Eficiencia de una máquina: Cómo calcularla con ejemplos prácticos

Table of Contents

The efficiency of a machine: OEE

OEE is a metric used to measure the overall efficiency of equipment in productive maintenance programmes. This metric includes effectiveness and efficiency of a machine and is a common resource in Lean Manufacturing as it serves to resolve the following issues:

How often is the machine available for operation?
At what speed does it run when in operation?
How many acceptable parts have been produced?

To calculate the efficiency of a machine the following formula is used to determine the OEE :OEE = Availability x Performance x Quality

OEE = A x P x Q

What is the efficiency of a machine?

The three components of the OEE calculation formula are defined below.

Availability (A):

Availability is the unit of time the machine is available to run divided by the total possible available time. This metric does not include any performance figures relating to the operation of the machine while it is running.

AVAILABILITY = Operating time / Planned production time

The availability used to determine the efficiency of a machine, only includes the scheduled, planned or assigned operating time of the machine, and should not be confused with another common metric called utilisation. Utilisation can include all hours of the day, regardless of scheduling, and is most effective for capacity planning and analysing fixed cost absorption.

Availability therefore looks at the machine itself and focuses more on the absorption of variable costs.

Uptime = Planned production time - Planned downtime

Planned downtime includes meal breaks, meetings and any other regularly scheduled breaks that are independent of the machine.

Performance (P):

Also known as efficiency, it is a measure that indicates how well the machine performs while running within the operating time.

PERFORMANCE = Parts Produced / (Ideal Speed * Running Time) * 100%

Where:

Parts Produced = Unplanned scrap + acceptable parts.

Ideal Speed = Optimal speed at which the part should run on the machine.

Uptime = Planned production time - Planned downtime

Quality (Q):

Another parameter defining the efficiency of a machineis quality which is a measure of the number of parts that are within specification compared to how many were produced. In some cases, there is a planned scrap production.

Planned scrap is a problematic term because all scrap is a lost profit, even if it is included in the budget and cost. If a competitor figures out how to eliminate it, a disadvantageous cost structure is created and new business is less likely to be won.

For example, if the machine must heat some parts or learn a process, these parts should not be included in the calculation. However, this represents an opportunity to find a way to permanently avoid these heating parts or initial scrap parts is a credible improvement.

QUALITY = Acceptable parts / Total parts * 100%

Where:

Total Parts = Acceptable Parts + Unplanned Scrap Parts

A challenge in bulk production processes is that parts from one operation may not be recognised as defective until later stages. Not in all cases is it possible to carry out a full criteria inspection, so defects may be detected further downstream of the machine that created them.

This means that, in reality, the quality part of the efficiency of a machine would have to be recalculated with the lowest value of Acceptable Parts.

Example of a machine efficiency calculation

To determine the efficiency of a machine, Let's look at an example for which the following data is known for an 8-hour shift:

A total of five planned break times totalling 50 minutes.
10 minutes of unplanned downtime due to a tooling failure
The ideal machine speed for producing this part was determined to be 400 parts/min.
150,000 pieces produced during 8-hour shift
25,000 parts were scrapped for being out of specification.

Let us calculate each element of the OEE:

Availability (A):
There is a total of 480 minutes in a shift. An extra 50 minutes were planned, so these minutes will be removed from the denominator. Therefore, the denominator of the availability is (480-50) / 480 = 430 minutes (this is the planned production time).

The numerator is the running time which eliminates the total unplanned downtime, which was only 10 minutes due to tool failure. Therefore, the uptime was 420 minutes.

Therefore, A = 420 minutes / 430 minutes = 97.67%.

Note that another common metric that companies measure is utilisation, which in this case would be 420 / 480 = 87.5%. In other words, regardless of the reason for the lost downtime, the team utilised 87.5% of the potential time during the shift.
Performance (P):
The denominator refers to the 420 minutes of operation. If the machine was supposed to produce 400 parts per minute, multiplying this by 420 minutes gives the number of parts that should have been produced, which is 168,000 parts.

In reality, the machine produced 150,000 pieces due to some losses. Therefore, P = 150,000 pieces / 168,000 pieces = 89.29%.
Quality(Q):
Since 25,000 pieces were discarded, 125,000 of the 150,000 were acceptable. Therefore, Q = 125,000 / 150,000 = 83.33%.

To obtain the OEE, simply multiply the 3 values above to find the efficiency of a machine:

OEE = 97.67% * 89.29% * 83.33% = 72.7%.

If you want to learn more, see this example of how to make the efficiency measurement in industrial power plants: OEE calculation.

Major losses affecting the efficiency of a machine

Losses affect the efficiency of a machine and the three components of OEE. Breaking down the losses into these categories helps the team prioritise improvements. The losses affect one of the three products (A, P or Q) and the area with the lowest percentage is probably a good place for the team to focus its improvements.

Damage losses

Sudden or unexpected equipment failures that cause the efficiency of a machine is lower as it is less available. Contributing factors include:

Major mechanical breakdowns
Electrical system failures
Structural failures

Set-up and tuning losses

The efficiency of a machine is diminished by the downtime and defective products that occur when production of one part is stopped and the equipment is set up or adjusted to meet the requirements of another part. The degree of loss depends on factors such as:

Process standards
Level of equipment maintenance
Consistency and quality of tools
Operator skill level
Standardisation between machines

Idling and minor stops

Production is interrupted by a temporary malfunction or when the machine is idling. Contributing factors include:

Defective products leading to line stoppage
Interruption of production flow, lack of product or raw material, tooling
Dependence on assembly components or other inputs
Operator on another machine or other tasks
Temporary equipment breakdown

Start-up losses

This type of loss affecting the efficiency of a machine, is a loss of performance that occurs during the first stages of production: from machine start-up, warm-up, learning phase to the moment when the machine is producing regularly and with quality. The degree of loss depends on factors such as:

Equipment maintenance
Tooling
Raw materials
Operator skill level

Speed reduction losses

Refers to the difference between the design speed of the equipment and the actual operating speed. Some parts may not be able to operate at the maximum speed of a machine. Factors include:

Mechanical problems
Risk of producing unacceptable parts at higher speeds
Operator training

Quality defects (scrap and rework)

Other events affecting the efficiency of a machine are quality losses caused by malfunctioning of equipment or tooling. The degree of loss depends on factors such as:

Maintenance of equipment
Tooling
Raw materials
Operator skill level or compliance with SOPs

In order to minimise the six major losses in industrial processes, it is very useful to implement solutions of machine monitoring in industrial manufacturing.

Defining world-class machine efficiency (OEE)

The definition of "World Class" depends on several factors and the exact inputs for the calculation. World Class OEE is shown differently by many authors and companies. It is a relative value, as competition increases and expectations rise, the acceptable value for a "World Class" OEE is higher.

The most important thing when it comes to improving the efficiency of a machine is to use a consistent and standard definition and to include the equipment definition in the Data Collection Plan and in the Monitoring Plan. This applies to any metric definition for which there are different industry-accepted formulas.

But, like any metric, the efficiency of a machine must be defined with a clear understanding of the inputs, their meaning and the types of decisions they might trigger. Therefore, it must be ensured that the metrics will drive the best overall decisions.

There is no single metric that explains productivity, efficiency and rejection, but all three categories are wide-ranging and require clarity for an OEE value to provide information on the efficiency of a machine that is fair and meaningful.

How to establish the definition of machine efficiency?

It is very important that all stakeholders using the OEE metric know how it is calculated and what is included and excluded, to allow everyone to focus their efforts on improvements. It is therefore essential that the company or team defines the metric and maintains consistency.

Once defined, time should be spent educating stakeholders and asking them to do a couple of sample calculations to solidify their understanding.

When there is disagreement about the efficiency of a machine as defined, is at least good enough to provide a directional metric. This means that by measuring OEE consistently over time and across machines, you can tell whether the machine's OEE is getting better or worse, even if the number is extremely high or low relative to world class.

This is more important than trying to determine whether a % is good, bad, world-class, etc. The question is whether it is getting better or worse. efficiency of a machine.

In short, the efficiency of a machine consistently throughout the company and use it for directional purposes.

Which efficiency ranges of an industrial machine can be considered as suitable?

OEE and its straightforward percentages can be misleading. It is very rare that one metric can tell the whole story, no matter how comprehensive its formula may seem. A human element is always needed to check and balance the numbers.

In addition, it has to be considered that a lot of labour can be added which will probably improve the efficiency of a machine. It is important to improve one metric without sub-optimising others.

For example: If there are two machines that can run a particular part and assuming that the availability and quality are the same for each machine.

Availability: 93.75% (both run 7.5 hours out of 8 hours)

Quality: 90.00% (both make 10,000 pieces unplanned scrap + 90,000 pieces acceptable when making a total of 100,000 pieces)

It has to:

The ideal rate on MACHINE 1 is 200 parts/minute for that part.

The ideal rate on MACHINE 2 is 250 parts/minute for that part.

MACHINE 2 is newer and equipped with better technology, so it can produce the same parts faster without sacrificing quality levels.

Normally the part is always programmed on MACHINE 2 because it gets the same level of Quality and Availability and runs much faster than MACHINE 1.

Typical throughput for MACHINE 2 is 225 pieces/minute for a 450-minute (7.5-hour) run time, producing 101,250 pieces. However, if MACHINE 2 is full or down for repair that day, it is sent to MACHINE 1 to run.

During the same 450 minutes, MACHINE 1 produces a total of 87,750 parts, an average of 195 parts/minute.

Looking at the Performance percentages:

Yield MACHINE 1 = 87.750 / (200*450) = 97,5%

Yield MACHINE 2 = 101,250 / (250*450) = 90.0%

Now, calculating each OEE:

OEE MACHINE 1: 93.75% * 97.5% * 90.0% = 82.2%

OEE MACHINE 2: 93,75% * 90,0% * 90,0% = 75,9%

Does MACHINE 1 have a better OEE and the part should be produced there? No, because 195 parts/minute is not acceptable when it normally runs at 225 parts/minute on MACHINE 2 with the same Quality and Availability levels.

This is even more important when the company knows that this type of part must be produced at 225 pieces/minute, so any lower quantity will reduce the margin, assuming everything else remains constant.

One could use 250 pieces/minute as the ideal rate in the denominator when calculating the throughput of MACHINE 1, but then this would not really be the ideal rate. efficiency of the MACHINE 1.

The company should keep this part in MACHINE 2 and work to reduce speed losses in order to increase the level of efficiency of the MACHINE 1.

In other words, if the OEE measurement is forced too hard, it may incline operators and supervisors to simply run the parts on a machine with a slower maximum or ideal speed just to show a higher OEE.

Total Productive Maintenance (TPM) or better capacity planning should be used to get closer to the root cause of why the part could not be produced on MACHINE 2. These Key Process Input Variables (KPIV) are the inputs that a team must correct, prevent and control to improve the efficiency of a machine.

Discover other ways to calculating productivity through OEE: Best practices you can apply on the shop floor.