Adding ribs on a cowl screen 2

[Berserk]

Hello,

UGNX5.0.4.1 MP6 Win-XP sp3

Is there a way to create a rib that would have the base consistent at 1.1mm and the top at 0.8mm when the surface you attach the rib goes up and down and the rib is almost straight at the top? I guess what would happen is that the rib would have variable draft.

TIA!

Productive Design Services

http://www.productivedesign.com

 

[Berserk]

Hello,

Here is an image of one of the ribs. I have added a 0.5degree draft and as you can see, the top becomes 0.25mm at the thinnest section and the base is a consistent 1.1mm.

Is it possible to create a consistent 0.8mm thickness at the top?

UGNX5.0.4.1 MP6 \ WinXP-SP3
Productive Design Services
www.productivedesign.com

 

[Berserk]

Here is a UGNX5 part of the rib.
The original data does not have parameters.

UGNX5.0.4.1 MP6 \ WinXP-SP3
Productive Design Services
www.productivedesign.com

 

[cowski]

Is this part going to be injection molded? If so, there is a minimum draft requirement on tall standing ribs (you will need to check with your toolmaker for their recommendation).

As far as answering your question, I would try to sketch the cross section of the rib and attach the bottom of the rib to the lowest face. Perhaps dimension the top of the rib to the highest face. Then trim away the top of the rib to shape. I'm not sure it would work, but is the first thing I'd try.

 

[JohnRBaker]

Attached is one approach where I created surface representing the desired face of the rib and then used them to trim away the model. You should be able to follow the procedure if you playback the model one feature at a time.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[Berserk]

Thanks John!

Cowski, yes it is injection molded. Toolshop requested a minimum thickness of 0.8mm at the top and maximum thickness of 1.1mm at the base.

UGNX5.0.4.1 MP6 \ WinXP-SP3
Productive Design Services

http://www.productivedesign.com

 

[hudson888]

Berserk,

I'm going to answer your question as an engineering problem rather than a CAD one. That looks a lot like a piece of interior Automotive trim so I get that you don't want sink marks and that somebody has most likely handed you a set of best practices that dictate all sorts of things. I agree that 0.8 is an absolute minimum thickness at the tip of the rib in fact I would have said 0.9, you should rightly be worried that teh rib won't fill. The 1.1 at the base is designed to avoid sink marks, but if you don't have enough draft the rib is going to stick in the tool and can will also pull a sink due to the resistance it may have to releasing. So we used to use the 60% rule which would have allowed up to 1.5 at the base, now with newer softer materials and conservative moulding practices some people are recommending a 40% rule which says only 1.0 at the base, which is too thin to design anything useful.

John's example works as far as providing the technical solution to your problem but it is perhaps a little more work to have to do this on each and every rib, plus it simply doesn't have enough draft. Only about 0.1 degrees.

What I have attached for you shows a draft vector in the file, and has the dimension of thickness of the rib at the base using the PMI. I have used 0.25 degrees the absolute minimum I'd ever go to 0.8 constant at the tip the absolute thinnest you'd ever want to use, and allowed the base to blow out to 1.22 which is still less than 50%. If you're concerned you could locally thicken the 2.5 wall to 3.0 to ensure that the part doesn't sink.

The other thing some engineers occasionally do if the rib isn't designed to bottom out on another part but is just for reinforcement is to allow it to be under thickness at the tip (in your case it would be 0.7) and if she fills great and if not it then it may not be critical to the design.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum

 

[Berserk]

Thanks for the information. The tool shop would be creating a straight lifter on one side of the rib to assist in removing the part from the mold.

Just in case you guys are curious, the rib is for a cowl screen for the Cruze.

UGNX5.0.4.1 MP6 \ WinXP-SP3
Productive Design Services

http://www.productivedesign.com

 

[hudson888]

Well at least I'm glad to see you guys finally took NX-5. I could almost have guessed just by the recommendations.

If they're going to use a lifter on the one side why not at least put all the draft on the other that way you'll have the best of both worlds, no sink marks and possibly a decent thickness at the tip giving the rib some chance of filling properly.

Best Regards

Hudson

www.jamb.com.au

Nil Desperandum illegitimi non carborundum