Is Welding Worth It?

[Gdeaver]

We weld, rivet, bolt, bond our robot assembles. Isn't engineering about evaluating and choosing the best method to solve problems?

[Spark]

If you use thin sheet alum it can sometimes be better to weld. Though usable, rivets and bolts could rip out or bend the metal. A long weld, not just a spot weld, has more surface area connecting the two pieces. However, if you need precise pieces it's easier to rivet or bolt. I'm not saying keeping welded pieces flat is impossible, just harder.

[ChristianSpring]

Welding is the most appropriate thing to do in this situation.

[Kevin Ray]

Originally Posted by MrBasse

Why do you grind your welds down? Are you looking for a smooth appearance or for a strong joint? In my opinion, nothing looks better than a smooth stack of weld material laid down just right especially on aluminum.

+1 Nothing looks nicer than a stack of dimes laid down.

[Golfer4646]

Every team is different, but my team has avoided having any welding on our robot at all. The reason being that should a weld break, we are (pretty much) guaranteed to not be able to fix it in the pit. We also have a sponsor that provides us with bolts for each year, as well as another sponsor that helps us with fabricated parts (usually laser cut and bent if needed), making a sheet metal chassis held together with gussets and bolts what we have found is the best option for us given our resources. We have also done drivetrains in the past made primarily from 1x2 aluminum, also held together with gussets and bolts.

[Max Boord]

Originally Posted by courtney.john28

For the three years I've been on my team, we have always chosen to assemble with steel rivets that fit with stock versaframe gussets. There have always been problems with sheered rivets (especially during our 2014 season) and the problems seem to continue to an extent this season. I've started looking into welding to solve these issues but I was wondering what you guys think of this change. Is it worth the change?

What size rivets are you using? If its the 5/32" rivets that fit in the predrilled holes then theirs your problem. 4592 was having them pop out last year quite often and this year switched to 10-32 screws and aluminum 3/16 rivets and had no problems since then. Also the quality of rivet installation makes a huge difference. Getting a pneumatic rivet gun if your not using one already is a great way to improve quality over a hand rivet gun and speed up mechanism assembly.

Welding will most likely work but its a more catastrophic failure and I would not risk it unless you have a drop in replacement for any welded sub-system or have someone experienced in welding aluminum. Another option is to gusset and weld as the gussets will both provide extra strength and hold the pieces together making them easier to weld.

[scaryone]

If a weld breaks at competition? Gusset and rivet to reinforce the failed or failing weld. Not the end of the world. We have outsourced welding before but just purchased a TIG. We have students interested in that craft as a trade. Can't think of a better reason to weld when it is structurally applicable.

[Shahil_FRC]

In the past from 1996-2010 all of our frames have been welded, generally using 6061-T6 as the base material. But we also would have our frames sent out for annealing and heat treat post welding because of the HAZ reducing the welded areas back down to T0... This added much delay in getting a rolling chassis up.

After switching to bolted and riveted construction we haven't looked back, mind you we had our frames welded by aerospace welders and we still popped welds in the pre bumper era.........

[Tom Line]

Benefits to Welding:
1. It gives some added flexibility to the design process

Benefits to Rivets:
1. Most teams send things out to be welded. This takes time. Even if you think it doesn't - it does.
2. You can take a rivet out. Removing a weld is much harder.
3. You can replace rivets. You can add rivets. At a competition.
4. Rivets are rivets. Not all welds are welds. Welds can look perfect from the outside but if the welder didn't get penetration it will fail at the worst possible time.
5. Rivets are easy.
6. Rivets are cheap.
7. Rivets don't have a safety downside.
8. It's rare you run out of rivet map gas, rivet rod, or jam up your rivet wire auto-spooler.
9. If a rivet joint gets wiggly - add more rivets. If a weld joint gets wiggly, you've got problems.

To be absolutely fair - we welded our chassis this year. We have every year since 2008. We also welded our arms. The connection between our chassis and our arm snapped on our practice bot due to lack of weld penetration. The weld on our arm snapped on our comp bot 3 times because it simply wasn't strong enough. The solution at the competition was flat plates over the weld - riveted on.

In summation, unless you have someone who already knows how to tig weld and you're keen on teaching your students, or you have an over-abundance of time, I'd stick with riveting and focus on other portions of your robot process.

As an afterthought.... look at some of the critical joints on 254's robot. They are both welded, and riveted.

[Cory]

Originally Posted by Tom Line

As an afterthought.... look at some of the critical joints on 254's robot. They are both welded, and riveted.

They are generally only riveted to serve as fixturing for the welder, so that no hand alignment is necessary. Since we've started doing that we've gotten huge increases in quality and reduction in time it takes for the welding to be completed.

[Tom Line]

Originally Posted by Cory

They are generally only riveted to serve as fixturing for the welder, so that no hand alignment is necessary. Since we've started doing that we've gotten huge increases in quality and reduction in time it takes for the welding to be completed.

Interesting lesson learned. Maybe we will put it into practice too.

[kevincrispie]

Originally Posted by Cory

They are generally only riveted to serve as fixturing for the welder, so that no hand alignment is necessary. Since we've started doing that we've gotten huge increases in quality and reduction in time it takes for the welding to be completed.

Can't recommend this enough. 971 also generally rivets together assemblies before welding. It allows us to fixture the assembly the way we want before its welded, which makes it much easier for the welder, much easier to transport to the welder's shop, and helps eliminate inconsistencies due to the welding process. We have seem much better results with pre-riveted welded assemblies.

[Seth Mallory]

Originally Posted by kevincrispie

Can't recommend this enough. 971 also generally rivets together assemblies before welding. It allows us to fixture the assembly the way we want before its welded, which makes it much easier for the welder, much easier to transport to the welder's shop, and helps eliminate inconsistencies due to the welding process. We have seem much better results with pre-riveted welded assemblies.

192 also rivets before welding many of the parts.

[sanddrag]

Add 696 in there for one more ditto.

[Tom Line]

Originally Posted by Max Boord

What size rivets are you using? If its the 5/32" rivets that fit in the predrilled holes then theirs your problem. 4592 was having them pop out last year quite often and this year switched to 10-32 screws and aluminum 3/16 rivets and had no problems since then. Also the quality of rivet installation makes a huge difference. Getting a pneumatic rivet gun if your not using one already is a great way to improve quality over a hand rivet gun and speed up mechanism assembly.

Welding will most likely work but its a more catastrophic failure and I would not risk it unless you have a drop in replacement for any welded sub-system or have someone experienced in welding aluminum. Another option is to gusset and weld as the gussets will both provide extra strength and hold the pieces together making them easier to weld.

We also switched over to aluminum rivets with steel mandrels. They are a lot harder to rivet, but all too often we had poor quality Chinese rivets that would break the mandel above the rivet. Never happened again with the steel mandrel, and our forearms all look like popeye's