Unit 10: Computer aided design (CAD)

LO1: Be able to produce 3D models using a range of modelling tools

Produce solid models using a range of sketch based, applied and advanced solid modelling features

Instructions and answers for tutors These instructions should accompany the OCR learner resource activity which supports Cambridge Technicals in Engineering Level 3.

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The Activity:Below is the outline provided for the learner activity. This document gives a step-by-step approach for the production of an industrial valve wheel that utilises a range of solid features including extrudes, revolves and swept features.

It is encouraged that the tutor works through the guide step-by-step with the learners, demonstrating each stage at the front of the class whilst the learners follow along or subsequently undertake each step after it is demonstrated. This allows the tutor to explain the tools being used in each step, challenge any misconceptions and ensure learners understand the importance of using appropriate geometry and fully constraining sketches.

Tutors could throughout the duration of the lesson element ensure they explain the use of construction geometry, encourage learners to use relations/mates where possible, fully-define/constrain sketches with appropriate dimensions and consider the method they use when creating components to allow easy modification of geometry (design intent.)

Following the completion of the demonstration learners could aim to complete the model of the pulley wheel in Activity 2 independently. This will embed the learning associated with revolves and applied features undertaken throughout the demonstration completed in Activity 1.

The tutor could facilitate this learning and assist learners throughout the modelling process again, reinforcing misconceptions, ensuring effective use of dimensioning and relations/constraints and encouraging a logical approach to the modelling process.

This activity offers an

opportunity for English

skills development.

This activity offers an

opportunity for maths

skills development.

Suggested timings:Activity 1: 1.5 hours

Activity 2: 30 minutes

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Unit 10: Computer aided design (CAD)

LO1: Be able to produce 3D models using a range of modelling tools

Produce solid models using a range of sketch based, applied and advanced solid modelling features

Learner activity sheet

Activity 1: An overview of parametric solid modelling packagesModern day industrial Computer Aided Design (CAD) packages are predominantly feature-based,

parametric modelling systems and create models using either solid or surface combination or a

combination of both.

Components within solid modelling systems are made of features. These features can take a variety of

forms but can be considered generally as simple shapes or blocks that build up to forma complete

component.

There are generally two different types of features:

1. Features created using sketches such as extrusions or lofts/blends.

2. Features applied directly to the model by selecting geometry. For example, fillets/rounds, chamfers, draft.

As these features are created they are usually listed in a model tree or feature tree that records and

shows the order that features are created in, similar to the history in Internet explorer. This ‘tree’ can be

interrogated to make modifications, re-order the creation of features or delete elements of the model.

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The model above can be visualised as 5 features. A rounded extrusion on the top plane, a second

rounded extrusion, a cylinder and 2 holes.

This model can be seen again here alongside the model tree that was created during its construction.

This shows how the process of creating this component should be implemented.

ParametricParametric models created in modern day solid modelling packages contain linked information. This can

take the form of dimensions, relationships/relations or other model information. The

relationships/relations and dimensions within a model are linked which means that models can be

modified easily and therefore features and associated data such as assemblies and drawings will update

Dimensions that are used in features to define things can be called driving dimensions. These may

include; the diameter of a circle, or the length of a line. Relationships or relations define links between

geometry e.g. two lines that are the same length two holes that have the same diameter or a series of

parallel lines.

CAD software interfacesThe interfaces of CAD environments differ from one modelling system to the other but they generally

follow some similar conventions. Almost, all CAD systems are designed for use with Windows operating

systems and will therefore include familiar icons and be arranged in a common format. In addition, as per

many Windows based software packages, most of the systems are structured with Tools and Toolbars

that give access to the elements of the system such as, sketches and features and described earlier.

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Finally, modern day CAD systems tend to include a broad range of resources to assist the modelling

process. These include; part libraries, tutorials, environments, help and support information and links to

online communities. These resources should be used to assist the modelling process and develop skill

and competency with the software.

Create a component using a range of solid modelling toolsThe imagery below shows examples of an industrial valve wheel with a turning handle. This lesson

utilises solid modelling features to create a component similar to the valve wheels pictured below.

The lesson utilises a range of solid modelling tools and features. The features used are:

Revolve Sweep Extrusion Fillet/round Chamfer Hole.

Producing the first revolve1. Create a new component/part in the CAD software.

2. Create a revolved feature with the following dimensions. It should have dimensions 22mm high,

37mm diameter and revolved 360°.

The feature requires the use of the following sketch tools: line, centreline, arc, dimension.

Ensure that the feature is appropriately constrained/defined. Use dimensions or relationships/relations

suitable to the software package being used.

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The completed feature is shown below. Rename this feature in the model/feature tree to Centre Hub.

3. Create a second revolve feature.

The revolve profile is ‘slot shaped (two arcs, two lines). This should be created on the same plane as

the sketch for the initial revolve.

The sketch should be revolved around the same axis/centreline used to create the Hub feature.

The sketch should be revolved 360°. The completed feature is shown below. Rename this feature

Wheel Rim

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4. The spokes of the wheel are created using a sweep and a pattern feature. The sweep merges the two

other features into a single solid model. A sweep is constructed using two sketches: a sweep path

and the sweep profile.

On a suitable plane create the sweep path with the dimensions below. The ends of the sweep path

are connected to the centre of the slot sketch for the Rim and the mid-point of the centreline of the

Hub feature.

Sketch the sweep profile on a plane that is perpendicular to the end of the sweep path. The sweep

profile is circular in profile. The diameter should be 15mm.

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Sweep the profile along the path. Rename the feature to Wheel spoke.

5. The spokes on the wheel are now copied using a pattern or array feature. The spokes should be patterned around the central axis of the Hub feature. They should be equally spaced around 360° and 4 copies should be produced.

6. The model now requires an extrusion/boss feature to be added to the rim of the wheel to

accommodate the turning handle.

The feature should be sketched on the top, flat face of the Wheel Rim (see below.)

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The location boss should be 12mm radius, 60° tapered (see below) and coincident to the outer

tangent joining line of the Wheel Rim feature. The feature should then be extruded up to the bottom

flat face of the Wheel Rim feature or a depth of 15mm.

7. The model now needs the holes required to locate the valve and the handle.

Firstly, add a keyway hole to the base of the Hub to accommodate the stub for the valve. The sketch

is shown below. Extrude as a cut through the entire Hub feature.

Secondly, insert the hole into the boss feature added in step 6 for the handle location.

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The hole is M10 and 10mm deep. A suitable standard should be selected from within the Hole tool in

the software package being used.

8. Fillet radii are now required where the spokes join the hub and the rim of the wheel.

Using the fillet/round tool add fillets on each edge of 2mm. The completed fillet radii are shown below.

9. A chamfer is now required on the top edge of the Wheel Hub.

Using the chamfer tool add a chamfer to the top edge. The chamfer should be 45° × 0.75mm. The

completed feature is shown below.

10. The model of the industrial valve wheel is now complete. Save and close the component. Version 1

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Activity 2Following the completion of the demonstration learners should aim to complete the model of the pulley

wheel below independently. This will embed the learning associated with revolves and applied features

undertaken throughout the demonstration completed in Activity 1.

The tutor should facilitate this learning and assist learners throughout the modelling process again,

reinforcing misconceptions, ensuring effective use of dimensioning and relations/constraints and

encouraging a logical approach to the modelling process.

1. Following the completion of the instructional activity carried out in Activity 1, apply your knowledge of the features used to produce the models below.

From the information provided below model the pulley wheel.

Note: Revolve should be used to produce the overall geometry. All fillets are 3mm

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