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  • Documentation

    CAD Edit (CAD Mode)

    SimScale offers an environment to interact with your CAD model and perform CAD-related operations, after uploading it, as a part of preprocessing and also while in the middle of setting up your simulation.

    Within the Workbench users can perform CAD editing operations such as delete, extrude, or scale CAD parts and comfortably focus on optimizing their CAD model. Once edited, users can save the edited copy while still retaining active access to the original CAD model.

    To edit the CAD model from the Workbench select the imported geometry and click on the ‘Edit copy’ button in the panel:

    edit a copy cad
    Figure 1: Access CAD editing from the SimScale Workbench by selecting the imported geometry and then clicking ‘Edit a copy’ as shown.

    Or just click on the icon to open the context menu as shown below:

    edit a copy cad mode
    Figure 2: Access CAD editing by clicking on icon and then ‘Edit a copy’ in the context menu.

    CAD Editing Interface

    The interface for CAD editing opens in the simulation Workbench itself. Existing or new simulations can be easily accessed while editing the CAD geometries. The interface looks as shown in Figure 3:

    cad mode interface simscale
    Figure 3: CAD editing interface has four important sections viz., 1. Operations Toolbar, 2. History, 3. Scene Tree (for geometry), and 4. Finish/Cancel to conclude the operation.
    1. Operations Toolbar: All the supported CAD operations are listed here. All the operations have been further explained in this document.
    2. History: The history of all the performed operations will be listed here in order under the copy of the original CAD geometry.
    3. Scene Tree: The original geometry with its solid bodies and faces is enlisted here. Toggle Show faces to see and keep a track of all the faces of each solid body present in your geometry.
    4. Delete draft/Save: Click ‘Save’ to create your modified geometry. The new geometry will be listed as a copy of the original under the Geometry tree. Click ‘Delete draft’ to return to the Workbench without applying the changes.


    A user can only work on a copy (draft) of the original CAD. This means that it is not possible to edit the original geometry under any circumstances and the CAD edit operations can only be performed on its duplicate copy.

    CAD Edit Operations

    The following operations are supported with more coming soon. The operations are categorized based on their application.



    The Delete operation helps you to delete a face from the CAD model by selecting ‘Delete’ from the operations toolbar and then assigning one or multiple faces to be deleted.

    Delete face operation in CAD mode with healing methods
    Figure 4: Delete face operation with healing methods: Heal and Cap. More than one face can be assigned.

    The settings panel also allows choosing between the available healing methods, viz. Heal and cap while the face delete operation is being performed. Choose Leave Open to opt out.

    In the following section, all the healing methods are described using simple geometry as follows:

    reference geometry to demonstrate healing methods
    Figure 5: Reference geometry used to demonstrate the healing methods for the face delete operation is a cylinder with an extra curved face.

    The reference geometry is a cylinder with one of its edges rounded to produce 1 curved and 3 planar faces.


    The Heal method will try to fill up the surface lost to the delete operation by trying to either expand or contract the adjacent faces until they intersect.

    shrink healing method in face delete cad mode
    Figure 6: The Heal method. Deleting the top face should return the exact same result as if the operation wasn’t performed. Deleting the curved face should raise the side face and expand the top face until they intersect.


    The Cap healing method will try to fill up the surface lost to the delete operation by connecting the adjacent faces without changing them.

    cap healing method in face delete cad mode
    Figure 7: The Cap healing method. Deleting the top face should return the exact same result as if the operation wasn’t performed. Deleting the curved face should create a face that connects the previously connecting faces without changing them.

    Leave Open

    This healing method will leave a void as a result of the face delete operation and no additional efforts will be taken to heal the connecting faces.

    no healing method in face delete cad mode
    Figure 8: The Leave Open method. Deleting the top face and the curved face should just remove it, creating a sheet body. In case there survive faces that are not in contact with any of the remaining faces they will still be part of the same sheet body.


    With the Move operation, you can extrude a face in the direction of its normal. Select ‘Move’ from the operations toolbar to open the settings panel for this operation. There are two methods to move faces. For illustration let’s consider the highlighted heat sink face:

    cad mode move operation on heat sink
    Figure 9: Selecting a face for performing the Move operation. More than one face can be selected.

    First, select the face and then choose one of the following methods:


    Specify the distance up to which the selected faces need to be moved/extruded.

    cad mode move operation with distance method
    Figure 10: Selecting the Move method to Distance will extrude that face up to the desired value.

    Up to Entity

    Specify the entity face up to which the selected faces need to be moved/extruded.

    cad mode move operation with up to entity method
    Figure 11: Selecting the Move method to Up to entity will extrude that face up to the plane of the entity face.


    With the Extrude operation, you can extrude a face in the direction of its normal by specifying the distance or the face of an entity up to which it should extrude. Select ‘Extrude’ from the operations toolbar to open the settings panel for this operation. There are three methods to extrude faces. For illustration let’s consider the highlighted-blue face:

    extrude operation simscale
    Figure 12: Settings panel for Extrude operation.

    First, select the face and then choose one of the following methods:

    Add New

    Add a new face to the existing one, while it is extruded in the normal direction. This operation creates an additional part.

    Selecting the Add new method to Distance will extrude that face up to the desired value.
    Figure 13: Selecting the Add new method will add a part to the geometry.

    Did you know?

    Using a negative value in the Add new type extrusion would result in the removal of a part of the geometry dividing it into two parts instead of adding a new part.


    Extrude the face, merging it with the previous one. Thus, the number of parts remains the same.

    Selecting the Merge method to Distance will extrude that face up to the desired value.
    Figure 14: Selecting the Merge method will extrude the face maintaining the same number of parts.


    Extrudes the face in the normal opposite direction, giving a removal operation.

    Selecting the Remove method to Distance will extrude that face up to the desired value.
    Figure 15: Selecting the Remove method will subtract a part of the geometry.


    To perform extrude operation on multiple faces at the same time, ensure that all selected faces have the same normal.


    Specify the distance up to which the selected faces need to be extruded. All those Extruded operations in this section were made using the distance extrusion method.

    Selecting the Extrude method to Distance will drive that face up to the desired value.
    Figure 16: Selecting the Extrude method to Distance will drive that face up to the desired value.

    Up to Entity

    Specify the entity face up to which the selected faces need to be extruded.

    Selecting the Extrude method to Up to entity will drive that face up to the desired value.
    Figure 17: Selecting the Extrude method to Up to entity will drive that face up to the desired value.



    The Delete operation will delete the solid bodies present in the CAD model. Click on ‘Delete’ under Body in the operations toolbar and assign one or more volumes from your CAD model before hitting ‘Apply’.

    Delete bodies in CAD Mode
    Figure 18: Assign bodies to be deleted. More than one body can be assigned at once.

    Close Sheet

    There are instances where the CAD is missing one or more faces (these CAD models are called sheet bodies) and you are unable to proceed in the simulation process. In such cases the Close Sheet operation for bodies (volumes) is helpful. In the settings panel, select the bodies with missing faces to close and choose a closing method.

    settings panel close sheet cad mode simscale
    Figure 19: Settings panel for the Close Sheet operation requires you to select sheet bodies and a closing method to apply.

    Closing Method

    The Closing method defines how to close the sheet body using either the Cap or the Grow method. These methods are described below using an example of Crystal Towers:

    crystal towers
    Figure 20: A CAD model of Crystal Towers used as a reference for the Close Sheet operation. The middle tower is missing a face on the top.

    The tower in the middle has a missing face on the top. Hence, the close sheet operation is perfect for this CAD model.


    The Cap method looks for the minimum possible surface path to close the sheet body and is the default closing method.

    cap closing sheet method
    Figure 21: The missing top face for the middle tower is now closed with a face with a minimum possible surface area

    Applying this method to the middle tower closes the top face with minimum possible surface area.


    The Grow method will try to extend the connecting faces to the missing face until they meet at a vertex.

    grow closing sheet method
    Figure 22: The middle tower is extended up to a point where the connecting faces meet.

    Applying this method by picking up the middle tower extends the connecting faces of the missing face elongating the middle tower until they all meet at a point.

    Facet Split

    Facet Split allows users to split the CAD model into multiple faces based on the defined maximum split angle. This operation comes in handy when dealing with .stl files as they often consist of only a single face.

    facet split cad mode
    Figure 23: Use the Facet Split operation to split your CAD model into multiple faces based on the maximum split angle.

    The angle can be added in degrees between 0 and 180 and is by default 30.


    In order to detect interfaces between two solids or a solid and a fluid, we need to perform an imprint. This action cuts the interface between two bodies that are in physical contact into recognizable surfaces. Please refer to our article where a detailed explanation of what an imprint does is well mentioned.

    In the CAD mode, click on ‘Imprint’, then assign all the parts that need to be imprinted, and hit ‘Apply’.

    body operation imprint
    Figure 24: Detect interfaces between bodies by performing an imprint operation on them.


    In case the uploaded model does not match the original dimensions or the dimensions of your choice, the Scaling operation can be used to adapt the model size accordingly. With scaling, the simulation setup parameters might also change and care should be taken to avoid unreliable results.

    Scale bodies within the CAD Edit mode
    Figure 25: Scaling operation can be used to adapt the model size accordingly using a scaling factor.

    Assign all the bodies that need to be scaled. The settings panel also contains a slider to set a scaling factor while also allowing direct entry of the value.


    The Split operation allows users to cut individual CAD bodies into two parts based on the position and the orientation of the plane defined.

    split operation in CAD mode
    Figure 26: Split operation in CAD edit where the model can be split into two parts

    The orientation of the splitting plane is defined by specifying the normal to the plane. The part lying on the side where the normal vector points is retained, while the other part is removed. The user has the option to keep parts from both sides of the plane as well.


    You might run into situations where your CAD model has multiple overlapping parts. This might pose a hindrance to the simulation physics causing the simulation setup to fail. If this is the case try our set of Boolean operations. These operations allow you to perform union, subtraction, and intersection operations between different parts. These are described below:


    To perform the boolean operations the user must select two or more bodies that share overlapping volumes. If there are assigned bodies that don’t overlap they will be excluded from the operation. Even if no parts overlap, the operation will still show as successful but no changes will be shown in the viewer and in the scene tree.


    The Union operation is used to merge two overlapping entities into a single entity. The resulting body encloses the volume of both overlapping entities. This is shown below:

    union operation in cad mode
    Figure 27: Union boolean operation is used to merge two or more bodies into a single body.

    The CAD geometry consists of two overlapping bodies, Part 1 (cube) and Part 2 (sphere). Their different colors represent two separate entities. These two bodies are separately identified in the scene tree. To perform the Union operation select the two bodies and hit ‘Apply’.

    result of union operation simscale
    Figure 28: A successful union operation of two bodies resulting in a single body, shown in the scene tree by listing only one part.

    On success, the CAD geometry shows a single body identified with the name Part 2 in the scene tree and the same color. This signifies that the two bodies are united into one single body.


    The Intersect operation is used to create a new entity out of the common volume between the overlapping entities. You just need to select the involved entities. Using the same example as in Figure 27 the intersection operation results in the following CAD model:

    intersect boolean operation
    Figure 29: Intersect boolean operation between overlapping bodies results in a new body whose surfaces are enclosed by their common volume.

    The result is a quarter of a sphere.


    The Subtract operation can be used for the following operations:

    • To remove the common volume from one of the entities while keeping it intact in the other
    • To remove the common volume along with one of the entities

    The settings panel for this operation is shown below:

    subtract operation cad mode
    Figure 30: Subtract operation can remove the common volume and the tool body or the common volume from the target body only.

    The settings panel asks the user to select target bodies and tool bodies. A target body is a body to subtract from while a tool body is a body to be subtracted. In this example, we choose to subtract the sphere (in pink) from the cube (in blue).

    One more important step is to choose whether to keep the tool bodies or not. If Keep tools is selected then the common volume gets subtracted only from the target body. The final result still has two separate bodies.

    If Discard tools is selected then both the common volume and the tool body gets subtracted. The final result now has a single body. Both the results are shown the figure below:

    keep tools versus discard tools in subtract boolean cad mode
    Figure 31: Difference between Keep tools and Discard tools feature for the subtract boolean operation. The former results in the same number of bodies while the latter removes the tool bodies.


    Under this section, there are operations that allow users to move the part volumes within their geometry by either translating them whole up to a certain distance or rotating them by a specified angle.


    As the name suggests, the Translate feature aids in translating the body or bodies up to a certain specified distance in the specified directions. Similar to the Move operation, there are two methods to proceed:

    X, Y, Z

    With this method, you can specify the distance up to which the selected volume needs to be translated in each direction. A negative value would translate in the opposite direction. Kindly follow the orientation cube at the bottom right to avoid confusion.

    Following the same example from Figure 9, this time instead of moving the face of the heat sink we will move the whole heat sink body in the positive y-axis by a distance of 0.025 \(m\).

    translate xyz cad mode
    Figure 32: Selecting the Translate method to X, Y, Z will translate that body to the desired coordinates.

    Up to Entity

    In this method, you just have to assign the face of the entity up to which the assigned volume needs to be translated. This time we assigned a face of the chip for the algorithm to translate the heat sink such that its foremost face is coplanar with that of the chip.

    translate up to entity cad mode
    Figure 33: Selecting the Up to entity method will translate that body up to the plane of the entity face.

    The following schematic perfectly represents the possibilities of a successful up to entity translate operation:

    translate operation schematic to represent possibilities in cad mode
    Figure 34: The possibilities of success and failure using the up to entity translate operation


    As the name suggests, the Rotate feature aids in rotating a body or multiple bodies about a specified axis. This axis of rotation passes through the center of an imaginary bounding box whose dimensions represent the minimum and maximum coordinates of that body (or bodies combined) in the x-, y-, and z-direction.

    Let’s look at the following example:

    rotate operation settings
    Figure 35: Rotate feature allows rotation of one or more bodies about a specified axis.

    Here, different parts of the airplane wing are being rotated about the positive y-axis. This means that all these parts will rotate, in the anti-clockwise direction, at the same time about the central axis of the bounding box pointing in the positive y-direction. It is advised to refer to the orientation cube while assigning the rotation axis. Clicking on the inverse button inverse button will result in the reversal of the axis assigned (negative y-axis in this example).

    result of rotate operation
    Figure 36: Result of the Rotate operation above


    Often there are instances where the CAD model has too much detailing that is insignificant from the simulation point of view. This may include threads on a bolt or pattern imprint on a tire. These fine details can cause simulation overhead by requiring a fine mesh and subsequently a high consumption of core hours.

    With the Simplify feature, these fine details can be replaced with primitive shapes like cylinders or boxes that occupy minimum bounding dimensions.

    simplify settings panel cad mode
    Figure 37: Simplify feature allows replacement of a detailed body with a box or cylinder primitive
    replacement with box and cylinder test
    Figure 38: Examples showing the difference between replacement with a box against a cylinder

    Multiple bodies can be replaced in a single operation either with a cylinder or a box. By default each body is replaced separately however this can be toggled off to generate a single resultant body.

    different replacement options in simplify
    Figure 39: Multiple bodies can be selected at once for replacement and can be replaced individually or as a group.


    The Wrap Surface operation is intended to generate a simulation-ready CAD model in situations where it contains a lot of artifacts like self-intersections, holes, cracks, overlaps, unimportant features, etc. Cleanup of such CAD can be very complex and extremely time-consuming, often even impossible, making it unsuitable for meshing.

    The settings look as follows:

    wrap feature in cad mode
    Figure 40: Settings panel for the Wrap feature. Select the whole model or parts to be wrapped.
    • Bodies to be wrapped: Whole CAD model or a part of the model to be used as an input to the wrapping procedure.
    • Wrap Type:
      • Fit to surface: This will try to make a wrap closest to the original body, however, it will not make any attempts to preserve any features like sharp edges. This operation is more robust and stable.
      • Snap to edges: This will try to fit the resulting surface to sharp edges in the model. Sharp edges are currently defined as edges on the geometry where the angle between adjacent surfaces is larger than 30°.
    • Resolution: This controls the wrap precision. Values between 1 and 10 are accepted. Higher values produce geometry that closely represents the input surface. Lower values result in a faster, but coarser representation.
    • Allow Tunnels: If toggled on, will allow the result to be topologically more complex than a sphere. This means tunnels or even multiple disconnected surfaces.
    • Cap Tunnels: If toggled on, the algorithm will try to close all detected tunnels, pockets, and gaps and simplify the model while still maintaining other significant features.
    • Tunnel Detection:
      • Automatic: Detects the tunnels automatically.
      • Manual: Requires the minimum tunnel diameter that is needed to be recognized.
    • Wrap each body individually: An option to wrap all selected bodies at once as a group or wrap each selected body individually.
    wrap surface result for car
    Figure 41: Car model containing a number of features and a lot of self-intersections (left). Car model after wrapping – simplified and ready for meshing (right).


    Fix Interferences

    Fix interferences should be your option when trying to fix the interfering bodies in your CAD model automatically. Just click on the icon and hit ‘Apply’. It should get rid of all the interfering parts. Users should note that, in this automatic operation, the smaller body is subtracted from the larger body.

    Don’t forget to run an interference check again just to be certain (see Interferences below). You should see a “No Interferences found in your CAD Model” message.

    Add CAD

    The Add CAD operation allows you to add parts to an existing CAD model in SimScale. As an example, the Electronics Box geometry below is missing one Large Capacitor:

    two cad models in simscale add cad mode
    Figure 42: Before performing an Add CAD operation, make sure that both models are uploaded to SimScale.

    In CAD mode, you can create a new ‘Add CAD’ operation to have both CAD models combined:

    add cad configuration in CAD mode
    Figure 43: Setting up a new Add CAD operation in CAD mode

    As a result of the operation, the capacitor is added to the electronics box geometry:

    result of the add CAD operation
    Figure 44: Result of the Add CAD operation

    It is worth noting that the new CAD part is added respecting its original coordinates. If the new part needs to be re-positioned, please consider using a translate CAD edit operation.


    Flow Volume

    A CFD simulation is performed on the actual fluid volume. For an internal flow problem, this means that the fluid volume needs to be extracted from the CAD geometry or, be created around the CAD geometry for an external flow problem.

    This can be performed in the CAD editor using the Flow volume operation. More information on flow volume extraction can be found here.

    External Flow Volume

    To create an external flow volume, you need to enter the minimum and maximum dimensions for the volume in the x-, y-, and z-direction. Optionally, select a seed face that corresponds to any face on the CAD geometry.

    external flow volume cad mode
    Figure 45: External flow volume extraction requires minimum and maximum dimensions, and an optional seed face.

    By default, this operation retains all the CAD parts. You can specifically exclude them by selecting them under Excluded parts. If unsure, the parts can also be deleted later using the delete operation for the body (discussed above).

    Internal Flow Volume

    To create an internal flow volume you need to specify a seed face and one or more boundary faces ( lies between the external environment and the internal).

    internal flow volume cad mode
    Figure 46: Internal flow volume extraction requires a seed face and one or more boundary faces.

    Similar to external FVE internal FVE also retains all the CAD parts. You can exclude them under Exclude parts option.


    Users should note that faces selected for operation in a flow volume extraction process, such as seed face and boundary face, cannot belong to the excluded parts (volumes) of the CAD model.

    Internal Caps

    The Internal caps operation creates cap faces for the inlets and outlets of the internal flow domain and groups them into a sheet body. The operation can currently only be used with the Immersed Boundary analysis type. Internal caps operation creates faces (caps) that cover the inlets and outlets of the internal flow volume. The faces can later be used for the definition of boundary conditions. Read more about this operation here.


    This operation allows the creation of a cylinder, which is especially useful in simulations involving rotating zones. There are two methods to create cylinders: Custom and From faces.

    When using the Custom method, the center of rotation, axis of rotation, radius, and height of the cylinder need to be specified by the user.

    cad mode custom cylinder
    Figure 47: A preview of the cylinder is visible in the viewer before accepting the cylinder settings

    The Custom approach requires global coordinates to be provided for the creation of the cylinder. In case you don’t have those readily available, the From faces approach might be preferred.

    When using the From faces approach to create a cylinder, the user needs to select the Faces which should be covered by the cylinder:

    cylinder operation cad mode from faces
    Figure 48: The box selection tool, highlighted by the blue arrow, can help to quickly select the faces of interest

    With this approach, a cylinder that envelops all selected faces is created. Furthermore, a Clearance factor is applied, ensuring that the cylinder is slightly larger than the assigned faces. For simulations involving rotating machinery, a Clearance factor of 1.1 is recommended.

    As a result of the Cylinder operation, a brand new volume is created:

    additional cylinder created rotating zone
    Figure 49: A new volume named Cylinder will be visible after running the operation



    Your CAD model is not ready for the simulation setup if it has interfering solid parts. Interfering/Overlapping solid parts can result in the failure of geometry operations performed while editing the geometry and more importantly cause the meshing algorithm to fail. Hence, it should be avoided at all costs.

    To check for interfering parts click on the ‘Interference’ icon and wait for a message while the operation runs in the background. A valid CAD model with no interfering parts should display the message on the left as shown below:

    cad mode interference check
    Figure 50: If you have a CAD model with multiple solid parts don’t forget to run an interference check.

    To fix interferences manually use boolean or delete-body operations described above. Additionally, for automatic fixing of interferences use the Fix interferences feature discussed under Models.


    When preparing your CAD model there are often undesired gaps that are not visible or overseen and can lead to mesh quality issues or prolonged run times. These gaps need to be identified and fixed at an early stage. For example, in a CHT case, all the components must be in contact with each other to capture the heat transfer correctly. The below geometry has thin gaps because of which contact cannot be generated between the mainboard and the chip.

    Small undesired gaps in the geometry which is usually overseen leading to missing contacts.
    Figure 51: Small undesired gaps in the geometry which are usually overseen leading to missing contacts.

    To detect these small gaps click on the ‘Gaps’ icon and then specify the ‘Maximum distance’ to define a gap tolerance and then hit ‘Detect gaps’. All gaps that are equal to or less than the maximum distance will be detected. Depending on the CAD model this can take a while and will display a message as shown in the below figure.

    Specify a maximum distance upto which gaps in the CAD model should be detected.
    Figure 52: Specify a maximum distance up to which gaps in the CAD model should be detected.

    After running the operation, the following results can occur, depending on the Maximum distance:

    Find gaps in the CAD model up to a specified tolerance (Maximum distance) by clicking on Detect gaps
    Figure 53: Find gaps in the CAD model up to a specified tolerance (Maximum distance) by clicking on Detect gaps.

    Upon expanding the detected gaps and selecting a face, the corresponding face will be highlighted in red color on the model. These gaps can be fixed either via Move>Face or Translate operations.

    Last updated: July 16th, 2024