Introduction: Plastic Injection Molding and Extruding

About: Professional work in various electrical and mechanical fields, obscure sense of humour and typically willing to help... Currently under contract designing environmental monitoring equipment.

Plastic Injection molding is simple with the right equipment. All that you need is a heater and some plastic.

Recycled plastics will yield the best results if kept to their respective groupings. Refer to the recycle symbols and do not mix types.

ABS is my plastic of choice, I used an old HP inkjet printer as the raw materials for this example.

I used a commercially available temperature control for this project but I have posted an accurate precision temperature controller in another Instructable.

All told this project took me about 2 hours and about $50 to assemble and test...

shown below is a 3mm ABS extrusion being done

NOTE: I have added a section with an example of a crude press lever.

Step 1: Important Notice!!!!


Hot plastics are NASTY and EVIL!!!!… USE gloves and a face shield at minimum. For example… Hot ABS is at minimum 110 Degrees Celsius or 230 Degree Fahrenheit and will stick to you plus will continue to burn you after it burns your skin off… Use extreme caution!!!!

Materials required will be shown as used. This as a free-form Instructable. Be sure to read through entirely before deciding if you should build. I built and documented this on the fly as I built it for myself…

I recommend using this in an extremely well ventilated area like outside. The initial set up will produce smoke if the plastic is overheated...

Step 2: Select Your Injector Body

The local big box retailer will yield most of the materials for this project. The material chosen were driven by the type of heaters that I had available to me. The heaters will be discussed later.

The main injector body is made up from a section of Black pipe.

Check that the interior of your pipe is seam free… If not you will need to smooth the edges with a drill bit of appropriate size, for a ¾ inch black pipe you will need a drill bit of 0.5906 inches.

This will provide clearance for the later installed plunger which is discussed later.

I used a 3/4 inch pipe that started out at just over 20 inches long. it needs to be threaded on one end.

Step 3: Create a Plunger

The plunger needs to be as snug to the inside of the pipe as possible without binding.

Check the interior dimensions of the ¾ inch pipe using a standard and metric mechanic socket set.

I found a 15mm – 3/8 inch drive socket from Sears was ideal fit. Check the interior of your pipe with similar tools for a tight yet non-binding fit.  A loose fit will allow for plastic to slide past the head and back towards the shaft which will result in waste which is not desirable.

My plunger shaft is made from a 3/8 inch socket extension attached to the 15mm Craftsman socket.

The socket is placed the wrong way onto the extension and permanently fastened. This can either be drilled and pinned or welded. I chose to weld since it was quickest and I had the materials available to me. The socket must be permanently fixed to provide satisfactory results.

If you want to use ½ inch black pipe the tightest socket that I found is a Craftsman 5/8 by ¼ inch drive socket. Always check fit before using.

Step 4: Make the Injector Body

Cut and shape the pipe as shown according to the length of heater and the main plunger assembly. The cuts were made with an angle grinder using a 1/8 inch cut-off blade. Loud but quick...

The idea here is to create a loading port for the plastic that is to be melted and a guide for the plunger assembly.

The port needs to be free of any sharp edges and loose metal, after cutting it is finished with a file or burr remover.

Cutting the pipe will leave one threaded end of the pipe will be the outlet port and should not be modified.

Step 5: Attach the Heater

The heating comes from 2 heater rods made by Ogden ratings of 400W at 240V. These were purchased from eBay at $1.00 each. You will need 2 at this rating. Others are available at various pricing… the length of these will determine the entire length of the injector body as shown in the pictures. The heater will run the entire length of the injector body below the plastic inlet port that was cut earlier.

You will also need a piece of standard 1/2 inch copper water pipe about 4 inches long and 2 slotted metal brackets that are 8 inches long.

Using stainless hose clamps, fasten the heaters to the black pipe using the slotted metal brackets and copper pipe as a spacer as shown.

The goal here is to create a solid metal support for the proper functioning of the heaters and temperature probe.

The copper pipe is a hollow space for the temperature probe to sit and provides an accurate heating temperature adjustment.

I used a commercially available temperature control for this project but I have posted a precision temperature controller in another Instructable.

The wiring for this is per the instructions which are usually printed on the power relay of the controller. The heaters require the voltage that is printed on them, in this case 240V.

Step 6: Insulate the Assembly...

The entire assembly is wrapped with fiber glass heat insulation material which is available from most ceramic supply houses. This reduces heat loss and allows for more rapid heating. It is necessary and will reduce the chance of injury and will be more economical in the future. The insulation is wrapped and held it in place using aluminum tape which is available from most big box retailers…

Do not compact the insulation. Keep it loose and held in place by the tape...

place insulation over the entire heater section of the injector body paying attention not to pack it between the injector body and temperature probe.

The finished section will look a little bulky.

Step 7: Attach to Frame.

The frame I used was constructed from the same slotted angle steel as used earlier.

The frame design is largely dependent upon the use of the injector assembly. Since I initially needed to use this as a simple extrusion device I made a frame that was just 2 upright bars with 2 horizontal cross sections for the injector body support. Other frame design will be covered in a later instructable.

The attachment points are critical though.

Attach the heater body to the frame at the top above the plastic inlet port cutout and at the bottom on the lower part of the reducer. This will provide the support for the pressing action that will follow. I used stainless steel hose clamps for attaching the injector body..

Step 8: Fit the Nozzle

The extrusion quality and diameter of plastic is entirely dependent upon the nozzle. The 3/4 to1/2 inch reducer at the bottom of the injector body needs to be fitted with a brass reducer from 1/2 inch to 1/4 inch. The the further reduction to nozzles is also in the form of brass barb fittings.

Many brass barb fitting sizes are available for the making of plastic extrusions or ingots for the later re-use in injection moldings.

Step 9: Lenghten the Extension

The plunger will need to be a little longer than the initial welded part. Again you can drill and pin this or weld, I happened to weld this again using my oxy/acetyl torch.

I added the 6 inch extension to the plunger assembly.

Step 10: Manual Press Lever

The frame that I used was slotted angle from a local Big Box retailer. It came in 4 foot sections so I bought 5.

The support legs and lever supports are heavy duty shelving brackets from the same retailer.

I cut and shaped a piece of 3/4 inch black pipe (rough shown for demonstration) The cuts did weaken the lever and this is to be rectified during a later build.

I also used a 1/2 inch steel rod for the lever pivot point.

This lever is crude but effective. It is about 3 feet long The lever to plunger support is about 8 inches long.

You may need to press in on the lever to plunger pivot point to make sure that the plunger enters the heating chamber properly.

Step 11: Heat and Use

I have found that a 1/8 inch brass barb fitting will steady pressure will give a uniform extrusion of just a little less than 3mm. This extruded rod is of use to the Makerbot products. And allows for re-use of failed projects and the further re-use of plastics that would be normally thrown away...

The fore for the plunger was supplied using my weight on a t-handle attached to the top of the plunger assembly. This is a crude method and a pull down handle will be added to the frame for the future Instructable on injection mold making using this same set-up.

The plastic to be used will have to be cut into strips of pieces to fit into the inlet port opening above the insulation pack.

You may notice some smoke at the initial start up of the machine, this is normal.

Be sure to pre-heat the machine to a couple of degrees above the melting point of the plastic before adding the plastic. Wait a couple of minuted and apply pressure to begin the extrusion.

The length of the extrusion is determined by the amount of plastic used and can be lengthened by adding more plastic to the inlet port after withdrawing the plunger.

Note that too much heat will cause smoke and burn the plastic, both of which are highly undesirable.

Again do not touch the extrusion until it cools.

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