Proceedings of 13th International Conference. Mechanika. 2008
EFFECT OF PROCESSING PARAMETERS ON TENSILE STRENGTH OF 3D PRINTED PARTS A. Fajić*, Dž. Tufekčić**, A. Topčić*** * Federal Ministry of Development, Entrepreneurship and Craft, 88 000 Mostar, BiH, E-mail:
[email protected] ** University of Tuzla, Faculty of Mechanical Engineering, 75000 Tuzla, BiH, E-mail:
[email protected] *** University of Tuzla, Faculty of Mechanical Engineering, 75000 Tuzla, BiH, E-mail:
[email protected] Abstract: One of the main driving forces of manufacturing companies is continuous need for short-term development of new products and decrease of expenses, so that profitability and competition is maintained. Rapid Prototyping Technologies provide that bridge from product conceptualization to product realization in reasonably fast manner, without the fuss of NC programming, jigs and fixtures. The process of Three Dimensional Printing - 3DP, which is based on original MIT 3DP technology (Massachusetts Institute of Technology –MIT) and improved by Z Corporation, nowadays it is intruded in direct and indirect parts manufacturing regardless its level of complexity. This RP process offers very good ratio between used materials, price, application and a quality of printed models. Main driving factors in a real-life application of the printed models are their mechanical properties, dimensional precision and surface texture quality. In this paper we are presenting research of the effects of process parameters and post processing on the tensile strength of three-dimensional printed models. KEY WORDS: Rapid Prototyping Technologies, 3D printing, process parameters, post processing, tensile strength 1. Introduction In comparison to classic manufacturing the time and approach in modeling of new product has dramatically changed, for the reason of significant accomplishments in various fields of information and manufacturing technologies. The rapid prototyping technologies – RP intrude the upgrade of CAD/CAM/CAE technologies by reducing the time and costs of the new products development [1]. The 3D printing process is based on generating of solid structure of the physical model by the successive deposition and binding of build powder and implementation of suitable post processing operations to improve material properties depending on customer demand. The main research issues for 3DP can be categorized in four groups, related to: material improvement, process improvement, expansion of application range and customer satisfaction [2]. The first two categories can be considered as a basic research, while the second two represent applied research activities. Another major part of applied research is related to the establishing of the real capabilities of RP working equipment. Within domain of available materials and characteristics of 3D printers and with the aim of production improvement there are numerous possibilities for investigation of influences of process parameters on properties of manufactured 3DP parts. Our recent researches of the process properties showed that 3DP is most valuable for use in cases where time and price have priority versus applicability of printed model [3]. In this paper are presenting research of the effects of the layer thickness, build direction and post processing on the tensile strength of the three-dimensional printed models. 2. Research framework In research framework the printer model, base material and variations of processing and post processing parameters were investigated. For processing parameters we considered variations of build layer thickness and model orientations regarding to the build direction of the printer. For post processing parameters we considered variations of infiltration material and oven drying as a heat treatment. The 3D printer used in our research was model Z310 Plus from Z Corporation [4]. Used software i.e. printer driver, ZPrint for selected base powder type zp130 allows two values of the layer thickness: 0.0875 mm and 0.1 mm. Therefore, limited variations of the layer thickness are also considered as research constraints. First value of layer thickness was labeled with D1 and second with D2.
Considered model orientations with regard to the build direction of the printer are explained in Fig. 1. Coordinate system axes indicate trajectories of the main printer units. Axis X indicates the gantry trajectory, axis Y indicates the binder cartridge trajectory and finally, axis Z indicates invert build piston direction i.e. layer build direction. Binder ratio was set with respect to build layer thickness and base material according to the recommendation from printer software manual [4]. Used binder type zb58 is directly determined by selection of the base material (therefore, it is considered as research constraint). In most cases binder ratio is determined automatically by the algorithm implemented in software and it is higher for higher layer thickness.
BUILD BOX
Z
Z X
Y
K1
X Y
K
Fig. 1 Considered model orientations in printer build box Tab. 1 Considered model orientations legend Designation X Y Z K K1
Main model orientation X Y Z Y X
Main dimensions build plane XY XY YZ YZ XZ
Note Along the gantry trajectory Along the binder cartridge trajectory Along the layer build direction Transversally to the binder cartridge trajectory Transversally to the gantry trajectory
Considered post processing parameters (variations of infiltration material and oven drying as a heat treatment) are determined by selection of the base material. Their selection also has to be considered as a research constraint. The variations in post processing parameters in the experiment were: green model without post processing (label Z), heat treated green model (T), infiltration with ZBond i.e. cyanoakrylate (B), infiltration with wax (V), heat treated and ZBond infiltration (BT), heat treated and wax infiltration (VT), heat treated and wax followed by ZBond infiltration (MT). After determination of the research framework the experiment plan was build and summarized it in table below: Tab. 2 Factors and variations Factor Layer thickness Model orientation Post processing
Designations of variation D1, D2 X, Y, Z, K, K1 Z, T, B, V, BT, VT, MT
3. Experiment and results For the purpose of the investigation of process parameters and successive post processing on tensile strength, test specimens according to ISO 527-2:1993 [5] were manufactured. Measurement of breaking force on the test specimens was performed on the ZMGi 250 break testing machine with maximum force of 2.5 [kN] and with speed of 50 [mm/min] (ISO 527/1A/50 [5]). Preparation of test specimens for tensile strength investigation is illustrated below (Fig. 2).
a)
b)
c)
e) f) d) Fig. 2 Preparation of test specimens-Faculty of Mechanical Engineering in Tuzla, Bosnia and Herzegovina: a) printing; b) various model orientation; c) sorting by layer thickness and model orientation; d) wax infiltration; e) cyanoakrylate infiltration; f) sorted and designated In order to optimize the experimental investigation (variation of sufficient experimental points), experiment was divided into three phases. In the initial phase 3DP process variable parameters were taken into consideration just as the applied options of manufactured test specimens post processing defined points, as shown in Fig. 3. D1= 0,0875 [mm] D2= 0,1 [mm]
0,110
MT VT
0,105
6
7
8
BT
9
Post processing
Layer thickness
0,100
0,095
0,090
1
2
3
4
0,085
V B T Z
0,080
Y
X
K
K1
Model orientation
Z
0
1
2
3
4
5
6
7
8
9
10
Process point
Fig. 3 Research polygon for first experimental phase Polygon of experiment defined in this manner enables simplified comparison of obtained values across build layer thickness (D1, D2). This approach provides initial overview on influence of build directions (Y, X, K, K1) and post processing modes on the breaking force. Results analysis on Fig. 4 for defined build direction Y showed the positive influence of post processing on tensile strength for both build layer thickness (D1, D2). The positive influence of heat treatment (T) on the strength of „green models“is particularly recognized. In this case heat treatment (T) means heating of „green models“ (Z) with heating temperature T=70 oC and heating time t=20 min. Direct reinforcement of the „green models“ with cyanoacrylate produce unexpected lower values in comparison to models infiltrated by wax (V). This is opposite to the manufacturer recommendation [6], because reinforcement with cyanoacrylate with depth of penetration 1-4 mm per model intersection is suggested as the best method of „green models“reinforcement. Reasons for lower value of strength of test specimens reinforced with cyanoacrylate for both build layer thickness in comparison to those reinforced by wax
are to be found in insufficient depth of penetration of ZBond infiltrants (wax penetrates along entire cross section). This argument holds grounds even when lesser strength test specimens values infiltrated by cyanoacrylate for (D2) build layer thickness are gained as end results, taking into consideration the fact that increase in build layer thickness value increases the component porosity (decreases density) [4], and due to insufficient penetration of cyanoacrylate these test specimens possess lesser value. For these very reasons, the increase of porosity, and wax infiltration for increased build layer thickness (D2), enables enhanced outcomes, because the wax increase per allotment is present. The fact that heat-treated test specimens (T) for D2 build layer thickness produce higher values of strength (compared to test specimens infiltrated by cyanoacrylate) indicate negative influence of remaining „green models“ humidity on the depth of penetration of cyanoacrylate. Layer thickness D1 D2
Model orientation Y 2,4
GREEN MODELS (Z)
1,15
2,2
Layer thickness D1 D2
1,10
2,0 1,05
RM [MPa]
RM [MPa]
1,8 1,6 1,4
1,00
0,95
1,2 0,90
1,0
Z
T
B
Y
V
X
K
K1
Model orientation
Post processing
Fig. 5 Tensile strength of „green models“
Fig. 4 Tensile strength for Y build direction
On the Fig. 5 influence of build layer directions and thickness on the strength of the „green models“ are presented. It can be concluded that with increasing of build layer thickness D2 the strength of the „green models“ in all directions is decreased. Also, it is obvious that test specimens built in direction of printer head movement (Y axis) achieved highest values of strength for both build layer thickness. 0,105
MT
D1= 0,0875 [mm]
VT BT
0,095
Post processing
Layer thickness [mm]
0,100
0,090
1
2
3
4
0,085
0,080
V B T Z
Y
X
K
Model orientation
K1
Z
cc 0
1
2
3
4
5
6
7
8
9
10
Process point
Fig. 6 Research polygon for second experimental phase Because of positive influence of heat treatment on the strength of “green models” and low values of the strength of “green models” treated by cyanoacrylate, research polygon for second experimental phase was defined. Research polygon for second experimental phase is presented on Fig. 6. Research polygon was consisted from heat-treated test specimens produced by D1 build layer thickness in defined build directions, reinforcement of previously heat treated test specimens by cyanoacrylate (BT), wax (VT) and combined reinforcement of test specimens by wax and cyanoacrylate (MT). On the basis of results analysis presented on Fig.7 and with the comparison with results presented on Fig.5 it can be concluded that the strength of heat-treated „green models“ was increased for app. 50%. Reinforcement of heattreated test specimens by previously defined infiltrates (BT, VT) resulted with greater tensile strength of test specimens compared to directly reinforced „green models“ (B, T). This phenomenon was most expressed at “green models” infiltrated by wax (increasing of tensile strength for app. 45% per Y build direction). However, infiltration of heattreated test specimens by cyanoacrylate (BT) produce lower values of the strength compared to test specimens
infiltrated by wax, unexceptionally. Combination of reinforcement by wax and cyanoacrylate (MT) gives best results, but obtained values of the strength are slightly higher (cca. 10%) than values of the strength obtained by reinforcement of test specimens by wax (VT). Model orientation Y X K K1
D1= 0,0875 [mm]
3,6
3,2
RM [MPa]
2,8
2,4
2,0
1,6
1,2
T
BT
VT
MT
Post processing
Fig. 7 Tensile strength for layer thickness D1 On Fig. 7 the influence of build directions was presented. Generally, differences in the values of strength for post processed models are app. 10% per build directions. 0,105
D2= 0,1 [mm] 6
7
8
0,7 MT 9
10
Post processing
Layer thickness [mm]
0,100
0,095
0,090
0,085
0,6 VT 0,5 BT 0,4 V 0,3 B 0,2 T
0,080
0,1 Z
Y
X
K
Model orientation
K1
Z
0
1
2
3
4
5
6
7
8
9
10
Process point
Fig. 8 Research polygon for third experimental phase To enable comprehensive review of influence of build layer thickness on the breaking force of produced models for defined build directions and post processing operations from phase I and II (unless combination of reinforcement), research polygon was defined for third experimental phase. Fig. 8 shows research polygon for third experimental phase. Research polygon include heat treated test specimens with D2 build layer thickness, as well as reinforcement of previously heat treated test specimens with cyanoacrylate (BT) and wax (VT). Additionally, new build direction Z was imported (movement along of build platform-point 10). On the basis of results shown on Fig.9 and comparison of these results with results presented on Fig. 8 it can be concluded that increase of build layer thickness (D2) reduces the value of strength of heat treated test specimens for all build directions (app. 10%). The value of strength of infiltrant-enhanced test specimens rise (BT, VT, app. 10%). Also, for given D2 build layer thickness maximum values of strength for all types of test specimens along Y build direction were obtained. The value of strength of heat treated test specimens (T) in Z build direction (along movement direction of build platform) had the lowest value (app. 50%), exceptionally. Certainly, values of strength of enhanced test specimens (BT, VT) in this build direction will have the lowest values because of build mode.
Model orientation Y X K K1 Z
D2= 0,1 [mm]
4,0 3,6 3,2
RM [MPa]
2,8 2,4 2,0 1,6 1,2 0,8 0,4 T
BT
VT
Post processing
Fig. 9 Tensile strength for layer thickness D2 Nevertheless of achieved lower values of strength, it is important to emphasize the potency of ZBond infiltrant (cyanoacrylate) respective to the wax. Visual inspection of test specimens clearly showed low degree of penetration of cyanoacrylate along the cross section. That means achieved strength of such test specimens is in function of cyanoacrylate surface layer. Contrary to cyanoacrylate, wax penetration along the cross section of test specimens is clearly observed. Above mentioned facts indicate that future research should be focused on the identification of dominant factors and optimum design of cyanoacrylate infiltration process. 5. Conclusions By the analysis of obtained results for given phases of experiment, following conclusions can be drawn: • Investigation and measurement of the breaking force on produced „green models“ shown corresponding functional dependences of process parameters. Influence of the build layer thickness and the build direction are obvious. For lower values of build layer thickness „green models“ achieved higher values of strength in all defined directions (Y build direction-direction of printer head movement-is dominant). • Positive influence of defined post processing models on tensile strength of parts for both build layer thickness and for different build direction can be clearly recognized: - Positive influence of heat treatment on strength of „green models“ (strength of models is significantly raised) is particularly recognized. For lower values of build layer thickness heat treated test specimens have higher values of strength. - By the subsequent enhancement of heat treated test specimens, the highest values of tensile strength were achieved. This effect is in direct function of the type of infiltrant (cyanoacrylate, wax) and depth of penetration along the test piece cross section. By the increasing of build layer thickness, the increase of strength is recorded. - Generally, test specimens achieved different values of strength for different build direction. For higher build layer thickness all defined types of test specimens have the highest value in Y build direction. • Direct enhancement of „green models“ with the defined infiltrants is not recommended because remaining wet obstructs adequate penetration of infiltrant. This phenomenon is particularly emphasized in case of direct infiltration by cyanoacrylate (ZBond). References 1. 2. 3. 4. 5. 6.
Fajić A., Tiro D.: "Trodimenzionalno printanje i ostali postupci brze izrade", Univerzitet "Džemal Bijedić", Mašinski fakulet, Mostar, 2008 D. Dimitrov, K. Schreve, N. de Beer: "Advances in three dimensional printing – state of the art and future perspectives", Rapid Prototyping Journal 12/3, 2006 Fajić A., Tiro D., Galeta T., Topčić A.: "Research of 3D Printing Process Characteristics", The 5th International Research/Expert Conference, “Quality 2007”, Neum, 2007 ZPrint Software User Manual, Version 7.3, Z Corporation ISO 527: 1993 standard (ASTM D638) http://www.zcorp.com
