First, the terms. "Plastic Extrusion Machines" are used to make such things as pipe and plastic rod. You cannot produce coat hangers or shoe soles with an extruder. That takes an injection molder, and expensive tooling.

First thing to do is compile a list of possible items you might want to produce with this machine. This will give you a rough idea of the capacity you will need. The amount of plastic the machine can inject into the mold (shot size) is the first requirement to establish. This is normally figured in ounces of material. Unlike extrusion, which is a continuous process, injection molding is cyclical.

So, let's establish some requirements. You have to tell us what you will use the machine for.

Size, Quantity, Materials will all affect the decision.

More information please. Extruder or injection molder?

June 25, 2009 Search Smarter. Search by specification to find Plastic Fabrication products and services. Industry Trends & Events

Look at the commercial side of this web site. There's tons of information available.

This is a great wealth of information, Thanks! The naming was just what we call the machine around the shop. What I am really concerned is of course a molding machine based on a cyclical production.

Also, depending on the cooling capacity of the molding system you will need the cycle time as well as the mold shot size.

Lynlynch is correct about sizing the machine. Any machine supplier would be able to recommend the size of machine based on the part size and volume, number of cavities, etc. There are a few US injection molding machine suppliers left, and a number of foreign suppliers. Don't necessarily go with the cheapest, since you may end up with a maintenance and downtime headache. Ask for references from their recent customers. In addition to just the molding machine you will need a mold temperature controller, a material dryer, and material handling unit to keep the machine filled. Get some books on molding and send your production, maintenance, and setup people to some training or seminars to learn about injection molding. A good source of books and seminar information is the Society of Plastic Engineers www.4spe.org .

Before getting injection molds built, do some research on such things as runner and gate design, mold cooling, mold venting, types of mold steels, and plastic part design. Most of the plastic material suppliers have very good design and molding guides that can help with this. Most mold building companies have excellent machinists and mold builders, but they don't necessarily understand what is required to mold parts most efficiently. They will often do what saves them the most time, not what produces the best part as quickly as possible. You will need to come up with a list of specifications for the mold builder, so they know what are expecting and so all the mold builders you contact quote the same type of mold.

Until you get a good foundation in injection molding, you may want to stay away from the more difficult materials to run. Start with polystyrene, polypropylene, polyethylene, ABS, polycarbonate, PC/ABS, or nylon. It's not that you can't run other materials, but these are among the most forgiving, although polycarbonate and nylon require a little more attention to detail than the others.

Good luck! It's challenging, but if you do your homework, it can be rewarding.

Another consideration is the cost of operation. An electric press uses an electric motor turning a screw to open and close the mold plattens. A hydraulic press uses hydraulic cylinders to open and close the plattens. The electric in a given tonnage (the amount of force that can be generated to hold the mold halves closed, or clamped) uses less electricity per hour than a hydraulic, though I have seen instances where the electrics couldn't keep the mold clamped under injection pressure.

You also have a wide variety of options in contols and process monitoring; real-time digital, remote sensing digital, and good old analog. I would go for the best I could get to accomadate future work.