High-Performance Plastics

High-Performance Plastics

Design Optimization: Increasing Performance Through Substituting High-Performance Plastics For Metal

Key Points:

  • High-performance plastics may allow reduction in
    weight and cost while maintaining mechanical performance
  • Part count reduction may further reduce weight
    and simplify designs
  • Elimination of secondary operations saves time
    and expense
  • Production cost and production rate improvements
    with injection molding
  • The cost of prototyping and tooling for
    injection molding is not prohibitive

Progress often dictates reevaluating fundamental decisions

Design and manufacturing professionals are constantly challenged to improve the performance of their products, whether it be reduction in fuel or energy consumption in transportation applications, comfort in wearable devices, or the efficacy of medical equipment and medical devices.

In the ongoing reevaluation of what can be done to improve product performance, one of the most fundamental questions to ask is, “are we using the optimal material for this application”? 

This is no simple matter since in many instances, entire factories and their related supply chains are literally tied to the material selection of a core component.  Think of cast aluminum induction components for internal combustion engines for example.  However, to improve functional and financial performance in a meaningful way, material choice must frequently be reevaluated objectively.

Material substitutions require careful reflection

Considering the implications of substituting a new material for a product or sub-component noted above, the threshold for an acceptable benefit to cost ratio must be high.  In some applications, the reward is obvious: saving a few kilos in a race car means winning or losing, reducing the time to assemble a product might make it commercially viable or a no-go, improving the ability to sterilize a medical device could accelerate adoption.  In marginal cases, the math becomes more difficult, putting pressure on designers to seek fractional performance gains wherever they can be found.  In many important cases these gains are found in substituting older metal designs for high-performance plastics.

High-performance plastics have many advantages

Although high-performance plastics are no substitution for metal alloys for many applications, there are countless applications where metals cannot perform the role of a polymer.  It is between these two spaces where either a polymer or metal could perform the desired functions at an acceptable manufacturing cost in commercially meaningful volumes.  So, when one looks to achieve a high benefit, cost outcome by transitioning from metal to plastic components, where does one start?

  1. Evaluate a simple material substitution of the component design – Can a meaningful improvement be achieved with an engineering-grade polymer with essentially the same physical / geometrical design?  This is not often the case due to the much different mechanical properties between metals and high-performance plastics, but it may happen where the initial metal design was far from optimal, making a substitution of a lighter and less expensive-to-manufacture plastic component possible.
  2. Evaluate a redesign that takes the advantages of molded plastics into accountPlastic injection-molded components can be very complex at high production rates and low per part costs once the injection molding process has been proven out. This allows the designer to consider reducing part count in assemblies by combining functions into a single component.  This saves weight, production time, additional project logistics, and ultimately cost.  Additionally, molded polymers can incorporate aesthetics via more complex organic shapes and molded-in colors that again reduce secondary operations.  Finally, the wide spectrum of mechanical, physical, and chemical properties of polymers opens many new avenues for clever design not possible with metals.
  3. Evaluate combining the best of both worlds – Polymer components with overmolded inserts can combine the benefits noted above from the use of injection molding and those of metal features in certain critical areas such as threads, embedded wiring, metal tubing for fluid or gas lines, heat dissipation features, or aesthetic elements.     

Once the rudimentary analysis
suggested above is done, the detailed work starts.  From the design perspective, the full
analysis of the static and dynamic performance of the component under the
foreseen environmental conditions must be simulated, tested, and validated.  In parallel, the manufacturing team must plan
the component substitution, estimate tooling, training, and production
validation timelines and capital and operating costs.  Ultimately, the commercial team will merge
the data from the design and manufacturing teams to generate an expected return
on investment (ROI) for the substitution, essentially the mathematical
calculation of the benefit: cost ratio. 

Companies frequently substitute high-performance plastics for metal

Just think about the many products that were once metal that have been replaced by a superior injection-molded plastic component: consumer products, medical devices, sporting goods, and automotive components, all have excellent examples of significant improvement through substituting high-performance plastics for metal. However, there are far more untapped applications that may seem mundane, where the real potential still lies, and the cost of conversion is far lower. 

For example, we have helped clients in the electrical industry convert sheet metal assemblies with multiple fasteners and manual assembly, to sculpted single components that do not require assembly, painting, or electrical insulation. 

The direct per component cost is lower, assembly time is shorter, and the entire manufacturing logistics chain is simplified, all while delivering a superior end product.  This is the power of high-performance plastics.

Actually, incredibly often.  Just think about the many products that were once metal that have been replaced by a superior injection-molded plastic component: consumer products, medical devices, sporting goods, and automotive components, all have excellent examples of significant improvement through substituting high-performance plastics for metal. However, there are far more untapped applications that may seem mundane, where the real potential still lies, and the cost of conversion is far lower. 

For example, we have helped clients in the electrical industry convert sheet metal assemblies with multiple fasteners and manual assembly, to sculpted single components that do not require assembly, painting, or electrical insulation.  The direct per component cost is lower, assembly time is shorter, and the entire manufacturing logistics chain is simplified, all while delivering a superior end product.  This is the power of high-performance plastics.

Injection molding tools, especially for prototypes and short run production, can be very cost effective

Returning to the benefit: cost calculation, the amortization of tooling costs is a big factor in the denominator of the equation.  Even if these costs are capitalized, it is still a cash outlay that must be factored in to project planning when comparing machined, cast, metal injection molded (MIM), or stamped metal parts (to name a few of the most common processes).  For high volume production, the impact of a polymer solution can be dramatic, but even for low volumes due to advanced mold making and molding processes, like those employed at Xcentric, the costs to switch to a plastic component can start to pay off quickly. 

Firstly, Xcentric tooling costs a fraction of that of hardened steel tools and are producing end product literally in a matter of days for simpler projects, and two to three weeks for very complex products.  This accelerates cash generation for the customer and gives early feedback about the viability of the substitute component.  If additional iterations are needed for testing or validation, the lower difficulty of making modifications to the prototype tooling and process parameter changes keep costs under control and the project on track (for more information on project timelines in injection molding click here).  When these factors are combined with the direct and indirect manufacturing gains and end use enhancements, injection molding tools are well worth the investment.

Summary: Substituting high-performance plastics for metals can really pay off

Whether it be increasing the performance of the latest sporting equipment, or making the new kitchen appliance more attractive, or reducing the cost and weight of an aircraft interior component, plastic injection molding has proven endless times that it is a viable substitute for metal in very demanding applications.  So, the next time you and your team is considering methods of improving the performance of your products, consider every area where a plastic component might bring a performance or economic advantage.  You may be surprised that the benefit to cost works out very well indeed.

When To Choose Injection Molding Manufacturing

When To Choose Injection Molding Manufacturing

injection molding

Injection molding: one of the most important manufacturing processes

It may sound hyperbolic to state that injection molding is one of the most important manufacturing processes, without which the daily lives of people in industrialized countries would be completely different. But the evidence in terms of our common experience with the products in our homes, offices, restaurants, hospitals and more, suggests very strongly that if injection molding were not available, we would have less varied, less functional, and more expensive products around us.

Injection molding is by far the most effective and economical process for high volume complex plastic component production.

In this blog you’ll learn how to determine whether it is the appropriate manufacturing process for your application by examining: 3 factors of the product being produced: 1. material, size, and complexity, 2. manufacturing economics, and 3. prototypes and low-volume production.

Injection Molding Factor 1: Material, size, and complexity.

Material

The most important parameter when considering injection molding is the material requirement: the application must demand a thermoplastic or thermoset material that can be molded in a closed tool.  For the purposes of this blog, we will focus on thermoplastic materials which are much more common than thermosets, except in certain electrical, chemical, and thermal applications.

Today the choice of thermoplastic resins is enormous and encompasses a broad range of mechanical, chemical, physical, aesthetic, and economic characteristics that make them suitable for everything from toothbrushes to car bumpers.

Moldable polymers can be practically the full spectrum of colors, may be flexible or stiff, extremely strong and tough, and may have excellent chemical resistance.  However, it is the incredible combination of these properties that a single polymer can exhibit that makes them the material of choice for so many injection molding applications[1].

Size

The next factor to evaluate when considering injection molding is the size of the component to be produced.

On the small end of the spectrum there are micro-molded components used in medical devices that weigh a few tenths of a gram and easily fit in a 5x5x5mm cube.  On the other end we find components for agricultural equipment weighing more than 100kg with maximum dimensions well over 1500mm.

The majority of injection molded components, measured in billions per year, are caps, closures, disposable / single use products, toys, and personal electronics to name a few applications, which generally weigh in the 1-500g range.

Statistically, the world produces billions of molded plastic components per year, even excluding packaging such as beverage bottles.

-plasticsinsights.com


Complexity

The degree of geometric complexity further influences the choice of manufacturing process.

Injection molding can produce components with thousands of features, complex textures, combinations of materials in different locations in the same component, and molded-in metallic components in the exact same time it would take to mold a completely plain, featureless, single material, similarly sized component.

While there are some geometric limitations based on the physics of a molten liquid polymer filling a metal mold, solidifying, and then cooling pre- and post-ejection from the mold, the geometric possibilities are, for all intents and purposes, limitless.

Injection Molding Factor 2: Manufacturing economics – how to evaluate value

Following material properties, component size, and complexity, the design engineer needs to consider the manufacturing economics of the application.

In its simplest form, manufacturing economics is the exercise of maximizing the rate of value creation versus invested capital (including direct material and labor expenses, as well as tooling and equipment investments).  Or seen another way: minimizing the fully burdened manufacturing cost per component.

For a given capital expenditure, the rate of production of complex polymer components by injection molding can be many multiples of other means of forming the same geometry. This is where injection molding dramatically separates itself from other processes.

Doing a bit of back-of-the-envelope math for our telephone handpiece cover, let’s say we have our hypothetical factory floor with a CNC mill, an industrial 3D printer (as distinct from a desktop 3D printer), and a standard production injection molding machine lined up ready to start production.

An average CNC mill for a component this size new would cost $100-$150k, the industrial 3D printer $50-75k, and the injection molding press including a four-cavity steel mold $175k ($75k of which is the mold).

Ignoring the extra cost of automated fixturing and robotics needed to run production volumes in CNC machining, and eliminating the time required to unload and post-process 3D printed parts, the following table suggests the relative production performance of injection molding:

Manufacturing Process Comparison:
CNC Milling vs. 3D Printing vs. Injection Molding
Example: manufacturing a plastic office telephone handpiece cover.

One could CNC mill an office telephone hand piece cover from a block of the desired ABS, which would take, at best, tens of minutes per part and would not have the required surface texture.

Or, this same hand piece could be 3D Printed in an ABS material with similar, but different, properties and have compromises in surface finish and dimensional accuracy at the rate of a few per hour.

Lastly, a hand piece could be injection-molded every 20-30 seconds with exactly the desired material properties, surface finish, and geometry. For even higher production rates, multi-cavity injection molding tools would be used to increase the effective production rate.

Injection Molding

So, in this very simplified example we can see that the relative economics measured in invested capital relative to production rate (CAPEX / PPD), is substantially better than our hypothetical printer and CNC mill.  If the example component had been the same size but much simpler geometry, then the mill might improve to being only 1/5th as economical (which would still not be viable).  Or if the part were substantially smaller, then the 3D printer might also close to within 2-3X the CAPEX/PPD range of molding.[1]

Injection Molding Factor 3: Injection molding for prototype and low-volume production

The traditional injection molding tool manufacture and molding process is rarely the correct choice for prototype and low volume production expressly due to the cost and lead time as noted in our example telephone hand piece.

However, this is precisely where Xcentric delivers enormous value to our customers by helping them bring their plastic products to market on time, on budget, and with lower risk.

Proprietary Process Engine: From CAD to Production, Faster

Technically, how we do this is to provide the component in the right quality at the right time for the current product development phase of the customer’s project.  So, if the customer needs one or two parts for form-and-fit testing at the beginning of the project and the material does not matter, 3D printing is likely the solution.

If the customer requires the component to be in the polymer that will be used in production and have the same geometry and mechanical properties as the production article for testing or initial launch production, then we select injection molding.

Xcentric, however, has developed a rapid injection molding proprietary process engine that reduces the time to design, manufacture, and try-out injection molding tools down to a few days.  This is orchestrated by our proprietary XMBM expert system supporting our team of experienced mold makers and molders.  Secondly our mold manufacturing process is optimized for high-quality aluminum tooling, which helps us to be extremely efficient.  This allows Xcentric to deliver injection molded components in the customer’s choice of polymer in quantities as low as 25 parts in under 15 business days, and for some components in under five (5) business days [3].

Low volume production, for the sake of argument defined as under 10,000 units per year, can easily be accommodated with the same aluminum tools we use for 25 prototype parts.  When production volume increases, the tools would be designed for automated operation, adding cost and lead time, but still far below traditional hardened steel tooling due to the efficiency of our in-house tool production technology.

Today, Xcentric is often supplying a customer with prototypes and preproduction parts in semi-automated aluminum tooling for testing and early market entry, and then transitioning directly into automated aluminum production tooling producing over 250,000 parts for the same project.  This seamless transition saves time and is economical for the customer, and ultimately allows the customer to get their product to market in volume earlier than with steel tooling.

Injection molding is currently by far the most effective process for high volume complex plastic component production.  The benefits of injection molding for producing complex components from myriad polymers at high rates with low waste make it essentially the only viable manufacturing process choice for most polymer parts used in consumer, medical, automotive, and many industrial applications.

[1] Given the scope of the materials topic, details about thermoplastics will be covered in a separate dedicated article.
[2] This scenario already suggests a production rate that is beyond current 3D printing technologies when post processing and surface finish are factored in.
[3] Some limitations in project type and additional fees apply for expedited projects.

Design Tip: How To Use Undercuts In Plastic Injection Molding

Why Use Undercuts When Designing For Plastic Injection Molding?

Undercuts achieve complex plastic part designs for the injection molding process. For example, overmolding and insert molding.

An undercut is any indentation or protrusion that prohibits part ejection from a mold. It is a feature that the cavity and core cannot capture alone. It is die-locked which prevents the part from being ejected from the cavity.

what is an undercut

Purpose of Undercuts In Plastic Injection Molding

Some of the more common ways to use undercuts:

  • Create interlocking or snap and latch features. This allows for clamshell or housing designs to come together for quick and easy assembly
  • Capture side holes or ports for wiring,and button features
  • Capture vertical threads and barb fittings. Barb fittings are typically used in medical device products
  • Core out thick sections not captured by the core and cavity alone. This prevents the possibility for sink and warp
  • Provide threaded and custom inserts that are not in the line of draw. The insert itself can sometimes create undercuts

Purpose of an undercut

 

A thorough DFM will identify problematic areas within the undercut features. Therefore, it’s best to design it as you intend it and to keep the functionality of your design.


DOWNLOAD: Designing for Manufacturability Ebook


Medical plastic parts

Undercuts are commonly used in medical parts. At left, is a medical part with some key features. The internal threads on this part use a side action to unscrew from the part. Continue threads throughout the entire interior of the part. This will prevent the interior hand load from being die-locked.

medical undercut

The space between the inlet ports require a special undercut called a core-out. Core-outs keep wall thickness even and are a planned aspect of the design. Barbs are complex undercuts for medical parts that are necessary for tubing. Most manufacturers will mold this so that the barb is parallel to the parting line. Xcentric uses a complex undercut that includes a pin assembly. This is to allow for venting and capturing the barbs perpendicular to the parting line. The venting will prevent gas trapping and air burning which creates short shots at the tip of the barb feature.

Consumer electronics

Below is a cell phone housing that contains many undercuts. All the holes located on the side of the housing, for example. These functional features include buttons, port holes and hinges. However, each undercut adds to the complexity of the mold.

Undercut in consumer goods

There are also some recessed areas that we call internal undercuts. These are areas inside the part that cannot be captured from outside the part. Internal undercuts can be the most difficult for a manufacturer to capture. Considerations must be made to allow enough space for their removal.

Design requirements

Consider the following requirements to help ensure success when designing undercuts. Only part features captured by hand loads or side actions have design requirements. The first requirement is space. Design your feature (button, port hole, etc.) with enough space to remove the hand load without obstruction. Otherwise, the hand load will be die-locked. This will make it impossible to remove.

Requirements for undercuts

Next, design your part so the molder can pinch the hand load or action with the cavity or core. This will result in a tight shut-off for reducing parting line flash. Finally, add enough draft to your undercut to ease removal from the mold.

Challenges with undercuts

One challenge with molding parts with underucts is a lack of draft. Non-drafted areas are difficlut to remove. Demolding parts with insufficient draft will make it difficult to remove the side action manually. Alternatively, the hand load can be coated with nickel-plating. This will allow for a more non-abrasive connection between the part and hand load. Thereby making removal easier. Certain materials can also be challenging when incorporating undercut features. Some materials, like glass filled plastics, are more difficult to pull from the mold. In general, the harder the material, the harder the pull. So, it is essential to put as much draft as possible when using these harder materials.

Undercut challenges

Finally, cosmetic surfaces with undercuts are difficult to maintain. This is due to increase parting line exposure from the hand load. One solution is to reduce the amount of parting lines on the outside. This is done with an internal undercut.

Undercut best practices

Undercuts add complexity cost to the mold. This is why we recommend eliminating them when possible. To achieve this, design part features that are perpendicular to the draw line.

Undecuts best practices

We use hand loads for speed and time to market. This also depends on the part geometry or whether or not it is an external or internal undercut. The auto-slide is implemented based on a longer cycle  production to reduce overall per part cost. If speed is essential, we use manual hand loads.

 

Interested in obtaining more advice? Reach a Technical Engineer at sales@xcentricmold.com, or call (586) 589-4636

Learn More About Injection Molding with These Animations

Learn More About Injection Molding with These Animations

You’ve likely read about and understand custom injection molding. But there may be some terminology that you just need to visualize.  Watch what insert molding, overmolding and undercuts are all about and how you can utilize these injection molding features to help with your part design.

What is an Undercut?

What is Insert Molding?

What is Overmolding?

Get Overmolded and insert molded parts with unlimited undercuts fast!
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Xcentric Mold vs. 3D Printed Mold

Xcentric Mold vs. 3D Printed Mold

How do 3D printing molds match-up against Xcentric’s Advanced Mold Making and Proprietary Process Engine?

3D printing has come a long way in recent years.  According to IBIS World, it is currently a $492.4 million market and is expected to grow by 80% over the next five years.  This sort of growth will open up all kinds of new applications for 3D printing.  In fact, NASA has already experimented with using this technology with the hope that they can begin to establish on-demand machine shops…in space.  We’ll be doing the Kessel Run in under 12 parsecs in no time.  🙂
So, at this point, what can’t 3D printing do?
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