DFM stands for design for manufacturing and is a part of the product development process initiated when your design shifts from prototype development to new product introduction. When done correctly, it can lower your manufacturing and production time and costs significantly. In this article, we discuss three key things you need to know about DFM and how it affects the manufacturability of your product.
What is DFM and why is it important?
Design for manufacturing (DFM) is the practice of designing products with parts and assemblies that are easy to mass-produce and assemble. It is the next level of product design necessary to make products manufactured economically. Most seasoned engineers, due to years of manufacturing experience, build some design for manufacturing work into earlier phases however, the overall process is so detailed that its effort requires its own phase. There is a right time to do DFM, and it can be quite costly when done too late in the product development process. Generally, the right time for manufacturing design is after concept development is frozen, several rounds of prototypes built, and enough testing is completed where the technical team is confident in the design.
How do you perform a DFM analysis?
- Review and understand the design intent.
- Select materials that meet the design requirements while keeping in mind all cost-adding processes.
- Decide on a final manufacturing process for each part based on part geometry and projected volumes.
- Design parts so that selected stock sizes minimize material removal to reduce machining time.
- Carefully review tolerancing to assure proper fit, form, and function and determine the loosest possible tolerances. Tolerances should allow for a good product that is capable of being produced using the manufacturing method chosen.
- Review the complexity (cost) of a single part versus the assembly time for multi-part assemblies.
- For plastic injected molded parts, review wall thickness, draft, ribs, and texture for uniformity and consistency in the molding process.
- Review design of assemblies with careful attention to assembly order, number of parts, and assembly time required.
- Minimize the number of different sizes of hardware needed, thus reducing the tools required.
- Minimize the number of assembly fixtures and jigs required.
- Tolerance parts for easy measurement during incoming inspection. Try to prevent parts from needing to be sectioned when measured
- When products contain electronics, review safety requirements for both the assembly process and the end-use by the customer.
- Review proper product labeling to minimize risk and adhere to regulatory and industry requirements.
What are some key factors that affect design for manufaturing?
One thing that affects a product design the most is the process needed to manufacture. If you carefully design a machined part to minimize the number of setups, it can keep the cost low. For example, if all the machining occurs on one side, it eliminates the need to unclamp and reposition to another side, thus reducing time and labor costs. Another thing that can minimize the cost of machined parts is the number of tool changes required to produce them. For instance, if all the radii are the same and large enough, you can use the same endmill to remove material and generate the filets in the corners, eliminating the need for tool change. Also, using the same size holes or tapped holes throughout the part will minimize tool changes. Another option during DFM is to eliminate secondary operations that require moving parts to another machine. Like when a lathe part has details completed on a milling machine or an EDM (Electrical Discharge Machining) machine. With the advancement of CNC machining centers and the addition of fourth and or fifth axis machines, this has become less of a factor, although not all machine shops have these newer machines.
It is no surprise that the quickest way to reduce cost is to reduce the number of different parts produced. Depending on the function and user requirements this may not be possible, but there are a few strategies to lower part quantity without sacrificing product quality. Some parts may be able to be combined from multiple smaller parts into one large plastic part. Similarly, modular assemblies let you add extras to different product models without increasing part production for all units. Look at the components and see if you can use the same part in multiple places, such as using the same part for both halves of an outer case. By producing a higher volume of one part instead of smaller amounts of two parts you can drastically cut your piece part price. It also can impact inspection and assembly costs as you will not have paperwork and quality controls for separate parts.
Expected sales volume
The expected sales volume plays a role in determining part production. If production volumes are high enough, it may make sense to consider molding or casting the part. While both these processes involve substantial tooling expenses, you can reduce piece part price by amortizing tooling costs over the product lifetime. In some cases, a high-volume part may be initially machined, for the first few months, to allow for the design to stabilize. If there are no part design changes, the production method may transition to molding or casting as a cost reduction program.
The finish requirements of a part also affect design for manufacturing. Many finishes are available based on material and environmental factors. For example, metal parts will need at least one secondary operation to complete. The simplest option is stainless steel which requires only a cleaning process referred to as passivation. With aluminum parts, the choices are numerous, with anodizing in several colors, hard anodizing, nickel plating, painting, and powder coating being the most popular.
Tolerancing lays out what variations in the product dimensions are allowed before compromising the function of the product. Reviewing the tolerancing is a necessary aspect of the manufacturing design process. The tolerancing of a part affects not only the pricing but product assembly and function. Parts should be toleranced to ensure that they fit together and function within the range provided on the prints. An excessive number of dimensions or very tight tolerances on parts can cause inspections to take longer and cost more. Tighter tolerances also cost more to manufacture and lead to higher part fallout. The parts should be toleranced so they can be easily verified when inspected. There can also be cost issues if the tolerances require specialized equipment to produce or inspect. The good news is with the onset of CNC machining centers tighter tolerancing is almost a given. Typically, +/- .005” used to be the standard but now +/- .003” is no more costly due to the precision of machining centers.
Material selection determines not only raw material cost but also machining feed rates (time). With many products today being electro-mechanical, the design of printed circuit boards and component selection is critical. Careful consideration of the availability of components; obsolesce is a costly issue. Component heat transfer requirements can impact the performance and function of many electronic boards. Thermal analysis and safety are also aspects of the DFM review of electronics. A review of product performance verification is necessary to assure the safety of the assemblers. While this relates to hardware, the creation of software generally gets a close review and some updating. Testing and certification of products can have a significant impact on cost however, they are usually one-time certifications (CE or UL).
With the cost of labor, you need to consider the required assembly time. If simplifying parts change one part into multiple parts, requiring assembly, one needs to weigh the cost savings against the added assembly time and necessary hardware. The simpler a product is to assemble, the more cost-effective it will be. Additionally, moving to a single complicated part may save money if it eliminates the need for alignment fixtures or jigs. All these factors need evaluation during DFM.
It is difficult to encompass all the tasks and nuances of the DFM process in one article. Understanding that the process cannot start until you make prototypes and conduct sufficient testing is a key takeaway. Another would be that the process is rigorous and multistep, requiring careful integrated design work done by engineers well acquainted with the anticipated fabrication process. When doing design for manufacturing, there is no substitute for experience. If you are unsure how to get started or would like some expert advice on designing your tools, contact us and we would be happy to help.
Ready for DFM but do not know where to start?
About Synectic Product Development: Synectic Product Development is an ISO 13485 certified, full-scale product development company. Vertically integrated within the Mack Group, our capabilities allow us to take your design from concept to production. With over 40 years of experience in design, development, and manufacturing, we strive for ingenuity, cost-effectiveness, and aesthetics in our designs. Learn more about our new product introduction services and see how we can help your next project.