How to demold a Hole?

The matter might seems trivial… it gets a bit more complicated, when the hole axis is under significantly greater angle of molding direction :

 

An attempt to demold such hole using Draft in the older versions of CATIA ended up with error and a message, saying that Draft doesn’t know where to add, and where to deduct material, and that it suggests to change the direction of molding. Since probably R19, if I remember correctly, the operation works but gives such result:

 

Meaning, we get two sharp edges, but the hole is demolded, and we might say, that it’s optimal because it cuts out minimum amount of material ensuring easy molding. And the case could be closed at this point by adding Fillets on sharp edges… But if so, anyone who did that would have hardly a bright future as a CAD Engineer :-)…

And now it goes like the old saying, “you got that much solutions, as much Constructors there is”…

 

                                                                            METHOD NO. 1 – THE OLD SCHOOL METHOD 🙂

 

It’s about defining new direction of molding, which will be a compromise in the following way :

 

– move the direction of molding to the axis so as to make intersection,

– create bisecting line between the crossed lines (it’ll be a new direction of molding),

– measure the angle between the new direction and the axle (in my case 30,888 degrees),

 

– draft the hole using new direction of molding, and for the value of Draft Angle, use our measurement plus the value of the minimum angle of  molding (30,888 + 3).

Here’s the result :

It’s definitely a very fast method in terms of quick clicking-out, step by step, and it gives a nice surface of a hole without any sharp edges. But unfortunately, this method does not ensure the minimum loss of material – meaning the hole surroundings, in some way, will be weakened  compared to the quick&dirty method.

                                                                                          METHOD NO. 2 –  SURFACES

 

Maybe I’ll start from the picture and description straight away :

 

– create a cylinder consistent with the assembly axis of the screw,

– Intersect with bottom surface,

– from that Intersect, create Sweep with Draft direction and with the minimum angle of molding towards the pulling direction,

 

– the point of intersection of the axis with the bottom surface,

– the point set on the axis at a distance that passes the thickness of the material,

– normal plane  to the axis, passing through that point,

– intersection of that plane with Cylinder and Sweep,

– and two lines tangent to the curves previously done in that intersection,

 

– trim the previously made curves, so that we get a continuous contour,

– create two extremums in the direction of molding on the newly created contour, and on the intersection of the bottom surface with the cylinder,

– stretch multi-section surface between contours using extremums as Closing Points,

– cut out a hole in the surface :

 

The method provides us with a demolded hole with minimum loss of material…

It is labor-intensive, but it gives the best results. However, that’s actually something you don’t have to worry about, because Power Copy will help. I’ll leave that for now, because first, I’d like to move on to other subjects, such as stabilization of orientation of surface elements, in order to make that template genuine – on a “Click and Forget” basis.

 

 

 

 

 

 

 

 

 

Comments: 3

Amit Jamdhade August 4, 2017 o 12:12 pm

I have better solution which is simpler and quicker than that. Make remove body 0.2mm bigger than neutral surface and then add 0.2mm fillet on it. Then use fillet draft with you demoulding direction.


admin August 6, 2017 o 10:37 am

Is it better and more versatile than PC Template ?


Glen Salvi August 10, 2017 o 1:25 pm

I have always done it the same way than @Amit Jamdhade. I would just recommend to use a filet smaller than the thickness of your hole depth in order to avoid that filet to enter the removing zone.


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