This series of articles is directed toward companies who have or are planning manufacturing operations. The topics explored will be focused on optimizing those operations and maximizing the cost/benefit aspect.
Design for Manufacturing/Design for Assembly- How these simple disciplines will reduce unnecessary costs.
Would you believe that 80 percent of the cost of your product is baked in during the design and development process? That is, no matter what you do with the actual production process later, the bulk of the cost of your product was brought on board during the design activities. So, if that is the case, what steps can we take to minimize these costs? We do this by being aware of the long term consequences in the design phase and we follow some basic guidelines that deal with the manufacturing and assembly up front.
These basic guidelines are covered under the terms Design for Manufacturing (DFM) and Design for Assembly (DFA). We’ll talk about some of the specifics in a bit, but first let’s make certain that we have a grasp on the two terms “manufacturing” and “assembly”. We will use the term “manufacturing” to refer to the actual means by which a part is made. For example machining or molding are manufacturing methods. In some cases a complete product can result from one manufacturing process, but that is typically the exception. So, the product, or different components of that product, goes through several manufacturing processes before becoming a final product. Assembly is the action of putting the parts together to make a sellable product.
Let’s talk about manufacturability. In general, the materials and processes used in manufacturing a product are determined by:
Anticipated production volume
The size of your tooling budget
The shape and complexity of parts
Particular service and/or environmental requirements
Appearance
Accuracy of the process
So, with this mind, some of our favorite guidelines are:
Choose processes that minimize process time
Avoid unnecessarily tight tolerances
Avoid final operations such as painting, polishing and so forth
For each general process (machining, injection molding, PCB design) there is a list of guidelines that applies.
Another important factor here is the familiarity that the product designers have with the current manufacturing capability of your operation (or capabilities which you may want to bring in-house). It is always a good idea for the design crew to spend time working in the actual production operation thus allowing them to gain this familiarity and avoiding time wasted on processes that simply are not compatible with your operation or are
overly costly.
Why do we care about the assembly process and why should we be thinking about it while we are in the design process? Because if you make things easier to assemble, then the assembly process if faster and more cost efficient. Here are some specific items to consider for efficient assembly:
Make features in mating parts self-locating, thus eliminating separate positioning fixtures
Make it such that a minimum number of part re-positionings are required during assembly
Make parts multifunctional
Minimize the number of fasteners
If one part has no motion relative to an adjacent part, then you probably don’t need that part (it can be incorporated into some other part)
Poke yoke: make parts so that they cannot be assembled incorrectly
So we’ve done all this. How do we know if it did any good? There are a few means of measuring our success. First is product yield. Are we indeed producing a greater number of products with no increase in resources? Of course this means that we had a good handle on our productivity prior to any improvement activities. Secondly you can calculate and assembly efficiency value. This involves the estimation of assembly times and theoretical part counts. And lastly we can count up the number of times that we violated our DFM/DFA rules.
The authors may be contacted at Heather MacKinnon (h.mack.eng@gmail.com)John Herrick (john@herrickprodev.com).
