430. Product Pooling
Reducing inventory by sharing parts / components across product variants rather than holding stock for each finished SKU separately. Two main mechanisms:
- Component commonality — products share common parts
- Postponement (delayed differentiation) — defer customization until late in the supply chain
Both convert several high-variance finished-good demands into one lower-variance component demand — a textbook application of risk pooling.
430.1. Postponement: the HP DeskJet case
Classic Lee-Tang (1996) example. HP shipped printers configured for North America, Europe, Asia from a Singapore factory. Each region got its own SKU (different power supplies, manuals, plugs). Region-specific safety stocks per SKU.
Postponement: ship generic printers to regional DCs. Final regional configuration (adding power supply, labeling) done at the DC, right before delivery.
Effect:
- 3 finished SKUs → 1 generic + 3 small customization kits
- Safety stock for the generic stage uses aggregate demand across regions
- Customization kits have very fast lead time → minimal safety stock
Variance accounting:
| Per-region | Aggregate | |
|---|---|---|
| Mean demand | ||
| Variance | (independent) | |
| Coefficient of variation |
The aggregate CV is smaller — pooling effect for the generic. Total safety stock falls by a factor for the components that get postponed.
430.2. Component commonality (Baker-Magazine-Nuttle 1986)
Two end products and use:
- Some shared components — commonality
- Some unique components
For the shared component, demand is — pooled. For unique components, demand is each product’s own — not pooled.
Trade-off:
- More commonality → more pooling savings, but each product is harder to differentiate
- More uniqueness → more product differentiation, more inventory cost
430.3. Variance math
Let product demands be independent with . The shared component (used in both) sees:
vs separate components:
By the triangle inequality (and strict inequality when both ). Equality only when one variance is zero.
So sharing strictly reduces required safety stock for the shared component.
430.4. Practical examples
- Auto industry — Toyota uses common platforms across models (Corolla, Camry, RAV4 share many parts)
- Electronics — Apple uses common batteries, chargers, screens across product lines
- Apparel — DKNY makes generic shirts in white, dyes them to color at distribution centers
- PC manufacturing — Dell assemble-to-order from common components
- Pharmacy — generic drug → repackaged for retail / hospital channels
430.5. Limitations
- Customization later costs more per unit — postponed assembly is less efficient than dedicated lines
- Some differentiation can’t be deferred — e.g., physical form factors
- Information / coordination overhead — late customization needs accurate downstream demand info