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Reading Bakery Systems

Center Lining and SMED

In the earlier articles, We have explained what OEE stands for and what the values of OEE mean. We have explained how to define where you stand and the 6 steps to get the feeling for the issues at hand. Furthermore, We explained the 6 big losses, 5S and TPM’s autonomous maintenance. Here We do want to go into the issue of center lining and quick change-over, SMED

Availability is one of the multiplicators in calculating the OEE.

There are a few important factors that influence the availability:

  • Stop time for cleaning
  • Stop time for maintenance
  • Stop time due to machine failures
  • Stop time for format change-over

Each of the above-mentioned points involves dismounting parts of the equipment and resetting the equipment. If that is not correctly done, there will be interruptions starting up. Leading to more stops and loss of product and packaging material.

Wafer Center Lining and SMED

On the left side we show (in a simplified way) the loss caused by a change-over or cleaning/ maintenance. On the right side it shows two things: one, a reduction in the change-over time, the other, a steeper line going back to the theoretical speed. The red area shows the savings in time (and cost) when change-over is quick, and the start-up is guaranteed.

The change-over time is planned. The start-up moment is defined. The actual start-up curve may differ considerably from the planned stat-up curve. There may be stops to tweak, there may be incorrectly formed cartons etc. The losses in change-over due to an unplannable start-up curve can be considerable. One of the big losses in this period are the packs that are not sellable, losses in packaging material, labor cost without good product, and the additional cost for rework. Some companies modify the product format and packaging configuration to avoid this cost.

Center lining and SMED are the methods to reduce these losses with a vertical start-up.

The remedy is being able to set format parts, guides etc. exactly to the right position.  Generally, there are lists of the setting, but these are long, and errors are possible. So, the goal is to organize the information in such a way that errors are avoided or impossible.

If they are simply impossible, we speak of Poka Yoke (jap. ポカヨ) = avoid unintended errors.

If the avoidance of errors is not built into the machine by design, setting parts right must be made as simple as possible. That method is called center lining.

Center Lining

“The two objectives of center-lining are to

  • determine the best settings for a production process and to
  • ensure that the best settings are always used during production.

As a result, center-lining reduces variability in quality, increases machine efficiency and stabilizes production.” (Robert Hart, TRACC Publications Editor)

This definition mentions 2 aspects

  • Define the best settings
  • Make those settings reproducible

I have seen machines with 48 numbered adjustment points. Each with a scale and a list that gives the value for each of these points.

First making the changes at 48 points takes time (easily 45 minutes), but it is easy to make a small error in one of these points. That will lead to problems when starting production. It is very time consuming and frustrating to find out which adjustment is incorrect.

Center lining is an assembly of different methods to achieve simpler and more accurate setting of adjustments for a format change-over.

This helps to establish the base settings of a machine. Establish the correct setting of the adjustable format points of a machine in an easy way.

Center Linening and OEE

Showing the setting for each format. There must be clear instructions how to make this setting compensating the direction of the play in the system. All these setting must be in a list, allowing a check whether all points have been modified. The list also gives the required setting for that specific format. Making these changes to settings requires time and tools, sometimes even special ones.

Center Linening OEE numbers

SMED

SMED stands for Single Minute Exchange of Dies and come from the metal industry, changing dies in stamping equipment.

Single-minute Digit exchange of die (SMED) is one of the many lean production methods for reducing waste in a manufacturing process. It provides a rapid and efficient way of converting a manufacturing process from running the current product to running the next product. This rapid changeover is key to reducing production lot sizes and thereby reducing uneven flow, production loss and output variability (Wikipedia)

There are 2 objectives

  • Reduce the time required to change the setting of a machine
  • Make the start-up plannable. This item generated the biggest loss and therefore should have the highest attention.

Change-over is one of the 6 big losses. The cost of change-over may be such that it may limit the flexibility for marketing to adapt its products to the market requirements. Quick change-over enables marketing and product management to react better to the requirements of the market.

Analyze the cost issues of change-over and include them in the Loss/Cause/Remedy chart and include it in the pareto analysis. Only that will give the information whether this is a high priority or not.

Example:

The Bosch TTM top-load cartoner introduced in 2011 replaced the TTL-I top-load cartoner.

The capacity of cartons of the TTM is considerable higher. Notwithstanding the increase in capacity, the change-over time was reduced from 45 minutes to 4 minutes (2 persons) and the start-up time was reduced from a variable time to 0. Vertical start-up is guaranteed. 

You may want to see this: https://www.youtube.com/watch?v=TopV77VMnY0

SMED consists of two parts.

  1. The machine must be prepared for SMED. That means that the construction of the machine allows for easy and fast change-over.
  2. Defined and documented methods and procedures to do a fast change-over but also assure the correct settings to allow a vertical start-up.

Generally, SMED involves change-over parts. On the TTM machine there are no scales for adjustments at all. There are change parts or ancillary parts that define the position of format parts.

SMED and Centar Lining at OEE

SMED and Center Lining Process in OEE

The whole system is based on change parts eliminating adjustments. The concept is plug and play without adjustments.

Consequently, no errors can be made. At the same time there is the cost of the change parts. It must be calculated whether the cost of the change parts is justified in the total cost.
How to develop your own SMED and OEE

Source Bosch

Develop your own SMED

If the machine is not designed for SMED, you may follow the following suggestions. Copying the above method is difficult and the system is patented. But there are other options.

  1. Center lining: define the positions and standardize the procedure.
  2. Reduce or eliminate the need for tools. Change screws or nuts for hand knobs or hand levers. You may use clamps to eliminate even these. Build in a separate control that all clamps are closed. If one is left open it may have serious consequences
  3. Eliminate the repositioning of photo eyes by installing an eye at each position and a selector switch to activate the eye corresponding the product you want to run.
  4. Use color coded pneumatic tubing to avoid mixing things up.
  5. Replace pneumatic activators by linear servo, and the positioning can be programmed and stored. Selecting the corresponding program defined the positioning.
  6. If there are 2 defined position, make limiters, so the parts can only be moved from one end to the other end.
  7. You may develop spacer blocks that define the position of guides, stops, photo eyes etc. as an example for multiple sizes see below.

A Simple help to reduce change-over time are stops

Simplify the settings with such stops. A guide or a sensor position is defined by the length of a stop. There are different stops that correspond to different formats. Color coding simplifies this.

SMED and colour coding in OEE

This shows a real application. The length of the fingers will be defined in the SAT.

Single-minute Digit exchange of die

Source Bosch

In the next article We will go into the issue of education and training.

Related articles:

What Can Do for You? What OEE means and why, when you want to increase your margin

How to Start Measuring OEE and Define What and Where Are Your Problems?

Where to Start Mending: 5S and TPM - What Can OEE Do for You?

Where to Start With the Overall Equipment Effectiveness?

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