Heijunka is the levelling of production in both volume and mix, so a process runs at a steady rate rather than reacting to the immediate shape of demand.
It exists because demand variation amplifies as it travels upstream. A modest swing at the customer end becomes a larger one at assembly and larger again at the supplier, since each stage adds buffer against the variation it observes. The result is alternating overload and idleness at every level. Producing to a steady rate, with inventory absorbing the difference, stops the amplification where it starts.
Skladba produktov je rovnako dôležitá ako objem. Mesiac výroby produktu A nasledovaný mesiacom produktu B je z hľadiska objemu dokonale vyrovnaný, no z hľadiska mixu extrémne nevyrovnaný — každý dodávateľ pre produkt A stojí, kým beží výroba produktu B. Vyrovnanie mixu znamená malé množstvá z každého produktu v opakujúcej sa sekvencii, čo je cenovo dostupné len vtedy, keď sú prestavby lacné. Preto sa Heijunka a SMED implementujú takmer vždy spolu.
The trade is real: levelling requires holding finished inventory, which sits against the instinct to minimise it. A defined, visible amount of stock in exchange for stability across the whole chain is usually a net gain, but it is a genuine cost rather than a free improvement.
