Additive Manufacturing or 3D Scanning and Printing

 Additive Manufacturing or 3D Scanning and Printing :-

INTRODUCTION:- 

For centuries, clever inventors have worked to improve tools and everyday objects. In some instances, they discovered a serendipitous answer, but more frequently, they visualized and tested many materials and processes before a workable solution presented itself.

During the advent of the industrial revolution, Thomas Alva Edison tested over 1600 different filament materials including coconut fiber, fishing line, and even a hair from a friend's beard before finding in 1879 that carbonized bamboo fiber burned the longest in a bulb. 

In 1938, Chester Floyd Carlson invented electro-photography and a dry chemical photocopier that required 39 separate steps. He patented his machine in 1942, but wasn't able to construct a model that worked simply with the push of a button. It was 17 years until the Xerox 914, the first "modern" photocopier, was made in 1959. 

Fast forward to 1984, when Charles "Chuck" Hull invented and coined the term stereo lithography (patent 4575330 filed in 1984, awarded 1986) by experimenting with UV curable materials and exposing them to a laser. He found that by curing a second layer of material in a set pattern upon the previous layer, he could build a solid object. Hull went on to found 3D systems two years later.

THE RISE OF ADDITIVE MANUFACTURING:- 

Additive manufacturing came about via improvements in automation, computing power, and data storage. The ability to process large amounts of data produced by 3D modeling within acceptable time frames also contributed. 

To put it simply, computers were key. Whether using real time computer processing power directly to operate AM machines or through indirect actuation and integration of supporting applications and technology, AM would not be gaining worldwide acceptance and broad use today without the computer advances of the past 25 years.

The empowering computer characteristics include the following:-

1. Processing power. Large computer aided design (CAD) files would be unworkable in an industrial setting without advanced computing power. 

2. Machine control. Positioning of components (e.g., motors and lens) and integration of sensor data to control the build process is inherent to precise equipment positioning and operation. 

3. Graphics capability. Although AM need not have retina display quality to operate, today's users have grown to expect superior graphics and relate it to excellent graphical user interface, operability, and ease of maintenance. 

4. Networking. With the advent of onshore, offshore, and localization driving AM in the 21st century, computer communication, file sharing, and common file types are essential. 

Although early technical writers made the distinction between AM as involving larger industrial machines versus 3D printers as simple desktop models, this division is no longer the norm as 3DP has become ubiquitous with everything from building artificial jawbones to constructing homes. For ease of understanding, and since AM has become synonymous with 3DP across the Internet, I will use 3DP interchangeably with AM from here forward. 

There are three main 3DP technologies. Each has strengths and weaknesses attributed primarily to a material's applicability to a required project 

However, there are several common steps in nearly every 3DP process regardless of the machine employed:- 

1. Conceptualization and acquisition of a CAD file, which includes scanning an existing object or acquisition of a magnetic resonance imaging (MRI) or computerized tomography (CT) scan in medical applications. 

2. Conversion of the original date file to a .STL file format 

3. Transfer (and possible adjustment) of an STL file to a receiving 3D printer. 

4. Machine setup with requisite materials (e.g., metal powders, plastic filaments, concrete, and chocolate). 

5. Build. 

6. Part/object removal, cleanup, and recycling of unused material. 

7. Post print processing of part/object (e.g., sealing, curing, inclusion of electronics, and plumbing). 

8. Application (e.g., prototype analysis, fit check, transplant, and ingestion). 

 ➤Stereo lithography :- 

As noted in the timeline, Charles Hull discovered a way to cure liquid, radiation curable resins or photopolymers in 1984. By exposing resins to a scanning laser similar to those used at the time in laser printers, Hull's experimentation led to the fabrication of a solid 3D object by curing one layer upon the next. He called his setup a stereo lithography apparatus. And later, the design data file became known as .STL (Stereo Lithography or Standard Tessellation Language) file. 

Hull founded 3D Systems, which marketed "rapid prototyping" machines to industries seeking reduced design to market times. Then, as photo polymerization and photo cured resins became more widely used, different radiation types (e.g., X-rays, gamma rays, ultraviolet, electron beams, and visible light) were employed to cure surfaces and parts. 

Stereo lithography, sometimes called vat polymerization, starts with a container or well of a liquid resin. Next, following a CAD digital pattern, a laser traces a specific pattern in the resin which hardens. Following this, the platform is incrementally lowered and the laser traces the next CAD directed layer in the liquid resin cross-linking the molecules in the polymerization process until the pattern is completed into a solid final form.   

Basics of Stereo Lithography

➤Selective Laser Sintering:- 

Selective laser sintering (SLS) was invented by University of Texas, Austin graduate student Carl Deckard and his advisor, Joseph Bea man (patent 4863538 filed in 1986, awarded 1989). Referred to as powder bed fusion, the 3DP method employs a computer-controlled CO laser to precisely "sinter" or fuse particles of a powder feedstock into a solid. These particles may consist of plastic, ceramic, nylon, polymers, or metal depending on the final object or part specifications. 

The sintering takes place within a heated chamber filled with nitrogen gas that helps minimize oxidation and degradation of the powdered material. Additionally, infrared heaters are set above the build platform to maintain desired temperatures just below the melting or deformation temperatures. The powdered feed material is similarly kept at a constant temperature along with the build platform. This temperature regulation minimizes laser power required (e.g., preheating and for fusion) as well as diminishes the chance of warping during the build process due to uneven pockets and potential contraction. Once a layer is sintered, another layer of powder is applied and then fused by the laser to the first. This process is repeated until the design is complete. 

Once the SLS object or part is completed, it is encased and supported by the extra unused powder of the part build. The part is removed to another area where excess powder is carefully removed with fine tools and brushers, similar to those utilized in an archeological excavation. Forced air jets clear the rest of the powder from the SLS created object. Following post printing cleanup, the part may be painted or additional components (e.g., wiring) added.

SLS powder melting setup

➤Fused Deposition Modeling or Fused Filament Fabrication:- 

Another AM technology employs extrusion. It was developed by S. Scott Crump in 1989 (patent 5121329 awarded in 1992), who also founded Stratasys. This method, coined "fused deposition modeling," was trademarked by Stratasys and can be likened to a computer automated hot glue gun. The molten material (e.g., plastic filament or metal wire supplied and heated from a feed coil) is extruded via the nozzle into a computer (CAD) directed pattern where it cools immediately and hardens. The next prescribed layer is then piped upon the first layer on the build platform creating the part or object from the bottom up. 

The build platform is lowered as the servo motor controlled nozzle moves in an x-y-z design. Fused filament fabrication (FFF) builds are restricted by the angle of the slope of the overhang. This limitation is counteracted by support structures of different materials that enable complex geometrical designs and can be removed during post print finishing.

Fused filament fabrication uses ABS, PLA, polystyrene, polycarbonate, polyamides, and lignin in fabrication depending on the manufacturing specifications and final use of the completed object. ULTEM 9085 thermoplastic, for example, is used when fire retardancy is an important requirement as in aviation and aerospace applications.

Constant pressure is an important component of FFF since any extruded material must flow at a constant rate in order to produce a constant and standardized crosssectional diameter. The extruded material must be laid down in a semisolid state and solidified completely to maintain the desired diameter and shape. 

Another path to extruded solidification employs use of a curing agent, minute solvent amounts, or air drying of the semi-liquid material. Bio printing and components of tissue engineering (e.g., bone scaffolds) discussed later in the chapter also use alternate 3DP methods .

➤Electron Beam Melting:- 

Electron Beam Melting (EBM) is similar to SLS in that applied powder is fed by two powered feed nozzles. The metal powder is not melted with a laser onto a pre laid build platform as in SLS, but similar to FFF, the powder feedstock is melted as it is deposited. This allows for increased standardization and density during the build process. Each pass of the beam deposition head, then, precisely applies a stratum of solidified material in adjacent lines until the complex 3D pattern is complete. The EBM method may be slower due to this feature. 

Although beam deposition manufacturing methods are basically the same, approaches differ with regard to laser wavelength, power, spot size, powder or wire feed delivery, inert gas delivery, and actuator control and feedback mechanisms . The general layout of an electron beam deposition printer is shown.

General layout of  electron beam deposition printer

➤SCANNING:- 

Additive manufacturing, whether for industrial, artistic, medical, architectural, aerospace, or home application, starts with a design. Since, 3DP is a digital technology, when creating a new object or improving a complex part, a 3D printer does not work alone. It is tied to a computer "brain" which dictates design specifics (e.g., geometry and materials). Nearly every commercial CAD design package is able to transmit specifications to a 3D printer. 

The 3DP input from a CAD system is achieved via scanning or an original 3D model. Image input may be collected by scanning with a handheld device (e.g., I Sense, Geo Magic Capture, Fuel 3D, etc.) Some small scanners have a turntable where an object is placed on the rotating platform and scanned (e.g., Maker bot Digitizer Desktop 3D Scanner). Some scanners are incorporated within the 3D printer (e.g., AIO Robotics—Zeus 3D printer, scanner, and fax).

A 3D scanner records data from a real world object on shape and appearance (e.g., texture and color) and then compiles a 3D point cloud of geometric shapes from the sample's surface, which is then used to extrapolate the shape of the subject (i.e., reconstruction). 

Similar to a camera that collects surface information, a 3D scanner collects distance information about unobscured surfaces within its field of view. The 3D reconstructed image portrays the distance to each surface point on the object. Capturing all angles of an object may require multiple scans. Then the scanned data must be aligned, registered, and merged into the overall model. Large-scale industrial scanners handle extremely large data sets (e.g., Faro, Ametek, and Leica Geo systems). 

3D scanning is used in orthotics, prosthetics, hearing aids, prototyping, industrial design, quality control/inspection, wound repair, education, and replication of priceless art and artifacts. 

➤COMPUTER AIDED DESIGN AND COMPUTER ASSISTED MODELING:-

As mentioned, computers are key to AM and 3DP. They provide designers, engineers, artists, and medical science researchers the ability to open channels of creativity, innovation, concept modeling, development, and flexibility by providing a new vantage point.

When an original part is unavailable, software such as AutoCAD, Revit, Sketch up, and 3D Solid works offer a myriad of design options linked to manufacturing. These use polygonal 3D models, editors, and non uniform rational B-spline (NURBS— mathematical model used in computer graphics for curves and surfaces) to portray analytical surfaces and modeled shapes. 

The polygonal models break down a curved surface mathematically into hundreds or thousands of small faceted surfaces (i.e., a "mesh" model) of surface topography. This information is then manipulated via surface modelers such as Geo Magic, Rhino 3D, T Splines, Image ware, and others. The model is imported into CAD software with complex algorithms (e.g., design intent and feature tree) intact and ready for manipulation prior to build. 

➽ADDITIVE MANUFACTURING/3D PRINTING APPLICATIONS:- 

Primary considerations in selecting an AM or 3D printer are printing speed, CAD compatibility, cost of printer/materials, number/size of prototype(s) it can print, ease of use, multi material compatibility, diverse materials availability, opacity, color, and more. 

3D modeling and printing offers many advantages such as greater creativity, experimentation, testing, lower development times/model adaption, lower operation/distribution costs, printing of previously impossible and complex internal structures, and incorporation/reduction of constituent assembled parts into a fully assembled build. 

Recognizing the potential to leverage one or more of these benefits, many industries have increased or begun 3DP divisions.

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RESOURCES:- 

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS. 

MAC-GRAW HILL PUBLICATIONS. 

Stay Tuned .

©️Mukesh Ch. Joshi

@ joshimukesh410820@gmail.com