Select the right plastic material for machining!

Plastic vs Ease of Machining

Machining is an efficient manufacturing process and undergoing machining of plastics is quite pertinent for low volume production, objects with proximal tolerance dimensions, and for those with complicated mold structures. You will find a variety of plastics available for CNC machining. Some are extremely engineered and have exceptional performance while some are meant for lesser cost and minimal performance.

To decide upon which plastic material is appropriate for the CNC machining application, it is required that the customer comes up with a minimum of three properties for selecting certain material. A simple search is done so as to determine primary materials that have all the required three properties which are then prioritized accordingly.

Let us first look at different types of plastics available for machining and get a brief about each one of them.

Types of plastics available for CNC machining

  1. ABS Plastic

  • Sizes:

ABS Plastic Sheet – Dimension ranging from 12 inch X 12 inch to 48 inch X 96 inch, Thickness ranging from 0.060 inches to 4 inch

ABS Plastic Rod – Peripheral diameter ranging from 0.250 inches to 6 inch

  • Grades: General Purpose, Machine Grade, Scratch Resistant, Fire-Rated, UV Resistant, Orthotic Grade, FDA Compliant Grade

  • Characteristics of ABS Plastic:

  1. Excellent impact resistance

  2. Highly strong

  3. Easy CNC machining

  4. Conveniently thermoformed

  5. Cost-effective

  6. Gets easily bonded via adhesives

  • Usability of ABS Plastic:

  1. Machine housings

  2. Models and prototypes

  3. Retail shop fixtures

  4. Storage cases and display cases

  5. Instrument panels

  1. Acetal

  • Sizes:

Acetal Sheet – Dimension ranging from 6 inch X 12 inch to 48 inch X 120 inch, Thickness ranging from 0.031 inches to 6 inch

Acetal Rod – Diameter ranging from 0.187 inches to 12 inch

Acetal Tube – Peripheral diameter ranging from 25 mm to 230 mm

  • Grades: Glass-filled, FDA compliant, Static Dissipative, Medical, Elevated Bearing and Wear

  • Characteristics of Acetal:

  1. Outstanding machinability

  2. Lesser friction

  3. Highly strong

  4. Good wear characteristics regardless of wet and dry atmosphere

  5. Lesser moisture retention

  6. Excellent chemical resistance

  • Usability of Acetal:

  1. Bearings

  2. Gears

  3. Pumps and valves

  4. Electrical equipment

  5. Food processors

  6. Manifolds

  7. Wear pads

  1. Acrylic

  • Sizes:

Acrylic Rod – Cast peripheral diameter ranging from 0.250 inches to 6 inches, an Extruded peripheral diameter ranging from 0.062 inches to 3 inches, an extruded square peripheral diameter ranging from 0.125 inches to 1.500 inch

Acrylic Tubes – Cast peripheral diameter ranging from 1.250 inches to 12 inches, an Extruded peripheral diameter ranging from 0.250 inches to 6 inch

  • Grades: General purpose, Bullet resistant, Digital, 40% Impact modified, Sign-grade, Electrostatic Dissipative (ESD), 70% Impact modified, abrasion resistant, anti-reflective.

  • Characteristics of Acrylic:

  1. Easy machining and thermoforming

  2. Excellent weathering

  3. Excellent solvent bonding

  4. Strong and clear structure

  5. Dimensional stability

  • Usability of Acrylic:

  1. POP displays

  2. LED panels

  3. Transparent manifolds

  4. Indoor and outdoor signals

  5. Architectural structures and skylights

  6. Transportation uses

  7. Retail fixtures

  1. HDPE

  2. Expanded PVC

  3. PBT

  4. Nylon

  5. High Impact Polystyrene

  6. PEEK

  7. PETG

  8. Polycarbonate

  9. Polypropylene

  10. PVC

  11. PPSU

  12. PVDF

  13. PTFE

  14. Ultem

  15. PSU

  16. UHMW

Now that we know about the various plastic varieties available for CNC machining, let us have a look at the relevant properties that are crucial factors in deciding the plastic to be selected.

 

Basic properties for plastic selection

  1. Clear Plastics

  • These plastics are usually clearer and thus when subjected to CNC machining they convert to translucent or opaque form. Therefore, polishing needs to make the component clear. Some of the polishing methods adopted are machine polish, flame polish, vapor polish, and standard buffing.

  • Excellent options of clear plastics include Acrylic (PMMA), Clear PVC, Ultem, Polycarbonate (PC), Polysulfone, and Polyester (PET).

  1. Loading Strength

  • For structural strength, tensile (psi) and the compression strengths are crucial in selecting the type of plastics.
  • Some of the good options with excellent loading strength include PEI-Ultem, PPS, Delrin, PolyEther Ether Ketone (PEEK), and Nylon. Bad selections of material are LDPE, Teflon, Polypropylene, UHMW, and HDPE.
  1. Dimensional Stability

  • Once the metals are subjected to CNC machining, they lose their structural stability. This is due to the reason that they have an increased inclination towards soaking up moisture and increased thermal coefficient.
  • Some of the outstanding choices are PEEK, PET, Ultem, and PPS whereas the poor ones include UHMW, LDPE, Nylon, and HDPE.
  1. Thermal Stability

  • Plastics with increased resistance to temperature conditions are constantly in more demand in conventional and high-end industrial uses to magnify the overall performance and endurance.
  • Some of the suitable plastics that have increased thermal stability include PEEK, PPS, PTFE, Ultem, and Torlon. Bad types of plastics include ABS, Acrylic, PVC, and UHMW.
  1. Bio-compatible

  • Biocompatible plastics are required in medical devices to be able to function without any injury, allergies, or bad psychological results. Plastics are associated with USP Class VI classification. Some of the suitable choices include PEEK, Ultem, PC, UHMW, and PP.
  1. Limiting PV

  • A joint study of pressure and velocity helps us to decide the thermal and structural stability in situations of rotational wear. Some of the suitable options are PEEK, Torlon 4301, Nylatron, and Delrin AF.
  1. Impact Resistance

  • By impact resistance of plastics, we refer to their capabilities to endure abrupt shock or an impact. Some of the good options include Polycarbonate, PEEK, Nylon, and UHMW. The bad choices include Acrylic, Polysulfone, PET, and Noryl.
  1. Chemical Resistance

  • Chemical resistance of plastics is defined by their capabilities to endure chemicals that can affect their strength, colour, dimensions, durability, and other properties. The chemical resistance properties of plastics are quite irregular. While some of these materials exhibit close universal chemical resistance others are highly sensitive. So, you should check for certain chemical and plastic interplay in a reference guide. Some of the suitable options include Teflon, PEEK, PET, UHMW, PMMA, and CTFE. Bad choices are ABS, Polysulfone, Acrylic, and Noryl.
  1. UV Resistance

  • UV resistance of plastics is tested specifically in outdoor applications. The materials without UV resistance will age and become fragile. For this, it is suggested that the plastics are coloured black so that they have some innate UV resistance. Some of the appropriate choices include PC (UV stabilized grade), PBT, Ultem. Unsuitable choices are Nylon, PC (FDA grade), and Acetal.
  1. FDA

  • The Food and Drugs Administration, FDA approved plastics are the ones that contact eatables. Some of the suitable choices include PC, PMMA, PET, Delrin, and PEEK.
  1. Cost

  • The cost of the plastic material to be used also matters. The plastics subjected to high-engineering are quite costly. Some of the cost-effective materials include Polypropylene, Delrin, HDPE, and UHMW. Costly materials are PPS, PEEK, Radel HDPE, and Vespel.
  1. Steam Cleansing

  • For medical purposes, plastics are cleansed by steam which is similar to autoclaving. Some of the suitable choices include PEEK, Radel, Teflon, and Ultem.
  • Having known the properties that should be considered while subjecting plastics to CNC machining, let us have a look at the classification of plastics in terms of ease of machining.

Selection of plastics on the basis of ease of machining:

This section will provide you with information about the ease of machinability of extruded plastics. There is always an amount of 10 to 40% glass grade inside plastics. The presence of glass grade results in complications in machining. It results in reduced tool life and higher flatness problems.

We have categorized the plastics from 1-10 in accordance to their ease of machining.

Plastic vs Ease of Machining

 

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