An Informational Brief on Polymer Machining
Did you know that PPS (or Polyphenylene sulfide) products offer the broadest resistance to chemicals of any high-performance thermoplastic? It’s no surprise that this makes them a popular choice for industrial applications such as wheel bushings, chemical pumps, and compound clamp rings for semiconductor wafers.
With Machining PPS: A Plastics Guides, AIP provides you with a guide to this material and its machining process. First, let’s start with the basics: thermoplastics vs thermosets.
Machining Thermoplastics vs Thermosets
We’ve already said that PPS is a thermoplastic, but what does that mean exactly?
All polymers can more or less be divided into two categories: thermoplastics and thermosets. The main difference between them is how they react to heat. Thermoplastics like PPS, for example, melt in heat, while thermosets remain “set” once they’re formed. Understanding the technical distinction between these types of materials is essential to CNC machining them properly.
What type of thermoplastic is PPS in particular? It’s a semi-crystalline, high-performance thermoplastic that has an extremely stable molecular structure. The chemical resistance of PPS is often compared to PEEK and fluoropolymers.
Properties & Grades of Machined PPS
There’s a lot to like about PPS’s material properties. As we mentioned before, PPS has exceptional chemical resistance that makes its bearing grades especially favorable for the chemical industry or caustic environments. In particular, its resistance to acids, alkalis, ketones, and hydrocarbons lend PPS stellar structural performance in harsh chemicals.
Additionally, PPS materials are inert to steam as well as strong bases, fuels and acids. Combine that with a low coefficient of thermal expansion and zero moisture absorption, and you get a material that is ideal for continuous use in corrosive or hostile environments. PPS has replaced stainless steel for a lot of industrial applications for this reason.
Most impressively, PPS will not dissolve at temperatures below approximately 200 °C, no matter what solvent is used. In fact, all grades of PPS share UL94 V-0 flammability ratings, without requiring flame retardant additives, resulting in an excellent material for aircraft where flame resistance is paramount.
Some grades of PPS that we regularly machine at AIP Precision Machining include Ryton®, Fortron®, TECHTRON®, TECTRON® HPV, TECATRON PVX and TECATRON CMP.
The process of annealing and stress-relieving PPS reduces the likelihood of surface cracks and internal stresses occurring in the material. Post-machining annealing also helps to reduce stresses that could potentially contribute to premature failure. AIP’s special annealing process for PPS is designed to take the specific properties of PPS into account, and we advise anyone working with PPS to hire a manufacturer that understands its unique demands.
PPS is a fantastic material for machining. Its low shrinkage and stable dimensional properties make it easy to machine to incredibly tight, precise tolerances. A unique characteristic of PPS is that when dropped, it sounds just like a piece of metal hitting the floor.
PPS, like many other thermoplastics, is notch sensitive, so take care to avoid sharp corners in design. We recommend carbide tipped cutting tools for working with PPS as they provide an ideal speed and surface finish.
We also suggest non-aromatic, water-soluble coolants, such as pressurized air and spray mists, to achieve optimum surface finishes and close tolerances. Coolants have the additional benefit of extending tool life as well. No known coolants attack nor degrade PPS.
Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics, with any sub-manufactured metalwork processed outside our facility.
To learn more, read our article “Three Ways to Ensure Sterilization in Your Plastic Machined Medical Applications.”
PPS Machining Guide: Supportive Information
Ask the Plastics Professionals at AIP Precision Machining!
Do you know why AIP Precision Machining includes stress-relieving and annealing plastics as part of our machining process? We’ve talked about this a bit in our plastic machining guides (like our polymer machining brief on RADEL, but this post serves as a more thorough explanation of annealing does to improve your machined parts.
What’s the purpose of stress relieving and annealing plastics, then? Read on to learn the answer from the plastics professionals at AIP Precision Machining.
What is annealing, and how does AIP anneal its plastic parts?
Let’s start with the basic definition of annealing: it’s a heat treatment that changes the properties of a material to make it easier to machine. Annealing does this by increasing ductility and reducing hardness for the material.
AIP Precision Machining has programmed annealing ovens for plastics that heat the material above its recrystallization temperature. By maintaining the heat at that specific point, the structure of the material changes to become finer and more uniform. This process relieves internal stresses in the material.
The final part of annealing is allowing the material to cool back down once after it’s been heated for a suitable amount of time. Proper annealing requires precise temperatures and timing control to accomplish the right result, which is why AIP uses computer controlled annealing ovens for plastics.
Why is annealing & stress-relieving crucial for plastics?
While not every machined component has to rely on annealing, we at AIP believe it is an important part of the plastic machining process for several reasons. For one thing, it reduces stress in the material.
Plastics that experience internal stress can turn out warped or cracked, have inferior physical properties, or finish with unexpected changes in their part dimensions. Obviously, we want to avoid this as much as possible.
Reducing stress enhances the mechanical and thermal properties of a material by limiting the opportunity for cracking and other issues like the ones above. Since stress build-up can lead to part failure or reduced performance, stress-relieving improves the overall quality of your product.
By doing this, annealing extends the life of your machined plastic parts and components.
Is the process of annealing plastics the same for different materials?
Other materials that will undergo a lot of machining time, like some applications of PEEK, can require more intermediate annealing steps to make sure they maintain critically tight tolerances and flatness.
That means it’s essential for your machinist to know what plastic material you’re working with and what particular needs it has. Be sure you’re working with an experienced plastics manufacturer like AIP or else you risk having a lower quality product.
With over 35+ years of experience working with hundreds of polymers and composites, we’re more than just familiar with the machining process. We’re ready to handle any geometry and any challenge.
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How Aluminum Got Dethroned by Thermoplastics in Aerospace
Cup holders. Magazines. Suit cases. Aircraft engines. Here’s a riddle, what do these items all have in common? If you’re an aircraft operator, the answer is obvious: they all add weight, making them a drain on your fuel costs.
If weight is one of the main operating costs of an aircraft, then it’s no surprise that airlines want to lose a few pounds. Over the last 35 years, AIP has witnessed firsthand the incredible weight savings that can be gained from using lightweight polymers and composites for aerospace applications.
How Airlines “Slim Down” Operating Costs
How much can an ounce cost you? Plenty. In the case of United Airlines, removing a single ounce from its in-flight magazine has translated to saving $290,000 a year. Yes, a single ounce can hit an airline with up to six digits in costs.
If thinner paper can have such an impact on your bottom line, then you can imagine the significant cost savings that can come from manufacturing lighter aerospace components. What’s the most lightweight solution for aircraft operators today? We have one word for you: plastics.
What Makes Plastics the Secret to Aircraft Fuel-Efficiency
Aluminum was popular during the “Golden Age of Aviation” because of its strength and durability as well as its lightness when compared to other metals like steel. As a result, many aircraft components have traditionally been metal, from aircraft interiors, to landing gear, aircraft engines and structural components.
Now consider the fact that polymer and composite materials can be up to ten times lighter than metal. It’s no wonder that as more thermoplastic materials come on the market and new manufacturing opportunities arise, metal replacement has been seen as one of the best opportunities to reduce airline weight.
How big is the impact of switching from aluminum to plastic parts like PEEK and ULTEM in aerospace applications? Operators can earn weight savings of up to 60%. This translates to lower lifetime fuel costs, reduced emissions and extended flight range for operators.
“Weighing” the Option of Plastics in Aerospace
Weight alone is a massive reason to consider thermoplastics for aerospace, but weight isn’t the only factor at play in material selection.
After all, wood is lighter than metal, but there’s a reason we don’t build spruce airframes like the first plane from the Wright brothers: it wouldn’t be safe today to fly a wooden plane! Aerospace components need to be able to survive in corrosive, harsh environments as well as provide resistance to high temperatures.
In other words, it’s crucial that your mission-critical components aren’t just lightweight, but also high-performing.
At AIP, we carefully apply our decades of material expertise to select the right material for your application’s needs. Remember that your aerospace plastics manufacturer should understand the unique demands of your industry and your application, and have experience machining the material you require.
Want to learn more about how AIP reduces costs for aircraft operators?
Read how machined polymer components can take a load off aircraft interiors in our aerospace case study.
An Informational Brief on Polymer Machining
RADEL is a PPSU (or Polyphenylsulfone) widely considered to be the highest-performing of Solvay’s sulfone polymers. It’s no surprise then that we’ve regularly machined RADEL at AIP Precision Machining over the past three decades.
With superior impact strength and outstanding resistance to stress cracking, RADEL offers exceptional hydrolytic stability and toughness across a wide temperature range, making it a favorite of the medical, electronics manufacturing, and aerospace industries.
AIP has over 35 years of experience machining complex components from RADEL and various other thermoplastic materials. We are providing this Machining RADEL as yet another insightful technical brief about our polymer component manufacturing process, and how it differs from that of metal machining, injection molding, or 3D printing.
Machining Thermoplastics vs Thermosets
Plastic CNC machining is affected by what type of material you’re machining. Technical expertise is key to polymer machining, which is why you have to know the polymer structure and properties of RADEL before machining it.
There are two basic types of polymers: thermoplastics and thermosets. Thermoplastics soften in heat and become more fluid, while thermosets cross-link during curing, which eliminates the risk of a product re-melting in heat. Since these categories react differently to chemicals and temperature, it’s important to know that RADEL is a thermoplastic.
To be specific, RADEL PPSU is an amorphous, high-performance thermoplastic that is lightweight, available in bone-white or black colors, and can be either transparent or opaque. Like other amorphous thermoplastics, such as ULTEM, RADEL is thermoform capable, translucent and easily bonded with adhesives or solvents.
Properties & Grades of Machined RADEL
RADEL’s reputation as a high-performance thermoplastic is well deserved. RADEL PPSU has an impressive heat deflection temperature of 405°F (207°C) and is inherently flame retardant with low NBS smoke evolution, making it an ideal material choice for aircraft interiors. In addition, its retention of mechanical properties is superior to all other amorphous transparent polymers.
With improved impact and chemical resistance over PSU and PEI, RADEL PPSU has been tested for notched izod impact resistance as high as 13 ft.-lbs/in. It can endure over 100 joules of force without shattering, even with repeated exposure to moisture and extreme temperatures.
These inherent qualities allow RADEL PPSU to withstand unlimited steam autoclaving and provide RADEL with excellent resistance to EtO, gamma, plasma and chemical sterilizations as well. Unsurprisingly, its extreme thermal properties make RADEL ideal for reusable medical instruments and other applications where sterilization is key.
Not all grades of RADEL PPSU share the same exact properties, of course. Choosing the grade of your material that best meets your needs is an important part of AIP Precision Machining’s expert material knowledge.
One grade of RADEL PPSU we machine regularly at AIP Precision Machining is RADEL R5500.
RADEL R5500 is a unique polymer grade that meets the stringent aircraft flammability requirements of 14CFR Part 25, while also being a biocompatible, medical-grade resin that is FDA and NSF approved for food and beverage contact. From that, it’s clear that RADEL R5500 can be used for a wide range of applications, whether it’s for aircraft interiors, electronic burn-in sockets or surgical instruments. RADEL R5500 can be polished to a mirror finish and is available in both opaque and transparent colors.
Machining RADEL PPSU
Annealing RADEL PPSU
RADEL PPSU, like many polymers, can be received in the form of rods, sheets, tube or film. As we mentioned before, amorphous thermoplastics like RADEL are especially sensitive to stress-cracking, so stress-relieving through an annealing process is highly recommended before machining.
Annealing RADEL greatly reduces the likelihood that surface cracks and internal stresses will occur from the heat generated. Post-machining annealing also helps to reduce stresses that could potentially contribute to premature failure.
If the machine shop you are working with does not have a computer controlled annealing oven for plastics, then “head for dee hills” as they are obviously not RADEL machining experts.
Machining RADEL PPSU
Non-aromatic, water-soluble coolants are most suitable for ideal surface finishes and close tolerances. These include pressurized air and spray mists. Coolants have the additional benefit of extending tool life as well.
Many metal shops use petroleum-based coolants, but these types of fluids attack amorphous thermoplastics like RADEL PPSU. Many past experiences have shown parts going to customer without cracks, only to develop cracks over time due to exposure to metal machine shop fluids. Be sure to use a facility like AIP who machines polymers and only polymers.
Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics, with any sub-manufactured metalwork processed outside our facility. This minimizes the potential for metallic cross-contamination.
RADEL Machining Guide: Supportive Information
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There’s no doubt that plastics have become more and more popular in modern medicine. Short lead times are essential in this industry, and both 3D additive manufacturing and CNC machining provide fast production times. When is your medical application better suited for 3D printing, though, and when does precision plastic machining have the upper hand in plastic manufacturing?
There are a few key differences and similarities between these types of plastic manufacturing that you should keep in mind for your medical applications. It helps to have a basic understanding of each manufacturing process, first.
Subtractive vs Additive Manufacturing
CNC machining is a type of “subtractive manufacturing.” This means that the process generally begins with a solid block of plastic material which is cut or shaped into the desired product through “removing” excess material.
While CNC machining requires more initial setup than 3D printing, it offers repeatability, accuracy for both large and small parts, and a wide range of polymers and composites to choose from, as well as a variety of surface finishes. It scales easily between one-time jobs and high-volume production.
3D printing is “additive manufacturing,” which means the initial material is built layer by layer, rather than removed as in subtractive manufacturing. 3D printing creates three-dimensional objects from reading a digital file’s blueprint. When working with plastics, you’re primarily talking about FDM 3D printing. While FDM is widely considered the most quick and cost-effective way of producing custom thermoplastic parts and prototypes, it also has the lowest dimensional accuracy and resolution of any other 3D printing technology.
Another option for additive manufacturing is SLS 3D printing, which fuses together the particles of thermoplastic polymer powders. This version of 3D printing has higher accuracy than FDM; however, it comes at the cost of longer lead times, which can be expensive in the medical industry.
Choosing the Right Technology for Your Medical Application
As always, choosing the correct technology is dependent on your particular medical application. What you value in your completed product can help determine which style of plastics manufacturing works best for your needs. Some of your considerations should be:
Both CNC machining and additive manufacturing work with a wide variety of thermoplastics, but those plastics react to manufacturing in different ways. Some materials machine more easily than others, while certain thermoplastic materials are more prone to warping in 3D printing.
Your manufacturer should be familiar with your chosen material and be able to discuss the process of machining or 3D printing it with you. At AIP Precision Machining, we have 35+ years of material and machining expertise and we include consultancy as an integral part of our manufacturing process.
CNC machining ultimately provides greater dimensional accuracy and better performing properties than additive manufacturing. Machined thermoplastics possess both great mechanical and thermal properties with fully isotropic behavior. If your product requires unique, strong design with critical tolerances, then FDM 3D printing may not be not ideal; this type of printing is inherently anisotropic, meaning it isn’t the best option for mechanically critical components.
Medical applications, in particular, have unique considerations that ought to be taken into account, both for choosing your initial material and determining how it ought to be manufactured.
Precision CNC machining provides close tolerances for your applications with a fine, burr-free finish. In fact, 3D printed products for the medical field regularly go into CNC machining post-processing as a secondary step in order to accomplish better tolerances or a finishing cut, as FDM parts tend to have visible layer lines.
Extreme tolerances up to 0.002mm can be produced by AIP Precision Machining, which can be necessary in demanding industries such as the medical, aerospace and energy markets.
Both CNC machining and 3D printing have quick turnarounds, especially when compared to injection molding. Machining designs are crafted on the same computer applications used by 3D printers, so there is no cost associated with design changes for either type of plastics manufacturing. However, when time is truly critical, 3D printed parts can be delivered in 24 hours. Quality and functional usefulness, in this case, may be sacrificed for expediency.
AIP Precision Machining can guarantee your complex polymers machined in as little as 10 business days, with quality assured from concept to completion.
Volume of Production
Smaller batches, such as 1-10 plastic components, can be more cost-effective if produced with additive manufacturing. This is because using a non-standard blank size increases the cost of machining. Plastic machining, however, easily scales between small and large outputs.
If you require a high-quality product that possesses extreme mechanical and thermal strength, it is worth precision machining for that reason alone.
The Final Consideration? Experience.
The medical field often has no room for error when it comes to implants, spinal devices and orthopedic equipment. This is why—no matter what type of plastic manufacturing you choose—you want to be sure you’re working with an expert who understands the importance of sterilization, biocompatibility, and other traits that may be necessary for your application.
AIP is FDA and ISO 13485:2016 registered and has been audited by some of the most stringent OEMs in the orthopedic and medical device industries. We process our plastics with strict hygienic procedures.
Whoever you work with, be sure they understand the needs of your industry and have the experience to prove it.
Click here to learn more about the utility of each technology with regard to precision efficiency, materials and more.
Or, request a quote with AIP Precision Machining here.
An Informational Brief on Polymer Machining
One of the high-performance thermoplastics that AIP works with is ULTEM: a PEI, or polyetherimide. ULTEM was developed by General Electric Plastics Division (Now SABIC) back in the early 1980s. Polyetherimide (PEI) is an amorphous, amber-to-transparent thermoplastic.
Among other uses, ULTEM is popularly used in medical instrument components, aircraft interiors, missile and defense-related components, electrical insulation parts, and semiconductor equipment components.
AIP has over 35 years of experience machining complex components from ULTEM and various other thermoplastic materials. We are providing this Machining ULTEM as yet another insightful technical brief about our polymer component manufacturing process, and how it differs from that of metal machining or injection molding.
Plastic CNC Machining
Before discussing the process of machining ULTEM, it’s important to understand exactly what plastic machining is.
CNC (Computer Numerical Control) machining is a process in the manufacturing sector that involves the use of computers to control machine tools. In the case of plastic machining, this involves the precise removal of layers from a plastic sheet, rod, tube or near net molded blank.
The early history of CNC machining is almost as complex as a modern CNC system. The earliest version of computer numerical control (CNC) technology was developed shortly after World War II as a reliable, repeatable way to manufacture more accurate and complex parts for the aircraft industry. Numerical control—the precursor to CNC—was developed by John Parsons as a method of producing integrally stiffened aircraft skins.
Parsons, while working at his father’s Traverse City, Michigan-based Parsons Corp., had previously collaborated on the development of a system for producing helicopter rotor blade templates. Using an IBM 602A multiplier to calculate airfoil coordinates, and inputting this data to a Swiss jig borer, it was possible to produce templates from data on punched cards.
Parsons’ work lead to numerous Air Force research projects at the Massachusetts Institute of Technology (MIT) starting in 1949. Following extensive research and development, an experimental milling machine was constructed at MIT’s Servomechanisms Laboratory.
Due to the many different kinds of polymers and composites, it’s important to have strong technical expertise of polymer materials when machining plastic components; some plastics are brittle, for example, while others cut similarly to metal. The challenge of plastics is their wide range of mechanical and thermal properties which result in varying behavior when machined. Therefore, it’s important to understand the polymer structure and properties of ULTEM if you’re machining it.
Thermoplastics vs Thermosets
When it comes to polymers, you have two basic types: thermoplastics and thermosets. It’s crucial to know which one you’re working with due to distinct differences between how these two main polymer categories react to chemicals and temperature.
Thermoplastics soften when heated and become more fluid as additional heat is applied. The curing process is completely reversible as no chemical bonding takes place. This characteristic allows thermoplastics to be remolded and recycled without negatively affecting the material’s physical properties.
They possess the following properties:
- -Good Resistance to Creep
- -Soluble in Certain Solvents
- -Swell in Presence of Certain Solvents
- -Allows for Plastic Deformation when Heated
Thermosets plastics contain polymers that cross-link together during the curing process to form an irreversible chemical bond. The cross-linking process eliminates the risk of the product re-melting when heat is applied, making thermosets ideal for high-heat applications such as electronics and appliances.
They possess the following properties:
- -High Resistance to Creep
- -Cannot Melt
- -Rarely Swell in Presence of Solvents
Phenolic, Bakelite, Vinyl Ester and Epoxy materials would be considered examples of a thermoset, while ULTEM, PEEK, DELRIN and Polycarbonate materials are examples of thermoplastics.
The thermoplastic category of polymers is further categorized into Amorphous and Crystalline polymers per the figure below:
ULTEM is considered an amorphous, high-performance thermoplastic. Most amorphous polymers are thermoform capable, translucent and easily bonded with adhesives or solvents.
Various Grades of Machined ULTEM
ULTEM PEI (polyetherimide) is a high-strength amorphous polymer. PEI has more than just excellent heat and flame resistance. It can perform continuously up to 340°F thanks to its high flammability rating. That’s not all, though: this polymer is also hydrolysis resistant and highly acid-resistant. ULTEM PEI also outperforms both Nylon and DELRIN with the highest dielectric properties of thermoplastic materials.
While ULTEM is relatively chemical resistant relative to lower end amorphous polymers, you will need to carefully assess the chemical compatibility for the application. This material is also more notch sensitive than RADEL PPSU.
There’s more than one particular type of ULTEM PEI you can machine, and each has slightly different properties for perfecting this material’s use in different applications.
Here are two grades of ULTEM PEI we machine regularly at AIP Precision Machining:
ULTEM 1000 is an unfilled grade of ULTEM PEI. This is considered the “virgin” or “neat” grade of the resin… this basically means no-fillers. It’s well suited to interior aircraft components thanks to its impressive flame resistance and limited oxygen index. Its resistance to UV and gamma radiation and low NBS smoke evolution, low thermal conductivity, and ability to retain 85% of its tensile strength at 10,000 hours of immersion in boiling water make it useful for a variety of structural food processing components. ULTEM 1000 is also FDA, USDA, and NSF-compliant, as well as USP Class VI-compliant.
ULTEM 2300 is a 30% glass-reinforced grade of ULTEM PEI. This gives the high-performance polymer greater tensile strength and rigidity than ULTEM 1000, plus greater dimensional stability, meaning less movement with temperature or load changes. It possesses low thermal conductivity and excellent electrical insulation properties. Additionally, it reacts well to autoclave sterilizations, making it useful for reusable medical applications where repeated cycles are required. ULTEM 2300 is commonly used for structural components where light weight is valuable such as found in many aerospace and defense-related components. ULTEM 2300 is a common direct replacement for aluminum as it has a similar coefficient of thermal expansion to 6061-T6.
ULTEM can be received in the form of rods, sheets, tube or film. Stress-relieving before machining through an annealing process is crucial, as it reduces the likelihood that surface cracks and internal stresses will occur from the heat generated. This also helps prevent any warping or distortion of your plastic materials.
If the machine shop you are working with does not have a computer controlled annealing oven for plastics, then “head for dee hills” as they are obviously not ULTEM machining experts.
Glass-reinforced ULTEM will require coolants during drilling operations, as they are especially notch sensitive. Non-aromatic, water soluble coolants are most suitable for ideal surface finishes and close tolerances. These include pressurized air and spray mists. Coolants have the additional benefit of extending tool life as well.
Many metal shops use petroleum-based coolants, but these types of fluids attack ULTEM. Many past experiences have shown parts going to customer without cracks, only to develop cracks over time due to exposure to metal machine shop fluids. Be sure to use a facility like AIP who machines polymers and only polymers.
Another difference between glass-reinforced ULTEM and non-filled ULTEM is that non-reinforced thermoplastics can be machined with high-speed steel cutting tools. You’ll want hard metal tools for reinforced materials.
Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats and machines only plastics, with any sub-manufactured metalwork processed outside our facility.
ULTEM Machining Guide: Supportive Information
Strict Hygienic Procedures for Precision Machining
It’s no secret that cleanliness and sterilization are crucial for applications in the medical industry. Any manufacturer you hire for machining your plastic component should be aware of this, and taking actions to prevent any contamination from taking place.
Here are three ways you can ensure that your medical application is being precision machined by a manufacturer committed to following strict hygienic procedures.
1) Check Industry Standards
Ensuring sterilization starts with picking the right manufacturing company, and you’ll want to be sure they take the matter of contamination seriously. To start, check their commitment to quality management and industry standards.
All product manufacturing companies must follow industry standards like International Organization for Standardization (ISO) and Food and Drug Administration (FDA). Before you work with a manufacturing company for your medical application, look at their certifications.
For example, ISO 13485 specifies requirements for a quality management system where a company demonstrates it can provide medical devices and related services to consistently meet customer and regulatory requirements. ISO 9001 focuses on meeting customer expectations and continually delivering satisfaction, plus reflects constant improvement from the company.
If the manufacturer you are interested in using does not have any of the above standards, then you may want to ask them why.
Here at AIP Precision Machining, we have been successfully audited by some of the most stringent OEMs in the orthopedic and medical device industries, and are ISO 13485:2016., ISO 9001:2015 , and FDA registered.
2) Plastic Machining isn’t Metal Machining
Be wary of any manufacturer who machines both plastics and metals in the same facility. The tiniest sliver of metal embedded in a plastic part can have widespread ramifications, such as an unexpected electrical problem in the medical device.
Additionally, it’s common for metal machining companies to use oil-based cutting fluids. Any equipment that machines metal, then, can contaminate your plastic parts with those fluids. Many plastic materials are especially sensitive to those petroleum-based liquids, and they can degrade when in contact with them; others are hydroscopic and will absorb the oils.
It should be noted that plastic parts manufactured using equipment that machines metal parts will not meet FDA-approval, or the other industry standards mentioned above. The safest way to avoid this is to hire a plastics expert, not a metal machining company.
AIP takes the matter of sterilization seriously, and ensures the highest level of sanitation down to the sub-molecular level for its products. By designing, stress relieving and machining only plastics, AIP significantly reduces the threat of metallic cross contamination and therefore allows for the highest hygienic products possible.
3) Look for Experience
The most important factor to take into account overall is experience. Your supplier should be familiar with the types of polymers and composites you need machined, and should additionally know the best machining process for your application.
For the medical industry, you want to know that your manufacturer is experienced with the complex needs of your applications. For example, if your components are going to come into contact with body tissue or fluids, then they must be biocompatible per ISO 10993.
Which is to say: If you’re machining implants, your plastics will require different needs than if you’re machining reusable surgical instruments. Both require, however, careful attention to detail. A surgical instrument must be designed with sterilization compatibility for regular cycles in mind, while an implant requires biocompatibility to be safe for use.
Be sure that your manufacturer is familiar with the processes that come with your application, and check that they’ve done it before.
With 35+ years of experience, AIP is well acquainted with precision machining for the medical industry and guarantees careful material selection and processing for your medical applications.
The #1 Best Way to Avoid Contamination?
Overall, the best thing you can do to avoid contamination is to hire a plastic manufacturer with the experience and the credentials to complete your project to the highest standards of quality possible. Keeping the above three factors in mind will help you do just that.
To ask about AIP Precision Machining’s capabilities for precision machining medical applications, please contact us.
An Informational Brief on Polymer Machining
The recent popularity of PEEK (polyetheretherketone) in complex industries such as Aerospace & Defense and Medical & Life Sciences is well documented, and for good reason: this lightweight thermoplastic bears properties that make it ideal for a variety of specialized applications. This versatility makes PEEK equally capable of being used for implants and custom medical devices or machined lightweight aircraft components.
What is less known, however, is the process that goes into machining this plastic material. With over 35 years of experience machining this thermoplastic material, we at AIP have written a brief introduction to machining PEEK. We hope this gives you some insight into our polymer machining process, and how it differs from that of metal machining or injection molding.
Plastic CNC Machining
Before discussing the process of machining PEEK, it’s important to understand exactly what plastic machining is.
CNC (Computer Numerical Control) machining is a process in the manufacturing sector that involves the use of computers to control machine tools. In the case of plastic machining, this involves the precise removal of layers from a plastic material. The technique of utilizing drilling tools to carve plastics was introduced by MIT during the 1950s, and because this process is computer-controlled, products with extremely precise tolerances can be achieved.
Due to the many different kinds of polymers and composites, it’s important to have strong technical expertise of polymer materials when machining plastic components; some plastics are brittle, for example, while others cut similarly to metal. The challenge of plastics is their wide range of mechanical properties and varying behavior when machined. Therefore, it’s important to understand the polymer structure of PEEK if you’re machining it.
Thermoplastics vs Thermosets
When it comes to polymers, you have two basic types: thermoplastics and thermosets. It’s crucial to know which one you’re working with due to distinct differences between how those polymers react to heat and temperature.
Thermoplastics are capable of being repeatedly softened and pliable when temperature increases, meaning that when heat is applied, that results in a physical change for the polymer. They possess the following properties:
- – Good Resistance to Creep
- – May Melt Before Turning to Gaseous State
- – Soluble in Certain Solvents
- – Swell in Presence of Certain Solvents
- – Allows for Plastic Deformation when Heated
Thermosets, in contrast, turn into an infusible and insoluble material when cured by application of heat or chemical means, making for poor elasticity. They possess the following properties:
- – High Resistance to Creep
- – Cannot Melt
- – Insoluble
- – Rarely Swell in Presence of Solvents
Phenolic materials would be considered examples of a thermoset, while PEEK is an example of a thermoplastic.
In particular, PEEK is considered a semi-crystalline, high-performance thermoplastic. This gives it enough elasticity to be machined to various custom designs, with strong mechanical properties that provide resistance to fatigue and stress-cracking, as well as a good structure for bearing, wear, and structural applications.
Industrial Grade vs Medical Grade PEEK Machining
Depending on your application, you’ll want to machine either industrial-grade PEEK or medical-grade PEEK.
Industrial-grade PEEK is a strong, flame-retardant and abrasion resistant thermoplastic with high impact strength and a low coefficient of friction. It’s known for retaining its mechanical properties, even at elevated temperatures. As suggested by its name, this grade is most commonly used in aerospace, automotive, chemical, electronics, petroleum, as well as food and beverage industries.
Medical-grade PEEK adds biocompatibility per ISO 10993, high chemical resistance, and sterilization compatibilities to the above list of qualities. In addition, this thermoplastic is radiolucent, meaning it is not visible under X-ray, MRI or CT. Medical-grade PEEK includes polymers suitable for implants, such as PEEK Optima and Zeniva PEEK, which can stay in contact with blood or tissue indefinitely while mimicking the stiffness of bone. Other variations of medical-grade PEEK can be used for custom medical components and applications, such as articulating joints and spinal devices.
Most shops receive PEEK in the form of rods of various lengths, ranging from 6mm to 150mm in diameter. Stress-relieving before machining through an annealing process is crucial, as it reduces the likelihood that surface cracks and internal stresses will occur from the heat generated. Additional benefits of annealing include increased levels of crystallinity and the opportunity to limit dimensional changes.
If your PEEK components will undergo long stretches of machining time, it is likely you will require additional intermediate annealing steps to assure the ability to maintain critically tight tolerances and flatness.
Machining Industrial-Grade & Medical-Grade PEEK
Both industrial-grade and most medical-grade PEEK machine similarly, save for PEEK reinforced with carbon fiber. Silicon carbide cutting tools work well for natural PEEK, while diamond tools work well for PEEK reinforced with carbon-fiber.
For medical-grade PEEK applications, the best way to avoid jeopardizing the biocompatibility of the material is to machine dry. However, PEEK doesn’t dissipate heat the way that metals do, so often a coolant is necessary. In that case, air is the coolant option least likely to affect medical-grade PEEK’s biocompatibility. Any chips that are a result of machining medical-grade PEEK can be reused for industrial applications.
Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics, with any sub-manufactured metalwork processed outside our facility.
PEEK Machining Guide: Guidelines
(Courtesy of Invibio)
|Sawing||blank||Preheat material to 120 C degrees|
|Clearance angle—degrees||15 to 30||15 to 30|
|Rake angle—degrees||0 to 5||10 to 15|
|Cutting speed—m/min||500 to 800||200 to 300|
|Pitch—mm||3 to 5||3 to 5|
|Drilling||blank||Preheat material to 120 C degrees|
|Clearance angle—degrees||5 to 10||6|
|Rake angle—degrees||10 to 30||5 to 10|
|Cutting speed—m/min||50 to 200||80 to 100|
|Feed rate—mm/rev||0.1 to 0.3||0.1 to 0.3|
|Milling||blank||No material preheat is necessary|
|Clearance angle—degrees||5 to 10||15 to 30|
|Rake angle—degrees||10 to 30||10 to 15|
|Cutting Speed—m/min||50 to 200||200 to 300|
|Turning||blank||No material preheat is necessary|
|Clearance angle—degrees||6 to 8||6 to 8|
|Rake angle—degrees||0 to 5||2 to 8|
|Cutting speed—m/min||250 to 500||150 to 200|
|Feed rate—mm/rev||0.1 to 0.5||0.1 to 0.5|
PEEK Machining Guide: PEEK Variants
When it comes to choosing a thermoplastic material for your medical applications, product durability, agency approval, biocompatibility and cleanliness aren’t just desirable—they’re essential. Beyond even that, though, a host of other factors must be considered when determining which high-performance plastic or composite material to use for an implant, orthopedic surgical guides, body fluid contact components, spinal devices, or surgical instruments. Medical product applications are becoming more and more advanced due to critical performance and alignment requirements as well as the need for radiolucency to support minimally invasive procedures. Therefore, the choice of plastic material specified for a given application as well as a manufacturer with battle-hardened experience is the critical first step in your decision process.
AIP has well over three decades of expertise with thermoplastic materials, and understands how plastics react when machined. We are one of a very select few companies able to hold incredibly tight tolerances in plastic parts. AIP has been successfully audited by some of the most stringent OEMs in the orthopedic and medical device industries, and are ISO 13485:2016, ISO 9001:2015 and FDA registered.
Here are just a few initial, yet critical considerations that take place when we determine the thermoplastic to best suit your particular medical or life science application.
If your components are going to come into contact with body tissue or fluids, then those components must be biocompatible per ISO 10993; if the manufacturer you are working with is not familiar with this standard and cannot provide you with this certification for the material, then move on to a manufacturer with medical industry knowledge. This is especially true if the polymers will undergo long-term contact with body tissues and fluid, such as when used as an implant. Polymers can undergo degradation due to biochemical and mechanical factors in the body, which results in ionic attack and formation of hydroxyl ions and dissolved oxygen. In turn, this can lead to tissue irritation, inflammation, and other reactions with body-like corrosion, wear and potential death. Due to this, very few polymers are available as medical grade for medical application, with an even smaller amount considered a candidate for implants.
AIP Precision Machining includes machined PEEK implants among its many capabilities for custom medical applications precisely due to PEEK’s biocompatibility. PEEK is also inert to body fluids, making it exceptional for bone surgery as well as areas of traumatology and orthopaedics. Another valuable trait of PEEK is that this material has a very similar modulus to that of human bone. The similar modulus to bone reduces the potential for stress shielding. Stress shielding is common with metallic implants whereby the metal implant and bone do not become one nor work in unison to form a single construct. By using Invibio’s PEEK Optima or Solvay’s Zeniva PEEK as an implant material, the bone and PEEK will grow into a single construct mimicking the bone’s natural tendency to repair the fracture or fusion.
Plastics react differently to various sterilization methods, and if a product is not a single-use device and involves body tissue and fluid contact, then it may regularly undergo sterilization. The usual sterilization methods are radiation (gamma/e-beam), chemical (ETO), or autoclave (steam). ETO is rarely a concern, but radiation and autoclaving both require resistance from plastics. Several radiation resistant thermoplastics are:
When it comes to autoclaving, the best polymers for resistance are PPSU and PEEK, with both capable of handling exposure to thousands of cycles.
AIP takes the matter of sterilization seriously and ensures the highest level of sanitation down to the sub-molecular level for its products. By designing, stress relieving and machining only plastics, AIP significantly reduces the threat of metallic cross-contamination and therefore allows for the highest hygienic products possible.
A polymer can be exposed to plenty of disinfection chemicals in a hospital. That exposure can deteriorate plastics, and negatively affect part performance. Polymer chains can be affected by isopropyl alcohol, bleaches, and peroxides. Semi-crystalline polymers like PP, PE, PTFE and PEEK can be expected to have better chemical resistance than amorphous polymers like ABS and PC. However, it’s important to check the performance to be certain of resistances, as exceptions can take place.
With decades of experience working with thermoplastics, AIP guarantees extreme chemical resistance in its material selection for your medical applications.
Electrical & Thermal Properties
Dielectric strength and thermal resistance are necessary for medical devices enclosed in areas that require high heat resistance. Thermoplastics such as PC (Polycarbonate), PC blends, PPS (polyphenylene sulfide), PEI and PS (polystyrene) blends have electrical properties that perform well, some even at elevated temperatures.
AIP’s material library includes thermoplastics that exhibit extreme thermal performance, and we are familiar with machining them in applications for medical life & sciences.
Properties such as tensile and compressive strength, wear resistance, impact strength, and bending stiffness also must be considered when choosing your thermoplastic. Engineered thermoplastics such as PC, PEEK, PPSU, POM, PEI and reinforced grades of these same materials (glass, aramid and carbon fillers) perform very well in this respect, making them ideal for a variety of climate conditions, such as during transportation.
AIP provides thermoplastics that show extreme wear resistance, x-ray visibility or invisibility and high structural performance.
These are just a few of the many considerations that take place when choosing the right plastic for your medical applications. AIP offers you our full material consultancy from concept to completion, so that together, we find the right thermoplastic for your projects.
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