The Purpose of Standard Work in Manufacturing

The articles by Art Smalley‘s and  Mike Rother about Standards in The Lean Edge  puzzle me, because it seems we all mean different things by “standard.” On a manufacturing shop floor, in particular, I don’t see Standard Work as a basis for comparison, the best way known to perform a task, or a target condition.  Instead, it is a set of rules published for the purpose of ensuring that different people perform the same tasks in the same way. This is consistent with the Wikipedia definition of a technical standard.

A process can only produce a consistent output at a consistent pace on different shifts in the same plant, as well as in different plants, if it is performed on the same materials, with the same equipment, and by the same methods. That is what standard work is supposed to accomplish, and it is, for both human and technical reasons, more difficult than meets the eye.

So here are a few thoughts I would like to share on this subject:

Standard Work versus Craft Control

When operators on a manufacturing shop floor remain on the same job for years, they come up with their private tricks on how to perform it. They attach “cheater bars” to wrenches, rearrange parts around their stations, and develop the ability to detect anomalies by sight, sound, touch, or smell. By default, as operators perceive this knowledge to be the key to job security, they make sure it remains hidden away in their heads.

British 19th-century craftsman
19th-century craftsman

It leads to a situation that economist William Lazonick called Craft Control, in which management leaves the organization of work on the shop floor to the operators. The focus of Frederick Taylor’s “scientific management” was to replace craft control with managerial control, and it entailed the detailed specification of all operations by specialists. For decades after Taylor’s death in 1915, the management of American manufacturing companies engaged in a tug-of-war with labor to put an end to craft control, and ultimately failed,  resulting in shelves of binders full of specs that nobody pays attention to, except external auditors.

Human resource policies that involved laying off whenever business slows down were an incentive to retain rather than share information. And leaving operators on the same job for years made the specs unnecessary except to train new operators but, when you tried to use them for this purpose, more often than not you found them to be obsolete.

TPS/Lean pursues managerial control too, but in ways that differ as follows:

  1. Operators are hired for a career in the company and retained through downturns.
  2. They are frequently rotated between jobs and become multi-skilled, which requires them to share what they know.
  3. They participate in continuous improvement, leading to the integration of their private tricks into the shared specs.
  4. Instead of Victorian novels in binders, the specs are concise memory joggers on A3 sheets of paper posted above work stations. 

See last July’s post on What are standards for? for examples and details. These differences do not make it easy to implement, but they remove the key obstacles that account for the earlier failure.

Use of A3 instruction sheets

A3 instruction sheets above work stations help supervisors notice discrepancies between the standard and the practice of the operators. When there is such a discrepancy, however, the supervisors must investigate it rather than always “retrain” the operator to conform to the standard. The operator may in fact have improved the process; this improvement needs to be documented and  the standard updated so as to propagate this improvement to all other operators doing the same process. When walking through a shop floor that has such posted instructions, one should check the signature block to see when it was last updated. If it was five years ago, the sheet is useless. In fact, It should have been updated in the last six months.

In The Birth of Lean (p. 9), are Taiichi Ohno’s own words on the subject:

 “…the standard work display panels […] let the foremen and supervisors see easily if the operators were adhering to the standard work procedures. […] I told everyone that they weren’t earning their pay if they left the standard work unchanged for a whole month.”

Changing specs once a month for every operation seems a hectic pace, leaving operators barely enough time to master the new method before changing it. Perhaps it was justified in Toyota’s single machine shop, that Ohno was running  in the early 1950s. Managing revisions in a network with dozens of factories worldwide that is Toyota today is a different kind of challenge.

Avoiding Lean Wallpaper

Posting too many instructions, maps, charts, forms, before-and-after pictures, etc., is counterproductive. The result is visual clutter rather than visual management. Producing, posting, and maintaining displays is work, and it should be done selectively, when it has a clear purpose and is worth the effort.

In daily life, we use complex products like computers, cars, or kitchen appliances without posted instruction sheets. We can, because these products have been engineered for usability and mistake-proofed. Usability engineering is the art of designing human-machine interfaces so that users find the right actions to take without prompting or instruction; it is widely applied to household appliances, based on techniques described in Don Norman’s The Design of Everyday Things. In Taming HAL, Asaf Degani expands on these techniques for application to airliner cockpits and ship control rooms, and Chapters 1 and 2 of  Working with Machines summarizes them as they apply to production equipment. Usability engineering is about making mistakes unlikely, but not impossible; this is why, whenever possible, it is supplemented by mistake-proofing. The following pictures illustrate one of the usability engineering principles. In Pixar’s “Lifted,” the young alien taking a test cannot tell which switch to press; Don Norman shows an example of a control room in a nuclear power plant where technicians have replaced identical joysticks with different beer keg handles to make them easier to tell apart.

Toyota in recent years has been pursuing a reduction in the amount of information posted on the shop floor. They simplified the tasks to eliminate the need for posted instructions, which also made it easier to train new people. This has been going on in several plants worldwide for several years, resulting in continuing improvements in quality and productivity. Instruction materials are kept off line and brought out as needed, like a car’s owner manual.