What is rapid prototyping?

The word rapid prototype contains two words- rapid and prototype. The word rapid represents fast, and prototype represents a real, dimensionally accurate, and working assembly of a new or existing product.
Rapid prototyping is described as a layer-by-layer manufacturing process in which different machine components like computer control, optical sensor, photosensitive sensor, deposition material, and others are used to develop an accurate dimensional physical working model.
In other words, rapid prototyping is a layered manufacturing process of a product using a 3-dimensional (3D) computer-aided design model.

Steps for rapid prototyping

Following are the basic steps of the rapid prototyping manufacturing process:

• Computer-aided design (CAD) model creation
• Conversion of CAD model to Stereolithography (STL) File
• Rapid processing or slicing
• Rapid prototyping or layering
• Post-processing or finishing

CAD model creation

In CAD model creation, the object or prototype manufactured is modeled virtually using computer-aided design (CAD) software like AutoCAD, Creo, and others. It is a basic process of rapid prototyping.

Conversion of CAD File to STL File

The standard format for rapid prototyping is STL that represents a 3D surface as planar triangles assembly. Therefore, the CAD file is converted into an STL file for rapid prototyping.

Rapid Processing

In rapid processing, the designer model is validated and repaired as per standards and slicing is done for the complete model. The number of layers made into the prototype or product is equal to slicing. The thickness and number of layers depend upon the built technique of the product.

The rapid processing program will also introduce some additional components to support some overhanging parts of the assembly.

Rapid prototyping or layering

In rapid prototyping or layering, the layer by layer manufacturing of the final product is done. The rapid prototype machine develops a layer over another layer by supplying product materials like polymer, plastic, powdered metal, and others. It is a completely autonomous process and does not need any human resources.

Post processing or finishing

In post-processing, the cleaning, post-curing, and finishing of obtained assembly or prototype are done. During cleaning, additional materials like supports and other things are eliminated from the prototype. In post-curing and finishing, surface treatment and painting are done to improve the appearance and strength of the prototype.

What is the advantages and disadvantages of rapid prototyping?

Advantages of rapid prototyping

Following are the various advantages of rapid prototyping:

• Rapid prototyping provides a variety of products with good dimensional accuracy.
• It saves product testing time.
• No additional tool is required in the manufacturing of the product.
• It reduces material wastage.
• It saves production time and delivery time.
• It decreases product cost and costly product mistakes.
• The errors in design can be easily identified.
• It increases the product lifetime by adding or eliminating necessary features to design.
• It is an autonomous process and requires very less manpower.
• The changes in the product can be easily done by the designer corresponding to the product feedback.

Disadvantages of rapid prototyping

Following are the various limitations or disadvantages of rapid prototyping:

• The rapid prototyping machines with high precision are very costly.
• The physical properties of the rapid prototyping product are poor as compared to traditionally manufactured products.
• The product manufactured by rapid prototyping has waviness.
• Rapid prototyping cannot produce some complex products.

Classification of rapid prototyping

Following are the various classifications of rapid prototyping:

• Stereo lithography (SLA)
• Selective laser sintering (SLS)
• Laminated object manufacturing (LOM)
• Fused deposition modeling (FDM)
• Solid ground curing (SGC)

Stereolithography (SLA)

Stereolithography (SLA) was the first rapid prototyping process founded in 1986. The stereolithography technology does 3D printing by using liquid photosensitive materials that solidify when they come in contact with ultraviolet light.

Following are the basic elements of stereolithography system:

• Resin vat
• Platform
• Elevator
• Laser
• Mirror
• Sensor

Resin vat

The resin vat is an element that contains the raw material of the model to be manufactured. It moves over the platform during the manufacturing process.

Platform

A platform is described as a plate made up of alloys containing holes supporting the manufacturing assembly or prototype from its base.

Elevator

The elevator is an element of a stereolithography system that controls the platform's motion in an upward and downward direction.

Laser

Laser is used as a source of concentrative ultraviolet beam of light that solidifies the liquid resin into solid state.

Mirror

A mirror is used as a reflecting element in a system to guide the movement of the ultraviolet laser beam along the horizontal and vertical directions.

Sensor

A sensor is an element that locates the coordinate and power of the ultraviolet laser beam and gives feedback to the control unit for necessary adjustments in 3D printing.

Selective laser sintering (SLS)

The selective laser sintering is described as a rapid prototyping process in which a huge strength laser is used to fuse the small particles of base material used in 3D printing of prototype or assembly.

The diagrammatical representation of the selective laser sintering (SLS) is shown as:

Advantages of selective laser sintering are

• Flexibility in the material used
• Functional and tough product is produced.

Disadvantages of selective laser sintering are

• Additional power line is deposited near borders.
• Roughness during stepped surfaces.

Laminated object manufacturing (LOM)

In the laminated object manufacturing process, the number of thin sheets of paper or plastic with resin glue are placed one over the other with the help of a heated roller. The laser is used to cut the profile of different layers. The gluing and cutting of layers are continuous until the final product is completed.

The diagrammatical representation of the laminated object manufacturing system is shown as:

Advantages of laminated object manufacturing

• Can use for a wide range of materials.
• Highly accurate and fast.
• The final product is durable.

Disadvantages of laminated object manufacturing

• The strength of the part depends on the glue used.
• The absorption of water can distort the model.

Fused deposition modeling (FDM)

Fused deposition modeling is a process in which a thread of plastic is supplied to the extrusion head, where it is converted into a liquid state and extruded through a hole layer by layer to build a model or part.

The diagrammatical representation of the fused deposition modeling is shown as:

Advantages of the fused deposition modeling

• Easy handling and fabrication.
• Minimum wastage.

Disadvantages of the fused deposition modeling

• A small range of materials can be used.
• Difficult to produce small diameter elements.

Solid ground curing (SGC)

Solid ground curing is a process that uses photosensitive resin, layer by layer to develop a model. In this process, the model is formed over a glass plate kept between the cover with liquid plastic and ultraviolet light. The light passes through the glass plate and hits the liquid solidifies, and the remaining part remains liquid. The process is repeated simultaneously, and finally, a solid form of liquid is removed, giving the desired assembly.

The diagrammatical representation of the solid ground curing (SGC) is shown as:

Advantages of the solid ground curing (SGC)

• It can produce complex work pieces.
• High accuracy and best surface finish

Disadvantages of the solid ground curing (SGC)

• High cost of photo-sensible resin.

Common Mistakes

Following are the common mistakes performed by students:

• Sometimes, students get confused between the rapid prototyping process and other conventional manufacturing processes.
• Sometimes, students forget to convert the CAD file into an STL file before processing.
• Sometimes, students get confused about the raw prototype materials.
• Sometimes, students get confused between the process of stereolithography (SLA) and solid ground curing (SGC).

Context and Application

The topic of rapid prototyping is significant in various courses and professional exams of undergraduate, graduate, postgraduate, doctorate levels. For example:

• Bachelor of Technology in Mechanical Engineering
• Bachelor of Technology in Production Engineering
• CAD, CAM and CIM courses
• Master of Technology in Design
• Master of Technology in Production Engineering
• Doctorate of Philosophy in Design

Related Concepts

• Computer-aided design
• Fabrication processes
• Machine and product design
• 3D-prototyping

Practice Problems

Q1. Which of the following is a basic function of rapid prototyping?

1. Building layers
2. Removing layers
3. Rolling
4. None of these

Correct option: (a)

Explanation: Rapid prototyping consists of various manufacturing technologies that are applied for high-speed extrusion, high-speed casting, and many other processes. One of the basic functions of rapid prototyping is building layers.

Q2. Which of the following component helps in solidifying liquid resin?

1. Laser
2. Elevator
3. Platform
4. Sensor

Correct option: (a)

Explanation: Liquid resin is expressed as the fluid which blends with a hardening agent and forms durable solids. In order to solidify the liquid resin, a laser is used extensively.

Q3. The solid filament is supplied in which of the following process?

1. Solid ground curing
2. Laminated object manufacturing
3. Fused deposition modeling
4. None of these

Correct option: (c)

Explanation: In fused deposition modeling (FDM) the solid filament is utilized as a plunger for creating pressure in the molten metal.

Q4. Solid ground curing is used for _____?

1. 2D testing
2. 1D printing
3. 3D testing
4. 3D printing

Correct option: (d)

Explanation: Solid ground curing (SGC) is described as the three-dimensional (3D) printing innovation that helps to make machinery parts as well as models.  

Q5. Which type of file is used in rapid prototyping processing?

1. CAD file
2. STL file
3. PDF file
4. HTML file

Correct option: (b)

Explanation: A stereolithography (STL) file is utilized in rapid prototyping because it expresses the surface geometry of a three-dimensional (3D) object, and various software packages widely support the file format.