RAPID PROTOTYPING TECHNOLOGIES Prof. Dr. Bilgin KAFTANOĞLU mfge.atilim.tr/kaftanoglu

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RAPID PROTOTYPING TECHNOLOGIES

Prof. Dr. Bilgin KAFTANOĞLUwww.mfge.atilim.edu.tr/kaftanoglu

Manufacturing Engineering Department

ATILIM UNIVERSITYANKARA

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WHAT IS PROTOTYPING?

Essential part of the product development and manufactuing cycle;

Assesing the form, fit and functionality of a design before a significant investment in tooling is made.

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Until Recently, prototypes:

were handmade by skilled craftsmen (i.e. High Cost); adding weeks or months to the product development time (increase time to market)

So: A few design iterations could be made before tooling went into production; Seldom optimization of designed parts or at worst parts did not function properly.

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Rapid Prototyping:

name given to a host of related technologies that are used to fabricate physical objects directly from CAD data sources;

These methods are unique in that they add and bond materials in layers to form objects.

Other names: Solid Freeform Fabrication,Layer Manufacturing

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With Rapid Prototyping,

Objects can be formed with any geometric complexity without the need for elaborate (very complex) machine setup and jigs and fixtures.

Objects can be made from multiple materials (Such as Aluminum and Polyamide, Copper and Steel), or as composites, or materials can even be varied in a controlled fashion at any location in an object;

The construction of complex objects are reduced to a manageable, straightforward, and relatively fast process.

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With Rapid Prototyping,

time to market in manufacturing is reduced;

the product designs are better understood and communicated;

rapid tooling to manufacture those products are made.

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The names of specific Rapid Prototyping processes:

• Stereolithography (SLA),

• Selective laser sintering (SLS),

• Fused deposition modeling (FDM),

• Laminated object manufacturing (LOM),

• Laser Engineering Net Shaping (LENS)

• Inkjet Systems and Three Dimensional Printing (3DP).

Each has its singular strengths and weaknesses.

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STEREOLITHOGRAPHY

• The most widely used rapid prototyping technology.

• Builds plastic parts or objects a layer at a time by tracing a laser beam on the surface of a vat of liquid photopolymer (Self Adhesive Material).

• Liquid photoplymer quickly solidifies wherever the laser beam strikes the surface of the liquid.

• Once one layer is completely traced, it's lowered a small distance into the vat and a second layer is traced right on top of the first.

• The layers bond to one another and form a complete, three-dimensional object after many such layers are formed.

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STEREOLITHOGRAPHY

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The platform in the tank of photopolymer at the beginning of a run.

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The objects have overhangs or undercuts which must be supported during the fabrication process by support structures.

These are either manually or automatically designed and fabricated right along with the object. Upon completion of the fabrication process, the object is elevated from the vat and the supports are cut off.

STEREOLITHOGRAPHY

The platform at the end of a print run, shown here with several identical objects.

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STEREOLITHOGRAPHY

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STEREOLITHOGRAPHY

The second most accurate and best surface finish of any rapid prototyping technology.

Wide range of materials with properties mimicking those of several engineering thermoplastics. Biomedical materials are available, and ceramic materials are currently being developed.

The technology is also notable for the large object sizes that are possible.

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STEREOLITHOGRAPHY

On the negative side,

Material is expensive, smelly and toxic;

Removing supports may adversely effect surface finish;

Parts often require a post-curing operation in a separate oven-like apparatus for complete cure and stability. Post Curing ensures that no liquid or partially cured resin remains.

The ultraviolet "oven" used to cure

completed objects.

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FUSED DEPOSITION MODELLING

• Second most widely used rapid prototyping technology, after stereolithography

• A plastic filament is unwound from a coil and supplies material to an extrusion nozzle.

The nozzle:

• is heated to melt the plastic and has a mechanism which allows the flow of the melted plastic to be turned on and off.

• is mounted to a mechanical stage which can be moved in both horizontal and vertical directions.

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• As the nozzle is moved over the table in the required geometry, it deposits a thin bead of extruded plastic to form each layer.

• The plastic hardens immediately after being extruded and bonds to the layer below.

• The chamber is held at a temperature just below the melting point of the plastic.

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FUSED DEPOSITION MODELLING Materials: ABS and investment casting wax, and more recently polyamide materials;

Researches for embedding Ceramic and Metal powders in polymer filament is going on.

ABS offers good strength;

Support materials:

Same material: Problems during removing;

Break Away Support System: Easily removed;

Water Works: Water-soluble support material.

(in ultrasonic vibration tank)

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• Office-friendly and quiet;

• Fairly fast for small parts or for those that have tall, thin form-factors;

• Very slow for parts with wide cross sections;

• The finish of parts have been greatly improved over the years, but aren't quite on a par with stereolithography.

• FDM offers great strength.

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INKJET

• Uses a single jet each for a plastic build material and a wax-like support material, which are held in a melted liquid state in reservoirs

• The materials harden by rapidly dropping in temperature as they are deposited

• After an entire layer of the object is formed by jetting, a milling head is passed over the layer to make it a uniform thickness

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INKJET

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INKJET

• Extremely fine resolution and surface finishes, essentially equivalent to CNC machines;

• The technique is very slow for large objects;

• While the size of the machine and materials are office-friendly, the use of a milling head creates noise which may be objectionable in an office environment.

• Materials selection is very limited and the parts are fragile

• Especially used in precise casting patterns for jewelry.

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INKJET

Jevelry Application A production cut in the middle

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3D PRINTING

• Developed at MIT;

• A measured quantity of powder is first dispensed from a similar supply chamber by moving a piston upward incrementally.

• The roller then distributes and compresses the powder at the top of the fabrication chamber.

• The jetting head subsequently deposits a liquid adhesive in a two dimensional pattern onto the layer of the powder

•The powder becomes bonded in the areas where the adhesive is deposited, to form a layer of the object.

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3D PRINTING

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3D PRINTING

• No external supports are required during fabrication since the powder bed supports overhangs;

• Offers the advantages of speedy fabrication and low materials cost;

• Probably the fastest of all RP methods;

• Recently color output has also become available;

• There are limitations on resolution, surface finish, part fragility and available materials.

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LAMINATED OBJECT MANUFACTURING

• object cross sections are cut from paper or other web material using a laser or a knife;

• The paper is unwound from a feed roll onto the stack and first bonded to the previous layer using a heated roller which melts a plastic coating on the bottom side of the paper

• The profiles are then traced by an optics system or knife

• Areas to be removed in the final object are heavily cross-hatched with the laser to facilitate removal.

• Excess paper is cut away to separate the layer from the web. Waste paper is wound on a take-up roll

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LAMINATED OBJECT MANUFACTURING• It can be time consuming to remove extra material for some geometries;

• The finish, accuracy and stability of paper objects are not as good as for materials used with other RP methods

• Material costs are very low, and objects have the look and feel of wood and can be worked and finished in the same manner

• Application: Patterns for sand castings.

• Limitations on materials, work has been done with plastics, composites, ceramics and metals. However, available on a limited commercial basis.

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Laser Engineered Net Shaping

• A technology that is gaining in importance and in early stages of commercialization.

• Designed for aerospace industry, especially to produce titanium parts.

• A high power laser (1400 W) is used to melt metal powder supplied coaxially to the focus of the laser beam through a deposition head.

•The head is moved up vertically as each layer is completed.

• Metal powders are delivered and distributed around the circumference of the head either by gravity, or by using a pressurized carrier gas.

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• In addition to titanium, a variety of materials can be used such as stainless steel, copper, aluminum etc.

• Materials composition can be changed dynamically and continuously, leading to objects with properties that might be mutually exclusive using classical fabrication methods.

• Has the ability to fabricate fully-dense metal parts with good metallurgical properties at reasonable speeds;

• Objects fabricated are near net shape, but generally will require finish machining.

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Before and after finish machining

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120x120x120 cm LENS Machine

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Selective Laser Sintering

Sintering:

• bonding of the metal, ceramic or plastic powders together when heated to temperatures in excess of approxiamately half the absolute melting tempertaure.

• In the industry, sintering is mainly used for metal and ceramic parts (Powder Matallurgy).

• After pressing (compaction) of the powder inside mold for deforming into high densities, while providing the shape and dimensional control, the compacted parts are then sintered for achieving bonding of the powders metallurgically.

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Compaction Sintering

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SINTERING

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Sintering in Rapid Prototyping

Sintering process used in Rapid Prototyping differs from the Powder Metallurgy, such as:

• Plastic based powders, in additon to metal powders.

• Local sintering, not overall sintering.

• Very short sintering period.

Laser (heat source) is exposed to sections to be sintered for a very short time. Hard to achive an ideal sintering.

In some applications, for achieving the ideal sintering, the finished parts are heated in a seperate sintering owen.

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• Invented by Carl Deckard during his Phd. studies in Texas University in 1987.

• Offers the key advantage of making functional parts in essentially final materials.

• The system is mechanically more complex than stereolithography and most other technologies.

• A variety of thermoplastic materials such as nylon, glass filled nylon, polyamide and polystyrene are available. The method has also been extended to provide direct fabrication of metal and ceramic objects and tools.

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Process:

1) Laser beam is traced over the surface the tightly compacted powder to selectively melt and bond it to form a layer of the object.

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Process:

2) Platform is lovered down one object layer thickness to accommodate the new layer of powder

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Process:

3) A new layer of powder is coated on the surface of the build chamber.

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Process:

4) The powder is supplied from the powder bins to the recoater.

This process is repeated until the entire object is fabricated.

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• The fabrication chamber is maintained at a temperature just below the melting point of the powder

• Heat from the laser need only elevate the temperature slightly to cause sintering. This greatly speeds up the process;

• No supports are required with this method since overhangs and undercuts are supported by the solid powder bed;

• Surface finishes and accuracy are not quite as good as with stereolithography, but material properties can be quite close to those of the intrinsic materials

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Three Types of Laser Sintering Machines:

1) Plastic Laser Sintering Machine

2) Metal Laser Sintering Machine

3) Sand Casting Laser Sintering Machine

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Plastic Laser Sintering:

• For direct manufacture of styling models, functional prototypes, patterns for plaster, investment and vacuum casting, for end products and spare parts.

• Volvo Steering Wheel

• Engine Block Pattern

• Plaster Invest. Pattern

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• A gear for Volvo Corp.

• Die Cast Parts (500 Al parts produced)

• Motor Housing

Metal Laser Sintering:

• For direct production of tooling, including for plastic injection molding, metal die casting, sheet metal forming as well as metal parts, directly from steel based and other metal powders.

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•V6-24 Valve Cylinder Head.

• Impeller

• Steering Block for a car

Sand Laser Sintering:

• Laser Sintering System for direct, boxless manufacture of sand cores and moulds for metal casting.

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METU SYSTEM

General Properties

Plastic Laser Sintering System X,Y Axes Alternating Scanning

Technical Specifications

Work Envelope:

-X Axis: 340 mm

-Y Axis : 340 mm

-Z Axis : 600 mm

Layer Forming Thickness:

0.15mm +/-0.05 mm

Max Laser Power: 50 W

Z Axis Production Speed: 30 mm / saat

Max Scanning Speed: 5 m/s

EOS EOSINT P380 Rapid Prototyping System

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Comparison Chart

TECHNOLOGY SLA SLS FDM INKJET 3D PRINTER LOM

Max Part Size (cm) 30x30x50 34x34x60 30x30x50 30x15x21 30x30x40 65x55x40

Speed average average to fair poor poor excellent good

Accuracy very good good fair excellent fair fair

Surface Finish very good fair fair excellent fair fair to poor

Strengths

market leader,

large part size,

accuracy,wide product

market leader,accuracy,materials,large part

size.

office okay,price,

materials

accuracy,finish,

office okay

speed,office okay,

price,color,price

large part size,

good for large

castings,material cost

Weaknessespost

processing, messy liquids

size and weight,

system price,surface finish

speed

speed,limited

materials,part size

limited materials,

fragile parts,finish

part stability,smoke,

finish and accuracy

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Additive Fabrication vs Subtractive Fabrication

• Additive Fabrication methods (RP) can not become complete replacement for the Subtractive Fabrication methods (Milling, Turning, EDM etc.)

• Subtractive methods:

• have reached an extraordinary level of development and they continue to evolve.

• they are fast, versatile, inexpensive, readily available and well-understood by large numbers of practitioners.

• in many cases they are quite sufficient to make prototypes rapidly,

• no equal when it's necessary to make very precise parts in final materials.

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Additive Fabrication vs Subtractive Fabrication

• Additive technologies are instead complementary to subtractive ones, if

the situation calls for:

1.complex or intricate geometric forms,

2.simultaneous fabrication of multiple parts into a single assembly,

3.multiple materials or composite materials in the same part.

Additive technologies make it possible to completely control the composition of a part at every geometric location. Thus, RP is the enabling technology for controlled material composition as well as for geometric control.

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Limitations of RP Methods

1) ACCURACY

• Stair Stepping:

Since rapid prototyping builds object in layers, there is inevitably a "stairstepping" effect produced because the layers have a finite thickness.

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1) ACCURACY

Precision:

• tolerances are still not quite at the level of CNC,

• Because of intervening energy exchanges and/or complex chemistry one cannot say with any certainty that one method of RP is always more accurate than another, or that a particular method always produces a certain tolerance.

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1) FINISH

The finish and appearance of a part are related to accuracy, but also depend on the method of RP employed. Technologies based on powders have a sandy or diffuse appearance, sheet-based methods might be considered poorer in finish because the

stairstepping is more pronounced.

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1) Secondary Operations

• Parts made by stereolithography are frequently not completely cured when removed from the machine. Final cure is effected in a box called a post-cure apparatus (PCA)

• Parts made by three dimensional printing (3DP) and MultiJet Modeling (MJM) can be very fragile and might not be able to take normal handling or shipping stresses. These parts are often infiltrated with cyanoacrylate adhesive or wax as a secondary operation to make them more durable.

• Metal parts will almost certainly require final machining and must usually undergo a thermal baking cycle to sinter and infiltrate them with a material to make them fully-dense.

• Other than powder-based methods all other methods require a support structure to be removed in a secondary operation which may require considerable effort and time.

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Support structure (red material), water-soluble, fused deposition modeling (FDM).

Support structure, stereolithography.

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3) SYSTEM COSTS

RP systems cost from $30,000 to $800,000 when purchased new. The least expensive are 3D Printer and FDM systems; the most expensive are specialized stereolithography machines.

In addition, there are appreciable costs associated with training, housing and maintenance. For example it can cost more than $20,000 to replace a laser in a stereolithography system.

4) Material

High cost. Available choices are limited.

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RP in Medical Applications

Oral Surgery

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Modelling in Medical Applications:

Models are created using medical imaging data obtained from

• a standard Computed Tomography (CT) or

• Magnetic Resonance Imaging (MRI).

Bone structures such as skull or pelvis are all imaged using CT. Soft tissue structures such as brain and organs are best imaged by MRI. The “slice” data from CT or MRI are processed into 3D images by using sophisticated software.

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Oral Surgery

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Oral Surgery

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Prosthesis Applications

A bone structure which was produced from ceramic powder embedded paper material in LOM.

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Bone Structure with the cranial vasculature highlighted in red. This model was made using SLS with a special material called Stereocol. (Coloured when exposed to high power laser)

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Actual living tissue cells are extracted from the patient and seeded onto a carrier which accomodates and guides the growth of new cells in 3D within laboratory environment.

TISSUE ENGINEERING

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THANK

YOU!

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RAPID PROTOTYPING TECHNOLOGIES Prof. Dr. Bilgin KAFTANOĞLU mfge.atilim.tr/kaftanoglu