on the products as well as small serious production, the absolute
accuracy of machine tools is increasing importance. Short product life times do
not authorize an iterative optimization of the product quality. This means that
accurate production in the first time is vital issue for part manufacturing.
Mohsen. Soori described unique method that a virtual meaning software system
for applying the effect of the 21 dimensional and geometrical errors of a 3
axis CNC milling machine on the machined component. As a result, an actual part
can be machined in virtual environment according to real condition (Soori, et
al., 2014).

       Few research articles addressed that an early
estimation process which is usually handled by highly skilled, in-house
experts. One of the main obstacles in this process is to accurately define the
relationship between product characteristics and the construction and fabrication
time necessary to manufacture the product and the errors which are occurred
during simulation of a part. C.K
showed novel method is using laser interferometer, that was showed in Fig 4, Co-ordinate Measuring Machine,
3D Probe Ball Bar system. In linear measurement, for forming the fixed length
reference arm of the interferometer, one retro-reflector is secured to the
beam- splitter (Gohel, 2014).

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