Undercut area and appropriate material

[Tisho]

Hello Community,

I need a tool and material advise about my design. The part is injection molded. The picture represents an extract of a much complexer part. It is heavy loaded(9kN radial) at about 100deg. The core is a slider(not in the Main forming direction).
The Bearings are pressed and the ball bearing is secured with a metal ring.

1. Can the slider go out with 0deg draft angles on the contact ribs(see the picture for ref)?

2. By what means can I form the undercut(collapsable core, filters)

3. Any suggestion for a proper material as the part can exert 9kN in radial direction at the ball bearing area at 100 deg. This design tends to replace aluminium as the stresses can reach 250MPA at Al design?

I am working mainly on part design and I have limited(basic knowledge) on tool equipment. I will appreciate your tips.

Thank you.

Tish

 

[Tisho]

I don't know why the picture is not showing up. Uplaoded again in this post

 

[patprimmer]

Can you post the file as a jpeg.

Is that a 100 deg angle. If so to what.

If it is 100 deg temperature, is it F or C

Regards
Pat
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[Pud]

Could you indicate where on the planet you are located?

Difficult to suggest Al replacement material suppliers...

H

http://www.tynevalleyplastics.co.uk

 

[Tisho]

1. 'Can you post the file as a jpeg' . I tried. The upload function is not working today. I'll give it a try later. Btw PNG is very nice alternative to jpeg.

2. 'Is that a 100 deg angle. If so to what.If it is 100 deg temperature, is it F or C'
- This is 100deg Celsius- the part is exposed to this temperature for a short time < 20min. The part should function faultlessly at 80deg C. I am sorry for the misunderstanding.

3.'Could you indicate where on the planet you are located?'

I am in Stuttgart, Germany, Central Europe, Planet Earth .

Let me know if you need more info.

Greetings
Tish

 

[Tisho]

I managed to get it working today. Picture uploaded as a jpeg.

Greetings

Tish

 

[MikeHalloran]

I don't see a way to make that exact part.
A collapsible core would be fouled by the extended inner tube and probably by the radial ribs.

If you replaced the internal projections with slots through the wall, then you could replace the simple retaining ring with one having external tangs to engage said slots.





Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

You have another problem.

Ball bearing races are more flexible than you think.
The statistically projected lifetime will only be reached if the outer race is fully supported, e.g. by a complete bore, not by an array of ribs.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

I have not done the sums, but you will need something fairly strong.

Glass reinforcement will cause dimensional control complications but that can be resolved with careful design and maybe a prototype mould.

If it has to be unfilled, you will probably end up with something expensive like PEI or Polysulphone.

You can solve the retaining ring problem by reducing the length of the ring sector so a section of the core can be rotated and extracted through the gaps between the reting ring sections.

Zero draft or near zero draft should be possible for the short distance required. It is essential to polish in line of draw if you are to have any chance.



Regards
Pat
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[Pud]

Some other materials to consider - which are marketed as "metal replacement" are:

Grivory - made by EMS Chemie (Swiss)

http://www.emsgrivory.com/index.cfm?id=93&myLang=de

Ixef - made by Solvay (Belgium)

http://www.solvayadvancedpolymers.com/products/bybrand/ixef/0,,321-2-0,00.htm

Amodel - Solvay

http://www.solvayadvancedpolymers.com/products/bybrand/bybrandamodel/0,,391-2-0,00.htm

Zytel HTN - Du Pont (Which is a PPA I think)

Probably others but have only used the above lot.

For your design, you need to talk to a toolmaker about collapsible cores.

All the comments above are valid. Remember that all plastics exhibit creep - your initial press fit stress will drop off with time - accelerated with elevated temperatures.

Also: Great Mercedes-Benz museum in Stuttgart - only had a day there but could spend a week easily!

Cheers

Harry

http://www.tynevalleyplastics.co.uk

 

[Tisho]

"... you could replace the simple retaining ring with one having external tangs to engage said slots."

Can you provide some a simple sketch or visual representation of this Idea. Sounds very interesting. I am also working on something. Please, check the attached the updated picture for my alternative.

http://files.engineering.com/getfile.aspx?folder=5d7cadde-145a-4409-8d33-5d4bd18d9e6f&file=4.JPG

"The statistically projected lifetime ...complete bore, not by an array of ribs."

Hmm, that requires a lot of attention. The shaft in the bearing is not rotating aggressively. Quite slowly but the transmited forces from the shaft, through the bearing in the housing are significant (radial and axial ~ 10kN and 15KN corresp.)

I want to suggest a new design on the attached picture regarding the radial ribs supporting the Ball bearing. I am ending with a wall thickness of about 4.2 mm.Won't that sink/shrink a bit and destroy my pressing tolerances? I shouldn't underestimate the creep as PUD mentioned. It is the first time I am designing a pressed Bearing in thermoplastic part and I realy want to hear your opinion on that. ANY suggestion how to get this bearing fixed will be wellcomed.

"...retaining ring problem by reducing the length of the ring sector...." I will carefuly consider this design, too.

Material Theme: PEI or Polysulphone. I can see that you are targeting amorphous materials. Is this cause of of the better dimensional and thermal stability? I looked at some examples of these materials and their tensile stress at break could appear insufficient. For Ex. at Ultrason GF30(PSU) 120MPA and Ultem GF30(PEI based) is about 165MPA. The stress concentration at some areas of the design is about 250MPA(36.2 KSI)

http://www.campusplastics.com/campus/datasheet/Ultrason®+S+2010+G6+UN/BASF/20/0ad950aa

I am quite impressed by some processed PEEK,PA66/6T glass and carbon reinforced, where the tensile stress at break can reach

between 280MPA and 330MPA at Room Temp and are relatively stable until 100deg Celsius. They are also very expensive.

PUD thank your for the material hints.The products of Grivory and Dupont are already in my target list but I will check the others too.

Truely is the Mercedes Museum really nice.


Greetings and Regards

Tish

 

[MikeHalloran]

I personally prefer a retaining cap with screws to an internal retaining ring. I don't care for the sectional support where you have inverted the ribs. I'd be inclined to move the parting line between body and cap down to the centerplane of the bearing, or perhaps beyond, so the bearing race can be supported by the joint flanges, which are contiguous. Or to make the retaining cap screwed on over the bearing cup, so the race is supported by the body, and by the cap over that.

It may be time to back up and consider some other options. You have gone rib-happy here. Sometimes a simpler part with thicker walls can turn out better.

About sink marks: They are mostly a cosmetic issue. There is no great need to worry about them in a structural part.



Mike Halloran
Pembroke Pines, FL, USA

 

[Tisho]

Thanks for the feedback Mike.

You've been of a great help on this case.
Actually this geometry is a part of a complexer part. It is formed with a slider which forms a part of the outer walls too. The flange on the outside is present, ensuring better stability in radial direction. I am trying to avoid rotation of this slider because of some crown configuration of vertical ribs on the flange and interference with other cores/sliders.
Later this month I am going to have a meeting with some Resin suppliers and I am going to update the discussion.


Greetings,

Tish