Effective Machine Construction and Calculation with AutoCAD® Mechanical

Effective Machine Construction and Calculation with AutoCADŽ Mechanical 2009 Speaker: Helge Brettschneider – MCD Media/Consulting ML319-4 Session

About this Session: At this session we will take the advantage of the 2D mechanical engineering with AutoCAD Mechanical 2009. We will talk about Tips and Trick to improve productivity and we also look at the different calculation functions to check that your design intentions are reliable and meet Project demands. Release the power of AutoCAD Mechanical and optimize your drawing creation techniques on the daily basis.

About the Speaker: Helge Brettschneider Helge started using Autodesk Software in 1987 while working as a mechanical engineer. Now as an Autodesk certified consultant, he assists clients in various sectors of mechanical engineering and design disciplines. He has authored various articles about Autodesk Inventor and Inventor Studio and has directed several videos about Inventor and Autodesk University. Helge has always sought easier ways of doing things to help customers find the best business solution and stay one step ahead of the competition.

eMail: Helge.br@mcdcad.de Blog: WWW.MCDCAD.EU

Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

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Effective Machine Construction and Calculation with AutoCADÂŽ Mechanical 2009

Index About this Session: .................................................................................................................................... 1 Helpful general commands in ACADM

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The centerline cross with hole command ................................................................................................. 4 Better draw a ACADM Rectangular instead of polylines .......................................................................... 5 List of commands for Rectangle creation: ............................................................................................ 5 Construction lines and Otracking .............................................................................................................. 8 Real holes .................................................................................................................................................. 9 Section Lines ........................................................................................................................................... 10 ACADM Hatch ......................................................................................................................................... 10 Power Dimensions / ACADM Dimensions in general.............................................................................. 11 Automatic Dimensioning..................................................................................................................... 12 Break Dimension ................................................................................................................................. 13 Linear and symmetrical Stretching ..................................................................................................... 13 Standard parts and Generators

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Inserting bolted connection .................................................................................................................... 14 The shaft generator ................................................................................................................................ 16 Conical geometry ................................................................................................................................ 16 Some Calculations

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Shaft calculation...................................................................................................................................... 17 Process Overview for Shaft Calculation .............................................................................................. 18 Dialog Options..................................................................................................................................... 18 Belt and Chain calculation....................................................................................................................... 19 FEA (Finite Element Analysis) .................................................................................................................. 21 Options in the FEA Dialog ................................................................................................................... 22 General Functions of the FEA 2D – Calculation Dialog ....................................................................... 24

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Helpful general commands in ACADM With AutoCAD as platform technology you have the best toolset for drawing creation but to create a drawing in the Manufacturing industry you need more than this. You need to have a functionality that assists your Engineering process and so AutoCAD Mechanical provide the basic toolset with the right extensions that helps to shorten the among of time for creating a drawing of your Engineering intention.

The centerline cross with hole command Beside the basic line and circle command you have a command that is called centerline cross with hole. At least it would be better to call it centerline cross with circle, this is what it creates.

This command is handy for drawing circles in various scenarios as you can see below:

Important is that this command a great tool to create concentric circles, to create a centerline cross with more than one hole, enter the pipe symbol | between the diameter values.

For example: 15|25|40

Tip: “Searching for the Pipe character?”

The shift-backslash is where the pipe symbol resides on the US 101 (and possibly US International).

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

Better draw a ACADM Rectangular instead of polylines The AMRECTANG draws a polyline in a rectangular shape. A good approach is to just call up the command and the hit strait away the return button to turn on the dialog box it makes it easier to choose the best method of creation.

Here you find two different types of methods on two tabs. The two point approach helps you to insert a rectangular in an existing geometry and the second type of method with the green dimensions, defines the shape by selecting the start point and different length/height values sets. If you are quiet sure which on meets your needs, you can also type in the command name of the method.

List of commands for Rectangle creation: AMRECTANG

Creates a rectangle starting with the first corner and defining the endpoint.

AMRECTCWH

Creates a rectangle starting with the center using the full base (width) and full height.

AMRECTBWH

Creates a rectangle starting with the base middle using the full base (width) and full height.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

AMRECTBY

Creates a rectangle starting with the base middle by defining the endpoint.

AMRECTCW2H

Creates a rectangle starting with the center using half the base (width) and the full height.

AMRECTBWH2

Creates a rectangle starting with the base middle using half the base (width) and the full height.

AMRECTLY

Creates a rectangle by selecting the height middle as starting point, and by defining the endpoint.

AMRECTCWH2

Creates a rectangle starting with the center using the full base (width) and half the height.

AMRECTLWH

Creates a rectangle starting with the height middle using the full base (width) and full height.

AMRECTCY

Creates a rectangle starting with the center using the endpoint.

AMRECTCW2H2

Creates a rectangle starting with the center using half the base (width) and half the height.

AMRECTLWH2

Creates a rectangle starting with the height middle using the full base (width) and half the height.

AMRECTXWH

Creates a rectangle starting with the first corner using the full base (width) and full height.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

List of commands for Square creation: AMRECTQBT

Creates a square starting with the base middle using the full base (width).

AMRECTQLR

Creates a square starting with the height middle using the full base (width).

AMRECTQBY

Creates a square starting with the base middle using half the base (width).

AMRECTQLY

Creates a square starting with the height middle using half the base (width).

AMRECTQCR

Creates a square starting with the center using half the base (width).

AMRECTQXY

Creates a square by selecting the starting point using the full base (width).

AMRECTQCW

Creates a square starting with the center using the full base (width).

Tipp: When you use the mechanical rectangular you can double click on the geometry at any time to change size and start point definition of the element

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Effective Machine Construction and Calculation with AutoCADÂŽ Mechanical 2009

Construction lines and Otracking

With the construction lines feature, you can create construction lines that extend to infinity in one direction (rays) or both directions (xlines). You can also create circular construction lines.

Construction lines do not change the extents of the drawing, so their infinite dimensions have no effect on zooming or viewpoints. You can move, rotate, and copy construction lines the same way you move, rotate, and copy other objects.

You can use construction lines as references for creating other objects. For example, you can use construction lines to find the center point of a hole, prepare multiple views of the same object, or create temporary intersections that you can use for object snaps.

When you create construction lines, the program places them on layer AM_CL by default.

Construction lines appear in red.

Improve productivity with Otracking: AutoTrack™ helps you draw objects at specific angles or in specific relationships to other objects. When you turn on AutoTrack, temporary alignment paths help you create objects at precise positions and angles. AutoTrack includes two tracking options: polar tracking and object snap tracking.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

Construction lines are very helpful and there are several situations where we really need them.

But sometimes they are confusing, so consider using the OTrack from AutoCAD instead of creating construction lines. This helps you to work faster and more affective the creating and deleting construction lines.

Real holes

In addition to standard parts, the standard part library contains pre-drawn through holes, blind holes, counterbores, countersinks, through slots, blind slots, tapped through holes, tapped blind holes, external threads, and thread ends.

The insertion process is similar for all standard features. Select the hole or slot to insert and determine the view, insertion point, hole length, and nominal diameter. You can also insert user holes and user slots, which have user-defined diameters.

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Positive effects, when using real holes are: When you insert a hole or a standard part in the drawing, the program inserts an object reference, which contains information about the hole or the part, automatically, so you are able to use these two commands to speed up the drawing process.

AMPOWERVIEW command to project a hole to another drawing view.

Use AMSTDPREP to change the representation type of the standard parts in the drawing.

Section Lines

Use AMSECTIONLINE to draw different types of section lines. This command provides the standard section line and two additional section lines with different line types. The length of the wide lines corresponds to the text height, set for the dimension style GEN-ISO-ORD. If the line is three times shorter than the text height, the program draws the entire line section wider.

ACADM always determines, from the whole drawing, the next free section line reference letter, and uses that as the default letter. Lines you draw with the AMZIGZAGLINE or AMBROUTLINE commands will automatically placed on layer AM_4 and lines you draw with the AMSECTIONLINE command will appear on layer AM_5.

ACADM Hatch AutoCAD Mechanical works with a different hatching function than standard AutoCAD. This mechanical hatch exist sins AutoCAD 10, a time period where standard AutoCAD wasn’t able to create an associative hatch and to ensure that all the content works on old drawings it is still the same functionality. It’s not mandatory to use this mechanical hatch, it is up to you which you prefer, if you like to use the associative hatch from basic AutoCAD, no problem. In case of changing the geometry the existing hatch will be handled like the standard mechanical hatch (For Example: adding the size of a tapped hole). The contour will be analyzed and you maybe have to add some new hatches in case of new closed loops.

Tip: Insert the hatch at first and then insert the needed holes (if possible use AMPOWERVIEW). If you proceed in this way the hatch will be trimmed by the hole command.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

Power Dimensions / ACADM Dimensions in general

Power Dimensions are dimensions created by AutoCAD Mechanical's dimensioning commands.

This tool is designed specifically for mechanical engineering requirements, providing abbreviated dialog boxes that conveniently control and expand only the variables relevant to this domain.

The AMPOWERDIM command automatically recognizes objects and defaults to the appropriate dimension type. You can use the same command to place linear, angular radial, diameter, baseline, and chain dimensions. With the AMAUTODIM command, you can create multiple dimensions with minimal input, resulting in instant groups of appropriately spaced ordinate, parallel, or symmetrical dimensions.

Tip: Working with fits is much easier when you expand the dialog to the full size with using mating button.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

Automatic Dimensioning

The AMAUTODIM command measures all contours of an object at once. You can dimension separate objects, as well as objects within blocks. Select the object to dimension and then specify a point marking the origin of the dimension. AMAUTODIM searches for the contours of the object and dimensions them. The command can create baseline, chain, and symmetric dimensions as well as convert one type to another. Place the dimensions in the drawing area using distance snap, which spaces the dimensions appropriately. You can create dimensions for both axes in the same command session.

Tip: When you created a set of Basline dimensions and later on you need to delete on from this set of Dimension, please use the Powererase command instead of using the delete key from the keyboard. In that case the remaining dimensions will be automatically realigned, as you can see in these two pictures below.

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Break Dimension

Sins the old days, there is a function that gives you the ability to create a break in the extension lines and dimension lines, without exploding the dimension object. But this function is not associative like the new Break Dimension (Command “Dimbreak”) from AutoCAD that came in with the 2008 Update.

Linear and symmetrical Stretching

You can stretch or shrink geometry associated with a Power Dimension by using the AMDIMSTRETCH command and changing the dimension text. You can use the command on linear dimensions and symmetrical dimensions.

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Standard parts and Generators Inserting bolted connection The screw connection tool connects two plates. A screw connection can consist of a screw, nuts, washers, and holes, which you can select in the Screw Connection wizard. It is not necessary to select all of these standard parts for a screw connection, but you must select at least one. The dialog of screw connections shows only standard parts that you can combine.

For example, it shows cotter pins only if you have selected slotted nuts as part of the screw connection.

Tip: When you call up the dialog of the screw connection you can use the back button to have access to the available templates of the connection.

On one hand, you can insert a bolted connection without calculation, but normally you have to integrate technical aspects that need to respect during the definition of the used components selection. During the calculation process we have include: 

Material (firmness) class



Load case and quality



Assembly method

The methods used in the calculation are based on the VDI guidelines 2230.

Description of VDI “VDI Verein Deutscher Ingenieure (English: Association of German Engineers) is an organization of 126,000 engineers and natural scientists. Established in 1856, the VDI is today the largest engineering association in Western Europe. The role of the VDI in Germany is comparable to that of the American Society of Civil Engineers (ASCE) in the United States. The VDI is not a union. The association promotes the advancement of technology and represents the interests of engineers and of engineering businesses in Germany.”

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

After selecting the individual components or selection a template for the bolted connection you need to select a size on the right of the dialogbox. A little lower you find the button for starting the calculation for screw diameter estimation.

Static nature loads: centric applied axial force

excentric applied force

applied shearing force

Dynamic nature loads: Centric applied axial force

excentric applied force

applied shearing force

After defining the Material class, applied force and nature of load you have to decide which tightening method will be used. You have here 3 where you have to choose one. The selected method will affect the size of selected parts for bolted connection. The results of your calculation will be displayed in the Results section at the bottom of the dialog.

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Effective Machine Construction and Calculation with AutoCADÂŽ Mechanical 2009

The shaft generator You can use the Shaft Generator to create rotational symmetric parts that make up a shaft or other round geometry. Shafts are generally composed of consecutively placed segments. These segments are drawn from left to right or from right to left. Each shaft segments can be inserted, deleted, or edited to change dimensionally. There are two types of commonly used shaft segments, Cylindrical and Conical. In addition to these, you can also draw segments with standard size wrench geometry, threads, gears, and standard profiles. You can break a shaft segment, or draw grooves, fillets, and chamfers. The Shaft Generator also allows you to place standard parts such as bearings, retaining rings, parallel keys and undercuts on the shaft geometry.

The shaft generator can create all of the geometry mentioned above either internally or externally. You can also automatically display the shaft side view or cross sections for different cutting planes parametrically, with the side and section views updating automatically when the shaft is modified.

Tip: Prior to creation of side views or section views you should use the options button to configure what will included in the view representation

Conical geometry There are two buttons in the Shaft Generator dialog box used to create conical shaft geometry; Slope and Cone. Both methods allow graphical and keyboard input, but the Slope method gives you greater accuracy control. You can determine the dimensions of conical geometry by using your keyboard to respond to command line prompts.

Tip: If you didn’t have all values available for creating a standard cone you should enter D for dialogbox on the command Line after using the slope button in the main dialog. The missing values will be calculated by changing the fields.

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Some Calculations Here are some more calculation abilities for this handout I just picked some of them with the focus on a daily base demand.

Shaft calculation Shafts carry machine components like axles, but are always rotating and transmit torque. Most shafts and axles have at least two supports (on floating or non-friction bearings). Loading forces, such as gear forces, belt or chain tension and the like, generate equal and opposite support forces on the bearing.

Thrust force can be also generated in a shaft from axial force and helical or bevel gears.

Additionally, tensile stress or compressive strain is generated in its cross sections.

Because shafts always carry torque, cross-sections undergo torsional strain. Torque applied to a shaft does not usually rotate throughout the full length of the shaft. It is induced by or transferred to a mechanical part (e.g. belt or gear).

The command shaft calculation serves for the calculation of: 1.

2.

3.

4.

5.

6.

7.

Deflection Line Bending Moment Torsion Moment Supporting Force Torque Rotation Angle Equivalent Tension Safety Factor

All results can be inserted in the drawing as diagrams.

Note:”You only can perform a calculation when you have a prior drawn shaft!”

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

Process Overview for Shaft Calculation 1. From the Content toolbar, choose Shaft Calculation.

2. Enter C to create a contour for the shaft calculation.

3. Select the shaft with a window, and press Enter.

4. Select the centerline of the selected shaft.

5. The Shaft Calculation dialog box is displayed.

6. Enter the Revolution Direction, select the support, and define the loads and the material.

7. Choose Moments and Deformations.

8. Choose OK. 9. Specify a rectangular area.

10. Place the result block into your drawing.

Dialog Options

The following options are available: 1. Revolution Direction - Determines the revolution direction of the shaft (clockwise or counter-clockwise).

2. Supports - Inserts a support. The shaft can be supported by fixed and moveable supports. Any combinations of these two support types are allowed (even statically indefinite cases).

3. Torsion - Inserts a torsion moment controlled via dialog box.

4. Point Load - Inserts a radial point load controlled via dialog box.

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

5. Gear - Inserts a gear load controlled via dialog box.

6. Table - Opens a material dialog box with the values for E-modulus, stretch limits, Poisson constant and brittleness.

7. E-Module - Displays the elasticity modulus belonging to the material. Enter other values, as needed.

8. Poisson - Displays the value for Poisson constant.

9. Stretch Limit - Displays the value for the stretch limit.

10. Edit - Edits the loads (quantity and direction). Click Edit and select the load. The corresponding load dialog box is displayed so that you can edit the settings.

11. Delete - Deletes supports and loads. Select the desired supports and loads. You return to the dialog box after pressing Enter.

12. >>> - Closes the dialog box temporarily and switches to the drawing. Press Enter to return to the dialog box.

Belt and Chain calculation

AutoCAD Mechanical performs calculations for belt or chain lengths based on existing geometry. A dialog box displays the available representations for chains and belts and for pulleys and sprockets. A library function helps saving and recalling the respective components.

Chain drives are interlocking, wrapping drives, where an endless chain wraps around two or more sprockets. Chain drives, as with spur gear pairs, serve to transfer force and motion between parallel shafts. Chain drives can bridge the distance between axles that typical gearwheels cannot.

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Effective Machine Construction and Calculation with AutoCADÂŽ Mechanical 2009

Chain drives are not as flexible as belt drives, but can be used when space, power translation, or axis distance make incorporating a belt drive unfavorable. A facet of a chain's length that must be accounted for is the polygon effect at the sprocket. The polygon effect occurs particularly in smaller synchronous belts having relatively low teeth numbers; the turning transmission is not constant, due to the cyclic changes of the chain peaks and valleys. The length of a chain therefore does not correspond to its centerline.

Belt drives can transfer a lot of power with respect to their dimensions and weight; they run quietly without slip, and require relatively little shaft load or support. Belts do not have the polygon effect; therefore the length of the centerline is the length of the belt.

Both calculations essentially follow the same procedures. The chain or belt length calculation routine, used for both calculations requires that you insert at least two circles into your drawing to represent the pitch circle diameter of the pulleys or sprockets. Alternatively, you can insert sprockets or pulleys using AMSPROCKET. The pulleys and chain wheels are displayed as circles. You must select the reference circle to carry out a calculation. The circles establish the tangential conditions required for the chain or belt. We recommend carrying out length calculations on separate layers or in an extra drawing, to view the simplified presentation. To insert a chain or belt, or a sprocket or pulley, you must create and calculate a base arrangement first.

When a chain is drawn, it follows a polyline. This polyline is generated by the length calculation function.

Pulleys are represented as circles. The circles correspond to the pitch radius of the pulley. The tooth profile is calculated from the selected block of the library. The pulley orients itself on the shape of the synchronous belt. The pitch circle corresponds to the length of the pulley at the pitch line.

A sprocket is defined by the number of teeth. The diameter of the roller corresponds to the diameter adjacent to the sprocket.

Note: “The teeth of the pulley correspond to the shape of the teeth for the belt of the library.

However, in reality these shapes differ slightly.�

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

FEA (Finite Element Analysis)

The FEA function calculates stress and deformation in a plane for plates with a given thickness.

It also calculates stress and deformation on a cross section with individual forces and stretching loads, and having fixed or movable supports. The FEA routine uses its own layer group for input and output. FEA is not designed for solving all special FEA tasks. Its purpose is to provide you with a quick idea of the stress and deformation distributions.

A FEA task is a closed cross-section outline in which a number of internal outlines and contours can be found. The following pre-conditions are required: 1. The contour has to be drawn before starting the FEA routine.

2. The internal and external contours are not allowed to touch one another.

3. The contour or cross section has to create a closed surface.

Multiple FEA tasks are permitted within the same drawing. If the contour changes, a new FEA task has to be solved.

After invoking the command you are prompted for an interior point, which has to be inside of the corresponding contour.

Select a point within the cross-section. The FEA routine finds the external and internal contours enclosed in the area defined by the cross section. If 3DFACE entities already exist in the selected contour, you are prompted to decide how to proceed: Existing or [New Solution]<Existing>:

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Effective Machine Construction and Calculation with AutoCAD速 Mechanical 2009

If you select Existing (default), you are still working with the old task. If you select New, the old calculation is deleted and the routine starts a new calculation. Use this option if the contour has changed. The FEA 2D Calculation dialog box is displayed.

Options in the FEA Dialog

The following options are available: Loads and Forces - Inserts and defines the specified loads and forces.

Inserts and defines a point force

Inserts and defines a line force

Inserts and defines a fixed support

Inserts and defines a fixed line support

Inserts and defines a moveable support

Inserts and defines a moveable line support

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Effective Machine Construction and Calculation with AutoCAD® Mechanical 2009

Edit Loads and Forces –Edit the defined border conditions Changes the size of the existing forces and force line Changes the direction of the existing forces and supports Moves the existing forces and supports to another location Copies the existing forces and supports to another location Deletes existing forces and supports

Material – Edits the defaults values of the property fields Selects the default material from the table

Default Thickness – Determines the thickness of the cross section

With the two buttons below the “d=” value field you specifies whether elastic deformation in the z-direction is possible or not

Mesh – Defines and generates the mesh required for the calculation Starts the mash generation

Specifies the value for the average mesh width

Refining - Shortens (or rarely lengthens), the sides of the mesh triangles in order to achieve more precise (or rarely, quicker and less precise) calculation.

Manual Refining - Specifies the mesh-refining factor. Two icons provide the following refining options: 

Circle - Continuously refines the average mesh width in the basic mesh to the border.



Window - Refines the selected window.

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Effective Machine Construction and Calculation with AutoCADÂŽ Mechanical 2009

Automatic Refining - Provides an automatic refining function for the regions with the largest Von-Mises stress values.

Results - Performs the calculations.

Creates isolines and isoareas.

Creates main stress lines.

Creates a deformed mesh

Selects an output file for storing the complete FEA task Turns on the node numbering in the mash

General Functions of the FEA 2D â&#x20AC;&#x201C; Calculation Dialog Deletes all results, stress, deformations and node/triangle Deletes all results, the mesh and the copied contour. You can decide whether you want the loads and forces to remain in the drawing Displays the FEA dialog, where you can configure colors settings and others Closes all dialogs and leaves the command without saving the changes

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