Unit 12: Mechanical simulation and modelling

LO2: Be able to carry out simulations to assess the manufacturability of components or products

Use draft analysis techniques to assess the manufacturability of injection moulded or cast componentsInstructions 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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It is important when designing components for casting or injection moulding that the geometry of the design incorporates some key features that will allow for successful production. This is generally to ensure that the component is rigid, does not warp or shrink and can be easily ejected from the mould or die.

CAD software packages have multiple modelling tools that allow for these geometric features to be easily added to component design. From a modelling perspective these tools include; Shell, for hollowing out a part and leaving consistent wall thickness. Draft, for creating sloped faces and walls on a part which will allow for easy ejection from a mould or die and Rib, used to add strengthening ribs across hollow geometry to ensure rigidity in the final component. These tools are covered in Unit 10 Computer Aided Design (CAD). It is advisable that learners are familiar with these features to support the content of this lesson element.

Once model geometry has been created, it is important to analyse it before committing to production to ensure it contains all the necessary features required to manufacture it. Software packages have multiple tools that can assist this process. See Lesson Element Undertake simulations to assess the manufacturability of injection moulded components which focusses on the assessment of draft on a model to ensure all the walls/faces of the component have appropriate draft angles to ensure effective ejection from the mould. The draft analysis tool highlights faces in a model that have positive, neutral or negative draft, informing the user of where drafting issues may occur.

Tutors could guide learners step by step through the analysis of a component as set out below.

These activities offer

opportunities for English

skills development.

These activities offer

opportunities for maths

skills development.

Activity 1: Draft analysisThe model geometry used in this Lesson Element represents a simple injection moulded case. This

geometry is also used as the basis for Lesson Element Undertake simulations to assess the

manufacturability of injection moulded components. Tutors could deliver these lesson elements

sequentially as part of developing learners’ knowledge of injection moulding processes.

Below is a 3D model of the injection moulded case.

Figure 1: 3D model of an injection moulded case

The first part of the draft analysis is to decide which face represents the split line of the mould tool. This

will be used to define the direction of pull for the draft.

In this case the direction of pull is defined by a flat face. This is shown below and illustrated by the blue

highlighted edges of the face.

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Suggested timings:Activity 1: 30 minutes

Activity 2: 30 minutes

Activity 3: 1 hour

Figure 2: Direction of Pull and draft analysis results

The model should now change colour. These colours illustrate the amount of draft on the highlighted

faces. It is important to tell the system how much draft is required as minimum. In this case the system is

analysing the model for walls/faces that have at least 3°.

Any face that is green in the simulation has positive draft based on the direction of pull. In this case the

direction of pull illustrates the exit trajectory of the half of the injection mould tool that would form the

geometry of the internal cavity of the component. Any geometry that is highlighted yellow has zero draft

(the faces are 90°or parallel with the direction of pull). Finally, any geometry that is highlighted red has

negative draft. This means that the angle of draft on the walls/faces highlighted red is formed in the

opposite direction to that required for effective exit from the mould.

As can be seen in Figure 2 above, assessing the internal geometry of the component, the faces are

green and suitable for manufacture. It also illustrates that the outer geometry of the component is red.

This is because the external geometry will be formed by the opposite half of the mould tool which is

pulled in the opposite direction when being separated in production.

To assess the external geometry the Direction of Pull needs to change. Flip the Direction of Pull and the

colour of the faces should change.

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Figure 3: Opposite Direction of Pull – external geometry

Figure 4: External geometry – draft analysis

This clearly shows that the external faces of the model geometry have sufficient draft and could be

produced effectively.

Learners should save the results of their analysis.

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Activity 2Following the completion of the demonstration learners could be directed to the tutorial below on

YouTube. Learners can work their way through the tutorial independently to complete the task. Tutors

could supply learners with some similar model geometry or ask learners to create their own model with

similar geometry to that illustrated in the tutorial.

For extension work there are three parts to this tutorial that moves further into the development of

geometry for mould tools.

Tutorial link: https://www.youtube.com/watch?v=rn86kptKgj0

Activity 3Following the completion of the first activities in this Lesson Element, tutors could ask learners to

develop a design of their choice for an injection moulded casing.

Good examples to select could be a mobile phone housing or case, the top bezel of a laptop housing or

a hairdryer casing. See link below.

Image source: http://international.solis.com/tl_files/images2/mendrisioproduction/DSCF3469.jpg

Tutors could encourage learners to generate creative designs for their chosen component and model

them in 3D. Once complete the learners need to analyse their design using draft analysis as per the

process in Activity 1. They need to assess their geometry and make any modifications based on their

results.

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Unit 12: Mechanical simulation and modelling

LO2: Be able to carry out simulations to assess the manufacturability of components or products

Use draft analysis techniques to assess the manufacturability of injection moulded or cast components

Learner activity sheetIntroductionIt is important when designing components for casting or injection moulding that the geometry of the

design incorporates some key features that will allow for successful production. This is generally to

ensure that the component is rigid, does not warp or shrink and can be easily ejected from the mould or

die.

CAD software packages have multiple modelling tools that allow for these geometric features to be

easily added to component design. From a modelling perspective these tools include; Shell, for hollowing

out a part and leaving consistent wall thickness. Draft, for creating sloped faces and walls on a part

which will allow for easy ejection from a mould or die and Rib, used to add strengthening ribs across

hollow geometry to ensure rigidity in the final component.

Once model geometry has been created, it is important to analyse it before committing to production to

ensure it contains all the necessary features required to manufacture it. Software packages have

multiple tools that can assist this process

This Lesson Element will focus on the assessment of draft on a model to ensure all the walls/faces of the

component have appropriate draft angles to ensure effective ejection from the mould. The draft analysis

tool highlights faces in a model that have positive, neutral or negative draft, informing the user of where

drafting issues may occur.

Version 1

Activity 1: Draft analysisThe model geometry used in this lesson element represents a simple injection moulded case.

1. Open a 3D model of the injection moulded case.

Figure 1: 3D model of an injection moulded case

The first part of the draft analysis is to decide which face represents the split line of the mould tool. This

will be used to define the direction of pull for the draft.

In this case, the direction of pull is defined by a flat face. This is shown below and illustrated by the blue

highlighted edges of the face.

2. Select the face on the component.

Version 1

Figure 2: Direction of Pull and draft analysis results

The model should now change colour. These colours illustrate the amount of draft on the highlighted

faces. It is important to tell the system how much draft is required as minimum. In this case the system is

analysing the model for walls/faces that have at least 3°.

Any face that is green in the simulation has positive draft based on the direction of pull. In this case the

Direction of Pull illustrates the exit trajectory of the half of the injection mould tool that would form the

geometry of the internal cavity of the component. Any geometry that is highlighted yellow has zero draft

(the faces are 90°or parallel with the direction of pull). Finally, any geometry that is highlighted red has

negative draft. This means that the angle of draft on the walls/faces highlighted red is formed in the

opposite direction to that required for effective exit from the mould.

As can be seen in Figure 2, which assesses the internal geometry of the component, the faces are green

and suitable for manufacture. It also illustrates that the outer geometry of the component is red. This is

because the external geometry will be formed by the opposite half of the mould tool which is pulled in the

opposite direction when being separated in production.

To assess the external geometry the direction of pull needs to change.

Version 1

3. Flip the Direction of Pull and the colour of the faces should change.

Figure 3: Opposite Direction of Pull – external geometry

Figure 4: External geometry – draft analysis

This clearly shows that the external faces of the model geometry have sufficient draft and could be

produced effectively.

4. Save the results of your analysis.

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Activity 2Following the completion of the demonstration with your tutor in Activity 1 you can now attempt the

tutorial below on YouTube.

Create some model geometry similar to that in the tutorial.

Once complete try the linked tutorials that are available which move further into the development of

geometry for mould tools.

Tutorial link: https://www.youtube.com/watch?v=rn86kptKgj0

Activity 3Following the completion of the first two activities in this Lesson Element you are now required to

develop a design of your choice for an injection moulded casing.

Good examples to select could be a mobile phone housing or case, the top bezel of a laptop housing or

a hairdryer casing. See link below.

Image source: http://international.solis.com/tl_files/images2/mendrisioproduction/DSCF3469.jpg

Once your model geometry is complete you should analyse your design using draft analysis as per the

process in Activity 1. Once you have assessed the geometry you should make any necessary

modifications based on the results.

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