Metal Casting Design Considerations | Bunty LLC

The starting point of the casting process and metal casting design includes considering the factors that will determine the quality, performance, and manufacturability of the cast part. 

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The design process itself involves a detailed blueprint that uses various calculations that are dependent upon the requirements of the intended applications of the part.

From the metal’s castability to its machining requirements, there are a host of considerations to ponder over before even considering drafting up an initial blueprint. 

In the following sections, 10 of the most crucial metal casting design considerations are listed. 

They will give you a better understanding of the metal casting design process and how metal manufacturers use it to ensure the functionality and structural integrity of their metal castings.

Metal Castability

Metal castability is the measure of a metal or metal alloy’s ability to be shaped and molded into intricate geometries via the casting process. 

The metal’s level of castability directly affects the efficiency of the casting process and the quality of the final product.

The first factor manufacturers look at regarding metal castability is fluidity. 

Different metals exhibit varying levels of fluidity when melted.

Metals with low fluidity struggle to reach all corners and crevices of a casting mold, which often leads to incomplete or distorted parts. Conversely, excessively high fluidity can result in turbulence and even mold material penetration.

Shrinkage during solidification is another metal casting consideration manufacturers look at during the design phase. 

When molten metal cools and solidifies, it experiences contraction due to volume changes.

Metal manufacturers account for this inevitable shrinkage by calculating the metal’s shrinkage allowance and then incorporating additional volume or tapering in areas where it is needed. 

The final consideration is the most obvious, choosing the right metal from a list of the most castable metals. 

Several metals possess high castability, so manufacturers don’t have to stray too far and can keep their selection focused on this group.

This list includes: 

• Gray iron
• White iron
• Ductile iron
• Stainless steel
• Carbon steel
• Copper-based alloy
• Nickel-based alloy
• Aluminum alloy

Since the castability of a metal determines the ease with which it can be melted and poured into a mold, as well as its ability to flow and fill intricate patterns, it is one of the first design factors manufacturers look at during the casting design phase.

Mold Features

The shape, quality, and accuracy of a cast product are directly influenced by the features of the mold, which is why manufacturers look at several mold design factors before designing them.

The first factor manufacturers look at during the mold design phase is the draft angle as it can greatly facilitate the removal of the pattern design from the mold cavity during the design phase.

Altering the draft angle by providing a slight taper to the walls of the mold can reduce the chances of defects like cracks or distortion happening during solidification.

Another mold feature that manufacturers often consider before making the mold is whether or not they should include fillets and radii. 

Rounded edges, provided by radii and fillets, help smooth out any uneven corners or sharp angles in the casting. 

Not only does including fillets and radii reduce stress concentration points in the mold cavity but they can also increase fluid flow during pouring, resulting in improved mold filling and reduced turbulence.

The gating system design is yet another important feature that is looked at before designing a mold. It is a network of channels through which molten metal flows into the mold cavity. 

By accurately designing gates and runners, proper metal flow, minimal turbulence and air entrapment within the castings, and uniform cooling within the mold are achieved.

Some of the other key factors manufacturers evaluate before designing a metal casting mold include:

• Slag or dross formation: The presence of non-metallic inclusions in casting sand where they are acceptable (surface) or detrimental (sub-surface).
• Pouring temperature: The temperature at which a given alloy can be poured; the hotter the metal, the more production challenges will be present.
• Heat transfer rates: They influence how quickly a metal solidifies within a mold.
• Solidification patterns: A casting usually cools more quickly where it is touching the mold, crystallizing from the edge inward.

Considering mold design factors such as draft angles, fillets and radii, and gating system design is essential for successful casting. 

Furthermore, continuous evaluation of mold design based on heat resistance, durability, and solidification also helps in optimizing all areas of the casting process, resulting in the most efficient creation of high-quality products in the least amount of time. 

Gating System Design

Gating is one of the main considerations in mold design, but its importance extends well beyond this single factor.

For example, a well-designed gating system can balance and prevent defects such as misruns and cold shuts from occurring.

Through the strategic placement of gates and runners, casting defects can be reduced to a large extent.

Additionally, well-designed gating systems can have a strong influence on the solidification behavior of cast parts.

For instance, optimized gating systems can assist in controlling factors like cooling rates and directional solidification, which help manipulate grain structure and minimize defects caused by non-uniform solidification. 

Gating design modifications like tapering or insulation are often incorporated to promote controlled solidification throughout the casting. 

An added benefit of thorough gating design planning is the reduction of casting costs.

Optimizing gating systems for maximum function can lead to lower scrap rates and post-processing requirements like machining or welding.

To achieve the aforementioned benefits, metal manufacturers keep the following design features in mind:

• Control of metal flow: The gating system should effectively control the flow of metal, ensuring that the metal reaches all sections of the mold.
• Avoidance of impurities: The design should prevent the inclusion of slag, impurities, and gasses into the mold cavity.
• Quick filling: The system should allow for quick filling of the mold cavity without reducing the temperature of the metal.

• Temperature control: The gating system should control the temperature in the mold cavity to cool the metal stably.
• Metal addition: The system should be capable of adding metal without wasting much metal.
• Easy disassembly: After the casting has solidified, the gating system should be easy to disassemble.
• Economic and maximizing casting yield: The design should be economical and aim to maximize casting yield.

The design of the gating system not only induces proper filling of the mold but helps minimize defects and casting costs. 

Factors such as metal flow and temperature control, as well as efficient metal addition are all carefully considered when designing a metal casting gating system that is both efficient and cost-effective.

Parting Line Location

Parting lines serve as the boundary between the two halves of a die or mold. 

They are where the stationary half (also referred to as the cope) and the moving half (also known as the drag) of the die or mold join together. 

During the design and engineering phases, determining the location of the parting line is of utmost importance. 

This is because its positioning will designate which side of the die will be the cover and which side will function as the ejector.

The die cover serves as a protective shell that encloses the cavity where the molten metal is poured and the die ejector is a mechanism for removing the final cast piece from the mold once it has solidified.

Since the quality of a metal cast part is heavily influenced by the placement of the parting line, a well-thought-out parting line location needs to be identified so that defects in the finished product will not appear. 

The proper alignment and tight sealing of the die halves can effectively prevent leaks and flash formation during the casting procedure. 

Moreover, a precise parting line location and shape will limit detrimental effects on part functionality. 

Internal features such as ribs, bosses, and undercuts can all be enhanced by proper parting line locations. 

The complexity of the parting line geometry is also a key consideration as this factor often dictates how easily molds can be separated during the demolding process.

Faster and more efficient demolding processes lead to lower production costs and faster cycle times.

Manufacturers and engineers often identify the most optimal parting lines through various means, the most common of which include:

• Visual inspection
• CAD models
• Engineering drawings 
• Historical knowledge
• Past documentation

Aside from parting line location, manufacturers also take into account several other features to improve aesthetics

These features include:

• Types of parting lines: There are five main types of parting lines: vertical, stepped, inclined, curved, and integrated parting lines, each providing its unique benefits to metal cast parts.
• Multi-step parting: Sometimes the structure of the mold requires it to be parted several times from several directions to remove condensed material. 
• Surface textures and finishes: Engineers can disguise the lines with rough surface textures and matte finishes. They can also put sand on the lines and repaint them afterward to cover them up.
• Under protruding features: Setting the parting line under a protruding feature such as a rim or cap can also help to make it less noticeable.

Parting lines help prevent leakage and ensure proper alignment of mold halves, resulting in precise and accurate castings. 

Through careful analysis, manufacturers can design and place these lines in the right location, facilitating easy removal of the casting from the mold and reducing the risk of damage or distortion to the final product. 

Part Design

Part design influences various aspects of the casting process, from mold filling to machining operations. 

A part should be designed in such a way that it can be easily and efficiently produced through the casting process.

The initial part design will have a substantial impact on not only the casting process but also on subsequent machining operations. 

Designing parts with the correct wall thicknesses allows for easier removal of excess material during machining, reducing both time and costs.

One of the first considerations manufacturers look at when designing a metal part is the material they are going to use—different metals have varying properties and characteristics that can greatly impact the final product. 

For example, if a casting requires high strength and resistance to wear and tear, then materials like carbon steel or stainless steel are often the best choice.

Another consideration is the complexity of the shape of the part. 

Metal castings can offer great design flexibility, yet intricate shapes (e.g., concave shapes) can present a variety of challenges during the casting process.

Factors such as parting lines, draft angles, and undercuts all need careful consideration during the part design process to ensure successful casting production.

Part designers and manufacturers must also think about wall thickness and uniformity when coming up with a design. 

As was mentioned earlier, wall thickness can affect both the cost and quality of the casting. 

Thick walls may lead to longer solidification times and potential defects like shrinkage porosity or hot tears, while thin walls are prone to distortion and warping during the cooling phase.

Generally, manufacturers follow several steps when designing a cast part.

First, the manufacturer has to conceptualize the part. This includes understanding the part’s function, performance requirements, and operating environment.

Next,someone designs the part. This can be done using CAD software. A 3D model of the part is created, which includes all features of the final part: size, shape, and surface finish.

Since the part design will be highly influenced by the casting method used (e.g., sand casting, die casting, investment casting), it’s important to devise the right design process. 

This decision will depend on factors like the part’s complexity, required precision, production volume, and cost considerations.

Creating the pattern follows. The pattern is a replica of the final part, taking into account the shrinkage that occurs when the metal solidifies.

After that, the mold is designed to have a cavity that is a negative of the pattern. It may also include cores if the part has internal features.

Finally, there’s creating a prototype of the part, as well as testing it to ensure it meets all functional and performance requirements.

A metal casting part design requires a good understanding of the part’s requirements, capabilities, and limitations regarding the different casting processes that can be used. 

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With a thorough understanding of the part design process and continuous improvement efforts, manufacturers, engineers, and foundry managers can achieve efficient and reliable casting production.

Solidification Pattern

The solidification pattern in casting dictates the transformation of materials from a liquid to a solid state. 

Analyzing this pattern offers valuable insights into the behavior and formation of metals and other materials during the casting process.

Several factors influence the solidification pattern: the cooling rate, material composition, and the presence of impurities. 

Therefore, manufacturers must consider and comprehend these various factors to accurately predict how patterns will arise and react during casting, 

By carefully considering the appropriate patterns, the mechanical properties and overall quality of castings can be improved, while simultaneously minimizing defects such as porosity or cracks.

One commonly observed solidification pattern is known as columnar (dendritic growth). 

This pattern occurs when crystals begin forming at multiple nucleation sites within the molten material. 

Columnar crystals grow in distinct directions until they collide and merge, resulting in larger grains which help increase strength, fatigue resistance, and dimensional accuracy in castings. 

Another noteworthy solidification pattern is equiaxed (granular growth). 

In this scenario, nucleation takes place randomly within the molten material leading to the formation of spherical shaped grains.

Granular growth is frequently observed in castings subjected to rapid cooling.

To achieve the desired solidification pattern, manufacturers consider the following options while designing the solidification process.

First, there is the rate of cooling, which needs to be controlled. The better the thermal conductivity and the greater the latent heat of crystallization of the casting alloy, the stronger the ability to cast to a uniform temperature and the smaller the temperature gradient.

Avoiding shrinkage defects during solidification can be accomplished by using risers.

Then, there are directional solidification and unidirectional solidification.

The first one is a fast solidification process where cooling starts from the bottom of the mold and reaches the top. This type of solidification results in higher impurity removal. 

The latter, on the other hand, is a slow solidification process where cooling starts from top to bottom, resulting in a smoother surface. 

The casting shape also needs to be considered. The time of solidification is directly proportional to the volume of surface area. 

Therefore, the shape of the casting can greatly influence the pattern which is produced during solidification.

A well-controlled solidification process can lead to a casting with a better surface finish, less shrinkage and distortion, and more structural cohesion. 

Controlling the cooling rate and ensuring more uniform solidification makes it possible for metal manufacturers to achieve the microstructure patterns and mechanical properties the metal casting will need to fulfill its application requirements. 

Section Changes

Section changes refer to the fluctuation in thickness of a casted part. 

They are significant because they can alter the properties of the final product quite drastically.

The rigidity of a section serves as a governing factor when determining the minimum thickness that can be designed for a section. 

Thinner sections tend to cool and solidify at a quicker pace compared to their thicker counterparts. 

Consequently, this disparity in cooling rates can lead to inconsistencies in the microstructure of the metal, resulting in defects, particularly shrinkage.

To ensure the proper changes in thickness during casting, manufacturers give careful consideration to the avoidance of sudden transitions and sharp corners within the sections. 

The presence of sharp edges in a cast increases the likelihood of hot tears, shrinkage, and cracks during solidification.

Combating sudden transitions during solidification necessitates gradual transitions between sections to facilitate a more even distribution of stress.

Rapid fluctuations in section thickness can result in variations in cooling rates during solidification that can introduce internal stresses that compromise the integrity of the component. 

During the design phase, manufacturers incorporate well-thought-out section changes into their metal casting design by following these guidelines.

• Embrace the idea of infinitely variable shape: Use free-hand sketches for conceptual designing.
• Move mass around: Take mass out where it is not needed and shift it where necessary. 
• Use variability of section modulus over length: Use section modulus over section length to design for uniform stress.
• Avoid sharp corners and edges: Sharp corners, edges, and rapid changes in cross-section can be avoided in cast parts by adding fillets. Inside corners should be designed with fillets and outside corners with radii.
• Maintain uniform section thickness: Wherever possible, section thickness throughout should be held as uniform and compatible with overall design considerations.

While the above guidelines help manufacturers maintain a smoother surface change rate, close cooperation between the customers’ design engineers and the foundry’s casting engineers will still be necessary to optimize the casting design in terms of cost and performance.

Dimensional Tolerance

Dimensional tolerance is the permissible deviation in dimensions of a cast product in relation to its desired or specified measurements. 

Precise dimensional tolerance almost guarantees proper fitment, assembly, and interchangeability of components. 

Achieving the desired dimensional tolerance requires careful control of various variables throughout the casting process. 

The first step is paying close attention to mold design accuracy. 

The mold serves as the blueprint for the cast metal, and therefore any deviations or inaccuracies in its design can directly impact the dimensional tolerance of the final product. 

The second variable that must be considered is the selection and preparation of the material.

Different metals possess different characteristics, like thermal expansion coefficients and shrinkage rates. 

Selecting a metal or alloy with a similar coefficient to that of the desired dimensions will minimize any potential dimensional variations caused by thermal effects from occurring.

Aside from the previously mentioned guidelines, there are two other guidelines manufacturers tend to follow to ensure proper dimensional tolerances.

These include tolerance and machining allowance grades, as well as allowances.

Following a set standard such as The International Standard ISO  provides a system of tolerance grades and machining allowance grades for cast metals and alloys that can be systematically employed.

On the other hand, there are the allowances. 

The shapes of cast metal components reflect not only the functional requirements of the component but also the manufacturability requirements dictated by the casting process. 

For instance, castings must incorporate the proper draft allowances for successful mold-making and machining.

Manufacturers oftentimes use technologies such as computer-aided design (CAD) software and non-destructive testing (NDT) methods to help predict potential dimensional discrepancies before the actual casting process begins.

Precise measurements and tolerances can be predicted by controlling variables such as mold design accuracy, material selection and preparation, and utilizing advanced technologies. 

With careful consideration and implementation of such factors, the metal casting will produce parts with accurate dimensions that fulfill their desired requirements. 

Surface Finish

A good surface finish enhances the overall visual appeal and functionality of the end product. 

The term “surface finish” encompasses the quality and texture of the outer layer of a cast metal component. 

The surface finish does not necessarily have to be smooth or rough for that matter as surface texture will entirely depend on the design requirements. 

An impeccably smooth and glossy metal surface tends to exude a sense of opulence and precision, while a rough or textured surface can offer improved grip or enhanced adhesion for specific applications.

One influential factor that affects surface finish is the chosen casting process. For instance, in sand casting, the quality of the mold plays a crucial role in determining the final surface finish. 

A mold containing fine sand grains facilitates the achievement of a smoother surface compared to one constructed with coarse sand particles. 

In addition to casting process considerations, material selection also has a notable impact on surface finish. 

Different metals have different degrees of hardness and grain structure.

By consciously selecting the materials suitable for casting purposes, manufacturers can achieve not only visually appealing finishes but also add functional improvements like corrosion resistance to their end product.

There are a few other important considerations manufacturers look at to ensure a good surface finish for metal castings.

These include:

• Surface Preparation: This can involve removing any oil stains, moisture, rust, oxide, adhesive impurities, and residues before the finishing process is applied.
• Finishing Method: The method can include mechanical grinding, chemical treatment, heat treatment, spraying, plating, sandblasting, and other methods.
• Additional Post-Treatment: After the initial finishing process, additional treatments may be necessary to improve the appearance or performance of the casting (e.g., painting, powder coating, silk screen printing, and enameling).

When metal manufacturers pay careful attention to intricate details such as grain size in molds and the choice of post-processing treatments, they can design a casting process that has the potential to create beautifully finished and functionally optimized cast components suitable for various applications.

Machining Requirements

Choosing the correct machining option will provide for tighter tolerances, smoother surface finishes, and complex shapes that cannot be achieved through casting alone. 

However, excessive machining can result in increased production time and costs, so finding the right balance between casting dimensions and machining allowances is crucial for efficiency.

One strategy manufacturers use to minimize machining requirements is to optimize the casting design before machining ever takes place. 

Incorporating features such as uniform wall thickness, fillets, and radii at critical areas can decrease the need for extensive material removal during machining operations. 

Manufacturers also give careful consideration to draft angles during the design process as they can reduce undercuts, which will simplify subsequent machining operations. 

Integrating core pins and slides into the design can also aid in creating internal features that do not require additional milling or drilling operations.

Aside from the above, manufacturers also consider the following factors for their machining operations:

• Casting Shape: The shape of the casting can be determined by drawings, which include dimensional tolerances, indications of surfaces to be machined, and datum points for locating.
• Material Specification and Grade: The type of metal and its grade should be specified. 
• Number of Parts: The number of casting parts to be produced should be stated.
• Supplementary Requirements: Any additional requirements such as ASTM A 781/A 781M – 95 S2 Radiographic Examination should be considered.

Addressing the machining requirements during the design phase of metal casting can save time and costs while achieving the highest quality standards. 

Optimizing casting geometry for minimal post-casting machining operations and making informed choices in material selection are effective strategies to achieve this end goal. 

Conclusion

Metal casting design is a complex process that requires careful consideration of various factors that play crucial roles in casting success. 

Manufacturers plan part design, solidification pattern, and section changes ahead of time to achieve dimensional accuracy and a high-quality surface finish for their cast parts.

However, navigating these considerations can be challenging without expert advice. 

Perfect casting design requires informed decisions that balance design complexity, production efficiency, and overall cost.

Hi all, figured I'd make my first post something useful rather than a question. I know more about casting than blacksmithing, so I figured I’d help add to the casting section a little by providing a general overview of how to get started in casting, reference books, equipment needed, safety precautions, etc. Hopefully this will be something that can be referenced to give some direction to the people asking "how do I start casting metal" or "can I cast my own anvil", etc, since there seem to be a fair number of those posts. I just did a bronze pour and ended up repeatedly explaining the process to all of my neighbors in the building where I live and work, so all of this been in the front of my mind this week anyway. Before all the info I’ll show some pictures of the pour, since it always looks pretty cool.

View of my furnace running, with investment molds in the foreground:
Me checking on or poking something:

Taking the crucible out of the furnace:
Pouring:

Poured:
This is what was inside (16 acorns + gating system):
Acorn TIG welded to a steel stub (will be attached to a forged branch on a gate):
A bunch of acorns, ready to be attached to the gate:


SAFETY

Don’t do this unless you’ve done your due diligence. Ideally you would learn from someone in person, but if this isn’t possible you should read a few books (recommendations at the end of this post) and watch some videos of home metal pours on the internet. Molten metal in any quantity larger than a weld puddle is extremely dangerous, and not respecting it is for a serious accident. If you have questions, ask. Don’t blame me if you hurt yourself.

MOLTEN METAL
Once you have any quantity of molten metal, moisture becomes an extreme danger. A drop of molten metal on concrete (which holds moisture) will turn the water in the pores to steam, causing a small explosion which will propel liquid metal and chips of concrete into the air. Now think about what would happen if you spilled a whole crucible. ALWAYS CARRY AND POUR METAL OVER DRY SAND.

If you stick anything—a stirring rod, a skimmer, more pieces of metal to melt—into the crucible when there is molten metal in it, that object needs to be DRY. This is as simple as preheating metal on top of your furnace while it is running, and holding the end of any tools in the exhaust flame for a few seconds, but if you forget you will cause the molten metal to explode while you are standing there with your face over it. Likewise, your ingot molds (where you pour the leftover metal after filling your molds) need to be preheated on the furnace, or an explosion will occur. ASSUME THAT UNLESS SOMETHING IS TOO HOT TO TOUCH, THAT IT IS WET.

SAFETY EQUIPMENT
Goggles and a faceshield, not one or the other. Thick leather jacket, stick welding gloves, jeans, and heavy leather boots. That’s what I wear. Works fine to protect against the occasional bit of splatter, and at least won’t melt to your skin in a disaster scenario. Always keep a bucket of dry sand and a shovel on hand in case of a spill, and a chill bar (piece of heavy angle iron welded to the end of a three foot rod) to seize up the flow in case of a mold bursting or leaking.

HOMEMADE CRUCIBLES
Because of the serious dangers involved in working with molten metal, I strongly recommend NOT using a homemade crucible for anything hotter than aluminum (ie any copper alloys and cast iron). The proper crucibles will be discussed below with each individual metal, and a suitable homemade crucible for aluminum and other low-temp alloys will be explained.

Proper crucibles are essential, even if you make every other part of your setup:

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First I’ll give a quick overview of some different metals you might want cast, and then I’ll give some details about the general equipment you’ll need to make for a small foundry.

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METALS

STEEL
Alright, so first off, you are probably never going to cast steel at home, and you are definitely never going to make a steel casting the size of an anvil. That’s just reality. Getting a crucible furnace to the temperature needed to pour steel is possible, but it will turn your furnace into a consumable. I’ll address this first, since it seems like a lot of people are interested in casting steel.

Here are approximate melting points of some various metals (all temperatures in F):

Mild Steel:
Cast Iron:
Silicon Bronze:
Aluminum:
Lead: 680

Keep in mind that you need the metal to be superheated a few hundred degrees above these temperatures to successfully pour them, so for example iron will be poured around - (hotter for thinner castings). The temperature in your furnace will need to be even hotter than this, meaning that your internal furnace temperature will be close to . The refractory I used for my furnace is rated at , and as mild steel melts at around , you can see why melting it will rapidly destroy your furnace. Here is a picture of the refractory lining on my furnace where a drop of molten iron landed on it:



Bronze and aluminum will just stick to the surface, but molten iron literally eats right into it. The furnace gets so hot that you need one of the green oxy-acetylene faceshields just to view it with the lid open. It just can't handle the temperatures needed to melt steel.

CAST IRON
That said, with a properly constructed furnace melting cast iron is not at all difficult, however you need to use sand molds, as investment molds of the type you make at home (discussed below) cannot handle the temperature of molten iron (I’ve tried). Sand molding is an art form in itself, and getting it right will take a good bit of practice. There are a number of good books on this recommended at the end of the post. Finally, for cast iron, you need to purchase a clay-bonded graphite crucible. DO NOT MELT IRON IN SOMETHING YOU MADE YOURSELF. A crucible will run you $50-100. It’s an extremely cheap insurance policy, and is well worth every penny. Seriously. Not kidding. Virtually every piece of foundry equipment I have is homemade, except my crucibles for bronze and iron.

BRONZE
Ok, on to the nonferrous stuff. I personally only use silicon bronze for my copper-alloy castings, for a number of reasons. The first is it’s composition: Roundabouts 96% copper, 3% silicon, and 1% manganese. Here’s why that is important: brasses and other bronzes generally contain considerable amounts of zinc, tin, and/or lead in addition to the copper. To melt these alloys, you need to heat them above the temperature at which the alloying elements vaporize. This means that some zinc, lead, tin, etc will escape from the surface as a gas, especially when you stir or skim the melt. This means that besides exposing yourself to seriously toxic fumes, you are changing the composition of the metal every time you melt it. Silicon bronze does not change composition even after melting it dozens of time (as long as you keep a crucible only for that alloy), making it perfect for home use where we can’t test the composition of our alloys and where we want to immediately reuse the metal that makes up the gating system. Additionally, you can buy silicon bronze rods from most welding suppliers, meaning that you can weld it with an oxy-acetylene torch or a TIG welder and get a perfect color match (especially great for fixing small pits in castings, and welding two casting together and blending the weld in). For these reasons, I consider it worth the money to buy silicon bronze instead of using scrap bits of unknown composition.

For bronze, you really really really want to buy a crucible rather than making one. In particular, buy a silicon carbide crucible—again, around $50-100, and again, totally worth it. I’ve used a homemade crucible of the type described below for melting pure copper, since I didn’t want to contaminate my crucible for silicon bronze and I didn’t want to spend $100 on a one-time experiment. All was going well, the copper melted, I skimmed it, and then closed the lid of the furnace to heat it for another minute as the casting was going to be pretty thin and I wanted it really hot. When I reopened the lid to remove the crucible, it had failed and the bottom of the furnace was a lake of molten copper. If I hadn’t opted to put another minute of heat into it, it would have failed right as I was lifting it out of the furnace. That would have been about half a gallon of molten metal all over my legs and boots.

ALUMINUM
Aluminum works fine with scrap material, but for best results use cast (not extruded) aluminum. This means car wheels, bicycle parts, etc. are perfect, but tubing, sheet, beer cans, etc. not so much. Because aluminum melts at such a low temperature, you can safely use a PROPERLY CONSTRUCTED steel crucible, or better yet, a cast iron pot. To make the steel crucible, you can just weld a piece of thick-walled pipe to a thicker plate. I've used with much success a 1/4” wall, 4” pipe that was about 10” tall welded to a piece of 3/8” plate. I welded lugs on the side for tongs to grab. If you aren’t a competent welder please have someone else weld it for you, this isn’t the weld you want to fail. Also, as with any crucible, you need to purpose-make tongs that fit very well with no play.

LEAD
Lead melts at such a low temperature that you don’t even need a furnace, just a suitable steel or cast iron container and some torches. My neighbor recently cast an pound lead keel for a boat he’s building by putting the lead in a modified cast iron bathtub, melting it with a few roofing torches, and tapping it out of the bottom in to a sand-backed wooden mold. I don’t recommend wooden molds—the surface finish is not the best because of moisture in the mold, and the fire department was called because of the excessive smoking. Even without a furnace, all above safety precautions apply, and remember that lead is extremely toxic.


EQUIPMENT

Aside from your crucibles for bronze and/or iron, as well as a blower, you can easily make everything you need yourself. My entire foundry cost was easily under $, which includes a some good books (bought new, listed below), two crucibles, my furnace (cost about $300 in materials), a pottery kiln ($60 on craigslist, and only needed for lost wax casting), an electric blower ($25 on craigslist) and a slew of homemade equipment, mostly made from scrap steel. My furnace is overbuilt, and probably larger than many people on here would even need. You could spend much less on a simple setup. Here’s my entire foundry, packed away in a corner of my shop (it only comes out from time to time):



FURNACE
The central piece of equipment in a foundry is the furnace. For the scale we’re talking about, a crucible furnace is by far the most reasonable thing to build, so it’s all I’ll discuss. You can build a relatively furnace that run on propane or natural gas, which is basically just a vertical gas forge with a lid. However, these furnaces will have a hard time melting iron, if they can do it at all. I strongly recommend buying the manual from Colin Peck (in England) called “The Artful Bodger’s Iron Casting Waste Oil Furnace”. This is what I did, and would never build a different style of furnace. The design of the furnace body is simple and easily modified to use the scrap you have on hand, and he has perfected a burner design that uses a gravity feed to burn waste oil (used vegetable oil, used motor oil, and diesel all work well). There is no nozzle on the burner, so the fuel isn’t atomized, meaning you can use waste oil (free but contaminated with particulates) without clogging the burner. Also, since it is gravity fed there is no need for a pump, and oil at atmospheric pressure is MUCH safer than pressurized gas when you’re working with molten metal. Plus, it puts out much, much more heat than propane or natural gas—I can melt 30 pounds of bronze from a cold start in less than 45 minutes. Properly built, it burns very cleanly (zero smoking) and can easily melt cast iron. It could definitely melt steel if you wanted, but it will rapidly deteriorate the furnace lining. Using mostly scrap materials, I spent around $300 on my furnace. The cost is primarily the degree castable refractory (very highly recommended), which I believe cost $65 for a 50 pound bag (I used 3) about 5 years ago. I won’t give much detail about the furnace design since Colin is trying to sell his book, so you’ll have to buy it from him if you want the plans (please note, I in no way profit from this, nor do I even know Colin. It’s just such a good design that it’s all I care to recommend).



HAND TOOLS



There are various, simple tools that you need, all of which you can easily make yourself. Pictured here are the pouring shank (long thing that holds the crucible while pouring), crucible tongs (to lift the crucible in and out of the furnace), skimmer (angle iron welded to a rod, curved on the end to fit my crucible, used for skimming slag prior to pouring), and an ingot mold (angle iron with the ends capped and a handle, for pouring off leftover metal after the molds are filled). Other tools not pictured include a 1/2” steel rod for stirring, a chill bar (described above in safety equipment), a pair of tongs for loading preheated metal into the crucible. Really simple stuff. Also note that you don’t need a pyrometer to measure the temperature. Just take your 1/2” rod that you use for stirring and stick it into the melt for a second and then pull it out. If the molten metal slides right off the end, you’re ready to pour. If it clumps up on it, it’s not hot enough. That method has never failed me, for aluminum, bronze, and iron.

MOLDING TOOLS
This varies depending on whether you are doing sand casting or lost wax casting. I haven’t done sand molds in a few years and no longer have my tools for that, so I won’t try to catalog what you need, but it’s just simple hand tools, and a muller if you're lucky enough to cross paths with one. I would recommend going with Petrobond (oil-bonded sand) over water-bonded sand for a beginner, as it’s easier to deal with and maintain.

I won’t go into much detail here on the actual investment casting process, but if you are interested you should buy the last book listed at the end of this post. I will say though that “microcrystalline wax” is what you want to buy if you are making sculptural pieces. It gets very soft when heated from your hands, and can then take any amount of twisting or bending without cracking, and it blends into itself very smoothly. Like silicon bronze, it is a product so superior that it is well worth the money. Investment molds can easily be made from 1 part water, 1 part pottery plaster, and 2 parts coarse sand.

For this process, you will need to burn the molds out in a kiln to melt out, burn off, and finally vaporize the wax, as well as calcining the molds. You need to run it for a few days and slowly ramp up the temperature, eventually keeping the molds at for a day and filling them with molten metal when they cool to around 800. A standard pottery kiln works fine, but be prepared to wake up once or twice each night to check on the temperature unless you have a digital controller. Also, you can burn out other organic objects (vegetables, sticks, etc.) instead of sculpting something with wax.

SUPPLIERS/MATERIAL RESOURCES

Budget Casting Supply is your best bet for online shopping, but if you live in or near a big city you should really look for local suppliers. If you don't know of one, try searching on ThomasNet. If you're not familiar, that website is a searchable database of manufacturers and suppliers for industry—extremely useful. Often, places that supply foundry equipment or refractory never have walk-in customers, and if you explain what you are doing they are often very intrigued and go out of there way to help you. I still have yet to pay for any ceramic fiber insulation, though I've gotten plenty of it between various forges and my furnace—a large refractory supplier can generally give you a "sample" that is more than enough for whatever you're working on.

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That’s about all I’ve got for you without writing a book on this. Hopefully this will be helpful to some of you who are interested in adding casting to your metalworking skills. I’m more than happy to answer any questions you have, and if anyone is in the Philadelphia area and wants to see a pour just let me know and I’ll invite you to the next one.

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RECOMMENDED READING

-“The Artful Bodger’s Iron Casting Waste Oil Furnace” by Colin Peck
...available from the author at http://www.artfulbod...alcasting.com/. This manual is what I used to build my furnace described above. I don't think I would ever build a crucible furnace that was not based on this design. Terribly written, never even proofread, but invaluable nonetheless.

-“The Metalcaster’s Bible” by C.W. Ammen

-“The Complete Handbook of Sand Casting” also by C.W. Ammen
...Ammen’s books are very readable and straightforward. Get these regardless of whether you are making sand or investment molds.

-“U.S. Navy Foundry Manual” reprinted by Lindsay Publications
...invaluable resource, but not the kind of book you read straight through (ie, boring technical manual). Again, though it is written for sand casting in particular, much of the information is very pertinent to investment casting as well.

-“Charcoal Foundry” by Dave Gingery
...great for starting out, it’s sand casting in its most pared-down form. Perfect for a super-low-cost setup to pour some aluminum to see if you like it.

-“Metal Casting: A Sand Casting Manual for the Small Foundry” by Steve Chastain
...there are two volumes. Good books, but not necessary if you are only interested in investment casting.

-“Studio Bronze Casting: Lost Wax Method” by John Mills & Michael Gillespie
...for investment casting.

Also check Lindsay Publications for other books on casting, including some of those listed above.

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