Avoid closed cavities

Make sure your part doesn’t have any closed cavities, as this will make the resulting mold unprintable.

Delicate lattice structures

FIM allows for the injection molding of intricate and delicate lattice structures. When designing these, the feature thickness should be lower than the adjacent wall thickness, to avoid walls breaking during injection.

Scale your component

Some feedstock materials shrink upon cooling. To ensure that the final part is the correct size, scale the part accordingly when creating a mold.

Orientate part

Consider tolerances when orientating print on platform. Some slicing software supports pixel alignment, but if this is not the case the tolerance will always be at least +/- pixel size.

Consider staircasing

Prints are built in layers, so any walls which curve or slant along the Z-axis will have staircasing.

Always consider how to minimize the influence of staircasing, when designing molds for manual demolding.

Decide mold type

When designing your mold, you must decide what type of mold you want to design; FIM, split or reusable split. 

Select mold

Your mold’s exterior dimensions should fit an existing frame. Select the smallest possible mold, while maintaining a mold wall thickness of at least 5mm in all directions.

Consider spacers

Reduce printing and demolding time by cutting excessive material of your mold and make a reusable spacer.

Subtract 0.05mm from mold sides

When determining your mold dimensions, subtract 0.05mm from the frame dimensions to get the best fit between mold and frame. 

Oversize fillets

It is always better to make the fillets/chamfers a bit too big, rather than too small. 

Avoid elephant’s foot

To avoid getting an elephant's foot on most printers, add a small chamfer along the edges towards the build platform, 0.5 – 1.0mm should be enough. It can also help when demounting the part from build platform.

Printability

Split molds may be used, even if you intend to demolding by dissolving. Creating a split mold can improve the printability of your mold by reducing overhangs.

Faster dissolution

In cases where aspects of the component can only be safely released by dissolving the molds. A mixed method may be applied. Removing parts of the mold will speed up the demolding time and reduce costs, as less resin is involved.

Place split plane(s)

Partial: at least one mold half must be manually removable.

Manual: all mold sections must be manually removable.

Reusable: split plane should cut through runners and center of the injection point.

Avoid deep recesses

The split plane should be placed to avoid deep recesses, as these are harder to reach during the curing step.

Supported cores

Printed as well as steel cores must be supported in both ends, ideally reaching from end to end of the mold.

Grooves around split lines

Add grooves in split lines to ease separation. The groove makes it easier to place a spatula or similar separation tool in between the two mold sections.

Place bolt holes

Bolting should evenly clamp the mold assembly, e.g., for a rectangular mold, place a bolt in each corner. The most effective clamping is the closing pressure of the molding machine, so orientate the mold assembly to make best use of this.

Add 0,8 mm to bolt holes

Make bolt holes 0,8 mm larger in diameter than the bolt itself, i.e., M5 bolt = 5,8 mm hole.

Use keys

Use keys for precise assembly. Keys are part of the printed mold, so any resin or printer related scaling will occur on both the positive and negative key interfaces, ensuring a precise fit every time.

Make keys as big as you have space for.

Differentiate key sizes

If your mold is symmetrical, differentiate the key sizes, so the mold halves only fit together the right way.

Chamfer or fillet key edges

For ease of assembly fillet or chamfer the edges of your keys. Easy assembly makes for accurate assembly. When using force, you risk denting and distorting delicate features.

Place inlet(s)

Inlet runner placement must secure that the feedstock material reaches all areas of the mold before hardening. The deepest cross-section is ideal to provide the best flow and minimize voids and sinking.

Place outlets

Outlet runners should preferably be placed opposite of the inlet, and at or close to points at the end of fill. The outlets also capture any potential cold slug and make it possible for the operator to check if the mold has been properly filled.

Check flow

Main considerations that influence the flow in a mold are. material flow rate, part volume, part design, material type and grade, and processing conditions

Outlets near angles

Place outlets near all sharp angles and protrusions to ensure that the cavity is filled completely when injecting.

Dimension gates

Gates are a narrowing of the runners, which can help guide the feedstock material into the part cavity at the right angle and pressure. Gates with a diameter of 0,6-0,8mm can be twisted of.

Avoid unsightly marks

Place gates on the interior of the part, where possible, to avoid unsightly gate marks.

Use the parameters provided as the base line

Print directly on the Build Plate

Adjust wait time

The larger solid cross-section you print the longer wait time should be.

Wear PPE

Always wear the recommended personal protective gear (PPE), which can be found in the platform specific guide, and in the relevant safety datasheets.

Check resin

Ensure you have enough resin prior to beginning your print. Depending on your printer you may simply fill the drum vat, or for printers with an automated resin supply system, you will have to check the fullness of the resin bottle.

Print multiple molds

It will often take a few tries to dial in to optimal IM-parameters. When doing full or partial manual demolding, removing the part intact is an added complexity. We therefore recommend printing 5-7 of the same mold when testing.

Make the most of the printing time

The printers best suited for printing of molds build one layer in a single exposure, e.g., DLP or LCD-style machines. The printing time is therefore determined by amount of layers i.e., part height, and not general size. For effective use of the printing time, orientate your print horizontally, when the design allows for this.

Vary print placement

The film at the bottom of the resin vat may deform under recurrent localized stress. By varying the place of your print(s) on the platform, the film will last longer.

Storing cleaning chemicals

Always follow the storage recommendations outlined in the chemical’s safety datasheet. Failure to do so can pose danger and lessen the effectiveness of the chemicals.

Never leave prints in cleaning chemicals

Do not leave prints in cleaning chemicals for longer than recommended, as this can result in weakening of the mechanical strength of the print. The time recommendations can be found in the platform specific guide.

Visually inspect between cleanings

Inspect the print between every cleaning step, to ensure that the step has been performed satisfactorily.

The final clean print should appear dry and without stains.

Orient part for flushing

When flushing through the channels, the air will seek upwards, while the liquids will seek downwards. As such larger channel exits should be orientated downwards, to limit spraying. You may also choose to flush the part while partially or fully submerged in the cleaning chemicals.

Flush channels with cleaning chemicals

All channels and cavities should be flushed through with a syringe. Inject the cleaning chemical into the mold through the largest opening, This opening should be larger than the syringe tip to avoid splash back.

Remove excess cleaning chemicals

Blow excess cleaning chemicals out of the channels and of print surfaces using pressurized air or a syringe. Remember to check around the channel openings for blown out resin residue.

Placing prints

Place prints in the curing machine so they will be exposed to direct UV from all angles.

Curing time

Curing times are specified in the cleaning guide. As a rule of thumb, it is better to over-cure than under-cure, as under-cured prints will be too soft and remain contaminated by uncured resin.  

Don’t go overboard

While over-curing is preferred to under-curing, the curing is always superficial. The curing rays only penetrate the outer 1-2 mm of the printed molds. Thus, extreme over-curing results in brittle prints.

Keep curing cabinet closed during curing

The prints are UV-cured. Exposure to intense UV-light can damage eyesight.

Use clean gloves for cured prints

The cured prints can be removed with bare hands, but if you are unsure if the print has been sufficiently cured, do wear gloves. Make sure to wear clean gloves, so as not to contaminate a cured print with uncured resin. 

Review feedstock datasheet

Always check the datasheet for your feedstock material well in advance, as some feedstock materials may require preparation such as drying for eight hours prior to injection.

Temperature

The heat resistance of the resin is highly time dependent. Do not preheat mold beyond 50°C.

Injection temperature above 400°C is doable if the injection speed is high, and the packing time is kept short.

Pressure

Follow the feedstock material datasheet.

You may increase the pressure above the recommended to improve flow through winding channels and decrease injection time. 

Weld lines

A weld line occurs where two melt fronts reach each other at a temperature where they do not merge completely. On the resulting part a crack or a weak line will be visible. Avoid this by changing the mold design -  moving the outlet or adding more inlet channels.

Slip

Mold lubricants may interact with the resin, and can pool in the corners of the staircasing, resulting in uneven coating. If using lubricant only use a light layer and consider wiping off any excess prior to injection.

Reusability

Depending on design and feedstock used, molds may be reused 2-5 times without notable degradation.

Place filled prints in stainless-steel basket

Do not under any circumstances lower your hands into the vats in demolding station. Instead place the filled molds in a stainless-steel basket. Do not use aluminum as it will dissolve. 

Raise parts from the bottom

The dissolved resin sludge sinks to the bottom- For effective demolding, your basket should ensure that the prints are raised at least 3 cm above the bottom of the demolding vat. 

Ensure sufficient space between prints

Don’t overload the basket with prints, leave at least 1 cm of space around each print, to ensure that the entire surface is in contact with the demolding solution. 

Set temp. to 40-50C

The demolding vat should be heated to approx. 45C for optimal demolding. 

Leave prints to demold

Leave prints in demolding vat until the resin has fully dissolved, which will take 24-120 hours depending on the print size, quantity and current saturation of the demolding solution. 

Rinse demolded parts

Once parts have fully demolded, move the basket to the rinsing vat. This vat should be filled with demineralized water for best results. Move the basket up and down in the vat 15-25 times for proper rinsing. 

Partial manual demolding

Partial manual demolding can shorten the demolding time, while still yielding the FIM design freedom. Partial manual demolding may also be chosen in instances where staircasing prohibits manual removal of some of the mold sections. 

Staircasing

The key difference between a 3D-printed mold and a conventional metal mold is staircasing. Unlike a metal mold, the walls are not smooth. The print is built in layers the interface between which can cause snagging.

Softer plastics

Complete manual demolding is more likely to be successful with softer plastics, provided the mold design allows for this. This is because softer plastics are more pliable, and less likely to snag.

Heating

For feedstock materials which tolerate +80°C, consider that a short heating of the mold material will make it more pliable and easier to "peel away from" the molded part.

Feedstock shrinkage

Some feedstock materials shrink with cooling, depending on the part geometry this shrinkage can aid in releasing the part from the mold or hinder it further.