Like any industry, the Investment Casting industry features repeat customers. These customers develop a rapport with the individual investment foundries in their supply base. Both parties can prosper with the development of relationships featuring good communication and common understanding of what is possible.

When a foundry seeks to penetrate new markets with new customers, such common ground might not exist. At the same time, it is a fact that the Investment Casting industry can generate value and sales by replacing fabrications and forgings with castings. This entails approaching designers and buyers with information about investment castings. This means an educational effort. Fortunately, informational resources are plentiful if one seeks them out.

Even so, information transfer is only part of the challenge to those seeking to sell casting conversions. Those who design fabrications and who buy such components may have zero familiarity with any sort of casting process. Even when it is explained well, there are some all-new hurdles that crop up in the Purchasing cycle.

The potential customer realizes that a whole new language and skill set are required. For example, they likely have not considered casting tooling costs, ever. Also, it is common that only one foundry is making the value proposition (let us help you convert fabrication to casting so you can save costs), so a buyer might suddenly be facing a “sole source” situation.

This combination of factors can lead to skepticism and pre-emptive cancellation of conversion projects; it’s just too much for a newcomer to the investment casting process.  

This paper aims to address some technical and human challenges inherent in the process of selling investment casting conversions to designers and buyers of fabrications and forgings. The author empaneled respected members of the Investment Casting industry to validate points being made. He also included on the panel those who are engineers, product managers, and buyers with experience in the design and purchasing of investment castings. Both sides of the Purchasing transaction were represented to illustrate a consensus on these topics.

These panelists were presented with a series of statements about various aspects of investment casting design, sourcing, application, and manufacture. The panelists voted on these individual statements, and the voting numbers are presented in this paper. They were asked to vote on a scale of 1-10, on the ACCURACY of the statements: Is the statement true as it is written? They were then asked to vote again on the RELEVANCE of the statement: Does this statement matter to the investment casting conversion process? If I am designing/buying an investment casting, does this topic have a bearing on my work? 

Those scores were then tabulated as an average score, showing an industry consensus on the topic. For example, the numbers shown in the table below show the average response, on a scale of 1-10, of the responding panelists, pu on the Accuracy and Relevance of the statements shown below, about Investment Casting materials (more on this topic later):

Accuracy?    Relevance?
Investment Cast material is not necessarily the fabrication material.    9.92    9.85
Investment Cast material flexibility = design options.    9.85    9.92
Thirteen out of 14 panelists gave scores.

Lastly, panelists were encouraged to offer comments to emphasize points that may need further explanation. The individual attributions of these comments are confidential. 

This paper provides a quantitative measure of the truthfulness and applicability of various statements and shows that an industry consensus exists across both sides of the sales/purchasing table, while at the same time not confining the panelists to only ideas that the author has presented. Such a consensus can ease the transition for newcomers to investment castings.  

Investment Castings versus Forgings and Weldments

A casting might appear more expensive than a weldment at first. But a buyer has to weigh the total cost of the product, including reduced machining, reduced weight, etc. There are applications, such as in Figure 1, where using an investment casting will reduce:

• Overall cost.
• Weight.
• No. of SKUs (part numbers).
• Reduced assembly costs.

Also, though it is harder to quantify, the investment casting will also usually be more elegant and aesthetically pleasing than a fabrication. Investment castings can allow you to cast lettering and part numbers readily and attractively on the actual part (Figures 2 and 3).

There are also applications where an investment casting is not a fit. The foundry will tell you so. 

The most important factor is getting an experienced designer to consider a casting as a design option as early in the process as possible to avoid unforeseen roadblocks that could stall the process.

The most common barrier to the weldment-to-casting conversion process is tooling cost. That said, tooling cost is not what it used to be due to advances in additive manufacturing technology (more on this later), and it is a non-recurring cost.
Lastly, there is no need to be apprehensive about your options. As a buyer/designer, you likely have multiple domestic producers available in terms of your casting supply chain.

Accuracy?    Relevance?
You can often cut significant costs going from fabrication/forging to casting.    9.15    9.31
Tooling cost, a traditional barrier, is not what it used to be.    9.31    9.46
There are multiple domestic Investment Casting foundries.    9.77    9.77

Panel Comments on Investment Castings vs. Forgings and Fabrications:

• Beyond tooling costs, qualification costs need to be considered for existing designs (so earlier is better).
• Site visits at the foundry can inspire the beginning designer by showing other casting designs.
• Once the wax die is certified, you can count on the reliability of those dimensions for decades as compared to machining and forging.
• It is very part-specific, regarding how much money you can save.
• Your choices as a buyer will vary depending on alloy and size envelope especially.
• In my experience, the greatest barrier in going from a weldment to a casting is getting customer engineering design and support.
• In aerospace, you don’t traditionally convert forgings to castings. You are more likely to convert a part that was hogged out of barstock.
• There are more tooling options today.
• There are more tooling options available today. Printed tooling for cores, printed cores, etc.

What to Include in an RFQ for an Investment Cast Component 

If a decision has been made to produce a part as an investment casting, then at some point a request for quote (RFQ) will likely be generated to go to potential sources. As a buyer/designer, you likely have multiple domestic options in terms of your casting supply chain.

The buyer will want meaningful quotes to be submitted. Below are some guidelines for what to include in an RFQ for an investment cast component:

Drawings, including part number, part name, and revision level. 

• Casting drawing in pdf format.  
• If machining is required, there should be a machined casting drawing. 
• It would be beneficial to indicate any critical areas on the casting including preferred or designated machining locating areas. 
• Ideally, model files in the appropriate format will be provided. 

Material type 
• RFQ should list the type and grade of material required (should be on drawing, too).
Prototype or production? 
• This is important information, as it lets the foundry know whether to quote prototype or production tooling as well as whether assistance with rapid prototyping is required. 

Volumes 
• Estimated annual usage (EAU).
• Lot sizes and frequencies. 
• If prototypes are required, the volume of prototype pieces that are required.

Part Weight 
• Accurate part weight is critical and often misstated, even in the age of digital models. 
• This can have a significant impact on pricing.

Value-added operations 
• Any paint/powder/etc. 
• Machining. 
• Heat Treatment. 

Certifications 
• Any material certificantions or special testing. 
• NDT requirements including x-ray. 
• Which standards are required as part of the certification.
Timing 
• Time requirement to return the quote (outside tooling will add time to delivery of quote).
• Sample start date.
• Production start date.

Panel Comments on What to Include in an RFQ:

• At the prototype stage of the process, it is very important to glean manufacturability input from the foundry for your design. The prototype cost might not reflect the final cost, in either direction.
• 3D CAD models are critical. This is the 21st century. You need models to understand the castability of the part and the complexity of the tooling that will be needed.
• Foundries do a lot of quotes and land comparatively few jobs. Does it even make sense to send this RFQ to this shop? Are they a fit? Or am I wasting everyone’s time?
• Models are almost mandatory. If a part is being re-sourced and there is no model, we will commonly 3D scan the existing part anyway.
• It is a good practice for the vendor to reply to your RFQ the same day to at least acknowledge that they received the RFQ.
• There needs to be a fit between the customer and the foundry in terms of equipment and other factors.
• Be as straightforward as possible on EAU.
• Quotes take time, often several hours. “Fishing” quotes are easy to detect and are not taken seriously.
• After we get the RFQ, we will commonly have a conference call with recommendations and exceptions before submitting the quote.
• Casting drawings should specify surface condition requirements by surface; they should indicate allowances for gates, etc.
• If the part has export controls, this needs to be noted.
• Often the casting design may call for a simple and inexpensive part but overdoing the notes and restrictions can drive up the overall cost significantly.
• In general, the issue with RFQs is that they are not specific enough. They are stated in a way that backs the supplier into a corner, and the supplier will no-quote. 
• Any APQP and PPAP requirements should be presented right up front.
Investment Casting Tooling

With a few exceptions, investment casting tooling belongs to the customer. Investment casting tooling includes more than the die that produces the wax pattern. There are other types of tooling, such as straightening fixtures, machining fixtures, core tooling, etc. These items can vary, and some can rise in complexity and cost to rival the main die.

When getting a quote on tooling, your tooling costs, either up front or amortized, will vary from foundry to foundry depending on:
• Program requirements.
• Quantities.
• Lot sizes.
• Complexity.
• Other shop equipment (molding machines, robots, etc.).
• Ancillary processes (machining jigs, etc.).

For example, one foundry might quote a straightening fixture immediately, thinking it a necessity. Another might exclude such an item, thinking it unneeded. When comparing quotes, these line items should be noted.

Also, if a buyer sees a massive difference (multiples) in tooling prices between two sources, then this is worth an inquiry. It is possible something has been overlooked or misunderstood.

Lastly, rework, maintenance, and gating of tooling can be costly. This should be discussed openly.

Accuracy?    Relevance?
Investment Casting tooling can include many pieces.    9.92    9.92
Multiple factors drive tooling cost.    9.92    9.92
Large differences in tooling quotes warrant a close look.    9.92    9.92

Panel Comments on Tooling:

• Not all tooling quotes are the same. One shop might include a CMM fixture, etc.
• There is a lot of benefit to having a bona-fide tool room in the foundry; there is a synergy to the collaboration between the tool room, the wax room, the shell room, and the melt shop. 
• Unusually cheap tooling quotes warrant exploration. Why so cheap? Did they omit something? Chances are that when production starts there will be another tool required and another bill.
• Compression straightening can be 60% of the cost of a tooling package.
• Maybe the less expensive tool is made of a material suited to low volume.
• All tooling belonging to the foundry should be hard-tagged and photographed indicating its ownership for asset tracking purposes.
• The need for a straightening fixture can be 60% of the tooling cost. If the piece cost is low, this is justified to reduce labor.
• You can minimize straightening issues and tooling costs with casting design and casting process optimization using numerical simulation tools.
• The wax die can be tool steel or aluminum, for example. We could go on all day on the differences in tools.
• The use of external solubles instead of complex finished die tooling can make a huge difference in cycle time and finished cost.
• Tooling cost is heavily influenced by product volume. You might need a more expensive die for higher volume. More automated tools cost more. Piece price and tool price go together.
• Before building a tool, do a process simulation to optimize the gating, etc.
• Foundry quotes tend to neglect including gages even when the drawing indicates that a feature is to be gaged.
• Canadian/US exchange rate impacts tooling/casting quotes a great deal. At the time of this writing, the difference is 30%. 
• A multi-cavity die might be more expensive but would be suited to high volume parts. This might be worth it to offset higher piece price and the costs of delayed deliveries. 

Investment Casting Materials

Fabrication alloys are often limited by what has always been used for an application, or what is on the shelf of the fabrication shop (4340, A36 plate, etc.). However, metallurgy and heat treatment have advanced over time. There is a vast array of choices available for the designer when conceiving a part as an investment casting.

Fabricating alloys and investment casting processes/alloys have some overlap. The Investment Casting Handbook has an entire chapter that can help you select the optimal choice. With this in mind, suppose the casting alloy under consideration is different, and possibly weaker than the fabrication/forging alloy. It is true that it might need to be made heavier in certain places. It is also true that the investment casting process will likely allow the component to be thinned out and made lighter overall. Examples are readily found of investment castings being more lightweight, even with new materials.

Also, certain materials have better castability than others in terms of thin wall conditions and heavy sections. It is often advantageous to ask about this early on before the final design is settled. 

Accuracy?    Relevance?
Investment Cast material is not necessarily the fabrication material.    9.92    9.85
Investment Cast material flexibility = design options.    9.85    9.92

Panel Comments on Materials:

• An example of choosing an alternate material is that A201 aluminum is often specified for its high physical properties, but the castability is moderate to poor. On the other hand, F357 could give you similar (if lower) properties with better castability due to higher silicon. Perhaps the designer had not considered F357.
• We replaced a forging where the forging had superior mechanical properties. The casting had 30% lower strength, but the final part still weighed less.
• Sometimes it’s not easy to change materials in certain industries.
• There should always be a discussion on alloy selection. One potential alloy is cast often in your foundry and another is not; this means a great difference in minimum alloy purchase expenditures.
• 80% of the time, the cast alloy is not the same as the wrought alloy. The cast alloy is generally not as strong, so you have design modifications.
• Investment caster can and will help with this (material selection).
• A minor change in geometry can overcome a difference in material properties.
• A given foundry’s familiarity with certain materials might be a limiting factor, but it is worth exploring early on.
• Material changes scare OEMs; there has to be a business case for re-approval. If you design for manufacture, you should consider multiple methods.
• Certain foundries have go-to materials that they produce frequently. This can affect your costs.
• A designer should always look at the cast alloy instead of reflexively picking the wrought alloy (like 7071 aluminum). 

Lead Time 

Modern accounting and manufacturing trends demand shorter lead times than ever before. Also, the real world sometimes intrudes on our plans, and we end up with a need for a component right now. That said, the buyer needs to understand a few things about investment casting when this situation arises.

The investment casting process has an inherent time factor built into it. Even after development/launch, it is a time-consuming process to make a part. Creating wax patterns and subsequent shell room operations take days or weeks (the industry has been working on shortening this for a long time). The exact length can depend on part requirements.

If you need parts faster, you are probably looking for a solution with additive manufacturing at a substantial premium.
Also, subcontracted (subcon)processes (painting, machining, heat treatment, etc.) will add significantly to lead time, and the players involved might have limited control over these lead times. This is a real-world consideration, and engineering decisions have been made over this factor.

Accuracy?    Relevance?
Investment Cast lead time can be days or weeks.    9.92    9.92
Faster lead times might mean use of aAdditive Manufacturing.    9.92    9.92
Subcon operations add time,    9.92    9.92

Panel Comment on Lead Time:

• At the time of this paper, pre-form core manufacturers have limited capacities, and their lead times can run up to 20 weeks for a simple core.
• One customer was in such a hurry we just made full production from SLA patterns. 
• AM will not likely help on existing jobs with tools.
• Lead times can totally depend on your foundry of choice.
• Lead times are based on time to create the part, how quickly is the PO placed, and how quickly is the decision made. Sometimes 25%-30% of the lead time is the Purchasing decision-making process.
• SLA patterns allow for process development concurrent with tooling manufacture.
• With some of Additive Manufacturing options (like printing an actual part), the materials don’t have published accepted material properties.
• First articles can slow things down.
• Customers measure everyone on On-Time Delivery. 
General Quality Requirements
Quality requirements need to ensure the desired output, not more. Acceptance criteria for form, fit, and function need to be:
• Reasonable. 
• Attainable.
• Measurable.

Reasonable in this context means avoiding dramatic absolute verbiage, such as “no weld repair,” unless it is genuinely needed. They are often grounded in non-technical ideas on quality. For example, some aerospace castings are weld repaired, and there is an SAE specification for this. Such verbiage can result in multiple sources simply not returning a quote. 

Not all foundries are qualified to supply all needs; a visit/audit might be needed. It has to be the right fit in terms of equipment, certifications, size capabilities, etc. A site visit is almost always a good idea, and eventually an audit. 

Though it seems basic, a common occurrence as parts transition from fabrication to casting is contradictory specifications. A key to avoiding such problems is early clarity on the sequence (hierarchy) of compliance. For example, a common such sequence is:
1. PO.
2. Print. 
3. Industry Specs.
4. Local Specs.
 

Accuracy?    Relevance?
Quality requirements need to ensure the desired output, not more.    9.92    9.92
Not all foundries can meet all needs.    9.92    9.92
Be clear on 
sequence of 
compliance.    9.92    9.92

Panel Comments on General Quality Requirements:

• The print and model cannot conflict and have to cover everything.
• This (conflict in specs) does happen. A good foundry will have a review for contradictory specs.
• Think about function, function, function.
• The most important aspect is that you accurately describe what you are looking for, so your supplier understands what you require and so they can accurately forecast their ability to meet these needs. Often suppliers don’t fully understand the requirement and you only find out later.
• Fit, form, function, not perfection.
• If they intend to use subcontractors like heat treating, those same requirements need to be flowed down to them also. This needs to be made clear on the PO.
• Sequence of compliance is important. For example, gating allowance does not supersede required print dimensions per ASTM. 
• Be sure to understand system-level requirements beyond first articles.
• The designer should be judicious 
in not over-specifying NDT testing and tolerances beyond what is needed.

Quality Requirements, Test Bars/Coupons

Verification of material properties is done by test bars. As stated by one panelist, “It’s essential to have mechanical property test plans discussed before starting a new project. Separately cast then subsequently machined test bars are the best path forward for material assessment… [and] [buyers and suppliers] should discuss and agree on a mechanical properties testing plan, at the beginning of each new project.”

If you are going to utilize test bars for your components, there should be clarity regarding: 
• Are they cast integrally or separately cast?
• If cast integrally, does the location make sense?
• Handling during heat treat and other operations.
• Number.
• Coupons versus production volume.  

It is also important to recognize that the numerical value generated by the separate test bar does not necessarily reflect the properties of the entire casting, but rather the quality of the steel.

Accuracy?    Relevance?
Test Bars verify quality of the metal.    9.77    9.92
A plan for test bars needs to be in place before production.    9.92    9.92

Panel Comments on Test Bars:

• Cutting test bars from castings is expensive; you have to pay for the test and the casting.
• When you are developing a new part, it might be useful to measure variations in material properties in different areas of the casting. You should know where you are most sensitive, and you should measure key characteristics there.
• The same applies for flat tensile bars.
• Identifying test bars is an important topic.
• Most commercial castings can be verified without the need for test bars using chemistry and heat treatment lab results. This is an avenue for cost savings and lead time reduction.
• Test bars test for microstructure, but there can be defects in the test bars. They can point to defects in the casting.
• Ensure an adequate number of test bars in case of rework.
Conclusions
• A clear consensus exists across the Investment Casting industry, including the customer base on some critical topics in component purchasing and design.
• Investment castings can often offer an avenue to cost savings for OEMs as an alternative to fabrications and forgings. 
• Customer support makes a huge difference in the successful conversion from fabrication/forging to casting.
• The investment casting process offers multiple creative methods to optimize component design and material.
• Tooling quotes need to be scrutinized correctly.
• Open and early communication between the buyer and the potential supplier is critical to maximize savings and minimize costly missteps.
• Cooperation can also help to reduce lead time.
• Clearly specifying realistic quality requirements for fit, form, and function is recommended. This includes test bars, surface finish, and x-ray testing.
• Dimensional capabilities vary between foundries and often from job to job, depending on geometry.
• Drawings should be updated when they need to be updated.
• There can be hidden costs in the investment casting process. They can often be avoided or minimized readily.