Design for Manufacturing

When companies operate in silos, different groups do what is best within the confines of their own world. Design engineers may create products that are appealing to the customer, look amazing, and may even be built like a tank with bulletproof quality.

But this otherwise outstanding design may be extremely difficult to build, requiring complicated production methods. One of the major reasons for this lack of a design with manufacturing in mind is the aforementioned silo organization. A compartmentalized organizational structure impedes communication. In addition, designers may lack the insight to know what will be difficult to build in a Lean environment where consistency is essential.

Enter “Design for Manufacturing”, also referred to as “Design for Manufacturability” or “Design for Manufacturing and Assembly”. Regardless of what term you know it by, it is the process of reviewing a product prior to locking in a design. Design for manufacturing is simply the art of creating products that are easy and cost-effective to build.

Why is a good design for manufacturing program so important? Because the majority of the eventual cost of a product is determined during the design phase.

Deigning with production in mind helps minimize those costs. While DFM includes adherence to a set of design for manufacturing guidelines, the bigger benefit is the back-and-forth communication it requires. Designers must work with both the manufacturing team and the supply chain team to make sure that the design does not hinder smooth production. It is this structured development process that prevents inadvertently designing costs into a product.

The goal of design for manufacturing is to have a production plan created during the design phase. This should be done for every component part as well as the final assembly. The main challenge is that this can add to the initial cost of the design, even though it will eliminate problems and waste in the long run.

There are several main reasons that products are designed without manufacturing in mind. The first one that comes to mind is a lack of knowledge. For example, a designer might not know the specific limitation of the production equipment that is available to the manufacturing team or might simply not understand production processes well. In both cases, the design is one of omission. The engineer simply does not know that there is a better, easier way to produce a product.

Another hindrance that keeps a design from being easily manufacturable is a flawed system of metrics. Engineering teams are focused on the cost per unit as one of their design goals. Designing for manufacturing can make a product slightly more expensive on paper, even if in reality it improves the quality and reduces actual production costs in the long run on the shop floor.

This same sort of disconnect also pops up with materials groups. Resupply methods (vendor managed inventory, for example) may change engineering costs, or may drive workload to a manufacturing team. Some preferred vendors that provide outstanding service may also be slightly more expensive than others with a lower cost per piece. In the long run, the preferred vendor is cheaper. But to the design team, it is simply extra product cost because they don’t factor in the cost of managing problems. These are cases of local vs. global optima.

Another metric that can be misleading on planned product costs is scrap rate. Hard to assemble products can generate a high level of waste. But these production costs would not impact the metrics for a design engineering team. Because of this, they may choose designs that do not minimize waste.

Your company will likely need a champion to help drive a design for manufacturing program. This advocate should have the clout to make real change. Once the initial barriers come down, though, and the designers get on board with a different way of creating products, they rapidly become wizards at designing remarkably easy to manufacture parts.

Some Things to Consider When Designing for Manufacturing

• Design for manufacturing requires a process to make sure each part is evaluated, and a coordinated effort by the manufacturing, supply chain, and design teams.
• Simple is better. It is easier to build.
• Minimize the number of fasteners.
• Take tolerance stack-up into consideration. (Limit the number of parts that fit together in series, if possible.)
• Design with easy to use slots and tabs.
• Leave space to fit components and fingers during assembly. Engineers want compact designs, but they have to consider the assembly process and space for fingers to fit without getting battered by sharp edges and tight fits.
• Keep cleanliness in mind. Don’t make lubricants reservoirs hard to fill which can result in cleanup time on the assembly line. Minimize glue and other messy compounds.
• Delicate operations should be avoided. They are time-consuming and prone to poor quality.
• Easily damaged components should be limited.
• Designs should be modular, allowing easy balancing of work.
• Adjustments should be avoided.
• Scratch-resistant materials should be used.
• Products should be designed with fixturing in mind. Make sure space is available to use clamps to secure the product during production.
• Specialized or complicated production requirements should be avoided.
• Avoid using parts that can be mixed up or installed backwards.
• Avoid designs that dictate production sequence.

Each of these things makes the manufacturing process simpler and less likely to generate defects.

As a company moves towards design for manufacturability, you will also likely see more teamwork develop, and will see walls start to come down. It is always a positive thing to understand the impact your decisions have on other groups. A good way to start this journey is to have the design team actually help to manufacture the products they design. Consider a two or three week stint on the shop floor doing production work for all new design engineers, and spend at least one full day a month actually turning wrenches for seasoned ones. It gives them better perspective on their decisions.

Design for Serviceability

An offshoot of Design for Manufacturability is Design for Serviceability. The same principles apply, but the intent is to make it easy to rapidly troubleshoot and service the product. Often, for a company, a Repair by Replacement option is used for in-warranty repairs. With good, Lean processes, it can be more cost effective to scrap a defective product and give a brand new one to the customer than to spend a repair tech’s time figuring out what is wrong. From the company standpoint, this makes sense, especially if the cost is low relative to the sell price.

From the customer’s perspective, though, they might not want to foot the bill for a new product once it is out of warranty. Customers will likely gravitate toward your competitors if your products are exceedingly expensive or impossible to repair once the warranty is expired.

Design for serviceability means cases that can be re-opened without destroying them, limiting use of things like glue and rivets, and protecting delicate components from damage during repair.

Design for Manufacturing’s Impact on Lean Operations

Lean creates some special considerations for product design. First of all, there is little excess inventory on hand. Any design that is difficult to build and results in frequent damage to components can shut down a production line.

There is also very little flexibility in terms of cycle time. If a process cannot be completed in a consistent period, it creates an accordion effect on processes that are linked together, as they are in a flow production environment.

Lean also generates a lot of product improvement ideas. The communication created during the DFM process carries over to ongoing operations. This established relationship speeds up the pace of product changes.

Perhaps the biggest benefit of DFM on Lean, though is an intangible one. A continuous improvement culture is critical to becoming world class, and that doesn’t happen when there are us-versus-them mentalities throughout the organization. When production teams feel that the design team is on their side, the frontline employees in the company believe that there is a company-wide focus on getting better. They don’t feel like they are the only ones carrying the improvement burden.

Again, the ultimate goal of any design for manufacturing program is to reduce the long-term costs of production and the cost of poor quality that comes as a result of hard to produce parts.

Words of Warning About Design for Manufacturing

• Don’t reinvent the wheel. Numerous DFM guides are available online and in print form to help you get your design for manufacturing program up and running.
• Don’t let bad metrics dictate operations. Think through the behaviors that a metric will drive before implementing it. Be careful of metrics that optimize initial cost by sacrificing ongoing expenses down the road.
• Don’t let a poor organizational structure cripple a DFM program. Think product leadership, not functional leadership.

Take advantage of design for manufacturing opportunities. Communication is a key part of the DFM process. If a designer asks you a question about a production process, give your full attention. If you are rushed or swamped, work out some time away from your production process to really focus on the opportunity to improve a design. Failing to spot a problem early will mean you could be dealing with it for a long, long time to come.

Again, don’t reinvent the wheel. Numerous resources are available that can be used to scrutinize a design. I recommend creating a design checklist that is specifically tailored to your business. It should include industry specific things such as:

• Use larger tools over smaller ones. Smaller tooling often means more expense to create fixtures, and more breakage due to smaller mass. (Note that this does not mean larger machines. Just try not to work with tiny cutting tools if it is possible to avoid it.)
• Consider tolerance stack-up. If several components all lean toward one side of a spec, the product can be hard to build. Unfortunately, this can happen even when all the parts are in spec, making troubleshooting very difficult. Tighter tolerances often mean more cost but can prevent supplier nightmares.
• Avoid thin walls and long welds that can lead to deformation during fabrication.
• Use standard sizes and proven, off-the-shelf components when possible. Also use common sizes for fasteners, holes, and threads. The more supplier options you have, the better.
• Consider transport of components in the design. Some become susceptible to damage in transit, especially electronics connectors and tabs.
• Be careful about referencing parts on opposite sides of a fold. If the tolerance is tight, variations in folding can make parts hard to assemble.

This list is by no means all-inclusive of the things that can hamper production. It is simply intended to give an idea of what DFM may encompass.

In addition to creating a thorough checklist, ensure that solid design for manufacturing principles are built into your new product development process. It is this formal adherence to a process, complete with requirements for communication and mutual agreement between various functions, that will lead to the largest gains.

The biggest advice for senior leaders is to align the goals of design and production teams. When design responsibility has an over-the-wall style of handoff, metrics will be unlikely to mesh well.

Key Points about Design for Manufacturing

• The majority of product costs are determined in the design phase.
• Get a formal Design for Manufacturing process in place. It is not something that can be effectively done in an ad hoc fashion.
• Poor metrics drive poor designs that are hard to manufacture.

Start out by reviewing the metrics that are used to evaluate good performance by design teams. Check specifically if there is a bias toward design costs versus the long-term costs of a product. Look for things like lifetime buys of parts, or discounts for purchasing parts in large quantities.

Secondly, create channels of communication between design teams and production teams. Look for ways to align resources. Long backlogs of ECRs (engineering change requests), or a high rejection rate are both indicators of a misalignment of effort. Stronger communication and shared pain are a good way to spur action.

Finally, look at product-oriented leadership versus a functional focus. Product line managers are committed to global improvement and bottom lines on income statements. Functional managers are more focused on their own budgets which have a way of altering (increasing) other people’s budgets.