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August 23, 2026 5 min read
When you're replacing sheet metal on a classic car, a pneumatic punch and flange tool can save a surprising amount of time. It does two jobs with one tool: creates a recessed flange for overlapping sheet metal and punches clean, consistent holes for plug welding.
I use the Astro 605ST Straight Type Punch/Flange Tool in the shop for patch panels and other automotive sheet metal repairs. Here's how it works and where it makes sense to use one.
A punch and flange tool combines two common sheet metal operations into one pneumatic tool.
The flanging side creates a small offset or step along the edge of the sheet metal. This lets another piece of sheet metal overlap the original panel while keeping the two surfaces much closer to flush.
Flip the tool around and the punching side creates uniform holes along the edge of the panel for plug welding.
Instead of forming the flange separately and drilling every plug-weld hole by hand, you can do both operations quickly with one tool.
That's especially useful when you're making patch panels or replacing sections of sheet metal during a restoration.
The one in my toolbox is the Astro 605ST Straight Type Punch/Flange Tool.
I've added it to Inside My Toolbox with my take on the tool, what I like about it, things you should know before buying one, and where to find it.
SEE THE ASTRO 605ST IN MY TOOLBOX →
If you simply overlap two pieces of sheet metal, the joint becomes twice as thick where the panels overlap.
That's not always what you want.
Using the flanging side of the tool creates a recessed step along the edge of one panel. The replacement panel can then sit inside that recess instead of sitting directly on top of the original sheet metal.
That gives you several advantages:
Better panel alignment
A cleaner transition between the panels
Easier positioning during fit-up
More support along the joint
Less height difference to deal with during finishing
For certain patch-panel repairs, it can make fitting the replacement metal considerably easier.
The other half of the tool is just as useful.
Automotive bodies contain thousands of factory spot welds. During restoration work, we commonly duplicate those connections using MIG plug welds.
To make a plug weld, you need an opening in the outer piece of sheet metal so you can weld it to the panel underneath.
You can drill those holes individually.
It works.
But when you have a long panel with a lot of plug welds, drilling every hole gets old pretty quickly.
With a pneumatic punch, you simply position the edge of the sheet metal in the tool, pull the trigger, move to the next location and repeat.
You end up with clean, consistent holes without drilling and deburring every one individually.
Once you've punched the holes, fit the replacement panel and clamp everything securely into position.
Each punched hole exposes the sheet metal underneath.
When MIG welding the joint, start the weld so you're getting good penetration into the lower panel and then fill the hole until the two pieces are properly fused together.
After the welds are finished, they can be ground as necessary depending on the location of the repair.
Done correctly, a plug weld provides a strong attachment and is a practical way to duplicate many factory spot-welded connections during automotive restoration.
Even though you're making individual plug welds rather than running a continuous bead, you're still putting heat into thin automotive sheet metal.
Heat control matters.
Don't automatically start at one end of a long panel and weld every hole one after another.
Move around the panel.
Make a weld, move somewhere else, and give the previous area some time to cool.
Thin sheet metal doesn't need much heat before it starts moving. Once a panel begins shrinking or warping, you've created considerably more work for yourself.
A few extra minutes controlling heat during welding can save hours of straightening afterward.
A flanged joint isn't the right answer for every sheet metal repair.
There are plenty of situations where I prefer a properly fitted butt-welded joint, particularly on exterior sheet metal where I don't want an overlapping seam behind the repair.
But there are also plenty of places where a flange makes sense.
A flanged joint can make a replacement panel easier to position and hold during welding, and the overlap gives you additional support along the joint.
Which method I use depends on the panel, the location of the repair, backside access and what I'm trying to accomplish.
There isn't one joining method that's correct for every sheet metal repair.
Manual punch and flange tools are available, and they'll do the job if you're only making an occasional repair.
For regular restoration and fabrication work, I prefer pneumatic.
Connect the tool to shop air and you can move down a panel quickly without repeatedly squeezing a large pair of handles.
If you're punching a couple of holes, that doesn't sound like a big deal.
If you're preparing an entire replacement panel for plug welding, it absolutely is.
I've found this type of tool particularly useful for automotive sheet metal work involving:
Patch panels
Quarter-panel repairs
Rocker panels
Floor pans
Trunk floors
Wheelhouses
Cab corners
Inner body structure
Other overlapping sheet metal joints
It's one of those tools that doesn't seem essential until you start doing a lot of sheet metal work. Then you realize how much repetitive work it eliminates.
If you're doing classic-car restoration or regular automotive sheet metal repair, I think it is.
It's a simple tool that solves two common problems.
Flange the panel. Punch the plug-weld holes. Fit it. Clamp it. Weld it.
There's nothing complicated about it.
But anything that makes panel preparation faster and more consistent while reducing unnecessary work earns a place in my toolbox.
I use the Astro 605ST Straight Type Punch/Flange Tool in my own shop.
I've put the tool, my experience with it, what I like about it, and buying options together in Inside My Toolbox.
SEE THE ASTRO 605ST IN MY TOOLBOX →
Good sheet metal work isn't just about making a weld. Panel fitment, joint design, heat control, welding technique and finishing all work together.
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