How Design for Manufacturability Cuts Program Risk and Cost

When a supplier reviews a new part, there are often things they would've done differently if they had seen the design earlier. A tolerance may require machining that could have been avoided. The material may be difficult to form with the process being considered. A radius or other feature may complicate the tooling. None of these necessarily makes the part impossible to manufacture, but they can add cost or make production more difficult.

This is what a design for manufacturability review is meant to catch. Before tooling is released, the supplier reviews the part with the customer's engineering team and looks at how the design will translate into production. That can include the material, tolerances, geometry, expected volume, tooling, secondary operations, and inspection requirements.

The earlier that review happens, the more useful it tends to be. Changing a tolerance in CAD is straightforward. Finding out after tooling is built that the tolerance requires another operation is a different problem.

Table of Contents

● Why Timing Matters

● What Does a Design for Manufacturability Review Cover?

● How Early Should You Bring in a Supplier?

● What Should You Send?

● What Happens During the Review?

● Frequently Asked Questions

● How MacLean-Fogg Works With Customers

Key Takeaways

● A design for manufacturability (DFM) review checks a part's material, tolerances, geometry, volume, tooling, secondary operations, and inspection against the process that will make it, before production tooling is released.

● In a 2017 Design Science study of UAV programs at an aerospace company, decisions made before design freeze accounted for 86 percent of expected program cost. Problems introduced early but found late took more than 10 times the rework.

● The Forging Industry Association says design decisions typically drive 70 percent or more of product cost, and it recommends bringing in the forging supplier during preliminary design.

● A DFM review flags where a tolerance changes the process, such as adding a machining operation. The customer's engineering team then decides whether the application requires it.

Why Timing Matters

There is plenty of research behind the idea that decisions made during design have an outsized effect on what a product eventually costs to manufacture. The exact percentages vary, and there is no single number that applies to every component or manufacturing process.

One useful example comes from a 2017 Design Science study of unmanned aerial vehicle development at an aerospace company. In the program studied, decisions made before design freeze accounted for 86 percent of expected program cost. The researchers also found that problems introduced early but discovered later resulted in more than 10 times the rework.

The Forging Industry Association reaches a similar conclusion in its Product Design Guide for Forging. The guide says design decisions typically drive 70 percent or more of product cost and recommends getting the forging supplier and material supplier involved early in product design.

The numbers are less important than what happens on an actual program. If a manufacturing issue is found while the part is still being designed, the engineering team can decide whether to change it. Once tooling has been built and the production process has been established, there are fewer options and most of them cost money.

Take a tolerance on a formed feature. If the manufacturing team believes the process will not consistently hold it, the first question is whether the application really requires that tolerance. If it does, machining may be the right answer. If it does not, the customer may decide to revise the drawing. Either way, it is a useful discussion to have before the tool is built.

The same issue found later may require a tooling change, another operation, different inspection, or additional validation. On automotive programs, engineering changes can also affect PPAP requirements. AIAG's PPAP manual identifies changes to production design records, specifications, or materials among the situations that can require customer approval.

This is not a new idea. In a study of commercial product development practices, the U.S. Government Accountability Office documented how companies including Cummins and Caterpillar used prototypes, analysis, manufacturing input, and supplier involvement before committing to production. The reason for doing it early was practical: they wanted to find problems before they had built a production system around the design.

What Does a Design for Manufacturability Review Cover?

The review depends on the part. A forged component raises different questions than a molded plastic part, and a high-volume fastener is not reviewed the same way as a lower-volume machined component. In most cases, though, the discussion starts with the same basic information: what the part has to do, what conditions it will see, and how many need to be made.

From there, the manufacturing team can look at the drawing and CAD in context.

Tolerances are usually part of that discussion. Some dimensions need to be held tightly because they control fit, sealing, alignment, or another function of the part. Others may be tighter than the application requires. That distinction matters when a tolerance changes the manufacturing process. A feature that could otherwise be formed, for example, may need a secondary machining operation to hold a tighter dimension. The supplier can point out where the process is likely to have difficulty, but the customer's engineering team determines what the application requires.

Geometry gets reviewed the same way. In forging, draft, radii, and material flow all affect how the part can be made, and the Forging Industry Association recommends selecting a forging company as early as possible, preferably in the preliminary design stage. A molded plastic component has a different set of concerns, including wall thickness, ribs, radii, and draft. The details vary with the process, but they are all easier to work through before tooling is finished.

Material is another area where application and manufacturing have to be considered together. The material has to survive the loads, temperature, corrosion, and other conditions the part will see, but some materials are considerably more difficult to manufacture than others. At MacLean-Fogg's Chesterfield Township operation, for example, specialty materials including Inconel 718, Nimonic 80A, and stainless steel are warm formed to improve their formability compared with forming them at room temperature. Knowing the application and material requirements early gives the manufacturing team a chance to recommend a process that makes sense for both.

There may also be more than one reasonable way to make the part. MacLean-Fogg manufactures both cold-formed and machined components, and in some cases the two processes are used together. At MacLean-Fogg, a formed blank can provide the basic geometry of the component, and machining is then applied to the features that need it. The right sequence depends on the material, part geometry, critical dimensions, and production volume.

Inspection should be part of the same conversation. If a dimension is critical, the team needs to know how it will be measured and whether that method works at the expected production volume. It is possible to specify something that can be measured but is impractical to check efficiently in production. Finding that out during process development is preferable to finding it out on the floor.

How Early Should You Bring in a Supplier?

There is no single point in the development process that works for every program. In general, the supplier should see the part while there is still an opportunity to act on what they find.

● Early Design: Bring the supplier in while the material, geometry, and process are still open, when it is easiest to ask whether a part could be formed instead of machined.

● Before Prototype Tooling: The supplier can help define what the prototype needs to prove and whether the prototype process will show how production will run.

● By Design Freeze: The major questions around material, tolerances, geometry, and manufacturing process should be settled.

● Before Production Tooling Release: The team should know how every critical feature will be produced and inspected.

What Should You Send?

A current drawing and CAD are a good place to start, even if neither is final. The supplier will also need enough information to understand the application.

● Operating Conditions: Note the loads, temperature, and any vibration or corrosion exposure the part will see in service.

● Mating Components and Assembly: Describe what the part connects to and how it will be assembled.

● Volume and Program Life: Give the annual volume, the expected production ramp, and how long the program is expected to run.

● Material and Quality Requirements: List any required materials, quality standards, and validation testing.

● Critical Features: Mark the dimensions or features the engineering team already knows are critical.

● Known Problems: For an existing part, say whether it cracks, loosens, wears too quickly, takes too long to machine, or costs too much to produce.

What Happens During the Review?

A useful DFM review is usually a working engineering discussion, not a presentation.

The team walks through the application and the current design, identifies the requirements that cannot change, and then looks at the areas where there may be flexibility. The manufacturing engineers can explain what the proposed design means for the process, including tooling, material behavior, secondary operations, and inspection. If there are other reasonable ways to make the part, those can be compared before the team commits to one.

Sometimes the next step is a design change. Sometimes it is analysis, simulation, or a prototype to answer a specific question. And sometimes the review confirms that the original design and process are the right ones.

A good DFM review does not have to result in a change. It needs to give the team confidence that the manufacturing implications of the design have been considered before production tooling is released.