The Origins of
Just-in-Time
Kiichiro Toyoda proposed Just-in-Time production when
operations began at the Koromo Plant. This was the beginning of Just-in-Time
used in the current Toyota Production System.
I believe that the most important thing is to ensure that
there is neither shortage nor excess, that is, to ensure that there is no
excess labor and time for the designated production. There is no waste and
there is no excess. It means not having to wait for parts to be circulated
around. For Just-in-Time, it is important that each part be ready 'just in
time'. This is the first principle of increasing efficiency.
Eiji Toyoda, who was instructed by Kiichiro at that time,
explained the Just-in-Time concept in the following manner:
What Kiichiro had in mind was to produce the needed quantity
of the required parts each day. To make this a reality, every single step of
the operation, like it or not, had to be converted over to his flow production
system. Kiichiro referred to this as the 'just-in-time' concept. By this he
meant: 'Just make what is needed in time, but don't make too much.
According to the recollections of Jiro Iwaoka, who was in
charge of the machine shop at the Koromo Plant, Kiichiro "was using the
slogan 'Just-in-Time' even before we shifted production to the Koromo
Plant"
When operations started at the Koromo Plant, a Preparation
Office was established between the raw blank divisions and machining divisions
and an early-stage production system was adopted before the transition to
Just-in-Time production. The Preparation Office delivered only the raw blanks
necessary for that day's planned production to the Machining Shop, the
Machining Shop delivered completed parts corresponding to the raw blanks that
it received to the Assembly Shop, and the Assembly Shop produced only that
number of complete vehicles. When the planned quantity was manufactured and
delivered to the next process, that department shut down its line. Kiichiro
proposed a revolutionary management system that did not use transfer slips, but
it took a long time for the ideas to be understood.
As a result, for the time being, the Goguchi production
control system (discussed below) was used for production management. Regulation
was tightened during wartime, and a rationing system was implemented for
automobile production materials in 1939, making it impossible to acquire just
the necessary materials in just the necessary volumes, and just when they were
necessary. Later, Just-in-Time production initiatives were unavoidably
suspended.
The Just-in-Time concept was not fully realized until 1954
when the ‘supermarket method’ was proposed. This was the idea of having
subsequent processes take what they need from the earlier processes. The kanban
was proposed as a tool for carrying this out, and it is referred to as the
‘Kanban system’.
The name has undergone various transformations, but the
fundamental concept of Just-in-Time remains the same, and with the concept of
jidoka (‘automation with a human touch’), it is one of the two core elements of
the Toyota Production System.
Goguchi Production
Control System Adopted
As explained, it took considerable time to change employee
awareness for the Just-in-Time system to take root. For this reason, the
Goguchi production control system1-which had streamlined the Goguchi system
from around the time of the Kariya automobile assembly plant-was adopted as an
alternative.
The Goguchi production control system treats a certain
volume of products as one unit (one group) and uses a serial number to manage
the progress of production for each group. Tentatively, the first group of 10
products completed on a given day was called the No. 1 Goguchi, the second
group was called the No. 2 Goguchi, and so on, making it possible to determine
which process each group is in.
Operations at the Kariya Plant used a group effort system,
and each shop at the work site had its own administrative office. Production
units were determined by the administrative office for each shop and
decentralized management was performed, and as a result, the Goguchi production
control system was implemented at each shop and units were not consistent
throughout the plant.
At the Koromo Plant, processes were designed based on the
assumption that Just-in-Time would be introduced and the plant layout was
tailored for flow production. This meant that operation of the Goguchi
production control system could be streamlined. Rather than managing on an
individual plant-level like at the Kariya Plant, work units and group
quantities were unified throughout all processes and a uniform control system
was adopted for the entire plant. For example, if the No. 1 Goguchi and No. 2
Goguchi, each consisting of 10 vehicles, were to be completed on a given day,
groups of 10 of each part necessary for assembly were referred to as the No. 1
Goguchi and No. 2 Goguchi, and production progress was managed in each process.
The Goguchi production control system aimed to create
overall flow production based on the final assembly line by coordinating the
production of each part with the final assembly line. The system could not be
expected to operate entirely smoothly under a restricted economy as a result of
unstable supplies of materials, and it was also necessary to modify the system
according to changes in production status.
Although they made their starts under unusual circumstances
resulting from wartime and faced a variety of issues, the basic concepts of the
Goguchi production control system and Plant layout based on Just-in-Time became
the foundations of the later Toyota Production System.
Reforming and
Improving Vehicle Quality
When a defect occurs in an automobile, it is necessary to
quickly correct the problem, modify the design, and replace the original part.
In order to minimize losses from disposing of the original parts, it is
desirable to maintain small inventories and work in progress. Kiichiro Toyoda's
goals in proposing Just-in-Time were to reduce inventories of parts between
processes, cut the time needed for raising vehicle quality, and lower expenses.
When improvements were made to vehicles at the Toyoda
Automatic Loom Works Kariya Plant, not only were substantial losses incurred
from discarding inventories of parts, it took nearly one year for improvement proposals
to be implemented. Even so, it was nearly impossible to supply the improved
service parts. Kiichiro believed that the cause of these problems was the lack
of a developed plant organization (production system). The Toyoda Automatic
Loom Works plant carried out both loom and automobile production, but the
priority was placed on manufacture of loom parts and automobile parts
necessarily took a back seat.
The plant had large parts inventories because automobile
parts were manufactured in batches when production was possible. As a result,
when part designs were modified to make improvements, the inventories of
existing parts had to be discarded, resulting in substantial losses. In
addition, production of prototypes and commercialization took considerable
time, and it took nearly an entire year before improvement proposals for design
modifications could be implemented. Moreover, for each vehicle, 5 to 7 service
parts with modified designs were necessary, but production could not be
conducted in time, and it was nearly impossible to supply the parts.
Kiichiro expected to eliminate these problems and rapidly
improve vehicle quality when the Koromo Plant was completed, but the actual
conditions were quite different.
Number of problems with Toyota vehicles of the time were
pointed out: 1) engine overheating, 2) weak front springs, 3) differential gear
susceptible to breaking, 4) strange noises produced by the transmission, 5)
difficulty steering, and 6) Babbitt metal burning. Kiichiro planned to resolve
all of these problems at once and produce new vehicles at the Koromo Plant.
Evolution of Toyota.
Part 15: Model B Engine, Model GB Truck Developed
In about October 1937, when the Model GA truck had been
proved that it could withstand a certain degree of use, vehicle improvements
were completely suspended and all efforts were directed toward construction of
the Koromo Plant. In conjunction with the completion of the Plant, engines and
vehicle series were completely updated.
Model B engine
The Chevrolet engine that was used as a model for
development of the A engine was later improved and the output increased, so
development of a new engine for Toyota vehicles was also undertaken. The design
of A engine used imperial measurements to ensure compatibility with Chevrolet
engine parts so service parts could be used. At around this time, the
construction plan for the Koromo Plant was adopted and concerns regarding
supplies of service parts were eliminated, so a decision was made to conduct
new engine design using metric units with the premise that the new engine would
use Toyota vehicle parts only.
Work on the design of the new engine started in about May
1937 and was completed in about October. Prototype production of the new
engine, known as the B engine, began and full-scale production started with the
completion of the Koromo Plant in November 1938. The main specifications and
areas of improvement leading to the B engine are shown in Table 1-6.
Announcement of the
Model GB Truck at the Tokyo Toyota Motor Co., Ltd. head office
The B engine was used on the Model GB truck (released in
1939, an improved version of the Model GA truck), the Model AA passenger car
(1939), the Model AC passenger car (1943, an improved version of the Model AA),
the Model KB truck (1942), the Model KC truck (1943), the Model BM truck
(1947), the Model BX (1951), and other vehicles. Maximum output was increased
from 75 hp to 78 hp, and it was further improved to 85 hp in 1953. The B engine
was produced until the end of 1956, when it was replaced by its successor, the
F engine.
The Model GB truck equipped with the B engine was launched
at dealers nationwide on January 15 and 16, 1939. At the time of the
development, improvement to the Model GA truck was suspended to focus on the
Model GB truck, and the improvements to the GA were reflected in the GB.
Production of the Model GA truck continued until September 1940 to use up
inventories of parts.
Various improvements to the Model GB truck included the
steering worm gear (improved machining precision), the front springs (improved
strength), the spring hangers (improved strength), and adoption of an X member
frame (increased frame rigidity). The specifications of the Model GB truck
chassis compared to the Model GA are shown in Table 1-7.
Source: TOYOTA MOTOR CORPORATION
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