Thinking about working on a project with my dad reproducing some muscle car parts, have one part in particular we want to work on - trunk lock bezel. They are a chrome plated diecast part that is hard to come by for some cars. I want to make them from stainless to avoid the chrome plating step and make a more durable longer lasting part. I'm sure with the right machines it could be machined from solid, but I don't have those machines. I'd like to do a casting, then machine the features that need machined,and polish it.
Any idea on a ballpark per piece cost get something like this done? Qty is 25 - 100. Is investment casting the right method? I don't have a 3d model yet - I'd like to get an idea before I waste time making a model to find out it's too expensive.
Get an accurate estimate of the volume and weight of the stainless steel part. Then find a local dental lab and talk to them to see if they can do a piece that size. Dental labs routinely make small stainless steel investment castings and are certainly used to small quantity jobs, because every bridge or partial is unique. You will have to provide the wax models for each part you want cast. The lab or a manufacturing jeweler or an actual investment foundry can help with information on rubber or machined aluminum molds for making numerous wax models of a single item. Jewelers do not do stainless steel, but do know how to make duplicate wax patterns. Maybe there is a way to use a 3D printer to make wax models, but the printers I have seen work very slowly. Foundries are able to cast multiple items at once by connecting many small models with wax rods/wire into a sort of tree array. That keeps costs down.
Investment casting does involve some skilled hand work to prepare the wax model and attach sprues and runners, so it is not going to be a cheap process. Then the castings have to have all those sprues and runners carefully cut off, again a hand process.
Larry
Some dentists (not dental labs) now have handheld 3D scanner wands and minature 5D milling machines, together with special suites of the necessary software, to make inlays and crowns from unfused ceramic blanks. After milling, the ceramic is fired in a minature oven, right in the dentist's office. Once they grind out the necessary recess in your tooth, the whole scanning, milling, firing, installation and trimming process can take less than an hour. I have had the crown for an implant and an inlay done with this process, the inlay just this morning!
So, the day of stainless dental castings is (just now) beginning to fade away. Larry is correct, though, if you have wax masters, a dental lab can probably do the work. It will depend on the size (max dimensions and total mass) of the castings you need, as dental labs are naturally specialized to do work the size of a tooth.
You definitely want to talk to your foundry/lab about multiples, because there will be hundreds of dollars of per-run cost. The only way to get per-part costs down is to do lots of parts in a single run.
Hi All:
I read this thread with interest and perked up my ears when dental labs were first mentioned as a source for investment castings. (I used to be a dentist so I know the subject).
There are a couple of misconceptions worth addressing.
First, partial denture frameworks are not cast from stainless steel, they are cast from cobalt chrome which is harder than a woodpecker's lips and therefore expensive to work with.(think high 40's RC and fairly brittle)
It's also expensive to buy and expensive to cast because it needs a special refractory investment and has a higher melt temperature and lower density than gold which is what dental labs cast routinely.
(The fluidity, high density and comparatively low melt temperature is what makes gold easy to cast accurately, and the biocompatibility and ductility is what makes it attractive for dental restorations)
The whole process of making a partial denture framework is completely different from the process used to make a commercial investment cast part...a refractory model of the patient's teeth and gums is poured, a technician custom waxes the framework up by hand using plastic patterns of the individual bits that go into the framework, then the whole thing is sprued and gated and buried in more refractory investment.
It's then burned out and cast.
Only one part is cast at a time, and the whole works is devested, trimmed, polished, then the teeth are put onto it.
Back in my day, this was expensive...a completed partial denture was fifteen hundred bucks give or take.
The prices haven't improved since then.
So knock the idea out of your head that you can get a dental lab to make these for you.
A commercial investment casting house can work with stainless steels of all kinds, and can make these for you.
The problem is making the waxes.
Traditionally a metal mold was made and the waxes were shot just like injection molded plastic parts are produced, then they were assembled on a sprue, invested and cast.
The mold cost about like a prototype plastic injection mold costs...twenty grand at a guess for what I can see of the OP's parts.
Nowadays all that cost can be circumvented by 3D printing the waxes, but as has been pointed out, the cost per wax is higher because the 3D printing is so slow.
Another alternative is to get the parts 3D metal printed.
There are several competitors in the market, the most common is direct metal laser melting...EOS is the most widely known and used system, but there are others.
A new system has just come on the market and show exceptional promise...it is the Rapidia system which uses sintering to consolidate a green printed part made from a water soluble metal paste that's 3D printed just like a filament printer does, and it has similar resolution.
For low volumes these are an acceptable and lower cost way to get a metal part that is about equivalent to an investment cast part...not as good for consistency and detail in stainless as die cast part, but workable for many things and much cheaper for small volumes of parts.
That's where I would look first.
Cheers
Marcus
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In manufacturing, stainless steel investment casting is a testament to the blend of art and science, precision and craftsmanship. This process involves creating a wax model, building a ceramic shell around it, and then pouring in molten stainless steel, which is meticulous and detailed. It requires not only technical knowledge but also a deep understanding of the unique properties of stainless steel. This article delves into the key design considerations that can make or break the success of stainless steel investment castings, providing insights into the process, the benefits, and the challenges involved.
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Understanding Stainless Steel Investment Castings
Stainless steel investment castings are a cornerstone of many industries, providing strength, corrosion resistance, and excellent surface finishes. The unique properties of stainless steel make it an ideal material for investment castings, with various stainless steel alloys and grades offering a range of mechanical properties to suit different applications.
Investment Casting Process
The investment casting process is meticulous, beginning with creating a wax pattern that replicates the final product. This pattern is then coated with a ceramic shell, layer by layer, to form a mold. Once the shell is complete, it is heated to remove the wax and harden the ceramic, creating a perfect mold for the molten stainless steel. X-ray equipment is used throughout this process to ensure the integrity of the stainless steel precision casting part.
Designing for Optimal Results
When designing stainless steel investment castings, several key considerations must be remembered. The casting size should ideally be within the ounces to 50-pound range and fit into a 16″ cube with gating for the most economical results. Abrupt changes in cross-section should be avoided whenever possible, as symmetrical shapes with uniform walls and cross-sections cast with less distortion.
The stainless steel casting material should be designed to be gated in one location, preferably in a machined area. This yields more parts per mold but also aids in the dimensional stability of the casting and reduces the areas of the component that will show a gate contact area.
Considerations for Larger Castings
While larger and heavier castings are possible, they often come with challenges. The typical accuracy of an investment stainless steel casting process can be compromised due to the tolerances associated with larger sizes. Additionally, the costs can be significantly higher than alternative processes when investing in large parts.
Benefits of Stainless Steel Investment Casting Components
Investment cast stainless steel components offer several advantages. They provide high levels of detail, consistent and repetitive close tolerances, and can be used to produce intricate internal passages. No other casting process for high melting point alloys like stainless steel comes close.
Tolerances and Surface Finishes
Investment cast stainless steel components typically have tolerances of +/-0.010″ for the first inch of any linear dimension, then another +/-0.005″ per inch of additional linear size. The as-cast surface typically has a finish of 125 RMS, providing a balance between smoothness and the ability for the surface to hold a finish.
Combining Multiple Parts into a Single Casting
One of the key advantages of investment casting is the ability to combine multiple parts typically used for assemblies or weldments into a single casting. This simplifies the manufacturing process and can lead to significant cost savings.
Machining and Draft Considerations
Investment castings that require machining to finish any dimensions tighter than cast tolerances can be designed with much less material for finishing due to the stability and repeatability of the stainless steel casting. Unlike sand casting processes, no draft is required to produce investment castings, resulting in significantly more accurate dimensions of the stainless steel casting.
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Volume Considerations and the Use of 3D-Printed Plastic Patterns
For low volumes, the one-time cost of wax injection tooling may be prohibitive to use investment castings. However, for larger volumes (100 or more) and designs at low risk of changing, the cost of the injection tooling is generally a very low startup cost considering the cost savings in machining, reduced weight, etc. For low volumes and test runs, 3D-printed plastic patterns can be substituted for wax patterns, allowing the investment cast part to be still produced.
Time Considerations in Investment Casting
The overall time to produce an investment casting is generally 4 to 6 weeks due to the time needed to form the ceramic shell, which is a layer-by-layer application process. Investment casting is one of the longer casting processes, and the long lead times should be considered.
Wall Thickness and Flatness Considerations
Wall thicknesses in the thinnest part of the casting should be at least 3/16″, possibly heavier depending on several factors. The flatness and straightness of an investment casting can be difficult to maintain and should be considered when designing the casting. Mechanical straightening of the casting or a machining operation of the surface should be expected if flatness or straightness is paramount.
Limitations and Recommendations
Threads, gear teeth, and splines cannot be cast in due to runout issues between mating surfaces. Part numbers and logos should be cast using raised lettering inside a receded pad for best results.
The Role of Stainless Steel in Various Applications
Stainless steel plays a crucial role in a wide range of applications. From turbine blades and surgical tools to food processing machinery and coffee machine components, the versatility and durability of stainless steel castings make it an ideal material for investment castings. It’s also widely used in pump and valve applications, where its corrosion resistance and strength are highly valued.
Frequently Asked Questions
What types of stainless steel are commonly used in investment casting?
Various types of stainless steel are used in investment casting, including austenitic stainless steel, duplex stainless steel, and martensitic stainless steel. The choice depends on the specific requirements of the casting, such as corrosion resistance, heat treatment hardness, and mechanical properties.
Can investment casting be used for creating parts with internal passages?
Yes, one of the advantages of investment casting, especially when using stainless steel, is the ability to produce intricate internal passages. This makes it a suitable method for creating complex shaped components that would be difficult to achieve with other casting methods.
How does the surface finish of investment cast stainless steel components compare to other casting methods?
The surface finish of investment cast stainless steel components is typically 125 RMS, which is smoother than many other casting methods. This and the process’s ability to produce parts with excellent dimensional precision make investment casting a popular choice for applications where surface finish is critical.
The Path to Successful Stainless Steel Investment Castings
Design considerations play a crucial role in the success of stainless steel investment castings. From the initial design phase to the final product, every decision can impact the quality, cost, and performance of the casting. By keeping these considerations in mind, you can ensure that your investment castings meet the highest standards of quality and performance.
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