3D printed mold casting

Introduction to Metal Casting and Ways to Combine 3D Printing With Casting Workflows

Metal casting is an age-old metalworking process in which molten metal cools and solidifies in a mold to form metal parts. Despite its ancient roots, metal casting is still one of the most popular processes for companies looking to produce metal parts.

This article will cover what metal casting is, how it works, and walks you through the most common metal casting processes and the benefits manufacturers can attain by combining modern digital tools like 3D printing with traditional casting workflows.

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Metal casting step-by-step from the original design through final casting.

Since the advent of metal casting, the methods have evolved and varied. Its core techniques, however, have remained constant. Here is a general step-by-step process for metal casting:

Ring patterns 3D printed in Castable Wax 40 Resin.

In order to begin the metal casting process, a manufacturer first must develop a representation of the desired pattern. This pattern is essential in designing the mold used for the cast. It is traditionally made from wood, foam, plastic, or wax and ensures that the mold accurately produces the finished metal part. Today, 3D printing is also a common method to produce patterns, which allows designers to create accurate patterns directly from digital CAD software tools.

A pattern is not an exact replica of the desired part. It has additional elements that make the casting process possible, including gates that allow molten metal to flow at a steady rate and vents for gas to escape. Additionally, patterns are also larger than the parts they represent to account for the shrinkage that occurs during cooling.

When the casting piece is hollow, the manufacturer also creates a core of sand or metal to shape the internal form. This core gets removed upon completion of the casting.

The next step is creating a casting mold, which can be either reusable (non-expendable) or non-reusable (expendable). Non-reusable molds are usually made out of sand, plaster, wax, or by 3D printing, and just as the name suggests, they get destroyed in the casting process. Reusable molds are made out of metal and other durable materials and can be reused for multiple casting cycles.

Ceramic shells after burnout and 3D printed patterns in Clear Resin.

Molten pewter poured into a High Temp Resin 3D printed mold for metal casting.

During this step, the metal gets heated in a furnace until it melts. Depending on the application, manufacturers can use a variety of different metals, with the most commonly cast metals being iron, aluminum, aluminum alloy, steel, copper, and zinc, as well as precious metals like gold and silver. Once the metal melts, the manufacturer pours it into the mold cavity and allows it to cool and solidify.

Metal casting post-production.

Once the metal cools down and solidifies, the parts get removed from the mold. Depending on the mold type, this can be done by vibrations in a shakeout process, washing away the investment material, or by ejector pins. Then, excess material, such as vents, gates, and feeders, are removed from the parts. Finally, the parts get filed, grated, machined, or sandblasted to smooth the surface and reach the final shape requirements.

Though all metal casting techniques share the same core process, there are various methods better suited for different applications. Some of the most common methods include die casting, investment casting, and sand casting.

Die casting uses a steel mold and high pressure. (Source: buhlergroup.com)

Die casting is a metal casting process in which a manufacturer pushes molten metal into a steel mold cavity at a high pressure to quickly produce metal parts. In die casting, the manufacturer fixes two halves of a die or reusable mold together and uses a nozzle to inject pressurized molten metal into the die. When the metal cools, the die opens, and ejector pins push out the cast.

The two most common die casting processes are hot-chamber and cold-chamber casting. While the specifics of these processes vary, there are several shared characteristics of the die casting process as a whole.

Hot-chamber die casting is the most common of the two main die casting processes. Hot-chamber die casting machines have a built-in furnace to heat the metal within the machine. Once the metal reaches a molten state, the machine lowers a cylindrical chamber into the molten metal. The gooseneck shape of the metal injection system allows the chamber to quickly fill itself, and then push the material into the mold with air pressure or a piston.

Immersing the injection mechanism to fill it allows for rapid and streamlined mold injection in this casting process. Because the chamber is subject to direct heat from the molten metal, however, hot-chamber die casting systems are at risk for corrosion, making them a less viable option for metals with high melting points. Instead, it is better suited for materials with low melting points and high fluidity, like lead, magnesium, zinc, and copper.

By contrast, the cold-chamber die casting process works more slowly to avoid corrosion. With this method, a foundry worker ladles molten metal into the injection system. A piston then pushes the metal into the mold.

This process limits the corrosion that is more common in hot-chamber die casting. It is an ideal option for metals with high melting points, like aluminum and aluminum alloy.

The die casting process is rapid and produces highly detailed parts. It is ideal for the production of high volumes of complex parts and can also produce strong parts with smooth surface finishes. Die casting’s capacity to produce a high volume of parts makes it a crucial process in the automotive and aerospace industries.

As die casting tooling and equipment are expensive, this process is not cost-effective for smaller production runs. In addition, the malleability of metals used in the process can impact the complexity of the product.

Cast parts from SLA patterns printed in Clear Resin on a Formlabs 3D printer.

Investment casting, also known as lost-wax casting, is a process that uses wax, slurry, and molds to produce complex parts. It is one of the oldest metal casting techniques but is still valued for its ability to create precise metal parts with intricate shapes.

This process is still widely used for producing jewelry, dentistry, and art. Its industrial form, investment casting, is a common way to create precision metal parts in engineering and manufacturing.

Investment casting patterns are typically made out of wax or 3D printed polymers. The patterns are assembled into a tree-like structure and dipped into a slurry of silica, or put into a flask and surrounded by the liquid investment plaster. After the investment material dries, the flask is placed upside down into a kiln, which melts the pattern, leaving a negative cavity in the shape of the original model. Metal is melted and then poured, using gravity or vacuum pressure to pull the metal into the cavity. The casted parts are filed, ground, machined, or sandblasted to achieve final geometry and surface finish.

Sprue trees with cast rings.

Investment casting is a versatile process. It allows manufacturers to produce accurate and repeatable parts out of nearly any metal available for casting and complicated shapes that would be difficult or impossible with other casting methods. Casted parts also have excellent surface qualities and low tolerances, with minimal surface finishing or machining required.

These features make investment casting ideal for complex parts in automotive, aerospace, and industrial applications, medical tools, dental implants, as well as fine jewelry and art.

Investment casting is a complex and labor-intensive process. It requires specialized equipment, costly refractories and binders, as well many manual operations to make a mold. It can be difficult to cast parts that require cores and the process is better suited to small parts.

One half of a sand casting mold.

Sand casting is a metal casting method that was first in use 3,000 years ago but remains the most widely used casting method to this day. This process allows manufacturers to cast metal without relying on machining.

In the sand casting process, the manufacturer first creates a foundry pattern, or replica of the casting, most commonly from wood or plastic. The pattern is oversized to allow for shrinkage. Parts with features on one side only require an open-faced mold. For parts with multiple detailed surfaces, the manufacturer separates the foundry pattern into two mold boxes to form a closed cavity mold. The top half is called a cope and the bottom a drag.

Once the manufacturer creates the pattern, they tightly pack sand around the pattern. Then, they add sprues and gates to ensure that the molten metal flows smoothly through the mold cavity. The manufacturer removes the pattern then clamps the two halves of the sand mold together. Once the metal melts to a molten state, it is poured into the mold and left to cool. From here, the sand mold is removed using vibrations or high-pressure water. Finally, the manufacturer refines the part by removing sprues and gates, and polishing the cast metal part.

Sand casting is an adaptable process that functions outside the limitations of machinery. Because of this, it can create complex parts of virtually any size. Sand is inexpensive and plentiful, which lowers the setup cost and makes modifications possible. It is the only practical or economical way to produce very large castings. The lead time of sand casting is also short, making it a viable process for short production runs.

Sand casting’s versatility makes it a manufacturing option across a wide array of industries. It can produce medical equipment, automobile parts, electronic equipment, gas tanks, and engine blocks, and more.

Sand casting creates highly porous, textured metals. The shrinkage and rough surface finish also lower the dimensional accuracy of parts. This results in a low-strength final product that requires time-consuming post-processing to achieve a higher quality finish.

In order to choose the right industrial metal casting process, several factors must be considered. We’ve created this comparison table to help you compare die casting, investment casting, and sand casting in terms of types of metals, production volume, costs, production time, part complexity, and for which industries they are generally used.

	Die Casting	Investment Casting	Sand Casting
Compatible metals	Aluminum, copper, lead, magnesium, zinc	Most metals	Most metals
Production volume	High volume	Low to high volume	One-off to medium volume
Unit costs	Low	Moderate to high	Moderate
Tooling costs	High	Moderate	Low
Cycle time	Rapid	Long	Moderate
Industries	Automotive, aerospace, consumer products, furniture, power tools	Automotive, aerospace, jewelry, medicine, dentistry, art	Automotive, aerospace, industrial equipment, electronics, consumer products

3D printed jewelry ring pattern and cast metal part.

Engineers, designers, jewelers, and hobbyists can capitalize on the speed and flexibility of 3D printing by combining castings processes like indirect investment casting, direct investment casting, pewter casting, and sand casting with 3D printed patterns or casting metal into 3D printed molds. Cast metal parts using 3D printed rapid tooling can be produced in a fraction of the time invested in traditional casting and at a significantly lower cost than metal 3D printing.

Stereolithography (SLA) 3D printers offer high precision and a broad material library that is well-suited for casting workflows and can produce metal parts at a lower cost, with greater design freedom, and in less time than traditional methods.

Webinar

In this webinar, we will look at how desktop stereolithography (SLA) 3D printers are being used to directly print patterns, how to work with SLA patterns for investment casting, and how the benefits of generative design are increasing the demand for printed patterns.

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A 3D printed mold in Clear Resin for wax injection.

The process of making patterns from molds or tooling is referred to as indirect investment casting because it requires creating molds for producing the patterns in addition to final investment molds.

Rigid molds for wax (often referred to as tools) are commonly fabricated by machining aluminum or steel. Machined metal molds cost thousands of dollars to produce and take weeks of machining and polishing work before first shots can be run and pattern parts evaluated within a casting process.

With 3D printing, manufacturers can directly 3D print the mold for their pattern using materials like High Temp Resin or Rigid 10K Resin, resins with high-temperature resistance. For an optimal surface finish of molded parts, treat the interior surfaces of the mold by sanding and polishing for a smooth look, or bead blasting if a uniform matte look is desired. To ensure the final cast parts are dimensionally accurate, compensate for shrinkage by scaling up the printed mold. The exact shrinkage of the wax and the casting process can be obtained from supplier specifications.

3D printed molds for metal casting shorten the time between concept and first tests to a matter of days because manufacturers can directly print the tooling necessary for running and evaluating parts.

While molded pieces must follow design rules for moldability (e.g., no undercuts, draft is beneficial, etc.), you can achieve increased pattern complexity by using assembly jigs to combine multiple components into a single structure.

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3D printed jewelry patterns and metal casted rings.

Direct investment casting is a version of investment casting where the process moves directly from pattern creation to surrounding the pattern with investment material. It is ideal for producing parts with geometries that are too complex to be molded or for parts with extensive undercuts and fine surface texture details, where molding is possible but carries high tooling costs.

Traditionally, patterns for direct investment casting are carved by hand or machined if the part is a one-off or expected to be only a handful of units. With 3D printing, however, manufacturers can directly print the patterns, removing the design and time constraints common in other processes.

With 3D printing, engineers, designers, and jewelers can direct 3D print patterns in order to achieve shorter lead times and geometric freedom that exceeds the design for manufacturability constraints of molding processes. Formlabs developed a range of castable materials suitable for direct investment casting, in particular for the jewelry industry.

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The way jewelers work is changing, and castable photopolymer resins are leading the way. In this guide, learn how to cast fine jewelry pieces 3D printed on Formlabs printers.

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Sample part

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Grey Resin printed pattern and finished aluminum casting from an open-faced sand mold.

Similar to investment casting, 3D printing can be used to create patterns for sand casting.

In comparison to traditional materials like wood, 3D printing allows manufacturers to create complex shapes and go straight from digital design to casting.

Metal Miniatures made with pewter casting and 3D printing.

Pewter is a malleable metal alloy with a low melting point that can be used for making fully metal objects for decorative applications such as detailed metal miniatures, jewelry, scale models, and replicas of antiques.

With recent developments in temperature-resistant 3D printing materials, like High Temp Resin for Formlabs SLA 3D printers, it’s now possible to 3D print molds for direct pewter casting.

There are two options for mold designs: a sacrificial or pull-apart mold. In a sacrificial mold, there is a shell designed to be broken apart in the process. Pull-apart molds function with separate halves so the mold can be reused.

Compared to directly printing metal, the casting pewter in 3D printed molds offers significantly better detail and surface finish at a small fraction of the cost. Compared to wax casting, directly 3D printing a mold has fewer steps and requires less manual effort, while preserving the most possible detail.

Webinar

Watch our webinar to learn how moldmaking using 3D printed masters and reusable or sacrificial molds can allow you to produce parts in porcelain, precious and non-precious metals, silicone and biocompatible flexible materials, and more.

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Jewelry investment casting process with 3D printed patterns.

Businesses looking to boost design freedom or cut costs and lead times have a strong solution in metal casting with 3D printing.

Certain types of complex metal castings, such as large shapes with cross-sections and pieces with multiple cores, are difficult to create using traditional metal casting methods. 3D printing allows manufacturers to produce these complex designs. For example, jewelers can create intricate and custom designs that might be impossible without a 3D printed pattern.

3D printing also eliminates reliance on multiple machines or service providers to create parts. Instead, companies just need a digital file, a 3D printer, and printing material. This can cut costs and waste, as all the material used goes into the final product.

Finally, the combination of 3D printing with metal casting can cut costs and lead time. Rather than waiting weeks for expensive tooling before being able to cast a final product, a 3D printer can create a pattern or mold in hours.

Metal casting combined with 3D printing help companies quickly and efficiently create metal parts. With a Formlabs SLA 3D printer, you can expedite the metal casting process and cut costs along the way.

Learn more about the Form 3 desktop SLA 3D printer and request a free sample part to evaluate the quality firsthand.

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Ultimate Guide to Silicone Molding for 3D Printing (Part 1)

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as a PDF!

The simple post-processing techniques presented in this guide are an excellent way for professionals to create low-cost silicone molds, threaded inserts for enclosures, vacuum formed parts, and more.

Silicone molding is a powerful production method that, when combined with 3D printing, can allow you to make several copies of one product. You can also create a product in a material that is not supported by your 3D printer.

In this How To, we will show you some of the best practices associated with creating silicone molds around 3D printed parts.

Working time will vary depending on a number of factors. Creating a mold around our 3D printed part took us about 1.5 hours. Casting into our mold took about 15 minutes.

Supplies

3D printed mold box, hardware, vents & keys (read on for more info).

Master (the print you are molding)

Silicone

Resin and dye

Mixing cups

Mixing sticks

Mold release spray

Hot glue or cyanoacrylate glue

Funnel

Ex acto knife

Rubber bands, tape, or straps

Gloves

Respiratory mask

Eye protection

Need some of these products? We've curated an Amazon wish list for you.

Step 1: Choose a file to cast a mold around

Obtain a file that you would like to either make several of, or create in a material not supported by your printer.

We chose the cap to a perfume bottle to understand what the process would look like for a product development team attempting to produce several concept models of a prototype.

The next step is to create your mold box. This is the structure that will hold the silicone in place around your part when pouring. Your master will need to be suspended in this structure.

You can create mold boxes from:

Foam core board
Legos
3D printing

We chose to design and print ours as this method has a few benefits. Designing and 3D printing mold boxes allows you to:

Print in pour holes and vents
Easily calculate the volume of our mold
Create boxes that perfectly fit the parts you plan to create a mold of
Re-use mold boxes to create multiple molds

While 3D printing your mold box isn’t necessary, it provides you with a reusable customizable mold box that the other methods cannot produce.

Step 3: Prepare and Print

Because the silicone molding process is not very demanding on the 3D printed mold box or master, you can select standard print settings.

The 2021 Guide to 3D Printing Materials

Learn about polymers, composites, and metals all available for 3D Printing!

Supplies Used:
3D printed mold box, 3D printed master, Cyanoacrylate glue, Mold release spray, Vents & Keys

A: Spray your mold box, master, vents, and keys with mold release.

B: Choose points across model to glue vents

C: With our 3D printed mold box we were able to glue our master directly onto the pour hole during preparation.

D: Spray again with mold release for good measure

You can suspend your master using popsicle sticks, skewers, or 3D printed rods glued to the surface of the master in an inconspicuous place. The holes left in their place after your mold has cured will aid in resin flow through the mold.

Step 5: Open Bottles of Silicone (Parts A and B) and Stir Thoroughly

Supplies Used: Silicone (Part A & B), Mixing Sticks

As silicone comes in two parts, it needs to be mixed both individually and once combined with its hardener.

Mix slowly using separate mixing sticks.

Supplies Used: Measuring cups

A: Determine the volume of silicone needed to fill your mold
B: Measure desired amount of silicone and hardener separately in two measuring cups.

We calculated our mold volume by filling our 3D printed mold box with water and pouring the water into a measuring cup to find exact volume.

For two part molds like the one shown, you only need to mix enough silicone to fill half of the volume of your mold.

Once you have measured each part, combine the two parts into one mixing cup and stir slowly with a mixing tool.

Be cautious not to stir in air bubbles. Be sure to scrape the sides of the cup to mix in all material.

Once your parts are thoroughly mixed the curing process will begin.

TIP

Read instructions on your silicone for “pot-life”. This is how long you have to work with the silicone before it cures.

Supplies Used: Mixed silicone, prepared mold box and master

Pour silicone into the first half of your mold box.

When pouring, pour slowly into one corner of the mold box and allow the silicone to run to other parts of the mold box as it fills.

Stop when the silicone reaches the top of the first half of your mold box.

Once you have poured your silicone place small keys into the silicone. These will create negative spaces and allow the mold halves to fit together once poured. We will remove them before pouring the second half of our mold.

Depending on what type of silicone you are using it can take anywhere from 75 minutes to overnight to cure.

Temperature and humidity will affect curing times, so we recommend this process be done in a room temperature environment.

Step 10: Attach and Prepare Mold Part Two

Supplies Used: Mold box part two, hardware (nuts & bolts)

Once our mold has set, we will prepare to pour the second half of our mold.

A: Remove the keys you inserted in step 9.
B: Attach and secure second half of mold box.
C: Spray with mold release

Next, repeat steps 5-9 and create the second half of your mold using the methods mentioned above.

Step 12: Let Cure

Supplies Used: Pliers or Ex-Acto knife

Once both halves of your mold have cured you are ready to remove them from the mold box and begin using them to recreate parts.

A. Remove the hardware

B: Remove the mold from the mold box and open.

C: Remove the master and vents.

Supplies Used: Cured mold, mold release spray, rubber bands

Next, you will need to reassemble your mold.

A: Ensure that all parts of your mold are correctly aligned, and plug any holes created by vents.

B: Secure mold pieces using rubber bands, straps, or tape.

Tip

Another great application for 3D printing would be to design and print a box to hold the mold together when pouring resin, or modify the mold box we used to serve the same purpose.

TIP:

If your vents leave holes in areas where resin can spill out during the pour, they will need to be plugged.

Supplies Used: Resin (Part A & B), measuring cups, measuring sticks, dye.
Just as with silicone you will need to measure each part of the mixture taking into account the volume needed to create a part.

If you have made several molds, you can mix a larger quantity of resin and pour several molds at once.

Add dye to the part of the resin mixture specified in the instructions.

Step 16: Mix Resin

Combine both parts of the resin mixture and mix thoroughly being sure not to stir in air bubbles.

TIP:

Resins typically have a shorter “pot-life” than silicone meaning they will cure faster.

Step 17: Pour Resin

Supplies: Funnel

Once mixed, pour immediately into the opening of your mold using a funnel.

Pour slowly as not to overfill and spill resin.

Any resin that remains in the mixing cup will harden, but can typically be removed afterwards.

Step 18: Let Cure

Once poured, allow the resin to cure for the appropriate amount of time.

Supplies Used: Pliers

Once your resin has cured, you can open the mold and remove your cast part.

Any resin that escaped through seams or voids and cured is called “flash”. Flash will need to be removed from the part through post processing.

Below, you can see that we were able to recreate our perfume bottle cap in several different colors and opacities using silicone molding.

Visit one of our other applications pages for tips on how to take your print even further.

We recommend that you visit our pages on:

Silicone Molding Part II
Vacuum Forming
Sanding

Last but not least, remember to share your work with us on Thingiverse and social media @MakerBot.

We can’t wait to see what you make!

All the secrets of casting in 3D printed molds.

Hi all!

A little more than a year ago, a 3D printer was purchased. Moreover, it was bought not as a toy, but with a very specific task - to print injection molds for polyurethane.

While the printer was driving, many acquaintances and other specialists argued and convinced that it was necessary to order milled aluminum molds, install a centrifuge for casting, and so on and so forth. But how can I order a milled mold for a lot of money, if a) it is not clear whether I made the configuration correctly b) even if everything is correct, how many thousands of years it will fight back, subject to an incomprehensible demand for my molded products ...

In general, the printer arrived, learned how to print and went into battle.

The main problem of casting molds is to model them correctly in order to:

1. It was convenient to print with the required quality.

2. Consider fluid movement and potential bubbles.

3. Easy mold separation and product removal.

4. Fast mold assembly and disassembly.

5. Mould-tight.

After a few kilos of damaged plastic, the search for the right shape is over.

- the injection channel must be made from top to bottom, thus the slurry goes from bottom to top, squeezing out air

- The channel must be quite wide. since I use a catheter syringe (160 ml can be bought at a pharmacy or on Ali), it makes sense to make a diameter of about 5-7 mm. The slurry is relatively thick and harder to push through a narrow channel.

- the entrance to the channel is made on a cone slightly larger than the cone on the syringe, because when connected, they are mutually compacted, as it were, and the slurry flows strictly along the channel.

- The form itself must not have sharp or protruding corners, as well as overhangs, under which and for which the bubble can catch.

- along the contour I make a tenon-groove connection. first, it positions the two halves. secondly, the groove is smeared with silicone sealant (retaining elasticity) and this gives an additional seal against the flow of slurry.

- it is also possible to provide holes in the mold for fastening parts and their centering. Centering is very important! Even tenths of a millimeter will be reflected in the finished product as a not beautiful offset strip

Mountains are already written about the settings of the printing itself, the only thing is that I print forms mainly in ABS. Because, it is well and quickly smoothed out with acetone. By the way, finding real acetone is like finding real vodka. As a result, I guarantee the quality of the acetone of the pro shop, and the planet of the piece of iron. For the regions, auto paint shops are probably relevant. There is no acetone in construction markets and supermarkets such as obi and leroy, or it is called acetone, but plastic does not dissolve. I do all my production work outside of my home, so smells don't bother me. After dexterity with acetonite, you can achieve the result as in the photo and even much better.

Now let's move on to making the goo.

Before cooking, it is necessary to treat the molds with a wax separator, dry the wax (this is important), since not dried gives defects on the product in the form of flakes on the surface. Assemble/fasten the form and prepare dishes, disposable gloves, scales and other accessories.

I have been using Silagerm fluids for a long time. They have different ones. Silicone and polyurethane and more. For my purposes, Silagerm 6030 is suitable. The designation of the last digit is the shore hardness. In general, 30kA after complete solidification resembles a very dense rubber and stretches well (and 90I will be like oak plastic). The manufacturer claims up to 600%, but in fact the thicker the less it stretches. 1-2 mm will stretch just 6 times.

Two-component slurry, mixed by weight. For this, ordinary kitchen scales were bought. The manufacturer recommends kneading and pouring for a long time and knead again. In my experience, if there is a mixer, then there is no point in stirring for longer than 1-2 minutes. During kneading, you can add dye. I have it in a syringe for less. I usually pour the dye by eye and 5-10 ml is enough for 300-500g of the main liquid, in fact, a teaspoon of the dye is enough for half a kilo. something like this. When the liquid is mixed, the life goes on for minutes, depending on the density, it's different, but boobs should not be crushed. We quickly put the bucket in the vacuum.

What a vacuum chamber is for. While the slurry is stirred, many bubbles form in it. And even if you stir slowly and pichalno bubbles will still be. So it needs to be vacuumed. This will remove any bubbles and further stir the slurry.

Initially, the vacuum chamber was a glass jar, and everything interfered in it. When the volumes grew up, the question arose of increasing the volume of the chamber. The ideal option for price and durability was the Soviet pressure cooker. It is not so easy to find an unnecessary Soviet pressure cooker from friends and relatives! I had to buy a left-hander on the market for as much as 500r !!! ))

Unfortunately, there is no viewing window on it, but I already knew that the volume of the slurry increases several times during vacuuming, so the container is needed for mixing with a five-fold volume (300g - 1. 5l will just be). If the bubbles are not all removed (they can be seen, they pop up), you must quickly repeat the procedure.

Next, I draw in the liquid with a syringe (this makes it even more vacuumized) because direct pouring will again give ubiquitous bubbles, and I already press it into the mold. By the way, I forgot to write that the form should have exit channels and additional capacity at the top, since the material tends to spread and gradually settles down, respectively, the volume should be reserved for these processes. In either case, the sprues are trimmed, and the extra volume that comes out ensures that the mold is completely filled.

The form can be opened after two days. If everything went well. then the product will be free of defects, easily separated from the mold. The form itself can be immediately reused and until it becomes unusable.

Products according to the forms above:

By the way, the boot of the CV joint turned out to be so ribbed, because the form was printed with PLA and dichloroethane did not manage to smooth it out qualitatively.

Thank you all for reading! I tried to give out the maximum information that I have accumulated over the year. If you still have questions, ask, I will answer all.

Injection molding from 3D printed molds

Study of low-volume production of small plastic parts

BRIEF INFO

on a Form 2 printer and injection using a Galcom Model-B100 injection molding machine. Two transparent resin molds were tested: one large butterfly mold and one mold with four small butterflies in one block. A third mold for the USB stick case was tested in high temperature polymer. These molds were 3D printed by Formlabs and the castings were made by Galomb Inc and Formlabs in a variety of materials.

Formlabs and Galomb, Inc.

LOW-VOLUME 3D PRINTED PARTS

Most plastic products in the world today are made using injection molding. Using inexpensive desktop 3D printers and injection molding machines, molds can be created to produce small functional parts from manufacturing plastics.

For low volume production (approximately 10-100 parts), 3D printed molds save time and money. They also allow for a more flexible approach to manufacturing, giving engineers and designers the ability to easily modify molds and continue iterating their designs at low time and cost.

The Form 2 Stereolithographic 3D Printer (SLA) produces completely solid, smooth parts that can withstand the temperature and pressure of desktop injection molding. 3D prints produced using SLA are chemically bonded so that they are completely dense and isotropic, producing functional shapes with a quality not possible with FDM.

Formlabs has partnered with Galomb Inc., a manufacturer of low cost injection molding machines, to test and demonstrate the viability of SLA injection molds.

Fig. 2 : 3D printed molds in aluminum frames.

METHOD

Both clear and high temperature resins can be used to print small functional forms, with high temperature resins offering compatibility with a wider temperature range of

thermoplastic melts. Formlabs Clear Resin was chosen for its strength, high detail and smooth surface Clear Resin is preferred for its transparency as you can easily see when forms are being filled, but any of the standard Formlabs Resins (clear, white, black and grey) can also be used as they have similar mechanical properties. The plates were printed with a layer height of 100 µm and took approximately 5 hours per plate. Depending on the geometry, multiple shapes can be printed at once on the build platform to improve printing efficiency.

Fig. 3 : Printing setup in PreForm with cavities up.

Two forms were printed from transparent resin. Parts and subsequent molds were designed to match Galomb machine vise sizes, 1 in3 injection cylinder capacity, and Form 2 build volume. supports were polished.

The parts were then cured for one hour under a 405 nm UV lamp to achieve full mechanical strength and rigidity. For a better understanding of the impact of post-curing on parts, see the Formlabs UV post-curing booklet.

Fig. 4 : 3D printed molds in aluminum frames and die-cast parts.

The first was a large Formlabs butterfly logo and the second was four small Formlabs butterfly logos. Both molds had a cavity, narrow inlets, and sprue at the point of injection and were designed in Solidworks. The molds were inserted into aluminum frames to provide protection from the downward pressure and heating of the injection nozzle. Aluminum frames can also prevent the shape from deforming after repeated use. The frames shown in figures 2 and 4 were custom made by Whittaker Engineering in Scotland, but standard aluminum frames are readily available on request from injection molding machine manufacturers.

Plastic pellets can be purchased online or from suppliers such as IASCO-TESCO. To create different colors, the molten plastic was pre-mixed with powdered dyes prior to injection.

Using a Model-B100 benchtop injection molding machine, Galomb tested printing plates with 25 shots of LDPE. LDPE melts at approximately 325°F (163°C) and was chosen for its low melting point. Of note, Formlabs Clear Resin has an HDT at 0.45 MPa 73.1 ºC after post-cure (see Material Data Sheet). HDT is a measure of the thermal properties of a material, but does not rule it out for use, although LDPE has a higher melt temperature. Whether your 3D printed mold will withstand the injection molding process depends on the melt temperature of the injection material, part geometry, and cooling and cycle times.

RESULTS FOR CLEAR POLYMER

After 25 injections of LDPE, there was no noticeable deterioration in the surface of the molds (chips, cracks or scratches). LDPE is not prone to sticking to polymer molds when tested, but other plastics may require the use of a mold remover to assist in part removal. Adhesion of the part to the mold can cause mold wear during ejection. Release agent is widely available, and silicone release agent is compatible with Formlabs standard and high temperature resins.

The cycle time for each injection was approximately three minutes. This process was accelerated by using compressed air to cool the mold. Cyclic injection into forms printed on the Form 2 causes the form to heat up. To counteract this, the cooling time between open mold cycles must be increased. While the mold cannot deform, too much residual heat will reduce molding success if the mold is opened too early. Galomb also improved molding success by etching shallow (0.05 mm deep) vent holes (not shown) leading from cavity edge to mold edge so that air does not enter the cavity during injection.

Some of the injections showed a leak in the parting line due to deformation of the polymer mold during the cooling phase after several injections. Increasing the clamping force in the vise can help mitigate leakage, as can polishing the parting plane of the mold to make it as flat as possible. Galomb proposed incorporating channels into the mold design to include metal tubes and fill them with aluminum epoxy, as a strategy to strengthen the mold, reduce warping, and improve cooling time.

Fig. 5 : A range of injection molding parts made using 3D printed molds.

FURTHER TESTING WITH HIGH TEMPERATURE POLYMER

Clear resin molds have been successfully tested using LDPE, which has a relatively low melt temperature. Higher melt temperatures can cause thermal shock in clear resin printed parts, which manifests itself as a deformed mold surface.

Transparent resin molds experience thermal shock when exposed to higher temperature molten plastic.

Formlabs printed the shape of a USB device case in High Temp Resin to test

Plastic Troubleshooter

Melting Point	High Temp Polymer (HDT at 0.45 MPa = 289° C)	Clear Resin (HDT at 0.45 MPa = 73.1°C)
LDPE	163 °C
PP	177 °C
TPE	177 °C
PLA	180 °C
ABS	204 °C
HDPE	204 °C
EVA	204 °C
Polystyrene	226 °C

High temperature polymer molds showed no temperature degradation at the mold surface for any of the tested plastics.

*DURABLE RESIN polymer is under development and final specifications are subject to change.

High Temp and Standard are the polymers best suited for molding. Of the Formlabs resins, High Temp has the highest HDT at 0.45 MPa and low thermal expansion. It is also the stiffest material with the highest stretch factor.

The relatively high stiffness of High Temp Resin means that the mold will not deform when the part is removed. This makes the use of a release agent especially important for removing parts molded from rigid plastics such as polystyrene.

GENERAL TROUBLESHOOTING

Form overflow leak.

Leak occurs when the injected plastic is forced out between the two mold halves. This can happen when the shape is overflowing, or if the split plane is not completely flat. Adding thin exit ports to the mold can help mitigate leakage from overpressure within the mold, facilitate part removal, and eliminate entrapped air that can cause bubbles in the molded part. Although not shown, the plates were tested without the aluminum frame. The downside to this approach is that these parts use more material, which increases printing cost and time, and the forms can be more prone to warping. With this method, a steel washer placed between the printing plate and the nozzle of the injection molding machine protects the print from direct contact and helps distribute forces. In addition, pre-sealing the injection molding cylinder against a metal block helps ensure there are no air pockets to disrupt the plastic flow.

Printed lines visible on some parts; this can be reduced by printing the form with a lower layer height. The plates used in this study were printed at 100 µm, but 50 or 25 µm could also be used. This will improve the cleanliness of the plate surface, but increase print time and reduce tank life.

Final USB device case molded from high temperature resin.

DESIGN INSTRUCTIONS.

When designing a form, evaluate what will print successfully, as well as what will successfully form.

Adding one to three degrees of recess on surfaces perpendicular to the direction of the recess will allow easier part removal and minimize mold degradation. Fillets should be applied to the inside edges to reduce buckling from internal plastic stress and facilitate removal of the part.
Embossed and engraved parts must be offset from the surface by at least 1 mm.
If you plan to use an aluminum frame, The surfaces of the separation planes can be polished with fine sandpaper to reduce flare. add an extra 12mm thick plate to the back of the mold plate to account for compressive forces and ensure complete sealing.
Be sure to orient the mold halves in the PreForm so that the cavity is facing up. This will prevent reference marks inside the cavity and make post-print processing easier.

90° angle

2° recess

Optimum condition 2° recess and round.

PROCESS SUMMARY

STEP 1:

Part design in CAD.