Lost Wax Casting Process

This is a little photographic tour of my lost wax casting process. It is a mix of photos I have taken throughout the years - some probably look a bit on the funny side due to funky filters when I first got an iphone (that lets you know just how old some of these are!). It is a pretty detailed though brief tutorial for those interested in doing their own lost wax casting, and it also gives a look at how much work goes in to each ring. All of my waxes are made individually. I really enjoy working with softer waxes. I've used hard waxes for some things when needed, but they aren't my favorites. I've made several of my own tools and have repurposed tools from my ceramics class. I also have a couple sets of really nice Kate Wolf tools - those tend to work better for hard, carving waxes.

You can find more information on our web, so please take a look.

Spruing allows the wax to melt out of the mold during burnout (see below) and for the metal to get to your piece when casting - not having enough sprues or having them in an improper location can cause your piece to not turn out if the molten metal cannot adequately flow to all areas of the piece. After all sprues have been attached it is now time to weigh the waxes.

This is very important and is often forgotten: The weight of the wax is used to determine how much metal you will need for the casting. Because each metal has a unique specific gravity - you will need to know that number and multiply by your wax weight. I use this chart from Hoover and Strong. 

After the waxes are weighed, it's time to attach them to the sprue base or button. Then the flask is lowered over the waxes. As a rule of thumb, you should leave at least 1/4" of space between the edge of the flask and the waxes. I've pushed it and nothing bad has happened, but that doesn't mean that it won't. You can have a blow out where the hot molten metal breaks through because there was not enough investment. The same is true with the top of the flask; if the wax is too close to the top, the metal could break right through. And for vacuum casting, this could be a costly mistake as the metal would most likely damage your casting table. Though from experience the investment just gets sucked off and the mold ruined before you even have a chance to cast. Also, with vacuum casting, there needs to be at least 1/8th" of space between the top of the investment and the top of the flask - so make sure to not have the waxes too close to the top of the flask. Centrifugal casting is a little different and you can build the investment up if you need to. 

Now you are ready to invest! You need to know the size of your flask and how much investment you will need. For the smallest and cutest flasks I use, 4 = 1lb (or each one is 1/4lb). Measure the water out first and pour it in a rubber mixing bowl. Now weigh out the investment. Investment contains silica - so you should wear a dust mask or respirator if you don't have a really good exhaust system. The photo below is not what I call "really good exhaust" and I do have something a little nicer now.

Set the timer for 8 minutes. This is the longest that your investment should be disturbed. Once it starts setting up, you don't want to be messing with it. I start the timer and then pour the investment in to the water.

Mix for 3 minutes - when it turns to 5 min, it's time to vacuum.

Vacuum the investment for 2 min - this is the first step in vacuuming. Bubbles are good - this is the vacuum getting all the air out of the investment. It will "boil" up and you need to vacuum for at least 20 sec after that, 2 min total is best though.

Now, pour the investment in to the flask. It's a good idea to have tape around the top of your flask to keep the investment from bubbling over and making a huge mess. When pouring, pour down the edge of the flask, not directly on the waxes as it could cause the wax to move slightly and perhaps against another wax or too close to the edge.

Now for the vacuuming of the flask! If you are vacuuming more than one flask of the same size, make sure to mark them. I use a piece of chalk to write a number corresponding to the wax weights - the chalk doesn't burn off in the kiln so its easy to distinguish when getting them quickly. Vacuuming removes air that might have been trapped around the waxes and still in the investment from pouring - vacuum for approx 1.5 minutes - don't go over your 8 minutes. It bubbles up and over like an ancient tar pit! The rings were pretty small in this flask, so I didn't fill it up all the way to reduce the bubbling over.  If there was a little bit of investment left over after the time is up, you can pour the little bit on top. (Reminder: With vacuum casting, you need to leave at least 1/8th" at the top to aid in the suction during the casting. If doing centrifugal casting, it can go over the top of the flask.)

Now it needs to sit for about 10 - 15 minutes undisturbed until it sets up, then it needs to sit for about 1.5 - 2 hours before you can start the burnout process in the kiln. (Unless you are doing the super fast burnout, but that is a whole other story.) If there are any drips on the top, clean those up before putting them in the kiln so they will sit flush when casting. 

Once the flask is ready - it goes in the kiln and starts the burnout process. Burnout times are anywhere from 2.5 - 12 hours. The 5 hour burnout is perfect for doing just a few smaller flasks. My ramping schedule looks like: Hour 1: 300 degrees, Hour 2: 700 degrees, Hour 3 and 4: degrees, Hour 5: degrees - and hold. Hold temperature may vary depending on the metal. For larger flasks, larger waxes, natural materials or a really full kiln, up to a 12 hour burnout.

Once the kiln has been at the holding temp for an hour, it's time to start heating up the crucible and the metal.

Make sure the crucible is red hot before adding the metal.

Once the metal has melted, give it a pinch of flux, a stir with a carbon stirring rod (and make sure to heat it up first or the metal will stick to it) I came up with a special design of fire bricks to hold the torch or torches...  With my hands free, I can get the flask out of the kiln.

Make sure to check to see that the pathways are clear - if burning out natural material, some ashes might be stuck. You can check it before you start melting the metal if you think there might be an issue you'd need to clear up, otherwise, a quick check on the way to the casting table is just fine.

Also note the giant fireproof glove. I wish they made them in smaller sizes!

Place the flask upside down on the casting table (same as investing table, just make sure the toggle switch is flipped to "Cast") with the holes facing up. Turn on the vacuum pump. Position the crucible over the flask - make sure to always keep the torch on the metal. Removing the torch can cause oxygen to get in and that is bad. These photos show a larger style of crucible I used to use. I now have the little whip handles that are much better for small quantities of metal and ease of pouring. As you are pouring, keep the torch on the metal and pour quickly. Pouring too slowly or moving the torch can cause the metal to freeze up and your casting won't work. Once the metal is poured, turn off the torch and the vacuum pump. Release the vacuum by flipping the toggle off of cast and move the flask away to let it cool.

Wait until the metal is no longer red hot. I check it under a dark area of the table before quenching.

Now that the metal has cooled a bit and it is time to quench - this will vary depending on the metal used. Make sure the flask is completely under the water. You want it to all be bubbling completely underneath the surface of the water. (The above is an example of not being completely under the water. Don't do this.) If you have used cast in place stones or some alloys you don't want to quench when the metal is hot. You need to let some completely cool - an hour or so as to not crack the stones or cause the metal to be shocked. Regular sterling is fine to quench after a few minutes.

With competitive price and timely delivery, Yitai sincerely hope to be your supplier and partner.

This is what the pieces look like right out the flask completely caked with the investment.

The castings above have been scrubbed clean of most of the investment, but there are still bits around the harder to reach areas. Soaking them in vinegar is a great inexpensive way to remove the investment and to clean the metal! At times I have left them in there over night or longer depending on small detail areas. And it's nice to arrive in the morning to find the metal clean! It does take longer than an ultrasonic cleaner, but if you don't have the money or the space, but have time, vinegar works just fine.

These were completely cleaned up with vinegar.

These are after the ultrasonic cleaner, before being pickled. Most of the time, I just scrub and do a quick few minutes in the ultrasonic if they need it before going in the pickle/acid.

The two photos above have been completely cleaned and pickled. 

And now its time to clean them up! Removing the sprues, grinding, filing, sanding, adding texture to camouflage where the sprue had been, adding a patina, and the final polish all await your piece! There are a lot of steps in between these two, lots of little abrasives and polishing and texturing, just depends on the ring in how much extra work they need for the final finish.

*update Feb - I hope to have a downloadable, expanded pdf available for purchase later this year.

If you are interested in getting your own lost wax casting set up - you can check out this basic supply list I created.  

Appreciate the supply list or enjoyed the lost wax casting tutorial and want to donate a few dollars? Click the button below

Investment casting, also known as lost-wax casting, stands as a cornerstone technique in the realm of modern manufacturing, especially when it comes to the production of high-precision components. This centuries-old process is celebrated for its exceptional ability to produce parts with intricate details, complex geometries, and superior surface finishes directly out of the mould, thus minimising the need for additional machining. The versatility of investment casting allows it to cater to a broad spectrum of materials, including but not limited to, stainless steel, aluminium, carbon steel, and various specialty alloys, making it a go-to choice for industries where precision is utmost important.

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What is Investment Casting?

Investment casting, also recognised as precision casting or lost-wax casting, stands as a distinguished manufacturing technique that enables the creation of components with complex contours, exacting dimensions, and refined surface finishes. Esteemed for its adaptability across a vast array of metals and alloys, investment casting is pivotal for producing parts that present challenges in other casting methods or would necessitate significant machining. Here, we explore the detailed process of investment casting and highlight A & M Manufacturing Company Ltd&#;s capabilities to provide the investment casting service within this specialised field.

1. Pattern Creation:

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4. Dewaxing:

The transition from wax to void occurs in the dewaxing stage, where the assembly is heated, melting away the wax and leaving behind an empty ceramic mould. This pivotal process gives lost-wax casting its name, highlighting the transformative nature of this technique.

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After the molten metal is cast, the assembly cools, allowing the metal to solidify. The ceramic shell is then carefully removed, revealing the newly formed metal parts, which are then separated from the central sprue.

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Ensuring the highest standards, the final cast parts are subjected to rigorous inspection for accuracy, surface quality, and integrity. This step underscores the commitment to excellence that defines the investment casting service provided by A & M Manufacturing Company Ltd. All finished parts are inspected by both our partnered Chinese investment casting foundries and ourselves in the UK.

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• Complex Geometries and Intricate Details: Investment casting excels in creating components with complex shapes and fine details that other manufacturing processes might not capture effectively. This includes undercuts, hollows, and unique textures, achievable due to the precision of the wax patterns and the flexibility of the ceramic moulds.
• Exceptional Surface Finish: The smooth surface finish achieved through investment casting often eliminates the need for further machining or finishing, significantly reducing post-processing costs and time. Surface finishes as fine as 1.6 to 3.2 micrometres Ra can be directly achieved from the mould.
• Material Versatility:
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• Design Flexibility:
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  • Designers and engineers can incorporate complex internal features and passages into castings without the limitations faced with other manufacturing methods.
• Reduced Assembly Operations: Investment casting allows for the consolidation of multiple parts into a single casting. This not only reduces the need for assembly and welding but also enhances the overall strength and integrity of the component.
• Precision and Tolerances: The accuracy of investment casting, with tolerances ranging from CT4 to CT6, minimises the requirement for additional machining, ensuring parts are produced to precise specifications and fitment criteria right out of the mould.
• Cost-Effectiveness for Small to Medium Runs: While particularly suited to small and medium production volumes, investment casting offers a cost-effective solution compared to other processes when considering the level of detail and complexity achievable, especially when factoring in reduced tooling and machining costs.

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Factors to Consider when Choosing an Investment Casting Service

When selecting an investment casting service, several critical factors must be meticulously considered to ensure the chosen provider aligns with your project&#;s specific requirements. A & M Manufacturing Company Ltd stands as a beacon of excellence in the field, offering a comprehensive investment casting service that meticulously addresses these essential considerations:

Quality Assurance:

The foundation of a reputable investment casting service is its commitment to quality. Certifications such as ISO and relevant industry-specific accreditations are non-negotiable, as they attest to the provider&#;s adherence to international standards of quality management and operational excellence. A & M Manufacturing Company Ltd prides itself on meeting these rigorous standards, ensuring that every component we produce meets the highest quality benchmarks.

We hold ISO , IATF and AS quality accreditiation and we are equipped with comprehensive inspection equippment such as spectrometer, X-ray machine, 3-point internal micrometer, NDT equipment, ultrasonic detectors, universal testing machine (UTM), CMM and many more. We work closely with our partnered foundries in China and Taiwan, all parts are inspected by both our partners and ourselves in the UK before sending our to customers.

Material Expertise:

Investment casting&#;s versatility in material compatibility is one of its strongest advantages. A proficient investment casting service, like that offered by A & M Manufacturing Company Ltd, showcases an extensive ability to work with a diverse array of metals and alloys. From common materials such as stainless steel and aluminium to special alloys such as wear-resistant alloys and heat-resistant alloys and precious metals such as titanium, our expertise ensures that your components are cast using the optimal material to meet your application&#;s specific mechanical and environmental requirements.

Design and In-House Tooling:

Having access to experienced in-house engineers who can offer assistance with part design and optimisation is invaluable. This support can significantly enhance the manufacturability and functionality of the final product, therefore improve our investment casting service. A & M Manufacturing Company Ltd&#;s investment casting service includes comprehensive design and engineering guidance such as in-house tooling design, material guidance, technique guidance, 3D-printing and rapid protoptying, helping clients navigate the complexities of casting design to achieve the best possible outcomes in terms of cost, performance, and manufacturability.

Production Capacity:

Whether your project demands a short run of highly specialised components or large-scale production, the ability to accommodate both small and large volume production runs is essential. A & M Manufacturing Company Ltd&#;s investment casting facilities are equipped to handle projects of varying scales efficiently, ensuring we can adapt to your production needs without compromising on quality or lead times.

We possess one of the most advanced silica sol investment casting techniques in the world. Over the years, through continuous innovation, we have fully replaced the environmentally harmful binder (water glass) with a silica sol binder. This has greatly improved the working environment and significantly enhanced the quality of our castings. Furthermore, our silica sol investment casting service offers several additional benefits:

• Drying time for the silica sol shells has been drastically reduced from 8 hours to just one hour per layer, significantly boosting production efficiency and shell strength.
• The application of silica sol technology to encompass a wider range of materials, including carbon steel and various alloy steels, while also enabling the production of larger investment casting parts weighing up to 50 kg. This expansion not only diversified our offerings but greatly reduced production costs, especially for carbon and alloy steels that were historically costly to produce using silica sol binders.
• The introduction of a fully automated shell-making process, incorporating mechanical handling and automatic drying. This system has the capacity to create up to 8 layers of shells, with each layer managed by a separate automated unit, ensuring precise control and eliminating human-operated variability.
• We have created shells with markedly greater strength compared to conventional silica sol binders. At the same time, we have succeeded in reducing shell thickness by nearly half. This decrease in thickness improves shell permeability and is instrumental in achieving the high-quality surface finish of our castings.

Turnaround Time:

In today&#;s fast-paced market, the efficiency in delivering projects within desired timelines can be a deciding factor. Our investment casting service is structured to provide swift turnaround times, ensuring that your project progresses from design to delivery as quickly as possible while maintaining our exacting standards for quality.

Cost-effectiveness:

Balancing the superior quality of investment cast components with competitive pricing is crucial. A & M Manufacturing Company Ltd achieves this balance by leveraging our advanced manufacturing techniques, material expertise, and process efficiency to reduce costs where possible. This approach allows us to offer cost-effective solutions without sacrificing the high-quality standards our clients expect from our investment casting service.

UK stockholding facilities:

In addition to our manufacturing capabilities and investment casting service, we offer flexible supplying options, including UK stockholding facilities, to accommodate varying customer needs and preferences, facilitating efficient logistics and timely delivery.

For more lost wax investment castinginformation, please contact us. We will provide professional answers.