Hello All,
I have been trying to create a form block for a sheetmetal project that our company is undertaking. we are creating all the parts nessecary to put together a tailrotor for a helicopter. The ribs have been a bear to dial in but I am really close. the width of the widest point in the rib has a tolerance of +/- .0025" Now when I put the rib in the middle of the tolerance and create a formblock with a 3 degree draft for springback the block ends up being .003" small below the -.0025" limit. besides making the formblock larger (which I would have to make the rib larger because it (the formblock) is refenced to the rib) is there something I am missing in order to have the finished form part come out in the +/- .0025" tolerance? and to clarify abit...if you take the finished block and add .024" (the total material thickness of both legs) it comes out less than what it appears to be in the rib model. Make sense?
1. I drew the rib to spec
2. created new assy. with rib as base comp.
3. inserted new component (formblock)
4. used the inside face of rib as sketch plane and inside edge of rib legs as profile for FB. Extruded 1.00"
5. did a sweep cut 3 degrees for the draft (.012" 2024-O)
6. installed features such as .03" radii for bend radius all around.
is there something else I need to consider when making the form block or should I just deal with making the ribs larger in order to get the block out to the size that I need.
Any imput is GREATLY aprreciated!
Thank you in advance,
Tim
p.s. the screen shot is of the nominal size for the rib and the points of where it needs to be measured to. this rib acutally has a limit of 1.716-1.711.
I have been trying to create a form block for a sheetmetal project that our company is undertaking. we are creating all the parts nessecary to put together a tailrotor for a helicopter. The ribs have been a bear to dial in but I am really close. the width of the widest point in the rib has a tolerance of +/- .0025" Now when I put the rib in the middle of the tolerance and create a formblock with a 3 degree draft for springback the block ends up being .003" small below the -.0025" limit. besides making the formblock larger (which I would have to make the rib larger because it (the formblock) is refenced to the rib) is there something I am missing in order to have the finished form part come out in the +/- .0025" tolerance? and to clarify abit...if you take the finished block and add .024" (the total material thickness of both legs) it comes out less than what it appears to be in the rib model. Make sense?
1. I drew the rib to spec
2. created new assy. with rib as base comp.
3. inserted new component (formblock)
4. used the inside face of rib as sketch plane and inside edge of rib legs as profile for FB. Extruded 1.00"
5. did a sweep cut 3 degrees for the draft (.012" 2024-O)
6. installed features such as .03" radii for bend radius all around.
is there something else I need to consider when making the form block or should I just deal with making the ribs larger in order to get the block out to the size that I need.
Any imput is GREATLY aprreciated!
Thank you in advance,
Tim
p.s. the screen shot is of the nominal size for the rib and the points of where it needs to be measured to. this rib acutally has a limit of 1.716-1.711.
The rib that I have the screen shot, is measured at the widest part of the rib. The limit is 1.711 to 1.716 which if you made it in the middle would give you a +/- .0025" tolerance. After getting the rib in the middle of the limit I imported it into any assembly, created a new part using the inside face of the rib as the drawing plane, converted entities of the inside edge of each leg to retain curvature of the rib, added features like the doming for springback, sweep cut for the draft and then a fillet for the bend radius. All this to me makes sense for making the form block so that the rib would come out dead on. But to the guys on the floor and inspection they said that if we machine the block per the model it will actually come out a little smaller than said dimensions, due to the removing of the material for the radius, which is only .030". and after doing some quick measurements with some construction lines it seems that they are right and the rib would be on the small side of the dimension and in some cases below the lower limit by .003". I guess what I am looking for is if there is something that I need to do differently and take into consideration when creating the form block. If you look at the assy of the form block and rib it looks like it would work like a charm. Anyway, I hope this helps clear the muddy water.
I will look at what you have this evening. I will have some time then to give your problem a proper review.
Cheers,
You will want to seperate your punch and form insert geometry from the actual sheet metal part. When creating tooling for parts, your tooling will rarely match your finished part in the forms.
You need to account for springback, any kind of wiping of the form and also any set radius you will add to set the bend. You can probably get your flange to kick around to close to 90 degrees by adding a set radius in your tooling.
I usually add construction geometry to my feature sketches that my tooling will be made to. You can do this in a seperate layout sketch.
Attached are a few screenshots of some forms we just sent through our shop. The phantom lines are what the tooling was designed to. The solid line is what the finished part will be.
I attached some SW2008 models of a form insert and punch which show what you are trying to accomplish (last 3 .png images). The radius on the forms are smaller then my finished radius and I also account for the spring back in the form. The form is shorter then the actual finished part to account for that springback.
You also might consider making a multi piece form block. Rarely do you get your forms correct on the first shot. You will want to make your block easily adjustable. What if your airfoil form is good, but the spar attach form needs tweaked. You could have a situation where when you fix one form you wreck the other forms that were good. Multiple pieces doweled and fastened will allow you to make adjustments without having to potentially re-do the entire form block.
Cheers,
Attachments
Thank you for the feedback. I know what your saying about not getting the form block right the first shot. I think this is our third attempt and that is why I am trying to be extra careful. I is so much harder too having a .005" window. Anyway, I was doing them this way because that is the way they had been approached before but the form wasn't linked to the rib and because we have editted the contour of the rib we needed to adjust the form contour to match so this is the way I thought I could solve the problem of having to edit 2 seperate models.
The only problem that I may run into with the 2 peice form is budget. We have been slowly desensitizing management to the fact that to produce repeatable quality parts we need to spend more time and money on tooling but I think that they haven't completely come to terms with that yet.
Now when you are saying "set radius" what exactly are you referring to?
Anyway, thank you for your response and your input. I will give it a go and see what I can come up with.
Thanks,
Tim
You need to get some reference books on Die Design. The SME has a great book called the Die Design Handbook that would help you understand metal forming. They have several other books that will give you the knowledge you need to design tools.
http://www.sme.org/srch/search...&advCat=all&st=N&fz=N
http://www.sme.org/cgi-bin/get-item.pl?BK90PUB4&2&SME
http://www.sme.org/cgi-bin/get-item.pl?BK85PUB2&2&SME
http://www.sme.org/cgi-bin/get-item.pl?BK84PUB22&2&SME
Yes, the are a bit pricey, but cheaper then throwing away tools.
In the last three pictures I show a part with a .010 thickness, when forming around the 90 degree bend I have a .002 set radius, in other words in that area of the tool the distance between the form insert and the punch is only .008 thick. This sets the radius and will kick the part around the corner. You notice that the punch does not contact the form insert on an angle. The form insert is relieved at an angle to allow the material to kick around the corner.
Cheers,
If this is going to be a hydro-formed part, it looks to me that what you're doing should work. The way I laid it out, using a 3° springback and a .03 bend radius, your form block should be .0017" smaller than your ribs Inner Mold Line - per side.
'Course, in all honesty - I've never had to hold quite that tight on tolerances. Usually ±.015 per side - .030 overall. This is for fuselage formers, and usually .040 or greater material.
Maybe you should do a test part to prove out your technique?
Thanks for the feedback. That is what we were coming up with too, except it was .0015" which made it .003" smaller in total. Either way we are still needing to make it bigger to get the dimension within the limit.
I know it is usually the case to work with +/- .030" which makes things soooo much easier, but I guess this will help refine the SW operator!
We are going to set up and do one block and see how it works and probably go from there.
I would still like to keep this open to see if there is are any grandpubas when it comes to this problem. How does Boeing or McDonald Douglas do it? We seem to be playing by a different set of rules then they did back in the day.
We do test hits all the time to see how different materials will react in the forming process. From there we use the test info to help us design our tools. For materials we have lots of experience forming we draw from that experience to make the decisions on how we will design the tool the first time. Sometimes we get it right, most time though we need to make adjustments to achieve the tolerances we desire. We work in the +/-.005 or less range all the time.
As you design more tools and gain more experience with your materials and processes you will get closer to designing the tool right the first time.
Cheers,
I know there isn't any change to bending metal. I actually worked on the floor for 18 yrs building repairs and manufacturing parts to a MUCH W I D E R tolerance than these. So for me it is more of a challenge. I am not an engineer nor have I had any of these classes, but I am trying to learn as much as I can.
And I thank each and everyone of you that has helped me in this problem!
And please don't take this wrong. I am trusting that both you and Steve know what you are talking about and I will take your advise and wisdom to heart. In my experience too, I have found there is someone that has been there and done certain things even more than the most experienced person. So just in case there might be one more person that may blow us all out of the water with the most simplest and obvoius remedy is what I meant by that.
Cause the day that we say we know everthing is the day we get schooled
No worries.... I am always amazed at what the grand pubas did in the past with none of the fancy tools we have today. Sometimes I think we get to wrapped up in the tools and not enough of gaining knowledge on the fundamentals.
Have you been watching the When We Left Earth special, about NASA on the Discovery Channel. Those guys were something. The things they did and in the time frame they did it in is amazing. I have a feeling what they did would never happen today, we are to risk adverse as a society.
I am old enough to remember the space age as it was happening live, with Walter Cronkite broadcasting for CBS. It was wonderous then and even more so today.
Cheers,
Your right especially about space not happening today. With all the regulations in works the drawings would never make it out to the printer. We are working on an old Turbo STC for a Cessna 185 and it took a year and a half just to revise it! And this was something that had already been approved back in the '80's
Anyway, no more ranting!
Thanks again!
Tim
I hear you. Been around aviation my whole life. There is a reason why we only have experimental airplanes in our hanger.
My fiance' is an A&P, but does not work on spam cans. Only works on Experimental, Aerobatic types. Steel tube/fabric and wood construction, with a bit of composites on occasion.
Need to find yourself a nitch market and specialize in that area of aviation. For Len there are not to many guys who can do all that he does, so he can charge a good rate for his time.
My other website www.acrodesigns.com
Cheers,
How is it going? Say my super what me to submit this "problem" to Hawkridge as a 'trouble ticket' I really don't agree with it, I this it is more technique and knowledge than an SW problem, so I guess what I am asking is it even worth the trouble? or should I do it just to satisfy her desires?
Thanks,
Tim
I have some ideas on how to make your tooling work better, but it is really hard to explain on the forum.
Cheers,
I have the rib and block up in the first few posts, if that doesn't work, email me at tim.mix@metalinnovations.com and we'll communicate that way or you can call me at 503.678.2807.
Cheers!
Tim
I forgot you posted the files already. I will give it a more detailed look. May not be until the weekend though.
Cheers,