This story was updated on 10/5/.
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Unless an engineer is directly involved in manufacturing, they may only be slightly familiar with “lean” principles. Long considered a way to greatly improve manufacturing efficiency, lean can be applied to any business or production process, in any industry.
For example, lean is now being used extensively in the healthcare industry to improve efficiency and reduce costs. The principles can even be used on a smaller scale—to organize your office, workspace, or laboratory, for example.
Lean was originally created by Toyota to eliminate waste and inefficiency in its manufacturing operations. The process became so successful that it has been embraced in manufacturing sectors around the world. For an American company, being lean is critical for competing against lower-cost countries.
The goal of lean is to eliminate waste—the non-value-added components in any process. Unless a process has gone through lean multiple times, it contains some element of waste. When done correctly, lean can create huge improvements in efficiency, cycle time, productivity, material costs, and scrap, leading to lower costs and improved competitiveness.
Lean isn’t just restricted to manufacturing. It can improve how a team works together, manages inventory, and even interacts with clients.
The Lean Enterprise Institute (LEI), founded by James P. Womack and Daniel T. Jones in , is considered the go-to resource for lean wisdom, training, and seminars.
According to Womack and Jones, there are five key lean principles: value, value stream, flow, pull, and perfection.
Value is always defined by the customer’s needs for a specific product. For example:
This information is vital for defining value.
Once the value (end goal) has been determined, the next step is mapping the “value stream.” This includes all the steps and processes involved in taking a specific product from raw materials and delivering the final product to the customer.
Value-stream mapping is a simple but eye-opening experience that identifies all the actions that take a product or service through any process—design, production, procurement, HR, administration, delivery, or customer service. The idea is to draw a "map" of the flow of material/product through the process, with a goal of identifying every step that does not create value and then finding ways to eliminate those wasteful steps.
Value-stream mapping is sometimes referred to as process re-engineering. Ultimately, this exercise also results in a better understanding of the entire business operation.
After the waste has been removed from the value stream, the next step is to be sure the remaining steps flow smoothly with no interruptions, delays, or bottlenecks. In the words of LEI: “Make the value-creating steps occur in tight sequence so that the product or service will flow smoothly toward the customer.”
This may require breaking down silo thinking and making the effort to become cross-functional across all departments, which can be one of the greatest challenges for lean programs to overcome.
However, studies show that this will also lead to huge gains in productivity and efficiency—sometimes as high as 50% improvement or more.
With improved flow, time to market (or time to customer) can be dramatically improved. This makes it much easier to deliver products as needed, as it means the customer can “pull” the product from you as needed (often in weeks, instead of months).
As a result, products don’t need to be built in advance or materials stockpiled. This reduces the need for an expensive inventory that needs to be managed, saving money for both the manufacturer/provider and the customer.
Accomplishing steps 1-4 is a great start, but the fifth step is perhaps the most important: making lean thinking and process improvement part of your corporate culture. Every employee should be involved in implementing lean.
As gains continue to pile up, it is important to remember that lean is not a static system and requires constant effort and vigilance to perfect. Lean experts often say that a process is not truly lean until it has been through value-stream mapping at least half a dozen times.
Lean can be infectious. Customers will notice big improvements as you implement lean, and will likely want to be part of your process. This collaborative thinking will also extend to your suppliers as well, who will want to use lean themselves to generate their own improvements.
"The core idea behind lean is maximizing customer value while minimizing waste," states LEI. "Simply put, lean means creating more value for customers with fewer resources."
A lean organization understands customer value and focuses its key processes on continuous improvements. The ultimate goal is to provide perfect value to the customer through a perfect value creation process that has zero waste.
As stated by LEI: "Lean accomplishes this by changing the focus of management from optimizing separate technologies, assets, and vertical departments to optimizing the flow of products and services through entire value streams that flow horizontally across technologies, assets, and departments to customers."
Mark Crawford is an independent writer.
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Your manufacturer should have ISO-certified testing facilities. Find out: Who will provide UL, ETL and other third-party testing? Where will that testing take place?
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:
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.
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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:
Using non-customized modules/modular assemblies in your design allows you 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.
Can the parts interlock or clip together? Look for ways to join parts without the use of screws, fasteners or adhesives. If you must use fasteners, here are a few tips:
Parts should be designed so that a minimum of manual interaction is necessary during production and assembly.
The more complex the process of making your product, is the more variables for error are introduced. Remember what Jeff said: All processes have limitations and capabilities. Only include those operations that are essential to the function of the design.
Unless it must be trade show grade, go with function rather than flashy for your surface finish.
Jeff talked a good bit about plastic injection molding in the videos. Here are four important questions to keep in mind about DFM and the injection molding process:
Which direction will the tool pull?
Here’s how it works: A tool (or mold) is made of two halves. The hot plastic liquid is poured into the mold, then quickly cooled. The two halves are pulled apart and there’s your part. If any feature in your part moves in a direction other than the pull of the mold, that will complicate the tooling and the tool will cost more.
Are there undercuts or features that will get trapped?
Undercuts are protrusions or recesses in the design that prevent the mold from sliding away from the part. They can get caught in the tool and cause damage. If the design element causing the undercut is absolutely necessary it’s possible to get around it by using a slide, but that increases the price of the tool. Better to get rid of the undercut by changing the design.
How consistent are the wall thicknesses?
The thick areas on plastic parts are designed that way for strength. But thickness also dictates how long it takes for the part to cool, and the longer it takes to cool the greater the chance for sink. Sink is not good. It is an area of weakness in the part. Also, longer cycle times increase part cost, as the amount of press time to mold the part is increased.
To address this problem, an engineer will thin a thick area out and reinforce it with ribs. Thin walls are not good either, however. Walls that are too thin can easily break. Depending on the part, wall thicknesses will run from 3 mm to 5 mm in thickness. Engineers will also look for transitions between thin and thick walls, making sure the transition is gradual.
Does the design need draft angles?
Straight sides or walls cause the part to stick to the mold, making the parts difficult to remove from the tool. Draft angles are slight tapers of the walls or sides of the mold which assist in the part ejecting properly from the mold. The greater the draft angle, the easier it is to get the part out.
The book Computer-Aided Manufacturing offers 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.
It’s been said that about 70 percent of manufacturing costs of a product — the cost of materials, processing and assembly — are determined by design decisions. If that’s the case, then you want to make sure you are adhering to the best design practices possible.
Any engineer worth their salt is going to also take a very close look at the tolerances specified in the part’s drawings. Tolerance is the total amount a specific dimension is allowed to vary, and manufacturers often receive drawings from customers with unreasonably tight tolerances that can wreak havoc on an RFQ.
Why you should ease up on tolerances:The chart below shows the drop in yield and the rise in cost as the tolerance increases.
The bell curve shows measurements on a particular dimension, including the Upper Spec Limit (USL) and Lower Spec Limit (LSL), which is based on the tolerances. The tighter the tolerance, the narrower the bell curve has to be for the dimensions to be in spec.
All manufacturing processes have limits on what is reasonable to manufacture — that's the gap between USL and LSL. Consult with your contract manufacturer or the trade organization for the process, if you are unsure. There is a lot of data on most common processes to give you guidance on what is reasonable to specify.
Tolerances should be driven by three things:
Managing tolerances is an essential part of a good DFM, and there should always be a justification for the numbers on the drawing.
You might be wondering what kind time you'll have to invest in the DFM? That really depends on the quality of the design that you start with.
One of our engineers likened it to proofreading an essay. For example, if you understand the writer's intent, it's much easier to make the corrections in the text. But if you're reading the essay without a clear understanding of intent, you might go back and forth with corrections before you come up with a finished copy.
The DFM is similar. Perhaps the design is clean, answering all questions for all parties. You'll be ready to go in a day or two. But depending on the number of questions, their difficulty, and the speed and thoroughness of the answers, you might be waiting a week or more. Take a deep breath. Your contract manufacturer will be able to give you a better idea of how long they think it will take. Remember speed isn't the goal: a quality product is.
A good DFM hopefully concludes by reducing the complexity of the design and satisfying the customer's requirements for price, specification, material and scheduling.
In other words, the design is deemed manufacturable and ready for the next step on the road to production.
But that's another blog post for another day
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