Two buzzwords that we often hear in our industry are “DFM” and “DFA”. These should be given consideration right at the beginning of a project and continue to be used until after a product has been manufactured. So, what do they mean? What are the differences? What’s the importance of DFM & DFA, and how do we do each one well? Design Development Engineer, Phil, discusses just this;

DFM stands for “Design for Manufacture”. DFM is the process of designing parts with a chosen manufacturing process in mind. Knowing the chosen manufacturing process during the part design phase will ensure the design of that part is optimised to suit the process, resulting in a better, lower cost product. The DFM process can be broken down into 4 areas; chosen manufacturing process, part design, material selection and finally the environment the parts are to be used in. Consideration must be given to each of these areas. If just one area is neglected, this could lead to expensive and embarrassing product failures further down the road.

The chosen manufacturing process and part design areas of DFM go hand in hand. As a design engineers, when designing a component, we will consider both the desired function / design intent of the component as well as the chosen manufacturing process. We will design the component to conform to the good manufacturing principles for the manufacturing process we have chosen. This will include considering things like physical size and shape of a component right down to intricate geometry of particular features. For example, when designing for injection moulding, we will design the part in a specific way. This involves following the common design rules for injection moulding, like adding a split-line to the part, adding different draft angles to areas of the part and ensuring there are no undercuts in the design (just to name a few!). However, if it was decided that the part was to be CNC machined instead, then the design features of a CNC machined part wouldn’t need to incorporate a large majority of these injection moulding design features.

When it comes to material selection, choosing which material your part will be made from can have a big impact on DFM. Not only will the chosen manufacturing process play a part in selecting the right materials, but other properties of the final product helps guide us into selecting the best material for the job. We look at the desired mechanical properties of the material for example; will it need to withstand a load? Will there be any living hinges incorporated into the design? Will there be any snap fits or clips? If the product is a medical device, does the chosen material need to be a medical grade, sterilisation safe, food safe or even hold a certain USP classification? These are all important areas which can drive the material selection aspect of DFM.

The thermal properties of a material is an area of material selection that also plays a part in ensuring the final product can survive and still operate in the desired environmental conditions. Does the product need to perform in a particularly low or high temperature environment? The best design in the world won’t matter if the product’s features cannot perform within in its normal operating temperatures. Knowing the application and what environmental conditions the product will be subject to, can make selecting the correct material a lot easier.

DFM is an important part of any product development cycle. It should be applied early on in the process for the most cost and time savings. Appreciating and giving consideration to these 4 areas of the DFM process will enable you to engineer and manufacture a product that performs to a high standard with robust, lasting performance. Addressing potential issues at those early stages of product development will help you get it right first time or at least require less prototyping and fewer product iterations.

DFA stands for “Design for Assembly”. Design for assembly is a process by which products are designed with ease of assembly in mind. For example, if a product contains fewer parts, it will take less time to assemble, thereby reducing assembly time and costs.

Although Design for Assembly (DFA) and Design for Manufacturing (DFM) principles are often looked at as one combined subject, they are actually quite separate methodologies. Design for Assembly is the optimisation of the product and the assembly process, while Design for Manufacture focuses on the manufacturing process and material selection.

The aim of DFA is to make the assembly process easier, faster, and more consistent therefore increasing productivity. Some of the main principles of DFA to keep in mind as you start your project are; minimising part count, built-in fasteners, use of standard parts, part symmetry and poka-yoke assembly specific design features. Giving consideration to these principles throughout the design process of your project will set you on the right path to achieving an efficient and successful design for assembly.

Minimising part count is an easy way to ensure your product is quick to assemble. Well-designed products which have fewer parts usually end up being more durable as well as easier to assemble and repair. Keeping the part count down will help cut assembly times and therefore assembly costs, as well as prevent confusion during assembly, resulting in fewer assembly issues. However, be mindful that overly complex components might unnecessarily increase manufacturing costs. This is why its always great to have a close relationship with your chosen manufacturer. Communication between designers and manufacturers is key to resolving complex part issues and helps to ensure parts are designed both efficiently and cost effectively too.

Built in fasteners should always be consideration when designing your product. Although bolts, screws and rivets are relatively inexpensive, the installation of these fixings is very time consuming. Built-in fasteners like snap fits speed up the assembly of the final product. Snap fits don’t require any special production equipment and can make assembly quick and simple.

Using standard off the shelf parts instead of costly custom manufactured parts such as bushings and gears will increase repeatability, save time during the assembly process, and reduce assembly costs. Incorporating off the shelf parts into your design will also speed up the design process, as there are fewer custom parts to design and engineer.

Designing symmetric components is another way to ensure an efficient DFA methodology. This makes the assembly process easier for workers as it reduces the time trying to identify which way round similar looking components should be mounted etc.

Finally, incorporating assembly specific design features into your parts, such as physical obstructions to prevent components from being fitted wrongly, or adding identifying physical features to parts making them easier to identify and assemble is one of the easiest ways to reduce assembly time. One of the simplest but most effective poka-yoke design features is the UK electrical plug & socket. The 3-prong design for the plug and socket, ensures the plug can only be connected to the socket in the correct, single orientation. Incorporating these poka-yoke design features into your part design will make sure your product can’t be assembled incorrectly and will avoid many potential issues down the line.

Hopefully this has given you a brief overview of the value that Design for Manufacture and Design for Assembly principles have in new product and medical device design. Giving consideration to these two methodologies can not only help you reduce the time to market and costs of your product, but also guide you to design a more robust, effective product that can last the test of time, and be easily used out in the real world! If you need help with your new product DFM & DFA optimisation then please get in touch.

Phil Sampey 17 March 2022


Get in Touch with Phil Sampey

Senior Design Development Engineer

Phil graduated from Staffordshire University with a degree in Automotive Technology. Since joining HD, Phil has primarily been working on a number of medical device projects, supported by his wide range of experience from prototype manufacturing, plastic injection moulding and CNC machined parts, to designing bespoke gearbox systems for various industries. Phil also assists with the management of our ISO 13485 & ISO 9001 QMS and network of approved manufacturing suppliers.

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