Why is this duct 2 piece?

[TheBoy]

This is the duct from the air scoop above the rad to the airbox on her car.

Why is this made of 2 parts, rather than a single piece? 




Confused of Brakkers.

[Sir Tigger KC]

Why have one piece when you can have two?        

[YZ250]

Could it be for flexibility reasons to aid fitment. 

[TheBoy]

Could it be for flexibility reasons to aid fitment. 

Can't see why? It's a rigid section, and quite short.  There is another section not in photo (that is one piece) that has a concertina bit at the end for flexibility.

[Kevin Wood]

Probably cheaper to mould it in 2 pieces then snap them together.

"Cheaper" is almost always  the answer on cars the4se days, sadly.

[TheBoy]

Probably cheaper to mould it in 2 pieces then snap them together.

"Cheaper" is almost always  the answer on cars the4se days, sadly.

I can't see would it would be cheaper to mould 2 and clip together, over moulding 1, but you could be right.

I think you's uses same setup, worth checking the duct to make sure the 2 parts haven't come apart - its the 2nd piece from the scoop above rad to airbag, starts just after concertina bit.  Seems really common, and obviously suck in warm post rad air rather than cooler pre rad air.

[Doctor Gollum]

The 2012 630i I just dismantled has polystyrene dash vent ducting 

[Marks DTM Calib]

Tooling will be the answer, a single piece tool will be very complex with moving parts

[TheBoy]

Tooling will be the answer, a single piece tool will be very complex with moving parts

Yet the other part of this duct - not in pic - which links air scoop to this part is single piece, and arguably more complex? I guess they take the cost hit on that piece, and pinch the pennies on the piece I'm gluing together, taping and cable tied whilst trying to source a replacement.

[TheBoy]

The 2012 630i I just dismantled has polystyrene dash vent ducting 

Insultation? Weight? Just German?

[Doctor Gollum]

The 2012 630i I just dismantled has polystyrene dash vent ducting 

Insultation? Weight? Just BMW?

The last one for certain. Their design team are certified lanyard wearers. I mean who else uses 9, 11 and 14mm bolts? Or three different size Torx screws to attach the same piece? And then hide one that can't be accessed until you've removed the part it fastens?

If you ever own an 2nd generation 6 series and lose your keys, you can cut open the door skin with a Stanley knife. So weight saving could also be a possibility.

[YZ250]

.........
I mean who else uses 9, 11 and 14mm bolts? Or three different size Torx screws to attach the same piece? ..........

Audi.    They throw in a couple of triple squares as well, just so you have to take out an extra socket rail.  For example, the under belly tray has normal screws, headed screws and XZN bolts on the same panel. It's a German thing. 

[TheBoy]

Its a German thing. Including your beloved mobile parts bin known as Mercedes.

[Valentin]

1) Feasibility : if the part would have been made in one piece, this would involve a silicone mold or a rotomolding or blow molding because of the rounded and wavy shapes. Silicone cannot handle heavy production cadence, rotomodling takes too much time, blow molding cannot make strong thick parts.
a - We can see on each end of the biggest part, the square section is complete and integrates clips : it purposely is for good strength when clipsing each end to the other parts around. We can also see that in those 2 square sections, there is a parting line : meaning the mold is made of 1 bottom cavity that shapes the complete bottom end to end, then 2 sliders that slide out on each side shaped like a square, then 1 top cavity that shapes the inside of this big part. All the 3 movements made by the mold clearly shows how the draft angles are designed and we can see round marks that are in fact mold ejectors to confirm the direction of ejection.
b- The smaller part is made the same way, without the 2 square sliders. We can see the round marks and confirm the direction of ejection.

2) Cost : even if it's 2 parts, it's most likely to be injected in the same mold with 2 channels. As there is low chances to order only one part and not the other for spare parts. Blow molding could have worked but maybe this part requires the be strong or is designed to handle constraints we don't expect.

3) Versatility : the smaller part maybe has different versions to match different situations (several engine bays, additional air intake with a hole or a tube etc...)

Conclusion : there is always a good reason behind a design that looks questionnable. The cost is almost always the principal point to then take decisions on the other aspects like feasibility, materials, accessibility while maintenance etc..

I work on plastic molding pretty much all year long

[TheBoy]

Understood, but its still shite, given that they all seem to separate, and effectively let under bonnet air in rather than cool air.