MMK251 Services Marketing: Subtractive Vs Additive Manufacturing

Introduction:

The creation of digital representation of the object is extremely important with its geometrical attributes, texture and colour. This role is successively played with the help of Additive Manufacturing (AM) and Subtractive Manufacturing (SM). The traditional way of trimming of materials with the help of high-end tools is known as SM. On the other hand, the process by which the digital 3D data is used in construction the component in layers is known as AM. AM process effectively used the software platform that is commonly found in visual aids, tooling components, functional models, direct manufacturing etc. This paper describes the effective usage of additive (3D Printing) and subtractive (CNC machining) manufacturing process machines over various fields and several comparison and contradiction have also been discussed briefly.

Subtractive manufacturing processes:

The process of cutting away the material from the certain block of material to bring that block to a required shape is termed as the Subtractive manufacturing process (Guan, Qin, Liu, Yin, Peng, Lv, Sun and Wu, 2016).  This traditional process could be done manually but accurately this could be done through the CNC machine. As per the requirement of the designers, the CNC machine could perform the cutting task, which is concentrated on the three axes (say x, y and z plane) of the material. In doing so there could be a less chance for the designers to flip the material. There is a major advantage of adapting subtractive manufacturing since this process has the ability to extremely machine a miniature piece of material into a living hinge. This process could not be achieved with the 3D printing (Yang, Yhang, Song, Chen, Shen and Yang, 2016). Certain parts could be created with the help of the additive manufacturing that needs living hinge component while special components could be created with the help of a living hinge.

Industrial application:

Subtractive Manufacturing purely depends on granulating a part from a work piece of a superior bare by a computer numeric controlled (CNC) machine. The work of the CAM (Computer Aided Manufacturing) software transfers the CAD model to a tool path automatically to be used by the CNC machine. This will dictate the computation of the CNC machine with certain commands that includes sequencing, milling tools, and tool motion direction and magnitude. The milling machine could combine the burs of various shapes since the dental restoration features are said to be highly uneven. The tool positioning has the maximum accuracy when it is positioned at a distance of 10 meters. Certain compensation is also given by the CAM software for the diameter of the cutting tool that guarantees the milling bur not a leave the segment of the work piece until a desired surface is reached.

This particular dental CNC machine consists of multiple axes milling device, which will accelerate the dental work pieces with the 3D milling. This is the most traditionally used milling machine in the dental care unit. The most commonly used 3 axes milling system works with the estimated path value. Hence these milling machines have a minimum calculation along with the cumulative milling time. Unless, relocation takes place manually for the specimen, the 3 axes milling machine could not produce convergence, divergence, and extremely definite features or mill all the surfaces. It is necessary to incorporate 180° rotation for the blank for the machine that allows the 3D milling at the exterior and the interior surfaces that could also promote the convergence and divergence for the milled surface, which could also promote high definition for the surface features. Moreover, the speed of the milling machine could also be improved by introducing 2 milling burs concurrently. But a maximum prosthesis could not be promoted by the three axes machine due to the movement restriction by the milling tool.

The 4 axes machine could promote additional movements when compared to the 3 axes machine. This is very useful in comparison that has a long lifetime on comparison. The 5 axes milling machines promotes the rotation that could promote a complicated geometry rotation. They could promote a smooth surface for the external surface. This could be promoted by the tangential movement of the milling bur. For the manufacturing of complex part of the system it is essential to use the 5 axis milling machine that could make the curved holes. This could also produce complex acrylic denture base shapes. For dental purposes, the worth of the restoration is independent of the number of axes.  As an alternative, it replicates the method of dispensation of work pieces and CAD path of milling.

Additive Manufacturing Process:

Additive manufacturing popularly said as rapid prototyping or 3D printing has gained its attention recently that uses the principle of addition of materials in a layer with the particular processes. This requires an additional material to be fitted which seems to be designed with the help of certain software in a 3-dimensional structure. This can be directly implemented in the real-time application purpose, thereby decreasing its time and the complication. Instead of removing the materials, the addition of materials serves the system as a better head conductor and makes them lighter (Giuntini, Chen and Olevsky, 2016). This could remove certain constrains that are created by the conventional manufacturing by adding the materials layer by layer. At first, the materials are added in a thin powdered layer to the building platform and with the help of the laser, the powder diffuses in certain points by a computer-generated component design data. Then another layer is placed that fuses the material to form a predefined structure. The additive manufacturing technology can be used in wide variety of fields starting from the medical and marine application to the electronics and consumer accessories (Molla, Bjork, Olevsky, Pryds and Frandsen, 2014).

Industrial Application:

NASA engaged Wyle Labs’ Integrated Science and Engineering Group in Houston to assist in preparing the Robonaut 2 (“R2”) dexterous robot. This is said to be a real-time example that says that AM could be better in the time and cost savings. The work of this robot is to work with the astronaut that could undertake the risk and the complex tasks that could be highly dangerous.   The dexterity and the form factor of this robot are designed in such a way to work on the difficult environment with the astronauts. One of responsibility of the Wyle Labs’ in this contract was to build a one-to-one scale high-fidelity mockup of robot for use in the replication of possible missions. The external mockup of robot has to duplicate the geometry and the appearance of the original robot. The R2 is trained and simulated in such a way that it has to withstand rough handling.  The cost of this robot is $180,000 and the robot was delivered at the time duration of 8 months. Wyle twisted to RedEye on Demand, a module producer that uses the fused deposition modeling (FDM) method of AM with ABS Plastic. Once the CAD files have been received, it took about 2 weeks to complete the mission of RedEye that could cost about $36,000. This is said to be a disruptive technology that illustrates as an example for the Additive manufacturing.  AM technology is been used as a prototype and distributed manufacturing in various industries that includes design, engineering and production, automotive, aerospace, consumer products, medical and dental, and also it is widely used in various other industries. The robonaut 2 created by NASA is shown in the figure given below.

Figure 1 : Robonaut 2 created by NASA 

Similarity between Additive and Subtractive Manufacturing:

The energy intensity has been high reduced for both the AM and SM. Moreover the generated waste could also be minimized for both the technologies. Make-to-order manufacturing at the point of use in space and time to the exact specifications is required for these technologies. Moreover, the digital system should be improved for these technologies.

Difference between Additive and Subtractive Manufacturing:

For comparing both the AM and the SM manufacturing process we have defined a part that has been printed by both the methods. Figure 4 shows the block printed by additive manufacturing process. The block has a well defined feature and finish. The CNC milling machine encompasses a much diverse process than the 3D printer (Buffa, Campanella, Fratini, and Micari, 2016). Sufficient supervision should be provided for carrying out the process at CNC machine though similar files are being used for making the part. This is because the materials are removed from the block during the process. This part is sufficiently made with the help of wax. Previous studies have stated that the CNC machine could provide best finish or end product when compared to the 3D printer (Shao, Tang, Li and Peng, 2015). Figure 5 shows the block created by the CNC machine. This particular block has certain problem when this case is closely compared. The inner crevice of the M has not properly curved due to the miniature dimension and the size of the tool used for cutting. We could change the drill-bit of the machine by replacing it with the smaller one. But this could increase the complexity of the machine thus increasing the processing time.

Figure 2: Block created by the 3D printing

Figure 3: Block created by the CNC milling machine

After the manufacturing process, it is necessary to compare the measurements with the certain parameters (Wang, Wu, Ma, Lu and Yuan, 2016). There is a necessary usage of the scale factor that compares with the original model and this could be due to the occurrence of size restrictions. The end product of the CNC machining material could be slight thicker in their dimensions whereas with the 3D printing the end product could shrink from their original size due to their plastic material shrinking after the process of printing and cooling. Several parameters that are sufficiently measured for both the SM and AM process are as follows:

• Setup – Amount of steps and setup time for each machine
• Ease of use – how easy is it to use the machine
• Percentage of wastage of the material (%) – wasted material due to the process of printing and cutting
• Machining speed – Manufacturing the parts rapidly at certain time period
• Accuracy – Comparison of accuracy made with the model
• Surface finish – smoothness of the part surface

Discussing about these parameters it is said that the surface finish of AM is comparatively low when compared to the CNC method (Stráská, Jane?ek, ?ížek, Stráský and Hadzima, 2014). All the other parameters, Additive manufacturing leads its place that could be modeled with the help of CAD software platform. In fact, several trials could be possible only by the AM process.

Conclusion:

Although several equipments have been used in the process of AM and SM by quickly varying the parts, it is not necessary that they should have a convenient usage with the sufficient equality. In case of prototyping, this has an ease usage but this could not be applicable for educating environment. SM and AM has its own pros and cons. It’s pretty difficult to create a case of one type over the other as a broad recommendation (Wang, Zhang, Hu, Cai and Peng, 2017). This recommendation is based on the result and their application purpose. If an end product should be created at a faster rate that has the capability to create numerous parts concurrently then AM could be the best choice of selection. But while considering the surface finish of the material, then AM should be avoided that could shrink the material by size. Hence SM could be adapted in this case. It is intellectual to use the combination of both the SM and AM. We could design and create the parts by means of AM technology while SM could have a best end product with the smoother surface.  

References:  

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Stráská, J., Jane?ek, M., ?ížek, J., Stráský, J. and Hadzima, B. (2014). Microstructure stability of ultra-fine grained magnesium alloy AZ31 processed by extrusion and equal-channel angular pressing (EX–ECAP). Materials Characterization, 94, pp.69-79.

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