How to calculate downtime when you need to modify the production line

Diagramma Gantt

It is not written anywhere that modifying the production line should be a leap in the dark. Calculating the right times of plant downtime (and thus avoiding nasty surprises, headaches and problems with customers) not only can, but must, if it is true that time is money. 

To avoid, therefore, that the plant shutdown is prolonged more than planned, I want to give you some tools to make you understand what are the right times to consider when making changes to the lines and how to find out if your supplier is really able to meet the deadlines declared.

Plant downtime

Phase 1: the preliminary study

Let’s start from the fact that you have already chosen the supplier and that the project has already been approved.

The first thing to do is a study to find out how much the individual activities will impact on production and how long each of them takes.

You have to divide the activities into groups:

  • Mechanics 
  • Electrical system and services (compressed air, water, etc. )
  • Modification or addition of electrical panels
  • Software
  • Test without production
  • Testing
  • Production assistance and staff training 

For each item, the supplier (or the suppliers if there are more than one) must tell you how long he plans to spend it. The indications must be divided into 3 ways:

  • Works possible before plant shutdown 
  • Work feasible only with the plant stopped
  • Work possible even after the restart 

You are missing a last piece to be able to make a real diagram of the activities that makes a minimum of sense: for each activity you have to know when it can be carried out in relation to the progress of the other activities of the same supplier or others.

For example, you cannot start connecting the utilities if the mechanic has not installed them.

Let’s take a simple example to understand what we are talking about.

Suppose we want to add an automatic scale to dose a powder component in the mixer and that this component is in a Big-Bag.

What macro activities should be planned?

  • assembly of the Big-Bag station
  • pipe laying
  • assembly of the scale structure on the mixer
  • laying of the connection pipe between the scale and the mixer 
  • laying cables from the switchboard to the users
  • laying and connection of compressed air 
  • wiring of users in the field and in the switchboard
  • modification of the electrical panel 
  • installation of new software 
  • sequence test without product 
  • production test
  • staff education 

Some of these activities can be carried out with the plant running and do not affect the production or safety of the personnel. 

For example: you can already mount the Big-Bag station and probably lay the pipes. You can almost certainly also change the electrical panel without adding new boards to the PLC and without connecting live cables. Maybe you can also run the cables from the switchboard to the users leaving the cables longer if you have not yet assembled the mechanics.

For each of these activities you need to know how long it will take you and therefore how long before the various suppliers will have to be ready.

The same study, in even more detail, you have to do when you stop the plant for the most delicate changes.

You also understand that a generic indication written on the offer or in some e-mails can not and should not be enough for you. You must demand a detailed document from each supplier.

In fact, you should demand it before you entrust the job to him. It will help you understand if the supplier is sufficiently experienced and if he has understood all the difficulties of the job.

Then don’t complain if they told you everything was done in a week and after three you’re still there swearing. 

Phase 2: the preparation

Putting the timeline of activities on paper is not enough to give you the right guarantees.

Before starting work, you must check that each supplier is ready and has accomplished what is within his competence.

  • Do not stop the system if you have not seen the modified software in simulation 
  • Do not start the work if all the components you need have not arrived

A few weeks before the start of the works you must ask for a meeting with the managers of the suppliers to once again establish the activities to be carried out, the timescales and the methods.

This is because once the project has got to the heart and each supplier has already worked on it and purchased the materials, they will certainly have the clearest ideas and will be able to correct any errors in the initial planning. 

Phase 3: the realization

The moment has come. Your job is to make sure that each supplier follows the program and reacts as quickly as possible to the problems that will arise. Because rest assured that there will be some problems: intervening on an already built system is a complex activity and it is difficult to foresee everything on paper.

Maybe you are thinking that by relying on a single supplier who is the project leader, is not your problem, because if he deliver late or create damage you don’t pay for it. 

Reality is a little more complex. It is true that, often, testing is reached with a part of the order still to be invoiced. But it is equally true that a delay in production of even a week between non-invoicing of orders and the possibility of losing customers is worth more than the remaining portion to be paid.

Also, having problems with the supplier right away is never a good thing.

For this you must be present firsthand. 

How to understand if the times indicated are correct

If the supplier does not have direct experience of these works, he may underestimate the time needed. 

The problem is that, once the work has started, you will hardly be able to do anything to reduce the time or simply postpone the work.

So how do you know if the time schedule is correct? 

There are more or less invasive and complex interventions. If you are not an expert, you will find it really difficult to evaluate and contest a program, but there are general rules that you can use as a compass.

The following list gives you an idea of ​​what can or cannot be done depending on the time available (of course, each intervention is different and must be carefully evaluated on a case-by-case basis).

With a week of downtime you can:

  • replace the dosing system and mixer software (without mechanical and electrical modifications)
  • add one or two components to the scale (linked on the same transport line)
  • change the PLC and the software of one mixer (without changing the panel)
  • install manual dosing stations

With two weeks of downtime you can: 

  • install a new fully equipped powder or oil scale
  • install new feed belts for the mixer 
  • change the electrical panel of a mixer or a small plant
  • replace PLC and software for complex systems without changing the electrical panel 
  • add new silos or Big Bag stations also with independent transport lines
  • test a small new compound system

With three weeks of downtime, you can: 

  • replace panels and software of a complex line
  • test a new medium system with 3 scales, belts, a mixer and some manual stations
  • heavily modify an existing system with new scales and components

When to do the work 

Everyone wants to do the modification work during the scheduled stops. In most cases, in the Christmas period or in August.

This is logical and shareable, but these periods often have several pitfalls that must be considered when organizing the project:

  • if you are closed, the sub-suppliers to whom your suppliers have turned are also likely to be, so finding spare parts or new parts can be complicated
  • during the Christmas period there are usually many “essential” holidays so that work is inevitably broken up. This lengthens the total time and is not optimal for complex interventions
  • before starting again with the actual production, you must do tests with the modified system; therefore, you need your own staff: check that you have the availability of your operators
  • even structured suppliers like us (we are 20 of which 10 are programmers) can safely manage, and give the right guarantees, only a limited number of jobs during holidays period; so do not wait until the last moment to place your orders but anticipate them as much as possible (consider at least 6 months from the beginning of the project)
  • if you are the person in charge of the project, your presence is necessary during all phases, this means that your holidays or family holidays could skip.

What I can advise you is to plan the stop well and evaluate if you can use alternative periods to make small changes

Often adding a few days to a holiday in another period you can do more than working during Christmas, with less problems and spending less .

Final advice always valid

The modification of plants in production, whether it be software, electrical or mechanical modifications, requires specific experience from suppliers

Unlike testing a new plant, where a delay involves limited problems, acting on a plant in production is much more risky, because if you make mistakes you don’t produce and therefore you don’t sell.

For this reason, the advice is to rely on expert suppliers who have already carried out jobs similar to those you want to do, who can prove it and have testimonials from companies in your sector. 

Even if the change seems trivial, do not simply entrust it to the cheapest. Evaluate their experience; how it intends to proceed with the work plan; and, if the change requires a change of software, you must be able to see the modified software before work begins.

Unfortunately it is something that I often see done by some “colleagues”: changes to the software (simple ones, but actually even complex ones …) are made directly on site or at least terminated during testing, skipping the whole test phase in office. 

You think you can save (time and money), but this practice can cause problems even after months and also on parts of the plant that in theory have not been modified. 

Just miss the name of a variable to have problems and risk blocking the line.

Our rule is that a software does not come out if it has not been fully tested, even in case of simple changes.

With over 600 systems installed worldwide in 25 years of activity, every year we manage many requests for modification or updating of systems.

Our specialization allows us to guarantee the truly necessary downtime and indicate the exact day on which production can resume.

If you need to make any changes regarding automation but also mechanics, my experience is at your service for free to help you not make planning mistakes and choose the right supplier.

You can find me in Multi Data at +39 059537902 or by email:

Buona vita

Claudio Tosi

    Claudio Tosi

    Nato nel 1974 a Modena, si è diplomato all'istituto superiore Enrico Fermi in elettronica e telecomunicazioni. Dopo l'anno di militare ha iniziato il suo percorso professionale come tecnico programmatore presso la Multi Data s.r.l. Dopo oltre 20 anni di lavoro, si occupa di seguire i nostri clienti nel settore plastica e gomma, aiutandoli a migliorare la produzione e ridurre errori e costi.

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