3D PRINTING

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Additive manufacturing or 3D printing is a process of making three dimensional solid objects from a digital model. 3D printing is achieved using additive processes, where an object is created by laying down successive layers of material. 3D printing is considered distinct from traditional machining techniques (subtractive processes) which mostly rely on the removal of material by drilling, cutting etc.

3D Printing is an SFF Process which creates parts in layers.Each layer is formed by spreading powder and selectively Joining the powder by ink-jet printing of a binder material.

What is a 3D Printing Process?

Three Dimensional Printing is a process under development at MIT for the rapid and flexible production of prototype parts, end-use parts, and tools directly from a CAD model. Three Dimensional Printing has unprecedented flexibility. It can create parts of any geometry, and out of any material, including ceramics, metals, polymers and composites. Furthermore, it can exercise local control over the material composition, microstructure, and surface texture.

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Process

Three Dimensional Printing functions by building parts in layers. From a computer (CAD) model of the desired part, a slicing algorithm draws detailed information for every layer. Each layer begins with a thin distribution of powder spread over the surface of a powder bed. Using a technology similar to ink-jet printing, a binder material selectively joins particles where the object is to be formed. A piston that supports the powder bed and the part-in-progress lowers so that the next powder layer can be spread and selectively joined. This layer-by-layer process repeats until the part is completed. Following a heat treatment, unbound powder is removed, leaving the fabricated part. The sequence of operations is depicted below.

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Process Capabilities

The 3DPTM process combines powders and binders with unprecedented geometric flexibility. The support gained from the powder bed means that overhangs, undercuts and internal volumes can be created (as long as there is a hole for the loose powder to escape). 3D Printing can form any material that can be obtained as a powder – which is just about any material. Further, because different materials can be dispensed by different print heads, 3D Printing can exercise control over local material composition. Material can be in a liquid carrier, or it can be applied as molten matter. The proper placement of droplets can be used to create surfaces of controlled texture and to control the internal microstructure of the printed part.

The 3DPTM process surpasses conventional powder processing because while the 3DPTM components rival the performance of those made by conventional methods, there are no tooling or geometric limitations with Three Dimensional Printing. Because of its great flexibility in handling a wide range of materials and because of the unique ability to locally tailor the material composition, Three Dimensional Printing offers potential for the direct manufacture of structural components with unique microstructures and capabilities. Three Dimensional Printing is also readily scaled in production rate through the use of multiple nozzle technology which has been commercially developed for printing images on paper.

The Impact of Three Dimensional Printing

Three Dimensional Printing has led the field of Rapid Prototyping (RP) in the creation of functional parts and tooling directly from a CAD model. It was the first technology to achieve the fabrication of ceramic parts, and pioneered the direct fabrication of ceramic molds for casting. Three Dimensional Printing was a leader in the creation of metal parts directly and in the use of these parts for dies. Our work on ceramic preforms was the first demonstration of a functionally gradient material by RP. Most recently, we have pioneered the fabrication of structural ceramic parts using the 3DPTM process.

MIT has licensed the 3DPTM technology to six companies in diverse fields of use.

Three Dimensional Printing can substantially reduce the time to market for new products, enhance product quality by improving the coupling between design and manufacturing, and lower product cost by reducing development and tooling costs.

Furthermore, the flexibility of the process makes totally new technologies and applications possible and has already generated novel solutions to engineering problems. 3D Printing is at the forefront of the coming revolution in manufacturing brought about by Rapid Prototyping

3D printing is usually performed by a materials printer using digital technology. Since the start of the twenty-first century there has been a large growth in the sales of these machines, and their price dropped substantially.

The technology is used in the fields of jewellery, footwear, industrial design, architecture, engineering and construction (AEC), automotive, aerospace, dental and medical industries, education, geographic information systems, civil engineering, and many others.

Additive manufacturing (AM) also known as 3D printing is defined by ASTM as the “process of joining…

Applications:

Ceramic Shells for Direct Casting of Metal Parts

Three Dimensional Printing is the only process that fabricates ceramic molds directly from a computer model with no intervening steps. With 3D Printing, a ceramic shell with integral cores may be fabricated directly from a computer model. This results in a tremendous streamlining of the casting process as compared to the traditional lost-wax casting process (see figure below). Soligen, Inc. has licensed the 3DPTM technology for producing shells, and has helped companies achieve dramatic reductions in turnaround times for metal castings.

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Typically, molds by 3D Printing are fabricated using a refractory powder such as alumina and an inorganic binder material such as colloidal silica. After firing, the loose powder is removed from within the shell resulting in a shell which is similar in composition and properties to those now made in the lost wax process by dipping wax forms in ceramic slurries. However, no part specific tooling is needed 3D Printing has produced metal castings for a wide range of applications including aerospace, medical implants, automotive.

·      Direct Metal Tools

Metal parts for injection molding tooling inserts and for direct use have been built using the 3DPprocess and placed into use. ExtrudeHone Corporation has licensed the 3DP technology for the fabrication of metal parts and tools.

Parts have been created in a range of materials including stainless steel,

tungsten and tungsten carbide. Printed parts are sintered for strength, then they may be infiltrated with low melting point alloys to produce fully dense parts. The 3DPTM process is easily adaptable to a variety of materials systems, allowing the production of metallic/ceramic parts with novel compositions.

The possibilities of this process include:

·         Direct production of injection molding tooling

·         Direct production of metal prototypes and end-use parts

·         Improved rate and dimensional control for injection-molded parts

3D Printing can be used to create tooling with integral cooling passages which are conformable to the molding cavity and near to its surface. Such channels can be printed in virtually any geometry and with virtually any interconnectedness. Tools with cooling passages can be used to control the temperature accurately and yield reproducible parts with predictable properties. Fast thermal response tooling can be created by printing passages for liquids near the surface and then providing a low thermal mass back-up structure, possibly by printing a truss structure (shown below). Textures may be printed onto the cooling channels themselves to further enhance heat transfer.

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A cooling passage printed conformable to the Cooling cavity.

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Fast thermal response tooling with conformal cooling passages with a cellular/truss structure behind it for thermal isolation.

With such tooling, the temperature of the tool can be raised before injection and then quickly dropped after injection. This results in demonstrated and significant improvements in part quality (by reduced residual stress) and increased production rate.

·      Composite and Functionally Gradient Parts

1.     Functionally Gradient parts with Local Composition Control

A unique capability of the 3D Printing process is the ability to locally tailor the material composition of a part. This is made possible by precise control of a multiple-material printhead (see figure below). An appropriate data structure is all that is required to generate parts with multiple materials. This allows the part designer to locally tailor properties such as strength, toughness, or heat transfer, for example. Any material gradient can be imposed over any region, and locally, half-toning algorithms can be applied.

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2.     Macroscopically Toughened Composite (MTC) Parts

It has been shown that silicon carbide reinforced aluminum alloys can display higher Charpy impact values if the SiC particulates are clustered into well organized arrays of “macro fibers” as compared to uniformly dispersed particulate reinforced composites. This concept has been demonstrated with 3-D printed preforms at MIT. Since these pseudo fibers can be printed into any array and can be infiltrated by techniques developed at MIT, a more flexible and low cost approach to the manufacture of MTC components is now possible.

The part shown to the left was produced as follows. Here, the pseudo-fibers are supported by densely printed end blocks. The printed preform is removed from the powder bed after heating to set the binder. It is then inserted into a die and pressure-infiltrated with molten metal. After removal from the die, a net-shaped component is produced with little need for additional machining. The concept of macroscopically toughened composites has many possibilities:

·        enhanced material properties including:

·        toughness

·        wear

·        thermal or electrical conductivity

·        thermal expansivity

·        ability to locally vary toughness or wear properties

·      Medical Applications: Drug Delivery Devices

MIT has issued Therics, Inc. a license for the production of time-release drug-delivery devices. Using a multiple jet printhead, extremely accurate quantities of several drugs can be printed into a bio-compatible, water-soluble substrate designed to time-release these drugs into the bloodstream.

3D Printing, now used primarily as a tool for processing metal and ceramic prototypes, has many advantages over other rapid prototyping technologies. It is capable of specific spatial deposition of multiple materials with fine resolution and control over local composition and microstructure. It is particularly worthy for fabricating functionally graded structures.

These aspects of the 3DPTM process offer new possibilities for the fabrication of drug delivery systems. The ability to spatially control the deposition of multiple drugs, the level of porosity, and the strategic positioning of matrix modifiers will be important in designing the next generation of chronopharmacological drug delivery systems. 3D Printing has the ability to fabricate oral dosage forms for sustained release, controlled release, targeted release, cyclical release, or any combination of these. More precise spatial and temporal placement of drug into the body will reduce the size and number of doses, and this will thereby increase the therapeutic efficiency and safety of drugs, and help assist patient compliance.

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3D printed model / 3D printed model

Objet Bio-Compatible material (MED610™) is a rigid material featuring great dimensional stability and colorless transparency. The material is ideal for applications requiring prolonged skin contact of over 30 days and short term mucosal-membrane contact of up to 24 hours

Much of the current research still concerns proving itself with the 3D Printing concept. Recent testing shows that 3D Printing is able to deliver precise drug dosage control, and cross-sample contamination was not detected. It has also been shown that samples with varying bulk densities and porosities can be fabricated, and that this in turn leads to great flexibility in the release kinetics. We are now engineering composite tablets which contain both regions of an erosion-type and a diffusion-type release mechanism. These composite devices are currently being designed for specific applications involving the delivery of antihistamine and anti-inflammatory medications.

·        Porous Ceramic Filters

Specific Surface, Inc. has licensed the 3DPTM process for the production of porous ceramic filters with complex internal structures. The flexibility of 3DPTM allows the filter design to be tailored by a combination of geometry and particle size. This results in filter products with up to 10 times greater efficiency than conventional filters. One use of their products is in coal-burning power plants, which use the filters to remove particles from stack gases.

·      Experimental Geometries

1.Surface textures

Front-end CAD systems, combined with the geometric flexibility of 3D Printing have the potential for creating some dramatic new geometry. In the parts shown here, a surface texture was defined in CAD and then mapped onto different solids. Such surface textures can be used to enhance heat transfer or create a prescribed surface roughness, for example.

2. Truss structures

Truss structures of any complexity can be generated and printed by 3DPTM. This feature can be used for thermal isolation (injection molding), or to create a part with prescribed weaknesses (casting). In one application, a ceramic shell was designed with truss structures supporting and surrounding the shell wall. This shell was designed to fail as the poured metal cools, thus eliminating the problem of “hot tears.”

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3DP part with fine surface feature mapped onto a                                                        Lattice structures by 3DP

geometric solid

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