Solid Freeform Fabrication (SFF)

Prepared byAkshay Shah

ME – CAD/CAM

Introduction Let us define the term Fabrication:

Fabrication is the processing of raw material or any semi finished product in the final shape by different methods such as welding, forming, sheet metal operations or casting.

Solid Freeform Fabrication (SFF) is related to rapid prototype process.

Rapid Prototype A physical prototype is built, in order to test

various aspects of design, illustrate ideas before any production process.

This type of prototype is mainly made on lathe or milling machines and are termed as subtractive methods.

For complex shapes subtractive method is difficult to create and time consuming.

So, Rapid Prototyping is used as an alternative method to subtractive method, in which they add and bond materials in the form of layers

Images related to Rapid Prototype

History Of 3D Printing1984 - 86

Charles Hull invents 3D printing and coins the term “Stereo Lithography”

1992First 3D printer built by 3D Systems

1999First application of 3D printing in the medical

field - creating the human bladder

Solid Freeform Fabrication Definition: Solid freeform fabrication (SFF)

refers to a category of manufacturing processes in which parts are built by depositing one cross-sectional layer of material on top of the next. It is very much like "printing" a succession of slice images one on top of the next so that thickness is gradually built up.

Working of SFF

Techniques of Solid Freeform Fabrication

Following techniques are mostly used for solid freeform fabrication

1. Stereolithography apparatus (SLA)2. Fused Deposition Modelling (FDM)3. Selective laser sintering (SLS)

Stereolithography Apparatus

In this technique a UV light source scans a photosensitive polymer which partially cures under the energetic light source. After each layer is formed, the elevator is lowered to allow uncured liquid to flow over the top of the part, in preparation for scanning the next layer features. Post curing following laser scanning of the entire part completes the production cycle.

Fused Deposition Modelling (FDM)

A SFF process in which thermoplastic precursor material is heated and extruded from a head carried on an XYZ table to produce a 3-D part

Working of FDM Pre-processing: Build-preparation software slices

and positions a 3D CAD file and calculates a path to extrude thermoplastic and any necessary support material.

Production: The 3D printer heats the thermoplastic to a semi-liquid state and deposits it in ultra-fine beads along the extrusion path. Where support or buffering is needed, the 3D printer deposits a removable material that acts as scaffolding.

Post-processing: The user breaks away support material or dissolves it in detergent and water, and the part is ready to use.

Schematic Layout of FDM

Selective Laser Sintering (SLS)

The use of a Computer-controlled,. High-power laser to melt or sinter powder together is the basis for University of Texas developed DTM Corporation's Selective Laser Sintering (SLS) system.

A thin layer of powder is spread over a base and a laser selective scans the powder bed, sintering or melting the material together.

The base is lowered slightly, a new layer of powder is spread over the selectively sintered layer, and laser scans again, this time selectively sintering or melting powder together into the preceding layer.

The process is continued to generate a complete part.

Schematic layout of SLS

Comparison of different SFF techniques

Future of SFF Traditional Manufacturing

Solid Freeform Fabrication

Some Application of SFF1. Making core for sand casting2. In various implants of different organs

in human body

Making core for sand casting

There are two SFF applications in sand casting pattern making and core making.

Patterns are used to form the imprint in the sand mold.

Core arrays form the internal cavities or passageways of cast metal parts, such as internal geometries of engine blocks.

In conventional core making, cores are fabricated in many pieces that would have to be assembled with core paste and placed in the mold and gauged for accuracy of fit. Cored holes and features are usually limited to ¼”diameter.

Core Making by SFF

Implant of different organs Scientists, including an Indian-

origin researcher, have created a 3D-printed bionic ear that can "hear" radio frequencies far beyond the range of normal human capability. Using off-the-shelf printing tools, the scientists at Princeton University explored 3D printing of cells and nano particles, creating the bionic ear.

References1. http://nptel.ac.in/courses/112102103/162. http://www.srl.gatech.edu/education/ME6105/Projects/Fa11/rapid

prototyping/3. http://www.inventionpartner.com/rapid-prototyping-processes.ht

ml4. McGraw-Hill Machining and Metalworking Handbook, Third

Edition5. Advances in Multiple Material Solid Freeform Fabrication, Richard

H. Crawford, Joseph J. Beaman, David L. Bourell, and Kristin L. Wood, Laboratory for Freeform Fabrication, The University of Texas at Austin,2001

6. Solid Freeform Fabrication An Advanced Manufacturing Approach, D.L. Bourell, J.J. Beaman, H.L. Marcus, J.W. Barlow

7. Louhbourough University 20008. Solid Freeform Fabrication, IEEE Spectrum 19999. https://medecms.gov.mt/en/resources/News/Documents/Youth%2

0Guarantee/3D%20Printing.pdf10. http://www.dtic.mil/dtic/tr/fulltext/u2/a274552.pdf

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