Re: Is Welding Worth It?
 

Re: Is Welding Worth It?
 

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.

Re: Is Welding Worth It?
 

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.

Re: Is Welding Worth It?
 

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......... ::ouch::

Re: Is Welding Worth It?
 

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.

Re: Is Welding Worth It?
 

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 :D

Re: Is Welding Worth It?
 

Anyone have suggestions for which epoxy to use for bonding aluminum?

Re: Is Welding Worth It?
 

We use Hysol E60HP

The long cure time is a bit of a pain but the extra strength it gives you is worth the wait. We have used it for years with great results. Rough up the surfaces you are bonding and you aluminum will break before the bond does.

Re: Is Welding Worth It?
 

You can go down the rabbit hole with this. But. More important than the specific epoxy is surface prep. Epoxy works best in shear with lots of surface area. Preferably you would want to strip the oxide layer of the aluminum. At the very least scuff it with 80 grit. The surface should be thoroughly cleaned and de-greased. Reference one
West systems has a lot of how to for epoxy.

Re: Is Welding Worth It?
 

Welding can be a lot of fun and in my opinion has more pros in terms of creating a lighter and more durable chassis, however there will be some issues if we are letting the students weld. We need to make sure we have a ventilated and high ceiling shop, PPE needs to be addressed to everyone, and who ever is welding needs to be highly supervised. Another perspective is just creating a better designed robot. Stronghold was tough.

Re: Is Welding Worth It?
 

This is quite a vague question that depends much on the team. As Andy A said, 95 welds where it makes sense for us. Welding, especially with sheet metal, opens up a lot of design flexibility that we enjoy taking advantage of.

As with any choice in FRC it's not the choice itself that matters, but the execution. We design self-fixturing or easy-to-fixture components, accessible welding locations, and have access to a lot of nice equipment. A team should not expect to get a welder and see success, it will take practice and expertise to do well.

Using a welder safely is no more difficult than using any other piece of shop equipment safely. In fact, a welder is probably safer than many pieces of shop equipment an FRC team might use.

I would not recommend 'sticking only with 6061.' After welding, an aluminum is generally in the "T0" state, in which 5052 has 28ksi UTS and 13ksi YS whereas 6061 has 18ksi UTS and 8ksi YS. This is just one example, there is much research to be done! Some alloys, such as 7005, can age at room temperature back to essentially full strength.

Furthermore, welding in FRC shouldn't be limited to aluminum only. Low alloy steels are easy to weld or braze, offer great strenth:weight ratios, and are not expensive. There are other design considerations for sure, but steel should be 'on the table' when discussing welding.

Surface prep is paramount here. Look at the epoxy supplier's suggestions for surface prep. I would recommend 3M DP 190, 420, or 460 for most applications, and Hysol 9309 for critical applications (it has glass beads to arrest crack growth and ensure an optimal bond gap). I would strongly recommend an elevated temperature cure rather than an ambient temperature cure for time and strength reasons.

Re: Is Welding Worth It?
 

Not so fast there - we use 5/32" rivets on almost everything, including our drive base (except this season which was brutal) and haven't had any issues.

Our team has found that drilling the correct size hole is the real key to having rivets stay in and be secure. For 5/32", you should be using either a #20 or #21 drill bit. Refer to the handy table on this page - http://www.engineersedge.com/rivet_application.htm

Re: Is Welding Worth It?
 

192 students has been welding for 20 years. Most of our welders learn in the in the fall with some starting the year before. Only a few have welded for years. Early on it was .125 or thicker. About 8 years ago I showed some students how to check for penetration by breaking welds with a hammer.::ouch:: With the increase skill due to their critiquing their own welds we now weld .062 and thicker. 192 also rivets and has found that 3/16 and 1/4 rivets work rather nice and have few problems.

Re: Is Welding Worth It?
 

We've been using E-120HP (same family) and have been happy with it.

We clean and degrease the surfaces after abrading for a better joint as well.

Re: Is Welding Worth It?
 

We've discussed welding but haven't gone down that path. Our frames for the past 3 years have been riveted with 3/16" stainless rivets (they were free...). We sheared no rivets and the frame was easily repaired when it needed to be.