5 ms·

> Door fit is a major issue for anyone and everyone. You simply cannot engineer doors to fit right, the assembly line guys always have to pull it, twist it and

by abeppu 6y ago

> Door fit is a major issue for anyone and everyone. You simply cannot engineer doors to fit right, the assembly line guys always have to pull it, twist it and ‘align’ it. I know nothing about manufacturing for cars or anything else, but ... why can't doors be engineered to just fit? In terms of absolute tolerances, I'm guessing all the stuff in the engine or transmission for a typical car is far more stringent, right? Is there something specific to the manufacturing process for doors or frames that is less controlled or precise?

throwaway201103 6y ago
I would guess it is because doors are large pieces of stamped sheet metal, as are the other body parts they mount to. They span a fairly large opening. There's probably a certain amount of flex and variation compared to cast and CNC machined engine parts. Doors in a house always need to be shimmed during installation to get the frames square and latches working properly. A car door will have tighter tolerances, but similar issues. The point is these adjustments are (or should be) made in the factory, not with post-delivery reworking.
jacquesm 6y ago
Because of material inconsistencies that are hard to get rid of (sheet metal is rolled to thickness out of a non-uniform billet, and cools non-uniformly as well due to edge effects, so you get small hardness and thickness variations) the material will deform in unpredictable ways during stamping. This causes very small deformities but over the size of a whole door it adds up leading to door being off by up to a few mm even when using exactly the same tooling during manufacturing. Welding then further deforms the door, even when it happens robotically and in a jig. The chassis typically suffers from the same effects. When the chassis warps one way and the doors warp in the other you can end up with poor fit. So manufacturers will do what they can to control for this but it will always be an issue as long as the input material is as inconsistent as it is. Unlike software, the real world is messy, and while of course it is technically feasible to mill a whole door and a chassis out of a billet it wouldn't be economical. So we adjust during manufacturing to cover the variations.
- emerongi 6y ago
  Do you work in the auto industry? How do you know the specifics of these issues so well?
  - jacquesm 6y ago
    I had a metal workshop and materials science has always interested me. Trying to accurately and repeatedly cut sheetmetal is an interesting - and ultimately very frustrating - experience. You can easily get to a certain degree of accuracy and above that it rapidly becomes hard or even impossible to make progress.
- Gravityloss 6y ago
  Since the doors and bodies come from separate production lines, you could use computer vision to very accurately measure them and then match up those with the best fit so you need to do the least adjustment. Alternatively you could pre-bend the doors in a machine for each body, after welding. But probably cheapest indeed to have a station late in the assembly line with people manually twisting the doors to fit, as is the standard practice.
benhurmarcel 6y ago
For what it's worth, I work on airliners and heard several times that doors are often a problem also. Not just passenger doors but also cargo and landing gear doors. They're hard to get right, and often need tweaking especially at the start of a program.

by abeppu 6y ago

throwaway201103 6y ago

I would guess it is because doors are large pieces of stamped sheet metal, as are the other body parts they mount to. They span a fairly large opening. There's probably a certain amount of flex and variation compared to cast and CNC machined engine parts. Doors in a house always need to be shimmed during installation to get the frames square and latches working properly. A car door will have tighter tolerances, but similar issues. The point is these adjustments are (or should be) made in the factory, not with post-delivery reworking.

jacquesm 6y ago

Because of material inconsistencies that are hard to get rid of (sheet metal is rolled to thickness out of a non-uniform billet, and cools non-uniformly as well due to edge effects, so you get small hardness and thickness variations) the material will deform in unpredictable ways during stamping. This causes very small deformities but over the size of a whole door it adds up leading to door being off by up to a few mm even when using exactly the same tooling during manufacturing. Welding then further deforms the door, even when it happens robotically and in a jig. The chassis typically suffers from the same effects. When the chassis warps one way and the doors warp in the other you can end up with poor fit. So manufacturers will do what they can to control for this but it will always be an issue as long as the input material is as inconsistent as it is. Unlike software, the real world is messy, and while of course it is technically feasible to mill a whole door and a chassis out of a billet it wouldn't be economical. So we adjust during manufacturing to cover the variations.

emerongi 6y ago
Do you work in the auto industry? How do you know the specifics of these issues so well?
- jacquesm 6y ago
  I had a metal workshop and materials science has always interested me. Trying to accurately and repeatedly cut sheetmetal is an interesting - and ultimately very frustrating - experience. You can easily get to a certain degree of accuracy and above that it rapidly becomes hard or even impossible to make progress.
Gravityloss 6y ago
Since the doors and bodies come from separate production lines, you could use computer vision to very accurately measure them and then match up those with the best fit so you need to do the least adjustment. Alternatively you could pre-bend the doors in a machine for each body, after welding. But probably cheapest indeed to have a station late in the assembly line with people manually twisting the doors to fit, as is the standard practice.

benhurmarcel 6y ago

For what it's worth, I work on airliners and heard several times that doors are often a problem also. Not just passenger doors but also cargo and landing gear doors. They're hard to get right, and often need tweaking especially at the start of a program.