3D Modelling in SolidWorks - Part II - Creating blocks sketch entities, Analyzing an assembly motion, COSMOSXpress

A Tutorial on 3D Modelling in SolidWorksBy Samarth Mahajan

This tutorial is our own walk-through of the instructions given in this document http://www.scribd.com/doc/6793563/Blocks-to-Assembly  . We have taken screenshots at a number of steps which might (hopefully) give you a better idea of SolidWorks than the original document.

As you must have guessed from the last tutorial, SolidWorks can be used as a great tool before undertaking a project for mechanical design purposes. Did you know that you can even conduct a stress analysis on a model or the analysis of an assembly in motion using this software?
In this second part of the SolidWorks series we will highlight some important tools in SolidWorks which can come in handy for engineering design purposes and are generally not present in other modelling packages.
This tutorial includes the following parts:
  • Create blocks from single or multiple sketch entities
  • Analyse an assembly motion
  • Use COSMOSXpress to do stress analysis
The first two topics pertain to the subject of Kinematics of Machines and third topic addresses the practical needs of Mechanics of Solids. Both these subjects are studied by Mechanical Engineers at UG level.
With blocks, you can quickly develop conceptual models of mechanisms or linkages. These models ultimately include several parts that pivot, slide, or rotate. The benefit of modelling mechanisms with layout sketches is the speed and flexibility with which designers can experiment with design variations.
Here we take up a Four Bar Linkage.

Sketching the Linkage

  1. Open a new part and select the Front plane.
  2. Click Line  (Sketch toolbar), and coincident with the origin, sketch a horizontal line.
  3. Click Smart Dimension  (Dimensions/Relations toolbar), and dimension the line to 76.
  4. Click Line  (Sketch toolbar), and using inferences as you sketch, add three non-parallel and non-perpendicular sketch entities.

As you drag the pointer, the line length updates dynamically.

  1. Press Esc to clear the tool, and click in the graphics area to clear the selection.

Making Blocks

  1. Click Make Blocks  (Blocks toolbar).
  2. Select the horizontal line for Block Entities, and in the PropertyManager click.
  3. Click in the graphics area to clear the selection.

You have created a block. Note that:Block1-1 is displayed in the FeatureManager design tree under Sketch1.

  • The geometry of the block in the graphics area is displayed in gray.

  1. Repeat steps 1-3 with each line entity.

  1. Click Rebuild  (Standard toolbar).

  • Four blocks, identified as Block1-1 through Block4-1, are displayed in the FeatureManager design tree under Sketch1.
  • The geometry in the graphics area for all blocks is displayed in gray.

Adding Relations

  1. Right-click Sketch1 and select Edit Sketch.
  2. Click Add Relation  (Dimensions/Relations toolbar).
  3. In the graphics area, select the bottom left point.

  1. In the PropertyManager, under Add Relations, click Fix.

  1. In the graphics area, select the horizontal line.
  2. In the PropertyManager, under Add Relations, click Horizontal, and then click.

Testing the Linkage

  1. Click in the graphics area to clear the selection.
  2. Select the end point on the right, and drag the Four Bar linkage.

This completes the block that we set out to create i.e. the four bar mechanism that you are left with.

Design Analysis

1.  Assembly Motion
SolidWorks can be used to animate an assembly, which is useful when analysing the motion of a working machine. Let us try and animate a simple four bar mechanism.

Add A Motor

To add a motor to an animation:
  1. Open 4bar1.sldasm from the add motor directory that has been provided alongside the tutorial.
  2. Click the Motion Study 1 tab (at the bottom of the graphics area).
  3. Click Motor  (MotionManager toolbar).
  4. In the PropertyManager:
    • Click Rotary Motor.
    • For Motor direction, select the face of Part2 in the graphics area.
  5. Under Motion:
    • For Motor type, select Constant speed.
    • For Constant speed motor, enter 30.
  6. Click.
  7. In the MotionManager, drag the key for 4bar1 to 6 seconds.
  8. Click Play from Start  (MotionManager toolbar).
To suppress and unsuppress mates during a Motion Study:
  1. In the FeatureManager design tree, expand the Mates folder.
  2. For Concentric2, right-click at 2 seconds select Place Key.
  3. Place another key at 4 seconds for Concentric2.
  4. Set the time bar to 2 seconds.
  5. Right-click on Concentric2 in the FeatureManager design tree and select Suppress.

    The mate is suppressed between the 2-second mark and the 4-second mark.
  6. Click Calculate.
This is all that you need to know to animate an assembly in SolidWorks.

2. COSMOSXpress

COSMOSXpress offers an easy-to-use first pass stress analysis tool for SolidWorks users. COSMOSXpress can help you reduce cost and time-to-market by testing your designs on the computer instead of expensive and time-consuming field tests.
This exercise uses a simple hook model to introduce you to the following topics:
  • Starting COSMOSXpress
  • Learning the basic steps of design analysis
  • Assessing the safety of the design
  • Evaluating the accuracy of results
  • Documenting your project
The hook, made of Alloy Steel, is fixed at the hole and loaded with a 1500 lb force as shown in the figure.

Opening the Hook Part Document

  1. Open aw_hook.sldprt provided in the Part 2 folder alongside this tutorial.
  2. Click File, Save As and save the part file as aw_hook-test.SLDPRT.

This allows you to use the original file again.

Starting COSMOSXpress and Setting Options

Click COSMOSXpress analysis wizard or click Tools, COSMOSXpress.

Setting options

On the Welcome tab, you set the default system of units for COSMOSXpress. You can also set a folder for storing analysis results.
To set the analysis options:
  1. Click Options.

The Options screen appears.

  1. Set System of units to English (IPS).
  2. Click to browse to the folder you want and click OK.
  3. Check Show annotation for maximum and minimum in the result plots.
  4. Click Next.

A check mark appears on the Welcome tab, and the Material tab appears.

Assigning Material

In this step, you assign a material to the part from the SolidWorks material library. The hook is made of Alloy Steel.
To assign Alloy Steel to the part:
  1. Click the plus sign next to Steel to see all materials in this class.
  2. Select Alloy Steel.
  3. Click Apply.

COSMOSXpress assigns Alloy Steel to the part and the text "current material: Alloy Steel" appears in the screen. Notice also that a check mark appears on the Material tab.

  1. Click Next.

The Restraint tab appears.

Applying Restraints

On the Restraint tab, you enter information on how the part is supported.
To fix the face of the hole:
  1. Click Next to continue.
  2. Type a name for the restraint, for example, FixedHole.
  3. In the graphics area, click the face of the hole.

Face<1> appears in the selection box and the restraint symbols appear on the selected face.

  1. Click Next.

FixedHole appears in the restraint box and a check mark appears on the Restraint tab.

  1. Click Next.

The Load tab appears.

Applying Load

Now you apply a 3000 lbs downward force.
To apply the force:
  1. Click Next to continue.
  2. Select Force and click Next.
  3. Type DownwardForce in the restraint name box.
  4. In the graphics area, select the two faces shown in the figure.

Face<1> and Face<2> appear in the selection box.

  1. Click Next.

Applying Load (continued)

  1. Click Normal to a reference plane.
  2. In the FeatureManager design tree, click Plane2.

Plane2 appears in the Select a reference plane box. Note that the force direction is upward.

  1. Click Flip direction.

The force direction is reversed.

  1. Type 1500 in the force value box.

  1. Click Next.

DownwardForce appears in the force set box and a check mark appears on the Load tab.

  1. Click Next.

The Analyze tab appears.

Analyzing the Model

To analyze the part:
  1. Click Yes (recommended) to accept the default mesh settings.
  2. Click Next.
  3. Click Run.

The analysis begins and a progress indicator appears.

A check mark appears on the Analyze tab and the Results tab appears.

Viewing Results

The first screen of the Results tab lists the minimum factor of safety of the model approximately as 7.6 which means that the model is not expected to fail under the specified loads and restraints.

Calculating the maximum force

Based on the linear static assumption of stress analysis, we can calculate the maximum force as follows:
  • applied force per face = 1500 lbs
  • estimated minimum factor of safety = 7.6
  • In general, critical regions of the part will start yielding if we apply a new load equal to the current load multiplied by the calculated minimum factor of safety
  • In this case, critical regions of the part will start yielding if we apply a force of approximately 1500 X 7.6 = 11,400 lbs to each of the two faces

Changing the Element Size

To study the effect of changing the element size on the results, you change the default element size and reanalyze the part.
To change the element size and reanalyze the part:
  1. Click the Analyze tab.
  2. Click No, I want to change the settings and click Next.
  3. Drag the slider to the right most position.

The Element size updates to 5.3705 and the Element tolerance updates to 0.26853.

  1. Click Next.

Note that exclamation marks appear on the Analyze and the Results tabs.

  1. Click Run.

When the analysis is complete, the Results tab appears.

The new factor of safety is 7.7, which is about 2% difference from the original 7.6. This small difference indicates that the previous results are accurate

Generating Equivalent Stress Plot

This step plots the equivalent (or von Mises) stress distribution in the part.
To view stresses:
  1. On the Results tab, click Next.
  2. On the Optimize tab, select No and click Next.

  1. Click Show me the stress distribution in the model and click Next.

COSMOSXpress generates the equivalent stress plot.

Note that annotations for maximum and minimum von Mises stress appear by default on the plot. Note also that a yield strength marker appears at the bottom of the plot legend.

  1. Click any of the following:

  • Play to animate the stress plot.
  • Stop to stop the animation.
  • Save.

The Save As dialog box appears. Type a name for the animation file and click Save.

  1. Click Next.

A list of the available results appears.

Generating Resultant Displacement Plot

In this step, you plot the resultant displacement of the model.
To view resultant displacement:
  1. Click Show me the displacement distribution in the model and click Next.

COSMOSXpress generates the resultant displacement plot.

You can animate and save the animation of the resultant displacement plot as you did for the equivalent stress plot.

  1. Click Next.

A list of the available results appears.

Generating an Analysis Report

To generate an HTML report:
  1. Click Generate an HTML report and click Next.
  2. Click Cover page, Introduction, and Conclusion and click Next.
  3. Enter the information for the report title, the author name, and the company name. Click Browse to include a logo. Type the date of the report and click Next.
  4. Type the desired text for the introduction and click Next.
  5. Type the desired text for the conclusion and click Next.
  6. Enter a name for the report file. Click Printer friendly version so that the report graphics are printed properly.
  7. Click Next.

The report generates and displays in your default web browser.

  1. Click to close the report window.

Exiting COSMOSXpress and Saving the Analysis Session

  1. Click Close.

A message box appears to ask if you want to save the COSMOSXpress data.

  1. Click Yes to save the COSMOSXpress data.
This is the end of this exercise and with it we also end the SolidWorks series. Next up will be a tutorial on Google SketchUp, which is one of the newest entrants in the field of 3D modelling.