Copper Inserts and Copper EJ Pins?

[SBerg]

Anyone familiar with copper ej pins in copper inserts? We have had conflicting advice on the required pin clearance.

[Matthew Hajicek - Singularity]

We do copper inserts, but never copper pins.

[betts]

Are you talking Be-Cu material? I don't remember using both together. I would probably add .0005 in clearance if the material will allow it. What type of material is the part? Also the possibility of plating the pin would help if allowed.

[SBerg]

Yes Be-Cu..... We started out with about .0005" clearance and they started to bind up. Then we diamond coated the pins and are still having a binding issue. I will also add that the molds are being built at three different shops and all are having the same issue. We are also trying to see if steel pins will work better with the copper inserts. Also, since yesterday we came across additional documentation regarding the use of copper on copper issue which allows for .0015" to .002" clearance. So, work in progress....

[crazy^millman]

Well I guess the question that has to be asked is what was the rate of Thermal expansion considered to be. Copper is one of those materials more suspect to problems due to heat. Take a 1" diameter pin with a 1/4 Wall. The part will grow alot different than a 1" solid pin. The mass and the amount of Thermal growth for the amount of volume as well as the shape have to be considered. Then clearance if looked at after those different rates of thermal expansion taking cooling and heating into account are considered. .0005 to me is crazy clearance to even consider for normal steel pins, much less copper that grows and does such different things with any heat coming it's way.

[betts]

Yes Be-Cu..... We started out with about .0005" clearance and they started to bind up. Then we diamond coated the pins and are still having a binding issue. I will also add that the molds are being built at three different shops and all are having the same issue. We are also trying to see if steel pins will work better with the copper inserts. Also, since yesterday we came across additional documentation regarding the use of copper on copper issue which allows for .0015" to .002" clearance. So, work in progress....

 

I should have added that I have used steel pins in Be-Cu inserts/cavity/core blocks and not had an issue with anything.

[crazy^millman]

I should have added that I have used steel pins in Be-Cu inserts/cavity/core blocks and not had an issue with anything.

 

Yes because they are not the same metal. Anytime you take items that are the same metal other things have to be considered. Seen it time and time again where Hard metal and Soft Metal were used with perfect results. Then someone thinks they can re engineer things and go with the components with both hard metal or both soft metal with major problems. The idea of a wear item to give item is just that. When you change that design so many other things have to be considered. That steel was acting like a strengther to the core pins. The Copper does not have the same memory that the steel does so extra allowances have to be made for the lack of strength. Was that considered? What did the sharpie test tell you when it was tested under tensile load and under a stress. These different tests allow an engineer to see what the plasticity and form error results were under different loads? How much compression is needed and how much push back is the pin encountering?

 

Classic example few years ago. 17-4 PH connecting rod called out for the 747-8 on the back thrusters. The ball joints were also called out at 17-4 PH. I told all the engineers and design people it would never work. They told me about this program and that program and how this book told them this and that about strength. I told them I did not care they were taking a material that was prone to welding to itself in assembly and putting it against itself. They assured me they had this coating and this treatments and things have changed and it would be perfect. I laughed and said need to be 17-4 PH for one and Ti 6Al V for the other. I was told to shut my ignorant self up and just make the parts. So we made 150 of them in a hurry so they could meet their wonderful JIT schedule. They were able to assemble 2 sets without failing one time and upon trying to assemble those sets the 2nd time they failed as well. Guess what the failure was? The parts welded together in assembly. Complete seizure and had to be cut apart to be removed from the air craft. Everyone got together and had emergency meetings as now 8 planes were sitting on the assembly line without this need competent we made. We were getting called all kind of names, but see I am a pack rat about emails and I pulled out my emails warning them all about this problem and everyone quickly shut up. The engineering team looked at using my originally recommendation and decided that was the best course of action. To this day those parts are made that way and not the way they were originally engineered.

 

Metal is a funny creature and when you start changing things it not just as simple sometimes as putting this and putting that together. You need to see the story the metal is telling you. All metal will tell you something if you stop and look at all the different things that are going on. Seems like what works here should work there, but again not as simple as it might seem and when you are looking at copper especially with Beryllium added to it all kind of weird things can go on. We use to backward grind HSS Drills to drill hole in some Be-Cu grades. No direct cutting edge what so every and it would drill a hole all day long and the hole would not shrink 5%. The second we tried with a brand new drill with a good cutting edge forget about. Beryllium is a weird acting alloy and depending on percentages all kind of creeping and growing and other things can be going on. Great wear material, but normally stiffened or support by some other structure almost never the only thing present in a high wear high use environment. I see what you said and sorry my experience tells me ti is a bad idea unless in a very short very limited area, but I am shooting darts at a dart board some where half way across the planet and the blindfold is not helping me really see what all is going on.

[Matthew Hajicek - Singularity]

Excellent advise Ron. Another consideration would be if the pins and insert are of different alloys, then they'll have different thermal conductivity and thermal expansion than eachother.