How accurate is steel punching?

[taws6]

Hi, I am new to the site, so I hope I'm posting in the right section.

I am having some steel perferated with a hexagonal pattern for a project I have.
The percision has to be perfect (5mm holes, 9mm staggered centers in a 1mm thick sheet of steel).

I have herd the best way to do this is with lasor cutting.

The company I am using told me they would punch out the steel with CNC equipment as it is only 1 mm thick.
Now, I know very little about metalworking, is punching going to be an accurate way of producing this, or should I look elsewhere?

Please excuse my ignorance, but "punching" to me, sounds like a "hammer n' chisle" job!

Many thanks, Paul.

[Al_The_Man]

CNC punching can be very precise, within what accuracy do you need?
punching makes a nice clean hole also.
Get them to show you an example of other work they are doing and it should give you an idea.
Al.

[Mcgyver]

there is no such thing as perfect, think in terms of tolerance. I guy I know has some very expensive laser equipment...he says they can hold a couple of thou, cnc stamping is probably similar - but why take my word for it, ask whoever is doing it what tolerances he can hold, if its acceptable, specify that tolerance and and away you go.

the punch he's talking about is a large cnc machine with a carousel head of punches, I've not seen under but presumably there is a carousel of matching dies that also spin into position. automatically locates over the work, loads the right tool and punches the hole. standard in sheet metal work, results look good and are accurate. go to his place and have a look at the machine you'll see what i mean, should be a very professional looking result.

[Geof]

Originally Posted by taws6 ...The percision has to be perfect (5mm holes, 9mm staggered centers in a 1mm thick sheet of steel)...

You must define your concept of 'perfect'.

For instance if you want the hole size to be with 0.01mm of your specified size you must state that; 5.00mm +/-0.01mm

Similarly for your spacing you must state a tolerance; such as 9.00mm +/-0.01

And this kind of tolerance is pretty much impossible with laser or punching. it would probably require drilling and reaming the holes on a VMC.

If you can accept a tolerance of +/-0.10mm then you are within the realm of laser or punching.

You just have to decide what you need and define what you need and recognise that as the tolerance gets smaller the price will get higher.

In addition you mention a pattern; this can influence how you specify the hole spacing. If you simply specify from hole to hole and there are many holes it would be possible, if the manufacturer worked to the upper tolerance limit, to have a large accumulative error. For instance if you specify 9.0 +/-0.10 and the hole to hole spacing is consistent at 9.08 that is within your stated tolerance. However, over 100 holes the accumulated error is 8mm so the final hole is almost an entire hole space further from the first hole than you may expect. To avoid this you have to specify the distances from a common reference point and apply the +/- tolerance to these distances.

[taws6]

Hello.

Thank you for your replys.

This steel is for a grill on a car, so if it looks right it's close enough, I just wanted to make sure it wasn't going to look wrong.

The company in question is in China, so previewing their work is a bit out the way! As it is a small order, many companies in the UK want a small fortune ( I agree it will be time consuming/tooling charge etc ).

Mcgyver, excelent insight into how it is done/works, certainly dispells my worries about "hammer n' chisel job".

You have answered my question very in depth, and I thank you all for your time and experties.

Many thanks,
Kind regards,
Paul.

[Geof]

Originally Posted by taws6 ...This steel is for a grill on a car, so if it looks right it's close enough, I just wanted to make sure it wasn't going to look wrong...

This is an application where to look right it has to be very very close. My example of 100 holes across with an accumulated error almost equal to a hole spacing is probably quite relevant. And if you consider they might do the holes starting at one end, going across, moving to the next row, coming back, etc., you can see that if there was an 8mm accumulated error in one direction in one row then the opposite direction in the other it would not look right.

I can assure you the human eye and brain are extraordinarily good at seeing irregularities it what should be regular patterns.

[ctate2000]

Punching is accurate. A good turret punch will hold .005 inch or better on position. The quality of the hole is related to the tooling. If the punch is in good condition and the die clearence is correct you will find the hole size to be same as the punch size (nothing is perfect). If the punch is wrong then the hole will be wrong.

[chan luci]

Hi Paul.

If you are worried about quality and the inspection part, we can look over that issue also and can cater to the tolerances you need. A drawing would certainly help and we can (turret punch) punch in cnc or do laser depending on the type of accuracy you need. Just check with our web site for details. Each machine and its tolerance are described ober there under each heading. Any qty can be supplied by us, small or big.
Thanks
Chan