Warpage of FDM parts: Experimental tests and analytic model

doi:10.1016/j.rcim.2017.09.007

Robotics and Computer-Integrated Manufacturing

Volume 50, April 2018, Pages 140-152

https://doi.org/10.1016/j.rcim.2017.09.007 Get rights and content

Highlights

•
Analysis of thermal distortions on parts built by extrusion-based additive manufacturing.
•
Measurement of geometric deviations on block-shaped specimens in ABS thermoplastic.
•
Main original finding: maximum warpage occurs at intermediate values of part thickness.
•
Suggested explanations: shrinkage on multiple layers, occurrence of plastic deformation.

Abstract

Similarly to most additive manufacturing processes, Fused Deposition Modeling involves the processing of material by thermal cycles which can create distortions (warpage) in the built parts. The paper aims to characterize this defect on block-shaped parts in ABS thermoplastic resin as a function of some geometric variables related to the process: the size of the part in the three directions, and the thickness of deposited layers. For this purpose, the geometric deviations on parts manufactured with different combinations of the above variables have been measured and statistically analyzed in order to identify the influence factors and to estimate their individual and interaction effects on warpage. The results have given one main further insight compared to previous studies, namely the occurrence of a maximum distortion at intermediate values of part height. The attempt to explain it has suggested two additional hypotheses for the physical explanation of distortions: the extension of thermal stresses to multiple layers due to heat conduction from the last deposited layer, and the occurrence of bending stresses beyond the yield point of the material. These effects have been modeled by analytic equations in order to verify whether they can help improve the accuracy of warpage estimation.

Introduction

Fused Deposition Modeling (FDM) is among the most widespread processes for the additive manufacturing (AM) of prototypes, tools and low-volume products. It consists in melting thermoplastic material by a vertical extruder and depositing it on a horizontal build platform, where it cools into a solid part. Due to the controlled relative motion of the extruder and the platform in the horizontal plane (x- and y-axis), an individual layer of the part is built as a continuous bead of deposited material. After a layer is completed, the platform is lowered along the vertical direction (z-axis) to allow the deposition of another layer, which welds to the previous one. The calculation of layer contours from a digital model of the part (slicing) is the basis for the generation of extrusion trajectories by appropriate programming software.

The increasing use of FDM for the manufacture of fixtures and functional parts is driving attention on the geometric accuracy of the process and on the related trade-offs with build time and cost. Depending on the application, specifications may be needed on FDM parts with regard to deviations from specified dimensions and geometric characteristics (e.g. form, orientation, surface profile), microgeometric errors (e.g. roughness), and build defects (e.g. delamination, voids, poor detail resolution). This paper deals with warpage, a geometric defect that is mostly observed on flat, thin parts and is usually explained as illustrated in Fig. 1. The material extruded at melting temperature cools due to the large thermal gradient to surrounding air. This causes thermal contraction (shrinkage), which is prevented by the supporting platform and brings about tensile and compressive stresses throughout the part. At the end of the build, the part is removed from the platform and the stresses are released causing a bending distortion in the opposite direction of the former support reaction.

The above issue is known to be dependent on many variables related to material properties, part geometry and process parameters. In previous studies, analytic and simulation models have been developed to allow estimating the amount of warpage on parts with simple geometry for different combinations of influencing variables. Further developments seem to be needed for a full understanding of the specific mechanisms leading to warpage. Based on this objective, the paper reports some experimental tests focusing on the main geometric variables related to both the part (in-plane and vertical dimensions) and the process (layer thickness). The results of the tests show that some variables may have different effects to those highlighted in literature. Physical explanations are suggested for these effects, and their quantitative influence on warpage is evaluated by a simple analytic model.

The scope of the work is limited to parts with simple geometry (thin rectangular plates), made of a single material (acrylonitrile butadiene styrene, ABS) and built on an industrial-grade FDM machine. The latter assumption means that the process takes place within an enclosed chamber held at a proper temperature in order to keep shrinkage at a minimum. It is believed, however, that some insights of the work can be extended to different geometries (e.g. flat parts with complex profile), materials (e.g. polylactic acid, PLA) and machine types (low-end 3D printers with open workspace and possible heated platform).

Section snippets

Background

Recent reviews [1], [2] have discussed prior research efforts aimed to measuring, predicting and controlling different types of geometric errors on FDM parts. Compliance with geometric specifications has been clearly recognized as an additional criterion for process planning along with build time and cost [3].

Benchmark studies have initially focused on dimensional accuracy [4], [5], [6], [7], [8]. Deviations from specified dimensions have been shown to improve on recent industrial-grade

Material and methods

Samples of parts were built with the FDM process in order to measure the amount of warpage depending on part dimensions and layer thickness. All parts are rectangular plates with dimensions l and w in the horizontal plane (with l ≥ w) and h in the build direction (Fig. 2(a)). The machine used for the tests is a Dimension Elite manufactured by Stratasys (Eden Prairie, MN), which can build parts with two different thicknesses Δh (0.178 and 0.254 mm). The build process is automatically driven by

Experimental results

The set of factors considered in this work includes three variables related to part geometry (l, w, h) and one related to process planning (Δh). It was thought that a first screening of part-related factors could be helpful before including the process-related factor in the analysis. Therefore, a first experiment was conducted at constant layer thickness, resulting in the selection of a subset of part dimensions with significant influence on warpage. In a second experiment, the selected set of

Interpretation

Some effects noted in the experimental tests are different from those already pointed out in literature. The most evident case relates to Δh, which seems to have a critical range somewhere between 2 and 4 mm (more levels would be required for a tighter bracketing of the maximum) whereas previous studies had shown an inverse correlation of warpage with layer thickness. This inconsistency might depend on physical mechanisms not yet discussed in the explanation of accuracy issues in the FDM

Analytic modeling

The two proposed hypotheses are now developed in order to verify whether they can actually explain the observed influence of part height on warpage.

Conclusions

The experimental results reported in this paper have allowed to verify and explain some known basic facts about warpage. For rectangular plates in ABS built by the FDM technique, thermal distortions are largely dependent on the maximum dimension on the horizontal plane, which seems to have a similar role to the length of a beam deflecting under a uniform bending moment. The choice of increasing layer thickness to reduce build time, which is known to impose compromises on surface finish, has

Acknowledgment

The authors are grateful to Timothy Minton (Brunel University) for his help and advice.

Compliance with ethical standards

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The authors declare that they have no conflict of interest.

References (66)

R. Ippolito et al.
Benchmarking of rapid prototyping techniques in terms of dimensional accuracy and surface finish
Ann. CIRP
(1995)
L.M. Galantucci et al.
Analysis of dimensional performance for a 3D open-source printer based on Fused Deposition Modeling technique
Procedia CIRP
(2015)
A.K. Sood et al.
Improving dimensional accuracy of Fused Deposition Modeling processed part using grey Taguchi method
Mater. Des.
(2009)
O.A. Mohamed et al.
Optimization of Fused Deposition Modeling process parameters for dimensional accuracy using I-optimality criterion
Meas
(2016)
P.J. Nuñez et al.
Dimensional and surface texture characterization in Fused Deposition Modeling (FDM) with ABS plus
Procedia Eng.
(2015)
P. Minetola et al.
Benchmarking of FDM machines through part quality using IT grades
Procedia CIRP
(2016)
A. Boschetto et al.
Design for manufacturing of surfaces to improve accuracy in Fused Deposition Modeling
Robot. Comput. Integr. Manuf.
(2016)
P. Jacobs
The effects of random noise shrinkage on rapid tooling accuracy
Mater. Des.
(2000)
S.N. Economidou et al.
Optical sensor-based measurements of thermal expansion coefficient in additive manufacturing
Polym. Test.
(2016)
A. Kantaros et al.
Fiber Bragg grating based investigation of residual strains in ABS parts fabricated by Fused Deposition Modeling process
Mater. Des.
(2013)

Z. Zhu et al.

Investigation of part distortions as a result of hybrid manufacturing

Robot. Comput. Integr. Manuf.

(2016)

A. Guerrero-de-Mier et al.

Bricking: a new slicing method to reduce warping

Procedia Eng.

(2015)

H.J. Yang et al.

A study on shrinkage compensation of the SLS process by using the Taguchi method

Int. J. Mach. Tool. Manuf.

(2002)

C. Schmutzler et al.

Compensating warpage of 3D printed parts using free-form deformation

Procedia CIRP

(2016)

K. Carr et al.

Verification of form tolerances Part I: basic issues, flatness, and straightness

Precis. Eng.

(1995)

C. Bellehumeur et al.

Modeling of bond formation between polymer filaments in the Fused Deposition Modeling process

J. Manuf. Proc.

(2004)

B.N. Turner et al.

A review of melt extrusion additive manufacturing processes: II. materials, dimensional accuracy and surface roughness

Rapid Prototyp. J.

(2015)

P.H. Lee et al.

Review: dimensional accuracy in additive manufacturing processes

O.A. Mohamed et al.

Optimization of Fused Deposition Modeling process parameters: a review of current research and future prospects

Adv. Manuf.

(2015)

C.W. Ziemian et al.

Computer aided decision support for Fused Deposition Modeling

Rapid Prototyp. J.

(2001)

C.J.L. Pérez

Analysis of the surface roughness and dimensional accuracy capability of Fused Deposition Modeling processes

Int. J. Prod. Res.

(2002)

T. Grimm

Fused Deposition Modeling: a Technology Evaluation

(2002)

C.C. Wang et al.

Optimizing the rapid prototyping process by integrating the Taguchi method with the Gray relational analysis

Rapid Prototyp. J.

(2007)

A. Noriega et al.

Dimensional accuracy improvement of FDM square cross-section parts using artificial neural networks and an optimization algorithm

Int. J. Adv. Manuf. Technol.

(2013)

R. Singh

Some investigations for small-sized product fabrication with FDM for plastic components

Rapid Prototyp. J.

(2013)

R. Singh

Process capability analysis of fused deposition modelling for plastic components

Rapid Prototyp. J.

(2014)

W.J. Johnson et al.

Comparative evaluation of an open-source FDM system

Rapid Prototyp. J.

(2014)

A.K. Sood et al.

Parametric appraisal of Fused Deposition Modeling process using the grey Taguchi method

Proc. IMechE Part B J. Eng. Manuf.

(2009)

G.A.O. Adam et al.

On design for additive manufacturing: evaluating geometrical limitations

Rapid Prototyp. J.

(2015)

P. Fudali et al.

Comparison of geometric precision of plastic components made by subtractive and additive methods

Adv. Sci. Technol. Res. J.

(2013)

S. Mahmood et al.

Fast deviation simulation for Fused Deposition Modeling process

Procedia CIRP

(2016)

S. Agrawal et al.

Analysis of mechanical error in a Fused Deposition process using a stochastic approach

Int. J. Prod. Res.

(2007)

K. Tong et al.

Error compensation for Fused Deposition Modeling (FDM) machine by correcting slice files

Rapid Prototyp. J.

(2008)

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Full length ArticleWarpage of FDM parts: Experimental tests and analytic model

Highlights

Abstract

Introduction

Section snippets

Background

Material and methods

Experimental results

Interpretation

Analytic modeling

Conclusions

Acknowledgment

Compliance with ethical standards

Ann. CIRP

Procedia CIRP

Mater. Des.

Meas

Procedia Eng.

Procedia CIRP

Robot. Comput. Integr. Manuf.

Mater. Des.

Polym. Test.

Mater. Des.

Robot. Comput. Integr. Manuf.

Procedia Eng.

Int. J. Mach. Tool. Manuf.

Procedia CIRP

Precis. Eng.

J. Manuf. Proc.

A review of melt extrusion additive manufacturing processes: II. materials, dimensional accuracy and surface roughness

Rapid Prototyp. J.

Review: dimensional accuracy in additive manufacturing processes

Optimization of Fused Deposition Modeling process parameters: a review of current research and future prospects

Adv. Manuf.

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Rapid Prototyp. J.

Analysis of the surface roughness and dimensional accuracy capability of Fused Deposition Modeling processes

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Optimizing the rapid prototyping process by integrating the Taguchi method with the Gray relational analysis

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Dimensional accuracy improvement of FDM square cross-section parts using artificial neural networks and an optimization algorithm

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Rapid Prototyp. J.

Full length Article
Warpage of FDM parts: Experimental tests and analytic model