COURSE: ADVANCED MANUFACTURING PROCESSES
Module No. 5: OTHER PROCESSES
Lecture No-2 Rapid Prototyping Technology (RPT)
Background:
In this age of fast growth (rapid technology age), customer demands are increasing rapidly. Customers do not like to wait. The traditional processing time needs to be shortened. It is a ‘Buyers market’ today, instead of a ‘Sellers market’ as it used to be in the past. In the quest for fast manufacturing, all non-productive times need to be eliminated. The traditional method involves time loss on concept designing, manufacturing, assembly and testing. For example, in case of a foundry, lot of time is spent on pattern designing, making, getting the casting done and then evaluating its performance. This initially involves designing and redesigning, until a satisfactory product is developed, which is a very slow process. In order to get this time recovered, to overcome the slow trend and grow up with the requirements of the next generation, the most logical answer to the future of design and manufacturing is the Rapid Prototyping Technology (RPT).
Introduction:
Rapid prototyping (RP) is a technology wherein the physical modeling of a design is done using a specialized machining technology. The systems used in rapid prototyping quickly produce models and prototype parts from three-dimensional (3D) computer aided design (CAD) model data, magnetic resonance imaging (MRI) scan data and such data created from 3D digitizing systems. Using an additive approach for building shapes, the systems in RP join different materials like liquids or powder to form some physical objects. Layer by layer, the RP machines fabricate these powdered ceramic, wood, plastic and metal powders using very small and thin horizontal cross sections of the generated computer model. Rapid prototyping is an emerging technology, the definition of which is derived from the key concept - making it rapid. Rapid prototyping is creating a profound impact on the way companies produce models, prototype parts, and tooling. A few companies are now using it to produce final manufactured parts. It is
believed that rapid prototyping shall occupy a major share in manufacturing techniques in the years to come.
Steps in RPT
Creation of the CAD model of the (part) design,
Conversion of the CAD model into Standard Tessellation Language (STL) format, Slicing of the STL file into thin sections,
Building part layer by layer, Post processing/finishing/joining. Major RP Technologies:
1. Photo Masking or Solid Ground Curing technique. 2. LOM (Laminated Object Manufacturing)
3. SLA (Stereolithography)
4. FDM (Fused Deposition Modeling) 5. SLS (Selective Laser Sintering) 6. Thermo Jet Process
7. 3D Printing
8. Ballistic Particle Manufacturing (BPM) 1. Photo masking or Solid Ground Curing :
A mask is generated by electro-statically charging a glass plate with negative image of cross section of the required part. In the meantime, a thin liquid polymer is spread across the surface of the work-plane. The mask plate with a negative image of the liquid polymer is positioned over the thin polymer layer and exposed under the ultraviolet laser lamp for few seconds.
All parts of the exposed photopolymer layer get solidified with one exposure. However, the area shaded by the mask is left in a liquid form and is wiped off with vacuum suction head and replaced by hot wax which acts as a support to the solidified polymer layer. A face mill makes the surface of wax and polymer flat and to desired thickness. All the above steps are repeated till final model embedded in removable wax is obtained.
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ted for produ p is shown i ions when g sheet of pre-ctivates the layer of th layer of mat ater. The ba made signifi eat rectangul ction across broken awa eet, ceramic ucing parts f in Fig. 5.2.1 glued or wel -glued mater glue. Then a he object. Th terial. Then se plate mo ficantly wide
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RAPID MANUFACTURING:
Rapid manufacturing may be considered as an extension of Rapid-Prototyping technology. It involves automated production of parts by instructions directly fed by the CAD data which is modeled earlier. Currently, only a few final products are prepared by these machines. This technology is not suitable for mass production but for small batches and one-off production articles, it is cheaper since no tooling is involved. Some of the final components that are produced are: customized dinner-wares, helmets for individual heads (customized), jewellery patterns, spark erosion electrodes and reverse engineering parts.
Applications of RPT:
It is mainly used in modeling, Product Design and Development, Reverse Engineering applications,
Short Production Runs and Rapid Tooling,
In medical applications, RPT is used to make exact models resembling the actual parts of a person, through computer scanned data, which can be used to perform trial surgeries,
RP techniques are used to make custom-fit masks that reduce scarring on burn victims, Selective laser sintering (SLS) has been used to produce superior socket knees,
Very tiny, miniature parts can be made by electrochemical fabrication, In jewelry designs, crafts and arts.
Future developments:
As the Rapid Prototyping Technology gets further advanced, it can lead to substantial reduction in build-up time for manufacturing.
Further improvement in laser optics and motor control can improve the accuracy.
The development of new materials and polymers so that they are less prone to curing and temperature induced warpages.
Much anticipated development is the introduction of non-polymeric materials including metals, ceramics, composites and powder metallurgy.
Currently, the size is also a restriction; capability for larger parts shall be expected in the near future.
Currently, the demand is low and with the further technology advancement, awareness and training, this can be increased.
Advancement in computing systems and viability to support net designs from a distant country to be fed directly on the RP machines for manufacturing is a new possibility.
Limitations and Challenges ahead:
Unfamiliarity with the application of RPT exists. Therefore, its complete adaptability and how exactly this new and advanced technology will be of help and is not known.
In view of high equipment cost, very few organizations can invest in these new machines. Currently, RPT is more limited to modeling, specimen making and designing.
The RPT is at present limited to making of paper and plastic type products only. Replacing steel by composites is still not easy and people fear its implications.
RP companies usually limit the marketing efforts and industry awareness; hence most engineering and manufacturing professionals are not fully aware of the RP potentials.
The Fig. 5.2.6 indicates some common appliances, wherein the blades of fan, covers and components of oven, projectors are made by the rapid manufacturing techniques.
F Fig. 5.2.6 So ome applica ations of Ra apid Manufa acturing
