The core idea of lean manufacturing is to relentlessly work on eliminating waste from the manufacturing process in order to maximize value for customers. Simply, the lean goal is that every activity that uses resources must create value, such as less time, movement and cost. Lean manufacturing focuses on eliminating wastes within 7 areas that include: transport, inventory, motion, waiting, over-processing, overproduction and defects.
Achieving lean depends on the ability to recognize and eliminate waste, create and implement synchronized systems, and build in (and maintain) the visibility and top-down and bottom-up involvement that leads to continuous improvement. Most importantly, lean is a journey, not just a one-time event.
When striving for a lean manufacturing environment, one of the characteristics is to have very small amounts of work-in-process (WIP) moving rapidly through the entire process. This is different from mass production where parts are assembled, then moved in large quantities to the next process where they wait for their turn, and then are processed and moved as a batch to the next process.
One-piece flow, the opposite of batch processing, is the movement of a single product through the manufacturing process. One piece flow redirects the workforce away from non-value added activities (waste) and focuses on the manufacturing process. With batch processing, large amounts of wastes exist in waiting, transporting, and storage of inventory. Workers maximize their output at the expense of downstream processes and increased work-in-process.
With one-piece flow, the work in progress (WIP) is drastically reduced which minimizes exposure to defects in the manufacturing process and allows for quicker reaction to fluctuating customer demands. Implementing one-piece flow with U-shaped manufacturing cells is a great way to eliminate waste in most manufacturing environments with moderate amounts of variability in production size and product mix. One-piece flow will have a tremendous impact on manufacturing lead times, production delays, inventory levels, and warehousing space requirements.
With a U-shaped manufacturing cell, the operator finishes their work in the same location they start in, eliminating the waste of walking from the end of the line back to the start. A U-shaped cell can be set up to allow two operators to work back to back if the workload requires it. Space in the plant is also reduced.
One-piece flow creates a smoother production process, with steady workloads and shorter lead times. It’s important the units of work performed in each position have equivalent cycle times in order to keep the process smooth. This technique is called “Line Balancing.” Working in a line configuration only allows balancing with the operations to the right and left of a station. A U-shape cell allows balancing with stations right and left, but also behind and to the right and left, which doubles or triples the possible combinations of tasks and allows better balancing even when there is some variation in product mix, models and customer demand.
Cellular manufacturing is a system to transfer products between stations (i.e. U, J, or L shaped cell), a method to feed parts into the stations (flow racks, bins, or carts), and a means by which to flow finished goods and packaging out of the system. Right-sizing machinery to meet customer demand, instead of minimizing part cost, is essential to the success of cellular manufacturing. Placing smaller and slower equipment in close proximity to other equipment and processes helps eliminate wasted space, walking, inventory build-up and lower initial cost.
Set Up Tips
- Always flow product in the same direction, counterclockwise.
- Cross train employees to be able to perform all or most functions within the cell to increase responsibility, quality, and traceability.
- Use a U-shaped cell when possible to minimize the distance between the beginning and the end of the process.
- Use the First In First Out (FIFO) picking methodology to shorten lead times, reduce errors and improve order accuracy.
- Position workstations as close together as possible to eliminate wasted space but not so close as to hinder maintenance or create discomfort for employees.
- Create a system for flowing sub parts into the system in an optimal manner, considering ergonomic principles.
- Keep the path of flow within the U-shaped cell clear and unhindered.
- The benefits of implementing cellular manufacturing in the appropriate environments can have a positive impact on a business. Automotive assembly plants have found that U-shaped cells save space in plants because there are so many intricate subassembly processes included in the assembly of a vehicle. For example, putting together an engine block or dashboard in one of these cells allows a highly specified process to take place that doesn’t crowd and eat up space on the main assembly line.
Reconfiguring machinery into cells reduces material handling and warehouse footprint. When properly executed, a company will simultaneously shorten their lead times and dramatically reduce work in process inventory. Having a cross trained workforce gives a factory increased flexibility to meet variations in demand and a better understanding of a quality product.
Maintaining a consistent flow of materials lineside requires a balance of the right parts placed at the right locations so they can easily and quickly be picked and placed within the assembly cells. Combining flow and assembly cells techniques is becoming quite a popular approach in automotive manufacturing, providing great flexibility and fostering a reduction in time and work space requirements.
Brian C. Neuwirth is VP of Marketing and Sales at UNEX Manufacturing, the trusted industry leader in order picking solutions that maximize space usage, increase pick rates and improve ergonomics. UNEX offers a full range of order picking solutions, including their patented carton flow solution Span-Track, a full line of gravity conveyor products tailored to the order picking process and UNEX Flow cells for durable, modular and portable storage for the manufacturing floor.