Flow
Value Stream Mapping
Description
Value stream mapping is a qualitative and quantitive tool that describes in detail how a process operates. It forms part of the 5 principles of lean.When should it be used?
Value stream mapping should be used to help visualise an entire process flow to enable understanding and analysis.What will you get?
. Linkages between activities and information.
. Identification of value added and non value added activities.
. Identification of all associated documentation.
. Opportunities for improvement.
. Apparent decision points within the flow.
. Quantitive analysis which enables identification of the opportunity and
provides input to the business case for change.
The process
. Identify the steps within the process.
. Layout the process clearly, for example, on brown paper.
. Draw linkages within the process.
. Identify linkages to other areas.
. Obtain example documentation.
. Add metrics, for example, timings, capacity, changeover time, delays,
inventories etc.
. Flag opportunities and weaknesses.
. Establish value added vs. non - value added.
. Value stream mapping identifies the information and material flows and
demonstrates how one flow interacts with another.
. The basic premise should be to make exactly what the next step in the process
requires, just when it needs it.
. This principle is often called just-in-time (JIT).
. It is worth noting that JIT requires the correct timing and the correct quantity.
. Mapping 'AS - IS' allows identification of ideas and consideration of limitations
from the current state will help develop the future state.
. The 'TO - BE' map may encourage further criticism of the current state and
hence further improvements.
. These activities may be done currently.
Description
Kanban describes the way in which work is 'pulled' on demand internally within a production or assembly operation or externally from a plant or supplier. It involves the use of signals (usually simple) as a means of instructing work to take place. As a result it regulates the flow of activities within a process.When should it be used?
Kanban is able to be used in lots of different environments although it lends itself to repetitive production. However, kanban has evolved in its complexity and different types of kanban can meet most needs. The different types of kanban are too many to describe in detail in this guide but include: single card, product, generic, signal, dual card and move.What will you get?
. Immediate alignment of customer demand with supply/production.
. Regulation of stock i.e. production stops when set levels have been reached.
. Facilitation of stock reduction.
. Clear the use of stock as a tool to buffer against variability.
The process
. Determine the process(es) to which kanban is to be applied.
. Establish the most appropriate type of kanban.
. Calculate the number of kanban cards and size.
. Train staff in the rules of kanban.
. Implement and monitor.
. Refine.
Description
Takt time is known as "Beat Time" or the "Drum Beat". Lean production uses takt time as the rate or time at which a product is completed. If the takt time is 5 minutes, every 5 minutes a complete product is output from the end of its production line.When should it be used?
Takt time should be used with lean operations projects is classed as a fundamental part in the planning process, cell balancing and facility design. It must take into account available work time and should plan for maintenance stoppages and shift patterns.What will you get?
Takt time will allow you to synchronise processes to avoid bottlenecks and meet customer demand.The process
. Calculate demand (what your typical customer requirements are every
day/week/month).
. Calculate available work time (taking into account shift patterns and
stoppages etc.
. Calculate the takt time
= Available time
Customer demand
For example, if a customer requires 100 units per day, the takt time = 7.5 hours 100 units
= 7.5 hours x 60 minutes 100 units
Giving a takt time of 1 product output = 4.5 minutes
. Compare current operator cycle time against the takt time.
. Identify steps to re-balance work and adjust processes to assist the avoidance
of work build up or waste due to waiting.
. Inputs received to carry out work should be considered and steps taken to
adjust these to match the takt time.
. Recalculate takt time on a regular basis to ensure current circumstances are
reflected, and adjust manning levels accordingly.
Description
Demand smoothing aims to resolve the problems caused by variation and uncertainty in demand, such as reduced customer service, excessive inventory, unnecessary costs - often referred to as the Forrester or Bullwhip effect.It achieves this by analysing the support chain and applying different techniques to balance supply and demand. Techniques include: improved communication between elements of the support chain (e.g. very often problems result from lack of understanding), common visibility of information (e.g. a shared IT system) improved planning and scheduling.
When should it be used?
It should be used where there is variation and uncertainty in demand within the support chain. Typically this will be exhibited by the symptoms that are inverse of the benefits detailed in the following section.The process
. Measure demand variation, discuss it and make individuals responsible for
variation.
. Encourage suppliers to work towards a regular flow of goods/services to reduce
uncertainty.
. Reduce variation in the work as much as possible.
. Use buffering if appropriate.
. Communicate along the supply chain to share information and agree a common
takt time (see page 58).
. Give priority to regular work rather than same or lower priority one-off tasks.
Description
Lean manufacturing involves the elimination of waste, and identification of value: The process flow analysis is one way of looking in detail at a particular value stream in order to ascertain waste that occurs within a process. The process flow charting methodology is well known, initially founded by the American Society of Mechanical Engineers (ASME).When should it be used?
Many organisations will already have process charts, but it is often a good idea to review them with some scepticism. There are often major differences between the "official" charts and the activity that occurs in the "real world". The process chart helps to identify wasteful actions, and documents the process completely.What will you get?
From the "real world" process map the following information is available:-
. The proportion of value adding time
. The time split between different activities
. Highlight immediate problems
. Identify, via Pareto analysis, the areas of greatest opportunity record or
benchmark the current status
The process
A component or suchlike is identified and tracked through the process. As the component progresses the type of activity that occurs to it will change. This is captured via a series of symbols shown below.Process step Information required
Operation Process time, quantity processed
Inspection Inspection time, quantity inspected
Formal store No of parts, time in storage
Transport Move quantity, distance, equipment
Delay Stored quantity, equipment, time of delay
Decision Consequence of decision
The symbols give a good visual representation of the value (Green) against the waste (Red) symbols. In addition data and information at each symbol should be captured, in order to fully analyse the process in more detail to understand where specific improvements can be made.
A process map is a 'snapshot' of activity at a moment in time. Figures recorded at each step should be as observed at the time of data collection.
Once completed a process can be improved by using the 5 Why tool at each process step. The non value steps should be eliminated, combined or reduced to allow a process with better flow and more value to be developed.
Description
Lean drives towards continuous flow, which only happens when parts are processed one at a time. Do not confuse batch size of one with one piece flow. Any batch size can be processed one at a time in a properly designed cell.When should it be used?
Wherever there is flow. Some processes are not practical to flow one by one, such as heat treatment or plating, but consideration should be given to combining several small batches into one for a common treatment specification.It is a major advantage in areas of poor quality because it avoids overproduction of inferior product, whether it is recoverable or not.
What will you get?
. Quickest possible feedback when there is a quality problem.
. Visibility of flow problems
. Awareness of problem potential
. Avoidance of waste, provided the operators are empowered
(to stop work when quality is a risk)
The process
. Design the cell.
. Agree the Work combination.
. Make handover points visible.
. Give the operators the authority to stop production when the handover
point is not available because the downstream process has not taken
the previous part.
. Strive for smaller batch sizes by focusing on quicker changeovers.
This photograph shows an operator placing a part in a handover jig. It serves to prevent overproduction (visual management of WIP) and to highlight a downstream problem.
Description
A major part of a lean operation is its ability to make only that which the customer wants, at the shortest possible notice without holding finished goods stock. This is achieved by pulling parts through on demand, rather than pushing them through to a schedule. Simple in concept, but the transition can be traumatic if a structured implementation is not adhered to, particularly the communication of how to use the signals.When should it be used?
The technique should be used in cells where there is flow of product with a history of high stock level or redundant stock. It is applied to any product made on a regular basis in a cell designed for one piece flow.What will you get?
. Low stocks for runners and repeaters
. Minimum throughput time
. Control of schedules
The Process
. Establish the true data for supplier lead time, queue time and batch size
. Determine the mean rate of demand
. Calculate the size of each colour zone
. Apply the colour zones to the physical stock area
. Train the operators and material handlers in the operational rules of the
pull system.
Description
Correct cell design will transform the performance of any business. It is the lean ingredient which will remove the opportunity for waste (excess cost) at the point of adding value to the product.When should it be used?
Whenever products can be grouped by similar process with a common benefit of improved flow and/or reduced stock or effort. In other words almost anywhere apart from jobbing shops, where period flow control is used instead.What will you get?
The result is a cell which can produce product in the minimum time for any given batch size, with the minimum amount of stock and the fewest man hours involvement.It will also give ownership to the cell occupants and control over their day to day tasking. This will engender an attitude for continuous improvement - essential in a competitive market.
The Process
First you must identify the product families. These will come from strategic analysis (determining the core business) and matrix analysis (determining the part family groupings). Consideration must be given to process flows, customer interest, capacity bottlenecks, current waste, material commonality, people skills, cost of stock and many others.
. All tasks must be timed and distances travelled measured.
. A Value Stream Map would be a big help for this too.
. Determine which product(s) occupy the majority of the cell time.
. Calculate the capacity of the cell and ensure it meets the requirements of
the forecast.
. Add parts to the cell which follow the same route (or could follow it with
process sequence changes).
. Lay the cell plant out in cardboard on the shopfloor.
. Test the process routes and process actions using the operators.
. Make the necessary changes to layout, processes, plant, and then
implement it.
Description
String diagrams can determine the flow of products, material handling, vehicles or movement of people during changeover or maintenance processes.When should it be used?
The string diagram should be used when the most efficient route or flow needs to be established.What will you get?
A layout diagram that traces the flow of the product in question, calculating the length of flow between points.The process
In the example below, a high percentage of the distance travelled is non-value added and found in two areas. The first, being the requirement for the technician to walk from the bay to the SNCO office (other side of the building) to ask for an SNCO check. An SNCO check is an inspection or measurement carried out by the SNCO at set stages in the build process. The number of SNCO checks runs well into double figures for the whole build process. The distance is compounded due to the requirement for the SNCO to then walk to the bay to make the check before returning to his office. Distance travelled can be reduced considerably for both the technician and the SNCO by relocating the SNCO into another office within the centre of the strip and build area on the shop floor. The second being, the requirement for the technician to walk a module reject slip up to the docks cell every time a module is rejected in the strip process, and to collect a module build slip every time a replacement module is required for the build process. This non valued added activity can be eliminated by utilising the internal IT system where module rejection slips are e-mailed to the dock cell and the dock cell issue module build slips at the request of the shop floor.