The lean assembly line is a critical part of the broader lean manufacturing method – which is now a common approach modern manufacturers take to cut costs and achieve greater profits.
So what does a lean assembly line actually involve, how do you set one up, and how do you avoid common mistakes? We give you the answers in our one-stop practical guide.
What is the lean manufacturing method?
Lean manufacturing as a philosophy has three critical components:
- Deliver value to the customer
- Eliminate waste
- Continuously improve company processes.
The central idea is to cut costs as much as possible by working smarter, not harder. Thus optimisation and automation techniques are vital for successful going lean, including better workflow processes, inventory management software, automated bookkeeping, and even robotics.
Lean business thinking has become increasingly common across industries – especially in recent rocky economic times – and has a firm place in global manufacturing.
Learn more about going lean:
- Lean Manufacturing: What is it, How is it Done & Why?
- Five key elements of lean businesses
- How lean manufacturing is used in the food industry
What is a lean assembly line?
A lean assembly line is one to which the principles of lean manufacturing have been applied. Put simply, a lean assembly line is one where the right materials are in the right place at the right time – to ensure maximum production efficiency at all times.
A lean assembly line introduces simplicity as much as possible into the manufacturing flow, and anything that disrupts the forward momentum of a product is eliminated or mitigated.
One of the core issues fuelling the rise in lean assembly thinking is the increasing variety of modern products. It’s quite common now to see more than one model produced on the same line, and each change to models can bring waiting time. These small waiting times can build all the way down the line, and start to impact lead times drastically.
Lean assembly lines employ an array of techniques to try and mitigate the issue of time wastage (among other process inefficiencies). We’ll talk more about some of these later, but they include process mapping, inventory management, sequencing, automation and more.
Advantages of a lean assembly line
The three key advantages of using a lean assembly line contribute to overall efficiency and greater profits:
- Improved lead times: Going lean is an act of streamlining. This leads to greater process efficiencies and faster work, allowing businesses to cut production delays and improve lead times. Generally speaking, reducing delays also can and often does lend itself to improved customer relationships.
- Minimisation of waste: Waste during production is money down the drain. Anything that does not add value to the process can be minimised with lean thinking. Whether you’re wasting less materials or wasting less time, this streamlining can provide better sustainability outcomes, produce fewer unsold products, and mean less time that your staff are waiting for something to do.
- Improved profit: As you can see, both of the above can lead to improved profit margins. Through lean assembly, you’re reducing the time it takes to make a product as well as reducing the waste that comes out of that process, thus trimming the fat off your costs while still delivering value and quality to the customer. You may even find you can produce a higher volume as a result, potentially increasing revenue further.
Challenges of a lean assembly line
As with any manufacturing system, the lean assembly line comes with its challenges, including:
- A long transition period: A lean assembly line is not a switch that can be flicked to ‘On’ and then that’s the whole thing done. Depending on your current business situation, there may be quite a lot to either invest in or do – and then there’s staff training to consider. So the process of changing can take some time.
- Requiring improved equipment maintenance: You’ll often find in regular manufacturing that if a machine breaks down, employees will move to an alternative machine. However, it’s common in lean manufacturing to maximise the use of all equipment, all of the time, meaning there may not be many if any backup machines available. As such, if there is a failure, it can delay production times while repairs are made.
- Requiring a similarly efficient supply chain: Manufacturers typically adopt a JIT business model when going lean, as this is a potentially huge way to cut supply chain and inventory costs. But JIT comes with a host of potential challenges built in – not least of which is that, by its very nature, it requires steady and consistent supply. So if there are hiccups in the supply chain, this may also cause delays.
How to design an efficient lean assembly line: 4 key principles
Here we look at the four core principles of a lean assembly layout, and the different aspects of setting up and managing a lean assembly line that need to be considered if you’re going to use this type of production method.
We can’t provide a specific step-by-step instruction manual because, of course, every business is different – and what works for your facilities may not work for someone else’s.
To get started, consider these four key ideas and how they apply to your unique context:
1. Start with a clear value stream
Mapping the value stream is one of the five core principles of lean manufacturing as a whole – see the articles we linked to at the top of this article for more on these principles.
Essentially, to start creating a lean assembly line you must know two things:
- How your products create value for customers (i.e. what problems they solve)
- What the activities are that are required to produce those products and generate that value
From here you can start to work down.
So if you know what customers want and you know every step in the product lifecycle to achieve that end, you’ll be able to determine which machines your staff need, what tools, what materials, and so on. You’ll also be able to determine your VIP products – your top earners – so you can start there and then slowly work back towards less important products.
- Bonus tip: You may find that this means you choose to swap from vertically siloing your plant layout by process-based departments (e.g. cutting, fabrication, etc.) and start to think more horizontally, with workstations combined across the factory in order to reduce movement and materials handling.
2. Go for functionality over form
Pleasing aesthetics and style for the sake of branding can be important, but in a lean production facility functionality trumps form.
So what does that look like? An example is where your machines focus on easy-to-use visual controls rather than easy-to-look-at aesthetics. Visual controls include simpler solutions such as colour coding, standardised worksheets or instructions, clear floor markings and signage, and so on. Basically, functionality means anything that makes it easier and more efficient to get the job done in a standardised, predictable manner.
The use of floor space will also contribute directly to function. The plant doesn’t need to look good, but it does need to function. That doesn’t mean maximising the use of space; it means being efficient with space. You don’t need machines to take up the whole floor, so long as each workstation is designed efficiently, reduces waste, cuts down walking and transport distances, and so on.
- Bonus tip: Not sure how to optimise your floor layout for function? Talk to your people! They know what they need to produce the best possible outcome and they will be the best collaborators you have in order to improve efficiency while maintaining job satisfaction and comfort.
3. Optimise flow
Common obstacles to flow include long setup times, process bottlenecks, big batch-oriented machines and large travel distances. The flow of your new lean assembly lines must take these obstacles into account and try to reduce them as much as possible.
This is why you start with value stream mapping. It gives you an end goal to work towards that will let you visualise each step of the process that adds or does not add value to production, so you can carefully plan out how your plant’s equipment will enable that goal – rather than disrupt it.
Some things to think about:
- Try to minimise process reversals where possible.
- Could you remove sub-assemblies from the main production line, giving them a separate sub-assembly line, in order to improve the efficiency of customisable goods?
- How ergonomic are your individual work cells? Improved ergonomics can improve productivity, not to mention worker wellbeing.
4. Continuously improve
Above all, lean manufacturing – and lean assembly lines as a by-product of this system – requires continuous improvement.
What’s efficient today may not be efficient tomorrow. The world is constantly changing, and your business will likely change too in order to keep up. If nothing else, customer demand will change over time, which will impact your value stream, thus requiring further optimisations.
This is the fifth and most important principle in lean manufacturing, commonly referred to as the ‘pursuit of perfection’. Evolution should be a part of your organisational culture, and you must always be on the hunt for things to improve. This may require new training and communication policies for staff, so they have the tools they need to identify, qualify and notify you about potential opportunities.
Common mistakes to avoid when setting up a lean assembly line
There are some common pitfalls manufacturing businesses fall into when setting up an assembly line – we’ve listed them here so you can avoid making the same mistakes:
1. Not involving operators
With such a strong focus on process, it can be all too easy to forget that the thing making the process flow forwards is people. The most optimal equipment and workstation layout on paper may not actually be the best for people, especially in a plant with large batch sizes or high variability of products.
You and your engineers must always talk to the people on the ground before making major changes. They will help you understand their needs, how their work flows from one station to another, and whether or not their suggested changes will help or hinder their ability to work efficiently – while reducing the risk of injury.
2. Forgetting staff education
Still on the topic of staff, another common mistake is rolling out all these big changes without adequately educating operators on proper use of the new layout. And not just operators – managers and team leaders must also understand the what and why – called ‘lean training’ – so they can champion the change and assist in spreading the right education.
People tend not to like change. But they’re far more likely to accept it – and even enjoy it – if they understand why it’s happening and how to get the most out of it.
3. No process for continuous improvement
You can write ‘continuous improvement’ into your plans as much as you like, but unless you actually build a written process that encourages this step, and integrate it fully into layers of the business, it’s unlikely to take place in the real world.
People are busy. Unless something is easy to do, chances are most people will put it off and then forget about it. In this situation, if someone were to see an opportunity for improvement but they did not feel they had the time or the process to suggest the change, they probably wouldn’t – and so an opportunity goes wasted.
Think about your communication processes, your company culture, the example you’re setting from the top down and your onboarding process. Do these encourage communication about opportunities, and do they make it easy?
How to use the A3 method to optimise a lean assembly line
A3 methodology, developed initially by Toyota and named after the size of paper once utilised as a part of the system, is an additional process you can use to help optimise your assembly line.
The A3 method is a problem solving and analysis tool, used to help people better collaborate on a topic aligned to that topic’s goals. While the specifics vary between businesses, generally it involves seven key steps, which are reported on a single, A3-sized piece of paper at the end.
We’re going to go over it simply here so you get an idea, but encourage further reading into this topic if you’re interested in the concept.
The seven steps of the A3 method are:
- Define the current state of the project, including its importance to the value stream.
- Understand the history of the project, the source of past problems, and any opportunities you’re already aware of.
- Set a desired outcome. What do you want to achieve as a group? What metrics can be used to measure this outcome?
- Perform a root cause analysis. Ask why things are happening, and keep digging deeper and deeper until you find the true cause of a problem.
- Identify corrective actions (known as countermeasures) that will address the root cause. Ensure these are aligned to the goal – and that your people are aligned on the actions.
- Implement the corrective actions. Assign individuals responsibility over their part in the action, to ensure accountability. Measure success based on previously accepted KPIs and metrics. Set due dates for time-sensitive work items.
- Follow up after an agreed amount of time to check results. You must be able to identify if the plan was executed, the goal met and the desired outcome achieved. The entire A3 methodology can be re-implemented from step one if the desired outcome was not achieved. Or if it was achieved, new improvements should be standardised and written as policy to ensure their continued use.
Lean assembly line example: The Toyota Production System
The famous Toyota Production System (TPS) is the grandfather of lean manufacturing and of the type that most other followers of lean methodology are trying to replicate. TPS changed how businesses around the world approach manufacturing, and has even been described as the most important innovation in manufacturing since the assembly line itself.
There is quite a lot to the TPS as it’s been developed over a very long period of time. However, Toyota itself claims it boils down to two key principles:
- Jidoka: This is the concept of ‘automation with a human touch’. Human engineers at Toyota handcraft each line component to the company’s required standards. Then, through continuous improvement, they look to increasingly simplify operations until any operator can step onto the line and produce the same result. In this way, Toyota’s equipment is simple and cost-effective, as well as safe.
- JIT: For Toyota, the Just-in-time model can be summed up by this mantra: “Make what is needed, when it is needed, and in the amount needed.”
Interested in learning more? Read Toyota’s full description of the TPS here
Using inventory management software to manage a lean assembly line
Let’s think back to one of the core challenges we mentioned earlier in this article: supply chain efficiency.
To achieve a truly JIT business model without constantly running out of materials requires meticulous, real-time inventory management. This generally can’t be achieved without smart inventory management software.
What does inventory management software do?
Inventory management software helps manufacturers know what to order, when, and in what quantity – and it’s immediately clear how essential this sort of functionality is if you’re running a lean, Just-in-time manufacturing model.
Inventory software combines a wide variety of features to assist in streamlining your stock management, such as real-time inventory tracking, reorder alerts and reports, serial number and batch tracking, digital bills of materials, manufacturing process management, automatic kitset production, and more.
Essentially, inventory management software is about visibility. What stock do you have, where is it, how long has it been there, and do you need more? When set up correctly and integrated throughout the business, it creates a real-time picture of your inventory and helps build a more stable, efficient supply chain that is capable of meeting your JIT requirements – and supporting your lean assembly line.
- Learn more about modern inventory management techniques
Sources used for this article: