Punching Operation

try drilling the holes slightly undersized, then finish the operation with the correct taperred reamers using the same gang drills. punching holes require a hardened back-up piece specifically designed for the punchs. it is a boxed member? or did i misunderstand.

jlstitt's recommendation (using reamer) will give the best surface finish, and the most accurate hole size. (You didn't mention tolerance requirements.) 

If you choose to use a punch (or ganged punches), there must be a corresponding die for each punch -- and the punch & die must be aligned precisely. Each hole will require roughly 3 to 4 tons of force, or more.

The simplest option is to contact cutting tool manufacturers for advice. Using a different style of bit, edge geometery, cutting speeds/feeds, etc., can drastically effect the finished hole.

Could you have them Laser cut? a lot neater than drilling i'd say.

do you want the holes on one face? or you want through holes on opposite faces?

drilling method already described above should suffice. laser cut is a very good option and not expensive if you have quantities to work and require precision.

what tolerances are you specifying? can a draw (taper) in the hole be allowed?

you may consider water jet cutting or plasma cutting as options too.

the fact that you are presently drilling is sufficient to tell me that water jet should be good for you.

A single station hydraulic or flywheel press punch sounds ideal for this. Using a good quality punch and die, burrs should be at a minimum and cleaned up with a deburring knife. For the pitch, sliding the box on a guide to pre-set stops should give the repeatability you need.

This could be designed an fabricated in your shop with parts that are easy to obtain and at reasonable costs.

From the OP: "...on extruded aluminium box section of sq 25..."

The hole is 18mm, the walls are 3mm (combined 24mm), and the tube is 25mm. Not really a lot of room in there for a die. Add to this, an overall length of 6 meter.

I'm not certain I would go with punching, even though the OP mentions it in his thread title.

for a better solution . . . let us know whether the holes are through holes or only on one surface . . .

Venu,

If you decide to do this with a punch, I think you will face and have to answer four problems.

1. You will have the punched-out slugs inside the box, and they will have to be kept out of the way of the die as it is positioned. This can be done by keeping the central portion of the die thinner than the sides, so there is a channel down the center of the square tube. An alternative way is to do the punching with the tube sloped or even vertical so the slugs slide out (however most punch presses are not built for this orientation of punching).
2. You will need press the die tightly against the inside surface of the box when the punch is working, but looser when the die (and punch) are being positioned to the next hole location. This could be done by providing the die with a rocking base or a pivot point and a lever arm so pressing on the lever arm through an earlier hole some distance back holds the die tightly against the back of the work face while the punch is working. Then releasing the pressure on the lever arm would allow it to move "freely" to the next location.
3. You will need to position the die accurately so it lines up with the punch for every hole. One way to do this is with tapered alignment pins that go through two previous holes you have already punched. They would then bring the die into final alignment and hold it there during the punching.
4. You will need a means to accurately index the punch and die to the next hole location. If I understood your original question, all the holes are with the same uniform spacing, center-to-center. Indexing the punch and the work is fairly easy, with an alignment pin or stop that works off the previous hole. Indexing the die is much more of a challenge because it is inside a square tube that is quite long (6m is close to 20 ft). One method would be to put it on bearing rollers so it can move freely when not held with alignment pins and then either drive it forwards in the tube with a tiny wheel on a pin through a previous hole or by the use of very strong magnets that would attempt to keep it in a preset location on the punch press' table while the tube is slid to its next position. Another method would be to have a long (>6m) bar that holds it in its approximate position under the punch while the square tube is moved. With either method, you would rely on the alignment pins for the final and accurate positioning of the tube, punch, and die.

I think these four points will allow you to do the work you describe. Some of the other posts give good alternative suggestions. I hope you can find the method that works best for you.

--John M.

Hello Mueller,

a) and when you use a punch, how in 19mm of space (not accounting for inner radius at corners) will you position the die for an 18mm hole?

[ 19mm = (25-3-3)mm ]

b) even if you are able to do this and all else that you discuss above - will it be economical?

hence i repeat that waterjet, plasma or laser cuts may be better thoughts if drilling is not workable for productivity and quality.

welcome your views again.

- Soeb

Soebfatehi,

I hadn't done the math! Thanks for pointing out the obvious and unseen problem. In a larger dimension tube my comments would make sense, but with only 1mm total between the hole and the inner dimension of the tube, I agree with you that punching would be virtually impossible.

Thanks--JMM

Thank You for all giving the suggestions,

I saw a ladders made by Werner, they also have a box section and they are punching Square holes??? how they made it??? length also 6mtr and equal pitch. really this made me to think for punching operation in box section.

Thank you

Venu