Mold Better Plastic Parts | 3 Key Considerations

Mold Better Plastic Parts | 3 Key Considerations

Want to Mold Better Plastic Parts? Keep These 3 Factors Top-of-Mind

Material selection, manufacturability & moldability, and proof-of-concept validation. These are 3 considerations that should be top-of-mind for every product designer and engineer who want to mold better plastic parts.

In this blog we provide an overview of these 3 critical areas with troubleshooting questions and supporting design guides to help optimize your plastic parts for the injection molding process.

As always, Xcentric’s team of experienced design consultants and application engineers are available to guide you from idea to production. Contact us any time at 586-598-4636 or

Material, Manufacturability and Moldability, and Proofs-of-Concept Help Achieve Perfect Plastic Parts

Achieving your design intent for fit, form, and function is not easy. Though there are many variables to consider when designing parts for plastic injection molding, these three factors can help produce your end product on time and on budget with less risk.

Material Selection

Material is one of the most important variables when designing for plastic injection molding. This is because it impacts nearly every aspect of your plastic part.

For instance, the look and feel of the surface finish, the part’s strength and durability, and it’s chemical or environmental resistance are all driven by the polymer chosen. And, if you are designing for medical or healthcare, the material must meet stricter use criteria and regulations.

For many applications, choosing an injection molding partner with an inventory of stock plastic material can help reduce cost and speed time-to-market.

Xcentric’s material experts compiled a list of 6 Common Plastic Resins complete with advantages and disadvantages. For a larger list of polymer options, check out Xcentric’s current stock material inventory.

Here are some questions to help guide you through the material selection process:

1. What is the expected use?

  • Will the parts need to be flexible or rigid?
  • Will parts need to withstand extreme pressure or weight? How frequently?
  • Will the parts be exposed to extreme temperature, chemicals, or moisture?

2. What are expectations for surface finish and texture?

  • What finish is required? Will the finish impact performance – for example, slip resistance, glare reduction, or UV protection.
  • Is color matching required?
  • Will text be printed on the parts? Is embossing required?
  • Will your part require overmolding?

3. Are there regulatory requirements?

  • Are you designing medical parts for implantation?
  • Will parts need to withstand repeated sterilization?
  • Will parts need to be approved by the FDA? Will the end products be used by children or pets?

Free 8-Piece Surface Finish Sample Kit

Xcentric’s 8-piece sample kit can help you choose the optimal surface finish for your material.

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Manufacturability and Moldability

We take for granted that the plastic products we use in everyday life will function as intended. But designing for injection molding is a tricky process. Analyzing for manufacturability and moldability can help to ensure your parts can be manufactured.

Manufacturability (DFM): Part-centric optimization

A DFM analysis ensures that your part design can be manufactured. DFM addresses a wide range of considerations includes wall thickness, material shrinkage, draft angles, and undercuts for example.

Identifying these issues early in the product development process can help to mitigate the risk of part failure that results in expensive redesigns and time delays.

Once your part is designed for manufacturability, the next step is to ensure it can be produced using the injection molding process. This is done by analyzing the tool for moldability.

Moldability: tool- and process-centric optimization

Complex geometries and part features like undercuts and threading can be a challenge to mold consistently. Designing for moldability, which is tool- and process-centric, ensures the tool will be able to produce your part to the desired fit, form, and function using the injection molding process.

One way to make this determination is with a Mold Flow analysis.

Mold flow analysis

Mold flow analysis is software that simulates an injection molding cycle using your specific material and design parameters. It provides a variety of diagnostic reports that provide mold designers insight into how well the plastic will fill the mold cavity. It also enables them to identify and predict potential flaws that would otherwise result in expensive design changes and time delays.

The analysis runs a variety of diagnostic reports to provide critical data such as Fill Time, Plastic Flow, Confidence of Fill, and Quality Prediction.

The final consideration that can help you to mold better parts is following the rapid prototype process to create a realistic proof-of-concept.

Don’t skip the proof-of-concept prototype! 

Rapid prototyping is the process of using a manufacturing technique, like injection molding or 3D printing, to create a realistic proof-of-concept prototype of your end product. It enables product designers to move quickly from CAD to physical part or assembly to testing and provides invaluable information to support creation of production tooling.

The proof-of-concept is analyzed for fit, form, and function in real-world testing and then iterated on based on performance. Once testing and validation are complete, and any modifications required are made, the design can be moved to production with confidence.


Evaluation of material selection, performing manufacturability and moldability analyses, and validating a physical proof-of-concept will go a long way to ensuring your plastic part achieves its design intent.

We’ve included links in this blog to resources that will help you dive deeper into each of the three factors.

Xcentric is always here to support our customers from ideation through production. Get us involved early in the process so we can help bring your concepts to market faster than ever.

Working on a project?

Let us help you get that first prototype underway and have that part in your hands in as few as five days. Our engineers help you through the design process. Get your project started now!

6 Common Plastic Resins for Injection Molding

6 Common Plastic Resins for Injection Molding

6 Common Plastic Resins For Injection Molding

There are hundreds of plastic resins on the market. Each one with unique properties, advantages, and disadvantages. Which can make material selection a bit overwhelming.

Never fear. Xcentric’s team of material experts are here to help!

We have extensive experience working with plastic resins. And we understand how different properties can impact your parts—during and after production.

In this blog we provide details for 6 common plastic resins used in the injection molding process. You can also download the Quick Guide for easy access.

Quick Guide: 6 Common Plastic Resins

Injection Molding

ABS: Acrylonitrile Butadiene Styrene

As far as plastic resins go, ABS is by far one of the most popular and versatile. It’s an affordable, highly moldable engineering plastic with mechanical and electrical properties that make it one of the most widely used thermoplastics in the world.

With ABS you get the collective benefits and properties of three monomers. It combines the strength and rigidity of acrylonitrile and styrene polymers with the toughness of polybutadiene to deliver superior hardness and toughness.

In addition, ABS provides a colorfast, high-gloss surface finish. Finally, this resin has excellent stress, impact, creep, and heat resistance. It can be heated, cooled, and re-heated without changing its characteristics.

Common applications include:

  • Small appliances
  • Medical device
  • Enclosures for electronics and electronic assemblies
  • Office equipment
  • Toys

Design Considerations

Parts molded with ABS are susceptible to forming knit lines. Knit lines are visible lines on the surface of the part. One solution is to use optimal wall thickness to help slow cooling. Recommended wall thickness for ABS is 0.045 in. – 0.140 in.

Medical part molded using ABS plastic resin.

Advantages and Disadvantages of ABS Plastic Resins

Understanding the advantages and disadvantages will help you make an informed decision for your product design.


  • Structural/Dimensional stability
  • High impact resistance
  • High rigidity and strength
  • Heat and chemical resistance
  • Abrasion and stain resistance
  • Surface brightness and high-gloss finish


  • Maximum continuous use temperature approx. 70 °C ( 160 °F )
  • Poor solvent and fatigue resistance
  • Poor UV resistance unless protected
  • Poor bearing properties (high friction and wear)
  • High smoke evolution

PC: Polycarbonate

PC polymers are amorphous engineering thermoplastics with a toughness down to -20°C. They are naturally transparent and can transmit over 90% of light as good as glass.

Because of these properties, polycarbonate resins are often used as a light-weight alternative to glass. PC is also a good choice for high-impact resistance requirements.

Some applications include:

  • Bullet-proof glass
  • Medical device components
  • Light fixtures
  • Green houses

In addition, PC is a natural UV filter which makes it an optimal material for eyewear.

Another feature of PC is its pliability. In fact, it can often be processed at room temperature without breaking or cracking. This property makes it a popular material for prototyping—especially when transparency is required.

Design Considerations

Though it provides outstanding impact resistance, polycarbonate is susceptible to scratching. Therefore, for applications where this will be an issue, consider adding a scratch-resistant coating.

Advantages and Disadvantages of Polycarbonate Plastic Resins

PC is a great light-weight alternative to glass. It is a popular plastic that provides product designers flexibility in their part designs.

Still, there are some disadvantages that may eliminate PC from your material selection process. Here are some advantages and disadvantages of PC to consider.


  • High impact strength and toughness down to -20°C
  • Naturally transparent. Can transmit over 90% of light as good as glass
  • Can be designed to 100% protection from harmful UV rays
  • High dimensional stability
  • Pliable at room temperature without breaking or cracking. Good for prototyping
  • Good Heat resistance and thermally stable up to 135°C


  • Though resistant to high impact, PC plastics are susceptible to scratching
  • Considered hazardous for food the release of Bishphenol A (BPA)

PC/ABS: Polycarbonate-ABS

PC-ABS is one of the most widely used industrial-grade thermoplastics. It is a high-impact engineering polymer that combines the strength and heat-resistance of polycarbonate with the flexibility and high-quality surface finish of ABS.

In addition, PC/ABS plastic provides improved processing during the injection molding process. Product designers and engineers often choose it for functional prototyping, tooling, and low-volume manufacturing. This because PC/ABS is likely to provide stronger parts and prototypes that mimic the material properties of the final product.

Advantages and Disadvantages of PC/ABS Plastic Resins

Though PC/ABS can provide the best properties of two polymers, it is critical to understand key pros and cons to ensure it will achieve your fit, form, and function.


  • High impact strength even at low temperatures
  • Heat resistance
  • High stiffness
  • Easy processing
  • Low overall shrinkage and high dimensional accuracy


  • Poor solvent resistance
  • Low dielectric strength (not a good insulator)
  • Low continuous service temp. (melts easily)

|Download: Quick Guide: 6 Common Plastics for Injection Molding

PP: Polypropylene

Polypropylene is a crystalline thermoplastic. It is tough, flexible, and provides outstanding heat and chemical resistance. It’s one of the cheapest plastic resins available. PP is used both as a plastic an a fiber.

Applications include:

  • Automotive manufacturing
  • Furniture assembly
  • Textiles
  • Aerospace

 In addition, PP is a good option for special parts like living hinges.

Design Consideration

PP may be the cheapest resin, but that doesn’t mean it will always meet your requirements. For example, if your part requires impact resistance properties, consider PC/ABS instead.

Medical fluid delivery component molded with PP.

“I worked with a customer recently who wanted to use polypropylene because it was the most expensive option. But after reviewing the part, I realized it was multi-part assembly that would be at risk of being dropped. So I suggested PC/ABS instead because it will provide more structural integrity and impact resistance than PP.” 

Drew Davis, Application Engineer at Xcentric

Advantages and Disadvantages of Polypropylene Plastic Resins

Polypropylene will likley be the cheapest option. But that doesn’t always make it the best choice for your injection molding project. In fact, selecting the wrong material can add to your production costs in the end.

Instead, consider these pros and cons of using polypropylene before making a material selection.


  • High impact strength even at low temperatures
  • Heat resistance
  • High stiffness
  • Easy processing
  • Low overall shrinkage and high dimensional accuracy


  • Poor solvent resistance
  • Low dielectric strength (not a good insulator)
  • Low continuous service temp. (melts easily)


Nylon is a semi-crystalline polyamide with low density and high thermal stability. Polyamides are a group of technical thermoplastics with properties that range from the hard and tough PA 66 to the soft and flexible PA 12, for example.

In general, nylon plastic resins provide fantastic wear resistance, good coefficient of friction, and very good temperature and impact properties. Further, nylon also provides chemical resistance and has proven to be a good oil resistant plastic.

This balance of properties make nylon a good candidate for metal replacement in some applications that require toughness and weight reduction. For instance, automotive parts and industrial components.

Design Considerations:

Nylon absorbs water. So if your part will be exposed to moisture, nylon may not be the ideal plastic because it could damage the dimensional and structural integrity.

Advantages and Disadvantages of Nylon

Nylon is easy to process and can be a cost-effective solution for your injection molding project. Like all of the plastic resins on our list, it’s important to understand how the properties will impact your design intent.


  • Excellent abrasion & wear resistance
  • High tensile and compressive strength
  • Low coefficient of friction.
  • Lightweight option that’s 1/7th the weight of conventional materials
  • Easy to machine


  • High shrinkage in molded sections
  • Lack of stability
  • Does not absorb water well

POM: Polyoxymethylene (Acetal)

POM, also known as acetal, is a naturally white semi-crystalline engineering thermoplastic and is characterized by its high rigidity to −40 °C. It is used in the injection molding process to produce parts that require high precision, stiffness, and low friction. It has excellent dimensional stability and resistance to abrasion, heat, water absorption, and creep.

Because of its low coefficient of friction, POM is good material choice for producing high-performance engineering components, medical equipment, and electrical housings. By nature, POM is a slippery material, which makes it a good fit for products that require sliding mechanisms and gears.

It is important to note that POM has a very high shrink rate of about 2%.

Design Consideration

If you are designing parts that have large variations in wall thicknesses, POM can be dimensionally unstable. Large parts molded with POM are more likely to experience warping than smaller parts. Therefore, consider adding fillets or strengthening ribs.

Advantages and Disadvantages of POM Plastic Resins

POM is one of the most common plastics used in the injection molding process. Here are some advantages and disadvantages to help determine whether POM is right for your achieving your design intent.


  • High strength
  • Rigidity to -40C
  • High resistance to impact, creep, abrasion, and solvent
  • Good  fatigue endurance and low coefficient of friction


  • High shrinkage of about 2%
  • Very poor resistance to UV radiation
  • Poor resistance to acids/alkalies
  • Burns easily, is not available with flame retardants
  • Does not absorb water well


Don’t be discouraged when choosing a plastic resin for your part design. Xcentric can  help guide you through the process to help bring your concepts to life faster and on budget. Get connected with an Xcentric team member today: or 586-598-4636. If you you’re ready to get started with a project, simply upload your part to request a custom quote

Lifetime Mold Guarantee | Xcentric | Since 1996

Lifetime Mold Guarantee | Xcentric | Since 1996

We often get asked about our Lifetime Mold Guarantee.  What is it?  How does it work?

Xcentric offers a Lifetime Mold Guarantee at no extra cost to you for the life of your project. We stand behind every mold we build and run.

plastic injection molding

Features and benefits of the Lifetime Mold Guarantee include:

  • No Part Quantity Limits – There are no part quantity limits for the life of your project.
  • High Quality Mold Components – We are committed to providing you with only the highest quality mold components.
  • Proactive Mold Maintenance – With our U.S. based tool room, we proactively maintain your mold. Each mold is serviced each time prior to and after running a project; saving you time and money.
  • All Parts Are Run on Electric Mold Machines – Our all-electric machines have the benefit of running at a higher speed and are more efficient throughout the entire production process. Independent motors and sensors control the process and prevent damage to the mold.
  • Our Propriety Process Engine is utilized to prevent part overshot and applying too much pressure in the cavity which can potentially break mold features.

For additional information regarding our Lifetime Mold Guarantee, contact one of our Technical Specialists today at 586-598-4636 or

Expanded CNC Capabilities

We have expanded our current CNC machining capabilities.  In order to precisely create your simple-to-complex parts, we offer the following:
  • Facilities with expanded 5-axis CNC machining centers
  • 3, 4 and 5 axis machines that save you time and money
  • Metal or plastic parts
  • A variety of surface finishes are available
  • Unlimited undercuts
  • Threads and holes
  • Our advanced processes give you competitive pricing and quick turnaround times
  • Parts up to 24” x 36” x 7”
  • ISO 9001: 2015, UL/ITAR
Would you like additional information on our CNC capabilities?  Contact our Technical Specialists today at 586-598-4636 or    
Draft Angles Can Improve Plastic Part Designs

Draft Angles Can Improve Plastic Part Designs

How Draft Can Help To Improve Plastic Injection-Molded Parts

Draft is an angle incorporated into your plastic part design to aid in the ejection process.

Optimize part designs early

Plastic parts should be designed with draft to prevent sticking and ejector pin push marks on the outward surface during ejection. Applying the proper draft angles or tapers on the surface of an injection molded part is critical to part moldability. Often times, draft is not considered when prototyping with CNC machining or 3D printing. It should be considered when either one of these prototypes will ultimately be injection molded. Not incorporating draft into your design upfront can directly result in costing more time and money later on in the manufacturing process.

Potential Pitfalls of Not Including Draft

Without draft being included in the design, parts may bend, have poor surface finishes, break, or warp due to stresses on the molded part. Which, if not dealth with can lead to sticking, breaking, surface finish imperfections and a variety of other issues causing manufacturing delays. In addition, the absence of draft may also damage the mold itself. You do not want your part to look like the photo below.

draft imperfections in injection molding

Proper planning can assist in avoiding costly mistakes.

Best Practices 

Although there is not one set draft angle for all plastic injection molded parts, below are some general guidelines:

• 0.5° on vertical applications
• 1.5° to 2° per side are standard for plastic injection molding
• 3° for light texture or shutoff (metal sliding on metal)
• 5° or more for a heavy texture

A good guideline is 1° of draft per 1” of cavity depth however keep in mind that a variety of factors will influence this such as material selection, wall thickness, shrink rates and manufacturing capabilities.

Draft best practices for injection molding

Do you questions or concerns about draft? Upload your design today at or let one of our Technical Experts assist you by contacting us a 586-598-4636 or email It is a good way of avoiding future moldability issues.

For additional information on draft, click draft.

Celling Biosciences Receives Complex Parts in 30 Days

Celling Biosciences Receives Complex Parts in 30 Days

Celling Biosciences Recieves Complex Plastic Parts in 30 Days

Medical and scientific devices pose three key challenges for companies like Celling Biosciences: time, quality, and cost. On one hand, to build a reputation for leadership in the closely watched biotech industry, you have to launch innovative products before your competitors can do likewise. On the other hand, if you can’t manufacture high-quality injection molding parts with complex geometries at market acceptable prices, you lose to those who can. Those were the concerns of Celling Biosciences’ engineering team in Austin, Texas when they sought for competitive bids to manufacture parts for a new clinical blood-therapy device.

Complex Geometries Are Difficult to Produce

In late 2017, Medical Design Engineer Jay Jones was issuing bid packages for this project. He had identified three competent parts manufacturers. Among them was  Xcentric Mold & Engineering. He first heard about Xcentric from a colleague: “You just have to try them,” he was told. And by late 2017, he had already used Xcentric on more than one occasion to successfully produce parts that incorporated increasing levels of design complexity. But now he had something that was very difficult produce. Celling Biosciences’ new blood-processor — called the Autologous Regenerative Therapies (ART) Two-Step Platelet Rich Plasma (PRP) device — had all the hallmarks of a serious production challenge.

Jay had reduced the number of components in the design from 23 to 8 but making some of these parts would not be easy. One mold was quite simple, producing the orange thumb wheel positioned on the top of the final product. The mold for the transparent base component, however, incorporated geometries requiring complex mold features such as threaded inserts, slides, and multiple hand loads — the stuff any engineer would acknowledge as a real test for an injection molded parts supplier. Accuracy, quality, and adherence to tight tolerances were absolutely necessary to create a final product that clinical labs would buy and rely on for day-to-day safe and reliable operation

Overnight Quote and Injection Molded Parts in 30 Days

The team at Celling Biosciences also understood the impact of launch dates on profitability.  Their existing parts suppliers would normally take from four to six weeks to develop a quote in response to a bid package. Although that kind of lead time is built into a typical product launch by medical device companies, it doesn’t help the bottom line, and nobody has to like it. Other suppliers would decline or request multiple concessions on complex designs. So after uploading their design files to three bidders, the team was astonished when Xcentric responded overnight with a bid and zero design change requests.

By comparison, one of the other two bidders responded in four weeks, and the last bid came in after six weeks had passed. So on the bid process alone, Xcentric had saved Celling Biosciences a significant amount of lead time. But that wasn’t the end of the story.

After conferring with his colleagues at Celling Biosciences, Jay accepted the bid from Xcentric Mold & Engineering. The contract called for the creation of aluminum molds and production of parts made from a PC/ABS blend. Expectations were for a low- to mid-volume production flow, around 3,000 parts per year.

celling bioscience

Figure 1. The ART Two-Step PRP

This was the first time that Celling Biosciences had awarded a product with such complex geometries to Xcentric Mold & Engineering, so Jay had the usual sense of anticipation about delivery of the final product. His previous experiences with Xcentric, however, had been excellent, and he was confident that they would be able to handle the complex geometries in the ART Two-Step PRP. But he was unprepared for the fast production turnaround. Xcentric delivered the “first shots” (the first production parts) to his office within 30 days — including delivery time! Jay put it into his own words: “I was holding the finished product only a week after the second bidder sent a quote and two weeks before the last bidder responded! It’s the kind of timetable nobody in the industry can match.”

Complex Geometries at the Right Price

Despite the complex geometries of Jay’s design, Xcentric had fulfilled its promise of a fast turnaround for customers:

“No matter the complexity of your design or the quantity of your order, Xcentric can deliver a wide variety of plastic and metal custom parts in as fast as 1-15 days.”

The final success factor was the low cost of the Xcentric bid. The company had delivered a complex, high-quality product at a lower cost than competing bidders, while maintaining the whole production chain in the United States. Taken as a whole, Xcentric helped Celling Biosciences bring a complex product much earlier to commercial stage and within budget.

If you are interested in receiving more information, contact us at or 586-598-4636.

For more information on injection molding, click injection molding .