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CNC Machining in HDPE

High-Density Polyethylene or HDPE is an engineering plastic that is employed extensively in the packaging industry. CNC machining in HDPE can also be used to create components for the construction, electrical, and automotive industries, among others. HDPE has an excellent strength-to-weight ratio, as well as good chemical and moisture resistance.

hdpe plastichdpe plastic

About HDPE for CNC Machining

HDPE is sometimes called PEHD (polyethylene high-density) and is part of the polyethylene (PE) family of plastics. Despite its name, HDPE has only marginally higher density than LDPE (low-density polyethylene). However, the difference in strength between the two plastics is more significant than the difference in density. This makes HDPE a great choice for applications that require high strength and low weight. CNC machining in HDPE is similar to that of other engineering plastics.

HDPE at a Glance
ApplicationPackaging and containers, Piping, Conveyor screws
AdvantagesChemical & moisture resistance, High strength-to-density ratio, FDA-compliant for food storage
DisdvantagesHigh thermal expansion, Adhesives generally do not work on HDPE
Lead TimeLead time is generally a minimum of 3 days. However, this can increase depending on availability or if the parts are to be internationally manufactured.
Price$$
TolerancesMachining tolerances of 0.005” (0.13mm) are achievable.
Wall ThicknessA minimum wall thickness of 0.03” (0.8mm) is achievable. This can vary depending on the wall thickness to planar dimension ratios.
Max Part SizeThe maximum size of the part is determined by the machines available and the complexity of the part.

Generic HDPE

CNC machining in HDPE produces strong but lightweight parts. HDPE parts also have excellent corrosion resistance against a wide range of chemicals. Typical applications include boat components, piping, and containers.

HDPE Properties
Tensile Strength, Yield (MPa)Elongation at Break (%)Hardness (Shore D)Flammability RatingGlass Transition Temperature (°C)
25.962262.380.6130

Finishes

Like other plastics in the PE family, HDPE is highly resistant to coatings. It resists adhesives for much the same reason and, as such, needs to be bonded via plastic welding. HDPE is most often available in black or white but can occasionally be found in a wider range of colors. Due to the above factors, HDPE parts are usually left in their as-machined state.

  • As Machined: The challenges of CNC machining in HDPE are similar to those experienced with other engineering plastics. The machined surface of HDPE comes out with a matte finish.
accura clearvue

Cost-saving Design Tips

CNC machining in HDPE can produce lightweight and low-cost components. Below are some additional cost-saving tips to make production more economical.

  • Sub Assemblies: HDPE is purchased as sheet or bar stock in varying sizes. Designing parts as separate components that can then be assembled into the final whole is often a good idea. As mentioned above, HDPE does not work well with adhesives but can be welded. Alternatively, mechanical fasteners can be used to bolt components together. 
  • Annealing: HDPE is prone to developing surface cracks when exposed to the heat and stress of machining. Annealing HDPE will help prevent cracks that may render the part useless.
    CNC machining design tip
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