Unit 17: Computer aided manufacturing (CAM)
LO4: Be able to produce components using additive
manufacturing techniques
Preparation and production quality using 3D printing
Instructions and answers for tutors
These instructions should accompany the OCR learner resource activity which supports Cambridge
Technicals in Engineering Level 3.
These tasks are about the 3D model and the quality of the 3D printed component. The tasks are similar but not identical
to the Learning Outcome 3 lesson where the quality of CNC manufacture is considered. For additive manufacture the
quality is an interaction between the output from CAD and the settings of the 3D printer.
These activities offer
These activities offer
opportunities for
opportunities for maths
English skills
skills development.
development.
Suggested timings:
Activity 1: 2 hours
Activity 2: 4 hours
Activity 3: 1 hour
Version 1
Activity 1
Introduce learners to the need to export files from CAD to CAM and that Additive Manufacturing methods
require more parameters than CNC. Highlight the need for a format to describe the component in
geometrical values (STL) and that some Additive methods need colour information as well (VRML/3XD
formats). Show that both these formats are inadequate to carry full information (e.g. texture and material
type) and that the industry is now developing 3MF as a future proof format.
In this task, learners will work with STL format as this is currently available to export from all 3D CAD
software. Learners will explore how the size of the triangles in an STL mesh can be altered before
exporting to give the optimum resolution of the part. They will find that the density of the STL mesh
affects the size of the file exported; the finer the mesh the larger the file (Binary STL files are always
smaller than ASCII).
This task could be carried out in pairs to stimulate discussion. Assist the learners to select suitable 3D
CAD models for 3D printing based on the machine(s) you have available and avoid models that will need
support material. The table would be expected to show larger file sizes for finer STL settings. Discuss
with learners the need for different settings according to whether the output is for a prototype or a final
product. Learners can use CAD software (e.g. solid edge to display a faceted model preview;
alternatively they could use Meshmixer or MeshLab in wire frame view or netfabb Studio in repair mode.
Notes
Most CAD programs have a choice of STL settings or an optimal output for a given 3D model as shown
in:
http://www.redeyeondemand.com/stl-file-format/ or http://3dprintingsystems.com/export-to-stl/
(note that the Pro Engineer (Pro/E) settings apply also to PTC Creo).
Advice for Solidworks includes the following:
 Move the Deviation to adjust the deviation (chordal) Tolerance, which controls whole-part
tessellation. Lower numbers generate files with greater whole-part accuracy.
 Move the Angle to adjust the angle Tolerance, which controls smaller detail tessellation. Lower
numbers generate files with greater small-detail accuracy, but those files take longer to generate.
Version 1
Activity 2
This task assumes you have a 3D printer that uses FDM.
Learners will need access to the 3D printer software or could initially use Repetier Host (which is free of
cost) for evaluating the settings. The obvious outcomes are that denser fill settings will use more material
and take longer to make, but discussion could also include the value of the component and the type of
finish needed for its function. Less dense structures may be useful to reduce the component mass. STL
files with finer meshes will allow better finish but this may be overridden by the layer thickness setting.
Learners may be surprised by the amount of time needed to produce the components.
Activity 3
Possible responses:
Feature
Additive
Subtractive
Material choice
Limited but improving
(note consumer/industrial
differences)
Wide choice
Ease/difficulty of use
Easy to set up
Needs experience
Time required
Depends on layer thickness but can
be very slow
Depends on surface area to be machined
Quality of finish
Layered needs treatment after
manufacture
High quality
Accuracy
Depends on nozzle size and
temperature
Highly accurate
Complexity of part
No limit on complexity
Limited for 3 axis machines (no
overhangs)
Design changes
Easy to switch
Needs setting up
Cost
Plastics inexpensive
Depends on material
Waste
Very little (supports only)
Large amount and can be difficult to
recycle
Version 1
We’d like to know your view on the resources we produce. By clicking on ‘Like’ or ‘Dislike’ you can help us to ensure that
our resources work for you. When the email template pops up please add additional comments if you wish and then just
click ‘Send’. Thank you.
If you do not currently offer this OCR qualification but would like to do so, please complete the Expression of Interest Form
which can be found here: www.ocr.org.uk/expression-of-interest
OCR Resources: the small print
OCR’s resources are provided to support the teaching of OCR specifications, but in no way constitute an endorsed teaching method that is required by the Board,
and the decision to use them lies with the individual tutor. Whilst every effort is made to ensure the accuracy of the content, OCR cannot be held responsible for
any errors or omissions within these resources.
© OCR 2016 - This resource may be freely copied and distributed, as long as the OCR logo and this message remain intact and OCR is acknowledged as the
originator of this work.
OCR acknowledges the use of the following content: English and Maths icon: Air0ne/Shutterstock.com
Please get in touch if you want to discuss the accessibility of resources we offer to support delivery of our qualifications: [email protected]
Version 1
Unit 17: Computer aided manufacturing (CAM)
LO4: Be able to produce components using additive
manufacturing techniques
Preparation and production quality using 3D printing
Learner activity sheet
Activity 1
STL format is a surface model of the part made up of a triangular mesh. The size of the triangles can be
altered before exporting to give the optimal resolution of the part. Most CAD programs have a choice of
STL settings or an optimal output for a given 3D model as shown in:
http://www.redeyeondemand.com/stl-file-format/ or
http://3dprintingsystems.com/export-to-stl/
(note that the Pro Engineer (Pro/E) settings apply also to PTC Creo)
Advice for Solidworks includes the following:
 Move the Deviation slider to adjust the deviation Tolerance, which controls whole-part tessellation.
Lower numbers generate files with greater whole-part accuracy.
 Move the Angle slider to adjust the angle Tolerance, which controls smaller detail tessellation. Lower
numbers generate files with greater small-detail accuracy, but those files take longer to generate.
Select suitable 3D CAD models that you will use to 3D print and use the “export STL function” in the
CAD software to explore the settings available and the resulting file sizes. Save the files and right click to
examine Properties to find the file size. Display the file using software such as Meshmixer (in wire frame
view) to show the mesh.
Version 1
CAD
model
STL settings
(Deviation, Angle)
[coarse]
Output file size
(binary)
Output file size
(ASCII)
Comments
[medium]
[fine]
Activity 2:
The software used to prepare your STL files for printing will have a number of settings for control of layer
size (resolution), fill density and fill type. Changes in support material are omitted for now. This task is
about exploring the settings to see their effect on (1) time taken for printing, (2) amount of material
required and (3) the surface finish obtained. It is suggested that you work in small groups and divide the
changes in settings between you. Record your findings on a chart similar to that below.
You will be able to ascertain how much material is needed (this may be in print preview).
If you use Repetier Host software or similar you will be able to examine the layers after slicing to see the
internal structure of the model to be printed, the estimated printing time and the amount of material
required.
STL File
Settings
Time needed
Material
amount
Finish
quality
Comments
Layer size
Fill type
Fill
density
Etc.
Finally you will want to print the component in order to see the real finish, although this may take some
time and you may have to return to this task later.
Version 1
Activity 3
Having completed these Activities and those from Learning Outcome 2 you are in a position to compare
Subtractive and Additive Manufacturing processes. Discuss this in pairs and complete the table below to
summarise the differences.
Feature
Material choice
Ease/difficulty of use
Time required
Quality of finish
Accuracy
Complexity of part
Design changes
Cost
Waste
Version 1
Additive
Subtractive