Design For Manufacturing (DFM) is the process of designing parts, components or products for ease of manufacturing with an ultimate goal of making a better product at a lower cost. This is done by simplifying, optimizing and refining the product design. In general, five principles are thoroughly examined during DFM. They are:
- Compliance / Testing
DFM should occur very early in the design process, right at the start of the product design process. As the design progresses through the product life cycle, it becomes very expensive to make changes and also very difficult to implement those changes. Early DFM allows design changes to be executed quickly at the least expensive location.
Also, a well executed DFM should include all stakeholders – engineers, designers, contract manufacturers, mold builders and material suppliers. The fundamental intent of this “cross-functional” DFM is to challenge the design at all levels – component, sub-system, system and holistic levels to ensure the design is optimized and does not have unnecessary cost embedded in it.
Pulling all the stakeholders together early in the design process is easier if a new product is being developed. But if we are dealing with an established product, challenging the original design is a necessary element of a thorough DFM process. Many a lot of times, mistakes in the original design are repeated by replicating a previous design. Always question every aspect of the design.
- Look at the original drawings
- Tear down the product
- Look at competitive and near-neighbor products
- Talk to vendors / contract manufacturers
DFM is the most important exercise any product designer should do before embarking on the product development. Unlike software development where bug can be resolved by pushing in a new line of code, in case of hardware, it isn’t possible. Costly recall of hardware products is required if there is any faulty part in the product.
Let us take a closer look at the above mentioned 5 different factors
Manufacturing process is the first aspect to be looked into when designing a product. Manufacturing process chosen must be the most optimal one for the product. Different manufacturing processes have different MOQ requirements for the product to become price competitive. One has to thus choose the process carefully. You wouldn’t want to use highly capitalized process like injection molding which involves building of tools and dies to make a low-volume part that could have been manufactured using a lower-capitalized method, such as thermoforming. When determining the manufacturing process, one should take into consideration the following – quantity of parts being made, the material being used, complexity of the surfaces, the tolerances required and whether there were secondary processes required.
Good design is essential for a good product. The actual drawing of the part or product has to conform to good manufacturing principles for the manufacturing process you’ve chosen. In case of plastic injection molding, the following principles would apply:
- Constant wall thickness. This allows for consistent and quick part cooling
- Appropriate draft (1 – 2 degree)
- Texture – need 1 degree for every 0.001” of texture depth on texture side walls
- Ribs = 60 percent of nominal wall
- Simple transitions from thick to thin features
- Wall thickness not too small
- No undercuts or features that require side action – all features “in line of pull/mold opening”
- Spec the loosest tolerances that allow a good product
Always be sure to discuss the design with your contract manufacturer who can ensure that your design conforms to good manufacturing principles for the selected process.
It is also very important to select the correct material for the product. Below are some material properties to consider during DFM
- Mechanical properties – How strong should the material be?
- Optical properties – Should the material be reflective or transparent?
- Thermal properties – How heat resistant does it need to be?
- Color – What color does the part need to be?
- Electrical properties – Does the material need to act as a dielectric?
- Flammability – How flame/burn resistant does the material need to be?
Always make sure you discuss the material with your contract manufacturer before deciding on the material to be used.
The product must be designed to withstand the environment it will be subjected to. Different materials have different properties like electrical conductivity, corrosion resistance and so on. Make sure the product is designed to function properly under its normal operating conditions.
COMPLIANCE / TESTING
All products must comply with safety and quality standards. Sometimes these are industry standards, others are third-party standards and some are internal, company-specific standards.
FEW ADDITIONAL FACTORS TO TAKE INTO CONSIDERATION
The goal of DFM is to reduce manufacturing costs without reducing performance. In addition to the principles of DFM, here are five factors that can affect design for manufacturing and design for assembly:
1. Minimize Part Count: Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.
2. Standardize Parts & Materials: Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency. Material is based on the planned use of the product and it’s function. Consider:
- How should it feel? Hard? Soft?
- Does it need to withstand pressure?
- Will the part or product need to conduct heat, electricity?
3. Create Modular Assemblies: Using non-customized modules / modular assemblies in the design allows one to modify the product without losing its overall functionality. A simple example is a basic automobile that allows you to add in extras by putting in a modular upgrade.
4. Design For Efficient Joining: Can the parts interlock or clip together? Look for ways to join the parts without the use of screws, fasteners or adhesives. If you must use fasteners, here are a few tips
- Keep the number, size and variation of fasteners to a minimum
- Use standard fasteners as much as possible.
- Use self-tapping and chamfered screws for better placement.
- Stay away from screws that are too long or too short, separate washers, tapped holes, round heads and flatheads.
5. Minimize Reorientation Of Parts During Assembly & Machining: Parts should be designed so that a minimum of manual interaction is necessary during production and assembly.
6. Streamline Number Of Manufacturing Operations / Processes: The more complex the process of making the product, the more variables for error are introduced.
7. Define Acceptable Surface Finishes: Unless it must be trade show grade, go with function rather than flashy for your surface finish.
10 OUTCOMES OF AN EFFECTIVE DFM
Below are 10 generally accepted Design for Manufacturing principles that were developed to help designers decrease the cost of and complexity of manufacturing a product. The results of a successful DFM are quantifiable in a host of ways.
- Minimize the number of product parts: Reducing the number of parts in the product is an easy way to lower the cost of product as it reduces the amount of material and assembly labor required. Reducing the number of parts also means less engineering, production, labor and shipping costs.
- Use standardized parts wherever possible: Customization is not only expensive, it is also highly time consuming. Use standardized parts as much as possible. Standardized parts are made to meet the same quality metrics, every time and they are already tooled. So you save costs and you won’t have to wonder whether they’ll pass inspection.
- Create a modular design: Using modules can simplify any future product redesign, and also allows for use of standard components and the re-use of modules in other projects.
- Design multi-functional parts: Design parts with more than one function. It is a simple way to reduce the total number of parts.
- Design multi-use products: Different products can share parts that have been designed for multi-use. Can your product use standardized parts that can be used in multiple products?
- Design for ease of fabrication: Choose the ideal combination between the material and manufacturing process that shall minimize production costs. Generally designers opt for very tight tolerances which is an absolute no-go. Avoid expensive and labor intensive final operations as painting, polishing and finish machining.
- Design product to join without using screws, fasteners, adhesives: Is it possible for your product to interlock or clip together without the need for any screws / rivets? Screws add only about 5% to the material cost but add 75% to the assembly labor. Wherever fasteners are required, try to keep the size, number and type to a minimum and use standard fasteners wherever possible.
- Design part to minimize handling during production and assembly: Handling includes positioning, orienting and fastening the part into place. For orientation purposes, use symmetrical parts wherever possible.
- Minimize assembly direction: If possible, your parts should assemble from one direction. Ideally, parts should be added from above, parallel to the gravitational direction. This way assembly is facilitated by gravity rather than fought by it.
- Design part to maximize compliance: Rely on built-in design features like tapers or chamfers, or moderate radius sizes to guide insertion of equipment and to protect the part from damage.
About 70% of the manufacturing costs of the product are determined by the design decisions. So, it is really important to adhere to the best design practices possible.