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-   -   Various types of chassis sections used in Ladder frame construction (https://www.team-bhp.com/forum/4x4-technical/74050-various-types-chassis-sections-used-ladder-frame-construction-2.html)

Hey guys,

First post here, and I'm sorry to ressurect this thread, but its a topic I'm very interested in as there are limited resources on the design and construction of ladder frames.

I just wanted to ask if hydroforming of mail chassis rails is being considered in the manufacturing of SUVs/trucks for the Indian market? Right now this is all the rage in the states with trucks there, as it removes the need for welds which can be stress risors and which add to manufacturing expense. I have also recieved conflicting opinions that this might be a cheaper method for production than "C-in-C" rails.

Also, I'm not 100% sure about the definition of a "C-in-C" rail structure. I have attatched a simple CAD interpretation (the white circular bits are a simplified representation of spot welds) I created of what I believe this is based on posts in this thread - am I on the right tracks here?




Also why don't manufacturers consider welding two C-channel sections together on the neutral axis (ie. one C section on top, one C section on the bottom, welded along horizontally - a C attatched to a C, not a C in a C)? Surley this would be quite cheap and stress concentrations from the welds wouldn't be much of an issue as they are located on the neutral plane of bending?

Yes. This is a C in C construction. The white circular bits shown in image are rivets. You may either opt for reveting or spot welding. Riveting is generally opted when the thickness of the material is high. Usually Spot welding is done when the total stack up thickness of the materials is 4mm. for higher stack up thickness either riveting, bolting (Truck Chassis) or CO2 welding is done.

When welding is done the material from the two parts fuse and join together. If a C is attatched to a C like you say, then due to the fusing of the materials the thickness may reduce in the welded area. This would act as weak point and would result in crack formation from that point.

Can anyone please share a knowledge as how exactly different types of chassis can be welded together?
Say if someone want to combine a C-in-C Chassis with a constant section Box Chassis, what will be the best & safest method to do that?

Never heard of both. You're gonna extrude a 2 mm wall thinkness steel? Why (and how) would hydroform an open section when you can stamp it for 1/4 the tooling cost?

@Mpower generally chassis sections are 3-4mm thick, for M&M vehicles it is 3.6mm, stamping 3.6mm thick steel is such profiles becomes a tedious process, also hydroforming is preferred in situations where strict tolerances need to be maintained

Spike

This is great for strength as well.

However, Spike can u please answer to my previous post as below?

I have seen 5mm thick panels being pressed. I agree with Mpower. Why waste money on hydroforming tool when same can be done by stamping.


The general practice is to avoid C in C for long members because this kind of a joint has to either be CO2 welded (for smaller thickness panels) or has to be riveted or bolted (for higher thickness panels).

Hydrofoaming is a better and advanced process

I think for better understanding lets take example of some vehicles:

#Tata Safari, MS Gypsy: Hydroformed Box rails (Thickness 2.4mm approx)

#Mahindra Bolero, NGCS 550: Hydroformed Box Rails (Thickness 3.6mm, as stated by Spike)

# Mahindra Scorpio: CinC Welded rails (Thickness: variable?)

# Toyota HiLux, Fortuner: CinC Welded rails (Thickness: variable --but I guess they are thinner than Mahindra's)

# LandRover Series/ Defender: Box rails (With all sides welded together to form a rectangular box) Thickness: 2.6mm for stock & 3-4mm for aftermarket chassis

Can someone give exampe of a vehicle having riveted or bolted chassis? I am not aware of it..

(NOTE: All are just for information. I may be wrong. Expert's to correct please)

In all the above vehicles, the method of chassis building is different, yet they are known as best & durable offroaders. So is it the materials used? I think all chassis are made up of Steel (Only with LR we get Galvanizing option), OR is it the design of crossmembers or teh way the chassis rails are shaped decided the strength?

BTW, I like the Constant section Chassis of Bolero. Just my choice:)

Its mostly heavier-duty vehicles which feature bolted/ riveted chassis, such as truck chassis cabs and similar as below:

Riveted:



Bolted: Ford F650 chassis cab:





The first picture I posted shows that you can actually have long rail members in C-in-C sections, and you can also rivet them rather than TIG/MIG weld them.

My question is, how exactly do you attatch cross members to a C-in-C section? Do the cross member heights need to be lower than the mail frame rails and welded to them?

those holes on the rivetted chassis act as stress busters.

Spike

Those big holes on side wall of long members may be for weight reduction.

@Ranjitss well said, you are right:thumbs up, i forgot to add that point:Frustrati

Spike

+1. Common practice for any form of fabricated beam. Material on the web is essentially deadweight and cost. The big holes also give access.

Regards
Sutripta

Some of those small holes may be for bolting of cross members (As no cross members are seen for long distance). While some may be for mounting of other small parts and for clips to hold brake pipes and other wires.