15.2 Lean, JIT, and the Seven Wastes

15.2 Lean, JIT, and the Seven Wastes

Quick Answer: Lean eliminates waste to create flow. Just-in-time (JIT) supplies the right item in the right quantity at the right time. The seven wastes (TIMWOOD) diagnose where time and inventory hide. Pull and kanban authorize replenishment from real consumption, and heijunka levels the schedule so JIT does not amplify chaos.

CPIM Domain IX expects planners to speak lean fluently because inventory policy, lot sizing, and scheduling are where lean succeeds or fails. Cutting inventory without removing waste simply moves the crisis from the warehouse to the customer.

Lean Thinking for Planners

Lean focuses on maximizing value from the customer’s perspective while minimizing waste (muda). Value is what the customer will pay for—conforming product, on time, in the needed quantity. Everything else is a candidate for elimination or radical reduction.

For planners, lean changes the mental model:

• Large batches and long lead times are not “safe”—they are often waste that hides problems.
• MRP push can still overproduce if order policies ignore true downstream need.
• The goal is flow: short queues, small lots, quick response, and visible problems.

Lean does not mean “zero inventory always.” It means inventory is deliberate, minimal for the current process capability, and shrinking as capability improves.

The Seven Wastes (TIMWOOD)

The classic Toyota wastes are remembered with TIMWOOD:

Many organizations add an eighth waste: underutilized skills (unused human creativity). On the exam, TIMWOOD is the core set; recognize the eighth if a scenario emphasizes ignored operator ideas.

Why inventory is a special waste for CPIM

Inventory is both a waste and a buffer against variability. Lean does not ban buffers; it attacks the variability that forces large buffers. Planners should ask: Is this stock covering a root cause we could fix (long setups, poor yield, unreliable suppliers), or is it a temporary hedge during a controlled PDCA pilot?

Overproduction is often called the worst waste because it creates the other wastes—extra transport, storage, motion, and hidden defects.

Push Versus Pull

Push systems release work based on upstream plans or forecasts. MRP is fundamentally a push engine: it explodes demand and creates planned orders. Push is necessary for long-lead planning, capacity rough-cut, and purchased parts with long lead times.

Pull systems authorize replenishment when downstream consumption occurs. Pull limits WIP and finished goods because production stops when the pull signal is full.

Lean plants often use both: MRP for planning horizons and rate setting, pull for execution control inside the plant or with nearby suppliers. Exam traps include claiming MRP must be deleted to be lean. The better answer is to align lot sizes, buffers, and execution signals with flow—and use pull where lead times and stability allow.

Kanban Basics

Kanban is a signaling method for pull. A kanban (card, container, electronic signal) authorizes a defined quantity to be produced or moved when a downstream process consumes material.

Key design ideas planners must know:

• Container quantity — how many pieces each signal represents.
• Number of kanban — sized from demand rate, lead time, and a buffer for variability.
• Rules — no production without a signal; signal only for standard items; defective parts do not circulate as valid kanban.

When demand rises, empty containers return faster and the system produces more—up to capacity. When demand falls, signals slow and overproduction is constrained. That self-regulation is why kanban fights the overproduction waste.

Kanban fails when:

• Processes are unstable (yield swings destroy sizing assumptions).
• Changeovers are too long for the small lots kanban implies.
• Engineering changes and SKU proliferation create too many unique items for card loops.
• People bypass signals with “hot” jobs and informal expedites.

JIT Prerequisites

Just-in-time aims to deliver materials and make products only as needed. JIT without prerequisites becomes just-too-late. Before planners slash lead times and safety stock in the name of JIT, confirm capability:

JIT is a journey tied to CI. Each PDCA gain in quality or setup time enables a smaller buffer. Declaring JIT on day one while scrap is 8% and setups take half a shift is a planning failure, not a lean success.

Heijunka Overview

Heijunka means production leveling—smoothing volume and mix over time so the plant and suppliers see a stable pattern instead of end-of-month hockey sticks.

Without leveling:

• Upstream processes batch large runs of one item, then starve.
• Suppliers receive lumpy orders and pad their own inventory.
• Planners live in exception mode every month-end.

With heijunka:

• The mixed-model sequence repeats smaller quantities more often.
• Average production rate matches average demand over the leveling interval.
• Pull loops stay sized reasonably because demand on each cell is steadier.

Heijunka does not ignore seasonality or promotions. It levels within the planning response capability—often daily or weekly mix patterns—while S&OP still sets the overall volume. Planners support heijunka by resisting last-minute batching for local efficiency metrics that destroy flow.

One-Piece Flow and Value Stream Mapping

Two named lean items in ECM 9.0 deserve explicit treatment.

One-Piece Flow

One-piece flow (single-piece flow, continuous flow) moves one unit at a time to the next operation instead of moving completed batches. It is the logical endpoint of batch-size reduction and the strongest lever against the waiting, transport, and inventory wastes.

The arithmetic is what the exam tests. Three sequential operations of one minute each, run in batches of 100, take roughly 100 + 100 + 100 = 300 minutes before the first good part clears the third operation and the whole batch is complete. Run one piece at a time and the first unit clears in 3 minutes, with the hundredth finishing at about 102 minutes. Same work content, same capacity, dramatically lower throughput time and WIP.

One-piece flow requires balanced cycle times, very short changeovers (this is why SMED matters), high quality at the source — a defect stops the line rather than hiding in a batch — and reliable equipment. Without those prerequisites, forcing one-piece flow starves downstream operations. Exam trap: one-piece flow reduces lead time and WIP, not the labor content of the job.

Value Stream Mapping

Value stream mapping (VSM) documents every step — material and information flow — required to take a product from raw material to customer, then separates value-added from non-value-added time. A current-state map records, per step: cycle time, changeover time, uptime, batch size, inventory between steps, and the information signal that triggers the work.

The headline output is the comparison of process time to total lead time. A value stream where 4 hours of process time sits inside a 21-day lead time makes the improvement target obvious: the queues and batches between steps, not the operations themselves. Teams then draw a future-state map and build the kaizen plan that closes the gap.

For planners, VSM is where lean and planning meet: the map exposes exactly which inventories are decoupling buffers worth keeping and which are pure batch-and-queue waste. Exam trap: VSM maps information flow as well as material flow — a map showing only physical steps is a process flowchart, not a value stream map.

Putting Lean Tools Together for Exam Scenarios

A typical CPIM vignette might describe high WIP, long lead times, and frequent expedites. Strong answers usually:

1. Identify TIMWOOD wastes present (especially inventory, waiting, overproduction).
2. Check whether JIT prerequisites exist before cutting buffers.
3. Propose pull/kanban where execution control is the gap.
4. Recommend leveling if the schedule itself creates the waste.
5. Tie actions to KPIs such as lead time, turns, and OTIF.

Lean is not a slogan. For CPIM, it is a planning discipline: expose waste, stabilize, pull what you can, level what you must, and only then remove the inventory that waste once required.