[spock]

I have been away from injection molding for about ten years, so I am wondering if there have been any new developments in flash repair.

Example: simple round container mold, where a round stripper ring forms the bottom of part and ejects it from core. There is a taper on core
OD, and in ring ID, so that the two seat back together for the next cycle. Core material is BeCu, ring is S-7. After X amount of cycles, due to bushing wear,
miss alignment, etc. there is some wear "hobbing?" that develops, allowing flash where the core taper and ring taper meet.

Years ago, we repaired the worn tapers by having them chromed, then regrinding the tapers to fit again. This extended the life of the componets.


I have an oppurtunity to add work to my shop by repairing/replacing worn componets for a new local mold company. I do not have the ability in house to grind these tapers.
So, I am wondering:
1: are there any new materials being used that wear better?
2: is there an alternative to building up with chrome?

what I would like to do is come up with a solution that allows me to "clean up" the core taper, and just replace the stripper ring,
and leave the chrome out completely. This company uses about 5 sets of inserts running in 4 bases, to make the same product.
I would love to "stagger" the taper sizes between sets to allow me to possibly reuse the rings before replacement.
I think I could help keep costs down by turning the tapers as opposed to grinding them, providing I can hold the tolerance.

I would appreciate any input you may have!

[Chuck Reamer]

There is a material similar to BeCu called Tufmet, very wear resistant from what I understand. We have tried using it for a few applications, but some other problems arose and had to be switched out for a hardened 4140.

What about a fully hardened A-2, D-2 might be a little better than the S-7. You could also try to liquid nitride the ferrous material, about 60RC for .005" depth.

[Jim Estes]

I'm not sure about any new techniques or materials, copper stuff is getting very expensive. In my humble opinion, I would make both the stripper and the core from tool steel, just keep about 4-6 Rc difference in hardness and you shouldn't have any problems as long as the tapers are greater than 3 degrees.

Jim

[5axisguy]

We do alot of molds like your describing, we use high hard MoldMax (Brush Wellman) Uddeholm, for the cores, (because of cooling issues) then we usually Armolloy the core. Armolloy is basically a hard chrome plating about, 0001-.00015 thick. Then we use S-7 or H-13 for the strippers depending on the customer, these molds run tens of thousands of shots without any flash issues, if we do have to make any repairs down the road, usually we will redo the tapers and possibly weld the bottom of the core to advance it to regrind the shutoff angle. Even though we have a cnc cylindrical grinder, alot of times we hard turn the strippers, you can get a mirror finish using cbn tooling and the life is just as good or better than the ground ones. Sometimes on oval shaped strippers we wire cut them or I cut them on the 5x machine with good results as well. I think the key to success here is proper mold alignment, all are mold bases are finished on a Kuraki boring bar, all our molds have parting line locks and proper alignment, we always vent the stripper "rings" so to speak. We leave about .0007-.0008 gap between the stripper and the core, so in theory there should be very little wear if any. The angle which is around 5 or 10 degrees always shuts off on a flat or level of some sort leaving the stripper advanced slightly for the vent. The tapers only very slightly thouch if at all.

[jetski]

see a coater. We just had a tool coated on the unscrewing part of the tool (bearing area). The coating he put on was .008-.015 thick depending on the damage. It was a cold fusion process and my cores would have warped welding. This stuff groud great and looked like air hardend steel. But it ground almost like carbide hardly any sparks. It is wearing great.

[robinhood2b]

here in the UK most mouldmakers are now getting cores like this built up by laserwelding with the filler material the same as the core material and then grinding it back to shut off.

[spock]

I apprecaite the feedback. Since I started this post last year, I have built about 40 stacks of new inserts, and repaired a few. All the new and repaired cores were Moldmax highhard. Rings were s-7.
I was able to make new rings and I did use a diamond to turn them, worked very well. I then fit the core tapers on the lathe as well. None of my tools are currently flashing, so I guess that worked out.
But, I do not fit my cores/rings with a gap. i actually fit them to interfere very very slightly. (This is a 4 degree angle.) I may be off, but my theory was that my lathe finish, though absolutly slick, would wear a little as the "peaks" wore down. So I fit with a little preload. And, the molds these are in need plate work desperatly bad. i thought tight would be better. So far, they are running fine.
The company i made these for has no PM plan, so when the locators and bushings no longer work, at least the cores will still help line it up for a little while. Then, I can make some more....