Lesson 2: Flow problems and plant types

The five plants in the last lesson went wrong in different ways. This lesson has two parts. Part 1 gives the problems names, so you can spot them on a real shop floor. Part 2 looks at the shape of a plant, because the shape decides which problems you will meet most.

Part 1: The four flow problems

The problems fall into four families. Once you can name them, you start seeing them everywhere.

Problem	What it means	Typical sign
Resource over-activation	Producing items that have no immediate demand.	Piles of work in progress; finished goods nobody asked for yet.
Resource stealing	Using a resource to produce some items at the cost of others that are needed.	The machine was busy all day, but the urgent order didn’t move.
Material stealing	Using material to produce items with no immediate demand.	Plenty of one product in stock, while another is short of the same material.
De-synchronisation	A long gap between the arrival of the first and the last part an order needs.	Assembly has heaps of parts and nothing it can build.

They feed each other. Over-activation creates the piles that make stealing possible, and stealing creates the gaps that de-synchronise assembly.

Exercise: name the problem

The press shop runs a full week’s requirement of brackets on Monday because the set-up is long
Frames for an order have been waiting at assembly for six days; the matching forks arrived this morning
The last coil of steel went into a standard model for stock; a confirmed customer order is now short of it
The paint line stayed busy all shift on an easy colour, while the order due tomorrow waited for its turn
Machining keeps running parts for next month’s plan to keep its utilisation above 90%
A kit is “95% complete” for two weeks because one small bought-out part is missing

Part 2: Types of plant

Draw the flow of any plant from raw materials at the bottom to finished products at the top, and it takes one of four basic shapes. TOC practitioners name them after the letter they look like.

raw materialprocessing stepassemblybottleneckfinished product

The shape tells you where to look first.

V plants: one material, many products

A few raw materials split, step by step, into many end products. Think of steel, paper, textiles, plastics or food processing: one coil or one batch of yarn can become dozens of different items.

Typical problem: material stealing. At every split point, material can go to the product that is easiest or most efficient to make, instead of the one that is needed now. Stock of some items piles up while others are short.
Where the constraint sits: often early in the flow, frequently a big machine with long set-ups, which makes the urge to batch strongest.

A plants: many parts, one product

Many parts, made or bought separately, come together in assemblies. Think of machinery, equipment, vehicles, or projects.

Typical problem: de-synchronisation. Every work centre batches its own parts, so parts arrive for many orders at once, but complete for none. Assembly waits for the last part while the store fills with the others.
What helps most: releasing parts for the same order together, and starting assembly only with a full kit.

T plants: common parts, endless variety at the end

A modest number of common components is made, then combined at final assembly into a huge number of variants. Think of appliances, furniture, electronics or any configure-to-order product.

Typical problems: both stealing and de-synchronisation. Common parts get used for the wrong configuration, and assemblies wait for the one part that was used elsewhere.
A note on constraints: because so much of the trouble comes from mismatched parts, T plants often have no true bottleneck; the chaos itself eats the capacity.

I plants: one line, one sequence

Every product follows the same route through the same machines, like a dedicated line, a bottling plant, or a press line.

Simplest to plan: the sequence is fixed, and the constraint is easy to see.
Typical problem: over-activation. The equipment is often expensive, so the pressure to keep every machine running, and to build stock nobody ordered, is strongest.

Pause and think: an equipment maker builds each machine from 50+ parts. Which problem should its managers watch most closely?

Material stealing
De-synchronisation at assembly
Over-activation of the market
None: assembly plants are simple

Many parts converge into each product: an A plant. Every work centre batching its own parts “efficiently” means parts for many orders arrive partially, and assembly can’t start any of them. The capacity is lost not to too little work, but to too much of the wrong work.

Exercise: which type of plant is it?

A paper mill makes 40 grades and sizes from the same pulp
A company builds custom packaging machines from 300 parts each
A kitchen appliance maker assembles 120 models from a dozen common motors, panels and controllers
A bottling line fills, caps, labels and packs one product after another
A textile mill dyes and finishes one yarn into hundreds of fabric varieties

The common root

Whatever the shape, notice that none of the four problems is caused by a lack of capacity or effort. Each one is a local decision that made sense for the work centre: run the long batch, take the easy job, don’t stand idle. The next lesson looks at why sensible managers keep making those decisions.

Check your understanding

Answer all five. Get four right to complete the lesson.

1. Producing items that have no immediate demand is…

Resource over-activation
De-synchronisation
Exploiting the constraint
Good planning

It looks productive and creates piles of inventory.

2. De-synchronisation is measured by…

The utilisation of assembly
The number of set-ups
The time between the arrival of the first and the last part an order needs
The value of finished goods

The longer that gap, the longer parts wait and the later the order.

3. In which plant type is material stealing the biggest risk?

I plant
A plant
None
V plant

One material splits into many products, so it can go to the wrong one.

4. A machine was busy all shift, but the order due tomorrow didn’t move. That is…

Material stealing
Resource stealing
A breakdown
Fine, as long as utilisation is high

The resource was used for items that weren’t needed, at the cost of one that was.

5. What do the four flow problems have in common?

They are caused by lack of capacity
They are caused by lazy workers
They come from local decisions that make sense for one work centre but hurt the flow
They only happen in big plants

Each one is a sensible local decision. That is why they are so persistent.