Takt Time
Takt time is the rate at which a product must be completed to meet customer demand: it is calculated by dividing the available production time by the number of units required in the period. It is the "pulse" of the lean production system - if production is slower than takt, backlog accumulates; if faster, overproduction occurs. Takt time synchronises every station in the flow to the customer's pace.
Kanban
Kanban is a visual signalling system that authorises the movement or production of material only when a real downstream demand exists. Originating in the Toyota system, each kanban (card or container) represents authorisation to produce or move a defined quantity. The fundamental principle is pull: no station produces without an explicit signal from the next process, eliminating overproduction.
Kaizen
Kaizen (改善, "continuous improvement") is the philosophy and practice of incremental, daily process improvement by all employees, from leaders to operators. A kaizen event is an intensive short-term activity (typically 3-5 days) in which a team analyses a specific process, identifies waste, and implements improvements. Kaizen contrasts with the "big-bang innovation" approach by emphasising constant small steps.
Poka-Yoke
Poka-yoke (防ぐ, "mistake-proofing") refers to a process design mechanism that makes a human error either physically impossible or immediately obvious. Classic examples include asymmetric connectors that cannot be reversed, sensors that detect component presence before proceeding, or checklists embedded in systems. The goal is zero defects guaranteed by process structure, not by operator attention.
SMED (Single Minute Exchange of Die)
SMED is a lean methodology for reducing machine setup (changeover) time to less than ten minutes ("single digit minute"). The technique separates internal setup operations (performed with the machine stopped) from external ones (performable while the machine is producing), converting as many internal operations as possible to external. Short setup times enable smaller batches, greater flexibility, and faster response to demand variation.
OEE (Overall Equipment Effectiveness)
OEE is a composite indicator that measures the overall efficiency of an asset by multiplying three factors: Availability (actual available time vs. planned), Performance (actual speed vs. nominal speed), and Quality (good units vs. total produced). An OEE of 100% means production at maximum speed, for all planned time, with no scrap. A commonly cited world-class benchmark is ≥85% for discrete manufacturing, but the reference value depends on industry and specific configuration.
Cpk (Process Capability Index)
Cpk is a statistical index measuring how centred a process is relative to its specification limits and how variable it is relative to those limits. It is calculated as the lesser of (USL – μ)/(3σ) and (μ – LSL)/(3σ), where USL/LSL are the upper and lower specification limits. A Cpk ≥ 1.33 (4-sigma process) is a common industry target; Cpk < 1.0 indicates the process produces defects.
Andon
Andon is a visual and/or auditory signalling system indicating the status of production operations: green (normal production), yellow (problem in progress), red (production stopped). Any operator can and must activate the andon when a problem is detected, authorising line stoppage. The system enables immediate response and prevents defects from propagating along the production flow.
Heijunka
Heijunka (levelling) is the Toyota technique for production levelling that distributes production volume and mix uniformly over time, rather than following customer order fluctuations. Levelled production enables smaller batches, reduces buffer inventory, and makes the production flow predictable. The heijunka box is the visual tool that schedules production sequence and volume for defined time intervals.
Muda (Waste)
Muda is the Japanese term for any activity that consumes resources without creating value for the customer. The Toyota system identifies seven categories: overproduction (producing more than needed), waiting, transportation (unnecessary movement), overprocessing (excessive processing), inventory (excess stock), motion (unnecessary operator movements), and defects (defects and rework). Eliminating muda is the central objective of lean manufacturing.
Value Stream Mapping (VSM)
VSM is a visual analysis tool that maps the flow of materials and information needed to bring a product from raw material to the end customer. A "current state" map reveals waste and bottlenecks; a "future state" map designs the optimal flow. VSM is the starting point of any lean intervention because it provides a system-level view, not an individual process view.
Jidoka
Jidoka (自働化, "automation with a human touch") is the principle by which machines and processes are designed to stop automatically upon defect detection, separating human work from continuous machine monitoring. Jidoka ensures that defects do not propagate and forces root-cause problem resolution instead of covering problems with safety stock. It is one of the two pillars of the Toyota Production System, alongside Just-in-Time.
Just-in-Time (JIT)
JIT is the production principle and system aiming to produce and deliver the right quantity of product, in the right place, at the right time - eliminating inventory as a buffer. JIT requires reliable processes, rapid setups, synchronised supplies, and continuous flow. It is not simply "low inventory": it is the result of a synchronised supply chain and stable processes.
5S
5S is a workplace organisation methodology based on five Japanese practices: Seiri (sort - eliminate the unnecessary), Seiton (set in order - a place for everything), Seiso (shine - cleaning and inspection), Seiketsu (standardise - document and standardise), Shitsuke (sustain - discipline to maintain the system). Beyond visual order, 5S creates the conditions for detecting abnormalities and sustaining continuous improvement.
TPM (Total Productive Maintenance)
TPM is a maintenance approach that involves all production staff in the care and improvement of equipment, with the goal of maximising OEE and eliminating the Six Big Losses. The central pillar is autonomous maintenance: operators handle first-level maintenance activities, freeing maintainers for preventive and predictive activities. TPM transforms maintenance from a cost to an investment.
DMAIC
DMAIC (Define-Measure-Analyze-Improve-Control) is the Six Sigma methodological framework for improving existing processes. Define clarifies the problem and objectives; Measure quantifies current performance; Analyze identifies root causes; Improve designs and implements the solution; Control maintains results over time with control plans and SPC. It is the structured cycle that distinguishes Six Sigma from an empirical approach.
Six Sigma
Six Sigma is a statistics-based methodology for reducing process variability with the goal of achieving a defect rate below 3.4 DPMO (Defects Per Million Opportunities). The name derives from the goal of maintaining the process at six standard deviations from the specification limits. Six Sigma is applied via DMAIC projects (improvement) or DMADV/DFSS (design).
MTBF (Mean Time Between Failures)
MTBF is the measure of reliability of a system or component: the average time between consecutive failures. It is calculated by dividing total operating time by the number of failures. A higher MTBF indicates greater reliability. It is the basis for preventive maintenance planning and for the Availability calculation in OEE.
MTTR (Mean Time To Repair)
MTTR is the average time required to restore a system or component to functionality after a failure, from detection to restoration. A low MTTR indicates efficient repair processes. MTTR and MTBF together determine the theoretical availability of a plant: Availability = MTBF / (MTBF + MTTR).
WIP (Work In Process)
WIP refers to all materials and semi-finished goods at various stages of processing between the start and end of the production process. High WIP is a symptom of flow imbalance, bottlenecks, or overproduction. Little's Law formalises the relationship: WIP = Throughput × Lead Time. Reducing WIP is a fundamental lean goal because it lowers lead time and improves flow.
Cycle Time
Cycle time is the actual time taken by a single station or process to complete one unit, including active time and any small internal waits. It should not be confused with lead time (order-to-delivery time) or takt time (customer-required cadence). Balancing station cycle times to takt time is the objective of line balancing.
Line Balancing
Line balancing is the process of equitably distributing work among the stations of a production line so that each station completes its operations within the takt time, minimising waiting times and bottlenecks. Good balancing minimises the number of stations required (efficiency) and maximises continuous flow.
Bottleneck
The bottleneck is the resource or process that limits the throughput of the entire production system. According to Goldratt's Theory of Constraints, any improvement not applied to the bottleneck does not increase system throughput. Identifying and managing the bottleneck is the strategic priority in production capacity management.
Setup Time
Setup time is the time required to transition from the last piece of one batch to the first good piece of the next batch. It includes removing previous tooling, mounting new tooling, adjusting, and verifying. Minimising setup time (see SMED) enables small-batch production and greater flexibility.
Pull System
A pull system produces or moves material only upon explicit request from the downstream process (the "internal customer"). It contrasts with the push system, which schedules production in advance based on forecasts. A pull system reduces overproduction and WIP; kanban is the signalling mechanism typically used to implement it.
Push System
A push system plans production in advance based on demand forecasts and master schedules, pushing material from one operation to the next according to plan. It tends to generate overproduction and excess inventory when forecasts do not match actual demand. Traditional ERP/MRP systems operate in push mode.
MRP (Material Requirements Planning)
MRP is a computerised system for planning material requirements that, starting from the master production schedule (MPS), the bill of materials (BOM), and inventory records, calculates the quantities and dates of need for each component and raw material. MRP generates production and purchase order proposals. It is the central logic of manufacturing ERP systems.
Bill of Materials (BOM)
The BOM is the complete, hierarchically structured list of all components, sub-assemblies, raw materials, and quantities needed to produce one unit of finished product. The BOM can be single-level or multi-level (tree). It is the foundational document for MRP and every production planning activity.
Theory of Constraints (TOC)
Eliyahu Goldratt's Theory of Constraints states that every system has at least one constraint that limits its performance. The improvement process has five steps: identify the constraint, decide how to exploit it to the maximum, subordinate everything else to that decision, elevate the constraint, return to step one avoiding inertia. TOC introduces Throughput Accounting as an alternative to traditional cost accounting.
Lead Time
Lead time is the total time that elapses between the initiation of a process (or receipt of an order) and its completion (or customer delivery). In manufacturing, distinctions include manufacturing lead time (factory throughput time), procurement lead time (supply time), and customer lead time (time visible to the customer). Reducing lead time is a synthetic indicator of operational competitiveness.
Throughput
Throughput is the rate at which the system generates value (revenue minus purchased materials cost, in TOC terminology), or operationally, the quantity of units produced per unit of time. Throughput is limited by the bottleneck. Increasing throughput increases profitability; reducing local costs without increasing throughput may have no impact on profit.
Gemba Walk
A gemba walk (現場, "the real place") is the managerial practice of physically going to where value is created (the production line, the warehouse, the shop floor) to directly observe the process, ask questions, and identify improvement opportunities. The gemba walk is the foundation of the Toyota "go and see" principle, in contrast with management based on remote reports and metrics.
5 Whys
The 5 Whys is a root-cause analysis technique developed by Taiichi Ohno: faced with a problem, one asks "why?" repeatedly (typically five times) until reaching the deep cause rather than superficial symptoms. The technique's simplicity makes it applicable on the gemba in real time, without statistical tools. The answer to the fifth "why" guides the permanent corrective action.
Ishikawa Diagram (Fishbone Diagram)
The Ishikawa (or cause-and-effect) diagram is a visual tool for brainstorming and classifying potential causes of a problem. Typical manufacturing categories are the 6Ms: Machine, Method, Material, Man/Mind Power, Measurement, Mother Nature (environment). The diagram helps the team structure analysis and prioritise causes for investigation.
Pareto Chart
A Pareto chart orders the causes of a problem or defect categories in descending order of frequency or impact, overlaying a cumulative line. It is based on the 80/20 principle: typically 80% of problems stem from 20% of causes. The Pareto chart focuses improvement resources on the few causes generating the majority of defects or costs.
Control Chart (SPC Chart)
A control chart is a Statistical Process Control (SPC) tool that traces the values of a process indicator over time with statistical control limits (UCL/LCL, calculated as ±3σ from the mean). Points beyond the limits or non-random patterns (runs, trends) signal that the process is "out of statistical control" and require investigation. The chart distinguishes common-cause variation (random, inherent to the system) from special-cause variation (triggered by identifiable events).
SPC (Statistical Process Control)
SPC is the use of statistical methods to monitor and control a manufacturing process in real time, with the goal of ensuring it operates in a stable and consistent manner. The main tools are control charts (Shewhart, CUSUM, EWMA) and capability indices (Cp, Cpk). SPC distinguishes normal process variability from anomaly signals, preventing defect production rather than inspecting finished products.
Autonomous Maintenance
Autonomous maintenance is the TPM pillar that transfers first-level maintenance activities - cleaning, inspection, lubrication, minor adjustments - to production operators. Operators become the first line of detection for abnormalities: they know their equipment intimately and can identify subtle changes before they become failures. This frees maintenance technicians for planned preventive and predictive activities.
Supermarket (Pull Storage Point)
In lean systems, a "supermarket" is a controlled storage point for materials or semi-finished goods positioned between two production processes. Like a real supermarket, the customer (downstream process) takes what it needs, and the supplier (upstream process) replenishes only what has been taken. The supermarket is the lean alternative to continuous production in a one-piece flow not yet achievable.
Flow Production (One-Piece Flow)
Flow production organises the production process so that material moves continuously from one operation to the next without stopping in intermediate queues. The ideal is "one-piece flow" (unit batch), which minimises WIP, lowers lead time, and makes problems immediately visible. Flow is achieved through line balancing, setup reduction, and equipment reliability.
Changeover
Changeover is the process of transitioning from one product or model to the next on a machine or line. It includes both physical setup (tool and fixture changes) and process adjustments and trial piece production. Minimising changeover time (see SMED) is fundamental for production flexibility and small-batch production.
Preventive Maintenance
Preventive maintenance is the set of planned activities (inspections, replacements, lubrications) performed at regular intervals or based on counters (hours, cycles) to prevent failures and degradation before they manifest. It contrasts with corrective maintenance (repair after failure) and precedes predictive maintenance (based on actual condition monitoring).
Predictive Maintenance
Predictive maintenance uses sensors, data analytics, and machine learning to monitor the actual condition of machines and predict the time of failure before it occurs. It allows maintenance to be scheduled exactly when needed, minimising both unexpected failures and the costs of excessive preventive maintenance. It is a pillar of the "smart factory" and Industry 4.0.
ABC Analysis
ABC analysis classifies inventory items into three categories by importance (typically annual usage value): A (few items, high cumulative value, ~80% of value), B (middle class, ~15%), C (many items, low value, ~5%). The classification guides procurement policies, inventory control, and management attention: A items require rigorous control; C items admit simplified policies.
Safety Stock
Safety stock is the quantity of material held as a buffer to cover unpredictable demand variations or supply delays. It is calculated statistically based on demand variability, supply lead time, and the target service level. Excessive safety stock immobilises capital; insufficient safety stock causes stockouts.
RPN (Risk Priority Number)
RPN is the risk priority number calculated in FMEA (Failure Mode and Effects Analysis) by multiplying three factors: Severity (impact of the effect), Occurrence (probability of occurrence), and Detection (ability to detect the failure before it reaches the customer). A high RPN indicates that failure mode requires priority corrective action. RPN = S × O × D, each factor typically rated on a 1-10 scale.
FMEA (Failure Mode and Effects Analysis)
FMEA is a systematic, structured analysis that identifies potential failure modes of a product or process, evaluates their effects, and prioritises mitigation via RPN calculation. Design FMEA (DFMEA) applies to product design; Process FMEA (PFMEA) applies to manufacturing operations. Both are mandatory in automotive APQP (Advanced Product Quality Planning).
Control Plan
A control plan is a document describing the measurements, characteristics to monitor, control methods, reaction plans, and responsibilities for each phase of the production process. It is the operational document ensuring that quality control actions are systematically applied. The control plan is a standard output of APQP and the supplier approval process.
Cellular Manufacturing
Cellular manufacturing groups different machines and workstations physically close together (typically in a U-shape) to produce a family of similar products with continuous one-piece flow, reducing transportation, WIP, and lead time compared to functional departments. The U-cell allows a single operator to serve multiple machines (multi-machine handling) and enables varying staffing as takt time changes.