Principles Of Additive Manufacturing

Additive manufacturing (AM) is a general term for all technologies that produce parts by layer addition of material at the micron level, to achieve the required shape, besides of metal removal technique which is traditional subtractive process. During research period, AM the layer by layer manufacturing terminology has been standardised by the American society for testing and materials (ASTM) committee F42 on additive layer technologies.

In the beginning AM technologies were restricted because of commonly accepted leading name Rapid prototyping (RP) for the production of parts and prototypes, which was the term used for many years to describe all layer additive manufacturing processes. Advancement in the material, process and system hardware cleared that the parts could be manufactured with an adequate mechanical property to let for further applications. This allowed the production of end use models with layer additive technologies, so rapid manufacturing (RM) was adopted which distinguish the functional nature of the models produced from the prior RP parts and prototypes. Recently AM is used generally and RM and RP are only use to illustrate the particular application of AM technologies.

1.2.1: Principles of Additive Manufacturing

AM technologies fabricate models by fusing, sintering or polymerisation of materials in predetermined layers with no needs of tools. AM makes possible the manufacture of complex geometries including internal part detail that are approximately not possible to manufacture using machining and moulding processes, because process does not require predetermined tool paths, draft angles and under cuts.

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In AM the layers of a model are formed by slicing CAD data with professional software. All AM system work on the same principle; however, layer thickness depend upon parameters and machine being used and thickness of layer range from 10µm up to 200µm. Layers are clearly visible on the part surface in AM operation, which controls the quality of final product. The relation between thickness of layer and surface orientation is known as staircase effect. However, thinner the layer is the longer the processing time and higher the part resolution.

Layers in AM are built up at the top of the previous one in z axis. After layer gets processed the work platform is dropped down by the single layer thickness in z axis and the fresh material layer is recoated differently for number of other methods. In resin based system traversing edge flatten the resin, in powder based system deposited powder is spread using roller or wiper, in some system the material is deposited through a nozzle which deposits the required material. Because recoating time is even longer than the layer processing time. For that sake multiple parts are building together in the time of single material recoating build. Different software’s are available to position and orient part so that maximum number of parts can be built together. Available software’s are VISCAM RP and Smart Space used in MAGICS.

Some delicate parts produced through AM technologies need a support structure to hold the part in work platform during the build process. All AM machine uses different support structure that are designed from specific material for effective use of build parts. Commonly used support structures are thin small pointed teeth to minimising the part contact so that they can be removed easily with the hand tools.

1.3: Rapid Prototyping

Rapid prototyping processes are a relatively recent development, accurately described as layer manufacturing processes. The first commercial RP machine was released at the AUTOFACT show in Detroit (USA) in November 1987 by the company named 3D systems. The process begins with creating a 3D model using CAD software and it is identical for all built techniques. The model is then convert in to Standard Triangulation Language (STL) format, this format shows the 3D surfaces as an assembly of many planner triangles. At next stage STL file slice the 3D model in to layers. As we know the additive manufacturing is gradual process in which parts are manufactures through layers and each layers are joined and process continues until the final part formed. Post processing is usually required to improve the surface finish of the product.

RP’s additive nature allows is to create parts with complicated internal features which is not possible by other means like hollow areas and undercuts for that these parts sometimes supports are necessary. (palm, W. (1998, May). Rapid Prototyping primer. Retrieved November 4, 2010, from Learing factory Rapid prototyping home page: http://www.mne.psu.edu)

RP products often have low functionality and commonly used as a visual aids with in product development. However material selection decide the prototype testing for short term functionality parts. Most of the RP materials are polymer based, which is for limited part functionality. Although for little part functionality paper and starch based materials are used. RP modernised the product development with an ability to produce single and multiple physical models, facilitating the reduction of product development cycle time ranging for different industries.

1.3.1: Rapid prototyping technologies

There is a huge number of experimental RP technologies either in development or used by small groups of individuals. RP techniques those are currently commercially available including:

Stereolithography (SLA) is the first RP technique developed by 3D systems in 1987. SLA builds single layer at a time by tracing beam of laser on the vat of liquid UV curable photo polymer resin. UV light strikes the surface of the polymer resin and solidify the single layer of resin, when one layer is cured the built platform is dropped down by single layer thickness (Schmitt, Q. L. (2005). Rapid prototyping in dentistry: technology and application. Rapid prototyping in dentistry: technology and application , 11-13,42,44). A resin filled blade sweeps over the cross section and fill it with fresh material for further curing at the top of the previous layer, process continues until the model is produced. Material self adhesive property bond each layer and form a complete 3D model, fabricated part is cleaned in dawanol resin, alcohol and then cured in a UV oven. (wikipedia. (2010). wikipedia free encyclopedia. Retrieved November 1, 2010, from wikipedia web site: http://en.wikipedia.org/wiki/stereolithography)

Selective laser sintering (SLS) uses powdered materials. This is one of the systems major advantages that a part could be built in any fusible powdered material. SLS technology was developed in Texas University, which was commercialized in 1993 by company named DTM. In 2001 the DTM were bought out by 3D systems. (http://www.jharper.demon.co.uk/rptc01.htm)

This technology works by selectively sintering fine powder materials directly using an infrared (IR) laser from CAD. Numbers of thermoplastic materials are processed in SLS like nylon (polyamide) for rapid tooling application, aluminium filled nylon, polystyrene for sacrificial pattern in investment casting and gas filled nylon. Part produced through this process used as functional model as well as visual prototypes because of good mechanical properties.

However as compared to traditional tool steel the part had poor mechanical properties, so material required post processing to form dense models, thus it was very difficult to control the part accuracy because of introduced stresses in processing stage. With the combination of EOS GmbH and Electrolux a special alloy powder was developed, which did not develop shrinkage distortions. Moreover introduction of fibre laser technology allowed the introduction of Selective laser melting (SLM) since the fibre laser allowed the sintering of metals that were completely melted in to dense part with no need of post process infiltration.

Numbers of other technologies have been commercialised since 1991 such as laminated object manufacturing (LOM), fused deposition modelling (FDM), 3 dimensional printing (3DP). Recent technological availability of RP is increased with material diversity, which increased the efficiency of creating physical prototype in advanced product development.

1.4: Definition of Rapid Manufacturing

Firstly, it is essential to give a definition of rapid manufacturing. The way that several parts are manufactured will change in the future. RM has been explained as “the use of a CAD-based automated AM process to construct parts that are used directly as finished products or components” (Hopkinson et al. 2006, p. 1)

Since with the time change, the research on AM technologies and materials has advanced and the feasibility of fabrication of functional, low volume parts are increasingly in many industries. Many industries are examining the available technology and investigating the possibilities of design to increase the high functional component and to reduce product to market time. A key benefit of RM approach claimed that it proposes the opportunity of mass customization, however can be cost effective for individual short run part, clearing conventional designing constraints of manufacturing processes. RM greatly minimised wastage of raw material as compared to subtractive process, so got popular in aerospace industry, where expensive metal alloys are extensively used. The grade material such as titanium, ABS, nylon and aluminium has been the important part in the progress of RM technologies.

(http://www.hse.gov.uk/horizons/rapidmanufacturing.pdf)

The introduction of RM is not as simple as it first appears, although research in RM technologies and application are progressed by RP. The evolution is still in progress to link RM from research to actual manufacturing for that number of matters to be addressed that prevail need explanation and consensus before it can happen. RP produced prototype were not considered for product repeatability and quality measures. Since products of RM have proposed functionality, industrial certification and the requirements include material control, accuracy, speed, surface finish and part repeatability, so that RM is successfully applied in many industries including medical, automotive and aerospace to produce low quantity of small, high value parts with complex geometries that is difficult through conventional methods.

(http://www.rm-platform.com/index2.php?option=com_docman&task=doc_view&gid=129&Itemid=5)

In future, RM technology addition in industries can offer small complex design feature parts that ever imagined with great manufacturing facilities and the extension of approach. Development of advanced materials and equipment enable the fabrication of complex product by directly manipulating the matters on a molecular scale.

1.5: Selective laser melting (SLM)

1.5.1: SLM background

Selective laser melting machine was first introduced by Fockele and Schwarze (F&S) of Germany in 1999 with the support of Fraunhofer institute of laser technology that was steel powder based SLM machine. Later in 2004 first SLM machine named Realizer 250 SLM was released commercially after F&S coped up with MTT (MCP tooling technologies) and in 2005 high resolution machine named SLM Realizer 100 was released.

Since the release of the MCP Realizer SLM, other manufacturer such as Concept laser and EOS released machine with different process named Laser curing and Direct metal laser sintering respectively. Concept laser (GmbH) first released M3 Liner and M1 Cusing in 2001, later they released another machine named M2 Cusing to produce reactive materials like titanium and aluminium alloys. EOS released the machine named EOSINT M 270 DMLS in 2003 and termed as the most common machine for direct metal fabrication. In 2008 MTT and 3D systems proclaimed a distribution agreement for the rights to distribute SLM machines in Americas and Japan. In 2008-09 new version of SLM was released by MTT named SLM 250 and SLM 125.

1.5.2: Basic principles of SLM

SLM is a powder based additive manufacturing process that permits attaining 3D functional parts from a CAD data. SLM follows the same process route as SLS, where complete melting of powder occurs instead of sintering or partial melting.

Process begins with the deposition of thin layer of powder thickness ranging from 50µm to 75µm across a substrate platform. A high power fibre laser scans the powder surface, the generated heat melt the powder particles and form molten pool. Once the layer has been scanned, the platform drops down by single layer thickness in z axis and the fresh layer of powder is deposited and the process is repeated until the entire built is completed. Loose powders are removed once the fully dense part is complete. SLM parts must be completed in inert gas atmosphere such as argon to remove oxygen from the building chamber. Supports like thin teeth shaped are needed to secure hanging features due to shrinkage of material solidification. The substrate is removed from the build chamber once the process gets complete and supports are removed carefully.

SLM termed as the most viable techniques for direct fabrication of complex featured part of metals. SLM can permit the design optimization and production of the complex functionalities beyond the capabilities of traditional techniques, which is possible because of accuracy, versatility and the laser beam spot size. The small laser spot size minimizes the area to be melt enabling the manufacturing the part of high resolution. However, to be positioned SLM in RM category as a general method to achieve greater recognition in companies, methods and development need to be changed to perform and prove itself as being reliable, repeatable and cost effective production process.

SLM also known as freeform fabrication process and capable to build thin wall complex features models of high resolution and extends its capabilities than the conventional processes such as customised medical implant especially dental crown and bridge frame work, tooling inserts with conformal cooling channel and functional models.

SLM concerns primarily turn around the application of high powered fibre laser to generate high temperature to completely melt the powder, surface roughness is the main concerns of SLM because of high heat input causes material vaporisation and generation of spatter that subjected by melting and re-solidifying. But SLM parts cover committed microstructure parts and material properties that make possible this technique for the application.

Benefits of SLM:

Parts produced in this process are nearly 100% dense and have same mechanical strength as the original material

Almost no powder material is wasted, the loose powders which was not solidified can be reused

SLM offers minimum time to market, exact shape generation without an expansive moulds, process flexibility and great utilization of material

SLM powder bed technology permits cheap and fast powder metallurgy. The alloys to be tested can utilized straightly with in the prototyping apparatus and alloys can easily accustomed with the change of elemental ratio of powders

Drawbacks of SLM:

SLM is regarded as the high temperature gradient, which causes thermal stress build up and rapid solidification so coarse to grainy surface finished parts are produced

The inadequate availability of some materials in powder form restricts the range of material for processing. Process should be optimised for available material

(Selective laser melting, 10 December; http://raproto.com/?cat=31, accessed on 25/5/2011 and http://www.mtm.kuleuven.be/Onderzoek/a2p2/researchtopics/SLM, accessed on 26/5/2011)

1.5.3: SLM materials

SLM technology worked with all possibly relevant metals for part production. Process starts with identifying the physical behaviour of material being used with microscopic level of process understanding. In order to develop technique, the main quality aspect of parts being produced includes surface roughness, high functional strength, accuracy, density, hardness, residual stresses have to be observed before applied for the industrial applications. SLM system always develops parts with variety of materials and new ranges in which material property is easily changed with the property requirement with changing the mixture ratio. The range of materials are used that improved the new work powders such as tool steel, stainless steel, titanium alloy, aluminium alloy, cobalt chrome and inconel.

(http://www.mtt-group.com/data/pdf/extract/0413-MTT_2pp_SLM_A4_%20Flyer_v1.pdf)

Materials are described below according to property, alloy and applications:

(http://www.xyzinnovation.com.au/assets/slm-brochure_290709.pdf)

Titanium:

Mechanical properties: High strength, low thermal expansion, high corrosion resistance, excellent machinability and bio compatibility and low weight.

Alloys: Pure titanium, Ti-6Al-7Nb and Ti-6Al-4V

Applications: Medical implants, jewellery and design, F1 motor sport and aerospace

Cobalt chrome:

Mechanical properties: High strength, excellent corrosion resistance and bio compatibility and high toughness

Alloy: CoCr ASTM F75

Applications: medical implant, dental and high temperature

Stainless steel, tool steel:

Mechanical properties: High toughness, hardness and corrosion resistance and excellent machinability

Alloys: 316L stainless steel, H13 tool steel, 17-4PH, 50CrMo4, CrNiMo 13-4 and M333

Applications: medical implants, spindle and screws, plastic injection moulds and maritime

Aluminium:

Mechanical properties: Excellent alloying properties and processability and low density

Alloys: Al-Si-10Mg, Al-Si-12Mg, Al-Si9-Cu3, Al-Si-7Mg and Al-Mg4

Applications: Aerospace, automotive, consumer goods

Inconel:

Mechanical properties: Good mechanical strength, excellent corrosion resistance, outstanding welding ability and good creep rapture strength up to 700C

Alloys: Inconel 718 and Inconel 625

Applications: Aerospace, gas turbines, space shuttle and crafts, nuclear reactors and rocket motors

Integration of SLM in production systems:

Process chain

Function SLM process chain Part

Finish

(Machining)

Part Design

Process

Strategy

Process

Control

Process

Preperation

Designed for optimized Part orientation built strategy online defect Interface for

Functionality (quality/ build time) -built parameters detention machining

(light, weight, -support structure -under cuts etc -close loop control

energy efficient etc )

(www.materialscluster.lu/content/download/…/Wilhelm_Intermat2011.pdf, accessed on 30/5/2011)

SLM machines:

SLM50 Realizer:

World’s first SLM desktop machine to produce quickly and extremely accurately manufacture functional dental parts based on CAD data. It is well appropriate for dental laboratories and similar environments for the production of bridge and crown frame and brackets. This machine is capable to produce 100 parts/ months. SLM50 designed a component with height up to 40mm and diameter up to 60mm.

(http://www.industrialnews.org/2011/03/worlds-first-slm-desktop-machine-dental.html#ixzz1NtOkViL9)

SLM50 specifications

Construction volume Platform diameter 70 mm, max. construction height 40 mm

Thickness of layers 20-50 μm

Laser type Fibre laser 20 to 120 W

Power supply 16A, 230V

Power consumption 1.0 KW

Argon consumption approx. 30 Liter/h

Dimensions W800 x D700 x H500 mm

Weight approx. 80 kg

Software ReaLizer Control Software

Materials Cobalt Chrome, Stainless Steel 316 L,

gold-, silver-, palladium-, titanium alloys

(http://www.progold.com/GB/Files/Realizer.pdf)

http://1.bp.blogspot.com/-1XdSR-jq_tg/TZRWExUudDI/AAAAAAAAAEE/jRCp78C4t7M/s1600/SLM-50-1024×682.jpg

(http://www.industrialnews.org/2011/03/worlds-first-slm-desktop-machine-dental.html)

SLM100 Realizer:

Machine’s capability to design a component with 100mm high cylindrical construction area with 125mm diameter, because of the dropped laser spot size to 20µm. The machine can produce parts with delicate features, high surface quality and maximum wall thickness. SLM100 is appropriate for dental laboratories or related environments.

SLM100 specifications

Construction volume Platform diam. 125 mm Max. overall constr. height 100 mm

Layer thicknesses 20-100 μm

Laser type Fibre laser 20 to 200 W

Power supply 16A, 400V

Power input 1.5 kW

Argon consumption app. 35 l/h

Dimensions W900 x D800 x H2400 mm, SLM100A additional display support arm

Weight 500 kg

Software ReaLizer control software

Materials Tool steel H 13, titanium, titanium V4,

aluminium, cobalt chrome, stainless steel 316 L,

Inconel, Gold, ceramic materials under development

(http://www.realizer.com/en/wp-content/themes/realizer/ReaLizer.pdf)

(http://www.twi.co.uk/content/laser_slm.html)

SLM125:

The SLM125 machine presented with a range of laser from 100-200W with 30mm laser spot size diameter. This machine is capable to built pattern geometries of 200µm. Surface finish is controlled by laser scan approach, however build speed and surface finish is majorly depends on material that to be processed such as tool steel take more time than the aluminium and titanium. For fully dense part the both parameters surface finish and build speed should range from 15-30µm and 5-200cm3/hr respectively.

(http://www.sme.org/cgi-bin/find-articles.pl?&ME09ART20&ME&20090401&&SME&)

This machine has been designed for the simplicity to the users with in a industry with touch screen features, which cleans down the process. Robustness of the machine has given precedence to the adopters. The recoater blade used in this system is soft and carefully designed to reduce consumable cost by rotating same blade many times before replacement, and low filter element causes low gas consumption, results machine reliable and minimum in cost to users.

SLM125 specifications

Construction volume 125mm x 125mm x 125mm (x,y,z)

Layer thicknesses 20 to 100μm

Laser type Fibre laser 100-200 W

Power supply 16A, 400V

Power input

Argon consumptionm

Dimensions

Weight

Software ReaLizer control software

Materials Tool steel H13, titanium , titanium V4, aluminium,

cobalt chrome, stainless steel 316 L, Inconel

(http://www.mtt-group.com/data/pdf/extract/0413-MTT_2pp_SLM_A4_%20Flyer_v1.pdf)

MTT SLM25

(http://develop3d.com/profiles/box-clever)

SLM250:

This machine measures construction area of 250Ã-250Ã-250mm. The space in the processing area can be used to produce maximum number of parts with loading numerous parts at the top of each other. SLM250 is equipped with high power laser up to 400W with an automated filter machine to remove and recycle loose powders from the processing area. High part output makes it appropriate for industrial manufacturing process.

SLM250 specifications

Construction volume 250 x 250 mm , maximum construction height 220 mm

Layer thicknesses 20-100 μm

Laser type Fibre laser 100, 200 or 400 W

Power supply 16 A, 400 V

Power input 2.5 kW

Argon consumption app. 70 litres/h

Dimensions W1800 x D1000 x H2200 mm w/o sieving machine

Weight 800 kg

Software ReaLizer control software

Materials Tool steel H13, titanium , titanium V4, aluminium,

cobalt chrome, stainless steel 316 L, Inconel

(http://www.realizer.com/en/wp-content/themes/realizer/ReaLizer.pdf)

http://www.renishaw.com/media/img/gen/8a0166f5acc64a4190c81957ffe11b05.jpg

(http://www.renishaw.com/en/renishaw-acquires-mtt-investments-limited–14897)

D1: (http://doc.utwente.nl/52914/1/Wa1025.pdf)

D2: (http://pic.sagepub.com/content/220/6/857.full.pdf)

D3: (http://www.meditech.cf.ac.uk/pages/Individula%20Meetings/15th%20Nov%202007/presentations/R%20Bibb%20-%20PDR%20-%20ARUP%20Nov%202007.pdf)

SLM 125 machine run:

SLM 125 machine operated in the following manner:

Turn on from the back- MTT 125 screen showed up- Tap on the screen- Login with the user name MTT2- Tap light (light opens)- Tap to open the door- hold reset and open the door

Wiper reset: Tap to wiper and elevator on the screen- find wiper home- tap to substrate and set thickness to 0- press Esc- hold reset and open the door. Tap to wiper and elevator- find wiper home- Go to FWD POS- then unscrew the wiper arm from both ends

To draw material holder or wiper tension: unscrew both the nuts placed at the ends with pressing at the top. Attach back both the wiper tension and wiper arm to their respective positions- shut the door

Before placing the platform in the machine , first measure the base plate with vernier calliper then Tap to wiper and elevator- find wiper home- tap at substrate and set the thickness to 14.5- tap at table auto (it will built)- Tap at set datum- find table home. Go again- substrate set to 0- Go to top POS- Tap at Go to Centre to position wiper at the centre

C:UsersP10507465DesktopWiper_tension[1].JPG

Lift wiper and place paper then tight it. Clockwise rotation of screw to loose and anticlockwise to tight it. Later paper is removed. Just ensure that you should put the same pressure during screwing. After setting the wiper arm at the paper sheet thickness- close the door- tap to wiper and elevator- find wiper home

To clean filter assembly: Remove both caping placed at the top and bottom and do not forget to remove the rings- unbolt the holder- remove the filter (twist and draw)- clean the chamber- push filter to attach- bolt it

C:UsersP10507465DesktopFilter_Assy.JPGC:UsersP10507465DesktopFilter_removal.JPG

Tap to wiper and elevator- find wiper home- set datum- Dose to 3- Go to FWD POS- open with holding reset button. Close the door- find wiper home- Esc- select- auto (safe change filter valve- yes)- auto operation starts- click ok- Isolate change filter- confirm. Operation or part building starts and it logged out automatically after finishing the operation

Login again with user name MTT2- tap to wiper and elevator- find wiper home- Go to up- Esc- open the door

Cleaning: Slowly remove the powder with the brush- later hover it to clean properly. Unscrew the base plate- Brush again not to waste powder. Close the door- wiper elevator- find wiper home- Go to FWD POS- Esc- open the door holding reset button

Unscrew the wiper plate and clean- the red strip on the wiper arm turns black at worked portion means damaged. Unscrew material holder- brush the machine to restore loose powder to the holes (for titanium cleaning is really important)

Over flow cleaning: Unscrew loose powder holder underneath the platform. Put screw at close position and turn around to unscrew it to recover loose powders- screw it and place it in desired place including rings and caping

Set wiper back at the position to clean lense- unscrew it and clean it with proper handling

Dental suprastructure

The manufacturer is also is involved in the dental industry, for which the company manufactures products such as implant-supported suprastructures. Using patient-specific geometry data, acquired through medical imaging or 3-D scanning, the personalised structure is designed in software and printed in titanium. As a concluding step, the dental technician finishes off the structure and completes the final prothesis.

Through patented DentWise technology, geometry and surface retention related limitations set by traditionally moulded or milled suprastructures no longer apply.

“Through digital SLM technology, geometry and surface retention related limitations set by traditionally moulded or milled suprastructures no longer apply,” Mercelis says. “In addition, the implant connections are completed with high precision. Implant bars and bridges achieve a fit accuracy better than 20 µm at the implant interface. They also can integrate complex surface textures and sealing edges.” DentWise suprastructures are manufactured using ultra-strong titanium alloy (Ti6Al4V, grade V), which outperforms the commonly used titanium grade II in terms of mechanical propertie

(http://www.emdt.co.uk/article/selective-laser-melting)