effective machine construction and calculation with autocad® mechanical
DESCRIPTION
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.TRANSCRIPT
Effective Machine Construction and Calculation with AutoCAD® 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: [email protected] Blog: WWW.MCDCAD.EU
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Index
About this Session: .................................................................................................................................... 1
Helpful general commands in ACADM 4
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 14
Inserting bolted connection .................................................................................................................... 14
The shaft generator ................................................................................................................................ 16
Conical geometry ................................................................................................................................ 16
Some Calculations 17
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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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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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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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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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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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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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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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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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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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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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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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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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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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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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. Deflection Line 2. Bending Moment 3. Torsion Moment 4. Supporting Force 5. Torque Rotation Angle 6. Equivalent Tension 7. 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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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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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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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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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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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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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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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 – 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