Fixing a FRP (Fiber Reinforced Plastic) Sheet on the exterior panel of the CAB 2

[ShuklaPK]

Hi,

I am working on a product which requires fixing of a 2.5mm thick sheet (FRP Material) on the exterior panel of a Vehicle (0.65 mm thickness).

Constraint:
1. The fixed product will undergo various weather conditions (Hot-Cold-Hot (2 Deg. - 50 Deg. Celsius) + Rain + Wind(15-70 Kmph) & designed life should be minimum 2 years.
2. Lesser Cost.

Problem:
What fixing method should be used to attach the FRP sheet to the exterior panel?

My Solution:
Weld a Flat Head Bolt (Picture attached) on the Surface of the exterior panel after cleaning the panel surface, later drill holes on the FRP sheet as per Bolt size and fix the FRP sheet on the panel using appropriate size nylon Lock Nut.

If anyone can suggest a better method or can point out a flaw in my current method?

Thanks in Advance,

Pratik Shukla

 

[BrianPetersen]

Think about vibration and differences in thermal expansion. FRP covers a wide range of possible materials but plenty of them are prone to cracking.

Look at the way motorcycle fairings are attached to the frames underneath. Rubber grommet in the plastic, and either a steel sleeve through the grommet which is in turn bolted down, or a shoulder screw through the grommet.

 

[ShuklaPK]

Thanks Brian.

1. To mitigate the effect of exterior panel induced vibrations on the FRP sheet the idea to use a grommet sounds great. I will have a look at the motorcycle fairings & try the rubber grommets in my upcoming trial.
2. I understand that most of the FRP are prone to cracking, in my previous trial the part did crack at various locations, I have discussed the issue with my supplier and he says he can take care of this by playing with the material composition (Might add UV stabilizers, some strengtheners or other chemicals).

Regards,

Pratik

 

[MikeHalloran]

A few gobs of RTV silicone will secure most any any clean surface to most any clean surface.

You have to fixture it with, e.g. blue tape, for 24 hours or so.

RTV with fillers, sold at a reduced price as 'construction adhesive', forms weaker bonds.
OTOH, it may actually be removable; the neat product is ~permanent.



Same comments apply to 3M brand #5200 sealant, available in small tubes at Walmart.
It is based on urethane, not silicone, but is ~permanent.





Mike Halloran
Pembroke Pines, FL, USA

 

[MikeHalloran]

If you really want to remove the FRP at some future time, the 3M 5200 may loosen its grip with application of boiling water or steam. The RTV will not.


Mike Halloran
Pembroke Pines, FL, USA

 

[ShuklaPK]

Thanks Mike.

I considered the option of using adhesives with sealants to secure fasten the FRP sheet to the cleaned panel surface.

But I backed out because:

1. Cost:
a. The RM cost of the adhesive as a whole( Applied at >3 meters of at least 1 inch dia. adhesive).
b. To maintain uniformity while adhesive application, I can't get it done manually. Also, installing robots, considering the volume I am working on is not feasible.

2. Adhesion Strength:
a. I consulted many of my friends working in OEMs, all of them were against using adhesive to attach FRP considering 2 years of Product life i.e. exposed to various whether conditions here in India.
b. The FRP supplier uses a releasing agent on the mold to eject the part out. Considering the variation in the concentration of this releasing agent, adhesion strength of the RTV silicon or 3M 5200 might not be consistent.

* The Adhesives used for fixing Windshield on Windshield flange of Passenger Cars can also be used*

Please correct me, if you don't agree with my understanding about the subject.

Thanks
Pratik

 

[BrianPetersen]

There are good things and bad things about every way to do this job. If it has to be a bolt-on piece (my assumption) or if it is not meant to be removed easily (MikeHalloran's assumption) is a rather important factor that you haven't supplied the rest of us with any information about! If, or how well, the joint has to be sealed against intrusion of the elements (rain, dust, etc) is another one.

 

[MikeHalloran]

You didn't reveal the panel size or the production quantity or rate before.
We are not looking at your sketches or prototypes.
Better questions yield better answers.

Presence of a release agent is a valid concern.
... which can be addressed with a solvent wipe,
provided that the supplier doesn't start putting release agent in the resin.

WRT your proposed solution:
Is the vehicle panel surface made of painted steel?
If so, you have to remove the paint where you want to weld a FH screw to it.
You might also want to remove the plating from the screw head, e.g. by grinding, so you don't contaminate the weld with zinc.
Instead of using common screws, you could use threaded weld studs, which attach very quickly with a stud welding gun. You still have to remove the paint.
You might want to use a template to locate the studs; transferring arbitrary stud locations to a blank sheet is laborious and error-prone. Better to prepunch the holes in standardized locations.
Here in The Colonies, you would probably get a lot of pushback about having exposed nuts and stud ends projecting from what is otherwise a smooth surface. Worst case is producing a bunch of vehicles that way, and having trial lawyers go after you for not mitigating a foreseeable hazard to pedestrians. Never mind that pedestrians don't normally launch themselves into contact with vehicles; we now design vehicles to protect pedestrians in interactions with vehicles. Hopefully you have fewer lawyers scrounging for work.



Mike Halloran
Pembroke Pines, FL, USA

 

[BrianPetersen]

A nut welded to the inside of the panel with a screw going in from the outside would be a better choice than a stud welded in with exposed projecting threads. The screw can then be a pan-head or similar type that doesn't have sharp edges sticking out, and it looks better, too. Lots of motorcycles have exposed chrome-plated screw heads where the fairings are attached to each other or to the underlying frame.

There's plenty that the rest of us don't know about the application under discussion here.

 

[Tmoose]

Did you say if the FRP used polyester resin, epoxy resin, or vinyl ester, or maybe something else entirely ?

Are both panels nominally flat?

With the info provides so far I am not sure if this product has been disqualified yet.

http://solutions.3m.com/wps/portal/3M/en_US/Adhesives/Tapes/Industries/Architechure/VHB/

 

[ShuklaPK]

Thanks Mike & Thanks Brian for giving your valuable time & inputs on this thread.

I agree on the fact that, I should have provided more information in order to receive a better reply.
I am new here and this is my first thread, hence I thought of keeping it succinct.

I will try to frame my questions in a better way from now on.

Regarding the FH Bolt welded on Panel:

1. In all scenarios, I have planned to remove any sort of plating/paint/contaminant from the surface. Welding will be done from clean to clean surface.
2. The projected portion of the bolt is a concern where I plan to use a rubber/Plastic cap (Aesthetically Better).


@Tmoose

1. I will use FRP with epoxy resin as the Matrix & Glass Fiber mat as the Reinforcement.
2. The panels will be offset to each other. Can't say flat as the profile is curvy at some places and flat at some.

Regards
Pratik

 

[BrianPetersen]

If you use studs sticking out and the component being installed is not flat (i.e. those studs end up being non-parallel in three-dimensional space), bear in mind that the part has to be physically installed overtop of those misaligned studs. This is another reason for using a nut welded to the inside and a screw installed from outside, because then this doesn't matter - you are not trying to distort the part in order to fit its holes over non-parallel projecting threads.

 

[SwinnyGG]

I would go one further and suggest a rivnut or rivet with a standoff or spacer to set the panel gap. This would be much faster than welding, do less damage to the modified vehicle if you ever have to remove this added equipment, and has the benefits Brian is talking about as well.

 

[ShuklaPK]

The projected bolt thing is really a concern considering assembly of the component on the CAB.
I would like to thank all for their inputs on this thread. I will share my trial experience, once it is completed.

Regards
Pratik

 

[loki3000]

what kind of a product is that?