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Plastic Injection Molding Service

If you need online injection molding we are one of the most capable and affordable sources and we can get the job done right. Download our Free CAD software today and design your custom part or convert an existing file. Order online for ultimate speed and convenience.

Injection molded parts

We stock a wide variety of materials, use state-of-the-art machines and diligently follow all design specifications. We continually strive to improve and optimize our processes and maximize customer convenience. Our customers range from inventors to businesses to government agencies. We are focused on quality and customer service.

How plastic injection molding works

Injection molding produces parts by forcing molten plastic into a mold where it cools and hardens. Granular plastic is fed by gravity from a hopper into a heated barrel. As the granules are moved forward by a screw-type plunger, the plastic is forced into a heating chamber, where it is melted. As the plunger advances further, the melted plastic is forced through a nozzle into the mold cavity. The mold remains relatively cold so the plastic solidifies almost as soon as the mold is filled. Custom steel tooling is required and adds to the initial cost but is quickly amortized.


Injection molding provides low cost at moderate to large quantities. This method of making plastic parts is an extremely versatile process for producing a wide range of parts with an excellent finish. Almost any 2D or 3D shape can be achieved. However draft is required in most cases as the shape must allow ejection from the mold. Side holes and even threaded holes are possible though they complicate the tooling.

Types of Parts 

Examples of parts made by molding include: GearsEnclosuresBracketsRobot PartsWashersFront PanelsMotorcycle PartsAuto PartsToy PartsKnobsPulleys, packaging, appliance parts, power tool components, electronic enclosures and valves. 


The following materials are some of the ones commonly molded: NylonAcetalPolycarbonatePolystyreneAcrylicPTFEABSPVC.

Cost reduction 

Cost reduction options include:

  • Minimizing size of part
  • Minimizing material volume
  • Minimizing side holes and recesses 
  • Arranging multiple pieces in one mold by connecting them with small bars ~0.1″, however the sub-components must not have widely varying volumes 
  • Minimizing side features and threaded holes
  • Using living hinges

Design Tips

You don’t have to be an expert to design parts for plastic molding (injection molding). And although you don’t want to consider plastic molding for very short runs, plastic molding can pay off in some cases in as little as a hundred pieces.

In designing parts for plastic molding here are the few key things to remember:

  • Keep wall thickness uniform.
  • Avoid large solid areas that will not cool properly.
  • Allow for 2 degree draft to allow your part to be extracted from the mold without difficulty.
  • Avoid sharp inside and outside corners.
  • Avoid very thin walls.


The following terms are commonly used for this manufacturing process:

  • Ejection pins are rods that push the part out of the mold. 
  • The gate is the location where plastic is injected. 
  • The parting line is the location where the two mold halves meet – a thin line will appear at this location. 
  • A living hinge is a thin connection provided between two sections of a molded part so that it can be used as a hinge, e.g. a box, with a lid, molded as one piece. 
  • Insert molding is where a rigid part is inserted into the cavity prior to injection – a screw driver with a plastic handle is an example of insert molding.  

Injection Mold Cooling 

After the heated plastic is injected into the mold it must cool before ejecting the final part from the mold. The shape of your part will effect how the part cools and must be considered during design.

The two key aspects to consider in cooling are:

  • How long it will take to cool.
  • How material will shrink, thereby effecting the accuracy and uniformity of your part after it cools.

Where the shape is thickest it will shrink the most. For example, in a 5 sided box with internal cylindrical posts for mounting a circuit board, you may see slight recess dimples on the outside of the box underneath where the posts occur as the posts will tent to pull the material in slightly.

Generally we recommend:

  • Use an approximately uniform wall thickness throughout your design. 
  • Keep walls between .030″ and 0.15″. Walls up to 0.2″ or slightly more are possible but not advisable.
  • It should not be possible to fully hide a 0.3″ diameter ball anywhere inside the material.

Often it is possible to take a solid shape that may have cooling issues and redesign it to be hollow to improve cooling. Sometimes this may requires making two hollow parts that snap or screw together to give the appearance of a solid part.

How to Proceed

We can quote your job using conventional CAD files or you can use our unique free CAD software where you can: design your part quickly and easily, get instant pricing, and order online.

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