Applying Lean Manufacturing Processes To Injection Molding

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Lean manufacturing is well into its fourth decade as a landmark efficiency and production principle. From the late 1980s through to today, lean manufacturing (or just “lean”) has helped countless manufacturing firms and facilities streamline their production, improve their quality and, ultimately, improve their bottom line.

Injection Molding

As with so many business principles that enter mainstream consciousness and vernacular, however, lean manufacturing is often mischaracterized and misused as a term and a practice. You wouldn’t have to look far to find a company that states that it adheres to lean principles, but neither the time, work and effort necessary to be truly lean; nor the results of disciplined lean practices, are anywhere to be found. This article is intended to introduce some of the principles of lean manufacturing for injection molding; hopefully helping you to avoid those pitfalls and realize the benefits of a lean manufacturing implementation.

Lean manufacturing is commonly recognized to have been originated by Toyota management to address inefficiencies at its automotive manufacturing plants in the mid-1980s. An overarching belief of lean manufacturing (and one that’s most easily applicable to injection molding) is to eliminate any and all waste in a production process. Waste is defined as any effort or resource expenditure that does not add value for the end customer.

This principle, in the original Japanese, is known as “muda,” and is commonly broken into seven types of waste, which we’ll examine here. Note, as we go through each type of waste, the concept of “waste” is broadly defined under lean manufacturing, and is not limited strictly to material waste (though that is included).

  1. Waiting: Any time spent waiting for resources necessary to production, where production isn’t occurring, is considered waste. Waiting can be necessary for people, machine time, materials, transportation and more. All of it contributes to longer production cycles, longer time to the customer or market, and a negative impact on the bottom line. As, in manufacturing, time is money. Inventory
  2. Inventory: At any point in the production process, excess inventory is considered waste. Meaning, if you order an excess of raw material (more than is needed for your current production run) that’s considered waste. Regarding an excess of finished product — for example, production runs that yield more parts for which you have orders. The time and effort required to store excess inventory offers no benefit to your end customers, and only creates more work and expenditure on your part.
  3. Transportation: While of course transportation is necessary in manufacturing — getting raw material to a facility, feeding it through a machine, fulfilling orders and so on — in lean manufacturing, the goal is to reduce transportation to the bare required minimum to carry out a customer’s order. Excess, inefficient transportation adds to production time and increases your costs.
  4. Motion: This waste item is similar to transportation, but takes on a broader sense. Wasted motion refers not only to moving parts around, but also to the processes required to create those parts. Whether they are machine motion or human motion, the goal in lean manufacturing is to reduce all movement to the bare minimum that produces an order to the customer’s specifications. Excess motion, in lean manufacturing, is seen as increasing the risk of damage or injury to a part, machine or worker.
  5. Overprocessing: With overprocessing waste, excess work is done to a part beyond what’s required by a customer. This might mean tighter tolerances than requested or required. It might mean extra embellishments to a product, such as an unrequired surface finish. Or, it might mean using material of a higher grade than required. Overprocessing could also refer to unnecessarily stringent plastic injection molding quality control or rejection standards, beyond what the customer or the application requires — all of which result in unnecessary resource expenditure.
  6. Overproduction: In a nutshell, overproduction refers to producing parts before they’re necessary for the customer or the assembly of the end product. One clear problem that overproduction can lead to is excess inventory, since you have pieces that are unaccounted for by customer orders. Overproduction could also refer to the waste inherent in producing parts of an assembly in an unsynchronized fashion, where one part of an assembly or product is produced earlier or more quickly than another. Thus, resulting in the need to store those components until all elements are ready. Not only does this create excess component inventory, it also creates a staggered and potentially confusing production and assembly process.
  7. Defects: The goal of any manufacturing process is to keep the number of defects or rejected parts as low as possible, of course. By codifying this type of waste, lean manufacturing addresses it as a paramount contributor to production inefficiency, and keeps the issue of defects within the framework necessary to be truly lean.

Now that you understand the seven types of waste in lean manufacturing, you’re better equipped to address them. Step one is taking a realistic, objective view of your processes and identifying where these types of waste might be occurring (or where they even have the potential to occur. Some additional steps that you can take — which can be facilitated by injection molding — include:

Seeking methods of low- or medium-volume production: With practices such as silicone molding, injection molding is more viable as a process for shorter production runs, not just the multi-million part runs with which the process is often associated. Low-volume production can help to reduce or eliminate excess inventory.

Quality Assurance

Examining your QA standards and methods: While you should absolutely be concerned about the quality and integrity of your parts, you should also be sure to avoid overprocessing waste — whether in your own QA standards or those of your customer.

Reviewing processes at a high level: Taking a 1,000-foot view of your overall processes can help you identify several types of waste. Most obviously, transportation and motion waste, along with overproduction. If your business has scaled and you haven’t done a thorough review of how all your processes fit, you may be experiencing any of those types of waste — or more.

Lean manufacturing is much more than a buzzword, and it’s remained a bedrock part of business efficiency and optimization for so long for a reason. This overview is just the beginning of the tenets and practices of lean manufacturing, but they serve as a good start for you to add these efficiencies to your operation.

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