East Midlands Digital D&T Support Centre Part of the CAD in Schools Initiative Rapid Prototyping 11...

East Midlands Digital D&T Support Centre

Part of the CAD in Schools Initiative

Rapid Prototyping

11th March 2009

Integrated Electronics Course



Computer Numerical Control(CNC)

Rotating cutter removes material

Rapid Prototyping (RP)Material is added in layers



Rapid prototyping is the automatic construction of physical objects using solid freeform fabrication.

The first techniques for rapid prototyping became available in the late 1980s and were used to produce models and prototype parts.

Today, they are used for a much wider range of applications and are even used to manufacture production quality parts in relatively small numbers.



Rapid Prototyping (RP)

SLA - Stereo Lithography

LOM - Laminated object manufacture

FDM - Fuse deposition modelling

SLM - Selective Laser Melting

3DP - 3D Printing



Stereo Lithography (SLA)

A laser solidifies layers of liquidpolymer resin.

Durable, highly accurate models.

Slow for large, detailed models

Cost £100k - 500K

http://home.att.net/~castleisland/home.htm



Laminated Object Manufacture (LOM)

Heavy duty knife cutter creates paper or cardboard layers which are stuck together.



Fuse Deposition Modelling (FDM)

Corn starch powder or plaster

Material

Adequate detail

Machine = £14K+

Quick build timeLow cost models

Models are fragile



Selective Laser Melting (SLM)

High powered laser melts metal powder to produce solid metal

components

MCP Technologies - http://www.mcp-group.com



ABS materialGood detailMachines cost £18K+Quick build timeLow cost models

3D Printing (3DP)



Three-dimensional printing is a type of rapid prototyping. The Dimension printers build functional 3D models from the bottom up, one layer at a time from acrylonitrile butadiene styrene – ABS – plastic.

Dimension 3D Printers

Files are imported into the printer’s software which slices and orients the parts and creates any necessary support structures. The software plots a precise deposition path that the printer follows.

ABS – in filament form within auto-loading cartridges – is fed into an extrusion head, heated to a semi-liquid state and deposited in layers as fine as 0.010" thick. After completion of the build, support structures are removed.

http://www.dimensionprinting.com/



Dual-Tip TechnologyDual-Tip Technology

Dimension 3D Printers

Support MaterialSupport Material Modelling MaterialModelling Material



Case design

Cases and enclosures for electronic circuits can be designed with any 3D software capable of exporting STL files

ProDesktop

ProEngineerSolidWorks etc etc.



Case design

Modelling strategies

Top-down: starts with a concept or overall form before moving to the detail of components that can create that form, eg car design starts with the finished vehicle and works down to consider the details that it will be made up of.

involves several components or sub-systemsin a product being designed or redesigned and thenpackaged together into an overall product e.g. a computer.

Bottom-Up:



Case design

Modelling strategies

Part family design:

Reverse enginering:

involves the creation of a master model and the final product is one of a series of different designs that vary from that master only in their dimensions(eg a set of gears).

is the creation of a new model or product from an existing one. The new model will be based on the old one but have some number of alterations eg a computer mouse developed from a previous design.



Case designWhy are modelling strategies useful to usas designers?

You need not worry too much about having a definite strategy foryour CAD model as it is not always possible to plan this right fromthe start. For example, we may have a loose idea so cannot fullydecide what it is we want to model. You can however start considering your modelling strategy whilst designing. What is important is that you understand that a good modelling strategy, or an awareness of modelling strategies, should enable you to:

• model your design ideas more quickly

• make changes more easily

• produce a CAD model which is appropriate for the post processes you wish to apply to it (ie what you do with it at later stages)



Consider a modelling strategy to design and make a case for a usb flash drive

Think about:

• Which shapes are symmetrical (could they be mirrored?)

• Which shapes are identical (could they be patterned?)

• Critical dimensions (cannot be changed)



New Design In Context Available in

ProDesktop and Pro Engineer

Work around CAD model of circuit and components to design cases

USB board model

Draw profile

Extrude profile



Cut out interior to accept circuit board using extrude feature



Assemble to test model before exporting



Important considerations when designing for 3D printing.

Size matters!• Wall thicknesses must not be less than 1.5mm.

• Keep models as small/compact as possible

ABS modelling material is expensive - £250 per kilo!

(multiply the amount used by 0.25 to work out the cost)



Creating and exporting an STL file

In order to create physical models from CAD modelswe need to export them to an .stl format that machines can understand. This universal format allows the machine to recognise the model’s geometry and manufacture it.

An .stl file works by tessellating a series of triangles over the form of the model to reproduce it exactly. These trianglesare often referred to as facets. For example, a simple cube may looksomething like this:



The number of facets created within an .stl file controls how accurately the file reflects the original model and the level of detail in what is manufactured by the RP machine.

The smaller the number of triangles or facets the lessdetail/accuracy there will be in the .stl file.

Alternatively

The larger the number of triangles or facets the more detailed the output from the .stl file. This is shown in examples on the right




Therefore, when exporting an .stl file we need to control the numberof facets (triangles) by setting the chord height and the angle valuesto control the level of detail in the final model.


In ProDESKTOP select: file > export > Stereo Lithography FileName the file appropriately and Save in a location you can easily retrieve it from.Set the Chordal (mm) value to 0.005Set the Angular (deg) value to 1and Select: OK



Importing an STL file to Catalyst

The 3D printer is controlled by it’s own software ‘Catalyst’ which accepts STL files created in most 3D CAD packages



•The most important thing with rapid prototypes is spending enough time to remove excess support material once they have been moulded

Finishing RP Models

• Spray with filler primer (available from most car accessory shops eg Halfords)

• Spray with colour spray paint (ideally car body paint)

• Allow to dry between coats and rub down with wet & dry paper

• Finish with polish or rubbing compound (Solvol-Autosol works)

•Take care not to lose any detail created in your model just by not being careful enough at the finishing stage.

East Midlands Digital D&T Support Centre Part of the CAD in Schools Initiative Rapid Prototyping 11...

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