DIY moulder Part 2

[Robin Hewitt]

The moulder is just about built, now I need to do the nozzle and make a mold
Big potential to go horribly wrong. I have a plan which may or may not be credible and lots of questions

I'm molding USB plug shrouds in glue together halves. For the molds I plan to use slices of 4" diameter CZ121 brass rod, simply because it's tough, cuts cleanly and milling cutters stay sharp forever. I will fit inch thick steel boxes to hold 1.25" thick brass slices. Round pockets cut 3/8" deep in the steel and 5mm caphead bolts around the rim pulling the brass down.

Closing force on the mold is 4.5 tons, injection pressure adjustable up to 2260psi. Injecting Cycolac ABS from GE Plastics at around 200 degC (490 F). Room to fit water cooling in the molds if I need it but I'm not anticipating a very fast cycle time so may get away without it. Last ABS mold I had made they didn't want to go <1.5mm thick over any kind of area, is that good info?

I've discovered that UK nozzles are usually tipped hemispherical, US nozzles are chamfered 45 degrees, the US system sounds easier.

The nozzle is CZ121 and about 1" long overall. I'm thinking to drill it 3mm (1/8") through, does that sound right? Any ideas on how far I should insert it into the mold, how far back do I flat spot the end?

I'm a bit vague on this so I stopped making it hoping for some help, see pic.

[Pres]

Robin, congratulations on having the huevos and talent to build your own IJ molder.
Looks good. (hope mother nature feels the same way)

I think the US (mostly) uses a 0.5" radius nozzle.

It seems that a radius would make sealing better when things are a bit out of alignment or deflect due to pressures and heating.

Making a 0.5" outside radius is a bit more difficult, but the mold radius is then quite easy requiring just a 1" ball em.

Whatever you choose, good luck.
Pres

[Pres]

p.s. maybe start with a 1.5mm nozzle hole and enlarge it if it seems that quicker filling is necessary.

Downside of a bigger nozzle hole is longer to "freeze off" (assuming your runner is the same size) and less mixing of the material.

Since it is not a reciprocating screw machine you'll need all the mixing you can get for a homogeneous melt and color mixing.

hth,
Pres

[Robin Hewitt]

Quality information, I'm doing far too much guessing

Just noticed I forgot to drill the holes in the lugs that will hold the guard.

Every time I turn it on I immediately put my hands in my pockets, a survival reflex I picked up for bone crunching/slashing machines, just in case I get a mad urge to stuff fingers into the mechanism

Have to sort that out PDQ

[ZipSnipe]

Good to see you at it Robin. This one of my favorite builds , great job.

[Pres]

I'll sure second that!

It is a very impressive creation you have accomplished.
Keep up the nice work.

It might turn into one of those 90-10 machines.
(when it is 90% complete, the remaining 10% comsumes
another 90%. - but that's also a fun part of it!

Pres

[Robin Hewitt]

Originally Posted by Pres It might turn into one of those 90-10 machines. (when it is 90% complete, the remaining 10% comsumes another 90%. - but that's also a fun part of it!

Could be, can't even test the injector hydraulics until I have a mould, it might rip the barrel off

The solenoid that opens the feed gate arrived rated continuous rather than the more powerful 25% duty cycle I needed. The distributors were useless, eventually sweet talked a freeby out of the manufacturer

The ejector plate is 0.5mm askew at one corner, have to pack that.

The solid state relay won't turn on the pump motor, now hard wired. Odd, thought I'd tested it

I've bought a 12 foot bar of 7075 T6 for the moulds. I have found a supplier for small orders of nitrided ejector pins, guide pillars and bushings. Taper mills are available but pricey.

The big delay is probably adding DRO scales to the mill, the cheap Chinese ones, look like digi calipers with the jaws missing, ordered a set of 3 today.

My .003" backlash isn't usually a problem but I think it could be. The scales resolve to 1/20480" but don't seen to like having their GND connection messed with, they jitter when you try to interface them.

I'm going to try a high impedance op-amp buffer close in and the merest suggestion that they should match my GND. If I can persuade them to drift within 16 volts of reality it should work

[Pres]

Originally Posted by Robin Hewitt ... I'm going to try a high impedance op-amp buffer close in and the merest suggestion that they should match my GND. If I can persuade them to drift within 16 volts of reality it should work

Seems like you are making good progress with a multitude of concerns.

Hopefully, the op-amp won't be triggering on the noise that seems so plentiful around a milling machine.

Might be you'll just have to tune each one 'till it looks good.... more time req'd...

Good luck,
Pres

[ZipSnipe]

Cheap dro scales suck or at least the one I bought did. Any vibration turns it on(killing the batteries) and its accuracy was off by .005 aka garbage. But maybe you'll be lucky with yours. Let me ask you this what are you gonna use to control the molding machine? Have you found a program that can handle the various movement and ejecting and such?

[Robin Hewitt]

.005 out sounds ghastly assuming that's inches.

How so .005 out? Was that jitter or over a distance or what? I'm expecting +- 5 counts of jitter?

I notice the scale still sends data even when switched off, I'm told that trying to fit an external power supply is a big no-no does it eat batteries all the time or only when you put it in fast mode?

The scale manufacturer does seem to avoid any electrical contact with the machine so I'm letting it float. The jitter problem may be interference so I plan to screen it, as I don't need to see the display or press any buttons this is easy.

The pcb physically connects the scale slider to the mill. In the picture the top 3 holes match the bolt holes on the slider, the bottom two connect to the mill. This keeps the flea squeak 1.5 volt data connects as short as possible. To switch the mode lines close in I'm using tiny, surface mount reed relays with lots of decoupling.

Then I added end sensors, then I put in a jumper link to decide if the left hand sensor should zero the display, then I ran out of pins on the RJ45 connector and had to stop

I have already written some software to read/control the moulder.

OUTPUTS
Direction of the rams
Power to the rams
Pump motor on/off
Feed it measures of plastic
Over-ride the thermostat and kill the heater

INPUTS
Ejection complete
Mould nearly shut
Mould resists closing
Injection ram fully up
Thermostat active
Haven't done the plastic empty sensor yet

There is also a rate of flow sensor I was planning to use to decide how much plastic was needed to refill the melting pot. However I now think that is easier to measure by timing the injection ram return stroke.

[Robin Hewitt]

Panic over, a primitive test but the scale read true