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How to Create 3D Printed PVA Molds Ready for Metal Fluid Casting

How to Create 3D Printed PVA Molds Ready for Metal Fluid Casting

With 3D printed PVA molds you can easily cast highly detailed objects from Metal Fluid.

Not every object can be cast in a traditional two-part folding mold, mostly because some details and more complex shapes couldn’t be retrieved from it. Disposable 3D printed PVA molds are a good alternative in such situations, enabling you to cold-cast highly detailed objects from Metal Fluid.

3D printed PVA molds
Metal figures cold-cast from 3D printed PVA molds
Metal figure cold-cast from a 3D printed PVA mold

Utilizing 3D printed PVA molds

Designer Eliza Wrobel wanted to cast a set of Egyptian-themed figures (originally designed by Zorum). She decided to make disposable 3D printed PVA molds that would enable her to recreate the high level of detail from the original 3D model. First, she took the models and designed simple mold forms with inlets around them.

3D printed PVA molds
PVA mold model in Voxelizer software

In Voxelizer software, Eliza was able to prepare her molds for printing by using a PVA preset and adjusting it for 1.75 mm Plastic Extruder mounted on ZMorph 2.0 SX multitoool 3D printer. It took several hours to 3D print the molds. They were ready to use straight out of the machine – no post-processing was needed at this stage.

3D printed PVA molds
PVA mold printing using ZMorph 2.0 SX multitool 3D printer

3D printed PVA molds are perfect for Metal Fluid casting because they don’t deform once the material starts to give back heat. Metal Fluid is a mix of metal grit in a resin binder that looks, feels, and weighs almost exactly the same as brass, bronze, and other metals. Once the material was poured into the molds, it needed a few hours to stiff.

3D printed PVA molds
Metal Fluid cold-casting using 3D printed PVA molds

After putting them in water for 24 hours, 3D printed PVA molds dissolved completely. Eliza was then able to clean her model from residue material and star post-processing of the metal objects.

3D printed PVA molds
Metal figure after dissolving the PVA mold

Casted figures required sanding to eliminate 3D printing layers and a resin residue that settles over the metal. After that, it’s good to clean the model of any dust and use polishing paste to bring out the patination effect on the metal. This way the figures got a stylish, antique look.

3D printed PVA molds
Sanding and post-production of a metal figure

Many possible applications

3D printed PVA molds can be used to cast highly detailed objects from Metal Fluid that couldn’t be made with any other DIY or low-cost casting method. This way freelance designers, artists, and small companies owning a multitool 3D printer can create their own unique metal figures, statuettes for prizes, paper buttons, bookends, stylish decorations, and even silver jewelry.

3D printed PVA molds
Metal figures cold-cast from 3D printed PVA molds

This method could also be successfully applied to create antique replicas and high-quality movie props at a fraction of previous costs. It’s much easier and less time-consuming than traditional mold making and metal casting too.

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Painting & Finishing Tips for your 3D prints

7 Useful Advice on How to Paint 3D Printed Objects

As 3D printing has a popular manufacturing method for craftsmen and hobbyist alike, many first prints disappoint enthusiasts as the model does not come out showroom floor ready. Most displays claiming to be 3D printed, have had a lot of post-production polishing. Having a truly finished product is far from professional exclusive, and the work pays off. Your post-production polishing is only as good as the surface you’re working with. In turn, advice on how to paint 3D printed objects must also focus on how a model is printed, and pre-painting steps.

paint 3D printed objects
Source: The Golden Drops / Virtual Magic

1. Know Your Model, Know Your Material

Not only are certain materials better for malleability or sturdiness, various printing plastics are vastly different on how to paint 3D printed objects. ABS can be smoothed by acetone, while PLA works better with ethyl acetate. Different materials can also react to the first polishing in distinct ways as well. For example, metallic filaments are best left in a tumbler for an average of 12-36 hours. Quality wood filaments can usually be sanded like real wood. ABS is more heat resistant and works great for interlocking parts, PLA won’t warp as much during your print and is more rigid than ABS. Exotic filled filaments will mostly depend on the thermoplastic second ingredient.

costs of 3D printing
Various filament samples

2. Avoid edges

By edges, this refers to how much of your model is in contact with the print bed. This is more of a minor detail as most models can lose a few layers from the bottom during post processing and be fine. If your model is not one of these, then try to reposition your model until you find a way for it to sit with a minimal contact to the print bed.

7 useful #3Dprinting advice on how to paint #3Dprinted objects

 

3. Slow and small

Small and slow print settings will be your friend. A smaller extruder nozzle will result in a finer off-the-printer surface, this is best if you plan on using chemical vapors to smooth your print surface or if you want to preserve intricate details. Another element of cleaner prints is using additional fans that are directed at the print itself just beneath the extruder.

paint 3D printed objects
Printing toolhead with additional cooling fan

4. Adjust For Your Equipment

If you’re using the ZMorph multitool 3D printer or another high-grade printer, additional fans and extensive sanding may not be required. A great example of a lower need for post-process pre-sanding can be found in Victor Pons’s dragon door knocker. Right off the print bed, there wasn’t much need for filler as the printer didn’t leave much of any ridges so he could use bonding paint since the surface was already smooth. It allowed the hobbyist to spend more time going above and beyond. Just goes to show that everything effects how to paint 3D printed objects.

3D Printed Door Knockers
Source: Victor Pons

5. Always Optimize Your Surface and Prime

Once you have vapor treated, sanded, and or coated your model with epoxy or resin, you’re ready to paint. Almost any project should include automotive primer, don’t limit yourself to “3D printing” labeled materials. Acrylics, gesso, automotive paints, and even iron powder can breathe life into your project. Avoid epoxy on 90-degree angles, as it will round sharp details.

6. Plan Ahead

If you’re moving the model by hand, pick a spot on the outside to hold it by and apply paint, primer or epoxy to that area last. Nothing can be more frustrating than ruining hours of work with finger marks or moving layers of paint. If your model allows for you to use a stand, this would be best.

paint 3D printed objects
Source: The Golden Drops / Virtual Magic

7. Don’t Let Your Work Go To Waste

Don’t be afraid to experiment in order to find a paint that will bond well with your primer or the plastic surface. If your model will be handled a lot or needs an extra shine, use automotive clearcoat. Another variable includes primer, satin, gloss, and matte paints for different looks. Once you have a little practice, try weathering techniques like scuffing and dabbing on accent colors only to immediately wipe them away. When possible, use what you have to your advantage, like the natural lines in 3D printing to accent faux wood.

Example printing and post-production process

  • Optimize your model digitally.
  • Change your printer settings for quality rather than speed.
  • 3D print your model.
  • Vapor treat if you can.
  • Apply a filler putty where need be.
  • Sand (raise grain count by 100-150 after each sand).
  • Apply filler primer.
  • Sand.
  • Apply a standard primer or first paint coat.
  • Wet sand.
  • Paint (preferably with an airbrush). When painting multiple colors, use sealing painters tape and go light to dark colors if you need to layer colors.
  • Clearcoat, clearcoat, clearcoat.

Check out the video by 3D Printing Nerd in which he guides you through the entire process.

This is what makes the difference

This list has been crafted from our experience, observing professionals, and well-known enthusiasts to really learn how to paint 3D printed objects without any fluff or methods that are only rumored to work. So practice, practice, practice, your project will thank you for it.

Adjust the chemicals, materials, methods, and repetition as need be for the filament and model you’re working on. Always work with personal safety equipment, and in a well-ventilated area. Though this may seem like a lot of work, it is enjoyable to most to extend their projects after the initial print. As you move along the finishing process you’ll find constant reward as your print comes to smooth, shiny surfaces.

paint 3D printed objects
Cleaning ABS print with acetone

Post processing is the difference between design and a product that stays around for years to come. After a few test runs, you’ll have the skills to bring your models to showroom status. Use these pieces of advice as a modular procedure, as it can change to best fit nearly any project your heart desires.

Additional resources on how to paint 3D printed objects

If you want to explore the topic even further, then you should definitely check the following sources:

  • Top 10 3D Printing Tricks by Commando Designs

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Responding to production pressure with conformal cooling- by Marc Saunders

Mould tool with conformally-cooled inserts produced by additive manufacturing

Responding to production pressure with conformal cooling

Injection moulding allows plastic products to be produced in complex and intricate detail, often in sizeable production runs, with repeatable tolerances and high surface quality.  Mould tools must be designed to perfectly replicate the 3D design in the minimum cycle time.  Cooling of the plastic part as it solidifies within the mould tool is a critical factor, affecting both the cycle time and the quality of the part.

I explored the use of additive manufacturing (AM) to produce efficient mould tooling in my post Conformal-cooled mould tools – how to cut cycle times and boost part quality.  In this post I look at how these techniques have been applied by leading cleaning systems provider Alfred Kärcher GmbH & Co. KG to boost production of one of their best-selling pressure washers.

Image above – Kärcher casing components being removed from their injection mould tools

Before we look at the Kärcher application, let’s recap the principles of conformal cooling and look at the beneficial impact of AM on mould tool design.

Why use AM for conformal cooling of mould tools?

The goal of conformal cooling is to reduce the temperature of the plastic part inside the mould tool quickly and evenly.  The part cannot be removed from the tool until is has cooled sufficiently to detach from its mould.  Any hot spots will delay part release, may lead to warping and sink marks in the part after removal, and may compromise the quality of the component surface.

Cooling is achieved by passing a fluid through channels inside the mould tool so that the heat is conducted out of the plastic part, through the metal tool, and away in the fluid.  The speed and evenness of this cooling effect is driven by how closely the fluid channel tracks the surface of the tool, and the rate at which cooling fluid passes through it.  We also need to ensure that our mould tools are reliable, avoiding dead-spots in the coolant flow where sediment can gather and create blockages.

Image above – conventional cooling channels produced by cross-drilling require additional plugs to avoid dead spots.  The sharp corner also creates turbulence and limits the flow rate of coolant through the channel.

AM gives mould tool designers the freedom to design complex cooling channels that closely follow the component surface, whilst maximising laminar flow and eliminating dead-spots that might otherwise clog up over time.

In conventional moulds we have cross-drilled and plugged cooling channels in limited regions of the part like this:

By contrast, with AM we can design contoured channels that closely follow the surface of the tool like this:

So AM helps us to design tools that not only provide more effective cooling, they are also simpler to manufacture and assemble.

55% reduction in cooling time increases Kärcher’s productivity

Kärcher makes pressure washers that are sold globally, with more than two million of their K2 Basic model leaving the factory in Obersontheim each year (image shown left, courtesy of Kärcher).  The striking bright yellow casing is manufactured in two halves on six injection moulding machines.

The company needed to increase productivity from these moulds to keep up with growing demand.  Using conventional cooling, the total cycle time was 52 seconds, of which 22 seconds was required to cool the part from its melting temperature of 220°C to the de-moulding temperature of 100°C.

The mould tooling for these parts is substantial and complex, comprising a large cavity and numerous cooled inserts.  The original design is shown below.

The original cooling system for the inserts contains several separate cooling circuits as shown in the image below.  A total of 10 litres per minute of cooling water is used.

Thermography of the ejector side of the original mould tool shows the wall temperature at the end of the 22 second cooling cycle.  We can see significant variation in temperature across the mould, with hot spots that may compromise the component as it is removed from the mould:

The first step to speeding things up is to simulate the mould tool behaviour.  In particular, the hotspots need further analysis as they are responsible for the long cooling time.  A simulation of 20 cycles was undertaken, including an analysis of the wall temperature.  The modelled temperatures show good correlation with the thermography.

Now that we have a model of the current cooling design, we can make design changes to improve things, focussing on the hot spots.  In this case, a part of the solution is to add extra conventional cooling channels into the beryllium-copper mould plate on the nozzle side.

Next we develop new AM inserts for the ejector side of the tool, featuring conformal cooling to carry away the excess heat.  The image below shows these additional 4 mm diameter cooling channels applied to the problem regions:

In one region where there was insufficient space to include more cooling channels, Kärcher made improvements to the product design to alleviate the problem.

When we simulate the thermal behaviour with these new cooling systems in place we see significant improvement in the uniformity of temperature across the part, after a much shorter cooling cycle:

These simulated improvements are borne out by the thermal imaging of the new mould after a shortened cooling cycle of just 10 seconds:

The new inserts are made using AM to create the complex channels.  Some are built entirely additively, whereas others are ‘hybrid’ components which build up additive regions on top of machined blanks.  Vacuum-brazed cores from Listemann Technology AG also formed part of the solution.  The new ejector side assembly is shown below:

In Kärcher’s application, cooling time was reduced by 55% from 22 seconds to just 10 seconds.  Combined with further time savings in material feed and handling, the faster cooling helped to increase the production throughput from each tool by 40% from 1,500 to 2,100 parts per day.

Image above – original (left) and new (right) mould tool designs.

Summary

Conformal cooling enables mould tools to operate faster and to produce more consistent parts.  AM boosts this further by optimising heat transfer to make cooling both faster and more even.

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Using your 3D printer for the good of humanity

In 2013,  I was fortunate to see a video of a young South African boy named Liam who had just received a new prosthetic hand thanks to the work of Richard Van As and Ivan Owen. That one minute video changed my life. Watch it yourself and you’ll see what I mean.

Little Liam was so cute and had so much determination, his perseverance lead to a worldwide movement called e-NABLE. I joined the movement about 5 minutes after watching this video. Now, three plus years later, thousands of children across the world have received free 3D printed prosthetic hands and arms. I have printed and assembled more than 50 hands and two arms and enjoy the best hobby in the world.

 

To learn more check out www.enablingthefuture.org and www.enablecommunityfoundation.org or contact me and I’ll be happy to get you started.