This is a semi random collection of notes a home injection molding machines and mold making for such machines. A "home" injection molding machine is a manually operated machine that can frequently fit on a bench top on takes up a relatively small floor footprint.
If somebody wants to suggest additional information to add to this document, just send me the text in an email to wayne AT gramlich DOT net with "Home Injection Molding Notes Suggestion" in the subject line. Markdown format is preferred, but not required.
There are a number of books on the topic on manual injection molding machines:
-
Secrets of Building a Plastic Injection Molding Machine:
This is probably the original book about the topic of home injection molding machines. It is a bit dated, but definitely worth a quick read.
-
Cutting costs in short-run plastics injection modding:
This book focuses on the trade-offs for making lower cost molds for these manual bench top machine. This is a book is by Morgan Industries, Inc. and is geared towards their line of bench top molding machines.
There are a number of commercially available. As I run across them, I will add them to the list below:
Morgan Industries, Inc. produces a set of bench top machines call the Morgan-press. By the way, the Morgan-Press is the benchtop injection molding machine used by Techshop.
At present, I find the Morgan Industries web site to be a bit difficult to navigate, so I have added some links that probe into their web-site. Presumably, these links will break over time:
-
The Morgan-Press models.
-
The Morgan-Press features.
-
They also sell [a book about mold making( http://www.morganindustriesinc.com/plastic-molding-guide/). This is referenced above in the books section.
-
There is a PDF Manual on-line at Carnegie Mellon University (my undergraduate alma mater.)
These machines clamp the mold from the bottom.
This machine starts at roughly $20K and has a variety of add-ons. The anti-ooze nozzle sounds interesting.
The Amatrol learning system looks pretty decent.
Here are some links:
-
Amatrol PLS1 is the actual machine.
This machine clamps the mold from the side.
About $15K.
Medium Machinery makes an very capable looking injection molder. The web site is very easy to navigate.
About $3K. This is a lot of machine for $3K.
This machine clamps the mold from the bottom.
It is unclear if Iasco-Tesco is still in business. Hopefully, there are just rearranging their web site.
There is several year old [catalog for Iasoc-Tesco]( http://web.archive.org/web/20150213095804/http://iasco-tesco.com/images/catalog/iasco2013.pdf]. The Ultron looks pretty neat.
This machine clamps the mold from the side.
No on-line prices.
Galomb, Inc. sells an injection molder for about $4K.
Whenever I do research like this I generally do a buy vs. build investigation. The machine I really like is the Morgan-Press, but it is way out of my price range. The next machine I really like is the Amatrol, which is out of my price range. The next machine I like is the Medium Machinery and the price is well within my range, my only reservation is that the shot size is only 2oz, but I think I might need 4oz. Of all of the ones above, the one from Medium Machinery looks closest to what I have in mind.
To summarize, a manual injection machine has four basic parts:
-
Injection Shaft: (Top) An injection shaft that pushes the melted plastic into the mold.
-
Plastic Melter: (Middle) A place to melt the plastic. This is also the place where the plastic is added to the machine to the melting chamber.
-
Mold Clamp: (Bottom) A place to clamp the two mold halves together.
-
Frame: In addition to the three basic parts above, a frame is needed to hold it all together in the right locations and orientations.
Each of these is parts is discussed briefly in the sections below
My current thoughts on a frame are to use some Steel Slotted Angle for most of the frame. It may be necessary to double or triple up on some of the high force sections of the frame. This seems like a flexible to design a system where sub-modules can be moved up and down by unbolting some bolts and reattaching in the new location.
The injection shaft can be done either manually (like the Gingery or Galomb) or with a air piston. With an air piston, it is possible to set the final pressure exerted on the injection shaft using a air regulator. That feels like a much more repeatable strategy to me. In addition, an air piston perform larger shots. In general, I'd like to support 6 to 10 in^3 of plastic, whereas the manual injection shafts tend to be down in the .5 to 1 in^3 of plastic.
It is not clear to me how to compute the injection shaft diameter based on the maximum desired shot size. Once the diameter is known, the height of the melting chamber can be computed.
Once the diameter is know, presumably it is possible to compute the desired maximum force to exert on the injection shaft. MaMaster-Carr has a reasonable election Tie Rod Air Cylinders of various output forces and strokes. They are not particularly inexpensive. Presumably, once the desired force and stroke is selected, it is possible to shop around.
I would probably use a precision ground steel shaft from McMaster-Carr for the injector shaft. They are inexpensive and extremely accurate. I still do not know what diameter though.
My current design is based the heater block used by Vincent Gingery in his book (see above.) Rather than using a steel block, I would probably attempt to get by with an Aluminum block instead. I find Aluminum easier to work with on my CNC mill. Again, I do not know what size block to use. The larger the block the more heat retention. (Yeah, I know steel has a higher specific heat.) I would also machine up some stuff allow the plastic pellets to be shoveled into the heating block.
On thing I really like about the Medium Machinery design is that it has replaceable "Internal Plasticizer" shafts made out of what ooks like brass. That looks quite doable would allow me to change plastics and color by changing shafts.a
I would probably buy a couple of 400W cartidge heaters from McMaster Carr design them to be on each side of the injector shaft bore.
In an article from Makezine there is an article from somebody who modified their Gingery injection molding machine to use a PID controller. The person used a PID controller from Auber Instruments. It looks like the SYL-1612B what was selected. I would be tempted to use the same product and a couple of 10A 240VAC Solid State Relays.
I believe it would be best if there was some insulation wrapped around the heater block. This was done in an instructables document for a filament extruder. In addition, a protection cage to keep fingers from touching the melter system makes some sense as well.
It is unclear whether or not a threaded injection nozzle will be used. I am leaning towards one, but it is unclear where to get them right now.
There seem to be two styles of mold holder -- bottom clamp and side clamp. Both styles will work, but they impact how you design your mold. For a side clamp mold, the plastic is injected right at cut plain of the mode. For a bottom clamp mold, it is necessary to provide a tapered hole through the mold to reach the cut plane. This can be done with a tapered end mill. The Morgan-Press and the Medium Machinery used bottom clamp whereas most of the others seem to use side clamp. While I lean towards side clamp, I consider myself sufficiently ignorant of the issues that I could be swayed the other way.
Ideally, an air piston would be used to do the clamping. Alas, air pistons tend to be expensive. I thought it was totally ingenious how Medium Machinery used a simple bottle jack for their clamp holder. Bottle jacks are inexpensive. When I looked up bottle jacks on Harbor Freight, I found two almost identical 20 ton air hydraulic bottle jacks -- #95553 and #69593. (The only difference is where the air hose attaches to the air motors.) These behave just like the hand pumped jack use by Medium Machinery except that they can be pumped with air pressure rather than a manual pump level. The air motor drives the hydraulic fluid pump. The air pressure just controls the speed of the pumping not the set pressure. When you are all done, the little the T valve at the base is twisted release hydraulic fluid and let the springs retract the jack. I can live with that!
There is (at least) one disadvantage to side clamping. There also needs to be some pressure to press the mold up against the plastic melter. I have not figured out how to do this yet.
I am not sure I will ever get around to this project, but I thought it was useful to write down my ideas. Who knows maybe somebody else will pick up on the project and push it forward some more.
I would like to acknowledge that I have gotten some very useful information from the Yahoo Home Home injection Molding Group.