Rework of 4000 sheet metal parts-adding a larger hole

[David_W]

Got a problem at work where we've got some sheet metal plates, 1.5mm thick, mild steel, around 250x150mm total size. They've currently got a hole around 25x25mm, which needs to be around 63x67mm. I was thinking laser or punching.
Laser looks like a potentially more of a lead time than we'd like, how long would it likely take to get a press tool made and anyone got a rough idea of cost? I'm assuming 1.5mm steel probably sits within the capability of a half decent fly press?
(I'm sure I'm missing some needed information, I'm well within I don't even know what I don't know for this sort of operation)

 

[hotponyshoes]

Greenlee, q-max, rs, do rectangle punches.
Would be worth a look to see if they happen to have one that size?

 

[hotponyshoes]

I don't think Laser would be cost effective for reworking as they would each need manually loading and indexing into the machine.
Probably cheaper to have new ones cut from scratch unless you can find a laser cutter with an auto loaded that will go down that small and a magic eye.

If you could accept slightly rounded corners a plasma jig would do the job in-house

 

[David_W]

Greenlee, q-max, rs, do rectangle punches.
Would be worth a look to see if they happen to have one that size?

It's always reassuring when other people are thinking the same things! So they do one which would work (too big at 68x68, but meh, not a problem), but it's got a 30mm diameter guide/stud in the middle, which means that have got to enlarge the existing hole anyway, so then becomes a two step process. Also as it's a larger punch than I'm used to, it specifies that it must be hydraulically driven on the Greentree spec, which then means I've got to get that as well, so a couple of grand sunk into press/die and driver, which isn't a problem but combined with a pretty slow cycle time, probably makes it not economic.
I hadn't thought about plasma, my skills with that aren't great but would get better rapidly with 4000 to do!

 

[Mikes]

Use a smaller punch say 50 x 50 and do the enlargement in four bites. Would need careful setting up of the jig for each operation but other than labour (good job for an apprentice) would be relatively cheap.

 

[Agroshield]

Does the new hole always sit in the same relative position to the old hole?

If so, whatever you do needs to use the old hole to locate itself.

The part has a stud fixed to it, a bend in it and something pop-riveted to it. That makes manipulation difficult and the protrusions need clearance in the press.

A Greenlee-type punch, where the two halves need bolting together will be deadly slow.

Ideally, you need something where you can drop the 25mm sq. hole over a locating device, press a lever and the new hole is punched.

At some point, or some method, the labour cost is going to exceed a new part.

 

[bricol]

Think I'd be ringing around people with CNC laser, plasma or water jet - fairly simple couple of layout jigs you could dump a load of them into a laser cutter, while loading up the next batch on a second or third jig.

4000 components is going to take a while . . .

 

[hotponyshoes]

It's always reassuring when other people are thinking the same things! So they do one which would work (too big at 68x68, but meh, not a problem), but it's got a 30mm diameter guide/stud in the middle, which means that have got to enlarge the existing hole anyway, so then becomes a two step process. Also as it's a larger punch than I'm used to, it specifies that it must be hydraulically driven on the Greentree spec, which then means I've got to get that as well, so a couple of grand sunk into press/die and driver, which isn't a problem but combined with a pretty slow cycle time, probably makes it not economic.
I hadn't thought about plasma, my skills with that aren't great but would get better rapidly with 4000 to do!

You don't need to use the stud.
You can just make 2 guides that align the 2 halves of the punch externally.
As long as you start it in the correct place it will stay aligned by itself.
Likewise, you don't need Hydraulic.
My Hydraulic setup probably only cost £300 (but you might need to spend more to do 4k holes)
But any press with a high enough rating will work to push the punch through rather than pull it.
The greenlee pull-stud hydraulic system is ideal if you want to stick a new hole in an existing wall mounted control cabinet but, for what you want, just mounting the 2 parts of the punch in a bench press and making up some locators to hold the existing sheet against would be pretty simple.

It's 10mins to learn how to use a plasma.
Put a stright edge in a bit of scrap, run the torch along it. Measure the offset of the cut line.
Then make up a jig with a bigger hole than the one you want.
Drag the torch around that and you can't go wrong as you'll only ever cut into the waste part if you slip away from the edge.

Lidl do plasma cutters for about £100,
You could buy a few of those and make up a pantograph arm to cut multiple pieces at once.
It might even be possible to connect more than one plasma torch to the same machine?

 

[David_W]

The new hole isn't perfectly centered over the existing one, but as you point out, external jig would sort that out anyway. So 1k for the punch/die, get a flypress as my hydraulic press would cause an eternity of regret about 100 parts in and some time-waiting to get a price back from a laser cutter, at least this gives a baseline.
Although from this, I really need to try the plasma cutter, currently in its box, in anger. Even if it's not for this job, going to be useful...

 

[hotponyshoes]

The new hole isn't perfectly centered over the existing one, but as you point out, external jig would sort that out anyway. So 1k for the punch/die, get a flypress as my hydraulic press would cause an eternity of regret about 100 parts in and some time-waiting to get a price back from a laser cutter, at least this gives a baseline.
Although from this, I really need to try the plasma cutter, currently in its box, in anger. Even if it's not for this job, going to be useful...

If you already have a Hydraulic press you could get an air/Hydraulic Foot pump to drive it for the same price as a flypress.
Reduce the travel to the minimum required either with a riser block or a temporary collar around the ram to limit the return stroke.
Add some stronger return springs (or wrap it all in bungee cord) to make it retract quicker.
If you make up some sort of catch tray so you can flood the punch with lube and keep it in good condition you'll probably get half the cost of that back selling it on afterwards..

 

[tom2207]

id be starting with a q max punch and mounting it in a metalworker ,,, bit of a fence made up and an apprentice installed ,,,

 

[julianf]

My ex-neighbor used to have a pneumatic press.

With a standard square punch, and the right jig combination, the part could be punched in one corner, shifted (manually) to the other corner, punched again, the other corner, and then the last corner.

4000 would take some time, but it would be even more tedious doing them with a CNC, where you would have to load them, click go, wait, unload them, reload them, etc.etc.

The trick would be keeping focus and not punching a hole in your hand.

 

[gaz1]

2 pieces of wood one to slot into the hole thats already there

the next piece of wood smaller than the size you need to be used with the plasma torch put an arrow on the longer side and a mark on the metal

slot the wood and then get cutting a plasma will cut them quickly enough

 

[oldbikedavey]

That's one for a Hare production press, or something similar.
4000 items is a fair old chunk of work....

 

[hotponyshoes]

If you can get the tooling made up by Monday lunchtime and get started you could probably be done for an early finish on Friday

 

[Agroshield]

Another, another thing to consider is management of the slug once punched.

If the component is 'small', it could be worth having a horizontally-acting punch, then the slug just drops on the floor. Anything vertical means you have to remove the component and remove the slug before inserting the next one.

Arranging stacking/management of both the input and output will be crucial to speed. If your 'inbox' or 'outbox' only takes 10 items, you have to stop every ten pieces and shuffle things about. A second person feeding and removing would allow the first just to do the hole modification.

If using a plasma, maybe an empty 45 gallon drum with a jig on the top. Take the piece, slot into the jig, run the torch around the four sides, pull out and stack on the finished pile. Train yourself to touch the piece with only your left hand and hold the torch in the right hand.

 

[hotponyshoes]

Another, another thing to consider is management of the slug once punched.

If the component is 'small', it could be worth having a horizontally-acting punch, then the slug just drops on the floor. Anything vertical means you have to remove the component and remove the slug before inserting the next one.

Arranging stacking/management of both the input and output will be crucial to speed. If your 'inbox' or 'outbox' only takes 10 items, you have to stop every ten pieces and shuffle things about. A second person feeding and removing would allow the first just to do the hole modification.

If using a plasma, maybe an empty 45 gallon drum with a jig on the top. Take the piece, slot into the jig, run the torch around the four sides, pull out and stack on the finished pile. Train yourself to touch the piece with only your left hand and hold the torch in the right hand.

A lot of the greenlee punches (especially in the bigger sizes) are 'slug-busters'
They chop the offcut into 4 pieces during the operation.
If you had 2 people on the job, one loading and operating the press, and the other could take the piece back out and blow the slug cuts off with an airline.
A funnel mouth chute on the back of the press and send them into a bucket.

 

[hotponyshoes]

Just for fun.. someone could do the maths and see how long a leaver arm would need to be if you wanted to make up a hand-operation tool.
Would be a quick cycle time..

 

[Agroshield]

Just for fun, someone could do the maths and see how long a lever arm would need to be

I think this covers the maths:

[Solved] The shear strength of a sheet metal is 300 MPa. The blanking

Concept: Blanking force is given by: F = τ × As where, τ = shear strength, As = shear area Calculation: Given: &tau

testbook.com

Shear area would be (63+63+67+67)*1.5 = 390 * 300 = 117kN circa 12 tonne so something like a 240:1 lever ratio if you want to push 50kg.

 

[hotponyshoes]

I think this covers the maths:

[Solved] The shear strength of a sheet metal is 300 MPa. The blanking

Concept: Blanking force is given by: F = τ × As where, τ = shear strength, As = shear area Calculation: Given: &tau

testbook.com

Shear area would be (63+63+67+67)*1.5 = 390 * 300 = 117kN circa 12 tonne so something like a 240:1 lever ratio if you want to push 50kg.

Forget that idea then.
You don't want to be going up a stepladder 4000 times.

Edit: Although, those greenlee punches don't try and shear the whole thing at once.
They are more like scissors with 4 points that gradually shear through..
You would only need to lift the punch 1.6mm so you might be able to get a manageable length arm on it..

Edit again:
The lift would be 1.6mm plus whatever the travel on that particular punch is so still might be too much..