steel sheet metal clevis form tooling
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  1. #1
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    Default steel sheet metal clevis form tooling

    I have a small steel clevis I use in a product I sell. It is made from 3/16" 4130 steel. I currently use about 300-400 parts a year, and expect that number to increase. They are currently laser cut and formed on a press brake by another shop. In my pursuit of improved quality control and bringing the work in house I am hoping to buy or build the necessary form tooling to bend these in house. I am getting inconsistent parts, both in bends not being parallel to one another, and over/under bending. A pin passes through the two holes and currently hole alignment is not consistent enough. I am wondering if building a forming tool for this part would be a good solution, and if so where to begin in designing such a tool.

    Like I said, they are currently laser cut, I am wondering if punch tooling to blank the part would be practical in these quantities. If not I may consider machining them out of strips on the mill and then forming them.

    Only critical dimension is the distance from the center of the holes to the inside face of the clevis
    I attached a drawing of the part.

    Thanks Teddy

    steel-clevis.jpg
    Attached Thumbnails Attached Thumbnails steel-clevis.jpg  

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    Can you source suitable U-channel stock to make them out of? Profile and drill/mill hole as one op? Moves part from fab to machining, but the holes will always line up and the sides will always be square.

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    It should take just under 2 tons to form that part, so any press with a typical punch and v die section in a tight guide would work. Alternatively you can make a sort of sideways roller swing brake (?) that would do the job no problem, but may be finicky in setup and requires a decent machining capacity.

    The holes are likely misaligned because the press brake operator has no way to square the part to the back gauge. For small runs we use a square, but you have to do things exactly correct to not crush your hand or bend the square. (easy to do safely, but you have to set it up). For large runs we add a tab so that there are two points of contact on the back gauge, and then break off the tab after.

    Angular repeatability can be bad if they don't set up the press brake to use the same center every time, adjust the shims between jobs, or if they cut parts perpendicular to others (trying to use the sheet efficiently), and can be aggravated by the need for a small v die. A different forming radius could be beneficial here, but I'm not sure which way it needs to go.

    The first thing you should do as soon as possible is talk to the shop, give them a pin, and tell them that if a pin doesn't drop in without binding it's a reject.

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    This is typically what you get from sourcing a press brake operation. When I worked at the steel yard, it was +/- 3* so you could get a 42* and a 48*. Here at my shop, we a for +/- 1/2* tolerance which we hold fine on our 230 ton press brake.

    If you find a structural shop, +/- 5* is acceptable. If you find a specialty shop, hey will hold much closer tolerances like +/- 1*


    Those parts are easily held square to the bottom die. You can use a back stop and square them.

    My advice, wrong type of shop is bending these. Production, not quality.


    Sent from my 2PS64 using Tapatalk

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    I would continue to Laser the blanks unless you have somebody near by that can run temporary tooling in a punch press and you feel the demand will go up. Either would be economical but you will have a Blank Tool expense going the Punch Press route.

    Once blanked I would make a Wipe Form Tool for a Press Brake locating off the Holes. Depending on where you think you usage will end up you may want to design ejector springs in the bottom so you don't have to pry them out. Tapering the punch should allow it to slip off.

    If I was running these in my shop I would simply Laser them and coin the angles in. We make a part like that holding +/-.001 from the face to the CL of the holes after welding pin on the flat. We cut the holes .008 small, form holding +/-.002 and then comeback a "mill/ream" them in a fixture on a Bridgeport...over kill for you tolerance.

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    I've never found any 4130 U-channel. Sounds like a talk with my current supplier is in order. I've already given him a pin so I'll make it clear that if the pin doesn't fit I won't accept the parts.

    Regardless I am interested too hear if a form tool could be made for these. A single operation would ensure the bends were properly aligned.
    Thanks for the advice given guys


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    dynamic stampings in wisconsin can tool this for a few hundred bucks, they do a great job on short run stampings

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    you might want to price laser cutting from tubing, using a 5 axis machine.
    I think PBZ in Lititz Pa. does job-shop work on one. that would eliminate the forming step altogether.

    a punch die probably wouldn't pay for the quantities you are using, as well as not being as clean an edge.

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    At 600 parts per year you are looking at maybe 12 per week. This is where your thinking should start. The accuracy and edge finish on your laser cut blanks is key to locating the blank for further ops. Got pics of current as cut laser edges? Good close up pics? The devil is in the details.

    Laser cutting from tubing may work, or not. Get a few samples of tubing and split them in half after you measure them. Sometimes cutting them open can relieve stress from their rolling process.

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    I'd start by making a locator to attach to the press brake back gage and hold the part precisely. Most likely, would think hard about making a single-hit tool, but put it off til a third or fourth batch. I'm a waterjet + rapid prototyping shop, making this sort of part and the quick & dirty tooling for one-off and short run is my favorite kind of work.

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    That would be a simple forming die to build. You could run it in an arbor press. A square die on top and a square u-shape die on the bottom with locating pins for the holes. One shot in the arbor press and done. Stick with the laser cut blanks, stamping that quantity will be costly


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