Plastics are extremely versatile. There are more than 25,000 engineered materials available to manufacture complex applications, and high-performance blends and hybrids can be formulated to meet the very specific requirements of complex plastic parts and products.

The wide variety of plastics available opens up a number of possibilities, but selecting the proper resin takes a thorough understanding of your application. More specifically, it takes guidance from a proven injection molding partner.

For engineers working with the Kaysun team, the process usually entails four steps:

1. Discuss

Answering key questions during product design discussions with an expert plastics engineer helps us gain key insights into what the material needs to do:

  • What is the expected physical load for the product?
  • What is the mechanical function?
  • Will the product be used under conditions of fluctuating and/or extreme temperatures?
  • Will there be any exposure to chemicals?
  • Will dissimilar materials be used in assembly?

2. Research

Project-specific answers are used as the basis for a search in our extensive in-house database — founded on 60 years’ worth of injection molding work and materials knowledge — to find plastics with the appropriate characteristics, such as:

  • Strength
  • Rigidity
  • Chemical resistance
  • Temperature resistance
  • Flexibility
  • Impact resistance
  • Appearance
  • Conductivity/shielding
  • Frictional properties
  • Flame resistance

In conjunction with the database search, we consult with our resins suppliers to narrow the list of recommendations to the top 3 or 4 plastics that best align with project performance and pricing needs.

3. Recommend

We confidently deliver a focused list of materials for engineers to consider. This robust process ensures our customers’ engineering teams save time and money in the long run since certain aspects of the part design can be modified prior to production, avoiding potentially costly rework. Our refined 360° view of the entire part strategy — design, specifications, requirements, improvements — provides far more value than if an engineer is left to decide on materials based on material specs alone.

Thermoset or Thermoplastic?

Despite the many thousands of engineered materials available, plastics fall into two main types: thermoset or thermoplastic. The terms sound similar and both are appropriate for many applications but there is a notable difference in how they behave during processing:

Thermosets (e.g, liquid silicone rubber (LSR), epoxy, phenolic) join polymers on one application of heat and structure chemical bonds that harden permanently on cooling. The chemical reaction cannot be reversed, so thermoset parts cannot be re-shaped or re-melted. Thermosets have strength, chemical resistance, and temperature resistance that make them appropriate for medical implantables, electronic interfaces/touchpads, and wiring harnesses/housings.

Thermoplastics (e.g., thermoplastic elastomer (TPE), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS)) become plastic on heating and harden on cooling, without changing plastic chemistry. These resins can be re-melted, reused, and recycled.

Learn more about TPE and LSR by downloading our helpful infographic!

Whether designated a thermoplastic or thermoset, plastics are made up of polymers — long chains of repeated molecular units. The ways in which these chains align determine the plastic’s macroscopic properties. In turn, the macroscopic properties dictate the category in which the resin falls. Specific to thermoplastics, these resin categories are amorphous or semi-crystalline.

Amorphous

When polymer chain orientations are random, the plastic lacks a clear structure and is deemed amorphous. 

General Advantages

  • Softens over a broad range of temperatures
  • Easy to thermoform
  • Excellent bonding with adhesives and solvents

General Disadvantages

  • Vulnerable to stress cracking
  • Poor chemical resistance
  • Appropriate for structural applications only

 

Grade
(Low to High)
Characteristics Representative Resins
Amorphous Commodity
  • Low cost, temperature resistance, and strength
  • Good dimensional stability
  • Usually transparent
  • Acrylic (PMMA)
  • Polystyrene (PS)
  • Acrylonitrile Butadiene Styrene (ABS)
  • Polyvinyl Chloride (PVC)
  • Polyethylene Terepthalate Glycol (PETG)
  • Cellulose Acetate Butyrate (CAB)
Amorphous Engineering
  • Moderate cost, temperature resistance, and strength
  • Good to excellent impact resistance
  • Good dimensional stability and optics
  • Polycarbonate (PC)
  • Polyphenylene Oxide (Mod PPO)
  • Polyphenylene Ether (Mod PPE)
  • Thermoplastic Polyurethane (TPU)
Amorphous High Performance
  • High cost, temperature resistance, and strength
  • Good stiffness
  • Resistant to hot water and steam
  • Polysulfone (PSU)
  • Polyetherimide (PEI)
  • Polyethersulfone (PES)
  • Polyarylsulfone (PAS)
  • Polyarylethersulfone (PAES)

 

Semi-crystalline

When polymer chains arrange themselves in an orderly, densely packed fashion, the plastic is deemed semi-crystalline.

General Advantages

  • Resistant to stress cracking
  • Good fatigue resistance
  • Appropriate for bearing, wear, and structural applications

General Disadvantages

  • Sharp melting point
  • Difficult to thermoform
  • Poor bonding with adhesives and solvents

 

Grade
(Low to High)
Characteristics Representative Resins
Semi-crystalline Commodity
  • Low cost, temperature resistance, and strength
  • Good electrical properties and toughness
  • Negligible moisture absorption
  • Low COF
  • High-Density Polyethylene (HDPE)
  • Low-Density Polyethylene (LDPE)
  • Polypropylene (PP)
  • Polymethylpentene (PMP)
Semi-crystalline Engineering
  • Moderate cost, temperature resistance, and strength
  • Good chemical resistance, and bearing and wear properties
  • Difficult to bond
  • Low COF
  • Nylon (PA)
  • Acetal (POM)
  • Polyethylene Terephthalate (PET)
  • Polybutylene Terephthalate (PBT)
  • Ultra High Molecular Weight Polyethylene (UHMW-PE)
Semi-crystalline High Performance
  • High cost, temperature resistance, and strength
  • Good electrical properties and toughness
  • Excellent chemical resistance
  • Low COF
  • Polyvinylidene Flouride (PVDF)
  • Polytetrafluroethylene (PTFE)
  • Ethylene-Chlorotrifluroethylene (ECTFE)
  • Fluorinated Ethylene Propylene (FEP)
  • Polychlorotrifluroethylene (PTCFE)
  • Perfluoroalkoxy (PFA)
  • Polyphenylene Sulfide (PPS)
  • Polyetheretherketone (PEEK)

 

Additives and Alloys

Plastics’ characteristics can be changed by mixing or combining different types of polymers and by adding non-plastic materials. 

Additives are used to improve specific properties such as strength, rigidity, UV-resistance, and flame resistance — a versatility that’s proving particularly beneficial as more industries incorporate metal-to-plastic conversion into their production processes.

Metal-to-Plastic Conversion: Revolutionizing the Manufacturing Process

The most common categories of additives are particulate fillers and reinforcing fillers.

Particulate fillers can reduce costs and improve properties such as modulus, conductivity, heat and ultraviolet light resistance. Popular particulate fillers include:

  • Mineral
  • Silica
  • Ceramic
  • Carbon powder/fiber
  • Glass microspheres/fibers
  • Powdered metal

Reinforcing fillers improve mechanical properties. Popular reinforcing fillers include:

  • Long glass fiber additives to improve stiffness and strength, increase temperature performance (up to 150℉), and create a moderate surface appearance

  • Short glass fiber additives improve stiffness, increase temperature performance, and offer better aesthetics than long glass fibers. Since the glass content is 30% or lower, short glass fibers allow parts to look comparable to unreinforced plastic parts

  • Carbon, stainless steel, and Kevlar fillers improve conductive and/or shielding properties

As mentioned above, Kaysun’s extensive in-house database allows our plastics engineers to have greater insight into how different plastics will respond to various combinations of process variables because our engineering, materials science, scientific molding, and Design for Manufacturability (DfM) analysis expertise transcends the fundamentals provided by the plastics manufacturer alone. For example, we know how individual plastics will flow and fill in the tool based on parameters like melt temperature, flow rate, and cooling rate.

This kind of care, knowledge, and detailed data guides us in selecting the best plastic for your project, designing the ideal tool, and developing the most efficient and cost-effective injection molding process possible — all of which makes working with Kaysun a true value-added partnership. Click the button below to discuss how we can help improve your next project.

 

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