Tuesday, January 12, 2016

Machining Delrin: Tips For Better Design

Delrin is a type of hard plastic used to make components to the automotive, transport, medical and building/construction industries. Machining delrin is where the delrin material is used in to create the required components.
When it comes to machining delrin components design, there are not hard rules. However, there are some suggestions that you should consider in order to maintain reasonable pricing. Avoiding then, may result you higher effort and cost for the component.


Flatness


Through their cross section, plastics suffer stress gradients which are not relieved at the manufacturer by post processing. That means plastic's flatness stability is particularly lower than metals. Consider the following tips to improve.
  • Balanced design. Machining delrin components that feature a dish shape are particularly difficult to avoid warpage.
  • 0.76mm per a 101 mm square, unrestrained, is typical. Tighter tolerances need better fixture as well as more machining.
  • Instead of flatness, consider specifying parallelism. If the plastic part is attached to another, unrestrained flatness is not necessary. The plastic part will follow the contour.
  • Consider restrained flatness. As mentioned previously, if attached to another component, the plastic part will follow the contour.
  • Pick a high-quality material. Low-quality materials will easily warp. Also, for tight flatness requirements, harder plastics are better indicated.

Threaded Inserts


For one time assembly, threaded inserts are not necessary given right torque levels. That is because, inserts do not add considerable additional holding power. Applications that need repeated disassemble (often for cleaning) do benefit to avoid thread stretch. Instead of helicoils, heat staked inserts represents a better solution since it allows a higher pullout power. Helicoils are applied in materials that not heat stake well and have good toughness.

Polishing


Polishing is typically applied to clear plastics such as Polycarbonate, Acrylic, Polysulfone and Ultem, but it is important to finish improvement in opaque materials as well. Polishing methods include direct machine polish, flame polishing, vapor polishing, and buffing. Heavy polishing cannot be obtained by poor machining and melted surfaces in the machining process may result in stress cracking after polishing.

Finishes


To boost product performance, there is a higher demand for finishes.
  • A 0.0008mm to 0.001mm is considered a standard machine delrin finish and should not represent any additional cost to the procedure.
  • Finishes below 0.0008mm are reasonable and to be expected on close tolerance parts.
  • Finishes between 0.0002mm and 0.0005mm are typical for polished plastic components, especially for a turned component.
  • Finishes below 0.0002mm are tough to achieve and may require lapping.
  • Some plastic materials such as Teflon, cannot have a finish below 0.0005mm due to its porosity.    

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