## Some path such that the cutting engagement

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

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).