What is Lean Manufacturing and how does it differ from traditional production?
Lean Manufacturing is a production philosophy aiming to eliminate waste (muda) in every form to maximise value to the customer. Traditional manufacturing relies on large batches, buffer inventories, and functional departments; lean operates with small batches, continuous flow, and product-family organisation. The fundamental difference is that lean is "pull" (produce on real demand) versus the traditional "push" (produce according to forecasts).
What is takt time and why is it central to lean?
Takt time is the rate at which customers purchase the product: Takt = Available production time / Demand in the period. It is the "metronome" of the production system: when production is synchronised to takt, exactly what is needed is produced without excess inventory or stockouts. All other lean tools (line balancing, kanban, heijunka) aim to keep the process in sync with takt.
How is OEE calculated and what do the three factors mean?
OEE = Availability × Performance × Quality. Availability measures actual production time against planned time (affected by: breakdowns, setups, stoppages). Performance measures actual speed against nominal speed (affected by: micro-stoppages, reduced speed). Quality measures good units out of total produced (affected by: scrap, rework). An OEE of 72% (availability × 90%, performance × 95%, quality × 85%) is a typical calculation showing how losses compound.
What is the difference between preventive, predictive, and autonomous maintenance?
Preventive maintenance replaces or inspects components at fixed intervals, regardless of their condition. Predictive maintenance uses sensors and data analytics to intervene only when parameters indicate imminent degradation. Autonomous maintenance (a TPM pillar) transfers first-level maintenance activities - cleaning, lubrication, routine inspections - to production operators, freeing technicians for specialised work.
What is kanban and when is it appropriate to use it?
Kanban is a signalling system that authorises production or movement of material only when real downstream demand exists. It is appropriate in relatively stable and repetitive production flows with predictable demand. It is not suited to highly variable production or engineer-to-order products. Kanban can be physical (cards, containers), electronic (e-kanban in ERP systems), or displayed on shop-floor screens.
How is a kaizen event structured?
A kaizen event (or "kaizen blitz") typically lasts 3-5 days. Day 1: form the team and observe the current process (gemba walk, data collection, mapping). Day 2: analyse the data and identify waste. Days 3-4: implement solutions (layout, standards, signage, procedures). Day 5: measure results, present to management, and plan follow-ups. The team's autonomy in implementing changes is critical for success.
When is Process FMEA (PFMEA) used and when is Design FMEA (DFMEA) used?
DFMEA applies during product design to identify and mitigate failure modes related to design choices (materials, dimensions, tolerances). PFMEA applies during industrialisation to identify failure modes related to manufacturing operations and the production process. Both converge in the control plan. In automotive, both are mandatory in the APQP process.
What is Six Sigma and how does it differ from Lean?
Six Sigma is a methodology focused on reducing process variability using statistical tools (DMAIC, SPC, DOE) with the goal of ≤3.4 DPMO. Lean focuses on waste elimination and flow acceleration. Lean and Six Sigma are complementary: lean accelerates processes but can generate instability; Six Sigma stabilises but may not address waste. "Lean Six Sigma" combines both.
What is the Theory of Constraints and how is it applied in a factory?
TOC states that every system has a constraint (bottleneck) that limits output. The improvement process is: (1) identify the constraint, (2) exploit it to the maximum, (3) subordinate everything else (other processes must feed the bottleneck at its pace), (4) elevate the constraint, (5) return to step 1 to find the new constraint. In a factory, the bottleneck is identified by waiting times and the size of WIP queues in front of each machine.
How does production levelling (heijunka) work?
Heijunka levels both production volume and mix over time. Instead of producing all pieces of one type in sequence (AAABBBCCC), production is distributed evenly (ABCABCABC). The heijunka box divides the day into time slots (pitch) and assigns each a defined quantity of each item to produce. Levelling reduces variability transmitted to suppliers and upstream processes.
What are the "Six Big Losses" in the context of TPM/OEE?
The Six Big Losses are classified into three OEE categories: Availability losses (equipment failures, setup and adjustment); Performance losses (minor stoppages, reduced speed); Quality losses (startup scrap and production scrap). TPM aims to progressively eliminate all six. Equipment failures and startup scrap are typically the priority losses to address first.
How is a control plan structured?
A control plan has columns for: product or process characteristic, control method (visual inspection, measurement instrument, SPC), frequency and sample size, acceptance/rejection limits, responsibility, and reaction plan for out-of-control situations. It is prepared after PFMEA (which identifies critical characteristics) and must be updated for every process change.
What is the difference between capability (Cpk) and process control (SPC)?
Cpk measures whether a "static" process produces parts within specifications (capability), comparing process variability to design tolerances. SPC monitors whether the process is "in statistical control" over time (stability), detecting special causes of variation via control charts. A process can be in statistical control but not capable (inherent variability too high), or capable but out of control (an anomalous event). Both conditions are necessary to guarantee quality.
What is PPAP and why is it required in automotive?
PPAP (Production Part Approval Process) is the documentary process by which an automotive supplier demonstrates to the customer that it has understood the specifications, has the production capability to meet them, and has validated the process before starting serial production. It includes physical samples, dimensional analysis, PFMEA, control plan, MSA, and capability study. PPAP protects both parties: the supplier documents its capability; the customer has quality assurance before mass production.
How is 5S implemented in a production department?
5S is implemented in phases. Sort: tag every object with a red tag if not needed in the department; remove everything unnecessary to a quarantine zone. Set in Order: define a specific place for each remaining object, marked with floor markings and silhouette outlines. Shine: perform thorough cleaning and identify sources of contamination. Standardise: document procedures and conduct a periodic audit. Sustain: run regular audit cycles to maintain the system.
What is cellular manufacturing and when is it preferable to functional departments?
Cellular manufacturing groups different machines (lathe, mill, drill) in physical proximity to form a cell dedicated to a product family. It is preferable when: a stable-rotation product family exists, transportation and WIP between departments need reduction, and one-piece flow with multi-skilled operators (multi-skilling) is the target. Functional departments (all milling machines together, all lathes together) remain superior for highly variable production and maximum utilisation of high-specialisation equipment.