undefined | unit 5 advanced manufacturing method

CAD

Unit 5

Q.1 Explain the need of PLM.

A1)

The traditional philosophy of product design is based on the principle of minimizing the design and manufacturing cost.

In today’s competitive environment, where market is flooded with large number of identical products, for a success of a product, it is nt only important to minimize the design and manufacturing cost but also necessary to minimize the total product life cycle cost.

The product life cycle cost consists of: cost of product inception, design, manufacturing, service and disposal.

This had made it necessary to develop a plan to manage all the phases of product life cycle.

Hence there is the need of PLM to manage the entire life cycle of a product from inception to disposal.

Q.2 Write a note on Collaborative Engineering

A2) “Collaborative engineering is defined for the study of interactive process of engineering collaboration wherein, in order for serving their mutual intrests, multiple interested stakeholders or partners:

i) Resolve conflicts

ii) Bargain for individual or group advantages

iii) Agree upon course of action

iv) Attempt to achieve joint outcomes

The aim of collaborative engineering is to facilitate the individuals and organizations, across the boundaries of discipline, geography and culture, to work effectively with collaborative actions for achieving joint outcomes.

It is used most effectively in product design, manufacturing, construction, etc.

Q.3 Write down the steps in Rapid Prototyping.

A3)

CAD Model Creation:

First, the object to be built is modeled using a Computer-Aided Design (CAD) software package or coordinate measuring machine or laser scanner.

Solid modelers, such as Pro/ENGINEER, tend to represent 3-D objects more accurately than wire-frame modelers such as AutoCAD, and will therefore yield better results.

This process is identical for all of the RP build techniques.

2. Conversion to STL Format:

To establish consistency, the STL (stereo lithography, the first RP technique) format has been adopted as the standard of the rapid prototyping industry and acts as the interface b/w CAD software and machines.

The second step, therefore, is to convert the CAD file into STL format. This format represents a three-dimensional surface as an assembly of planar triangular facets.

STL files use planar elements, they cannot represent curved surfaces exactly. Increasing the number of triangles improves the approximation.

3. Slice the STL File:

In the third step, a pre-processing program prepares the STL file to be built.

The pre-processing software slices the STL model into a number of layers from 0.01 mm to 0.7 mm thick, depending on the build technique.

The program may also generate an auxiliary structure to support the model during the build. Supports are useful for delicate features such as overhangs, internal cavities, and thin-walled sections.

4. Layer by Layer Construction:

The fourth step is the actual construction of the part.

RP machines build one layer at a time from polymers, paper, or powdered metal.

Most machines are fairly autonomous, needing little human intervention.

5. Clean and Finish:

The final step is post-processing. This involves removing the prototype from the machine and detaching any supports.

Some photosensitive materials need to be fully cured before use

Prototypes may also require minor cleaning and surface treatment.

Sanding, sealing, and/or painting the model will improve its appearance and durability.

Q.4 Write a note on Stereolithography

A4)

Stereo lithography is the most widely used RP-technology. It can produce highly

Accurate and detailed polymer parts. SLA was the first RP-process, introduced in 1988 by 3D Systems Inc.

Working Principle

SLA uses a low-power, highly focused UV laser to produce a three-dimensional object in a vat of liquid photosensitive polymer.

Features

Material type: Liquid (Photopolymer)

Materials: Thermoplastics (Elastomers)

Min layer thickness: 0.02 mm

Surface finish: Smooth

Build speed: Average

Model and specification of process

This is based on selective polymerization of a photosensitive resin using ultraviolet light.

In this system, an ultraviolet laser beam is focused on the top layer of photo sensitive resin contained in a vat.

The beam is positions and moved in horizontal X and Y directions to polymerize the resin within the boundary a particular cross-section.

The cured layer of polymer is lowered by a platform attached to it, so that a fresh layer of liquid resin covers the cured layer.

SLA Process

Working

A vat containing a mechanism whereby a platform can be lowered and raised is filled with a photocurable liquid-acrylate polymer.

The liquid is a mixture of acrylic monomers, oligomers (polymer intermediates), and a photo-initiator (a compound that undergoes a reaction upon absorbing light).

At its highest position (depth a), a shallow layer of liquid exists above the platform.

A laser generating an ultraviolet (UV) beam is focused upon a selected surface area of the photopolymer and then moved around in the x-y plane.

The beam cures that portion of the photopolymer and thereby produces a solid body.

The platform is then lowered sufficiently to cover the cured polymer with another layer of liquid polymer, and the sequence is repeated.

The process is repeated until level b is reached. Thus far, we have generated a cylindrical part with a constant wall thickness. Note that the platform is now lowered by a vertical distance ab.

At level b, the x-y movements of the beam define a wider geometry, so we now have a flange-shaped portion that is being produced over the previously formed part.

After the proper thickness of the liquid has been cured, the process is repeated, producing another cylindrical section between levels b and c.

Note that the surrounding liquid polymer is still fluid (because it has not been exposed to the ultraviolet beam) and that the part has been produced from the bottom up in individual ‘slices’. The unused portion of the liquid polymer can be used again to make another part or another prototype.

ADVANTAGES

Achieving accuracy in industries

Capable of high detail and thin walls

Good surface finish

High part complexity

DISADVANTAGES

Some war page, shrinkage and curl due to phase change.

Limited materials (Photo polymers).

Support structures always needed. Removal of support structures can be difficult

Requires post-curing.

Application

Visual Representation models

Functional and tough prototypes

cast metal parts

Q.5 Explain Principle, Process and Working of FDM

A5) Fused Deposition Modelling:

(FDM) is a solid-based rapid prototyping method that extrudes material, layer-by-layer, to build a model.

It was developed by Stratasys

Working Principle

A plastic or wax material is extruded through a nozzle that traces the part´s cross sectional geometry layer by layer

Process

The FDM technique relies on melting and selectively depositing a thin filament of thermoplastic polymer in a cross-hatching fashion to form each layer of the part.

The material is in the form of a wire supplied in sealed spools which is mounted on the machine and the wire is threaded through the FDM head.

The head is moved in the horizontal X and Y directions for producing each layer through zigzag movements.

The supporting table moves in the vertical direction and is lowered after the completion of each layer.

FDM Process

Working

In FDM process, a gantry robot-controlled extruder head moves in two principal directions over a table, which can be raised and lowered as needed.

A thermoplastic filament is extruded through the small orifice of a heated die.

The initial layer is placed on a foam foundation by extruding the filament at a constant rate while the extruder head follows a predetermined path.

When the first layer is completed, the table is lowered so that subsequent layers can be superimposed.

In some parts, the filament is required to support the slice where no material exists beneath to support it.

The solution is to extrude a support material separately from the modelling material. The use of such support structures allows all of the layers to be supported by the material directly beneath them.

The support material is produced with a less dense filament spacing on a layer, so it is weaker than the model material and can be broken off easily after the part is completed.

The layers in an FDM model are determined by the extrusion-die diameter, which typically ranges from 0.050 to 0.12mm. This thickness represents the best achievable in the vertical direction.

In the x-y plane, dimensional accuracy can be as fine as 0.025mm

Q.6 Explain LOM process in detail with its advantages and disadvantages.

A6) Laminated Object manufacturing:

The main components of the system are a feed mechanism that advances a sheet over a build platform, a heater roller to apply pressure to bond to the layer below, and a laser to cut the outline of the part in each sheet layer.

After each cut is completed, the platform lowers by a depth equal to the sheet thickness (0.05 –0.5 mm).

The laser cuts the outline and the process is repeated until the part is completed.

After a layer is cut, the extra material remains in place to support the part.

LOM Process

Working

Lamination implies a laying down of layers that are bonded adhesively to one another.

The simples and least expensive versions of LOM involve using control software and vinyl cutters to produce the prototype.

Vinyl cutters are simple CNC machines that cut shapes from vinyl or paper sheets.

Each sheet then has a number of layers and registration holes, which allow proper alignment and placement onto a build fixture.

LOM systems are highly economical and are popular in schools and universities because of the hands-on demonstration of additive manufacturing and production of parts by layers.

LOM systems can be elaborate; the more advanced systems use layers of paper or plastic with a heat-activated glue on one side to produce parts.

The desired shapes are burned into the sheet with a laser, and the parts are built layer by layer.

On some systems, the excess material must be removed manually once the part is completed. Removal is simplified by programming the laser to burn perforations in crisscrossed patterns.

The resulting grid lines make the part appear as if it had been constructed from gridded paper (with squares printed on it, similar to graph paper).

Advantages

Wide range of materials

Fast Build time

High accuracy

durability

High part complexity

Disadvantages

Requires post-curing

Overheated roller may damage sheet

Limited materials (Photo polymers).

Support structures always needed.

Q.7 Write a note on SLS. State its application.

A7) Selective Laser Sintering:

SLS is a process based on the sintering of non metallic or (less commonly) metallic powders selectively into an individual object.

In this process a high power laser beam selectively melts and fuses powdered material spread on a layer.

The powder is metered in precise amounts and is spread by a counter-rotating roller on the table.

A laser beam is used to fuse the powder within the section boundary through a cross-hatching motion.

The table is lowered through a distance corresponding to the layer thickness (usually 0.01 mm) before the roller spreads the next layer of powder on the previously built layer.

The un-sintered powder serves as the support for overhanging portions, if any in the subsequent layers.

SLS Process

Principle of Working

It uses a moving laser beam to trace and selectively sinter powdered polymer and/or metal composite materials.

Features

Material type: Powder (Polymer)

Materials: Thermoplastics: Nylon, Polyamide and Polystyrene; Elastomers; Composites

Min layer thickness: 0.10mm

Surface finish: Average

Build speed: Fast

Applications

Form/fit testing

Functional testing

Less detailed parts

Parts with snap-fits& living hinges

High heat applications

Q.8 Explain the Principle and working of 3D Printing. State two advantages and two disadvantages of 3D printing.

A8)

Three-Dimensional Printing (3DP) technology was developed at the MIT and licensed to several corporations.

It was Produced by Z Corporation, USA.

Principle

An ink-jet printing head deposits a liquid adhesive that binds the starch powder material.

Working

In 3D printing (3DP) process, a print head deposits an inorganic binder material onto a layer of polymer, ceramic, or metallic powder.

A piston supporting the powder bed is lowered incrementally, and with each step, a layer is deposited and then fused by the binder.

3DP allows considerable flexibility in the materials and binders used.

Furthermore, since multiple binders print heads can be incorporated into a machine, it is possible to produce full-color prototypes by having different-color binders.

The effect is a 3D analog to printing photographs using three ink colors on an ink-jet printer.

A common part produced by 3DP from ceramic powder is a ceramic casting shell, in which an aluminium-oxide or aluminium silica powder is fused with a silica binder.

The moulds have to be post processed in two steps: (1) Curing at around 150ºC and (2) Firing at 1000º to 1500ºC.

The parts produced through the 3DP process are somewhat porous and therefore may lack strength.

3DP of metal powders can also be combined with sintering and metal filtration to produce fully dense parts, using the sequence.

The part is produced as before directing the binder onto powders. However, the build sequence is then followed by sintering to burn off the binder and partially fuse the metal powders, just as in powder injection moulding.

Common metals used in 3DP are stainless steels, aluminium, and titanium.

Infiltrating materials typically are copper and bronze, which provide good heat-transfer capabilities as well as wear resistance

Advantages

High speed

No wastage of material

Disadvantages

Requires post-curing

poor surface finish

need post-processing

Q.9 Write a note on Rapid Tooling

A9) Rapid-prototyping techniques have made possible much faster product development times, and they are having a major effect on other manufacturing processes. When appropriate materials are used, rapid-prototyping machinery can produce blanks for investment casting or similar processes, so that metallic parts can now be obtained quickly and inexpensively, even for lot sizes as small as one part.

Such technologies also can be applied to producing molds for operations (such as injection molding, sand and shell mold casting, and even forging), thereby significantly reducing the lead time between design and manufacture.

Several methods have been devised for the rapid production of tooling (RT) by means of rapid-prototyping processes.

The advantages to rapid tooling include the following:

The high cost of labor and short supply of skilled pattern makers can be overcome.

There is a major reduction in lead time.

Hollow designs can be adopted easily so that lightweight castings can be produced more easily.

The integral use of CAD technologies allows the use of modular dies with base-mold tooling (match plates) and specially fabricated inserts. This modular technique can further reduce tooling costs.

Chill- and cooling-channel placement in molds can be optimized more easily, leading to reduced cycle times.

Shrinkage due to solidification or thermal contraction can be compensated for automatically through software to produce tooling of the proper size and, in turn, to produce the desired parts.

The main shortcoming of rapid tooling is the potentially reduced tool or pattern life (compared to those obtained from machined tool and die materials, such as tool steels or tungsten carbides).

The simplest method of applying rapid-prototyping operations to other manufacturing processes is in the direct production of patterns or molds.

Q.10 What is STL file?

A10)

A STL file is a format used by Stereolithography software to generate information needed to produce 3D models on Stereolithography machines. In fact, the extension "stl" is said to be derived from the word "Stereolithography."

A slightly more specific definition of a stl file is a triangular representation of a 3D object. The surface of an object is broken into a logical series of triangles (see illustration at right). Each triangle is uniquely defined by its normal and three points representing its vertices.

The stl file is a complete listing of the xyz coordinates of the vertices and normals for the triangles that describe the 3D object.

When creating a stl file, the goal is to achieve a balance between unmanageable file size and a well-defined model with smooth curved geometries.

Often a stl file can be termed "bad" because of translation issues.

In many CAD systems, the number of triangles that represent the model can be defined by the user. If too many triangles are created, the stl file size can become unmanageable.

If too few triangles are created, curved areas are not properly defined and a cylinder begins to look like a hexagon (see example below).

Q.11 Write a note on 4D printing technique.

A11) 3D printed materials can be more flexible and useful, the structures of the material can transform in a pre-programmed way in response to any external stimulus. In general, self-changing structure of 3D printed part after post process is called 4D printing process.

In 4D printing process, 1D strand or 2D surface having multi-material feature, is created using the same 3D printing techniques.

Joint and folding angle strands

Printing 4D joint includes multiple layers of material. Composition of rigid polymer, expanding material and digital material depicts the folding direction and pattern. Those materials are placed above or below of each other depending upon the type of transformation.

Custom Angle Surfaces

Similar mechanism as folding strand described previously, series of flat two-dimensional structures were generated with edge joints. The position and spacing of materials at each joint specifies the desired fold angle hence positioned accordingly.

4D printed self-folding truncated octahedron demonstrating the “transformation over time” when submerging in water.

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