Making Parts

After adding a few lines of code and adjusting a few nobs on my machine I was able to quickly make a few parts!  I also figured out how to upload high resolution pictures to blogger so that should be a little better!














I still don't know what these parts are or where this mold originally came from.

Here is a video of the machine going:


Still to do:
1 make a mold of my own
2 program in a mode for automatic/ semi-auto operation.
3 maybe improve the cooling system

Pressure Transducer

One one my main reasons for doing this blog is to document the control rebuild on my injection molding machine. Well, I'm going to try to make some improvements where I can. One of my problems is that I don't really know what improvements need to be made! While reading through a document Dow put out, Injection Molding Processing Guide, I realized that my machine did every step in its sequence based on time. However, according to Dow, new machines did at least one step based on the injection pressure.  This is the part that was the most informative:

 Hydraulic Pressure
The injection molding process is generally divided into
two stages. The first is injection (or fill), and the second
is packing (or hold). During the first – or filling – stage,
it is suggested that you set your machine pressure
near its maximum setting and control the speed of the
ram with velocity controls. The machine will only use
whatever pressure is necessary to move the ram at the
set speed. This technique will help produce consistent
parts because the cavity is filled at a uniform rate, despite
differences in viscosity due to temperature fluctuations
and other factors.
It is very important to switch from the first to
second stage when the part is 90 to 95 percent
full. If you do not switch from first to second
stage pressure before the cavity is full, the high
pressure of the first stage pump may cause the
part to flash and may cause damage to the mold.
It is suggested to switch from first to second stage
based on either the position of the ram or the cavity
pressure. Switch-over based on the hydraulic pressure
and time is suggested if ram position or cavity pressure
controls are not available.

After reading what Dow had to say, I decided to adapt this structure to my machine. The remainder of this blog post is documenting how I did it.

My controller has a 10 bit analog to digital converter which it converts a voltage from a 0-5V to a number between 0 and 1023.

The pressure sensors in this range are very expensive; some of them I found were over $250. I found one on ebay that was less than optimal for my application. It was a 0-5V transducer that read from 0-400 Bar. I got it anyway because the price was right.

When I hooked it up to my machine I got 2.1V at 2500 psi. Using the transducer like this, I get a resolution of about 6psi. Here is a little chart showing how it works.

Pressure (psi)	voltage	10 bit      number
100	0.08	17
300	0.25	52
1700	1.43	292
2500	2.10	430

Note: My DAC could measure between 0 and 2.1 volts if I set a refrence point for it to 2.1 volts. I could get over double the resolution if I did this but I'm going to save that for later. This resolution might work just fine and I may want other sensors that may use the full range.
With this pressure transducer in place, I can use it to switch from injection to holding pressure when it hits the pressure I think the cavity is 90% full. 


http://arduino.cc/en/Reference/AnalogRead
http://arduino.cc/en/Tutorial/AnalogInputPins
http://arduino.cc/en/Reference/AnalogReference?from=Reference.AREF

 

Making a Mold U Frame

I got the machine to ooze out a blob of plastic, but in order to make any more progress on this machine I need to have a mold! Luckily, a nice guy I met in LA gave me an old mold he had laying around (I don't remember where he said he got it). This type of mold can't be used "as is" because it is a Master Unit Die or "MUD" mold. These molds need a frame to hold them in place. Several companies make frames and molds like this but they are kinda pricy (at least for a hobbyist like me).    

I measured this mold and found that it fits the 8490 size mold frame. I then got the dimensions from a few of the people selling them and designed my own. Mine was basically the same but I made a few adjustments so it would fit my machine and such.

DME CAD Library
http://www.crosstool.com
http://www.seasky-tooling.com
 
Here is a lot of steel I got from Speedy metals. With shipping it was $309 which is much less than the $3000+ I saw these going for. The picture on the right is just the metal rough cut.

After I got it all machined, I found that the mold didn't fit the minimum mold height of 8.5" so I made a 1" spacer. Here it is all bolted in the machine. There is still a little drilling and tapping to do but I couldn't help bolting it in and testing it. 

Here is the first part to come out! The material was wrong for the part so it flashed out and stuck in the mold but this is a big improvement from the big blob you saw last time.  

Next up: I will talk more about the control sequence I am working on. 

Mold height adjustments

I ended my last post saying I needed a mold, which I am working on. My machine can fit a mold with a base of 11x12 inches but until now I didn't know the heights it could accommodate. When I got it, it was missing the tool for adjusting for mold height. I quickly made a crank out of a piece of conduit I had laying around. It is ugly, but works. I found that the maximum mold height it 11.75 and the minimum is 8.5".
I wish the envelope was a little bigger :(

It Works!

Today I made my first object with this injection molding machine! It's just a big blob of plastic but it's progress! 

The clamp arrived and went on so easy! It stopped the leak from a huge hole in that pipe.

There are a few loose ends I need to tie up before I start making parts.
    -I have some more programming to do  to get the controller working smoothly.
    -I need to install a pressure transducer on the injection unit to trigger the second phase of injection
             (the old control used a timer but that doesn't seem like the best way to do it)
    -Oil cooling controller
    -One of the barrel heaters is giving me problems
    -And of course!  I NEED A MOLD!!! For this I will be building a knock off of a MUD quick change
       I plan on making mine compatible with  their 0809 size mold bases.

My first mold is going to be something awesome! Just wait and see!

More History on This Molder

I found a tiny manual in a box of parts which is titles "AMP plastic molding training manual" By E. V. Trunk. I searched Amp and found that they were the biggest company I had never heard of. You can read their company story here; it seems that they either changed their name or merged with another company called TE Conectivity. In short, they are a 10 billion dollar electrical connector company that started in 1956 making one thing to now making over 500,000 products and have 100,000 employees!

It seems like my machine came from their original Harrisburg PA facility. I remember that the guy I bought the machine from said it came from Pennsylvania. With this knowledge, I did a quick search on LinkedIn to see if I could find anyone who worked there around that time. I quickly found a few guys and sent them link requests; they could end up being valuable contacts.

There is a lot of good stuff in this little manual but the best thing is this:

This cleared up a few questions I had about the injection molding cycle, I'm glad I have it. The rest of the manual is available to download here. Please let me know if its of any worth to you!

As for the water leak, I talked to a guy at work (I work at a gas company) and he said I should try a  repair clamp. I ordered one and I will let you know if it works.

Almost there!

I ran into a problem with how I wired the limit switches.  I used unshielded wire, so, the electromagnetic field coming from my motor killed my control board. I bought a new board and re-did a lot of the work I had done, replacing a lot of the wire with shielded wire. Once the limit switches were done, the thermonic controls needed to be rewired to get them to work.  I thought I was about ready to run some plastic through this thing so I rigged up a scrap piece of aluminum to the stationary platen.

 After I had that piece in place I was planning on shooting plastic through the hole in the center. I was about to pour some plastic in the hopper when I remembered that the machine needs cooling water to keep plastic in the hopper from melting before it reaches the screw. I hooked up the hoses to my sink to provide temporary cooling and right away found a water leak coming from my machine. I hoisted the injection unit once again (I'm getting good at this!) and found the leak  in the center of the heat exchanger on the bottom side. The hole is about 1/2" in diameter and seems to have rusted through from the inside. You can see the heat exchanger below, it is the grey tube on the bottom of the compartment.

 I am trying to decide how to fix the problem, its going to be a major pain to fix it in place because its such a cramped space but trying to remove it could lead to more problems. Taking apart a 40 yr old plumbing job does not sound fun; specially, since I can't buy replacement parts if they break in the process.

While looking at the cooling system I saw that at one point the heat exchanger was hooked up to a valve that only flowed when the oil reached a specified temperature. It looks like this valve wore out, so, they just bypassed it and now the water flows all the time. This made it so the oil never overheated, but it also was never allowed to reach its designed operating temp. To fix it, I ordered a small temperature controller on ebay called a REX-C100 for just $15 and free shipping. From the data sheet, I should be able to program it to control the temperature and send an alarm to my main control board if it gets too high.

If I am happy with this little unit, I might replace all the temperature controllers with it. I would need at least 5 more of them if I did do it; 3 barrel heaters, 1 nozzle heater, and one mold heater/cooler. I do not trust the old controls and they don't show a temp reading so I would like to get rid of them if I end up getting this machine to work.