Paper id 2620146

International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637

FDM Rapid Prototyping and Conversion of RP Models to Investment Castings Hitesh Arya1, Gaurav Dawda2, Ashish Wankhade3, Mansur Syed4 Student, Mechanical Department, Hitesh Arya1 Student, Mechanical Department, Gaurav Dawda2 Prof, Mechanical Department, Ashish Wankhade3 Prof, Mechanical Department, Mansur Syed4 1 hitesharya04@gmail.com , gaurav.dawda619@gmail.com2, ashish_wankhade@rediffmail.com3, mansursyed11@gmail.com4

Abstract-- Rapid prototyping system makes it possible to manufacture prototype of complex shapes, including gear wheel prototypes. RP systems are increasingly employed in gear wheel testing. The use of RP systems is particularly vital to the process of manufacturing gear wheels of non-standard (non-involutes) tooth profile. For this kind of gear wheels, it is not possible to use traditional tools for tooth cutting; therefore the prototypes of such gear wheels are made by the RP methods directly on the basis of the 3D-CAD models .And the Tooling and Casting subgroups of the European Action on Rapid Prototyping (EARP) has undertaken a project to investigate the problems associated with using rapid prototype models as sacrificial patterns for investment casting. The accuracy and surface finish of the models and the castings were also assessed so that a comparison could be made. Models from each process were manufactured by different number of members of EARP and then three foundries were each given a set of models to convert to castings.

Index Terms-Minimum, Medium, Maximum

1.

INTRODUCTION

Rapid prototyping (RP) has received much attention in recent years and has been embraced as a powerful tool for the product development process. RP has been described as a technology for producing accurate parts directly from CAD models (typically in a few hours), with little need for human intervention. However, it is reasonable to establish what they mean by “accurate” or even “part” for that matter since material and geometric fidelity can be critical for product development. According to Webster’s dictionary, a prototype is “a first full-scale and usually functional form of a new type or design of a construction (as an airplane)”.

The question must be posed as to whether a rapid prototyping method is producing just that, or if the correct term is “Rapid Modelling”. Do the current RP technologies produce rapid prototypes or rapid models? Are the methods “rapid”? The key here lies in the use of rapid and prototyping. The current use of rapid is to time scale (hopefully a reduction) for the evolution of the first item.

Fused deposition modeling (FDM) is one of the few commercially available rapid prototyping technologies offering real possibilities of producing solid objects in a range of different materials including metals and composites. FDM systems, developed by Stratus’s Inc., currently fabricate parts in ABS (P400), investment casting wax (ICW044), and polyamide plastic (P301) and the machines can operate in a user friendly office environment.

A Prototype has come to be a physical approximation of

some or all of a product And there are two main techniques used to manufacture investment castings depending on the type of mould used.

2.

LITERATURE REVIEW:-

Alexander et al. develops an accuracy measuring model and the methodology for creating the cost model. Cup height is used to measure the accuracy of a component or part. The component orientation that minimizes components accuracy, build time and the amount of support material selected. The accuracy is calculated using the cusp height that considers the area of each component in the stereo lithography. The best orientation is chosen in terms of the user from the results calculated.

The ability to select the optimal orientation of build up is one of the critical factors since it affects the components surface quality, accuracy, build time and part cost. Various measures to be considered in optimization of build orientation for FDM are build material, support material, build up time, surface roughness and total cost. Experiments were carried out and results are analyzed for varying build orientations for primitive geometries like cylinder. A mathematical model was developed after validating the theoretical values of the surface roughness with measured values. This helps in reducing the experimental work and improves possibilities of virtual simulation of rapid prototyping components (cheng et. al.1995) This paper presents a generic system that performs a computer-aided optimization of component orientation in 10

International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637 consideration of the mentioned factors of influence as well as related effects. The proprietary development of the implementation of presented approach is based on the paradigm of object-oriented and generic programming and therefore is versatile. A vertical orientation would result in good component quality except the holes but also in a high number of layers and therefore in long build time. A horizontal orientation may lead to a cost-effective build time but also to insufficient dimensional accuracy.(S. Danjou 1, P. Koehler et. al.2009).

In this paper, they seek to characterize some of the properties of Stratus’s. Fused Deposition Modelling (FDM) process, as well as the effects of varying some of the build parameters of the components. Series of Samples were manufactured at FDM machine and tested for load using instant load frame. In the tension tests, the predicted behaviour does not correlate well with the measured behaviour when the correct material properties are used.

However, when the tensile strength in the transverse direction with a negative air gap is replaced into the no air gap material properties, the predictive model is quite accurate (John Michael Brock et. al.2000) Reported design methodology in use at Piaggio for connecting rod design, which incorporates an optimization session. However, neither the details of optimization nor the load under which optimization was performed were discussed. Two parametric FE procedures using 2D plane stress and 3D approach developed by the author were compared with the experimental results and shown to have good agreements. The optimization procedure which they developed was based on the 2D approach (hippoliti et. al.1993)

3. FUSED DEPOSITION MODELING (FDM)

directly from a CAD model using a layer by layer deposition of molten thermoplastics extruded through a very small nozzle. FDM is one of the few commercially available rapid prototyping technologies which offer the possibilities of producing solid objects in a range of different materials including metals and composites. The FDM systems, developed by Stratus’s Inc, currently fabricate parts in ABS, investment casting wax and elastomeric, and the machines can operate in a user friendly office environment. One of the latest FDM machines, the FDM3000[6], which is used in this study, allows building layer thickness from 0.178 mm to 0.356 mm and the achievable accuracy in the parts is ±0.127 mm.

The process starts with the creation of a component on a CAD system as a solid model or a closed surface model. The model is converted into an STL file using a specific translator on CAD system. The STL file is then sent to the FDM slicing and pre-processing software called Quick Slice, where the designer selects proper orientation, creating supports and slicing and other parameters to prepare the component program for sending to FDM machine. A proper orientation of STL model is necessary to minimize or eliminate supports. The STL file is then sliced into thin cross sections at a desired resolution, creating an SLC file. Each slice must be a closed curve. So any unclosed curves are then edited and closed. Supports are then created if required, and sliced. Supports can also be created as part of the CAD model and are imported as part of the STL file. The sliced model and supports are then converted into SML file which contains actual instructions code for the FDM machine tip to follow specific tool paths, called roads, to deposit the extruded materials to create each cross section. The designer selects various sets and road parameters to make sure that a proper SML file is created.

The SML file is then sent to the FDM machine, where the FDM head creates each horizontal layer by depositing molten extruded materials on a foam foundation until the part is completed. The part is then taken out; supports are detached carefully, and are ready for use.

4.

MATERIAL USED IN FDM PROCESS:

Acrylonitrile Butadiene Styrene (ABS): • This is the main build material used by the FDM. It is also used for the support material • Support Material --- used to fill in spaces that may otherwise have no material, for building purposes.

Fig 1:- Fused Deposition Modeling Fused Deposition Modeling (FDM) is a rapid prototyping (RP) process that integrates computer aided design, polymer science, computer numerical control, and extrusion technologies to produce the three dimensional solid objects

Acrylonitrile Butadiene Styrene (C8H8· C4H6·C3H3N) is a commonly used thermoplastic to make light, rigid, molded products. ABS plastic ground down to an average diameter of less than 1 micrometer which is used as the colorant in some tattoo inks. It is a copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and 40 to 60% styrene.

The result is a long chain of polybutadiene which is crisscrossed with shorter chains of poly (styrene-co11

International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637 acrylonitrile). The nitrile groups from neighboring chains, being polar, attract each other and bind the chains together, making ABS stronger than the pure polystyrene.

5.

FDM BUILD TEMPERATURES

Before the FDM machine can build the models, it has to meet certain temperature requirements to dispense the ABS plastic.

Temperatures are as follows: 1. Build Material: 270 degree Fahrenheit 2. Support Material: 265 degree Fahrenheit.

5.1. ADVANTAGES 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

The advantage to use FDM include the speed and safety of the machine The machine does not use any toxic material, so it can be installed in office environment Build time for the machine is faster than SLA There is no part clean-up needed for a component made by FDM Cost of the FDM machine is usually lower than that of the SLA machines There are only a few materials commercially available for the FDM: ABS, medical grade ABS, elastomer and. investment casting wax.

The process is clean, simple, easy to operate and produces no wastage Fast building for bottle like structure or hollow components True desktop manufacturing system that can be run in office environment.

There’s no worry of exposure to toxic fume and chemicals

5.2. DISADVANTAGES 1.

Poor strength in the vertical direction

2. Slow for building a mass component 3.

Accuracy is relatively low and difficult to build components with complicated details

6.

INVESTMENT CASTING

There are two main techniques which are used to manufacture investment castings depending on the type of mould used. These are either blocking moulds or shell moulds: 6.1 Block moulds – this was the main technique used until the mid-1950s, and involves pouring of a refractory ceramic around a wax pattern assembly contained in a flask. One of the main disadvantages of this technique is the cast metal is surrounded by a very thick ceramic shell. This is an insulator and causes slow cooling and, therefore, poor metallurgical structures are obtained. Another problem is the

solid ceramic block which inhibits the contraction of the metal as it cools and this can lead to failure of the casting.

6.2 Shell moulds – these are produced by “investing” a wax assembly with the several ceramic layers. The first layer is normally a fine coating so that a good surface finish on the casting will be obtained. Subsequent layers are made up of ceramic slurry and refractory granules. The shell will normally be made up of between five to eight layers depending on the cooling rate required and the subsequent metallurgical properties.

Once the ceramic has dried, the wax is removed by placing the block or shell in a steam autoclave at 150 to 200°C and 6 to 7 bar. The wax can be reclaimed and then used for moulding the runner systems. Although the coefficient of thermal expansion for wax is much greater than the ceramic, the shells usually don’t crack. This is because initially the heat melts the outer layer of the wax and these acts as a “buffer zone” which allows expansion of the main body of wax. After de-waxing, the moulds are fired in the furnace to give full strength and to bring them nearer to the melt temperature of the metal.

7.

USING RAPID PROTOTYPE MODELS FOR INVESTMENT CASTING

Investment casting and rapid prototyping have the potential for an ideal marriage in which both the techniques are suited to complex components. Two of the main commercial rapid prototyping systems, viz: Selective Laser Sintering (SLS) and Fused Deposition Modelling (FDM) are capable of producing wax models which can be used almost directly in investment casting. However, these waxes are very brittle in nature and it is difficult to transport them to a foundry without damage. The first use of rapid prototype components as sacrificial masters for investment casting started in 1989 with the use of block moulds. When using non-waxed rapid prototype components for investment casting, it is still necessary to remove the wax runner system. If this is done in a steam autoclave the expansion of the rapid prototype components leads to cracking of the shell. Therefore there has been a large amount of work undertaken by certain foundries to try to overcome this problem. Some rapid prototyping system suppliers have developed the different techniques to try to eliminate shell cracking. However, the number of foundries that can convert rapid prototype components into metal using investment casting is still very low. One aim for future must be to build rapid prototype components which require no special finishing and can be used by all foundries alongside conventional waxes 8.

METHODOLOGY:-

The methodology is described in following steps:-

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International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637

8.1 Specimen Selection:They have selected the simple machine component i.e. connecting rod of two stroke engine as their specimen.

After selecting the specimen, they had taken out the actual dimensions of the specimen. Optimized Connecting Rod has been modelled with the help of designing software CATIA; in general they had performed the reverse engineering. The Orthographic and Solid Model of optimized connecting rod is shown below.

8.2 Specimen Design:-

Fig 2:- CAD model of Connecting Rod

Fig 3:- CAD model of Connecting Rod 8.3 Fabrication of model:They have fabricated the actual prototypes of a specimen at different build orientations i.e. 0o, 45o, 900 along with different process parameters i.e. road width and air gap (min, med, max) on FDM TITAN T1 machine. ABS was used as a Raw material for the fabrication of the model or component. They have fabricated nine models i.e. for each angle, road width and air gap(min, med, max) was varied.

8.4 Observation and analysis:After getting the actual fabricated models, They have studied the readings of build time, support material, model material from certain software at 10o intervals (0o, 100...

90o). Fabricated models were tested for surface roughness at Parth Metallurgical Services located in Nagpur. Instrument named SRT (Times-TR 110) was used for the same.

Accuracy of the models was determined with the help of digital Vernier Calliper. Readings are tabulated as below.

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International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637

Table 1:- Surface Roughness Values of Connecting rod Sample no

Min 45o

Med 45o

Max 45o

Max 0o

Location

Ra Values(um) Top R1

R2

R3

Avg

R1

R2

R3

Avg

Dia 40 mm

13.69

14.76

14.47

14.31

15.28

14.9

14.52

14.90

Dia 18 mm

13.7

13.39

14.44

13.84

13.98

14.14

13.56

13.86

Rib

15.04

15.31

15.22

15.19

14.78

15.03

15.14

14.98

Dia 40 mm

15.26

15.4

14.92

15.19

14.92

15.16

14.77

14.95

Dia 18 mm

15.06

14.68

15.06

14.93

14.86

14.88

15.08

14.94

Rib

15.69

15.35

15.9

15.65

15.18

14.98

15.39

15.18

Dia 40 mm

14.44

13.83

14.03

14.10

14.2

14.57

14

14.26

Dia 18 mm

14.43

13.83

13.59

13.95

13.9

14.34

13.88

14.04

Rib

14.74

14.47

14.66

14.62

14.88

14.63

14.52

14.68

Dia 40 mm

13.76

14.22

14.02

14

14.2

14.32

13.84

14.12

Dia 18 mm

14.17

14.18

13.48

13.94

14.04

13.46

13.92

13.81

15

14.46

14.66

14.71

14.72

15.16

15.06

14.98

Dia 40 mm

14.12

14.52

13.84

14.16

14.29

13.96

13.32

13.86

Dia 18 mm

14.05

14

14.5

14.18

14.48

13.55

14.27

14.10

Rib

14.78

15.09

14.96

14.94

14.52

14.7

14.62

14.61

Rib Max 90o

Bottom

Table 2:- Dimension of Prototypes for Accuracy Sr.no

1 2 3 4 5 6 7 8 9

Build Type

Wt. (gm)

Dia 40 mm Inner Outter

Dia 80 mm Inner Outter

Rim

Notches

18.03

Dia 40mm 15.27

Dia 18mm 15.25

Max 0o Max 45o Max 90o Med 0o Med 45o Med 90o Min 0o Min 45o Min 90o

15

29.73

39.90

14.81

9.42

3.68

16

29.60

39.77

14.77

17.90

15.25

15.24

9.35

3.74

18

29.81

39.90

14.83

17.88

15.43

15.33

9.54

3.62

18

29.78

39.92

14.84

18.06

15.30

15.30

9.43

3.50

20

29.88

39.83

14.81

17.94

15.50

15.28

9.38

3.56

15

29.90

39.94

14.95

17.92

15.45

15.34

9.57

3.36

19

29.95

39.94

14.90

18.11

15.48

15.33

9.60

3.14

19

29.96

39.03

14.98

18.05

15.69

15.35

9.45

3.23

10

29.93

39.97

15.08

18.03

15.51

15.42

9.59

3.27

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International Journal of Research in Advent Technology, Vol.2, No.6, June 2014 E-ISSN: 2321-9637

9.

1.

2.

3.

THE BENEFITS OF RAPID PROTYPING TO INVESTMENT CASTERS The most obvious benefits are the savings that are resulting from the elimination of prototype (or low volume production) tooling Early patterns also allow the foundry to evaluate different tree layouts – very important if the ultimate design is for high volume productions and tree loading also impacts the costs If quantities of the casting are required before the production tool is ready, rapid prototyping patterns can be used as an alternative.

Once a foundry has decided to invest in a rapid prototyping facility, it must decide the criteria to select the technology. These will probably include: 1.

2.

3.

4.

5.

Pattern accuracy achievable.

Pattern surface finish Contamination from the pattern residues Stability and robustness to handling of the patterns Freedom from foundry defects, such as porosity and surface defects 6. Comparability with existing foundry practice 7. Size of the patterns 8. Cost per pattern 9. Ease of use 10. Reliability and support

10. DISCUSSION AND CONCLUSION There were several surprises from the results of this project.

The biggest surprise was the lack of accuracy on the various models. There has not been much published work to say what the accuracy should be on the real models. Several benchmarking studies have been undertaken, but these have usually concentrated on build times or costs. There are no internationally recognized standards for assessing the accuracy of rapid prototype machines or their models.

effect on the build orientation and the optimal orientation is determined.

For the Specimen taken i.e. Connecting rod which is manufactured at varying road width and air gap along with the Different angles, it is found that for the minimum road width and air gap build time and model material taken is more, followed by maximum and medium once. Also from the surface roughness values it has been observed that surface finish of maximum road width and air gap prototypes is excellent and it decreases with increase in the angles (00, 450, 900). Form the accuracy point of view better accuracy is obtained at the minimum road width and air gap.

REFERENCES:1. Gebhardt, A., (2003) Rapid Prototyping, Hanser Gardner Publications, Inc., Cincinnat 2. Chua, C.K., Leong, K.F. (2000) Rapid Prototyping: Principles and Applications in Manufacturing, World Scientific 3. Smart, R.F., “Investment casting – the way forward”, Metallurgia, Vol. 55, 6 June 1988, p. 288.

4 Smart, R.F., “Investment casting research pays off”, Metallurgia , Vol. 56 No. 1, 1989, pp. 30-3.

5. Chantrill, A., Private communication from 3D Systems Inc. Ltd, 1995.

6 Jacobs, P.F., Rapid Prototyping and Manufacturing: Fundamentals of Stereolithography , Society of Manufacturing Engineers, Dearborn, MI, ISBN 0 87263 425 7. Cheng, W.; Fuh, J.; Nee, A.; Wong, Y.; Loh, H.; Miyazawa, T.Multi-Objective Optimization ofPartBuilding Orientation in Stereolithography,Rapid Prototyping Journal, 1995, 1 (4), pp. 12-23 8. Chee Kai Chua; Kai Fai Leong, Chu Sing Lim (2003).

Rapid Prototyping. World Scientific. P. 124 9. Ferry Melchels et al 2011Biofabrication 3034114 10. J. P. Kruth, M. C. Leu, T. Nakagawa Progress in additive manufacturing and rapid prototyping

This Paper represent an approach that determines the optimal build orientation for FDM, Also the effect of process parameters like Road width, Air gap, build material, support material on the properties of component i.e.

Accuracy, Surface roughness and build time. The minimization of Build material and support material is also implicitly included in the work. The values of build time, Accuracy and surface roughness are determined for varying Road width and Air gap (Min, Med, Max) at each angle.

From the computed Values of Build time, Model material, Accuracy, Surface roughness, Support material Required ,its

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