Need help with a load cell application 4

[ak369]

I am looking for a particular load cell to use for an application in which the load cell will be used to determine the force profile inside of a chute that it is sent through.

I will try to be as specific as I can.

In the company I work for, there are presses which make parts, that in turn come out of chutes where they are collected.
These parts often end up bending as they are made out of steel.
In an effort to determine what is causing these parts to bend, we decided to try and determine the force profile inside of the chutes.
Someone recommended that I use a load cell, in which the load cell will be sent through the chute filled with parts in order to determine the force profile on the inside of the chute. The parts where the force profile is highest is most likely where the bent laminations occur.

The problem is, I barely know anything about load cells, and I need a particular load cell for this application. Essentially, it should be able to fit through a chute (I can provide the diameter if requested but it should be able to fit a load cell), and also help determine the force profile within the chute..

If anyone has any experience using load cells, please let me know.

I was checking out A&D

http://www.aandd.jp/products/weighing/pdf/loadcells.pdf

and the LC-5223-T005 load cell seemed fine. The presses are typically 250 or 300 tonnage, but this one had a 50 kN maximum capacity which was the highest on their website.

I think the beam load cells looked the best but which type or particular models would you recommend using?

 

[hendersdc]

This seems to happen frequently, and bent sections like that would show up visibly in lines of parts like are shown in your pictures so it should be easy enough to observe. I would suggest watching the process until you can definitively say "good parts went in to step B of process, bad parts came out". Keep narrowing down your search until you find the source.

Now that I have suggested the proper process to follow it is time for wild speculation...

That kind of bend could happen when a individual part or small stack of parts has space in front or behind it in the large stack and leans slightly. When the next parts come sliding down they run into the leaning part, which catches a little before sliding into the stack and causes the bend. If this is the case you could solve by keeping pressure on the part stack or by angling more and taking advantage of gravity.

 

[dhengr]

Mech. thread404-440378, 25JUN

Ak369:
Any restriction in the chutes, any to small a dia. location might cause the problem your photo shows. I would look first at any direction changes in the chutes. The way those laminations are packed in the chutes (flat face to flat face) in bunches of 15 or 20 lams. per bunch, they will not change direction, bend around a corner very easily, and this will require some added motive force to push them around that corner. Also, you photo shows that those bunches of 15-20 lams. are slightly misoriented w.r.t. each adjacent bunch. How does this figure into the problem? Those fins/tabs/”T” shaped legs (?) will bend quite easily due to fiction of the piece or an entire bunch due to its own weight, plus some motive force component, as they rub on and are supported by the chute. I would look at the chutes on that one press which it down, you won’t be in the way of production. Look for worn, scraped, polished, abraded areas in the chute. This will give you some ideas where to look when you actually shut a chute down to examine it for the same conditions. Is there a particular location along the length of the chutes which is causing the problem? Ask your boss and/or the shop guys to call you the next time they find some bent lams. in process, and stop the line till you get there. Then you and the shop guy clear out the chute enough so you can look back and see what caused the problem. This kind of effort may take several tries, but finally starts revealing a likely cause.

They do value your opinion or they wouldn’t have asked you to help solve the problem. But, there are opinions and then there are opinions everybody has one, and some are worth more than others because they are backed up by knowledge, facts, experience and good judgement. The guys who’ve been there 30-40 years have all of those, but all you have is book-learnin at the moment, so your facts better be spot on and your evidence/clues better be meaningful, for your opinion to count or be listened to. MintJulep wasn’t be harsh with you, he was just stating the facts of the matter, you’re in the real world now, so you gotta be able to take a little of that without hurt feelings. If you can find some good/helpful local mentors, you will see that they mean no harm, the right ones are trying to help, they even have a bigger-n-bigger kind smile on their face as they see you learning and trying, when they kick you in the butt, and tell you to start thinking a little, and then feed you a few more hints/clues, from their experience and greater judgement. Look for, ask your boss, who would make a good engineering mentor. Ask lots of intelligent, well thought out, questions out on the plant floor, those guys know a lot more about what’s going on than we engineers sometimes think, they aren’t all just covering their butts. Then really listen to what they are saying, they have a lot to teach us about how to do our jobs better. Reading btwn. their lines often prompts another question and gets them thinking a little deeper too.

 

[ak369]

@dhengr

I did exactly that today. I went to an operator, and he suggested several factors that were contributing to the bent laminations, especially the one causing the most scrap. I think going around and talking to people more experienced than I was, rather than trying to solve the problem completely on my own, is what helped. I'll try to answer the questions you guys proposed to the best of my abilities, and see if any of them help me solve these issues in my project.

Thank you all for your help.

 

[rb1957]

be careful who you take what advise from ... ??

a guy on the floor is probably the best expert in what happens on the floor, and how you have to "nudge" the machines to get them to work (but not so much that they "tilt" on you); but his explanations of mechanics of materials or other types on analysis should be taken with a grain of salt. of course there are people who cross boundaries and are knowledgeable of other disciplines.

another day in paradise, or is paradise one day closer ?

 

[ak369]

Sure, I'll try to take that into consideration before actually implementing any strategies. Thanks for the reminder.

 

[MikeHalloran]

Absent deleted pictures, I'm guessing that the laminations are punched in a die set, and fall out through a hole in the bottom, and the 'ski jump' that I see is responsible for orienting and stacking them into the open top holding chute that we can still see.

It would be nice to know the cycle rate of the punch press.
If it's big enough and slow enough, grabbing each lamination in turn from a receiving dish and transferring it to the open top holding chute might be a good job for a robot.
... which could also manipulate the part for inspection.

If the ski jump runs full of laminations all the time, i.e., they don't fly through it, there's a good chance that it's worn substantially from when it was built. You might want to dig in the dusty archives for drawings of the ski jump parts, and arrange production of new ones, or at least compare them to the drawings during down time. You need to lock out and tag out everything nearby for such an operation, and you also need an experienced millwright or machinist to help you work there, ( or do the work for you in a union shop ), so you don't get killed by the machinery.




Mike Halloran
Pembroke Pines, FL, USA

 

[ak369]

@MikeHalloran
I can ask the punch rate speed or the speed of the operation, however, that isn't entirely under my control (more in the control of the press operators on how fast they want to run it). As for the dies, they constantly rebuild and shim the dies in the tool rooms, i.e. they are under constant maintenance. However, the punch obviously punches out the parts, which travel through the chute.. if we were to automate that process entirely with a robot that can inspect the parts for any damage, and handle the parts more carefully.. then of course we would prevent a lot of damage. But I don't think that's the first step.

What one of the leaders in the press room told me is that sometimes the operators get impatient and end up pushing the parts down the chute because they come up too fast. I was suggested to try and use a chute brake, but I'm not sure if that added pressure would actually cause more scrap to occur. It would slow down the parts moving up so that the operators don't end up damaging the parts, but I'm not sure if it would be a good idea. What do you think?

 

[rb1957]

I think you're discovering part of the problem. Your process is out of control. The operators should not be able to speed up the machine to make more parts, particularly if this creates scrap and slows the overall production. Try to correlate speed of machine with occurrence of scrap.

another day in paradise, or is paradise one day closer ?

 

[MikeHalloran]

I suspect a 'chute brake' is something like a 'room stretcher'.
... unless there really is such a thing, and I have just never heard of it.

Perhaps I am misunderstanding how the laminations get into the chutes and how the operators normally interact with the chutes and the laminations. Can you describe the process in more detail?


Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

Hypothetically H-Dun-named customer cares about this, and will help you figure it out and fix it.

https://www.h-dsn.com/genbus/PublicDocServlet?docID=39&docExt=pdf

https://www.h-dsn.com/genbus/PublicDocServlet?docID=38&docExt=pdf

Or your scope of supply might be moved to Thailand or India.

Probably not the type of decision that an intern should make on their own.

 

[MikeHalloran]

I am sad for H-D.

Recent news notwithstanding,
any company that uses the 'word' "methodology" is doomed, IMHO.


Mike Halloran
Pembroke Pines, FL, USA

 

[dhengr]

Ak369:
Your second photo of 26JUN, 16:44 shows (showed) a chute coming up from under a press, and it also shows several scrap lams. laying on the deck. Start looking right in that area of the chute on the idle press and then on the chute show in the photo. That chute will have its center of curvature above the chute for upward curvature. The top of the lams. will have a smaller radius/arc of travel than the lower, bottom, bearing surface of the lams. That is, the lower bearing surface of the lams. must travel a greater arc per inch/degree of longitudinal movement of the stack, it will be loose, not compressed (which offers some resistance to bending) as the top will be; the bottom will also be where the friction from the lam. self weight will be and this is the bending force on the “T” shaped legs producing what your photo shows, a lateral friction load, bending the weakest section of the “T” shaped legs. Where is the pushing force (motive force) pushing on this stack of lams, and how does that relate to the problem? Are the lams. bending in the chute down from the press, or in the upward curvature of the chute? Study that.

Would some lubrication on the rubbing surface of the chute, a couple times a shift, or some slight/gentle vibration on the chute help things move along? What kind of steel are those lams. made of? I believe they want a soft/mild steel for these kinds of applications (winding cores), so the yield strength will be quite low, but that shouldn’t be the real cause or solution, it’s just an observation.

You are on the right track listening to others (the helpful, experienced shop guys, etc.), asking them meaningful, well thought out questions, and really thinking about what they have to say and how it might play into the problem. What Rb1957 meant in his post, 26 Jun 18, 22:01, “be careful who you take what advise from” was; always ask what ax does this guy have to grind, what knowledge, experience and judgement does he have to back up what he thinks and is telling me. You always have to make a judgement about the value of the info. you’ve been given, and how does that new info. fit with the rest of the facts of the matter.

 

[berkshire]

dhengr,
The material used for these laminations is, grain oriented cold rolled silicon steel, it is dead soft and will bend as soon as you look at it.
B.E.

You are judged not by what you know, but by what you can do.

 

[ak369]

@rb1957

I think I misspoke. The operators aren't the ones capable of controlling the speed of the process, that is up to the zone leaders and people who run the presses.

By the way, I don't think the speed of the operation is anywhere out of control. It is pretty much set and ran at a fixed speed. But my point was, if anyone wanted to change the speed, they would, but that normally doesn't happen.

@MikeHalloran
A coil is fed into the press which stamps out the steel laminations. The operators pretty much just pick the pieces up and put them into boxes. Some of the inspectors check the parts to make sure that everything is correct before the press runs, and if there is any problem with the parts, either the zone leaders or tool makers stop the press and try to fix any issues.

The "chute brakes" essentially are brakes that slow down the parts as they move out of the chute by applying pressure on the inside of the chute. By inserting them, we could probably slow down the movement of the parts up the chute. But I don't really know, it was just a wild suggestion.

 

[ak369]

@dhengr

Actually the T-shaped lams are from a different press which has a conveyor system.

In general though, I feel like it's hard for me to really observe any bends occurring because the chutes are closed.. I also suspected that the bend in any parts would most likely occur at the bottom of the chute if it happened due to the build up of pressure, but I'm not sure how to reduce that pressure. Also, as I mentioned earlier there is a tight interference fit between the parts and the chute (less than half an inch of space in some areas). So, essentially any pressure could easily bend the parts.

The bent laminations occur very randomly.. I might go to a certain press that I believe is causing a lot of bent laminations, and study the chute, and when the operator runs the press, observe that there aren't any bent laminations occurring at that particular time.

The bent laminations can happen at any press and any part, and even though there is a pattern of which parts get bent more, there is still no clear pattern from the data I have.

It just seems to be more of a general problem with the chutes itself, which is why I am trying to understand if there is any way we could reduce the pressure on the inside of the chutes, or some way that I could analyze it.

Ideally, if I could somehow calculate the pressure at the bottom of the chute, and the pressure on the top of the chute, and say "there is too much pressure in this particular area of this chute that can cause bent laminations", that would be ideal. But I have no idea how to do that. Going back to my OP, load cells weren't really the right idea.

Is there any way I could study that? I feel like my observation might not be enough in this scenario and I also lack the experience to quickly identify a problem.

As a general question to everyone on this forum, is there any way I could then lower that pressure or the tightness of fit between the parts and the chute?

 

[rb1957]

Sorry ak, you sound very keen and eager which are often good qualities but there are times to rein in this desire to rush in (there's an olde joke about young bulls and old bulls, but this isn't the place).

You've been asked (I presume) to try to solve this problem of bent workpieces. I doubt anyone thought you could do it on your own (and may be giving you rope to hang yourself with).

You've done a bunch of observations so I'd suggest going to your supervisor and saying "it looks very complicated", summarise your observations (as factually as you can), and suggest (and boy I hesitate to say this) that you form up a team to study the problem. Before this, read up on 6 sigma (yech) and CQI, etc so you can make sensible proposals. Clue, what form of CQI do you guys use now ? If none, then you're in for an up-hill fight. You can read up enough on CQI to get your hands around the topic. This could be the basis of a career ... succeed with this early project, get some formal CQI training, maybe even a Masters, become a (yech) "black belt", save the company lots of money, etc.

GL

another day in paradise, or is paradise one day closer ?

 

[ak369]

Thank you all for the good suggestions.