What are Loss Trees?
In general, Loss Trees are simply a listing of the losses (inefficiencies) which may exist in a factory production process. Loss Deployment is a cascade process that looks initially at the overall factory losses than increasingly at a more detail level down to a packing line or a single machine item.
Traditionally the initial TPM approach is to consider the 6-8 Equipment Losses.
With the addition of more loss categories, such as Management Losses the total number of losses can potentially increase to 20 or more.
These can be divided into 4 sub groups:
- Six major losses that reduce equipment effectiveness (see below)
- Losses that can impede machine reliability (Shut down losses e.g. planned stops)
- Man Losses – Four major losses which impede mans efficiency
- Management losses, (Lack of instructions/awaiting materials or Training/meetings);
- Operating Motion (Incorrect or missing procedures);
- Line organization (layout, ergonomics), Logistics (Poor efficiency materials supply etc)
- Measurement & adjustment (quality monitoring losses)
- Three Losses which can impede the effective use of production resources
- Yield, Energy and Die-Jig losses
Six Major Losses
Loss Type and Definition
Equipment Failure and Breakdown; Time of Unexpected losses over 10 minutes
Breakdowns (Mechanical & electrical failures) requiring or part or repair. Loss of Services (power etc.); Deterioration of a machine function requiring replacement of parts or repair.
Changeovers (Set-Up & Loss Adjustments), Time lost resulting from changeovers.
Size, product changeovers, machine cleaning; Including adjustments and changes to reach full speed.
Start-up losses; Time elapsed until operational conditions are achieved.
Time to start equipment at the beginning of the week; After periodic maintenance, meal breaks, holidays etc.; Including machine loading/unloading.
Minor Stoppages; Stoppage of less than 10 minutes
Stoppages caused by temporary problems eg. clearance of blockage (pack or material feed) not requiring parts change including minor stops for cleaning.
Speed Losses (Reduction); Caused by Equipment operating at reduced speed
Difference between design and actual speed reduction due to packing material or product issues; Temporary/permanent machine difficulties.
Quality Defects & Rework; Machine defects leading to out of specification product.
Product not right first time for physical quality problem which needs re-handling or reworking and the time for this.
One way of representing these major losses which gives a good overview of a factory performance is in a bar chart format as shown below. The losses may be represented as time, percentages or preferably as capacity (e.g. Tonnes) loss:
The Loss Trees for the Manufacturing (Make) process can be extended to include the Supply Chain, materials (Source) and service (Delivery). More losses can be added in addition to the above 6 major losses:
- Material Failure (Time Lost as a result of material quality failure),
- No demand plan (Time lost due to no orders etc),
- Trails & Testing (Time lost for set up and running trials),
- Plan Loss (Due to error in material/production planning),
- Source (Time lost waiting delivery of materials),
- Delivery Loss (Waiting for finished stock to be transported to Customer),
- Yield – Mass Balance (Total material variability from zero base line),
- Give-away (Product lost through weight control or Waste disposal),
- Service Energy Loss (Cost of Water/steam/electricity wastage),
- Indirect (Cost of support including people, materials, TPM support etc).
The preferred way of arranging and reporting these losses or their equivalent KPIs is via the
P Q C D S M I Structure:
- Productivity (eg. OE/equipment losses),
- Quality (eg. Rework/Defects),
- Cost (eg. Raw Material waste),
- Delivery (eg. Logistics losses),
- Safety (eg. Accidents Time loss),
- Morale (eg. TPM & other training),
- Innovation (eg. non vertical start-up).
When to use Loss Deployment?
Loss deployment in particular the six main losses are a cornerstone within the TPM culture and are applied to give understanding of equipment operational inefficiencies and the hence priorities for of focussed improvement activities which use problem solving tools such as the Ishikawa (4Ms) diagram to reduce losses.
The six big losses should be an integral part of the Factory Performance Benchmarking Process. The sixteen major losses are used in the wider calculation of Overall Equipment Effectiveness (OEE).
As part of the continuous improvement of the Benchmarking Process, loss-based K.P.I.s should be increasingly used. A core set of K.P.I.s and the corresponding Loss Tree will form part of the common measures needed for the successful implementation and operation of your site.