10 Injection Molding Terms Every Engineer Should Know

The plastic injection molding process is extremely complex with (quite literally) thousands of moving parts. As a manufacturing engineer, it’s not critical for you to know every finite detail of mold-closing mechanisms or the difference between every polymeric substance used in injection molding—but understanding the following 10 terms will make a conversation with a potential plastic manufacturing partner much simpler.

1. PRECISION MACHINING

In injection molding, precision machining refers to the process by which an injection mold is created with very narrow part tolerances. Creating a snug mold with a tolerance of +/- .0005” keeps the liquid plastic from flashing (e.g. seeping into crevices and ruining the final part).

2. 3D PRINTING

3D printing is an additive manufacturing process that deposits layers upon layers of material to build up a part. While 3D printing has become mainstream, it still can’t compete with the speed or sheer output of injection molding. However, it does play an important role in the injection molding process, and is often used to prototype a design concept so customers understand what their finished product will look like.

3. RAPID TOOLING

Rapid tooling describes the process of quickly creating a mold with a 3D printer or more traditional machining methods. The issue with rapid tooling lies in part accuracies and tolerances. While a 3D printer can create a mold accurate enough to produce a close replica of a part, the mold won’t have the tight tolerance needed to create hundreds of thousands (or millions) of perfectly shaped plastic parts.

4. THERMOSET

To create a thermoset part, cold material is shot into an extremely hot injection mold. This process cures the part so it can never melt again. This heat resistance is the primary function of thermoset material (most often silicone), but thermoset materials are unable to be recycled.

5. THERMOPLASTIC

To create a thermoplastic part, plastic material is melted and shot into an injection mold. Once this part cools, the mold opens and the part drops out. Thermoplastics like styrene and polycarbonate can withstand warm or even hot conditions—but at certain temperatures they will eventually melt again, and thus are able to be recycled.

6. TRANSFER MOLDING

Transfer molding involves placing a cold, putty-like material inside a cavity in an injection mold. Once the mold is closed, the machine forces the cold material into the hot mold cavity. This transference of the cool material into the hot cavity causes the material to disperse quickly. Once it has cooled, the mold is opened and the part is removed.

7. CLEAN ROOM MOLDING

Clean room molding is the process of creating plastic parts in a special room optimized to reduce the risk of contamination by dust or other particles. Clean rooms are used for injection molding projects that require a sterile environment, like medical equipment. The room is devoid of any fibrous or corrugated material, uses only electric machines, and filters air through positive airflow to maintain a certain level of cleanliness.

8. HORIZONTAL MOLDING

There are two types of plastic injection molding machines: Horizontal and vertical.

In horizontal molding machines, the mold clamps horizontally. Once the plastic part is created and the mold opens, the part drops into a bin and is taken away on a conveyer belt. Or, if the part is sensitive and can’t be dropped, a robot removes it from the mold.

9. VERTICAL MOLDING

Vertical molds lie flat so the part doesn’t fall out once the mold is opened. Because of this, it must be removed by hand or by robot.

The advantage to vertical molding is that parts can easily be added into the mold. For instance, if you want to add a round washer to your plastic part, simply insert the washer and close the mold—because of gravity, the part stays in place.

10. TWO-SHOT MOLDING & OVERMOLDING

Two-shot molding or overmolding are processes used to create parts that require two different kinds of plastic—like a toothbrush or a computer mouse.

In two-shot molding, the more rigid of the two materials fills the mold cavity. Then the top of the mold shifts and the second, more pliable material is injected. In overmolding, the rigid material is injected into a mold cavity, then removed after it has cooled and put into a separate mold, where the second, more pliable material is added.

The primary difference between these two molding techniques is cost, as overmolding takes twice as long as two-shot molding.

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Medical Device Injection Molding: How To Find The Right Partner

Medical device injection molding is used in everything from syringes to IV roller clamps to dialysis machine components.

While you must ensure that your medical device is manufactured to FDA standards and is ISO 13485 compliant, you also need to be certain that the company you select is the right one for your needs. A great medical plastic molding partner is indispensable, as they can help you ensure your part cost stays low while maintaining the highest standards of quality. Below, we’ve outlined a few things to keep in mind during the selection process.

CONSIDERATIONS WHEN SELECTING A MEDICAL DEVICE INJECTION MOLDING PARTNER

1. Clean Room Requirements

Depending on the function of your plastic part, you may need to ensure that it is manufactured in a clean room. Clean room molding is the process of creating plastic parts in a special room optimized to reduce the risk of contamination by dust or other particles. Clean rooms have a constant positive air flow, use electric (not hydraulic) machines, and are devoid of any corrugated material that could cause dust, all in an effort to ensure cleanliness. It may, for example, be necessary to use a clean room for your medical plastic device if the part is implantable, will come in contact with bodily fluid, or will be used in an operating room.

If your device does not need to be clean room manufactured but does require a more controlled manufacturing environment, look for a partner that is flexible with their manufacturing environments. Micron, for example, has a class 7 clean room, but can also use mobile enclosures over the plastic molding machine (by placing a curtained device over the area that offers positive air flow) and have machine operators wear a hat, gown, and mask.

2. Your Product Performance Requirements

A medical device injection molding partner should be able to assist you in determining what raw materials you need based on the specifications of your product. For example, if your medical apparatus  will not be implanted nor come into contact with a patient’s bloodstream, your plastic injection molding partner should steer you away from a class 6, implantable-grade material and toward something more appropriate for your needs and less expensive. Or if you’re creating a dental tool with a colored handle, the partner you speak with should ensure you select the right FDA-approved, food-grade-contact material.

3. The Injection Molding Company’s Area of  Expertise

Bigger is not always better when it comes to the size of your injection molding company—but attention to detail and an emphasis in the area you’re working with are critical.

Whether you need to create a smaller batch of specialized plastic parts or millions of plastic parts each day, you’ll want to find a medical molding company that has a solid track record for producing high-quality parts similar to yours.

For example, here at Micron, we are very effective at producing high-volume medical disposables due to our robust manufacturing process. In fact, we manufacture billions of parts used in medical devices each year. Our vast experience in process validation for medical plastic injection molding has given us deep insight into the nuances of the production process. We are constantly finding new ways to control the flow of materials, and we use automation throughout the entire manufacturing process (including inspection and packing), which enables us to pass cost savings along to our customers.

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How Does The Injection Molding Process Work? A Breakdown For Product Engineers

As an engineer, your focus is on taking a product idea and figuring out how to get it manufactured so it fits all your specifications and stays within your budget. But before you select an injection molding partner, it’s a good idea to brush up on what the injection molding process looks like.

The process outlined below lists the two most critical phases of the injection molding process; you’ll also find a list of things to consider before you partner with an injection molding company.

INJECTION MOLDING PROCESS STEPS

The process has come a long way since 1872, when the first injection molding machine was created by American inventor John Wesley Hyatt. Hyatt’s machine was very simple—it used a plunger to push plastic material into a mold.

The plunger was replaced in 1946 by James Watson Hendry, who added an auger in the injection barrel. While machines are now run with far more advanced machining, this same basic mechanism is used in the injection molding process today.

Step 1: Create your injection mold.

Before you can begin the injection molding process, you must have a mold with the shape of the part you want inside it. The injection mold is most typically made of steel (though some parts may require another material) and is created with very narrow part tolerances, +/- .0005 of an inch (to put it in perspective, a human hair is about +/- .0003”). This requirement keeps the liquid plastic from seeping into crevices, which helps avoid potential quality or visual issues with the completed plastic part.

If you are creating a high volume of plastic parts, you may require multiple cavities inside a mold, so every cycle creates many plastic parts. Here at Micron, we have the capability of creating a mold with up to 96 cavities—which can create millions of parts every day.

Step 2: Manufacture your plastic product.

  • The completed mold is placed in the injection molding machine.
  • The plastic pellets are heated until they are liquid.
  • The liquid plastic goes through a dryer, if necessary (as moisture in the plastic might cause splay or hydrolysis in the finished product).
  • The liquid plastic is conveyed into the injection molding machine through a vacuum.
  • The liquid plastic goes through a heated injection barrel, which is attached to a feed throat.
  • The liquid plastic is injected under pressure through the feed throat into a mold.
  • The mold—which is cooler than the liquid plastic—causes the plastic material to cool to a solid state, which forms the plastic part.
  • The mold opens and the cooled plastic part is ejected from the mold either by hand (in a vertical injection molding machine) or by force of gravity (in a horizontal injection molding machine).

SELECTING AN INJECTION MOLDING PARTNER: 6 THINGS TO CONSIDER

If you’re ready to make your product become a reality, you have to find the right partner for your injection molding needs. Below, we’ve outlined a handful of things to consider so you select the right partner.

1. Expertise

When beginning your search for an injection molding partner, narrow the possibilities by honing in on companies with experience in your industry or with similar products. A company with relevant experience probably has both the knowledge and technology necessary to develop or even improve your prototype, create it correctly, and manufacture it on schedule.

From there, you can narrow your search to a specific niche, for example: high-volume molding, over-molding, or two-shot molding. Also, be certain to ask about an exact technology you may need specific to your project. If they don’t have said technology, find out if they’re willing to acquire it.

2. Proximity

Many people wonder whether they should partner with a company in the U.S. or overseas for the injection molding process. If you’re asking this in your organization, consider these two questions:

  • Can the mold-making service you’re considering meet your quality standards? Quality U.S.-based mold-making shops source only the highest quality steel for their molds. If you do not specify the grade of steel you want from an injection molding company in China, you may end up with poorer quality materials.
  • Does the company you’re considering have tooling expertise, and are they willing to make tooling adjustments along the way? Ideally, the company you select to work with you on your injection molding process should be able to create your mold for you, or have the expertise necessary to ensure that your existing mold will hold up to the quality standards you require. Some companies—in the U.S. and in China—outsource for molds, which means less quality control on your end.

3. Capacity

Before choosing a partner for your injection molding process, consider how much volume the company can handle. If you need to produce 10 million units each year and the molder only produced 1 million units last year for all its customers combined, you should look elsewhere. Without that ability, you could end up with increased lead time, quality issues, and stock shortages. Alternatively, if you only need 5,000 units produced each year, you might not want to select a molder that deals primarily with multi-million-unit orders.

4. Capability

Is the molder able to build your mold, test it, help you select materials, assemble the finished product, and package, label, and ship it post-production? We highly recommend looking for an injection molding company that has these capabilities, as it makes your job a lot easier.

5. Customer Service

You’ll be working hand-in-hand with your molder for an extended period of time, so it’s important that the company values honesty, integrity, and transparency. To test this:

  • Watch how quickly the molder responds to small issues you identify.
  • Find out if they have a process for escalation of any issues during the injection molding process.
  • See how long it takes for the molder to return your phone calls or send you updates. If the company is slow to respond at the beginning of your relationship, imagine what it will be like down the road!

6. Precision

The pricing of the plastic injection molding process can be thought of as a combination of renting a company’s injection molding machine in addition to the cost of the operators, the cost of materials, and the cost of tooling and machining. The quicker a machine goes through a cycle time, the more parts you can create.

If a company has a solid injection molding process, it will have stringent standards regarding how to ensure every part is expelled from the mold at the right time to avoid defects, rejects, and cosmetic issues.

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6 Types Of Injection Molding Technology

Plastic isn’t the only thing that can be injection molded—metal can as well. This new technology is substantially more expensive than plastic injection molding and usually serves a niche market. The cell phone market, for example, sometimes uses metal injection molding to shield the cellular electronics from radio or microwaves.

4. Liquid Silicone Injection Molding

The majority of plastic injection molding is thermoset, meaning cold material is injected into an extremely hot mold to create a part. This process cures the part so it can never be melted again. But if you need a part to withstand very high temperatures or chemical agents—as you might with certain medical devices or car parts—you may need thermoplastic injection molding, which frequently uses liquid silicone.

5. 3D Printing

3D printing is a notable injection molding technology because of the role it plays in prototyping an injection molded part. Here at Micron, we create a 3D-printed prototype of a client’s part before we move the design to production. This allows us to discuss potential improvements in more depth than we could while reviewing an online rendering, for example. It’s also worth noting that 3D printing can be used to print actual injection molds using plastic or metal. Currently, the available 3D printing technology does not enable us to print with the narrow part tolerances required in an injection mold—but we imagine it may in the future.

6. Unique Material Formulations

While this isn’t a plastic injection “technology” in the traditional sense, the use of unique material formulations does advance molding capabilities. Injection molding companies may, for example, use a carbon or mineral filler, a blowing agent, and a lubricity additive to add certain properties to a part. For example, here at Micron, we have run 40% carbon-filled ABS (Acrylonitrile Butadiene Styrene) to achieve a degree of electrical conductivity in a plastic stud or sensor. The temperature of the mold and the plastic material are both important when adding a filler, additive, and blowing agent, so we are constantly refining our process to achieve the best advantage for these unique materials.

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The Use Of 3D Printing In Manufacturing Now & In The Future

In recent years, 3D printing has become extremely useful in manufacturing—and, more specifically, in plastic injection molding. Injection molding companies often use a 3D printer to create a part from a model, drawing, or concept plastic part. Depending on the size and complexity, it can take anywhere from 20 minutes to 48 hours to create a single 3D-printed part—but in most cases, you’d be able to hold a finished replica of your part in a matter of hours.

While it may seem like creating a 3D printed part before production is unnecessary, it’s actually a worthwhile time investment. The benefits of the 3D printing manufacturing process are:

  • You get to examine a physical replica of your part before you go into mass production, instead of relying on a drawing or concept.
  • You can see how your multiple plastic parts fit together and make any necessary corrections before your molding partner cuts an expensive piece of steel for your injection mold.
  • Your injection molding partner can consider potential issues before your product hits the manufacturing floor. For example, the plastics expert could bring up any potential issues with the way plastic will flow through the mold to create your final part.

3D printing is evolving rapidly—and we’re expecting big changes on the horizon. Here are three areas we think will revolutionize how 3D printing (also called additive manufacturing) will impact the plastic injection molding industry.

THE FUTURE OF 3D PRINTING & ADDITIVE MANUFACTURING

1. 3D-Printed Plastic Injection Molds

One major development in 3D printing today is the ability to print a plastic injection mold. Today’s 3D molding technology does not have the narrow part tolerances required to create a plastic injection mold that can withstand high volume, but we expect this to change in the near future.

Once part tolerances are solved, 3D mold-making will become a more viable option—and will have a number of benefit. For example, you cannot drill bit around a corner inside a block of steel—but you can can create virtually anything you imagine with a 3D printer. Additionally, the material used to create a mold in a 3D printer is less expensive than high-grade steel. The added functionalities and cost savings will impact what you’re able to mold and how much it’ll cost to mold it.

2. Using 3D Printing For Your First Run-Off

During the manufacturing process, the first run-off of your plastic part ensures that the part meets quality standards and works as far as fit and function. In the future, we expect 3D printers will be efficient enough to replace an injection molding machine for small production quantities, which could eliminate the upfront investment required for molds and reduce the lead time for the first articles.

3. Alternate 3D Printing Methods

FDM (fused deposition modeling) is the most commonly used 3D printing form. To create a 3D part using FDM, a thin string of plastic feeds into a heated tip (similar to a pen tip). The heated tip melts the plastic on contact, and then pushes the melted plastic onto the 3D printing tray in a certain direction to create a part. The plastic dries in layers as it comes out of the tip, and each layer dries quickly enough to hold the next layer—hence the term 3D additive manufacturing.

While the majority of 3D printing is currently FDM, we expect that a number of additional 3D printing methods will be innovated in the next 5-10 years. The more forms of 3D printing available, the more options you’ll have when it comes to prototyping, mold-making, and manufacturing your part.

KEEP IN MIND, 3D PRINTING WON’T REPLACE PLASTIC INJECTION MOLDING FOR DECADES—IF EVER.

While the 3D printing manufacturing process has evolved rapidly and will continue to do so, it will be many, many years before a 3D printer can match the volume, speed, and efficiency of a plastic injection molding machine. Currently, it could take roughly 30 minutes to print a 3D part that would take only seconds to make using injection molding.

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What Type Of Molding Process Does Your Prototype Require?

If you’re creating a plastic part, it’s important to know what type of injection molding process your part will require. Do you know if your part needs to be molded in a cleanroom environment, or whether you should use a vertical or horizontal injection molding machine? Our article below walks through eight unique types of injection molding, and the benefits and considerations of each, so you can make a more informed decision:

CLEANROOM MOLDING

Cleanroom molding is used to mold plastic parts that cannot be contaminated by dust or other particles that exist in a typical molding environment. A number of industries—including medical, pharmaceutical, aerospace, military, and biotech—often need their parts to be created in a cleanroom environment.

While there are nine different classes of cleanroom molding, class 7 and class 8 are by far the most popular. (Read this article for more details on which class your part might require.) Both class 7 and class 8 cleanrooms use positive air flow to ensure a strict particulate count; masking requirements, electric machinery, and packaging restrictions also help ensure cleanliness.

HORIZONTAL MOLDING

There are two types of injection molding machines: horizontal and vertical. In horizontal molding machines, the mold clamps horizontally. Once the plastic part is created and the mold opens, the part drops into a bin and is taken away on a conveyor belt (or is taken down with a robot).

Horizontal molding machines are used in about 90% of injection molding processes worldwide. Horizontal molding allows the molding cycle to continue uninterrupted because it utilizes gravity to eject the part from the mold. As a result, production costs decrease and production output increases.

Because the vast majority of molding machines are horizontal, there are many different technological options available. Your part can be run on a hydraulic machine, an electric machine (a necessity if your part requires a cleanroom environment), or a hybrid.

The downside to horizontal molding is that it is much more difficult to add inserts —and this is where vertical molding machines are dominant.

VERTICAL MOLDING

Vertical molding machines open and close in a vertical manner. When the mold opens, the parts are ejected from the cavity but still sit on top of the mold.

Vertical molding makes it easy to add inserts into the mold. For example, if you need to put a hook in fishing lore, a needle in a medical application, or a pin in a gear clock, gravity works in your favor when you use a vertical mold.

The drawback to vertical molding is that a consistent molding cycle is not guaranteed. This is because a robot (or person) must manually remove the parts from a machine—and if your parts are removed a second too soon or too late, they may not be uniform. Additionally, using a robot or manual labor for removal is likely to be more expensive than using a horizontal mold.

TWO-SHOT MOLDING & OVERMOLDING

Two-shot molding and overmolding are injection molding processes used to create parts that require two different kinds of plastic.

Let’s say you want to plastic injection mold a power screwdriver with two different materials: the housing, which is made of a more rigid material to hold the motor drive and trigger; and the grip, made of a softer material.

If you went with overmolding, your injection molding partner would injection mold the housing for the screwdriver first. That cured part would then be added into another injection molding machine, and the grip would be molded on top of it.

If you went with two-shot molding, your injection molding partner would use a specialty two-shot mold that includes a housing mold on one side and a grip mold on the other. Once the housing was injection molded, a large rotary plate would flip the mold around 180 degrees, and the grip would be molded using a separate material.

Two-shot molding requires a more expensive mold design—but the cycle time is cut in half as compared to overmolding. So if you have the part volume to justify the process, two-shot molding would result in faster production.

THERMOPLASTIC MOLDING

To create a thermoplastic part, plastic material is melted and shot into an injection mold. Once this part cools, the mold opens and the part drops out. Thermoplastics like styrene and polycarbonate can withstand warm or even hot conditions—but at certain temperatures they will eventually melt again, and thus are able to be recycled. The majority of plastic injection molding is done with thermoplastic materials. Thermoset materials, on the other hand, use transfer molding, which is a slightly different process described below.

TRANSFER MOLDING

Transfer molding is used to create thermoset plastic parts only. It involves placing a cold, putty-like material inside a cavity in an injection mold. Once the mold is closed, the machine forces the cold material into the geometry of the hot mold cavity. This transference of the cool material into the hot cavity causes the material to disperse quickly. Once it has cooled, the mold is opened and the part is removed, and, due to a chemical heat-based reaction, the part will keep its shape forever.

PRECISION MOLDING

There are three primary categories of plastic injection molding:

  • Large part molding allows for broad part tolerances, and the mold can often be fit together by hand.
  • Typical part molding, which has part tolerances of +/- .0005″.
  • Precision molding, which has part tolerances of +/- .0001″.

Precision molding requires machinery that works with very fine part tolerances. If your part requires these types of tolerances, talk to your potential injection molding partner. Many have experience with precision molding or can partner with another company that can achieve these tolerances.

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Blow Molding Vs. Injection Molding: A Comparison For Engineers

Blow molding vs. injection molding—what’s the difference? Both are common methods used to create plastic parts. And while some parts require both blow-molded and injection-molded components—for example, a medical device with a blow-molded container attached to an injection molded apparatus, or a military application with a blow-molded “payload” packet fabricated inside an injection molded projectile—the two methods primarily serve different markets.

The main similarity between them is that, before the molding process can begin, you must have a mold with the shape of the part you want inside it. The mold is most typically made of steel (though some parts may require another material) and is created with tight part tolerances (+/- .0005 of an inch). This keeps the plastic in an injection mold or a blow mold from flashing  (seeping into crevices) and creates a quality part.

Below are the basic steps manufacturers take for blow molding vs. injection molding.

BLOW MOLDING

Blow molding is a specialized type of plastic processing used to create hollow plastic parts. The most common type of blow molding is called extrusion blow molding, which is used to create plastic bottles or other hollow containers.

To create a blow-molded product, manufacturers perform the following steps:

  1. The completed mold is placed in the blow molding machine.
  2. parison (also known as a preform)which is a tube of plastic with one hole that allows air to funnel through, is heated until it becomes soft.
  3. The molten parison is placed into a blow mold that is cooler in temperature.
  4. An air tube is inserted into the hole in the parison.
  5. The mold is closed, and the air inside the parison blows the molten plastic (similar to blowing up a balloon) until the plastic forms to the shape of the mold.
  6. Once the part has cooled, the mold opens and the completed part is ejected from the mold.

The most notable drawback of blow molding is that it’s very difficult to create a precise, uniform part, because it’s essentially impossible to get the plastic to thin out evenly as air blows through it. Consider a milk jug; the handle is often the thickest part, but the walls of the jug vary in thickness from top to bottom. That said, uniformity isn’t typically an issue for plastic bottles, as they are produced in mass quantities and are primarily used as containers.

INJECTION MOLDING

Unlike blow molding, which can only create a hollow part, injection molding can be used to create a solid plastic part or a hollow part (through gas-assisted injection molding, for example).

To create an injection-molded product, manufacturers perform the following steps:

  1. The completed mold is placed in the injection molding machine.
  2. The plastic pellets are heated until they are liquid.
  3. The liquid plastic goes through a dryer, if necessary (as moisture in the plastic might cause splay or hydrolysis in the finished product).
  4. The liquid plastic is conveyed into the injection molding machine through a vacuum.
  5. The liquid plastic goes through a heated injection barrel, which is attached to a feed throat.
  6. The liquid plastic is injected under pressure through the feed throat into a mold.
  7. The mold—which is cooler than the liquid plastic—causes the plastic material to cool to a solid state, which forms the plastic part.
  8. The mold opens and the cooled plastic part is ejected from the mold either by hand (in a vertical injection molding machine) or by force of gravity (in a horizontal injection molding machine).
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3 Common Types Of Rapid Tooling Used In Prototyping

Rapid tooling is, simply, the creation of a mold in a shortened timeline.

Rapid tooling got its start in the 1990s, when engineers involved in injection molding wanted to see if they could build molds in a matter of hour or days instead of the weeks or months a machined mold would take. A rapid-tooled mold is ideal for prototyping a part and molding a few hundred plastic parts before full-scale, high-volume production starts. The part of the tool that is built in the rapid tooling process is the insert—including the core and cavity, and the side actions. Depending on the type of rapid tooling used, you may be able to get thousands (or tens to hundreds of thousands) of cycles out of the tool.

There are different types of rapid tooling available; the benefits of each vary based on your required materials, technology, accuracy, consistency, and size. If you’re considering rapid tooling for your prototype, keep these three limitations in mind:

The mold has to be strong enough to handle the injection molding process. Injection molding machines are measured by pounds per square inch that are being clamped—so if the mold material isn’t strong enough, it might not survive. Additionally, the mold must be able to withstand injections of (typically) hot plastic material.
The mold needs to be smooth enough for the plastic part to eject cleanly. Traditional steel machined molds are polished or smoothed to make ejection easy—but during some rapid tooling processes, material is built up in layers, which aren’t necessarily smooth. This means the rapid tooling mold could require additional work after it is created to make it smooth enough for prototyping.
The mold may not have tight enough tolerances. All plastic injection molds need a tolerance of +/1 .001”, or it may leak plastic and render the prototypes useless. Depending on the type of rapid tooling used, this may be difficult to achieve.
With that in mind, here are three of the most common rapid tooling methods available in prototyping:

1. 3D Printing In Plastic
3D printing plays a number of roles in plastic injection molding—and it has evolved to the point that some additive manufacturing machines can print a plastic injection mold. The benefits of 3D printing in plastic are threefold: The molds can be created extremely quickly (within a few hours, in many cases); the molds are inexpensive to create as compared to printing in metal; and the machines can create virtually any geometry needed. That said, today’s 3D printing technology doesn’t enable exceptional part tolerances. While you may be able to get a prototype run out of a 3D plastic injection mold, you won’t be able to get volume out of it.

2. Direct Metal Laser Sintering
Metal isn’t only used for rapid tooling through traditional machining (as we’ll discuss in #3)—it can also be used to create a plastic injection mold by fusing together metal particles to make a solvent in a process called “sintering.” In rapid tooling, the sintering process is done by spraying a cloud of powdered metal into a laser beam, which allows you to “draw” the shape of your mold with the laser. This process can be done using a number of different metals, including stainless steel, titanium, or cobalt chromium. And because the finished mold is made of metal, it is better equipped to handle heat transfer, pressures, and ejection capabilities.

One of the things that makes sintering unique is that it allows you to print in conformal cooling lines to help cool the plastic part more rapidly. Say, for example, you’re creating a mold for a deodorant cap with a unique shape on both sides. Because of the contouring of the lid and the thin wall it requires, you need to be able to cool the plastic once it enters the mold as quickly as possible to keep it from deforming. This cooling process is possible thanks to conformal cooling, which uses cooling lines buried within the steel.

Keep in mind that while sintering is fast, it’s not accurate enough to achieve the required +/-.001 tolerance right out of the machine. Instead, it will achieve a tolerance of +/- .004 or +/-.005, but to get the tighter tolerance, you will have to have to add the additional accuracy in by hand through the use of traditional machining or electrical discharge machining (EDM). Additionally, sintering can be expensive compared to rapid prototyping in plastic.

3. Rapid Tooling Through Traditional Machining
When the processes for rapid tooling came out, companies that built molds using traditional methods (like machining aluminum or steel) began to increase the speed of those methods to compete. Eventually, the term “rapid tooling” was applied to any tool that could be built quickly, including those created with more traditional methods. Some companies can turn a metal mold around in a few days to a week.

But this rapid tooling method isn’t without its limitations, one of which is geometry. If you need to cut a cavity of a shape, you’re limited by the cutter the company is using—you can’t cut a square corner with a round cutter. To address that issue, you’d have to burn in the corner you need through EDM. If you need a highly complex geometry in your mold, it could be more expensive to do rapid tooling in traditional machining.

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Precision Molding: Three Questions That Could Save You Money

If you need a plastic part molded with extreme precision—for example, to ensure there’s no air leak between two molded sections or to be certain there’s no visible seal gap line—you likely require precision molding. The difference between a typical injection molded part and a precision molded part is the tolerance, or acceptable range of variation in dimension: While the majority of injection molded parts have a tolerance of +/- .005″, precision molding holds tolerances between +/- .002″ and +/- .001″ (or less, in some cases).

Let’s say, for example, you’re planning to manufacture a military projectile. In order for the projectile to fit properly in the firearm, handle the acceleration when it’s launched, and explode on impact, it requires very high precision.

If your application requires precision molding, you can’t leave anything to chance—so you’ll want to ask yourself the following three questions before you begin the process:

1. Have you determined which areas of the mold require precision?

Because precision molding is more expensive than typical injection molding, be certain which aspects of your part require tight tolerances—and whether those tolerances can be achieved through injection molding—before moving forward. For example, a surgical handle may only require precision for the piece that will connect with a pin, not the entire handle. Identifying your precision requirements from the get-go ensures you’ll get what you need without wasting money. In the case of the surgical handle, your injection molding partner may advise you to add the tolerances you need through tooling after the injection molding process is complete.

2. Have you selected a plastic material with low shrinkage?

The plastic material you select for your part makes a big difference in whether you’ll be able to do precision molding. For example, polypropylene has a shrinkage range of +/- .014″ to +/- .022″, with an average of +/- .018″. This is a wide range for shrinkage, which makes hitting a specific tolerance extremely difficult. If you’re molding a toothbrush (which commonly uses polypropylene), dealing with shrinkage isn’t a big concern, as the toothbrush will function appropriately regardless of whether it’s slightly bigger or smaller than its counterparts. Acrylonitrile butadiene styrene (ABS)—another common thermoplastic polymer—has a much narrower shrinkage average of +/- .006″. That gives you a much better chance of hitting a tighter tolerance, but it still won’t reach the +/- .001″ or +/- .002″ tolerance needed for a precision part.

One way to hit high tolerances with your plastic material is to add glass or another filler resin (like carbon fiber or mica) into the material. This can minimize shrinkage and warp by providing more structure in the material. For example, if you include long glass fibers in a polymer material, the part will shrink more perpendicular to those fibers.

3. Can the mold manufacturer you’ve selected tool with high precision?

The process of creating plastic parts with tight tolerances begins with a high-precision mold. If each plastic part you create is not identical, you won’t have a precise product—and a precise mold ensures there’s no variation for each part. Because of this, it’s extremely important to select a mold manufacturer who understands the slow, steady process of building a high-precision tool. Keep in mind that selecting a mold manufacturer that specializes in rapid tooling is likely not your best option, as the goal of rapid tooling is to finish the mold quickly—but not necessarily precisely.

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Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold

Manufacturing Single-Use Products: 8 Things To Keep In Mind

A single-use product is meant to be used or applied once and then discarded. The term “single-use” is sometimes intended to mean “disposable,” though this isn’t always the case. A bullet and a booster rocket, for example, are both single-use products—but most people wouldn’t refer to them as a disposable. But many medical products, like tongue depressors and test vials, are perfect examples of single-use, disposable products. For the majority of single-use products, the primary goal of the manufacturing process is to keep the cost low and the volume high, all while maintaining quality standards. With that in mind, here are eight things you’ll need during the product design and manufacturing processes:

1. Inexpensive Materials
It’s important to find materials that are inexpensive yet still meet your industry-specific needs or standards. For example, if you’re manufacturing a mouth swab or a single-use dental pick, the material will need to meet FDA standards while staying beneath a certain price point. Your injection molding partner should be able to offer suggestions on types of material that fit the bill.

2. Fast Cycle Times
The quicker a machine goes through a cycle, the more parts you can create, which drives part cost down. If you’re evaluating partners to help create your single-use plastic product, be sure to find out the average length of their cycle times.

3. Automation
The more automated elements the injection molding process has—for example, robots that remove parts from the mold or put them into boxes for shipping—the more you can drive part costs down. The only exception to this is if you go overseas, where human handling of parts is significantly less expensive than it is in the U.S. This article will walk through the benefits and considerations of injection molding in China vs. the U.S.

4. Quality Assurance
If a problem in the production cycle goes unchecked, you may be recalling millions of parts—so you need a very robust quality assurance system around your manufacturing. For instance, Micron uses robots in approximately 70% of our machines and camera-based vision systems that check the quality of every single part. This helps ensure that only good parts go through the molding process.

5. Inexpensive Packaging
A common problem for many companies that manufacture single-use applications is the high cost of packaging—it could be more expensive than the product itself! This may be unavoidable for extremely inexpensive single-use products that require specific packaging (like a syringe), but you’ll want to explore your packaging options to keep costs as low as possible.

7. High Capacity Mold
If you’re able to run your parts using a 96-cavity tool, you’ll see more cost savings than if you run your part on a 16-cavity tool. This is primarily because a high-cavity tool allows you to get more pieces molded per hour, which means you’ll see lower charges passed along from the molder for things like electricity use, machine depreciation, maintenance, and overhead.

8. Economical Production Processes
To avoid slowing down cycle time, you’ll want to have an effective process design for gating and part ejection. Additionally, it’s important to ensure the hot manifold that delivers the plastic material to the mold cavity does so without any waste. These processes will help accommodate inexpensive single-use pricing.

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Edited by Leafly Mould Provides Injection Mold, Plastic Mold, Injection Molding, Die Casting Mold, Stamping Mold