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The implementation of the just-in-time requires lines that are thought to meet the stakes of flexibility and reduction of wastes.

Introduction

The implementation of the just-in-time requires lines designed to meet the stakes of flexibility and reduction of waste. It meets three criteria :

  • Give priority to part-to-part production : Produce part-to-part allow to solves problems one by one.
  • Adapting to demand  fluctuation: equipment will be designed according to the production scenarios envisaged with the Takt Time.
  • Isolated processes are to be avoided : The operations of the same line are grouped.

Traditional process

Just In Time Process

A simulation of one piece flow vs the traditional flow

1-Assigning Products

The allocation will be based on the customer’s distribution.

Case 1: Production synchronized with the customer

The lines will be a replica of those of the customer in terms of product allocation and cadence (including pause).

Case 2: Non-synchronized Production

We will take into account 2 criteria to allocate the products:

  • The product/process similarity: We will take the products that go through the same manufacturing processes. You can allow yourself a little leeway if the line is able to change configuration very easily.
  • The similarity in cycle times: One will admit a difference of 40% maximum between the longest and shortest cycle time.

2-Determine the cadence

Over-sizing or subsizing a line is equivalent in all cases to not complying with the 4 principles of just a time. We will help the Takt Time to define the rate at which the Position will Out ‘ a good Part .

3-Detailing the process

3.1 Dividing process steps into elementary tasks

We begin by defining all the actions necessary to realize the pieces that we have assigned. We’re going to ” “Dissect” the products, and work in groups to understand all the operations necessary to achieve them.

We will focus only on the steps of added value. In other words, we do not take care of the lay-out, the displacement or even the supplies.

3.2 Define the necessary movements and their sequence

It is based on the Therblig To define the necessary movements. This classification will allow us to work better on the aspects of Time and Ergonomics.

We will then classify them in the sequence in which they are to be performed.

4-Implement the Jidoka tools

The implementation of the  Jidoka principle is based on the application of different tools to help design a line:

5 – Provide for the control standards

We will determine the different steps of controls necessary by relying on the autoquality. Specifically for manual lines, a control will be expected at the end.

In the event that the retouching is possible, make sure that it is done offline.

6 – Predetermine a time

Using the tools of the Predetermination of Time or by testing on prototypes, we will define the estimated standard time for each operation. Caution, these times must incorporate the same adjustments used to calculate the adjusted time Takt.

Model of the Toyota Prius assembly line with Andon from the Toyota-City Tsutsumi Factory

7-Balancing tasks

Using the Takt Time, we will deduce the necessary personnel according to the scenarios, then determine the distribution of the tasks in order to balance  them by using the Simogramme.

Tips for building a sequence

 

Ungroup automatic operations that have a higher cycle time than the Takt time.

The sequence must follow the value-added flow. For example, if we have 4 identical lines and we know that the same operator can handle 4 machines, it will not handle 4 identical machines but the 4 machines of the same line.

Accept the Muda on a case by case basis.

If the neck is larger than the Takt Time, it is better to make 2 small flexible lines, rather than a larger line.

8 -Choose between an automatic or manual process

It should not be a priori on automation or not tasks. The choice will be based on the level of profitability of the solutions and “social” criteria. Automation is not an end in itself. We will always favor the maximum elimination of Muda before deciding to automate a task.

For more details, see the dedicated article.

Shoninka or Shoryokuka

As we know, automation is often a poorly viewed solution in the Toyota system, the resulting “gain” is translated into two terms to distinguish between the two situations:

  • Shoninka: Automation has generated a significant productivity gain and the consequence is the deletion of at least one person at the Position .
  • Shoryokuka: Automation has made it possible to increase productivity and reduce the painfulness of the Position, without having to increase productivity enough to remove a person at the workstation Position .

 

All this to put forward that an automation study is not necessarily intended to replace manpower but also to help    Reduce the painfulness of work, while maintaining see increasing the quality of the product or of the service.

9-Create the layout of the line

Depending on the product and the process, the just A time line can have different shapes. We find 4:

Straight process

Fish Ridge process

U-Cell

The ARC concept

Since 2015, Honda has developed a new line concept combining U-cell and straight line and named ARC: assembly Revolution Cell. It allows the same operator to be able to assemble several parts and to have several operators on the same Position. The length of the line and the Lead Time are reduced.

It should be noted that, empirically, a manual assembly line has a length that can be estimated according to the following formula:

Line length = 2 * Number of Operators * Part width

Some tips

All the Line edges and positions are on mobile rack.

There is no obstacle between the different posts spaced by 1,5M maximum.

Turntables and carousels are to be avoided because creating a dependency of operators between them and generating times of expectation.

The machines must be mounted on wheels.

The equipment allows the installation of the edges of lines.

10- Position Design

At this point we will proceed with the design of the Position . Depending on the type of Position, one will choose to design Position a workstation Manual workstation or  automatic machine.

The concept of Yatai

 

The design of a Position , whether manual or automatic, will have to meet the Yatai principle.

 

The Yatai are the small Japanese mobile restaurants. They have the advantage of being very flexible in every respect (maintenance, mobility…) and are part of the Japanese culture.

 

In terms of Lean, this image of the Yatai is used to show the need to have production processes: simple, flexible, having the minimum stock, knowing how to do what is necessary in relation to what is asked.

 

In other words, a Yatai is the best example of a process that allows customers to deliver what they want, when they want, and in the quantity they want.

11-Establishment of the Position

Once you have chosen the Position, you will Foresee “in the Lay-out That we have defined previously. It will depend on the flow of parts, storage areas…

12-The Working environment

The workingEnvironment takes into account from the conception of the Position all the elements external to the work as such: noises, physico-chemical risks, thermal conditions,…

13-Cleaning and maintenance

Final step, the design review of the Position vis-à-vis the needs of cleaning and Maintenance.  we will reflect on the access to the Position and the machines, the need for cleaning and the associated standards. And if the knowledge of the equipment is important enough, we will be able to sleep-and-already create the standards of maintenance.

14-Reception of the line

Often subject to ” Surprise “the Reception And the installation of the line is an important step. It validates the previous work and especially validates the ” Invoice “. Special attention will be paid to the Capability of the means, the holding of the cadence, the Reliability and Ergonomics.

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