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?
In this blog post, I show you how to substitute a metal part by high performance polymers. In this case the replaced metal is magnesium.
There are two approaches on how to substitute metals with other materials such as Polyphthalamide (PPA), a high performance polymer. In the first approach, we increase the cross-sectional thickness to provide increased stiffness. In the second approach, increased stiffness is achieved by adding ribs.
First approach: changing wall thickness
In general, deflection is proportional to the load and length of the part. Furthermore, deflection is inversely proportional to the modulus of elasticity and moment of inertia.
For the first approach we need the deflection (Y) equation of a beam with a uniform distributed load F (Equation 1). Both ends of the beam are fixed. Then, we equate the deflections of metal and plastic (Equation 2). FL3 is a constant since load (F) and length (L) remain the same. This leads to Equation 3. Now, we can insert the modulus of elasticity E for magnesium, which is 44.8 GPa. As PPA, we have selected Amodel® AS-1145 HS (45% glass fiber; impact modified; 6T/6I/6.6). As a result, the magnesium part stiffness is 3.25 times higher in comparison to PPA.
Metal replacement: first approach - changing the wall thickness
To achieve the same stiffness with the plastic part we have to increase the moment of inertia (I). This can be done by inserting Equation 5 (moment of inertia for rectangular section) into Equation 4. “b” is the width which is kept constant and “d” is the thickness of the section. We resolve the equation for “d” (assumption: the magnesium part has d = 2.54 mm) and as a result we get the new thickness of the PPA part, which is 3.76 mm.
The PPA part will be 48% thicker than the magnesium part and will achieve the same stiffness.
Metal replacement: first approach - changing the wall thickness
Second approach: adding ribs
Another way to increase the moment of inertia is by adding ribs to the plastic part. This will decrease the wall thickness and weight significantly.
We start with a 3.76 mm thick plate design made out of the same material, Amodel AS-1145. Therefore, the modulus of elasticity with 13.8 GPa remains for the plate and the ribbed design the same. If the moment of inertia of the ribbed design is the same as for the plate design, then the ribbed part will show equivalent deflection and/or stiffness.
We will assign 25.4 mm for the width “b”. Now, we can calculate the moment of inertia for the plate design (Equation 8). Based on the rib design (figure below) we can then calculate the moment of inertia for the rib structure (Equation 9).
Metal replacement: second approach - adding ribs
As a result, the ribbed design will be 9.5 times stiffer than the previous calculated PPA plate design and the original magnesium plate design which was 2.54 mm thick. Reducing the height of the rib by half would still result in a part which is twice as stiff as the magnesium part.
Conclusions
When replacing metal by high performance plastics, adding ribs will reduce the thickness and weight of your new part. Furthermore, stiffness can be increased dramatically, which allows for new part applications or even thinner parts in total.
Furthermore, modern CAE software is able to add automatically a rib structure by applying topology optimization tools.
Hello and welcome to this blog post where I show you how effective metal replacement with polymeric materials in automotive is done. A successful metal to plastic conversion can significantly reduce weight and CO2 emissions and increase mileage.
The training consists of 5 parts:
1. Update on the current challenges in the automotive industry
2. Clarification on why aluminum die cast replacement is beneficial
3. Deep dive on how metal replacement can look like including which high performance plastics can be used.
4. Explanation of metal replacement with a commercial example
5. Closure with key takeaways
Watch below the video on my Youtube channel:
1. Update on the current challenges in the automotive industry
Modern cars are gaining in weight and size. In the past 50 years, the weight increase was in average 10 kg per year. Globally, legislations are pushing Original Equipment Manufacturers (OEM’s) to design for better fuel economy, lower emissions and improved safety. In parallel, consumers are seeking a better performance of their cars at lower costs.
And in all this discussions comes now the central question: why is applying light weighting beneficial?
A suitable light weighting strategy in place allows OEM’s to fulfill regulations and consumer wishes such as active safety, customer experience, new energy vehicles and reduction emissions.
In Figure 1 the current regulation situation is shown. In the European Union (EU) only 95 g/km CO2 will be allowed by 2020. The EU has the strictest of all CO2 emissions limits. OEM’s have to pay high fees for their cars if those are not fulfilled. Currently, the new Worldwide Harmonized Light Vehicle Test Procedure (WLTP) pushes OEM’s even faster to improve their fuel economy. It is expected that China is moving fast in such a direction too.
Figure 1: Overview on the worldwide CO2 regulations for automotive industry.
The statement of Goldman Sachs sums it up in a concise way: “We expect a 15% (200 kg) drop in the average car body weight by 2025 as automaker race to meet CO2 rules”. The modern cars need to loose around 200 kg in weight. One way is to switch to aluminum which has 1/3 of the weight of steel. Another way is to increase plastics in the body in white structures (Figure 2).
Figure 2: Results of Goldman Sachs study.
Currently around 10-12 % of a modern passenger car is made out of plastics. Comparing the different structural materials used in cars, advantages of polymeric materials can immediately be seen. Steel has a density of 7.8 g/cm3. Aluminum has 1/3 the density of steel and plastics have half the density of aluminum, leading to a 50% reduction.
2. Why is aluminum die cast replacement beneficial?
In this section I show you why metal replacement with polymeric materials is beneficial for consumers and OEM’s. On one hand, aluminum prices increased 33% in the past three years (Figure 3). On the other hand, due to the significantly lower density of polymers in comparison with metals major weight reduction can be achieved.
Figure 3: Volatile material prices of LME aluminum.
Some of the technical advantages of replacing metals with plastics are for example:
1) Possibility of consolidating several metal parts into one plastic part.
2) Better resistance to corrosion or chemical attacks
3) Better acoustics (particularly relevant in electric vehicles)
4) Improved friction and wear properties of parts
So far, we made a quality assessment of why metal replacements in automotive are beneficial. Now, we make a direct quantitative comparison with a split into process, part and additional advantages (Figure 4). As an aluminum representative I have selected the alloy A380 and compared it to high performance plastics such as polyphtalamides (PPA), polyarylamide (PARA), and polyphenylene sulfide (PPS). I highlighted the major differences in orange. Manufacturing process for aluminum parts is in most cases a die-casting process which requires high operating temperatures. Aluminum allows parts with high dimensional tolerances and the casting is close to net shape. For plastics injection moulding can be used to ensure a high volume mass production at high production efficiency. As a result, besides allowing 50% lighter parts than aluminum, plastics may allow for cost reductions in the order of 10 to 30%. On the top of these advantages is the design freedom and linear performance up to 120-150 °C e.g. semi-aromatic nylons and PPS.
Figure 4: direct comparison of aluminum A380 and high performance plastics.
3. How a metal replacement can look using high performance plastics
Here, we discuss the plastic material selection for metal replacement. There are over 60 thermoplastic resins and over 100 additives you can add to your base resin, ending up with thousands of potential compounds. Therefore, you might ask: which of those compounds is the optimal material for my metal replacement?
Basically, a selection method consisting out of three steps will help you to find the right polymeric material. In a first step, we will select the resin morphology, deciding if we need an amorphous or semi-crystalline morphology. Then, in the second step we apply thermal, mechanical and cost requirements. Finally, in the last step the manufacturing process is considered and a final review is made (Figure 5).
Figure 5: material selection steps for metal replacement.
Amorphous and semi-crystalline polymers have their strength in different areas. Amorphous resins have excellent transparency combined with low shrinkage; low warpage and tight part tolerances can be achieved. Semi-crystalline resins have an easy processing behavior combined with chemical resistance, mechanical strength and wear resistance.
To be suitable for metal replacement in automotive a plastic parts has to exhibit certain mechanical strength and wear resistance and has to be able to withstand oils and fuels. Therefore, semi-crystalline morphology will be the clear choice. For most metal replacements at least the temperature stability and mechanical strength level of an engineering plastic is required. Figure 6 shows you the major commodity, engineering, and high performance plastics.
Figure 6: Overview of major commodity, engineering, and high performance plastics.
In the second step, the thermal, mechanical, and cost requirements are evaluated. An important criterion to rank materials in relation to each other is the strength to weight ratio (Figure 7). Comparing the aluminum grade A380 with the engineering and high performance plastics, it can be seen that Nylon 6.6 and PPS are in a similar strength to weight range. PARA as well as PPA with 60% glass fiber are even outperforming aluminum.
Figure 7: Strength to weight ratio of different metals and plastics.
So far we just considered values of our materials at room temperature. How PPA and PARA behave at higher temperatures? In Figure 8 you can see that PARA is not a high temperature polymer since it has a glass transition of 85°C. PPA’s, however, have higher glass transitions which can reach up to 135°C and higher. For standard operating environments, both materials are suitable for an aluminum die cast replacement.
Figure 8: Tensile strength of semi-aromatic Nylons and aluminum.
In the last step of the material selection we have to check the processing methods of the selected materials. Most parts are produced in injection moulding which comes with several benefits such as reduced post processing costs and moulded in threads if needed.
Apart of material selection we have to consider some more things for our project management to be successful in metal replacement. One point is the definition of the primary aims: which functions need to be fulfilled by the system and which function does each single component need to fulfill.
Another step is the product conceptualization: here it is important to look for design alternatives, feasibility studies, potential savings, and test programs with prototype parts.
Design in plastics is not difficult, it is just different. Design checks are needed to find out if there are no critical weldline situations. Part optimization by using e.g. moldflow studies combining with practical filling studies can be beneficial too. Finally, evaluation of the material suitability through test specimens and component testing should be done. After this your new plastic part can be ready for a pre-series test – congratulations when you reach this phase.
4. Explaining metal replacement with a commercial example
Now let’s close the theoretical part and have a look at an industrial example.
Engine support mounts are a good example for metal replacement. In this case a PA6.6 with 60 % glass fiber load was selected (Figure 9). It is a high strength type of Nylon and having a specific strength in the range of steel which makes it a good candidate for replacement.
Figure 9: Engine support mounts as a metal replacement example.
5. Key take aways
In Figure 10 I summarized what we have discussed in this post:
Figure 10: key takeaways of the metal to plastic training.
Thanks for reading this training and if you have questions or need help with your metal replacement, then please let me know.
Weight reduction to save
energy and costs has been and will continue to be a constant topic of interest in
the aircraft and automotive industries. In this regard, much has been done
toward replacement of metals especially the heaviest ones by lighter materials
still able to fulfill application demands. Nevertheless, there are other industries
where metal replacement and consequent weight reduction can also make life
easier especially when you have children. I am talking about children buggies. Most
buggies have between 8.5 kg and 10 kg. Heaviest ones may range from 12 kg to 17
kg in total weight (frame plus seat). The weight is a result of using aluminum,
which is already among the lightest metal materials (2700 kg/m3).
Furthermore, it is naturally resistant to corrosion. Is it still possible to
make buggies lighter while keeping their current application suitability? Yes,
by using high performance polymers.
Following, I will
present you a commercial example of the company Quinny that won the 2014 Red
Dot ‘Best of the Best’ Award for their 5 kg Yezz buggy [1,2].
5 kg Yezz buggy using PARA frames [1,2]
Why is it only 5 kg heavy
and still a high-end performer?
The frame of the buggy is
made of several frame parts using the high performance polymer, polyarylamide, commonly
known as PARA (or MXD6), reinforced with glass fibers (50 wt%) [3]. The weight reduction
is achieved by the reduced density of PARA, 1600 kg/m3. The high-end
performance comparable to metal is achieved by the aromatic amide macromolecular
structure of PARA, which provides this polymer with inherent high stiffness and
strength. For instances, the tensile modulus of PARA can reach values up to 23
GPa at 20°C.
In terms of processing, a
major added value of PARA is that it can be loaded up to 60%wt with glass fibers
for reinforcement purposes [4] without this to be noticed in the moulded part.
The latter will still exhibit a smooth surface with no evidence of contained glass
fibers. Such surface allows excellent painting and/or metallization. Additionally,
PARA has good flow properties at melting temperatures, which allow the moulding
of parts as thin as 0.5 mm. For these reasons, PARA can be a suitable material
when complex parts requiring high stiffness in combination with superior
surface quality are needed. Accordingly, premium automotive interiors could be
of interest.
Next time when you’re are looking for a buggy keep in mind that
there are lightweight solutions to make travelling activities with your
children easier.
Thanks for reading! Greetings, Herwig Juster
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