File Management
Good file management is essential in the success of your assemblies.  As you create new files your are creating relationships between those files – associativity – it is important you keep track of where those files are going.

Golden Rule: Keep .asm files and all associated .prt (or sub assembly files) local to each other – in the same folder

DO NOT use Windows Explorer to change the name of any of the part files once they are in an assembly, rename in Creo.

Analogy: web sites have links which contain the address and name of another web page (within the same site), if the target web page is independently renamed then any links to that page will be broken – a 404 error. If the page is renamed within a site authoring software such as Dreamweaver then the file name will be changed and any links to it within the site will be changed.

Create a project folder and set that folder as your Working Directory;

  • Navigate to the folder through the left hand Folder Browser
  • RMB on the folder > Set Working Directory
  • Now new files will be saved by default to that folder and components will be retrieved from that folder.

 

New .asm file

 

 

Process

When initially placing a component you are in Automatic mode and as each constraint is fully defined a new constraint is automatically created – watch for the Automatic label.

As soon as you interact with the existing constraints via the Dashboard or Placement tab then you are switched to User Defined mode and you need to start a new constraint once the previous one id fully defined – RMB > New Constraint

  • Drag components into the assembly environment from Windows Explorer or use the  Assemble function
  • For the first (base) component: RMB > Default Constraint
  • For subsequent components:
  • Use the 3D Dragger or Ctrl + Alt + MMB or RMB to approximately orient and position the component
  • Select a reference on the component and a corresponding reference in the existing assembly
  • RMB on the the resultant constraint label in the graphics area and switch type if needed
  • Dbl click the label to review and change its references
  • Use planar surfaces, cylindrical surfaces, datum planes or axis where ever possible.  Avoid edges, points and tangency.

 

 

To begin with, we shall bring components (.prt or .asm files) into the assembly environment and position them relative to each other with constraints such that they have no degrees of freedom (DoF) – that is they cannot move along the X, Y or Z or rotate around the X, Y or Z vectors.

See the Simulation section for creating assemblies with DoF which enable mechanism simulation and analysis.

 

Keep it simple and logical

Think about how the components might be assembled in reality, which references would be aligned – screw holes? edges? cylindrical axis?  If you run out of fundamental geometry then use Datum Planes

A rule of thumb is; you need at least three constraints to place a part.  There are exceptions to this rule – eg. aligning two axis which are perpendicular to each other will constrain a part.

 

Think about your references

To begin with, generally try and constraint a part to only one other part – this will make modification of the assembly a lot simpler.  If you are putting a wheel in a pair of bicycle forks, the wheel should only be related to the forks, not to the frame or the planes in the assembly environment.

To test how robust your assembly is try moving the base part and see if everything follows it or if the assembly fails.

Any squares next to the component name in your model tree mean a part is not fully constrained.  A small square over a large square shows that that part is constrained but its parent isn’t – therefore it still has DoF via its parent.  If you can move or rotate a part using Ctrl + Alt + MMB or RMB then it is not fully constrained.  A component which is not fully constrained is referred to as ‘packaged’.

2000.asm.not.fully.constrained

 

Choose robust stable references – a hierarchy of stable references:

  • assembly or part coordinate system – origin
  • default planes
  • solid planar surfaces
  • reference geometry planes or axis
  • edges, points or vertices

 

Default Constraint

Be logical about which part of your product to assembly first – if you were assembling a car you would probably start with the chassis and not the steering wheel.  This is the base part.

Firstly, make sure the base part is fully constrained.  The base part can be simply placed by using the default placement icon – this will align the default planes [xz, yz, xy] in the part to the default planes in the assembly environment.

Bring in the Component > RMB in the graphics area > Default Constraint

 

Primary constraints – Constraint Type

This is the first element of the constraint description.

Once the base part is assembled you need to think carefully how the subsequent parts relate to it.

2000.asm.constraint.list

 

ico.distance.constraint  Distance:  planar references (surfaces or datum planes) are set parallel to each other and at a set distance apart

ico.parallel.constraint  Parallel: planar references (surfaces or datum planes) are set parallel to each other but floating, their distance apart is dictated my other constraints

ico.coincident.constraint  Coincident: planar references (surfaces or datum planes) are set parallel to each other and touching each other

If you didn’t approximately orient the component before applying your constraint and it is in the wrong relative orientation then; Placement tab > Flip

 

Cylindrical or concentric relationship 

Select two axis or two cylindrical surfaces

 

ico.angular.offset.constraint  Angular offset

If you want two planar references at an angle to each other;

  • approximately position the components at an angle
  • select the two faces (1) – an Angular Offset constraint will be created
  • the component can still slide and rotate while maintaining the set angle
  • align two edges or axis (2)
  • the components can still slide along this ‘hinge’
  • align two faces normal to the ‘hinge (3)

2000.asm.angular.constraint

 

Constraint conflicts

There will be situation where you apply constraints and you will receive the ‘Contraint invalid’ message. This will commonly happen when the new constraint is ‘pulling against an existing constraint – they can’t both exist.

2000.constraint.invalid

First consider if it is the primary or secondary element of the constraint which is the conflict, in the case above is it the primary parallelism relationship or the Coincident distance?

2000.constraint.conflict

In this case there is a clearance gap between the two surfaces when the cylinders are concentric, this means the surfaces cannot be coincident, RMB on the active Coincident label and switch to Parallel – the surfaces are parallel to each other but there is not set distance, they are floating and the axis alignment dictates the distance

 

 

DO NOT USE THE ‘FIX’ CONSTRAINT – this will simply hold the part in its current position in the 3D environment but will not create any relationships between it and the other parts.  This constraint is used for temporary placement of a part. Using this constraint WILL lose you marks in your assignments.