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!

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.

Overmolding Tips: Save Time & Money

Overmolding Tips: Save Time & Money

Overmolding Tips: How to Save Time and Money When Designing For Overmolding

Overmolding is a process where a single part is created using two or more different materials in combination. The first material, often referred to as the substrate, is partially or fully covered by another material (overmold material) during the manufacturing process.  A wide range of materials are capable of being overmolded, including both hard and soft plastic resins.

Typically a substrate material or part is placed into an injection molding tool at which point the overmold material is shot into, onto, or around the substrate. When the overmold material  solidifies, the two materials become joined together as a single part.

Overmolding on a simple injection-molded part

Customers frequently request to make overmolding layers thinner than 1 mm for TPE (thermoplastic elastomer) “soft touch” overlays.  When we inquire as to why they are requesting this specification, we often hear that they are solely requesting this in order to save money on material costs or simply have no specific reason.  Such thin sections are a common source of issues. Not only is the “soft touch” feeling so slight that it cannot be noticed, but sections that are too thin do not allow the material to flow properly and adhere to the substrate. If not properly planned for upfront, lack of correct thickness can result in rework and spending significantly more time and money than originally thought.

Issues related to thin overmolding layers can sometimes be resolved by adding gates to the overmold which increases the L/T (length over thickness) ratio.  If gates are not an option, too thin of a wall will require reworking the part design adding costs, time and labor.  If a thin TPE layer “freezes up” during the injection molding process, it is not uncommon to have to rework both the substrate tool and the overmold tool and rerun the part.  Discuss your expectations early in the design process with our technical experts in order to ensure the best possible outcome for your product’s success.

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

For more information about overmolding, please watch our webinars.

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 .