Service Overview

Plastic Injection Molding Service

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.

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Injection Molding

works 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.

Advantages

  • Low cost at moderate to large quantities
  • Extremely versatile process for producing a wide range of parts
  • Excellent finish
  • Almost any 2D or 3D shape can be achieved
  • Side holes and even threaded holes are possible

Design Tips

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

Molded Plastic Parts are a popular choice for many products and components:

Auto Parts
Toy Parts
Dining Utensils
Robot Parts
Office supplies
Medical Devices
Electronic Enclosures
Appliance Parts
Handles and Knobs

Moldable Plastic Properties

Nylon


Nylon has good mechanical properties and good weldability, and is one of the most common alloys for general purpose use – especially for machining.

Widely used for construction of aircraft structures, such as wings and fuselages, yacht construction, utility boats and bicycle frames and components.

Acrylonitrile Butadiene Styrene


ABS has good mechanical properties and good weldability, and is one of the most common alloys for general purpose use – especially for machining.

Widely used for construction of aircraft structures, such as wings and fuselages, yacht construction, utility boats and bicycle frames and components.

High Density Polyethylene


HDPE is one of the most popular aluminum alloys used in sheet metal fabrication. It is readily bent, punched and sheared.

Known for its high corrosion resistance, especially in ocean water. Common applications include marine and aircraft equipment, fuel lines, street lights, household appliances, flooring panels, and railings.

Polypropylene


PP has generally good mechanical properties, and is heat treatable. Highly weldable although strength near welds can be diminished by up to 30% if not subsequently heat treated.

Mostly used in extruded shapes for architecture, including window frames, door frames, roofs, piping, tubing and furniture.

Polystyrene


PS is strong, with good fatigue strength and average machinability, but is not weldable and has limited resistance to corrosion.

Cost is relatively high compared to other Aluminum alloys. Often used in aircraft including wings and fuselages, rock climbing equipment and bicycle components.

Polyethylene


PE is strong, with good fatigue strength and average machinability, but is not weldable and has limited resistance to corrosion.

Cost is relatively high compared to other Aluminum alloys. Often used in aircraft including wings and fuselages, rock climbing equipment and bicycle components.

Acetal


Acetal is strong, with good fatigue strength and average machinability, but is not weldable and has limited resistance to corrosion.

Cost is relatively high compared to other Aluminum alloys. Often used in aircraft including wings and fuselages, rock climbing equipment and bicycle components.

Terms and Tips

  • Terms
    • 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.
  • Cost Reduction
    • 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″ (2.54mm), however the sub-components must not have widely varying volumes
    • Minimizing side features and threaded holes
    • Using living hinges
  • Cooling
    • Consider how long it will take to cool
    • Compensate for how the material will strink
    • Use an approximately uniform wall thickness throughout your design
    • Keep walls between 0.030″ (0.762mm) and 0.15″ (3.81mm). Walls up to 0.2″ (5.08mm) or slightly more are possible but not advisable
    • 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.
    • It should not be possible to fully hide a 0.3″ (7.62mm) diameter ball anywhere inside the material
    • Make the part hollow to improve cooling
    • Divide the part into multiple pieces that connect together

Resources

Cost-Savings Guide
Sheet Metal Fabrication
CNC Milling Services
Vehicle Parts