Injection Molding

Low Volume Injection Molding: Process and Tips Explained

low volume injection molding

Industries that deal with plastic products operate on a competitive ground and getting a product to market on time may determine your success. As a result, many businesses are leveraging low-volume injection molding technology to produce a small number of plastic products in the shortest time.

Low-volume plastic molding has a widespread use across various industries. However, it is important to understand what it entails and when to use it. This article discusses how low-volume plastic injection molding works, its benefits, and tips for a seamless process.

What is Low Volume Injection Molding?

Low-volume injection molding is a rapid manufacturing process that produces a small number of plastic parts in a single production run. It follows the typical injection molding process, i.e., melting the plastic material, injecting it into a mold, cooling so the molten plastic takes the mold shape, and ejection.

It has a widespread use in rapid prototyping and short-run manufacturing. On the one hand, in rapid prototyping, low-volume plastic parts are made to test their final product’s functionality and aesthetic value. On the other hand, in short-run manufacturing, low-volume plastic molding is applicable in making parts of small volume to put them into the market faster.

injection molding process

How Does Low Volume Injection Molding Work?

The process involved in low-volume plastic molding is similar to that of traditional injection molding. It includes the steps explained below:

Mold Design and Manufacturing

The first step in low-volume injection molding is to design the mold. Afterward, the mold and its components are made using 3D printing or CNC machining. After manufacturing the mold, parts like the ejector system are installed and the mold is loaded on an injection molding machine.

Mold Clamping

Now, use the clamping system of your choice to hold the mold in place. Close the gap between the mold halves.

Note: the clamping force should be equal to the injection force for the mold to prevent disruptive movement.

Injection and Cooling

The operator places plastic pellets inside the injection barrel. As the plastic melts in the barrel, it is mechanically forced into the mold cavity. The plastic material cools and solidifies in the mold cavity depending on the plastic type.

Demolding and Finishing

As the clamping plate moves backward, the mold halves open and the ejector pin pushes out the final part. You can apply release agents in cases of undercut injection molding. Trim off excess plastic and use suitable finishing processes as needed.

Benefits of Low-Volume Plastic Injection Molding

The following are some of the many benefits of using low-volume plastic injection molding for manufacturing.

injection mold

Cheaper Mold Cost

The mold tooling costs short run injection molding are comparatively lower. Unlike the traditional injection molding process that uses hardened steel, low-volume injection molding uses aluminum which is a more economical approach.

Quick Turnaround Time

Small-batch plastic injection molding ensures a quick turnaround time. With this process, you can complete an order on time and start making sales immediately.


Low-volume injection molding offers flexibility in manufacturing. Machinists can easily adjust designs without a huge financial burden to produce more complex parts. Furthermore, it serves to test a product before mass production. This is because one can receive feedback on how to improve a part’s functionality.

High-Quality Parts

The use of this technique is particularly advantageous when producing high-quality parts with lustrous surface finish. Aluminum molds peculiar to low-volume plastic molding dissipate heat faster than steel molds. As a result, low-volume plastic parts have fewer defects because of their fast-cooling rate.

Considerations and Tips for Low-Volume Injection Molding

Though low-volume plastic molding is an efficient manufacturing process, it is important to maximize it and get the most out of your investment. Here are some tips to consider when using this technique.

Choose the Right Injection Molding Material

Getting the most out of low-volume injection molding involves using the right thermoplastic. You should consider the application of the intended part and use it to choose a material with the perfect functional properties (such as strength, thermal/chemical resistance, durability) and aesthetic properties (e.g., color).

Optimize Wall Thickness

Wall thickness should be consistent (0.04-0.14 inches) across the low-volume plastic part. Thick walls can lead to warping, sinking or other defects while thin walls have lesser structural integrity, are sensitive to temperature changes, and are prone to defects such as warping.

Remove Sharp Internal Corners

Sharp internal corners can compromise the injection molded part’s integrity. As a result, it is better to use vertexes or rounded edges (radii) for improved moldability.

Use Draft Angles

Using draft angles creates low injection molded parts with tapered edges, reduces friction during demolding, and prevents mold/part damage. As a result, this will enable easier removal from the mold.

small batch plastic injection molding

How to Choose the Right Low-Volume Injection Molding Manufacturer?

The professional low-volume plastic molding manufacturer will streamline the whole process and make everything easier. Consider the following factors before choosing a third-party manufacturer.


The ideal contract manufacturer should have enough experience and industry knowledge. An experienced manufacturer will have relevant skills, advanced knowledge, and the capability to produce quality parts. Additionally, they must have a record of accomplishment in meeting injection molding tolerance.

Production Capabilities

The right low-volume injection molding service should be able to achieve the maximum possible output for small-scale or medium-scale production. Furthermore, the company should have the right equipment and be able to scale up when needed.

Cost Considerations

One of the reasons most people use low-volume injection molding is to cut costs. You may want to choose a contract manufacturer that fits into your budget. Different companies have different prices. However, one should not compromise quality to reduce injection molding costs.

Supply Chain Management

The company you are going for must carefully manage every aspect of business that involves procuring raw materials and other resources. A properly managed supply chain prevents the incidence of recall and associated costs. Additionally, it helps to avoid delays and under or oversupply of materials.

Customer Service and Communication

Make sure that the injection molding company offers 24/7 customer service and support even after the contract has ended. Additionally, the company must keep you updated throughout the manufacturing process. They should not tamper with your designs without adequate communication.

Low-Volume Injection Molding Applications

From medical to automotive, many industries use low-volume injection molding for diverse reasons. The technology is applicable in the following ways.

Bridge Manufacturing

Low-volume injection molding is a means of scaling up manufacturing and production. It serves as a gap between prototyping and large-scale production. By starting with small quantities, you check how the products are doing. If the response is favorable and demand increases, manufacturing more parts is easier as the most important tools and equipment are in place already.

Producing Smaller Series of Products

For businesses new in the industry, low-volume plastic injection molding is ideal for short-run production. Companies may not have enough capital to start large-scale production. In manufacturing, the less you make, the less you spend. When introducing a new product, this technique shortens lead times and minimum investment.

Making Specialty Products

Low-volume plastic injection molding serves as a means of manufacturing custom products or specialty products, i.e., products with unique designs that are peculiar to a company. The manufacturers often adjust the mold designs to accommodate additional features, specifications, and drawings. Using low-volume injection molding increases productivity and enhances the quality of a product.

low volume plastic parts

Low-volume vs. High-volume injection molding: What are the Differences?

The differences between low-volume vs high-volume injection molding are straightforward. The following factors make the two processes distinct

Production Capacity

The main difference between high and low-volume injection molding is the production quantity. Low-volume plastic injection molding comes in a limited quantity and may range between 100 to 10,000 parts. On the other hand, high-volume injection molding produces 10,000 parts and above.

Mold Type

The type of mold tooling can also be a difference. Oftentimes, steel molds are used for high-volume plastic injection molding. This is because steel is stronger and reusable. Aluminum molds are common with low-volume injection molding. Aluminum is softer and less expensive. Additionally, it is easier to machine aluminum so production can start almost immediately.


A key difference between high and low-volume plastic injection molding is the level of automation it requires. High-volume injection molding needs to be highly automated. It works continuously to increase production.

Unit Costs

High-volume injection molding reduces the cost of a single part. Most manufacturers give discounts as the number of parts increases. Producing in large quantities is more economical and helps you make more profits in the long run.

XinCheng Offers Low-volume Injection Molding Services

Looking for low-volume plastic injection molding services? XinCheng is your reliable custom injection molding service provider. We employ advanced mold design and engineering techniques to ensure the production of high-precision components with tight tolerances.

At XinCheng, we work closely with our customers to understand their specifications and design requirements. We also have professional engineering support in every stage of low-volume injection molding manufacturing for your projects.


Injection molding has been known as a mass-production technique for years. This definition has changed as one can now use it to produce small quantities of plastic parts. This reduced number of parts increases efficiency and shortens lead times.


What is the minimum quantity for injection molding?

The standard minimum quantity for injection molding is 500 parts.

How much does a low-volume injection mold cost?

The cost of a low-volume injection mold varies and may depend on the manufacturing technique used, the size, and the complexity of the design. It can range from $100 to $100,000.

What is shot capacity in injection molding?

Shot capacity, commonly referred to as injection capacity, is the total volume of the plastic material that the screw injects into the mold in one cycle.

Which mold is used for low-quantity work?

You can use either a single or multi-cavity aluminum mold for low-quantity orders. Single cavity injection mold produces a single unit and is preferred. Multi-cavity mold creates more than one part and speeds up production.

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Factors to Affect Injection Molding Cost and How to Reduce it?

injection molding cost

Injection molding is one of the most used manufacturing processes, especially for creating plastic parts and components. The highly versatile technique creates simple and complex parts with high precision and supports an extensive material option.

However, the plastic injection molding process may be pretty expensive. But some will tell you otherwise – injection molding is cost-effective, especially compared to other manufacturing methods. So, which of these is true? Injection molding costs could vary depending on a series of production factors.

This article gives a detailed review of the different factors influencing plastic injection molding costs and how to cut down these costs, including a typical quantities analysis of the cost per part of an injection molding project.

injection molding plastic parts

Factors That Affect Injection Molding Costs

There are several intricacies influencing injection molding costs, ranging from the parts you are fabricating, tooling costs, choice of materials, surface finishing, and even operator costs.

This section will carefully explore each factor that impacts the cost of injection molding. Let’s check.

1. Part’s Cost

The cost of the parts you are molding depends on various factors such as size and design complexity. Therefore, a clear understanding of how each influences the part’s cost may provide insights into optimizing the overall cost of injection molding.

Design Complexity

Regarding injection molding, the simple design principle is paramount. The rule is straightforward, encompassing all aspects of manufacturing, including injection molding: the more intricate the design, the higher the fabrication cost. To relate it more to injection molding, creating complex parts, will require the manufacturer to craft complex molds that suit such parts.

Therefore, we recommend careful examination of your design intricacies and corresponding mold requirements before injection molding. Any design intricacies that are considered unnecessary can be removed to promote cost-effective production.

Part’s Size

Understanding how the size of the part you are injection molding impacts manufacturing costs is also important. As a general rule, larger components incur higher injection molding expenses. In common, injection molding larger components requires more sophisticated injection molding devices and molds. Moreover, larger parts will utilize more production cycle times, increasing costs further.

plastic injection mold

2. Tooling Costs

The costs of the tools used in injection molding depend on a series of other factors. These include the choice of manufacturing process for mold creation, the material used, mold size, and complexity.

Choice of Manufacturing Process for Mold

Generally, injection molding molds are created via any of these processes: CNC machining, 3D printing, or EDM machining.

  • CNC Machining Molds: CNC machining is one of the most versatile manufacturing processes, suitable for high-precision parts fabrication. This process allows machinists to create durable steel or aluminum injection molds, regardless of design complexities.
  • 3D Printing Molds: 3D printing is suitable for creating almost all structures and parts. However, it produces less durable injection molds at a reduced cost. Therefore, it suits when manufacturers intend to test a part’s suitability before proceeding with bulk-volume part production. The go-to operation for creating 3D-printed injection molds is stereolithography (SLA).
  • EDM Molds: Electrical Discharge Machining (EDM) is an assertive technology specifically designed for processing complex and fine features. It’s a high-precision subtractive manufacturing process that ensures the meticulous creation of the mold, paying attention to all intricate details. It is reliable for creating molds from hard conductive metals and alloys, regardless of intricate design and tight tolerance specifications.

Mold Material

Typically, injection molds are fabricated using steel and aluminum. How the selected material affects the injection molding price is pretty straightforward. Both materials are excellent choices for manufacturing parts. However, steel has superior mechanical properties, mainly its toughness and durability, making it a better choice for bulk-volume injection molding.

Mold Design

As we know, molding for complex parts will require precision machining with a high level of expertise in creation. Therefore, such molds are more expensive than those for simpler details, shapes, and structures. Generally, manufacturers prefer to work with an aluminum mold when fabricating complex parts to save costs. Moreover, aluminum is more straightforward to machine and has reduced maintenance costs.

Mold Size

The size of the mold cavity is another factor that influences injection molding tooling costs. Manufacturing time and costs increase with increasing mold size. Also, the number of mold cavities affects the tooling and eventual injection molding costs. This is also straightforward: molds with single cavities are easier to fabricate with less time than those with multiple cavities.

3. Labor Costs

Like other factors we have discussed thus far, labor costs influence injection molding differently.

Operator Cost

While the injection molding process is almost automated, you still need an expert to oversee the entire process. This personnel will require remuneration, depending on their level of expertise.

Setup Costs

The costs of purchasing, configuring, and setting up an injection molding device influence the cost of injection molding. You’ll expect a business that uses advanced machines to charge a higher injection molding price than those that use basic ones.

Repair and Maintenance Costs

Besides the machine setup cost and operator’s remuneration, the machine will require routine servicing. This, among other repairs and replacing of faulty parts, also influences the cost per part of injection molded components.

plastic material for injection molding

4. Injection Molding Material

Indeed, injection molding is typically used to create plastic parts, which are relatively cheap compared to metals. Still, there is a variation, often based on their properties, availability, and usability. These factors influence the cost per kilogram of injection molding plastics. Most times, materials with better mechanical properties are usually more expensive.

For example, materials like polyethylene and ABS are excellent choices, because they showcase a good balance of cost-effectiveness and strength.

5. Production Volume

The amount of parts you are creating also imparts the molding cost. The production volume determines the amount of raw materials – mainly plastics and resins – the kind of machine you use, and the injection mold quality and strength, among other features. However, unlike other factors affecting cost, this is not a direct relationship, mainly when varying cost per part.

Therefore, let’s explain how the production volume can influence total injection molding costs.

low volume injection molding

Small-scale Production

Generally, you’d expect that low-volume production costs less. However, this isn’t always the case, as the part’s complexity and material choice, among other features, may play more significant roles. Therefore, the cost per unit cost of small-scale production may still be expensive. However, since it requires fewer raw materials and is small-scale, a simple aluminum mold will suffice, reducing costs.

Medium to Large-scale Production

There may be a cheaper cost per unit part for medium to large-scale production, as the overall tooling costs, among other factors that influence production costs, are shared over the total production. However, for bulk-production volume, we often require more sophisticated tooling, such as steel molds, so it can withstand the stress of manufacturing large numbers of parts. This increases the production costs.

6. Surface Finishing Options

The surface finishing and secondary processing operations also play crucial roles in the cost of an injection molded part. Typical surface finishing for these parts includes painting and powder coating, which help improve the part’s durability and appearance.

However, it is noteworthy that not all parts require surface finishing, especially if the manufacturing process is exact with little to no blemishes. Therefore, post-processing operations shouldn’t be compulsory, only when needed. Moreover, consider using the same service provider that helps in fabricating the part for surface finishing, as many may give a discount to their customers.

7. Parts Packaging and Inspection Requirements

While these two components seem negligible, they significantly affect the total costs of injection molding parts. The costs spent on parts packaging and ensuring quality control so that it attains industry standards also affect injection molding prices.

How to Reduce Injection Molding Costs?

While injection molding is relatively cheaper than other manufacturing methods, some practices may increase costs. Therefore, avoiding these features in your design may prove effective for cost-effective design for injection molding.

injection mold design

1. Simplify Design

Design complication is one of the main factors that increases the cost of injection molding. Therefore, optimizing your design will help avoid tooling costs, as a simple mold will suit your fabrication. Below are ways to simplify your part’s design and shapes.

Avoid Wall Thickness

Besides helping cut manufacturing costs, maintaining uniform wall thickness helps simplify your design. Therefore, there’s a reduced potential for injection molding defects. Moreover, it reduces the amount of raw materials for the intended part’s fabrication, with faster production times.

Avoid Using Custom Molds

Some design specifications may require fabricating custom molds to achieve the intended design. However, this significantly elevates the total costs. Therefore, if avoidable, streamline the design feature to use standard mold bases to help reduce injection molding tooling costs and the entire injection molding process.

Minimize the Number of Cavities

As we discussed previously, increasing the number of mold cavities may increase your injection molding costs. Indeed, these multiple mold cavities benefit the production output; however, they increase tooling costs. Therefore, balancing complex tooling requirements and injection molding setups is critical for total manufacturing costs.

injection molding process

2. Optimize Material Selection

The choice of material plays a crucial role in the total cost of any manufacturing process. However, your fabrication may sometimes require high-end materials, especially if the application calls for high mechanical resistance and durability.

For example, Polyoxymethylene (POM) and Polyether ether ketone (PEEK) are common when discussing industrial-grade hardened plastics. However, the latter is about four to seven times cheaper. In fact, PEEK is not a suitable plastic for injection molding parts.

Another effective means of cutting costs through material options is to consider reusing plastics, especially the hardened ones in the runners and sprues. However, we must notify you that this may affect the final product’s quality.

3. Reduce Unnecessary Parts Features

Cutting down unnecessary parts features, like injection molding undercut, overly complex geometries, and intricate details reduces injection molding costs. Focus more on the main details integral to the part’s optimum functionality. Other features are supplementary and subject to revision and may prove effective for simplifying your design.

4. Minimize Complex Finishing

We also mentioned that sophisticated surface finishing may increase fabrication costs. Therefore, sticking to more straightforward post-processing and finishing operations may prove effective for optimizing costs. However, it may diminish the overall product quality and durability.

5. Try Reusing Molds

Reusing injection molds for multiple fabrications can significantly reduce mold costs. If feasible, consider it as it helps prevent the need for new tools. Reusing molds also helps to increase production cycle times and costs accrued from new mold creation. However, you may need to modify the molds for different parts to ensure the product achieves optimum functionality.

injection molding components

Analyzing Injection Molding Costs for Different Production Volumes

This section will discuss, using a table, an overview of injection molding, comparing the cost with the production volume.

Cost AnalysisSmall-scale productionMedium-scale productionLarge-scale production
Production volume10 – 1,0001,000 – 10,00010,000 – 100,000
Material Costs (per part)$0.5 / part$0.5 / part$0.5 / part
Total costs of materials50500050000
Tooling costs (e.g., mold, machine)100500020000
Labor costs (per part)42.51.5
Total labor costs40025000150000
Total the cost of injection molding process55035000220000
Cost per part($)

Now, based on what we earlier wrote, you can see how the different factors affect the total costs and the cost per part. The variation in tooling costs is based on the sophistication of the machines and mold types that each production process will utilize.

For example, a 3D printed mold may suffice for small-scale injection molding, while medium-scale may use aluminum molds, and large-scale injection molding will need steel molds. Moreover, with increasing production, you require more extensive and more complex machines.

XinCheng Expert in Injection Molding Services

Besides having a basic understanding of injection molding, including the different elements that influence its costs, engaging in the process is something else. Also, these machines are expensive, therefore, it is best to partner with an experienced service provider for your project.

Our team at XinCheng is comprised of experts in the field of injection molding. We take pride in our ability to deliver high-quality and cost-effective molding solutions to meet our customer’s requirements. Whether you require low-volume prototyping or large-scale production runs, XinCheng has the capacity and expertise to offer injection molding services for your projects. Just contact us today!


The cost of injection molding services varies, depending on different production factors. Some of these include tooling and labor costs, design complexities, choice of molds, etc. Understanding these elements can help you make informed decisions towards reducing the cost of these services without diminishing quality. A typical means of cutting down these excesses is to rid your part of all unnecessary design complications that do not improve the part’s functionality.


Is injection molding expensive?

The cost of injection varies depending on various factors. They include design complexity, tooling, and labor costs, material choice, and production volume. However, injection molding is relatively more cost-effective than manufacturing methods like CNC and 3D printing, especially for large production runs.

How much is injection molding?

As we iterated, the cost of injection molding varies depending on different factors. However, the cost per part may be as low as about $2 to $5.

How long does the injection molding process take?

The time it takes for injection molding parts is also affected by similar factors that influence its costs. These include design complexity, material choice, mold complexity, setup time, etc. However, the cycle time for injection molding runs is short, measured in seconds. Other factors like cooling time and post-processing may also influence the total time it takes to create injection molded parts.

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Vacuum Casting vs. Injection Molding: Key Differences and Choose the Right Method

injection molding vs vacuum casting

Choosing the right manufacturing process can be overwhelming even for experts. Though vacuum casting and injection molding are distinct processes, they have certain similarities, sometimes making choosing difficult.

Using the wrong manufacturing technique may have a huge financial impact on your company. This makes it essential to have an in-depth knowledge manufacturing process before settling for any. As a result, this article compares vacuum casting vs injection molding and discusses the key differences between the two processes.

urethane casting mold

What is Vacuum Casting?

Vacuum casting, or polyurethane casting or urethane casting, is a manufacturing process that pulls molten plastic materials into a mold under a vacuum to create a part. The process of vacuum casting is easy. It involves manufacturing the master mold using CNC machining, 3D printing, or stereolithography.

After creating the silicone mold and removing the master mold, fill it with the material in a vacuum chamber with a predetermined temperature. Allow it to cool, and remove from the mold. Carry out post-production finishes as needed and repeat the process based on the number of desired parts. Note that the master mold determines the quality of the finished part. In addition, it is important to deburr the casting parts for the best surface texture and quality.

rapid tooling

What is Injection Molding?

Injection molding is a plastic-forming process that forces liquified material into a pre-manufactured mold. This low-velocity liquid takes the shape of the mold as it cools. Four distinct stages define injection molding- clamping, injection, cooling, and ejection.

The clamping stage keeps the mold in place and opens it up at the right times. After, the injection unit receives the plastic granules through the hopper before melting them and supplying the liquified material into the mold. The molten plastic begins to solidify after it comes in contact with the interior part of the mold. After sufficient cooling, you can open the mold to eject the final part. Proper mold design prevents defects and is important for undercut injection molding.

Key Differences Between Injection Molding and Vacuum Casting

Vacuum casting and injection molding are both semi-automated manufacturing processes. They both use a mold for fabricating parts. However, they differ in the following ways:

vacuum casting part


Injection molding cost, when compared to vacuum casting, is high. The amount one would spend on buying and setting up a standard injection molding machine may range between $50,000-$200,000. On the other hand, vacuum casting is less expensive because it uses silicone molds. This type of mold is cheaper and easier to manufacture when compared to the metal mold injection molding technique.

Tolerance and Precision

Injection molding achieves industries’ tight tolerances and creates parts with high accuracy and precision. However, vacuum casting’s tolerance level is lower. The fact that the silicon mode shrinks about 2% after curing makes the tolerance level of vacuum casting loose. You can minimize this shrinkage by closely monitoring the mold temperature and curing time.

Material Compatibility

Injection molding is compatible with various materials, including polymers, engineering plastics, and polymer blends. On the other hand, vacuum casting has material limitations. This manufacturing process works best with polycarbonates and rubbers because they are flexible.

injection mold components

Tooling Lifespan

The tooling lifespan of both processes varies and depends on the material makeup and maintenance. Injection molds are made from strong metals such as aluminum or steel. As a result, they have a long lifespan. Aluminum molds can make 2,000 – 10,000 parts, while steel molds have a better lifespan as they can make 100,000 parts before they wear out. Vacuum-casting molds, on the other hand, have a shorter life span because silicone becomes brittle with continuous usage. Usually, they can make 20-30 parts before they wear out.

Waste Generation

Injection molding generates more waste than vacuum casting. Wastes may come from sprues or runners when filling in the plastic material. These, as well as defective parts, can be recycled if uncontaminated. The only waste vacuum casting generates is the excess on the finished part.

ParametersVacuum CastingInjection Molding
Material CompatibilityPolycarbonates and rubbersPolymers, engineering plastics, and polymer blends
CostLess expensiveMore expensive
Tolerance and PrecisionLess tightTight
Tooling LifespanShortLong
Waste GenerationLess wasteMore waste

How To Choose Between Vacuum Casting and Injection Molding?

There is no standard approach to choosing the right manufacturing method in vacuum casting vs injection molding. Consider the following before using vacuum casting or injection for your project.

injection molding plastic parts

Production Volume

The intended production volume is a key factor when choosing a manufacturing method. Vacuum casting is better for prototyping and low-volume production, while injection molding is more suitable for high-volume production. Injection molding is suitable for large-volume parts production because its molds have longevity. On the other hand, vacuum casting produces fewer parts, with silicone molds capable of making around 30 parts before they wear out.

Lead Time

Before choosing a manufacturing process, one needs to consider the lead time. Vacuum casting is better in terms of production time. It is easier and faster to manufacture silicone molds than molds made of aluminum or steel. This advantage makes vacuum casting ideal for time-sensitive operations.

vacuum casting process

Part Size

The size of the part may also influence your decision. The silicone mold of vacuum casting has a size limitation and is better suited for medium to small-sized parts. For larger parts, go for injection molding. The size of the mold has no limit. However, you will need a larger injection molding machine to accommodate the mold size.


Injection molding and vacuum casting both have diverse industrial applications. Choosing the right one for your project may depend on the industry. Injection molding has applications in medical devices, packaging solutions, automotive components, and aerospace industries. Most of these parts are complexly shaped and must be accurate for functionality. Vacuum casting produces parts with fine details in consumer electronics, medical prosthetics, artworks, and automotive accessories.

XinCheng Helps Your Vacuum Casting and Injection Molding Projects

After deciding what to manufacture, choosing the appropriate manufacturing technique is the next step. For accuracy, choose a professional manufacturer for your project that is reliable. XinCheng is the right choice for all your injection molding and vacuum casting projects. From prototyping to mass production, we have experts who always offer cost-effective machining solutions. Our injection molding and vacuum casting specialists help you use the right process and material to get high-quality products. Just upload your CAD files and get a quote today!


When comparing vacuum casting vs injection molding, no one is superior. The choice depends on the specific requirements of your application. What is the key difference between vacuum casting and injection molding? How do I choose the right manufacturing method? We hope this article has answered all your questions.


How do I prevent injection molding defects?

Injection molding defects, including warping, air pockets, and weld lines, can affect the functionality of a part. They may occur due to insufficient mold pressure or uneven cooling of the final parts. To prevent this, increase the mold pressure and injection speed so the materials cool uniformly in the mold.

Is vacuum casting the same as vacuum forming?

Vacuum casting and vacuum forming do not mean the same thing. Vacuum forming creates complex shaped parts using a plastic sheet as the starting material. It involves heating the material before using a vacuum to suck it into a mold. The vacuum casting process differs by pouring the material into the mold and removing the final part after curing.

What is the size limit for injection molding?

In theory, there is no limit to the size of an injection molded part. However, most injection molding machines can accommodate a four-by-four inches part conveniently. Going for larger parts will require bigger and more expensive machines.

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Undercuts in Injection Molding: How to Achieve it Successful?

injection molding undercuts and no undercuts

The undercut injection molding technique enhances the functionality and aesthetics of products. In simple terms, an undercut is a design or shape that prevents the easy ejection of molded products from the mold cavity. It is evident that undercuts lead to complexity but still gain popularity because of the numerous benefits for the manufacturing industry. In this article, we will explore injection molding undercut designs and their uses.

Uses of Designing Undercuts in Injection Molding

Injection molding is a cost-effective way to produce different products with consistent precision and efficiency. It is a widely used technique in various industries. Undercuts in the injection molding process serve different purposes, and these are as follows.

undercut in molded parts

Enhanced Product Design

Designers’ innovative ideas attract customers, and undercuts make it possible by adding hidden features and complex geometries to a product. The designers achieve unique designs because of the flexibility and versatility of the undercuts.

Improved Functionality

Undercuts can improve the overall product functionality by enhancing its performance and making it more versatile. It allows adding functional elements like custom inserts, vertical threads, interlocking features, and barb fittings directly to serve a wide range of applications.

Reduce Secondary Processes

The undercut feature in injection molding, it eliminates the post-molding steps during the process. Designers can directly add some aspects to the molded parts. It saves the overall injection molding cost by reducing secondary processes.

snap fit connector

Reduced Assembly Complexity

Undercuts improve the assembly process by eliminating additional fasteners. It provides options like snap-fit connectors that result in the polished look of the product. It makes the assembly process easy and quick at the same time. The Undercut injection molding can incorporate this feature in electronics products and household appliances for firm assembly without the use of rivets or any adhesives.

Aesthetic Appeal

Undercuts improve the visual appeal of the injection products by adding different patterns and creating textured surfaces. This technology helps designers to make products that differentiate from others in aesthetic appeal.

Challenges and Considerations in Undercut Injection Molding

Undercuts in injection molding come with many benefits, but there are some challenges that you need to address to leverage their full advantages. These challenges and considerations are as follows:

Ejection Difficulties

The big challenge is the ejection or removal of the product from the mold cavity. After injecting liquid material into the mold cavity, it cools down, leading to the release process. But Undercuts can obstruct smooth removal and need ejection methods to avoid defects. These methods help to remove a molded product from the cavity easily.

Mold Complexity

Mold complexity is another problem that can cause mold release issues. So, one should not avoid the mold design phase because complex mold designs can create problems. It is necessary to focus on the complex angles of the mold to minimize the ejection issue and enhance the overall performance.

Draft Angles and Wall Thickness

Less or lack of draft angles in injection molding can be challenging because it doesn’t allow smooth removal of the molded product. If there are no draft angles in the vertical walls of the mold, then it stuck the part during the mold release step.

Lack of uniformity in the wall thickness near the undercuts can be another reason for preventing the molded product from being released. So, to avert manufacturing issues, it is necessary to consider draft angles and wall thickness because they may cause potential damage to the mold.

undercut in injection molding

How to Achieve Success in Undercut Molding?

You can consider some steps to achieve successful undercut injection molding. These steps are given below:

Advanced Mold Design

Achieving success in undercut molding depends upon the advanced mold designs, and there are some essential features that you need to consider for effective results in the final products these are as follows:

  • Parting Lines: Parting lines separate the two parts of the mold, including the core and cavity. These lines are also known as lines of separation and are essential for the ejection step in undercut injection molding. If there is a problem in the positioning of parting lines, it can interfere with the smooth removal of molded products. It can eventually cause damage to undercuts in the final product. You must consider it while considering design for undercuts.
  • Side-Action Feature: Side-action or side-core features can create undercuts or deal with intricacies on the side walls of molded parts. It follows the perpendicular motion to create undercuts of sidewalls. Its effective action adds complexity to the product for better functionality.
  • Hand-Loaded Inserts: Hand-loaded inserts mean manually inserting some custom components to achieve the required functionality during the injection molding. It incorporates elements that are not possible with standard mold features. As they are manual, these are easy to reuse again and again for the next batch.
  • Shutoffs: Shutoffs prevent the leaking of molten liquid from specific places in the mold. These are essential mechanical components to achieve complex shapes during undercut molding. It can replace the use of hand inserts or side-action cores. It facilitates undercut molding by eliminating the need for secondary operations.
  • Bump Offs: As its name suggests, it facilitates the smooth removal of the final product from the mold cavity. These components prevent sticking and friction between the cavity surface and the product. These are the best components to deal with flexible and elastic material.

Gate Selection and Placement

Success in undercut molding also depends upon the injection molding gates. These gates play a role in injecting molten material into the cavity. These gates control the flow of the melted material and keep it uniform. If the material spreads uniformly and accurately in the mold cavity, this results in a smooth and consistent surface of the molded product. So, it is necessary to design that accurately.

ejector pins and molding gates

Specialized Ejection Techniques

It is necessary to use specialized ejection techniques to eject the product from the mold cavity. Ejector pins can easily remove the product from the mold without damaging the undercut line. Injection Molding flash is another defect that should be removed to provide finishing to the final product.

Material Selection

Flexibility and compatibility of the material are other things that the designer must consider for achieving appropriate undercuts in molding. Choosing a suitable material is necessary to prevent damage to the product’s surface because of the friction between the mold cavity and the product. Material properties affect injection molding tolerance, so it is essential to consider both to ensure that the final product meets the specifications or not.

Applications of Undercut Injection Mold Parts

Injection Molding undercuts belong to various industries and provide diverse applications everywhere. Designers find it an effective way to bring hidden features into the design of any product to make it more effective and user-friendly.

medical device injection molding parts

Medical Devices

In medical devices, undercuts are crucial in improving usability and patient safety. Some devices are not functional in the absence of these grooves. There are medical devices like syringes, surgical instruments, and cartridges that need undercuts. Undercuts in needles make them leakproof by providing a proper grip to it. These grooves enhance functioning by maintaining secure connections between different components.


In the automotive industry, undercuts are present in interior and exterior components. It provides innovative solutions to enhance the functionality of automotive applications. It offers solutions to leaks for the smooth flow of fluid. Barbed hose connectors have undercuts that tighten the grip and prevent hose detachment under pressure.

Consumer Electronics

Undercuts add value to electronic devices by enhancing user experience. These undercuts or grooves provide stability to electronic devices by improving circuit connections.

Undercuts are the parts of different components of electrical appliances like Electrical connectors, battery compartments, control buttons, and switches for the smooth operation of electronic devices. It provides a unique texture to the devices that enhance the overall appeal of the electronic product.

Get Perfect Injection Molding Services with XinCheng

You can rely only on a trusted partner for quality injection molding solutions to achieve perfect undercuts in injection molding. At XinCheng, we can ensure you get perfect and precise undercut shapes for your products. Our team assists you from material selection to undercut machining because of the depth of knowledge in the manufacturing industry. We also can understand all the challenges and intricacies of undercut molding designs. Contact us today to get a free quote and DfM feedback.


Undercut injection molding is crucial to enhance the product’s precision, functionality, and aesthetics. It adds uniqueness to any product by incorporating complex geometries and hidden features. These features not only enhance the overall aesthetics but also improve the performance.


Why are draft angles important in undercut molding?

Draft angles are essential for mold release from the mold cavity to avoid damage to the product. These angles are incorporated into the vertical surfaces of the mold cavity to support the smooth ejection. Also, these angles or slopes are essential to protect the outer surface of the mold cavity from imperfections and defects in the molded product.

How to avoid undercut in injection molding?

Undercuts can increase complexity, and this may lead to increased production costs. So, if it is unnecessary, the designer must manage without the undercut.

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Acrylic Injection Molding: How to Mold PMMA Injection Parts?

acrylic injection molding

Chemically known as poly methyl methacrylate, PMMA is used as an alternative to glass, especially where strength, flexibility, and transparency are the main focus.

This article covers extensive information about injection molding acrylic plastic. Starting from learning what is acrylic injection molding to knowing deep strategies for getting the perfect injection molding part.

What is Acrylic Injection Molding?

Acrylic is also called organic glass or PMMA. The fascinating properties of this thermoplastic excite the manufacturers to use it for making some of the transparent products across different industries. Polymethyl methacrylate is heated to a certain temperature to melt, which helps it to fit in any required mold.

Upon melting, acrylic is injected into specifically shaped molds to get the resultant product after cooling. These acrylic molds are often custom-designed depending on the customer’s demand.

All this process is completed in highly accurate and professional injection molding machines.

injection molding process

Acrylic Injection Molding Process: How it Works?

The independence of customization in the injection molding process, combined with acrylic’s chemical and physical properties, makes this process popular. Three main steps required for getting the perfect acrylic molded product are:

Step#1: Making the Desired Acrylic Molds

The mold material and making procedure are selected depending on the cost, mold material, and number of molds required. Aluminum and tool steel are the most common materials used to make acrylic parts molds. To save on the cost, making a test mold by placing the desired object in a box and then pouring the melted mold material is preferred.

Once the material cools down, the object is removed, leaving a hollow space where casting material will be poured later to make the acrylic product.

aluminum mold for pmma

Step#2: Securing Both Parts of Molds

The resultant molds are manufactured in two halves. Therefore the two halves must be clamped together before injecting the acrylic plastic. One half of the mold is attached to the molding machine, while the other half is allowed to slide.

The two pieces of the molds are pressed against each other in a hydraulically operated clamping device. The time required to seal both parts together depends on the clamping pressure of the machine. For example, large machines have a more clamping pressure that needs more time to seal the molds.

acrylic materials

Step#3: Injecting Molten Acrylic into the Mold

Acrylic is added to the injection molding machine in the form of pellets. While passing through the injection unit, the acrylic pellets melt with pressure and heat. This molten plastic is injected into the compressed molds with a pressure that helps it stay inside them. The pressure and volume of the shot in each mold can determine the time required for injecting.

Step#4 : Cooling the Acrylic

When molten acrylic is added to the molds, it starts cooling down. Gradually the plastic will start taking the shape of the mold turning into the required shape of the part or product. Some kind of shrinking may occur during the cooling process, which is taken care of while designing the molds.

Further, when injecting the material, it is ensured that more material is injected to prevent shrinking. Cooling time is crucial to determine the perfect product after the exact time. The wall thickness of the mold plus the thermodynamic characteristics of acrylic helps determine the cooling period.

Step#5: Removing Manufactured Part From Mold

Now is the time to get the final products from the molds. An ejection mechanism in the molding machine is attached to the back half of the mold. The ejection mechanism releases the molds once enough time has passed. A small device in the molding machine helps to unstick the parts from the molds because as the parts shrink, they stick to the mold while cooling.

Draft angle in injection molding plays its role here. An accurately added draft angle to the molds during manufacturing will save the molded parts from tension while removing them with the ejection mechanism.

acrylic molding applications

Step#6: Post Processing

Post-processing means removing the surface defects of molded parts to enhance their aesthetics and functionality. Some most common post-processing procedures include deburring and painting.

When plastic is injected into the pressed halves of the acrylic molds, some of it manages to move in the space where the two halves join. After the products come out of the molds, they must often be trimmed from the sides to remove the excessive plastic. These leftover trimmings are later reused for making new parts and products by feeding them into the injection molding machine again.

Benefits of PMMA Injection Molding

Acrylic injection molding is a simple yet highly beneficial procedure for manufacturers and customers. Still, most of you need to know the importance of it, so let’s check out the benefits of PMMA injection molding.

1. UV/ Weather Resistant

Acrylic can filter ultraviolet rays, making it suitable for outdoor use. Combined with other substrates, this thermoplastic can be used for its versatility and good heat stability in various applications. In common, it has a record of staying transparent for years when used in external settings.

pmma injection molding parts

2. Easy to Use

When injection molding with acrylic, it is see-through, giving better quality control to manufacturing parts. It offers a transparency that can go up to 92%, almost comparable to glass. It looks like glass but is almost half in weight than the same size of glass. The lightweightness of this plastic helps with its usability in applications where heavyweight transparent glass cannot be used.

3. Safe for Everyday Products

Acrylic injection molding parts do not release BPA during the hydrolysis process. This means that acrylic can be used for manufacturing domestic products as it is non-toxic. Various everyday-use items can be manufactured with PMMA as it is safe.

4. Impact and Water Resistant

The impact resistance and strength of acrylic make it suitable for injection molding multiple parts. So places where transparent yet stronger injection molding parts are required, like face shields, prefer using this thermoplastic. Its strength combined with waterproof properties, helps to act as a shelter and protection for external surfaces of various products.

Drawbacks of Using Acrylic Injection Molding

1. Low Heat Bearence

The lower melting points of PMMA make it a good polymer for external applications. But this 160°C melting temperature is not good for using it in technical applications. Some of these issues are resolved with the help of low glass transition temperatures that range between 85 to 150° centigrade. But still, it is less resistant to heat as compared to glass, which can deal with even 1000° C without melting.

2. Low Mechanical Strength

The products manufactured with injection molding the acrylic plastic have lower mechanical strength. It leads to lesser loading capacities making them inefficient for mechanical applications.

3. Less Resistant To Chemicals

Some manufacturers have claimed that molded products made with PMMA sometimes have lower stability to resist different chemicals. Certain chemicals at an extreme level affect the product’s surface.

Factors Affecting Quality of Acrylic Molded Parts

Getting result-oriented acrylic molding isn’t that easy. You need to focus on some factors for getting high-quality acrylic molded parts.

1. Mold Design

It is important to focus on the mold design to ensure that you get the accurate parts. A faulty design may lead to losing time and money, so you must be careful. Some important factors to ensure acrylic mold quality include:


During injection molding, acrylic undergoes a shrinkage of almost 0.4%-0.61%. Although it’s less than the shrinkage in other plastics, it’s important to consider. Acrylic’s anticipated shrinkage can be dealt with by making appropriate improvements to mold design, melting temperature, and injecting pressure.

Draft Angle

The draft angle helps in the easy ejection of the parts from molds. Commonly a 0.5° to 1° draft angle is preferred for acrylic parts. Where the surface polish is a bigger factor, it is advised to maintain a greater draft angle.

acrylic mold design

2. Product Wall Thickness

The perfection of acrylic products with injection molding depends on the thickness of the wall. Usually, a 2 mm to 4 mm wall thickness is considered accurate for the end product. Wall thickness depends on the dimensional precision required by the particular industry. If the mold is thin-walled, filling up would be difficult. The manufacturer will need to control temperature, flow rate, and pressure.

3. Surface Finishing

Acrylic products are prone to get scratched especially when there’s a lack of proper surface finish. This ultimately affects the parts over time. Adding extra layers of surface finish keeps the inside parts protected. Here the surface finish acts like a protection sheet for the acrylic parts. So this makes the parts last longer with an improved quality.

4. Injection Pressure

Too high injection pressure makes the parts stick to the mold. These parts get damaged when removed from the molds, affecting the part quality. So maintaining the right injection pressure saves the parts from sticking to the mold, helping them with easy removal.


Is PMMA injection molding an expensive process?

No. The cost of material and labor reduces the injection molding cost when hundreds of products are manufactured in one batch. Additionally, acrylic thermoplastic is easy to work with, saving the time required for each batch and lowering the manufacturing cost per product.

What is PMMA?

A thermoplastic exhibiting valuable properties suitable for injection molding. With its stiff yet flexible nature, PMMA lets various industries benefit from its countless applications. It has a brilliant and transparent appearance resembling glass, yet it’s more impact resistant. The best part is its availability in multiple colors, which helps with its use.

What’s the working temperature for acrylic plastic?

Manufacturers can use this plastic at a high temperature between -30° to 90° Celsius. Once you start heating acrylic plastic, it gradually becomes soft and malleable, making it easier to be injected. It can easily retain the same shape as the mold on cooling.

Read More: Methods for Making Metal Prototypes


Injection molding PMMA is a highly professional process, from making the acrylic molds to removing the final product from the mold. Before getting over this process, you must go through every bit of it to avoid losing time and money.

Here at XinCheng, we are a professional and experienced on-demand manufacturer. We offer one-stop injection molding services, committed to turning your ideas into exact prototypes and products. Just contact us today to get a free quote!

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