Keywords

9.1 Introduction

Additive manufacturing covers an extensive range of processes and techniques with a wide array of capabilities to manufacture the final product. However, what all the different processes and technologies have in common is the way production is carried out, that is one layer at a time to build up the final product. In additive manufacturing, the first step is to generate a 3D solid CAD model of the object. Then this CAD model is sliced into layers to create digital information based on the geometry of individual layer. This digital information is then used to control the tool path which combines the material layer by layer into the final product as shown in Fig. 9.1 (Zhai et al. 2014). AM is not just used for creating prototypes, with improvement in process, hardware and materials it has become possible to manufacture finished products. Several AM processes have been introduced in the market and the ones which were considered the most relevant in the past and have the greatest potential for different industries in the future are described below.

Fig. 9.1
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Additive manufacturing process flow

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9.2 Stereolithography

Stereolithography (SLA) is one of the most commonly used AM processes for rapid prototyping and it is the first commercially available rapid manufacturing technology. SLA was developed by 3D Systems, Inc. in 1986 and it is characterized by photopolymerization of a material. In SLA, a photopolymer resin reacts with the ultraviolet laser and cures to form a solid layer upon layer to produce the final product. The first step in the process is to generate a 3D solid model in a CAD software which is then converted to a STL file in which the model is sliced into different layers containing information regarding each layer. This information will be used later to control the tool path. The part is built on a movable platform which is inside the vat containing the photopolymer resin as shown in Fig. 9.2. The UV laser scans the surface of the vat in X-Y axes per the STL file supplied and the resin solidifies precisely where the UV laser hits the surface. After completion of one layer the built platform descends by one layer thickness in the z axes (25–100 µm) and the built layer is recoated with photopolymer resin. The subsequent layer is then scanned and cured. This process continues until the entire object is complete, the excess is then drained and can be reused.

Fig. 9.2
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Stereolithography mechanism

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Once the part is completed, the resin support structure is removed and the cleaned part is put in a UV oven for further curing. After the curing process, finishing is carried out which might require sanding and filing the part to achieve the desired surface finish (Gibson et al. 2014; Melchels et al. 2010).

9.3 Digital Light Processing

Digital light processing (DLP) works on a similar principle as SLA, using a light source to cure photopolymers to manufacture the part. Unlike SLA, which is a bottom-up process, DLP is a top-down process and it is much faster than SLA as an entire layer is cured at once. The DLP printer mechanics are shown in Fig. 9.3.

Fig. 9.3
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Digital light processing (DLP) mechanism

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The DLP printer consists of 3 main components; build platform, resin tank (vat) and the projector. The DLP print process is very simple and is illustrated in Fig. 9.4. As illustrated in Fig. 9.4 the process begins with the build platform lowering down to the vat floor up to one layer thickness (A). The DLP projector which is placed beneath the vat, projects an image slice to cure one layer at a time (B). Then the vat is tilted to separate the cured layer from the vat floor (C). The build platform then rises by one layer height (D). The projector exposes the next image slice and cures the second layer (E). The process repeats until the product is complete (F). One of the advantages of DLP is that it requires a shallow resin vat to carry out the process, so less resin is wasted but similar to SLA the finished parts require post processing like removal of support structures (Wu and Hsu 2015; Bomke 2015; Petrovic et al. 2011).

Fig. 9.4
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Digital light processing (DLP) print process

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9.4 Fused Deposition Modeling

Fused deposition modeling (FDM) is the most favorable technique for rapid prototyping among all other layer additive manufacturing processes due to its low-cost machinery, ease of operation and durability of final parts. FDM is ideal for concept models, functional prototypes and low volume end-use parts. The FDM process, like other AM processes, begins by slicing the CAD model into layers. The information is then fed to the machine, which constructs the part one layer at a time. A thin thermoplastic filament is fed to the extrusion nozzle, which heats up the material just above its melting point and deposits it on the build platform in a prescribed pattern. The layers harden as soon as they are deposited and bond to the previously deposited layers. The extrusion nozzle continues to move in a horizontal x-y plane while the build platform moves down, building the part layer by layer as shown in Fig. 9.5. FDM also consists of a second extruder nozzle, which deposits the support material for overhanging geometries. Most commonly used modeling materials for FDM are ABS and PLA, whereas the support material is usually water soluble and it is easily washed away once the part is completed. Post completion process such as hand sanding can be carried on the completed part to achieve a smooth and even surface (Sood et al. 2012; Sun et al. 2008).

Fig. 9.5
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Fused deposition modeling (FDM) printer

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9.5 Selective Laser Sintering

The selective laser sintering (SLS) processes like other AM process begins with creating a 3D CAD model of the part, converting it to a STL file, which can describe the surface geometry of the part by translating it into several small triangles. The model data is then transferred to the build station control software where the part is sliced into thin layers and sent out to the SLS printer. The machine prepares the first layer as the roller spreads a thin layer of the powdered build material across the build platform. The laser then scans the cross section on the material in x-y axes per the 3D data fed to the machine. As the laser scans the surface it heats up the powder material and increases its temperature close to its melting point thereby fusing the powder particles together forming a solid layer. Material which is not part of the model geometry is left unsintered and acts as a support structure. The build platform then lowers by a single layer thickness and the leveling blade sweeps across the build platform and covers it with another layer of powdered material. The laser then selectively sinters the next layer and the process repeats building layer upon layer until the model is completed. Once the part is completed then the powder bed is removed and the part is obtained. The part is then brushed down to remove excess powder surrounding it (Kruth et al. 2003, 2005). The SLS process is illustrated in Fig. 9.6.

Fig. 9.6
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Selective laser sintering (SLS) mechanism

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9.5.1 Binding Mechanism in SLS

Sintering forms bonds between particles when they are heated. Selective laser sintering and SLS derived technologies use different binding mechanisms as shown in Fig. 9.7. Kruth et al. (2005) classified these binding mechanisms in 4 different categories.

Fig. 9.7
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Selective laser sintering binding mechanisms

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Solid state sintering (SSS) is a thermal process which gives rise to the formation and growth of necks between adjacent powder particles. This process is slow and occurs between the melting temperature of the concerned material (TM) and \(\frac{\text{TM}}{2}\). In sintering the atoms of the powder material diffuse across the boundaries of the particles, fusing the particles together and creating a solid piece as illustrated in Fig. 9.8. SSS is a slow process, thus it is necessary to preheat the power material to increase the diffusion rate of atoms (Kruth et al. 2005).

Fig. 9.8
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Sintered and unsintered powder particles

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Chemically induced binding is the second consolidation mechanism. Klocke et al. in their study investigated the SLS manufactured SiC ceramic part. During the manufacturing of this part the laser-material interaction time was kept short, which eliminates the possibility of diffusion processes taking place in SSS. Furthermore, no binder element was used during the process. The SIC particles disintegrated into Si and C when heated up at a higher temperature. SiO2 was formed because of free Si and acted as a binder element between SiC particles. Thus, the parts were composed of a mixture of SiC and SiO2 (Klocke and Wirtz 1997).

In liquid phase sintering (LPS) partial melting takes place depending on the type of powder used. LPS is further divided into different categories but each consists of two different materials, one of which is the structural material (unmolten core material) whereas the other one is the binding material. The different categories are as shown in Fig. 9.7.

The importance to increase the density of the final parts and to reduce/eliminate the post processing steps leads to the development of selective laser melting (SLM) which will be discussed further in the following section. In this process the object is built layer by layer by completely melting the powder particles in the built chamber rather than sintering them. SLM achieves full melting of powder particles as compared to direct laser metal sintering (DMLS) which works on the same sintering principle as it is derived from SLS. The group is divided into three subgroups, which are as follows (Kruth et al. 2005); single component, single material powder consists of powder particles made of a single material such as aluminum, titanium, etc. The laser completely melts the powder particles to form the 3D part. Single component, alloyed powder particle consists of powders with alloyed material in each individual grain. Many different kinds of SLM alloys have been tested and are commercially available in the market. In fusing powder mixture the processes are classified into SLM (complete melting of powder particles) or partial melting (some particles melt whereas others do not) based on the degree of melting.

9.6 Direct Metal Laser Sintering

Direct metal laser sintering (DMLS) is derived from SLS and works on the same principle of sintering powder particles layer by layer to manufacture a 3D part. SLS refers to the process being applied to many different materials such as polymers, ceramics, etc., whereas DMLS refers to the sintering process being applied to metals only. A variety of materials are commercially available for DMLS such as aluminum, stainless steel, inconel, etc. (Stratasys Direct Manufacturing: Direct Metal Laser Sintering. Materials. Stratasys Direct Manufacturing). Binding mechanism in DMLS is quite complex and may involve full melting, partial melting, liquid phase sintering or all of the above (Kruth et al. 2005).

9.7 Selective Laser Melting

A lot of research has been carried out on selective laser melting (SLM) and this process has been applied to several different materials such as aluminum, titanium, stainless steel, etc. Rickenbacher et al. (2013) carried out tensile, relaxation and creep test on SLM processed IN738LC material for high temperature application. The tensile test results indicated that SLM processed specimens showed higher strength properties than cast IN738LC. Lore et al. (2010) investigated the effect of SML process parameters such as velocity, hatching space and scanning strategy on the SML processed parts. Aman et al. (2014) studied the effects of two commonly used scan strategies in SLM. The material used was Inconel 625 and the two scanning patterns are as follows.

9.7.1 Rotated Strip Pattern

In this pattern, each individual layer is divided into a series of strips (red line in Fig. 9.9), which run across the whole layer (Anam et al. 2014). Raster scan vectors are used within each layer as illustrated in Fig. 9.9. In the rotated strip pattern approach, for each new layer the strips rotate counterclockwise approximately by 67° compared to the previous layer.

Fig. 9.9
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Rotated strip pattern

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9.7.2 Alternative Block Pattern

This pattern is similar to a brick stacking sequence. As shown in Fig. 9.10, each layer is divided into rectangular blocks, within each block there are raster scan vectors (Anam et al. 2014). The scan vectors rotate at an angle of 90° between in-line blocks and the blocks themselves shift by half a width between each layer.

Fig. 9.10
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Alternative block pattern

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Based on the study of different patterns Aman et al. (2014) concluded that SLM is a complex process and the microstructures depend on a variety of different process parameters, but the scanning velocity and scanning strategy significantly affect the orientation of grains. It was also discovered that the elongated grains grow favorably in the build direction. Murr et al. (2009) in his study compared the microstructure and mechanical behavior of SLM and EBM processed parts with conventionally wrought and cast products of Ti-6Al-4 V. The study concluded that EBM and SML processed parts demonstrated similar or superior mechanical properties compared to wrought and cast products of Ti-6Al-4 V. It was also noted that the tensile strength increased by 50% compared to wrought products. Hamza et al. (2016) in his study investigated the effect of different build directions on fracture toughness, tensile strength and density of 316L part processed by SLM. 60% higher ultimate tensile and yield strength was observed for vertically built part as compared to horizontal built part. Even the fracture toughness of 316L stainless steel part built in the vertical direction was 30% higher than the horizontally built part.

9.8 Applications of Additive Manufacturing

Additive manufacturing is fairly new compared to conventional manufacturing techniques, but it has already revolutionized the manufacturing industry. It has significantly changed the designing process, manufacturing and assembly in different industries. Nowadays additive manufacturing is no longer just used for rapid prototyping, but it has ventured successfully into rapid tooling, rapid manufacturing and repair (Azam et al. 2018). AM has been gracefully adopted by aerospace, medical and automotive industry. AM has also made its way into the oil and gas industry with huge success. GE has already begun 3D printing end burners for gas turbine combustion chamber and other companies like Halliburton are actively exploring the possibilities of utilizing additive manufacturing for rapid prototyping and manufacturing fully functional parts. It is estimated that by 2021 the global value for additive manufacturing products would go up to $10.8 billion (SmarTech Publishing 2021; R. A. of Engineering and Engineering Royal Academy 2013). Many different factors have led the transition from rapid prototyping to additive manufacturing. Advancement in technology, reduced cost and broad range of materials have pushed this technology toward manufacturing of consumer products and rapid tooling rather than being just used for rapid prototyping (Campbell et al. 2012; Azam et al. 2018).

9.8.1 Aerospace

Aerospace industry has always been an early adopter and innovator. The innovation in aerospace has always aimed at reducing the cost and weight of parts while maintaining the highest standards without compromising on safety. For the past 20 years, additive manufacturing has been employed by aerospace industry for prototyping, testing concepts and now it is being utilized to manufacture end-use parts (Hiemenz 2013). The forward fuselage of the Boeing F/A-18 comprises of almost 150 parts that have been manufactured through selective laser sintering (Radis 2015). GE Aviation for its passenger jet engine known as “LEAP” is using 3D printed fuel nozzles as shown in Fig. 9.11. LEAP consists of 19 3D printed fuel nozzles which are five times stronger than the previous model. In 3D printing these nozzles allowed engineers to simply design and reduce the number of brazes and welds from 25 to just 5 (Kellner 2014).

Fig. 9.11
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3D printed fuel nozzle

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NASA is breaking grounds with 3D printing in space to facilitate its astronauts. NASA’s space station 3D printer built a ratchet wrench (Fig. 9.12) along with 20 other objects during its first phase of operations. NASA is exploring the opportunity of 3D printing in space for tool manufacturing as well to manufacture objects which previously could not be launched to space (Harbaugh 2015).

Fig. 9.12
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3D printed ratchet wrench

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TWI employed the LMD process to manufacture a helicopter engine combustion chamber as shown in Fig. 9.13. The component consists of overhanging geometries but it was built without support structures by utilizing the 5-axes of the LMD printer. The thin walled part showed a density of more than 99.5%. The part was built in 7.5 h with 70% powder efficiency (Hauser 2014).

Fig. 9.13
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LMD processed helicopter engine combustion chamber

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In academic literature Seabra et al. (2016) optimized the topology of an aircraft bracket (Fig. 9.14) to be manufactured using SLM. Compared to the original part, the new part had 54% reduced material volume and weigh 28% less though the material was changed from aluminum to titanium which resulted in increased factor of safety by 2.

Fig. 9.14
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a Mesh of original component, b mesh of optimized component

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9.8.2 Medical

In medical industry customization is really favored as the products must be tailored fitted for each patient, available on demand and at a reasonable price. Additive manufacturing fulfills all these demand, thus it is highly preferred by the medical industry. Additive manufacturing offers patient-specific parts which are strong and lightweight consisting of lattice structures as shown in Fig. 9.15. Such structure was near impossible to manufacture using conventional technologies. Alphaform AG with its partnering firm Novax DMA manufactured a cranial implant for an Argentinian patient. The patient needed a large implant after a stroke-related surgery. A lot of different factors had to be considered such as it should fit perfectly, allow for fusion of bone tissues of the skull, etc. Nova DMA manufactured a lattice structure implant which was capable of meeting all the required characteristics. The implant was 95% porous, which facilitated the flow of fluid though it with least possible resistance and allowed for bone tissue fusion with the outer edges. The implant as shown in Fig. 9.15 was manufactured using EOSINT M 280 (DMLS) (Concept Laser: ConceptLaser—Fast! Direct Components in Vehicle Construction).

Fig. 9.15
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Titanium lattice cranial implant manufactured using additive manufacturing

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In 2014 the hip bone of a 15-year-old patient from Croatia was adversely affected by an aggressive bone cancer. The doctors had no choice but to reconstruct a portion of his hip bone after removing the effected bone tissues. The challenges were that the replacement bone had to be precise and as close to the original as possible so that it perfectly fits and all the angles match one another. Another challenge was to make it strong and lightweight. Alphaform manufactured the replacement bone using additive manufacturing with great success. The replacement hip bone fulfilled all the medical requirements and it is illustrated in Fig. 9.16. The implant consists of a large number of cavities which helped in reducing the weight and this perfect balance of strength and weight was only possible due to additive manufacturing technology (EOS: Medical: alphaform—production of hip implant by using additive manufacturing).

Fig. 9.16
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Titanium hip implant

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Adler Ortho Group is an Italian manufacturer of orthopedic implants and is widely known for its innovative designs. Utilizing Arcam’s EBM technology they manufactured the Fixa Ti-Por acetabular cup shown in Fig. 9.17 and launched it commercially in 2007 after being awarded the CE certification. The new acetabular cup promotes bone ingrowth and after its launch within one year 1000 acetabular cups were implanted with excellent post-op feedback from surgeons (rapidNews: The CE-certified Fixa Ti-Por Acetabular Cup. Manufactured with an Integrated Trabecular Structure for Improved Osseointegration).

Fig. 9.17
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Fixa Ti-Por acetabular cup

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9.8.3 Automotive

Additive manufacturing can drastically reduce weight and increase the strength to weight ratio, thus its highly ideal for automotive industry. Automotive industry has been using AM for new design and manufacturing of lighter, stronger and safer products with reduced manufacturing time and cost. AM is highly beneficial for manufacturing of small quantities of parts such as gearbox, driveshafts, etc., for luxury or motorsports vehicles (low volume vehicles) (Guo and Leu 2013).

In product development, rapid prototyping has become a standard practice. Designers and engineers at AMP Research printed a prototype of a fuel door using the Dimension 3D Printer by Stratasys. The 3D printer is based on the FDM technology and the fuel door, shown in Fig. 9.18, for General Motors’ Hummer H2 sport utility vehicles were manufactured using ABS plastic. The prototype allowed the engineers to test and evaluate the model before finalizing and sending it out for production (Stratasys: AMP Research From Concept to Reality in Record Time. Stratasys).

Fig. 9.18
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Fuel door prototype for Hummer 2 sport utility vehicle

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Ducati is well known for its innovative design, unique engines and advanced engineering in the motorbike industry. By introducing FDM technology by Stratasys into their design and prototyping phase, Ducati reduced the design and validation cycle by a considerable amount, thus consequentially reducing the time for launching of new products in the market. FDM has enabled Ducati to build functional prototypes and conceptual models from ABS, polycarbonate, etc. During the development process of Ducati’s Desmosedici race bike’s engine, the design team was able to cut 20 months by utilizing FDM and completed the designing and assembling of the engine in just 8 months. Previously the engines would have taken 28 months from designing to final assembly as most of the prototypes were outsourced (Motorcycle Maker Cuts Development Time with 3D Printing. Stratasys).

Concept Laser manufactures many different automotive parts from materials such as stainless steel, aluminum alloys, titanium alloys, etc. The advantages of using additive manufacturing for automotive parts include reduced manufacturing time, design freedom, no tooling changeover cost and overall cost (Concept Laser 2015; Concept Laser: ConceptLaser—Fast! Direct Components in Vehicle Construction).

9.8.4 Oil and Gas

Additive manufacturing is still in the early stages of adoption in oil and gas industry but it has a great potential for all sectors of this industry (upstream, midstream and downstream). Based on their new report “Additive Manufacturing Opportunities in Oil and Gas Markets” SmarTech Publication believes that AM will cut cost radically for oil and gas industry and it will open up a new era of opulence and opportunities. “I think there is a widespread understanding that the technology has the potential to be just as disruptive for oil and gas companies as it has been for the aerospace, automotive, healthcare and consumer electronics companies of the world. And that’s really exciting to me” says 3D Systems CEO Avi Reichental (Peters 2015; Sher 2016). Magma Global and Victrex are taking additive manufacturing for oil and gas industry to a new level with their new flexible m-pipe. Using laser sintering and Victrex’s PEEK thermoplastic composite material, they have 3D printed the new flexible m-pipe for use in oil and gas industry. The pipe which will be used for a hydraulic oil and gas pump is capable of being deployed at a depth of 10,000 feet and can handle high pressure and flow rate (Alec 2016; Victrex 2016).

Two companies Furgo and 3D at Depth came together to ensure that an abundant subsea well off the coast Oceania, Australia could fully reach final abundant status. The well in question was drilled decades ago and it was 110 m below the surface of the ocean. Almost no information was available regarding the wellheads, for example measurements, manufacturer, etc., and all this information was essential to acquire the abandoned status. To acquire this information the services of 3D at Depth were hired and using subsea LiDAR scanning 3D data regarding the damaged and outdated wellheads was collected. Using this data, a 1:1 model of the damaged part was printed using a FDM 3D printer. The model helped Furgo to fabricate tools for removing the existing cap and completing the decommissioning project (Goehrke 2016).

GE Oil and Gas at its Kariwa plant in Niigata prefecture, Japan has been utilizing a hybrid metal laser sintering 3D printer (LUMEX Avance-25 metal 3D printer) to manufacture different parts for company’s Masoneilan control valve, which is used for several different applications in the energy industry. GE Oil and Gas has been relying on AM for manufacturing these parts because AM offers freedom of design and intricate shapes can be manufactured with ease within a short time. These parts can be designed and fabricated in a matter of weeks compared to months that conventional manufacturing would take (Krassenstein 2015).

Mentioned above are just few examples of additive manufacturing in the oil and gas industry. The oil and gas industry would be the next big adopter of this technology. Companies like GE and Haliburton have already invested in this technology and are actively exploring its possible applications in oil and gas. Furthermore, rising costs, plummeting energy price and long delay in projects are few factors that are shifting attention toward the use of AM in O&G industry.

9.9 Conclusion

With growing interest of AM in various industries, the technology is constantly being developed and commercialized everyday. The purpose of AM technologies in industry ranges from rapid prototyping to producing end user functional products. Many AM processes are available today with the ability to control input parameters to produce a desired final product. The process parameters of the AM process affect the quality and properties of the final product and can be adjusted for a specific application, depending on end-use requirements. Therefore, sound understanding of specifications of the final product is necessary to choose the right AM process.