2nd International Conference on Mechanical, Production and Automobile Engineering (ICMPAE'2012) Singapore April 28-29, 2012
A new benchmarking part for evaluating the
accuracy and repeatability of Additive
Manufacturing (AM) processes
Dr Muhammad Fahad, Dr Neil Hopkinson
Deposition Modeling (FDM) and Three Dimensional Printing
(3DP). Each AM process builds parts in different materials
and by using a different working principle such as
photopolymerisation (by SL), sintering (by SLS), extrusion
(by FDM) and jetting (by 3DP). Since these processes operate
in a tool-less, additive manner, the parts built are enclosed in
an envelope and the machine vendors offer machines in
different build envelope sizes.
Benchmarking refers to the comparison of performance of
different similar systems (organisations, machines, processes
etc) with each other to establish a standard of performance. A
benchmark as defined by the Webster’s Dictionary is “a
standard or point of reference in measuring or judging quality,
value, etc”. In AM, benchmarking is used not only to compare
the strength/weakness of the parts but also to measure and
compare accuracy, surface finish, repeatability and resolution
of the geometrical features of the parts produced. According to
Wong et al, benchmarking helps in identifying the “highest
standards of excellence” for different products/processes so
that the subsequent improvements necessary to achieve those
standards can be made [3]. Wong et al also classified AM
benchmarking in three different types as follows:
Geometric Benchmark; used to measure the geometric
features of a part (i.e. tolerances, accuracy, repeatability and
surface finish).
Mechanical Benchmark; used to analyze the mechanical
properties (tensile strength, compressive strength, creep,
etc).
Process Benchmark; used to establish process related
parameters (part orientation, support structures, layer
thickness, speed, etc).
This paper is aimed at defining a new type of geometric
benchmarking part for evaluating the accuracy, tolerances and
repeatability of parts produced by different AM processes.
Abstract—Additive Manufacturing (AM) refers to a new
class of manufacturing processes that build physical parts in a
laye-by-layer (i.e. additive) manner. Even though a variety of
AM processes are now commercially available which differ
from each other in the way they build a part (i.e. sintering,
jetting, potopolymerisation etc), AM processes are still in their
early stages of commercialization and thus present a high
potential for research and development. Therefore, in order to
improve the technical capabilities (i.e. accuracy and
repeatability) of any AM process or in order to compare the
performance of different AM processes, a benchmark
geometry is essential. The benchmark geometry provides a
common basis for comparison/fine tuning of different
processes and must comprise of certain features/dimensions
that will ensure that the operation capabilities are fully
evaluated. This paper details such a part which is designed to
act as a benchmark part and can be used as a standard
geometry for evaluating different AM processes.
Keywords—Additive Manufacturing, Benchmarking, Accuracy,
Repeatability.
I. INTRODUCTION
A
DDITIVE Manufacturing (AM) is the name given to the
technologies that produce physical parts from CAD data
in an additive manner (i.e. adding successive layers of
materials). It is a generic term used to represent techniques
that can build components without the need of conventional
tooling in the first instance [1]. Although, the cycle time, cost
of material and equipment associated with AM processes are
high relative to those associated with conventional
manufacturing processes (e.g. CNC machining, injection
molding), the elimination of tooling cost and time, increased
design freedom and reduced cycle are the advantages that AM
processes offer [2]. Various AM processes have been
developed and are commercially available including
Stereolithography (SL),Selective Laser Sintering (SLS), Fused
II. ADDITIVE MANUFACTURING BENCHMARKING STUDIES
Various studies have been carried out relating to the design
of benchmarking parts for AM processes. Kruth [4] performed
one of the earliest benchmarking studies in the field of AM.
An inverted U-frame shaped part (Fig. 1)which contained
different features like vertical and inclined cylinders, flat and
inclined surfaces, squares, pegs, embossed letters and
overhangs was used. The part does not have any repeated
features and the repeatability was tested by producing many
parts. Lart [5] designed a small benchmark part (Fig. 2)
Dr Muhammad Fahad is with the Department of Industrial and
Manufacturing Engineering, NED University of Engineering and Technology,
Karachi, Pakistan, 75270.
(phone: +92-21-99261261; e-mail: mfahad@neduet.edu.pk)
Dr Neil Hopkinson is with the Wolfson School of Mechanical and
Manufacturing, Loughborough University, Loughborough, Leicestershire,
United Kingdom. LE11 3TU. (e-mail: n.hopkinson@lboro.ac.uk)
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2nd International Conference on Mechanical, Production and Automobile Engineering (ICMPAE'2012) Singapore April 28-29, 2012
comprising fine and medium sized features to compare the
ability to produce fine details. The study comprised circular
features (holes and cylinders), flat and angular surfaces in
different directions but large scale accuracy and warping.
Juster and Childs [6,7] used a square shaped part (Fig. 3) to
compare the accuracy and repeatability of parts produced by
different AM processes. Although repeatable features were
produced in this part but the part did not contained any plane
of symmetry to evaluate the repeatability of features. Iuliano,
Ippolito and de Filippi [8] also used a square shaped part (Fig.
4) to evaluate the accuracy and tolerances of various AM
processes. The part was not found suitable for evaluating the
accuracy of non-flat surfaces. Therefore, a shell of uniform
thickness, comprising of a cylinder merged with a sphere (Fig
5) was used to evaluate non-flat surfaces. Shellabear [9]
designed a simple part that contained surfaces at different
angles along the vertical direction. The part could only be used
for linear measurements as no circular/curved features were
included in the design. Mahesh, Wong, Fuh and Loh [10]
designed a square based part containing various features such
as square bosses, cones, cylinders and free-form surfaces (Fig.
6). Although, the part geometry comprised of different
features, the design did not show a plane of symmetry as the
features were not distributed equally onto the square base.
Hopkinson and Sercombe [11] used a square shaped part with
steps of uniform thickness in X, Y and Z directions (Fig. 7).
The part could only be used for linear accuracy and
repeatability was evaluated by building more than one parts.
Fig. 4. Part used by Iuliano, Ippolito and de Filippi [8]
Fig. 1. Part used by Kruth [4]
Fig. 2. Part used by Lart [5]
Fig. 5. Part used by Iuliano, Ippolito and de Filippi (For non-flat
surfaces) [8]
Fig. 3. Part used by Juster and Childs [6,7]
Fig. 6. Part used by Shellabear [9]
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2nd International Conference on Mechanical, Production and Automobile Engineering (ICMPAE'2012) Singapore April 28-29, 2012
Fig. 8. Part used by Hopkinson and Sercombe [11]
Fig. 7. Part used by Mahesh, Wong, Funh and Loh [10]
III.
A new benchmarking part was designed keeping in view all
the above features as well as making sure that the features are
repeated symmetrically in one single part (Fig. 8). The part
was designed on a flat base of size 270 mm x 50 mm. This
base size was selected to make sure that the part can be built
on most of the commercially available AM machines. To
ensure the true repeatability of all the features, the base was
divided into three section, each being 90 mm long. Each of
these 90 mm long section contained same features at exactly
same location/distances from the centre of respective section.
Table II summarizes the sizes of different features of the
designed benchmarking part.
DESIGN OF NEW BENCHMARKING PART
On the basis of literature review of various benchmarking
studies related to AM processes, it was noted that all the
designed parts contained various features to evaluate/compare
accuracy of features but none of these parts contained features
in a truly repetitive manner. Due to this reason, more than one
parts are required to build to evaluate the repeatability of a
process. Therefore, it can be said that true repeatability (i.e.
symmetry of features within the part) is an important
requirement in order to compare the repeatability within a
single build. Also, the literature review revealed the fact that
some
features
are
necessary
to
evaluate
the
accuracy/tolerances of parts produced by AM processes.
These features, along with their intended purpose [19] are
summarized in the table below:
TABLE II
GEOMETRIC FEATURES INCLUDED IN THE NEW BENCHMARKING PART AND
THEIR SIZES
TABLE I
GEOMETRIC FEATURES AND THEIR INTENDED PURPOSE
FEATURE
Base
NUMBER AND DIMENSIONS (mm)
1 (270x50x5)
12 (15 x 15 x 15)
FEATURE
PURPOSE
Cube
Flat Base
Flatness and straightness
Cylindrical
Hole
Solid
Cylinder
Hollow
Cylinder
Squareness, parallelism, linear accuracy and
repeatability
Roundness, cylindricity, accuracy and
repeatability of radius (internal)
Sphereness, relative accuracy and repeatability
of a continuously changing sloping surface
Roundness, cylindricity, accuracy and
repeatability of radius (external)
Roundness, cylindricity and coaxiality of
cylinders
Cone
Concity, sloping profile and taper
Angled
Surfaces
Angularity, accuracy and repeatability of angled
surfaces
Cube
Cylindrica
l Hole
Sphere
Sphere
Solid
Cylinder
Hollow
Cylinder
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3 (X direction), 3 (Y direction), 3 (Z direction),
All holes with diameter 10 mm and depth 15
mm
3 (15 mm diameter)
3 (10 mm diameter, 12 mm height)
3 (Outer diameter 10 mm, inner diameter 7 mm,
height 16 mm)
Cone
3 (9.65 mm base diameter, 18 mm height)
Angled
Surfaces
3 (30 degrees), 3 ( 60 degrees)
2nd International Conference on Mechanical, Production and Automobile Engineering (ICMPAE'2012) Singapore April 28-29, 2012
Fig. 9. Design of New Benchmarking Part for AM processes
evaluating
process, it
fabrication
Deposition
IV. FABRICATION OF BENCHMARKING PART
The designed benchmarking part was fabricated using
Selective Laser Sintering (SLS), a well established AM
process. The part was built using DuraForm (Nylon) powder
to concept evaluation purpose and is shown in Fig. 9. By
the physical prototype fabricated using SLS
can be said that the part design is suited for
on different AM processes such as Fused
Modelling, Stereolithography, 3D printing, etc.
Fig. 10. New benchmarking part built using SLS
part has been designed and fabricated (using an AM process).
This new benchmarking part not only includes all the
necessary features in a very compact manner, but it also
allows the measurement of repeatability of features by
incorporating the features in a symmetrically repeatable
manner. This part will not only help in establishing the
performance parameters for any AM process, but it will also
help in comparing various new and/or well established AM
processes in terms of their accuracy and repeatability.
V. CONCLUSIONS
A benchmarking part is an important aspect of evaluating
the performance characteristics of various AM processes.
Although, many authors/researchers have proposed various
designs of benchmarking parts for AM processes, none of
these parts comprehensively included all the features
necessary to establish the desired accuracy/repeatability
related parameters. In this study, a new type of benchmarking
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2nd International Conference on Mechanical, Production and Automobile Engineering (ICMPAE'2012) Singapore April 28-29, 2012
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