Just-In-Time

JIT manufacturing rests on fundamental principles that challenge traditional manufacturing assumptions about batch sizes, inventory buffers, and production scheduling. Understanding these principles enables practitioners to design systems that achieve true just-in-time production.

Pull vs. Push Systems represents the most fundamental JIT principle. Traditional manufacturing pushes materials through processes based on forecasts and schedules. JIT manufacturing pulls materials through processes based on actual consumption at downstream operations. Pull systems automatically limit work-in-process inventory while synchronizing production with demand.

Takt Time establishes the rhythm of production based on customer demand rate. Calculated as available production time divided by customer demand, takt time provides the cadence for synchronized production. Operations are designed to complete work within takt time, creating flow that matches production rate to customer consumption rate.

One-Piece Flow represents the ideal state where single units move through production processes without batching or queuing. While not always achievable, one-piece flow thinking challenges assumptions about batch sizes and motivates setup reduction efforts that enable smaller batches and shorter lead times.

Continuous Flow connects operations so that materials move smoothly without waiting or accumulating. Work cells, conveyors, and process synchronization eliminate the stop-and-go patterns of batch production. Where continuous flow isn't possible, controlled supermarkets with defined min/max levels maintain flow while limiting inventory.

Level Scheduling (Heijunka) smooths production volume and mix over time to reduce variation and enable efficient operations. Rather than producing weekly requirements of each product sequentially, leveled schedules produce daily or hourly quantities that average demand over shorter periods. This leveling enables JIT supply while maintaining production efficiency.

Visual Management makes production status and problems immediately visible without requiring reports or computer queries. Kanban cards, production boards, and andon signals enable rapid response to problems while maintaining flow through normal conditions.

Kanban systems provide the signaling mechanism that enables pull-based production, triggering replenishment only when downstream processes consume materials. Understanding kanban mechanics enables practitioners to design and implement effective pull systems throughout manufacturing and supply chain operations.

Kanban Fundamentals center on the simple principle that production or movement is authorized only by kanban signals. Physical cards, containers, or electronic signals indicate authorization to produce or move specific quantities of specific parts. Without kanban authorization, no production or movement occurs, automatically limiting inventory to calculated kanban quantities.

Production Kanban authorizes manufacturing of parts to replenish supermarket locations. When downstream processes withdraw parts, production kanban attached to those parts returns to the producing process, authorizing production of replacement quantities. The number of production kanban in the system determines maximum work-in-process inventory.

Withdrawal Kanban authorizes movement of parts between locations, typically from producing process supermarkets to consuming process input points. Material handlers follow withdrawal kanban signals, moving parts only when authorized and only in kanban quantities.

Kanban Sizing determines the number of kanban (and therefore inventory) required to maintain flow given demand rates, replenishment lead times, and safety stock requirements. The formula considers average daily demand, lead time, container quantity, and safety factor. Properly sized kanban systems maintain flow while minimizing inventory.

Electronic Kanban (E-Kanban) replaces physical cards with electronic signals, enabling faster information flow and easier system management. E-kanban integrates with ERP systems, provides real-time visibility, and eliminates lost card problems. However, visual simplicity of physical kanban remains valuable for understanding system status.

Kanban Rules govern system operation and maintain discipline. Key rules include: downstream processes withdraw only what is needed when needed; upstream processes produce only what is withdrawn; defects are never passed downstream; kanban quantity is gradually reduced to reveal and address problems. Adherence to these rules maintains system integrity.

JIT manufacturing requires supporting capabilities that enable synchronized production and rapid response to problems. Without these enabling elements, attempts to reduce inventory simply create stockouts and production interruptions. Successful JIT implementation develops these capabilities before dramatically reducing buffers.

Setup Reduction (SMED) enables the small batch sizes essential for JIT production. Traditional long changeovers forced large batches to spread setup costs across many units. SMED methodology dramatically reduces changeover times, making small batches economically viable and enabling production flexibility. Many organizations achieve 75-90% setup reduction through systematic SMED application.

Equipment Reliability ensures machines are available and capable when needed. JIT systems without buffers cannot tolerate frequent breakdowns, making TPM and preventive maintenance essential prerequisites. Equipment reliability must improve before inventory reductions expose production to breakdown disruptions.

Quality at the Source prevents defects from passing downstream and disrupting synchronized production. Without buffer inventory to substitute for defective parts, JIT systems require zero-defect quality from all operations. Mistake-proofing, statistical process control, and immediate problem resolution support quality requirements.

Supplier Integration extends JIT principles beyond factory walls to include material suppliers. Frequent deliveries of small quantities, supplier quality certification, and collaborative relationships enable suppliers to support JIT requirements without simply shifting inventory upstream. Many organizations develop supplier partnerships that include shared planning, quality data, and improvement activities.

Cross-trained Workforce provides the flexibility to respond to demand variation and production problems. Workers capable of performing multiple operations enable staffing adjustments that maintain flow as demand patterns change. This flexibility also supports line balancing and provides coverage during absences.

Visual Factory makes problems immediately visible so they can be addressed quickly. Andon signals, production status boards, and material location indicators enable rapid response that maintains flow. Without visual management, problems fester while inventory buffers temporarily mask their impact.

Implementing JIT manufacturing requires systematic approaches that build capability while progressively reducing inventory buffers. Premature inventory reduction creates chaos, while excessive caution delays benefits and maintains waste. Effective implementation balances these tensions through structured progression.

Current State Assessment establishes baseline performance and identifies capability gaps that must be addressed before inventory reduction. Assessments examine setup times, equipment reliability, quality performance, supplier delivery performance, and workforce flexibility. This analysis reveals prerequisites that must be developed.

Value Stream Mapping visualizes material and information flows to identify improvement opportunities and design future state systems. Maps reveal inventory accumulation points, information disconnects, and process constraints that prevent flow. Future state designs establish improvement targets and implementation sequences.

Pilot Area Implementation focuses initial efforts on contained value streams where success can be achieved and lessons learned before broader deployment. Pilot areas should have supportive leadership, improvement potential, and manageable complexity. Success in pilot areas builds organizational confidence and capability.

Progressive Inventory Reduction gradually lowers inventory levels to expose problems and create improvement pressure. Rapid reduction overwhelms problem-solving capacity, while slow reduction fails to create urgency. Effective implementation reduces inventory in controlled steps, addressing exposed problems before further reduction.

Problem-Solving Discipline treats exposed problems as improvement opportunities rather than reasons to increase inventory. When inventory reduction reveals quality issues, equipment problems, or supply disruptions, cross-functional teams address root causes. This discipline transforms problems into permanent improvements.

Performance Measurement tracks JIT metrics including inventory turns, lead time, on-time delivery, and quality performance. Metrics should reveal both progress and problems, enabling continuous adjustment of implementation strategies. Celebrating improvements builds momentum while highlighting gaps maintains focus.