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Sean Derrick

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How to Save Money with Design for Assembly (DFA)

Engineering Knowledge Base, Manufacturing Knowledge Base

So, what’s the big deal about Design for Assembly (DFA) and why devote a blog to it? To sum it up in one word… MONEY! DFA is a methodology of designing a product for ease of assembly. Tons of money can be saved if a designer or an engineer makes the effort to think about line assembly early in the process. Moreover, the earlier a company plans for assembly, the more they will save long term. Above all else, DFA is a quick and clean way for businesses to cut costs while making the jobs of their workers easier and happier.

 

Business 101 tells us that to increase profitability without increasing the unit price of the product, it will require costs to be cut. The assembly of a product is nothing but a cost to a company. It doesn’t matter if the product is assembled by expert craftsmen or a robot. The time devoted to assembly is a cost. The longer it takes to put a product together, the greater the amount of profit dollars are wasted. Companies pay each time a worker must untangle a part, flip an assembly over, or swap tools. Implementing ways to simplify your designs while maintaining product quality will reduce your costs. Furthermore, your workers lose nothing. You are simply making their job easier while increasing their output in the same amount of time. In a time when companies are fighting to cut costs and increase profits, exploring ways to reduce costs through DFA without the need to cut your labor is essential.

 

The idea of designing a product so that it is easy to go together sounds straight forward, but it is commonly overlooked because of lack of planning, training, or time. The worst and most egregious reason why DFA isn’t incorporated is the mantra, “Work is cheap” or “We can always find cheaper labor.” Even if the labor is cheap, why pay for what you don’t need? DFA helps companies because it increases throughput—how many units roll off the assembly line in a given time period.

 

The most holistic way to DFA is to put yourself in the shoes of the assembler and ask yourself, “How can I make this process easier?,” or “How can we build efficiency into a worker’s time?” You should be trying to get them moving to the next assembly, without sacrificing quality, as soon as possible. How can you make assembly easier? Remember the old adage, “Time is money.” It doesn’t matter if it’s a robot or an hourly worker’s time. If there is a faster way to finish the current assembly and move on to the next, then there are savings to be realized. Here are seven simple money-saving DFA tips with examples.

 

Seven Ways to Save Money with DFA

 

1. Standardize parts and fasteners.

Nothing slows down an assembly like grabbing the wrong length fastener or the right-handed version instead of the left-handed version. Each time a worker must go back to a parts bin is a time expense. Standardizing parts so fewer trips are needed is a quick and clean way to save time/costs. A good example is standardizing on a common fastener size. Why pay the extra time to have someone stop installing M6 screws and reach for ¼ – 20 unless absolutely unavoidable? Likewise, avoid handed parts. If the worker can save time by grabbing two identical parts instead of confirming they grabbed a left and right-handed part, that alone just saved the company money.

DFA Like handed parts example

 

 

 

2. Design parts for retrieval, handling, and install.

When trying to put something together quickly, having loose parts stick together is a sure-fire way to waste a worker’s time. How much time have you ever wasted trying to grab a shopping cart only to find two of them fused together? Now imagine that situation day-after-day at your job. When a worker needs to pull parts for an assembly, the company is paying for the time it takes for them to untangle, unweave, or simply unstick nested parts. When designing or specifying parts, be mindful of how the parts might arrive or become tangled or handled. Good examples of this issue are springs, E-clips, or cup-shaped objects.

the need for dfa - tangled fasteners

 

 

 

 

3. Minimize fasteners.

Fasteners such as screws and rivets are typically very inexpensive on their own. It’s the installation of the fasteners that is costly. In many assemblies, the labor of driving dozens of fasteners is the single greatest expense of the assembly. Ever notice how products often come without the fasteners installed and you have to install them yourself? When assembling a fastener, you are paying to have the fastener pulled from a bin, lined up, and driven to the correct torque—over, and over, and over again. That penny fastener (that you thought was inexpensive) can actually cost you hundreds of man hours over the life of the product. Doing some simple engineering calculations to figure out if five screws will work versus eight, could save your company a lot of money.

 

repetitive riveting

 

 

 

4. Simplify components.

Another significant way to waste to loose efficiency is to have your worker  grab more parts than are necessary. This is especially true with custom-made components. Always be on the lookout for ways you can combine components in order to reduce assembly time. Why ask a worker to assemble six items into a single subassembly when a single piece will do. A good example would be a multi-part, sheet-metal assembly. Many times, I have seen companies design complex, multi-part, sheet-metal assemblies that require unholy amounts of fasteners when a simple, one-piece, metal casting could replace it all. The common misconception is that the casting is more expensive. That is typically true when comparing the raw casting against raw sheet-metal cut outs. However, when you add in the price of the fasteners and the labor time—you will normally find a potential for cost savings.

DFA cutting cost with reduced elements

 

 

 

 

5. Reduce required tools and tool changes.

Every moment a worker has to stop and change tools is time they are not moving on to the next assembly. Often designers pair Hex, Torxs, and Phillips drivers together in a design because they weren’t paying attention, or “It’s the cheapest version of that fastener”. Even in sophisticated set ups, having the worker stop to change driver bits is time they aren’t moving forward. Not to mention it’s frustrating for the worker to get out a different tool to drive one screw. Commonize on driver styles and do the math. Many times, buying a more expensive fastener in order to have the same driver styles will save you money in labor.

 

multiple fastener types

 

 

 

6. Design for Self-locating Features.

Adding a simple chamfer, lead-in, or boss can mean reducing hundreds of lost man hours and lost money. A common waste of time is trying to assemble parts that need to line up—but don’t. Every time a worker must make three attempts to insert a pin because “the edges aren’t broken” is money the designer wasted the company. Likewise, adding a simple boss or dimple to hold a spring in place can save time and money. Another good practice is when assembling parts that are blind, or out of the assemblers’ view, make one part extra-long so it can start to line up before it’s out of the persons line of sight.

DFA for self locating parts

 

 

 

 

7. Optimize the Order of Operations.

I saved the best for last. When initially designing an assembly, keep in mind how the design will go together. Plan out the order of when parts will get added and how. Whenever possible simplify for the worker. When you design, remember that every time a worker has to stop and adjust the work is time lost. This includes flipping the assembly over to work in a different orientation. If the worker is spending time reorienting the part for the next step they aren’t completing it as fast as they could be. The absolute best scenario to work towards is having a design that stacks from bottom to top for the assembly. All you are asking them to do is to keep stacking items on top of each other until the product is complete and ready for shipment.

DFA and order of operations

 

As you can see, DFA is a big deal. When done properly, your business reaps the financial benefits and your team will thank you for an easier assembly process. We hope you found these tips useful as you analyze your specific operation. If you need help maximizing your productivity, let us know. DISHER can provide a free productivity assessment, and assist you with your product and manufacturing initiatives including engineering design and development, machine design, automation and robotics, quality and lean processes.

 

 

 

 

 

 

 

 

 

One thought on “How to Save Money with Design for Assembly (DFA)

  1. There are prototypes that I’ve designed that caused me to curse at the engineer (myself) by the time I finished putting it together. Things always go together easier in CAD than in reality. Thanks for putting this together Sean!

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