To establish an effective pacemaker, it's crucial to understand the concept of takt time. This represents the pace at which a product or component must be produced to meet customer demand. It is calculated by dividing the available working time per shift or day by the number of units required during that same period of time.
Understand takt time in view of setting a pacemaker
This metric synchronizes production with customer needs. It can adapt to demand fluctuations by introducing a buffer, such as reducing takt time by 5% if variability ranges between 95 and 105 units per shift.
In workflows with significant variability due to customized products or market uncertainty, a reduction factor of 20% may be appropriate. For more standardized production with steady and controlled flows, values between 5% and 10% are likely sufficient.
Takt time is a tool that provides visibility into the ideal production pace. It helps identify inefficiencies and improvement opportunities.
In some sectors, such as distribution, make-to-order production, and process industries, creativity is needed to define the required customer units. One solution is to define a unit as the amount of work that can be performed by the bottleneck process within one takt, for example 10 minutes, then split orders into multiples of this takt.
Continuous Flow and Pull Systems
Ideally, a value stream should operate on a continuous flow. However, there are often points where batch processing and accumulations cannot be eliminated. To avoid inefficiencies, a pull system based on supermarkets must be employed. These supermarkets control production by linking processes to actual downstream customer demand instead of independent scheduling.
So it is usually necessary to implement a pull system where continuous flow is interrupted, and the upstream process needs to work in batches.
In a pull system, only one point in the value stream is scheduled: the pacemaker process. Strategically positioned, this point synchronizes upstream processes with customer demand, which creates a uniform rhythm. The pacemaker directly impacts inventory levels, lead time management, and tied-up capital.
The Pacemaker Process in Manufacturing
The pacemaker is the most downstream continuous-flow process in the value stream. It establishes the direct link between production pace and customer demand. Downstream from the pacemaker, materials flow uninterrupted to the customer. Upstream, supermarkets or buffers manage demand variations or downtime.
The production plan is sent to the pacemaker process, while upstream flow is regulated by supermarket logic.
In make-to-order or design-to-order production, where customized products are involved, the production scheduling point should be as upstream as possible. However, confirmation of the frozen period schedule should be communicated to the pacemaker process.
Multiple value streams and shared processes
Often, flows are non-linear, and value streams may share processes. A practical example is a company with two value streams:
- One starts with mechanical processing, followed by welding, which feeds a supermarket. This supermarket is also supplied by external components. It then feeds a painting line where components are attached to trolleys moved by a chain system. After painting, the components proceed to an assembly line to produce industrial machines.
- The second value stream begins with purchased components feeding the supermarket upstream of the painting process shared with the first value stream. Painted parts then proceed to a second assembly line.
The products of the two value streams differ, but they share the painting line. The number of trolleys needed for each product from both flows is determined, converting product demand into the number of trolleys required per day. The takt time is calculated as the pace for painting one trolley, and scheduling is done at the pacemaker process, which is the painting system.
Mix Leveling
An essential element for production optimization is mix leveling. This approach distributes the production of different products in small, alternating batches rather than long batches of the same item. Levelling the mix enables quick responses to variable customer demands, reducing lead times and finished goods inventory.
Since the pacemaker is the bottleneck, its capacity to produce the required mix within the defined time, including setup times, must be evaluated. This evaluation should apply to all processes, even if their cycle times are shorter than the takt time.
Mix levelling involves more setups, but techniques like SMED (Single Minute Exchange of Die) and part standardization can reduce setup times while maintaining balanced production capacity in line with takt time.
Supermarket
A supermarket upstream of the pacemaker ensures synchronization between downstream flows and upstream processes. For standard products, when inventory levels in a supermarket lane reach the reorder point, a production order is triggered to replenish stock, typically doubling the reorder quantity. The reorder point is calculated considering average consumption during production lead time and a safety stock to handle variations.
For custom or make-to-order products, the production plan is sent to the start of the flow feeding the supermarket in advance, aggregating batches to increase upstream process efficiency. This ensures component availability when the supermarket pulls materials based on the levelled mix. The pacemaker still receives the frozen production plan.
For example, in a company producing various products to order, the flow might include receiving steel sheets, laser cutting, bending, and mechanical processing, followed by welding lines (varying by product), painting, and assembly. A supermarket is placed before the welding lines, and a picking and kitting phase prepares materials for welding.
This strategy aggregates production batches for laser cutting, optimizing sheet thickness grouping and mechanical processing by reducing setups. The supermarket enables transitioning from batches to a continuous flow. The monthly production plan for welding lines is consolidated and sent to the beginning of the process (laser cutting and raw material procurement) at least six weeks before shipping. However, only five days before shipping, the picking phase schedule is issued, ensuring materials are ready in supermarket lanes and driving flow through the welding lines.
Defining and implementing an effective pacemaker in the value stream requires a systematic approach, combining techniques such as mix levelling, supermarket usage, and pull systems. The pacemaker serves as the production's heartbeat, ensuring the production pace aligns with takt time and that the flow is agile and synchronized with customer needs.
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