Improving Design for Manufacturing (DFM)

Kashyap Vyas in Machine Design suggests that manufacturers spend one-third to one-half their time fixing errors, and close to 24 percent of those errors are related to manufacturability.

Therefore, there is plenty of wasted time, money, and material due to mistakes. The positive news is that by following principles of design for manufacturing (DFM) and design for assembly (DFA), we can spot these errors and likely avoid them early enough.

Design for Manufacturing (DFM) or Design for Manufacturing and Assembly is an essential component of the product development cycle. It consists of optimizing the design of a product for its manufacturing and assembly process. It also merges the design requirements of the product with its production method. Using DFM tactics reduces the cost of and complexities involved in producing a product while keeping its quality intact.

DFM was once a strict textbook idea that even failed to make it to paper at times. The concept of integrating software into the process to enhance and automate DFM was never an earnest endeavor. The early developmental stages of automated DFM and the implications are significant.

There are several ways to design a part and several active factors at play. These include:

• the intention for making the part;
• the best raw material for the particular function;
• available equipment;
• skilled technicians; and
• time-frame for production.

Aside from these, DFM and DMA focus on ways to make parts more efficiently – faster and with lower quantities of scrap, stronger, improved durability, not easy to damage during fabrication, and with as few errors as possible during assembly.

There is a two-fold benefit to you:

• Money saved
• Faster production

Structure of a Manufacturing Environment

Manufacturing environments are about two things – process and quality control. They are primarily concerned:

• making their procedures better;
• lowering costs to the barest minimum; and
• ascertaining that process and part accuracy sticks to required tolerances.

Six Sigma is a mature zero-defect manufacturing process. It is common within the manufacturing industry. Achieving Six Sigma is only possible through repeated destructive iteration to the manufacturing process.

However, it is a lot easier to achieve when parts and processes align with a few fundamental principles that make manufacturing more manageable. A product development firm with a concrete understanding of manufacturing processes is crucial. They can anticipate the issues inventors, entrepreneurs, and developers create when they move their product to mass-production (manufacturing and assembly).

Cost-cutting Rules for Design for Manufacturing

More parts are often less pleasant than fewer parts. It is suitable for designs to be as simple as possible. Injection molding processes of plastic parts significantly reduce the total parts number essential for a complex device.

The reason is that the housing and essential fasteners, cavities, and accessory parts can all have a similar design as the same piece of plastic. Other small details include: keeping efficiency at maximum using multi-cavity mold tools, designing molds to prevent injection modeling defects, and preventing unplanned manufacturing mistakes. The latter occurs through testing prototype parts early to contribute to your overall project cost.

Design your parts using mistake-proofing. Mistake proofing attempts to eliminate errors or make them one hundred percent detectable if they ever occur.

No non-conforming parts should leave the assembly process and onto store shelves. In the same way, no non-conformance events in the manufacturing process should go without detection.

To illustrate mistake proofing during the design process, you can design the connecting bits with unique connections such that any two pieces can only combine in one unique way. This way is the correct way. It prevents a laborer unfamiliar with the design or who is responsible for assembling thousands of parts daily from making any mistake. If it is impossible to make a mistake due to intelligent design, then your process is mistake-proof.

Improving Processes in Design for Manufacturing

Designing a product for manufacturing is one key consideration when performing new product development activities. Concerning high-volume production, being consistent, and being able to repeat manufacturability of products can make or mar the entire process.

Considerations to Improve DMA

CAD vs. Reality: The ideal mathematical world of computer-aided design (CAD) and engineer’s drawings, and the real world on the shop floor are vastly different. Drawings are excellent for visualizing how parts fit together and where bends are. However, they do not always consider how sheet metal behaves in the real world. For example, bends can cause holes to distort when their location is not correct.
Also, consider what the available equipment can or not able to do. An example is asking what tonnages the press brake machine can achieve.
Visiting the shop floor provides a first-hand view of the capabilities and limitations of each machine. It also allows discussing with the fabricators who know how to turn drawings into finished pieces.

How your metal behaves: Art Hedrick mentions in the Stamping Journal advises you to think like your metal. Metals have properties that vary by the type of metal and by grades within a single type. Elements such as luster, conductivity (heat and electrical), malleability, ductility, weldability, corrosion resistance directly affect how a given metal will respond to fabrication.

Let’s illustrate with your punch tool and your raw material. If they are the same grade of steel, they are likely to stick – called galling – and can distort the hole and damage the punch. Study how metals act in isolation and when in a mix. Also, anticipate how various grades respond when stamped, punched, bent, cut, or welded.

Best Practices for Part Features

Are you wondering how broad your flanges should be? Is it possible to avoid a tab tearing or cracking? Part features such as bends, tabs, holes, and joints sync with or oppose your original design. In the Machine Design article, Vyas provides a solid introduction tot his concept.

• Bend theory consists of guidelines on when to weld versus when to bend according to a recent article in The Fabricator. It also addresses the way to anticipate and ensure tears having bend relief cuts do not happen, and knowing which forming method is the best for the inside bend radius. Then it determines how wide a flange can be relative to the sheet thickness.
• Metal also has a grain, much like paper and fabric. It may be easier to bend or fold parallel to the grain, but in metals, this risks cracking at the bends. It results in a weaker and less durable part. According to Machine Design, the approach to recommend is to form lugs at an angle less than 45 degrees towards or perpendicular to the grain direction.
• Fasteners use holes to align components and provide access (in some cases). When the placement or dimensions of a hole are significant, ensure you have considered where it will be relative to bends, edges, and other features. Take the example of a hole too close to the edge that will stretch or tear if the metal surrounding it is not thick or strong enough. Similarly, the punch touching the material will draw some of the material in as it shears, penetrating the material. The material then distorts the area around the hole. This effect is more apparent if the sheet has many small perforations.

How High (or Low) Can You Go?

According to the Machine Design article, tolerances refer to the total quantity by which a feature’s dimensions are permitted to vary. They are much like a standard deviation ranging between minimum and maximum numerical values. An example is saying a hole must sit between 0.7500 and 0.7549 cm from the edge of the sheet.

It helps the designer and the manufacturer to specify tolerance values with all dimensions. The designer uses these values to eliminate ambiguity in fabrication and to tell the technician that the dimensions of a feature are crucial to the finished part.

On the other hand, the technician depends on tolerances to guarantee the part is correct at manufacture.

Connecting All the Dots

According to a recent article in Appliance Design, if it is tricky to assemble, then even the best-looking streamlined part with holes in perfect positions is a colossal waste. A way to simplify assembly is to reduce part count. Fewer parts suggest the following:

• fewer drawings to keep straight,
• fewer problems with tolerance,
• fewer tools,
• fewer bugs,
• fewer fixtures,
• fewer assembly stations and equipment,
• less requirement for assembly labor,
• less complicated overall supply chain.

A separate technique to error-proof is to build in holes, tabs, notches, and several other visual cues. These assist the technician in lining up pieces and ensure there is only one way to assemble a part. The latter is especially true with tabs.

Tabs can reduce the need for fixturing before welding if their placing is such that the part holds together temporarily. Assembly is easier for the technician if you include such features in your part design. Assembly will also be faster for your schedule.
Know that there is always the possibility of a better design. Grant Hagedorn in a recent Fabricator article summarized that reducing, simplifying, and mistake-proofing shop floor processes ensure dramatic cost reductions. The way this happens is through greater efficiency. He calls it the goal of good sheet metal design. Where a new design removes welding but makes the bending process quite complicated, the process is in reverse.

Conclusion

Designing for manufacturing is a highly relevant aspect of reducing total costs during product development. Understanding the issues, manufacturers face during production and what they are interested in will improve parts design in a way that prevents conflicts when a product is at that stage in its lifecycle.