RP description and process (.pdf) from Richard Bibb

 

CAD Model

Your virtual model is about to become real.  Before your model is exported for printing you will need to carefully consider how it is going to fit together and operate.

Where as previously you are likely to have ignored clearances between parts these will now have to be carefully considered and modelled.  Any assembled parts or fixing mechanisms such as screws or snap fits will have to be carefully considered.

Dimensional tolerances will have to considered in your modelling – talk to Phil Dixon regarding thermal shrinkage issues and general tolerancing considerations for our machines with regard to your project.

You will have to include appropriate clearances in your model. If you have details which need particular attention or are very small then maybe create a test piece which isolates that detail – particularly if the complete model has a significant cost.

 

To build an RP model you will need….

An .stl file (see stl info here) – If you have exported from a non-parametric modeller (ie. Rhino or Alias) or you exported surfaces, you need to make sure that the .stl is ‘manifold‘ or watertight.  If there are any open single sided edges in the .stl then the volume is not closed and will not build.

Also make sure your file is at an appropriate level of detail for the end use.  Fewer, large facets produce smaller, more handleable files but lack detail.  Equally, more facets of a smaller size will give you more detail but will result in a large file size.

 

Model mass properties from Creo

All volumes must be quoted in cubic centimetres

File > Prepare > Model Properties > Change

Mass Properties window > Calculate

 

Time for some maths!

The volume is display in an exponential notation and in mm^3 – you need to change it to cm^3

Exponential: move the decimal place by the quoted number: the figure in the example above = 73091.71

Units: 1000mm^3 = 1cm^3  – move the decimal point 3 places – the figure in the example above = 73.09171cm^3

Now use your common, does the figure seem about right? Visualise a cm^3, if your suggesting something the size of an AA battery is 1279.23cm^3 then something is probably wrong!

 

Requisition

  • Your individual part file size should not be greater than 10Mb – unless its physically a very big part your not going to see any extra resolution.
  • STL files to be submitted by attachment to an email to Phil Dixon – P.R.G.Dixon@lboro.ac.uk
  • Use separate emails for each machine; do not add parts for both the Connex and the Dimension on the same email
  • List parts by filename with quantity, machine and material required
  • State the total price
  • Attach a screen shot of the modelled part to the email – this will enable Phil to match the manufactured components to the email requests
  • Parts must be paid for at Stores to Alan Hopewell
  • Completed RP models are to be collected from Phil’s office (LDS.0.08) upon proof of payment

 

Costs

Dimension SST 1200: £1.25 per cm^3

Objet Connex 500: £2.50 per cm^3

 

 

Equipment in LDS: LDS012

 

Dimension SST 1200 – site

This process is generally better for bulkier parts without fine detail or thin walls.

This Fusion Deposition Modeller extrudes a strand of ABS polymer to produce a boundary and then infill for each layer that the model is sliced into.  It also creates a water soluble support structure.

This machine has a lower tolerance – +/-0.15mm – and is generally not good for small details. It lays a thread of extruded ABS which has a ‘road width‘ of 0.5mm and layer thickness of 0.25mm.

The water soluble support structure has to be removed after the part is printed.  Parts will be delivered with this process completed.

It has a reasonable definition.  The strength is very dependent on the model geometry and build orientation – although the ABS model material has a good strength, failure will generally occur when the layers break apart.

The modelling time is dependent on the model volume and the amount of supports required.

Build volume 254 x 254 x 305mm

Layer resolution 0.254mm or 0.330mm

Raw Material Tensile strength of ABS 40 MPa

Average model strength considering layering 22 Mpa

Density 1.05 g/cm3

Video: http://www.youtube.com/watch?v=cFcWFB0FlLo

 

Advantages:

Reliable

Clean and safe process

Strong, durable plastic parts

Soluble supports

Comparatively reasonable costs

 

Disadvantages:

Thin walls can be weak

Surface finish less good than some RP processes

Small features difficult

 

Cost: £1.25 per cubic centimetre

 

Objet Connex 500 – site

 

This machine gives good resolution and good accuracy, it also enables working mechanisms to be created and printed in several different materials at once.  You can combine one rigid and one flexible material to give a range of Digital materials, each with their own physical properties, see here for material datasheets:

http://objet.com/3d-printing-materials/overview

Materials we have in stock are:

Rigid materials:

VeroWhite (White)

Fullcure 720 (Transparent)

Flexible materials:

Tango+ (Transparent)

Due to the high material cost when swapping from one base material to another, you may have to wait until the machine is loaded with the correct material to suit your requirement.

All materials are UV cured and have an operational temperature ~50°C, any higher temperature tends to cause the model to warp and distort.

Maximum model size: D:490 W: 390 H: 200

Layer resolution: 0.03mm

Tensile Strength: Dependent material used and or mixed

Gel support material, remove by brushing, leaving to soak in water will cause the gel to swell and fall off. To remove any residue immerse in a 5% sodium solution, then brush & rinse.

 

Advantages:

Very accurate, very good surface finish

A range of physical properties

Multiple materials in one part

Transparent parts possible

 

Disadvantages:

Very expensive

Added CAD complexity for multiple material parts

 

Cost: £2.50 per cubic centimetre