Metal Replacement with Plastics: A 5-Step Roadmap

Hello and welcome to a new blog post. Today I present to you a metal replacement roadmap which contains five major steps and when all steps are followed, success in metal replacement will be secured. 

Why Change from Metal to Plastic?

There are many reasons to consider changing from metal to plastic. Some of the most important benefits include:

• Part consolidation and function integration: Plastic parts can be designed to integrate multiple functions into a single part, which can save on manufacturing and assembly costs.
• Weight saving: Polymer have a lower density compared to metals, so switching to plastic can help to reduce the weight of products.
• Lower processing costs: Plastic parts can be manufactured using a variety of processes, such as injection moulding, which can be less expensive than metal forming processes.
• Fewer or no secondary operations: Plastic parts often do not require secondary operations, such as painting or finishing, which can save on manufacturing costs.
• Freedom and flexibility of design: Plastic can be molded into a variety of shapes and sizes, which gives designers more freedom to create innovative products.
• Corrosion resistance: Plastic is resistant to corrosion, so it is a good choice for products that will be used in harsh environments.
• Surface aesthetics, color aspects, markability: Plastic can be easily colored and marked, which makes it a good choice for products where aesthetics are important.
• NVH reduction: Plastic can help to reduce noise, vibration, and harshness (NVH) in products.
• Possibility to reduce the product carbon footprint; lead free material solutions

Metal to plastic conversion roadmap

As outlined before, replacing metal components with plastic ones offers several benefits, including reduced weight, lower costs, and improved design flexibility. However, the process requires careful planning and execution to ensure optimal results. This roadmap (Figure 1) outlines the key steps involved in efficient metal replacement:

1. Metal Part Identification

2. Polymer Material Selection

3. Design and Engineering

4. Prototyping

5. Production

Figure 1: 5 Step Metal to Plastic Conversion Roadmap.

What are the 5 steps leading to successful metal to plastic replacement?

1. Metal Part Identification

• Identify the specific metal components targeted for replacement.
• Define the objectives and required outcomes for the replacement.
• Outline the preliminary requirements and boundary conditions for the new plastic component.

2. Polymer Material Selection

• Choose the most suitable polymer material based on the application requirements.
• Consider factors such as mechanical properties, chemical resistance, and thermal stability.

3. Design and Engineering

• Develop a detailed CAD design for the plastic component.
• Conduct CAE virtual testing and simulations to evaluate the design's performance.
• Refine the design based on the simulation results.

4. Prototyping

• Create a prototype tool for the plastic component.
• Produce molded parts using the selected polymer material.
• Perform thorough testing on the parts to ensure they meet the required specifications.

5. Production

• Release the final part design for serial production.
• Manufacture the plastic components at scale.

By following this roadmap, you can ensure a smooth and successful transition from metal to plastic components.

How a metal replacement project can look like

Example Medical Device Metal replacement  

The following example explains the replacement of surgical retractors (Figure 2), used in total hip replacement replacement (THR) surgeries as a case study for metal-to-plastic conversion. In general, replacing metal with plastic can improve performance and reduce costs in medical devices. High-performance polymers such as PEEK, Polysulfones, and PARA offer similar strength and stiffness to metals, with added benefits. 

In addition, environmental impact can be reduced by switching to a plastic solution. This could be demonstrated by a Life Cycle Analysis (LCA; cradle-to-grave) of a single-prong metal hip retractor. Since the repeated washing and sterilization could be removed, 435 liters of water for each surgical knee procedure could be saved [4].

Figure 2: Surgical hip retractor as an example of metal-to-plastics conversion [1].

1. Metal Part Identification

Orthopedic surgery retractors are traditionally made from metal due to the high strength and stiffness required. The document provides a comprehensive account of converting both single-use and reusable retractors to polymer-based designs using polyarylamide (PARA) and polyaryletherketone (PAEK), respectively.

2. Polymer Material Selection

For medical devices, essential performance requirements include chemical resistance and the ability to withstand sterilization processes, such as steam autoclaving or gamma radiation.

Material selection for both single-use and reusable retractors involves aligning with boundary conditions related to sterilization requirements and usage cycles. 

PARA (Ixef GS-1022), reinforced with 50% glass fiber, is selected for single-use retractors due to its exceptional strength, compatibility with gamma radiation sterilization, and superior surface finish. It delivers performance levels comparable to stainless steel (in this case 17-4 steel)  and can be injection molded, eliminating machining processes and reducing costs.

For reusable retractors, PAEK (AvaSpire AV-651 GF30) is the material of choice, offering a high stiffness-to-weight ratio, hydrolytic stability at elevated temperatures, chemical resistance, and durability even after repeated exposure to disinfectants and steam sterilization. Its ease of processing through injection molding and design versatility further highlight its suitability.

3. Design and Engineering

To replicate the stiffness of metal counterparts in plastics, adjusting the area moment of inertia through design modifications, such as using rectangular geometries or adding ribs was needed. Advanced design using computer-aided engineering (CAE) leverages plastic’s inherent advantages to enhance aesthetics and ergonomics, improving the overall device performance and user experience. A notable design modification for the hip retractor includes optimizing the handle for improved grip and stiffness.

4. Prototyping

Prototyping is crucial in evaluating the feel and functionality of new designs, with 3D printing techniques like selective laser sintering (SLS) employed to create initial prototypes. Validation processes for single-use and reusable plastic retractors involve testing to ensure performance metrics match or surpass those of the original steel retractors. Both plastic versions offer significant weight reduction, decreasing the overall weight of surgical equipment. Additionally, transitioning to plastic reduces the cost of reusable retractors by half and enables economically viable single-use designs.

5. Production

Manufacturing decisions favor injection molding for its cost-effectiveness in large volumes, design flexibility, and quick production turnaround, particularly given the estimated demand for hip retractors over three years.

Metal replacements with high-performance polymers in the medical industry are expanding. Plastic material suppliers, manufacturers, and designers are increasingly focusing their efforts on integrating plastics into medical device designs. Through this transition, the industry aims to meet the dual objectives of enhancing device performance and reducing costs in response to the evolving landscape of healthcare and technology.

Conclusion

Replacing metal components with plastic ones offers several benefits, including reduced weight, lower costs, and improved design flexibility. However, the process requires careful planning and execution to ensure optimal results. The discussed 5-step roadmap outlines the key steps involved in efficient metal replacement.

Interested in assessing the feasibility of metal replacement in one of your components?

Please reach out to me here.

Check out my other metal replacement articles: 

Metal Replacement with Polyarylamide (PARA) for Single-Use Surgical Instruments

Metal replacement with High Performance Polymers: How to Design for Equivalent Part Stiffness?

Replacing Magnesium Die Casting with Engineering and High Performance Plastics

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

🔥 There is a problem keeping you awake - My personal website for Polymer Consulting

📊 Discover your Polymer Material Selection score by taking quick test here

Literature: 

[1] https://www.meddeviceonline.com/doc/medical-device-metal-to-plastic-conversion-in-steps-0001

[2] https://www.findoutaboutplastics.com/2020/02/metal-replacement-with-polyarylamide.html

[3] https://www.syensqo.com/en/product/ixef-gs-1022-wh01

[4] https://www.syensqo.com/en/chemical-categories/specialty-polymers/healthcare/metal-plastic-conversion

Polycaprolactone (PCL): A Versatile Polymer for Prototyping and Small-Scale Modeling

Hello and welcome to a new post. As a polymer engineer, you'll encounter a vast array of materials, each with unique properties suited for specific applications and systematic polymer material selection is key to success. Polycaprolactone (PCL) stands out as a particularly interesting and useful thermoplastic polyester, especially in the realm of prototyping and small-scale modeling. Let's delve into its key characteristics and advantages.  

Polycaprolactone: Low-cost, biodegradable, and incredibly versatile: PCL is a hidden gem in polymer engineering.

What is Polycaprolactone (PCL)?

PCL is a biodegradable, semi-crystalline polymer with a low melting point (around 60°C). This low melting point is a defining feature, making it incredibly easy to process and manipulate using simple techniques. It's synthesized through ring-opening polymerization of ε-caprolactone.   

Key Characteristics:

• Low Melting Point: This is perhaps PCL's most significant advantage. It allows for shaping and molding using hot water, heat guns, or even just hand pressure.
• Biodegradability: PCL degrades through hydrolysis of its ester linkages, making it environmentally friendly compared to many other thermoplastics. The degradation rate can be controlled by varying the molecular weight and crystallinity.   
• Biocompatibility: PCL is non-toxic and biocompatible, making it suitable for medical applications, including drug delivery and tissue engineering.   
• Flexibility and Toughness: While relatively soft, PCL exhibits good flexibility and toughness, allowing for the creation of durable prototypes.
• Ease of Processing: PCL can be processed using various techniques, including melt extrusion, injection molding, and 3D printing (specifically Fused Deposition Modeling - FDM).
• Solubility: PCL is soluble in hot water and in various organic solvents, such as chloroform, dichloromethane, and toluene, which can be useful for solution processing and surface modifications.   

Advantages for Prototyping and Small-Scale Modeling:

1. Rapid Prototyping:

Due to its low melting point, PCL allows for quick and easy modifications. You can rapidly iterate designs by simply reheating and reshaping the material.   

This makes it ideal for early-stage prototyping where speed and flexibility are crucial.

2. Low-Cost Modeling:

PCL is relatively inexpensive compared to many engineering plastics, making it a cost-effective option for hobbyists, students, and small businesses.

The simple processing requirements also reduce the need for expensive equipment.

3. "Hand-Formable" Properties:

The ability to shape PCL by hand using hot water or a heat gun makes it incredibly versatile.

This is particularly useful for creating complex shapes or intricate details that may be challenging with other materials.

4. Educational Tool:

PCL is an excellent material for educational purposes, allowing students to experiment with thermoplastic processing and learn about polymer properties.

It's safe and easy to use, making it suitable for classroom demonstrations and hands-on projects.

5. 3D Printing Applications:

PCL can be used in FDM 3D printing, enabling the creation of complex geometries and functional prototypes.   

It is often used in biomedical 3d printing applications.   

6. Mould Creation:

Because of its low melting point, it can be used to create moulds for other materials that have a lower melting point.

Applications in Prototyping and Modeling:

• Conceptual Models: Quickly creating tangible representations of design ideas.
• Fit Testing: Verifying the fit and functionality of components.
• Ergonomic Studies: Assessing the comfort and usability of products.
• Custom Tooling: Creating custom tools and fixtures for specific tasks.
• Art and Sculpture: Sculpting and molding intricate designs.
• Medical Models: Creating anatomical models for educational or surgical planning purposes.

Considerations:

PCL's low melting point can also be a limitation in high-temperature applications. It is relatively soft, so it may not be suitable for applications requiring high rigidity or strength. Long term creep can also be a factor to consider.

Conclusion:

Polycaprolactone, the polymer behind products such as Polydoh, Polymorph,  Re-Form,  Plastimake, and NiftyFix is a valuable material for prototyping and small-scale modeling, offering a unique combination of ease of processing, biodegradability, and biocompatibility. Its low melting point and "hand-formable" properties make it an excellent choice for rapid prototyping, educational purposes, and various creative applications. As a polymer engineer and student, exploring the properties and applications of PCL can significantly expand your materials knowledge and practical skills.   

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

🔥 There is a problem keeping you awake - My personal website for Polymer Consulting

📊 Discover your Polymer Material Selection score by taking quick test here

Literature: 

[1] https://www.researchgate.net/publication/366581952_POLYCAPROLACTONE_THE_FORGOTTON_POLYMER

[2] https://www.atamanchemicals.com/pcl-solid_u30611/

[3] https://taylorandfrancis.com/knowledge/Engineering_and_technology/Chemical_engineering/Polycaprolactone/

[4] https://materialdistrict.com/material/polymorph/

Polyarylamide (PARA; MXD-6) and Recycling: How much regrind is possible?

Hello and welcome to a new post in which we discuss the usage of regrind when processing the high-performance Polyarylamide (PARA; MXD-6).

Recycling Process:

Polyarylamide regrind (sprues, runners, etc.), containing reinforcements such as glass fibers, can be recycled with virgin PARA compound. Important is to exclude any contamination such as oil, release agents, and other additives.

Impact on Mechanical Properties and Color Variation:

Several studies and experiments have shown [1] that a split of 70/30 (70 wt% virgin PARA / 30 wt% regrind) is preferred. The compound used in each cycle was 70% virgin compound (containing 50 wt% glass fibers) mixed with 30% regrind from the preceding cycle. Very little change was observed in the mechanical properties (tensile strength, elongation at break) after recycling. Successive recycling may cause a slight change in color. 

Recommendations:

Important is to confirm the recycling rate experimentally to ensure the finished part meets specifications. Also, drying the regrind prior to injection unless directly grinded and reinjected at the moulding machine. Mark parts to facilitate after-use recycling (check out the part marking codes here).

Thanks for reading and #findoutaboutplastics

Greetings

Herwig Juster

🔥 There is a problem keeping you awake - My personal website for Polymer Consulting

📊 Discover your Polymer Material Selection score by taking quick test here

Literature: 

[1] https://content.solvay.com/ixef-para-processing-guide

Become a Master in Polymer Material Selection - Learn & Apply the “6 POMS” Skills

Hello and welcome to a new blog post. Over the course of my career as a polymer engineer, I have sought to delineate the requisite skills for effective polymer material selection. Through discussions with polymer engineers responsible for successful plastic product development over the past decade, it has become evident that proficiency in six distinct areas is consistently demonstrated. These individuals not only possess comprehensive knowledge but also apply it rigorously across multiple product development cycles. Through iterative refinement and detailed analysis, these six areas have been systematically mapped. Consequently, I have formalized these competencies into what I now refer to as the "6 POMS" skills (Figure 1).

The 6 Polymer Material Selection Skills

Figure 1: Overview of the 6 POMS skills helping to become a Master in polymer material selection [1].

Let us discuss each of the 6 P's:

P- Properties: Understanding key polymer properties 

To effectively select polymers for specific applications, a thorough understanding of their key properties is essential. This includes familiarity with polymer structure properties like morphology, molecular weight, and thermal transitions. Knowledge of mechanical properties such as tensile, flexural, and impact strength, stiffness, and elongation is crucial. Additionally, a grasp of thermal properties, including glass transition temperature (Tg), melting temperature (Tm), and heat resistance, is necessary. The ability to assess chemical resistance to acids, bases, solvents, and oxidation is also vital. Furthermore, awareness of both long-term and short-term properties and their relationship to application requirements is paramount. Finally, understanding multi-point property data and its relevance to application needs ensures optimal material selection.

P - Part Design: Defining Application Requirements for Plastic Part Design 

The success of a plastic part depends heavily on its ability to meet the specific demands of its intended application. To ensure this, a structured approach to defining requirements is essential. This involves using tools like requirement checklists and methodologies such as the FLERP approach (Function, Loading conditions, Environmental Factors, Regulatory requirements, and Processing requirements).

A crucial aspect of this process is the ability to write clear and concise product specifications. This requires a deep understanding of the part's true functions, load cases, and material requirements. Additionally, it is important to consider the data needed for plastic part design, including material properties, processing parameters, and environmental factors.

Finally, cost considerations should be integrated throughout the design process. This involves evaluating material and manufacturing costs to optimize the overall design and ensure economic viability. By following these steps, engineers can effectively define application requirements and design plastic parts that meet the needs of their intended use.

P - Polymer material values: Translating application requirements to qualitative and quantitative material values

Translating plastic application requirements into actionable material values is a critical step in the selection process. This involves understanding how qualitative and quantitative application needs correspond to specific material properties. A systematic approach, such as listing all application requirements and their translated material values in a dedicated system or sheet, significantly enhances the selection process by providing a clear and organized framework for evaluation.

P - Process: Polymer material selection process

The process of selecting polymer materials involves several key considerations. It's important to determine if a structured, step-by-step approach is currently in place. Utilizing online databases like CAMPUS or Omnexus for material identification is common practice. A fundamental understanding of how to interpret technical datasheets for plastics is also crucial. Furthermore, the selection process should involve a degree of critical thinking, including challenging the use of established materials and exploring alternative options. Questioning the rationale behind choosing specific resins and ensuring they align with actual requirements is vital. Finally, the use of decision-making tools can significantly facilitate the selection of appropriate plastics.

P - Performance: Evaluation of material and part performance

Evaluating plastic material and part performance requires a comprehensive approach. Utilizing CAE tools, like injection mould filling simulation and FEA, enables virtual testing and optimization of plastic parts. Familiarity with standard ISO tests, such as tensile tests, is essential for quantifying material properties. Physical prototyping plays a critical role in verifying material and part functionality. Ultimately, experience in testing both material and part performance is crucial to confirm the suitability of the chosen plastic for its intended application.

P - Plastic supplier: Selection of material and supplier

The selection of plastic materials and suppliers involves active engagement and collaboration. Regularly discussing application requirements with polymer application engineers is crucial for ensuring material suitability. Direct contact with material suppliers to obtain samples supports the selection process by allowing for physical testing and evaluation. Seeking recommendations from plastics experts and material suppliers on new material developments ensures access to the latest advancements and potential solutions.

How to train the 6 POMS skills and become a master in polymer material selection? 

Start by taking my new developed Polymer Material Selection test and discover your polymer material selection score. Assess where you are currently ranking at the different POMS skills and increase your ability to select plastics better. It is a simple test which consists of 26 Yes/No questions. After submitting, you will receive a report containing your overall POMS score, the detailed score and recommendations for improvements.

I invite you to take the test, get your POMS-score and review the suggested improvements.

Thanks for reading & #findoutaboutplastics!

Greetings, 

Herwig 

New to my Find Out About Plastics Blog - check out the start here section

🔥 There is a problem keeping you awake - My personal website for Polymer Consulting

📹My YouTube channel

Literature: 

[1] https://www.polymermaterialselection.com/poms-score

[2] https://www.amazon.de/-/en/Polymer-Material-Selection-practical-systematic/dp/B0BSWM6BPD