Influence of CNC milling strategies on complex surface machining

Abstract

Milling strategies are an integral part of CAD/CAM systems. Every CAD/CAM system offers unique strategies to differentiate itself from the competition. The article deals with analysis of CNC milling strategies in CAD/CAM system Edgecam 2017 R2. Analysis is divided into two parts. In first part are analysed roughing strategies with focus based on time necessary for removal of material. Second part is focused on finishing strategies and achieving the highest quality of surface. In conclusion, the article deals with the analysis of existing milling strategies and the creation of a database for the assignment of optimal roughing and finishing strategies for specified components.

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IOP Conference Series: Materials Science and Engineering
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Influence of CNC milling strategies on complex surface machining
To cite this article: T Dodok et al 2020 IOP Conf. Ser.: Mater. Sci. Eng. 776 012002
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MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
1
Influence of CNC milling strategies on complex surface
machining
T Dodok1, N Čuboňová1, M Císar1, V Ivanov2 and D Wiecek3
1 Department of Automation and Production systems, Faculty of Mechanical Engineering,
University of Žilina, Univerzitná 1, 010 26 Žilina, Slovak Republic
2 Department of Manufacturing Engineering, Machines and Tools, Sumy State University,
2 Rymskogo-Korsakova St., Sumy, 40007, Ukraine
3 Faculty of Mechanical Engineering and Computer Science, University of Bielsko-Biala,
ul. Willowa 2, 43-309, Bielsko-Biała, Poland
E-mail: tomas.dodok@fstroj.uniza.sk
Abstract. Milling strategies are an integral part of CAD/CAM systems. Every CAD/CAM
system offers unique strategies to differentiate itself from the competition. The article deals
with analysis of CNC milling strategies in CAD/CAM system Edgecam 2017 R2. Analysis is
divided into two parts. In first part are analysed roughing strategies with focus based on time
necessary for removal of material. Second part is focused on finishing strategies and achieving
the highest quality of surface. In conclusion, the article deals with the analysis of existing
milling strategies and the creation of a database for the assignment of optimal roughing and
finishing strategies for specified components.
1. Introduction
Creating new strategies, respectively generating and optimizing new ways of tool movement across
the surface, is a multidisciplinary issue, requiring knowledge of machining theory, mathematics and
computer science. An important area is also the evaluation and comparison of already existing
strategies because proper selection can significantly reduce machining times and tool wear [1–3].
Strategies that optimize cutting conditions to achieve a constant tool load are common, contributing to
longer tool life and improved surface finish. Modern CAM systems support 2D, 3D to 5D machining.
With these programs, simulation, verification and various settings can achieve the desired shape,
accuracy, component quality and efficient production. The present article deals with analysis of CNC
milling strategies in modern CAD/CAM system Edgecam 2017 R2. Comparison of milling strategy is
based on two parameters in terms of machining time and achieved surface quality.
2. Surfaces in CAD/CAM systems
At present, all modern CAD/CAM systems are parametric, which allows to define the dependence
between individual components or assembly be using parameters, e.g. edge length is derived from
circle radius or creating 2D graphs containing dependencies [4, 5]. However, the problem arises when
it is necessary to create a 3D parametric surface that does not have direct modelling support in one of
the modern CAD/CAM systems. Typically, complex shapes are created using the "Spline" element,
which has different defined properties in each program, so it is impossible to create the same surface
in the same way in different programs [6, 7]. Mathematically defined surface does not have such
a problem, but it cannot be created in the CAD programs. While programs such as Matlab, MathCad,

MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
2
Mathematica, etc. are suitable for creating 3D surfaces, their main problem is that the output from
them is not supported by any standard format such as STEP and IGES. To import a mathematically
described surface, it is necessary to use the reverse engineering modules that are already part of some
CAD / CAM systems.CAD / CAM systems use two types of surfaces:
• Standard (general) surfaces – created by rotation (conical, cylindrical, spherical, annular surfaces,
etc.) and extruded surfaces. They are created by the EXTRUDE and REVOLVE commands using
a closed curve (solid model).
• FreeForm surfaces – represent a complex surface. Basic of these surfaces is created by complex
mathematical description. Representative of these surfaces are NURBS surfaces (figure 1) whose
definition is not possible by means of polynomial equations, but are based on poles, degrees of
freedom and distribution of the surface into segments formed by spline curve [4, 8] (figure 2).
Figure 1. NURBS surface.
Figure 2. The control structure of
a NURBS surface.
3. Milling strategies in CAD/CAM systems
Themilling strategies in CAD/CAM systems are predefined milling tool paths that are designed to
machine different types of surfaces. By using suitable machining strategies, it is possible to achieve
a reduction in machining time, improve surface quality, increase tool life and affect the dimensional
accuracy of machining. In order for high-speed hard machining to be economically applicable in the
manufacture of a component, certain technological principles must be strictly observed, not only when
choosing cutting conditions, tools, etc., but also when choosing milling strategies. Milling strategies
are generally divided into roughing, pre-finishing and finishing. Roughing strategies are used to
remove the maximum volume of material in the shortest possible time. Due to the dimensions of the
workpiece, the largest possible diameter of the tool is used. The principle of finishing strategies is
primarily to achieve the highest possible surface quality. In order to achieve the lowest cutting depths
in finishing cycles, production time is reduced. It is necessary to choose suitable tools in order to
achieve a high surface quality. CAD/CAM system Edgecam 2017 R2 will be used for the purpose of
these articles. In table 1 are chosen strategies for experiments.
Table 1. Edgacam 2017 R2 – Millingstrategies.
Roughing strategies
Finishing strategies
Concentric
Concentric
Waveform
Constant Cups Finishing
Lance
Profiling
Spiral
Lance
Project Flow Curves

MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
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4. Experiments
Various types of the components have been designed for the experiment (figure 3). The components
will be manufactured from aluminium alloy – AlMg4,5Mn with workpiece dimensions 100  50  30 mm.
These are mainly components with shaped surfaces that were created by rotation (cylindrical, spherical
surfaces, etc.).
Figure 3. Components designed for the experiment.
For machining was chosen CNC machine EMCO Concept Mill 105 with control system Sinumerik
840D. For roughing strategies were chosen end mill with diameter Ø16 mm and end mill with
diameter Ø4 mm. Ball milling cutters with a diameter of Ø5 mm and Ø8 mm were used for finishing.
Also proper cutting conditions were chosen based on workpiece material and possibilities of CNC
machine.
The aim of the experiment is to analyse the milling strategies generated in the CAD / CAM system
Edgecam 2016 R2 and to evaluate their impact on the productivity and quality of the machined
surface. Emphasis will be placed on the productivity of machining, i.e. production time and the quality
of the machined surface. Attention will also be paid to a parameter that indicates the length of the
NC code generated from each strategy. However, this parameter does not affect the machining
process itself.
4.1. Time of machining
In the figure 4 is possible to see time required for machining individual components by using selected
roughing strategies. Shortest time of machining was achieved with waveform strategy. This strategy
focus on utilization of maximal length of the cutting part of End Mill. In the figure 5 is possible to see
time required for machining of components by using finishing strategies. For this comparison were
chosen only components (no. 1–4) containing complex surfaces. Components no. 5 and 6 contain only
flat surfaces with 2D features. For this types of components are not suitable complexive finishing
strategies.

MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
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Figure 4. Time of machining for roughing strategies.
Figure 5. Time of machining for finishing strategies.
4.2. Surface quality
After completing the analyses of the time required for machining components, a consistent surface
quality was chosen for further comparison. Due to machine malfunction, the surface quality was
evaluated only based on simulation results. After the production of components, it will be necessary to
compare the results achieved in the simulation with the results on real components. Table 2 shows an
example of achieved quality with finishing strategies. Based on the simulations, it can be said that the
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C OM P ON EN T 1 C OM P ON EN T 2 C OM P ON EN T 3 C OM P ON E NT 4 CO MP O NE N T 5 CO MP O NE NT 6
TIME [H:MIN:S]
ROUGHING STRATEGIES
Concentric Wavefrom Lace Spiral
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C OM P ON EN T 1 C OM P ON EN T 2 C OM P ON EN T 3 C OM P ON EN T 4
TIME [H:MIN:S]
FINISHING STRATEGIES
Concentric Constant Cups Finishing Profiling Lace Project Flow Curves

MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
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best surface quality was achieved with strategies Constant Cups Finishing and Project Flow Curves.
The worst result was achieved using the Profiling strategy. Large amounts of residual material
remained on the surface of the component or more material was removed than necessary.
Table 2. A slightly more complex table with a narrow caption.
Strategy
Component 1
Component 2
Concentric
ConstantCup
sFinishing
Profiling
Project
FlowCurves
Lace

MMS2019
IOP Conf. Series: Materials Science and Engineering 776 (2020) 012002
IOP Publishing
doi:10.1088/1757-899X/776/1/012002
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5. Conclusion
The aim of the research was to analyse available CNC milling strategies in CAD/CAM system
Edgecam 2017 R2 and to create a database to facilitate selection of optimal roughing and finishing
strategies for specified types of components. Each of the tested strategies had different toolpaths,
machining times and after each strategy the machined surface has different quality. Based on
experiments, the following conclusions can be formulated for the milling strategies in CAD/CAM
system Edgecam 2017 R2:
• Time of machining – Shortest time of machining was achieved with Waveform strategy. This
strategy allow to remove a large amount of materialin a very short time.
• Surface quality – Best surface quality was achieved with strategies Constant Cups Finishing and
Project Flow Curves. The worst result was achieved using the Profiling strategy.
• Knowledge database – The creation of a knowledge base will enable a better understanding of the
importance of the appropriate selection of milling strategies. The database can be expanded by
further knowledge such as appropriate cutting parameters for different types of milling strategies.
The evaluation of milling strategies, knowledge of their possibilities and limitations creates the
preconditions for their correct use, which leads to faster creation of NC programs as well as to
reducing the occurrence of errors and the need for later fine-tuning of already created programs.
Despite the extensive possibilities of current CAD / CAM systems, there is still possibility for further
development, e.g. when designing new strategies, or improving simulations and increasing their
accuracy.
6. References
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milling CEEPUS Science Report Cracow 5 101–106
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[3] Wei E J and Lin M C 2005 Study on general analytical method for CNC machining the free-form
surfaces Journal of Materials Processing Technology 168 408–413
[4] Yao Z and Gupta S K 2004 Cutter path generation for 2.5D milling by combining multiple
different cutter path patterns International Journal of Production Research 42 2141–2161
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[7] Rudawska A, Reszka M, Warda T, Miturska I, Szabelski J, Stančeková D and Skoczylas A 2016
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