DFM is a part of phase 4 of our new product development process and is addressed at the beginning of launching a product through the new product introduction area. If you are new to product development, you may be asking yourself what exactly does DFM stands for and why is it critical to getting your invention to contract manufacturing? In this article we discuss three key things you need to know about DFM an how it affects your product design.
1. What does DFM stand for?
Design for manufacturing (DFM) is the practice of designing products with parts and assemblies that are easy to make and put together. It is the next deeper level of product design necessary to make products that can be mass produced economically. Most seasoned engineers, due to their years of manufacturing experience, can build some of this design for manufacturing work into earlier phases, but the process is so detailed its effort is larger and needs 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. The right time is dependent on several factors, but generally DFM is done ideally after concept development is frozen, several rounds of prototypes have been built, and enough testing has been done where technical team is confident in the design.
2. What are the steps of a successful DFM analysis?
- Review and understand the design.
- Select materials based upon the design requirements, 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 stock sizes can be selected to minimize material removal to reduce machining time.
- Carefully review tolerancing to assure proper fit, form, and function.
- Review the complexity (cost) of a single part vs the assembly time for multi-part assemblies.
- 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 required.
- Tolerance parts so that they can be easily measured during incoming inspection.
- When products contain electronics, safety needs to be reviewed for both the assembly process and the end use by the customer.
- Proper product labeling should also be reviewed.
3. What are some key factors that affect design for manufacturing?
One thing that effects a product design the most is the process needed to manufacture. If a machined part is designed with careful thought to minimize the number of setups this can keep the cost low. For example, if all the machining can be done from one side of the part, it reduces 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 require to produce the part. For instance, if all the radii are the same and large enough, the same endmill can be used to remove material and generate the filets in the corners, eliminating the need for tool change. Also, if the same size holes or tapped holes can be used throughout the part it will minimize tool changes. Another thing that can be done during DFM is to eliminate secondary operations that require moving the part to another machine. Like when a lathe part has a detail that needs to be done 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.
Expected Sales Volume
The expected sales volume plays a large part in determining how a part should be produced. If the volumes are high enough it may make sense to consider molding or casting the part. While both these processes involve substantial tooling expenses, the piece part price can be greatly reduced even when the tooling costs are amortized over the life of the product. In some cases, a high-volume part may be machined for the first few months to allow for the design to stabilize. If there are not changes to the part they may transition to a molded or cast part as a cost reduction program.
The finish requirements of a part effect design for manufacturing as well. Metal parts will need at least one secondary operation to either heat treat to harden or one of many finishes that can be selected based upon material and what environment the product with be used in. The simplest, stainless steel the process may just be a passivation which is a cleaning process. With aluminum parts the choices are numerous, anodizing in several colors, hard anodizing, nickel plating, painting, and powder coating are 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 key aspect of the DFM process. The tolerancing of a part can not only effect the pricing, but is a critical to how the product is assembled and how well it works. Parts should be toleranced to assure that it will fit together and function within the range provided on the prints. If there are an excessive number of dimensions or very tight tolerances on parts this can cause inspections to take longer and cost more. 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 will determine not only the raw material cost but also the feed rates (time) that can be used while machining. With many products today being electro-mechanical, the design of printed circuit boards and component selection is critical. Careful consideration needs to be given to the availability of components; obsolesce is a major and costly issue. The performance and function of many electronic boards can be impacted by the heat transfer requirements of the components used. Thermal analysis and safety are a key aspect of the DFM review of electronics. Product performance verification should be reviewed 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 a significant impact on cost, however, these are usually one-time certifications (CE or UL).
With the cost of labor, consideration needs to be given to the time needed to assemble. If parts can be simplified by changing into multiple parts that are then assembled, one needs to weigh the cost savings against the added time to assemble and the hardware needed. The simpler a product is to assemble the more cost effective it will be. Additionally, going to a single more complicated part may save money if it eliminates the need for alignment fixtures or jigs. All these factors need to be evaluated during DFM.
It is difficult to encompass all the tasks and nuances of the DFM process in one article. Certainly, understanding that the process cannot start until real prototypes are made and sufficient testing has been done, 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 really is no substitute for experience.