Partial Punching Cutout

[Nwaune]

Hello,

I am looking for a way to partially punch holes similar to those in metal electrical boxes.

We have an auxilary mounting plate for the interior/exterior electrical harness interface our tractor cab. We currently have 5 part number for the same plate. #1 has no deutsch cutouts, #2 has 2 cutouts ..... The goal is to keep our cab airtight to prevent chemical from entering.

We'd like to go back to just one part number with "punch outs" for different options. Does anyone know of technique we could use to do this? How about a company that has experience in this field?

We are using 14GA material but could probably go to 16GA.

Thanks for your help.

Nick

 

[jbel]

I have seen this done on metal stamping dies as part of the fabrication process. When the electrical box is formed in the die the punching operation also takes place. The distance the punchout tabs are displaced is set by the timing of the die as it closes. I am not sure of the distance required to make the tabs easily removeable but I would be concerned that it may comprimise the ability to keep the cab airtight.

Even if it works correctly in tryout, it can be a finicky thing to keep the depth of the punchout tab exactly correct due to the effects of die wear and associated dimensional changes in the die.

I would caution you about assuming that there is a quick answer for this problem as stated. What may appear to work initially may not have long term practicality and manufacturability.

As for the material thickness, it should not be an issue for either thickness. The 14 Ga. material should punch just fine. It may actually be easier to use because you are relying on only a partial thickness of the material to hold the punchout in place. The thicker material may hold the slug better.

 

[ajack1]

One way to do it is to have to press settings, where any piercing enters slightly deeper when putting in the half shears. What also helps is to have a sprung ejector in the dies of the half shears and a sprung stripper on the top tool, so as to push the “slug” back into the material.

It also helps to have a “blunt” piercing punch and also relieve two areas in the punch with say a ground angle, if you look at an electrical box this becomes more obvious, as all these things help stop the part becoming detached.

Not very well explained but I hope this helps.

 

[griffengm]

Nwaune,
Jbel is correct in his assement of the difficulty in what you propose if you are working in metal that will not be painted. If you form the knockouts and then paint it, there will likely be some sealing action from the paint or powder.
Another option is to keep the cab at a slightly higher pressure than the exterior. Think ventiation design.

Good luck.

Griffy

 

[aamoroso]

We punch knockouts all the time on our Strippit punching centers. One of the requirements of these knockouts sometimes is "water tight". Depending on method of paint it may help seal, but our knockouts are used in NEMA Type 3R enclosurues and they have passed the test certified by CSA.