3 (a) Discuss the advantages and disadvantages of welding compared to other types of assembly operations? ​​​​​​​3 (b) Explain the three main Rapid Prototyping Process. Discuss the advantage and limitation of each process.

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3 (a) Discuss the advantages and disadvantages of welding compared to other types of assembly operations?
​​​​​​​3(b) Explain the three main Rapid Prototyping Process. Discuss the advantage and limitation of each process.

EXPERT ANSWER

3. a) Merits and demerits of welding

Merits

  1. As no hole is required for welding, hence no reduction of area. So structural members are more effective in taking the load.
  2. In welding filler plates, gusseted plates, connecting angles etc, are not used, which leads to reduced overall weight of the structure.
  3. Welded joints are more economical as less labor and less material is required.
  4. The efficiency of welded joint is more than that of the riveted joint.
  5. The welded joints look better than the bulky riveted/butted joints.
  6. The speed of fabrication is faster in comparison with the riveted joints.
  7. Complete rigid joints can be provided with welding process.
  8. The alternation and addition to the existing structure is easy.
  9. No noise is produced during the welding process as in the case of riveting.
  10. The welding process requires less work space in comparison to riveting.
  11. Any space of joint can be made with ease .
  12. Demerits
  13. Welded joints are more brittle and therefore their fatigue strength is less than the members joined.
  14. Due to uneven heating & cooling of the members during the welding, the members may distort resulting in additional stresses.
  15. Skilled labor and electricity are required for welding.
  16. No provision for expansion and contraction is kept in welded connection & therefore, there is possibility of racks.
  17. The inspection of welding work is more difficult and costlier than the riveting work.
  18. Defects like internal air pocket, slag inclusion and incomplete penetration are difficult to detect.

Different rapid prototyping methods

Stereolithography (SLA) or Vat Photopolymerization

This fast and affordable technique was the first successful method of commercial 3D printing. It uses a bath of photosensitive liquid which is solidified layer-by-layer using a computer-controlled ultra violet (UV) light.

Merits

  • Fast implementation of prototypes in early stages of product development
  • Single-stage production process produces smooth surfaces even without finishing
  • Low material consumption: non-hardened synthetic resin can be reused
  • Production of both flexible and rigid 3D objects
  • Cost-effective production
  • Customized coloring
  • Multi-part assemblies are possible

Demerits

  • Depending on the material, components may be brittle
  • Support structures can limit design freedom
  • Components are only UV-resistant to a limited extent

Selective Laser Sintering (SLS)

Used for both metal and plastic prototyping, SLS uses a powder bed to build a prototype one layer at a time using a laser to heat and sinter the powdered material. However, the strength of the parts is not as good as with SLA, while the surface of the finished product is usually rough and may require secondary work to finish it.

Merits

  • Best for producing strong, functional parts with complex geometries.
  • High level of accuracy (though not as high as stereolithography).
  • Doesn’t require supports, saving printing and post-processing time.

Demerits

  • Very expensive. The machines can often cost $250,000+, and the materials cost $50-60/kg. In addition, the machines required skilled operators to use.
  • Cool-down time of 50% of print time can mean up to 12 hours of waiting. This leads to longer production time.
  • Parts have a grainy surface without any post-processing.

Fused Deposition Modelling (FDM) or Material Jetting

This inexpensive, easy-to-use process can be found in most non-industrial desktop 3D printers. It uses a spool of thermoplastic filament which is melted inside a printing nozzle barrel before the resulting liquid plastic is laid down layer-by-layer according to a computer deposition program. While the early results generally had poor resolution and were weak, this process is improving rapidly and is fast and cheap, making it ideal for product development.

Merits

  • FDM is a cheap and accessible 3D technology. This makes it perfect for beginners to 3D printing. It’s also the most commonly used rapid prototyping technology due to its ease of access.
  • The technology is simple to use, and printers are often user-friendly. This is because FDM is mostly a consumer rather than industrial 3D printing process so effort is made to make the 3D printers easy to use.

Demerits

  • The print quality of FDM / FFF 3D prints are not as good as those by SLA or SLS.
  • 3D printing with fused deposition modeling is slow. This makes it unusable in some industries when large numbers of parts are needed quickly.
  • The layer-by-layer printing in FDM can sometimes lead to problems with warping and minor shrinking.