Model Railroading > BNSF 72’ Frostline Reefer (Part 13) – Warp Factor

This is Part 13 of a series on the BNSF 72’ Frostline Reefer project.  (Parts 1 thru 12 were posted earlier.)
 
In an earlier post I mentioned I was going to incorporate Weld Warpage.  I have never seen an RTR model offered with car sides having Weld Warpage.  Possibly because some customers would assume the model was “defective”.  Most likely it is because to machine a randomly wavy surface is much more difficult than a flat surface.  Customers are still purchasing their cars without it.  Their competition doesn’t offer it, so why bother?
 
Pad printing would be more complicated due to the uneven surface, resulting is a higher reject rate.  Even if a manufacturer offered a car with Weld Warpage, when two of the cars were next to each other in a consist, the Weld Warpage pattern would be exactly the same for cars with different road numbers; which is not realistic. 
 
Weld Warpage
Like wood grain, weld warped side panels follow a recognizable pattern.  Though they are similar, each is unique. 
 
A year ago, my only options to model Weld Warpage were:
   1) Painting “shadows” to simulate it.
   2) Create actual physical “waviness”.   
      a. Use a soldering iron to VERY CAREFULLY deform the sides.
      b. Mill shallow depressions into the side panels, alternating with filler to build-up the surface. 
These would be time-consuming, but the results would be satisfying.  However, completing a single car is one thing, completing a fleet of cars is another.
 
With the introduction of CAD and 3D printing, not only can the sides of the Frostline Reefers have Weld Warpage, but each road number can have a different Weld Warpage pattern.  To my knowledge, this has never been done. 
 
Rivets
Back in the day, the sides of cars were riveted, and the sheet metal remained flat.  However, it is labor intensive to apply rivets.  Modern car sides are welded together.  This is usually done by robots that are programmed to weld a bead along a predetermined path.  Thought this is more cost effective, and faster, there is a significant amount of heat applied to the edges of the sheet metal.  What causes the car sides to warp? 
 
Mr. Sulu, Ahead Warp Factor 1
It is well-known that metal will expand when heated, and shrink when cooled.  The part not as well-known is when the metal returns to room temperature, it will be slightly smaller than its original size (prior to being heated).  This means the edges of the sheet metal will contract, while the metal in the center of the sheet remains the same size.  The sheet metal will “pucker”, which appears as waviness in the surface.  The result is Weld Warpage.  The pattern formed is somewhat random, based on the thickness of the metal, temperature applied, travel speed of the torch, etc. 
 
Here are some ways railcar builders could prevent warps (but none are practical):
 
-Increase the thickness of the sheet metal to resist the warpage.

1. Car would need to carry less cargo (weight) to compensate.
2. More metal = higher expense for construction.
3. Car would be heavier for merely a cosmetic reason.

 
-Create a rib cage of reinforcement under the siding to weld onto.

1. Adds more weight
2. Increases labor and material cost.
3. Car would be heavier for merely a cosmetic reason.

 
-Heat the entire car to a high temperature, then let it cool.

1. This removes the “stress” and the sheet metal will flatten as it cools.
2. A kiln that would fit an entire railcar would be enormous. 
3. The energy required to bring the entire car up to temp would be insane.

 
-Continually stitch-weld until all weld beads meet

1. Weld beads that are about 1”long, skip a few feet in-between beads
   
   • This distributes the heat
     
     • Heat doesn’t build-up in one area
     • Allows the heat to dissipate
   • Blow air onto the welds to cool them
   • Have a “chiller” plate underneath that draws-away heat
2. Make another round of 1” welds, that are in-between the existing 1” beads
3. Repeat making rounds until all weld beads meet, to form a continuous bead
4. Increases the weld time by several fold
   
   • There is a potential for a pin-hole (leak) when beginning a new 1” weld.
   • Inefficient use of robots, that cover the same path over and over.
   • Significantly complicates the set-up jigs.
   • Increases production time for merely a cosmetic reason.

 
Consequently, there are thousands of brand-new railcars leaving fabrication plants with warped side sheets.  It has become an accepted tradeoff. 
 
A Uniquely Warped Individual
Since the 3D printer does NOT use a mold, it can print unique versions of each car.  The geometry can be altered so each car has an individual Weld Warpage pattern.  (In order to tell the shells apart, the underside of each model will have the last 3 digits of the road number 3D printed into it.)  This leverages the flexibility of 3D printing, and creates something injection molding cannot easily match.  The result is a string of Frostline Reefers that could be displayed side-by-side, with a realistic Weld Warpage pattern, each being unique. 
 
In case you are wondering, I will NOT claim (nor try) to match the actual Weld Warpage pattern on specific Frostline Reefer prototypes.  As long as the Weld Warpage is unique per model, I’m happy.  To be able to hold a model up to a prototype, of a specific road number, on a specific side of the car, and be able to match the Weld Warpage EXACTLY would be quite an achievement, but I’m not that warped.  :-D
 
Would You Like Mustard and Relish With That?
In the future, when high-res scanning technology comes within reach of a hobbyist, then perhaps the Weld Warpage could be matched exactly.  Until then, it would be a significant amount of work for not much gain.  I’m proud to be a Rivet Counter, but not willing to earn the title of Warp Weenie (or whatever such a warp-obsessed individual would be called) by matching the warp PRECISELY to that level.  To have Weld Warpage modeled, unique per shell, is raising the bar high enough for me.
 

 



Edited 4 time(s). Last edit at 11/25/22 17:04 by tmotor.

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The goal is to have a “glint” shot of a string of BNSF Frostline Reefers with the caption, “Yes, it’s a model.”  :-D

Dave



Edited 2 time(s). Last edit at 11/25/22 00:09 by tmotor.

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I just throwing this out there because I've never tried it. I've been wondering how a hot air soldering unit might work for this type of work.

Season's Greetings, Chris!

> I just throwing this out there because I've never
> tried it. I've been wondering how a hot air
> soldering unit might work for this type of work.

For ABS plastic, it could work.  I don't have one of those hot air soldering units, but if it gets hot enough to melt solder, it will certainly melt ABS.  Of course, the issue is controlling the heat.  Perhaps foil masks could prevent heat from affecting too wide an area. 

I did try to deform the walls of a scrap gondola car with a soldering iron.  Not pretty.  Maybe with a lot of practice it could be mastered, but the heat was too localized.  (To that end, the air soldering may give more heat dispersion.)  It needed to be more spread-out, or it just poked a hole in the plastic.  Maybe with temperature control, and a tip that was spoon-shaped? 

For 3D printed resin, many are NOT affected by heat.  The resin hardens by reacting with UV light, not by being heated and cooled.  It is a chemical process, not a thermal one.  I have a digital Weller soldering iron.  I had it maxed-out at 700 F, touched it to the resin, and it didn't deform at all.  :-0

Take care and God bless!
Dave



Edited 1 time(s). Last edit at 11/25/22 17:08 by tmotor.