Process Simplification Process simplification is a basic concept, but is frequently over- looked by most. It is the idea of eliminating and simplifying steps in the production process. This is one of the most powerful variation reduction techniques you can employ.
Sustaining the Gains Sustaining gains is the concept that once a process improvement is achieved, the next step is to standardize it. Thus, we want to institutionalize the gains so they will be there forever. We then want to build on this gain. It is curious that almost everyone knows this, but almost no one does it, not even modestly. In my work with over 200 companies, I can’t give you one example of any company that does this well.
thereby make the process more robust. Poka-yokes are also used in the inspection pro- cess to achieve 100 percent inspection. There are two types of inspection poka-yokes:
those that control—that is, shut down—the process or isolate the product upon finding a defect; and those that warn the operator via an andon.
5 Whys 5 Whys is the cornerstone of the TPS problem solving effort. The “5 Why”
technique is simple enough in concept. However, it will not work unless those using this technique have both expertise and experience in the problem area. They must fully understand the cause-effect relationships to utilize this seemingly simple technique.
The check on the “5 Whys” is the “Therefore” technique.
Kaizen Kaizen is the concept of improving a process by a series of small continu- ous steps. Often times these improvements are small and hard to measure, how- ever the accumulated effect is significant. Over the years, kaizen has evolved to mean improvement.
CIP CIP stands for Continuous Improvement Process or Philosophy. Many can talk about it, but few can show a process flow chart for their CIP, and even fewer can ade- quately measure it. An example of a Continuous Improvement flow chart is shown in Fig. 4-1. In addition, the Toyota Production System advocates the concept of yokoten, which concerns extending the process improvements to other locations, as well as other similar applications, as part of CIP.
The JIT Pillar
Takt Takt is the design process cycle time to match the customer’s demand, normal- ized to your production schedule. It is the key calculation used when we synchronize supply to the customer. Takt is calculated by dividing the available work time by the product demand. The system is then designed to produce the product at this rate. If we produce at a cycle time higher than takt (hence, under-produce) we will not be able to supply the customer demand. If, however, we produce at a cycle time lower than takt (overproduce), we will either increase inventory or idle the line to stop the overproduc- tion. Both of these are wastes—recall that the #1 waste is the waste of overproduction.
For example, if we run our operation using two 10-hour shifts with a 30-minute lunch break and two 15-minute breaks each shift, and run five days per week, holidays included, and need to produce 500,000 units per year, our takt would be: {(365 – [52 × 2]) × (2× [10 – 1]) × 60)}/500,000 = 0.56 minutes or about 34 seconds. That is, to stay in step with the customer’s demand, considering our work schedule, we will need to produce one salable unit every 34 seconds. Consequently, since there are losses, our production cycle time will need to be shorter. For example, if OEE was 0.80, a production cycle time of about 27 seconds (0.8 × 34 seconds) would be required.
Balanced Operations Balanced operations are a simple industrial engineering technique to have all operation steps—of a cell, for example—operating with the same cycle time.
It is the first step in synchronizing the internal production. This technique, not unique to Lean Manufacturing at all, is designed to avoid the waste of waiting. However, this technique places a large emphasis on the ability to standardize operations so we can avoid variation in the process. If any step in a process has high variation, that step will naturally unbalance the entire line or cell.
A Continuous Improvement Methodology
0 10 20 30 40 50 60 70 80 90 100 (How to improve a process of n steps)
Step one Collect data for the process
Top five problems Qty Defect A Defect B Defect C Defect D Defect E
58 33 14 11 6
Step two Create Pareto analysis to prioritize problems
Continuous process problems Pareto analysis Jan-Mar
Count Percent
Total count = 122
0 13 26 39 52 65 78 91 104 117 130
(48%) 33 (75%)
14 (86%)
Defect-D
Defect-C
Defect-B
Defect-A Defect-E
11 (95%)
6
RIC 2S40 M3 1ER TURNO, PARAMETRO
0 10000 20000 30000 40000 50000 60000
PPM AVG =
0.019103 UCL
3/2/92 4/2/92 5/2/92
Step three Monitor top defect using a control chart
Defect A Material Manpower Measurement
Method
Machine
Gauge R & R Calibration
Maintenance Lubrication
Step four If cause is unknown perform a cause and effect analysis to identify root cause of the defect and fix it
Diode holder Width-INS
AVERAGES 1.47151.4725
1.4735 1.4745 1.4755 1.4765
AVG = 1.4740 LCL = 1.4718 UCL = 1.4763
RANGES
0.0000 0.0015 0.0030 0.0045 0.0060 0.0075
LCL = 0.0000 UCL = 0.0071 RBAR = 0.0031
123 45
67 89
1011 1213
1415 1617
1819 20 Step five
Standardize the fix using an Xbar R chart to control key process parameters
and modify PNCP Step six
Confirm that FTY has increased and the solution is standardized and effective.
If so, return to Step One and continue the process
Raw mat’l Oper 1 Oper 2 Oper n Final
product
Operation
84 86 88 90 92 94
1 2 3 4 5 6 7 8
FTY %
First time yield
Weeks
FIGURE 4-1 Continuous improvement fl ow char t.
Pull Pull systems are production systems that are designed to minimize overproduction, the most grievous of the wastes. Pull systems have two characteristics.
• They have a maximum inventory volume—for example, when using a kanban system.
• Production is initiated only by a signal from the customer, and that only occurs when some inventory has been consumed.
A pull system is one in which the customer, the next step in the process, removes some product that then is the signal for the upstream step to produce. For example, for some reason the finished goods inventory of our customer is full and the entire comple- ment of kanban cards are attached to the finished goods in the storehouse. Since kanban cards are the signal to produce, and they are all attached to the finished goods, produc- tion has stopped. Hence, our overproduction is limited to whatever we have in finished goods for the cycle stock, buffer stock, and safety stock. However, when our customer arrives and withdraws product, then the kanban cards are removed and circulated back to the production cell, signaling that production is authorized to begin. Once it starts production, the cell will produce only that volume dictated by the kanban, and these finished goods will then be placed in inventory. This process of replacing the inventory that was withdrawn is specifically named replenishment.
A manufacturing system with a limit on the maximum inventory, and production based on replenishment, is the essence of a pull system. The opposite of a pull system is a push system. In a push system, there is no maximum inventory, the downstream process produces until it is told not to, usually by the scheduler. It then pushes that product onto the next step whether the next step needs the production or not. Hence, on the production floor, there is no maximum control on the WIP, so WIP can grow uncontrollably. With this uncontrolled growth of WIP, lead time will grow, with resul- tant quality, delivery, and cost problems escalating.
Minimum Lot Size Minimum lot size is a means to reduce lead times. By reducing pro- duction lot size and transfer lot sizes, the process proceeds much faster. Two benefits are achieved. First, we reduce the lead time for the first piece through the process. This benefit is usually felt in quality responsiveness. If the first piece lead time is reduced, and there is a problem with the product, this information is fed back to the problematic station more quickly. The problem can be resolved more quickly, and if rework is required, fewer items will need to be reworked. (For a dramatic example of this effect, see Chap. 15’s discussion of the Bravo Line.) The second benefit is that the overall prod- uct will be completed more quickly, reducing production lead time for the lot. Mini- mum lot size, with the ultimate being “one-piece flow,” is the key to plant flexibility and product supply responsiveness.
Flow Flow is the concept that parts and subassemblies do not stop except to be pro- cessed, and then only for value-added work. It is more of a concept to be attained than a reality. It is the primary tool used to reduce production lead time. The typical tech- nique is to design the process so that as little inventory as possible exists at each work station, and the work stations are synchronized as close as practical. The design ideal is a multistation cell with no inventory between work stations. The ideal state we seek is one-piece flow with 100 percent value-added work only. This ideal state is frequently not possible, at least initially, because there are obstacles to flow. (The Seven Obstacles
to Flow are detailed in Chap. 5, with a case study in Chap. 15.) For example, let’s review a process running multiple products in which one of the steps is a large machine, say a press, that must undergo changeovers between production runs. To avoid stopping the process during a changeover, a buffer is built up both before and after the machine, so the rest of the production process can continue to run while the press is undergoing the changeover.
All the items in these buffers will arrive “too early” to be just in time. However, considering all the options, creating a buffer is the least-waste-generating choice for the process, so it was selected. This does not create the ideal system but it is the eco- nomically practical answer. In every case, if it is not currently possible to eliminate all inventory in a process, then the next best solution is to design a system with the min- imum amount of inventory. The amount is calculated, and posted at the work station as a maximum. Whenever the upstream process has produced that maximum volume of inventory, the upstream process must stop production to avoid the waste of over- production. Kanban is just one system that is used to avoid overproduction. Most other systems used to minimize inventory are based on limiting the physical storage space that the parts may occupy. This is simple and creates a very good visual man- agement tool.
Lead-Time Reductions Lead-time reductions are the essence of waste reduction in Lean.
They give the process both the maximum flexibility and maximum responsiveness to changes; especially changes in demand either in quantity or model mix. Read about lead-time reductions in Chap. 5, with a specific case study in Chap. 15, which shows how you can break through the obstacles to flow and significantly reduce lead time.
Leveling Leveling is spoken of in two terms. First, leveling is the concept to maintain a consistent nonvariant rate of production over time. It is also a waste reduction tech- nique called model-mix leveling, that calls for the simultaneous production of multiple products, or models of a product, from a given production line. To do otherwise is to create a batch in the system. We have already stated that Lean is a batch destruction technique. In a perfect world, we should level production to the individual production unit level. In practice, this often is not practical and sometimes not desirable. Conse- quently, we will frequently level based on the packaging requirements. That is, if we package 60 units in one carton, we will run 60 of that model and then switch production to another model. For example, if a certain manufacturer produces 50 models of a given product, all in equal volume, and he has the ability to run all 50 models, one piece at a time, it would be easy to implement perfect model-mix leveling. However, let’s say he packages 60 units to a box and the cycle time is 30 seconds, so it takes 30 minutes to fill a box. If this operation is run with perfect leveling, then at the packaging station there are 50 boxes being simultaneously filled, and every 25 hours a large batch of finished goods needs to be transported. If, however, the process is leveled so that one box is run at a time—this is called a “pitch”—then there is only one box at a time being filled. Quite frankly, this system of producing one pitch at a time makes the downstream handling more “level” and also makes the kanban system much easier to use. Considering the cur- rent conditions, leveling to a pitch is normally the optimum for any Lean system.
Kanban Kanban is the revolutionary practice of using cards, for example, to smooth flow and create pull in a Lean system. It is also a continuous improvement tool. The cards represent and account for all the inventory in the system. By controlling the
number of kanban cards, we control the inventory. Kanban is a technique used to control inventory, minimize overproduction and facilitate flow. The kanban cards are used to trigger replenishment. This will make the system more responsive to customer demand and shorten lead times because the signal comes directly from the customer and trig- gers replenishment. For a kanban system to be effective, all kanban rules must be rigor- ously followed. The Six Rules of Kanban, from Toyota Production System, Beyond Large-Scale Production (Productivity Press, 1988), are:
• Later process picks up the number of items indicated by the kanban at the earlier process.
• Earlier process produces items in a quantity and sequence indicated by the kanban.
• No items are made or transported without a kanban.
• Always attach a kanban to the goods.
• Defective products are not sent on to the subsequent process. The result is 100 percent defect-free goods.
• Reducing the number of kanban increases their sensitivity.
Cells Cells are work areas that are arranged so the processing steps are immediately adjacent to one another. This lets parts be processed in near-continuous flow either in very small batches or in a one-piece flow. This, in turn, allows minimization of the wastes of transportation and inventory—in this case, WIP (work in process). The most common shape is the “Inside U” cell. This cell minimizes walking distance when stand- ing operators are used. Cells have some natural advantages over the classic assembly line. First, the ability to use people for more than one activity in a cell allows the control of demand variations by staffing differently. For example, if a six-person cell were to cut production by 50 percent, it is commonplace to then staff the cell with only three people and have each person work two stations. This, of course, requires worker cross-training, but that is a staple of Lean Manufacturing. Second, cells are much more flexible. For example, in place of a 20-person assembly line, if we use four- to five-person cells we have a much greater model-mix capability without creating large batches and without having large time losses due to changeovers. But the coolest aspect of cells is that, although it is a very well kept secret, cells can be a natural variation reduction device.
Cells are a very interesting topic, see Chap. 13, Cellular Manufacturing for more details on cells.
SMED/OTS SMED/OTS stands for Single Minute Exchange of Dies and One Touch Setups. SMED technology is a science developed by Shigeo Shingo and is designed to reduce changeover times. The problem is simple. Any machine that has long change- over times must have an excess capacity to account for the downtime of the changeover.
Furthermore, to supply the rest of the downstream process during the changeover, a large batch must be stored up. Any effort to reduce the changeover times also reduces these two forms of waste: excess capitalization and overproduction. (“Single minute”
means a single digit number of minutes that is less than 10.) In actuality, the objective is to reduce the changeover time as much as possible. In some refined cases, the change- over is handled by having multiple fixtures on the same basic machine, and by simply throwing a switch the changeover is made. This is called One Touch Setups (OTS), or
sometimes One Touch Exchange of Dies (OTED). In his writing, Ohno refers to three basic elements of JIT. They are pull systems, operating at takt time with continuous flow.
Those may be the big three but JIT is seldom practical without some application of SMED technology. It is a major batch destruction technique. The basic procedure of SMED is simple, it is a three-stage process:
1. Separate internal from external setup 2. Convert internal setup to external setup 3. Streamline all aspects of the setup operation
When a SMED application is first undertaken, we have found the best tool is the simple Gantt chart, showing all the steps in the changeover. Gather the knowledgeable people on the changeover, and then list all the changeover steps. Categorize them as internal setup, external setup, or internal but can be external; also list the conditions to make it external setup.
This is the basic starting point. From here you delete any unnecessary steps and simplify any steps you can. Next, you convert as much internal setup into external setup so it can be done with the machine running. With only internal work left, the technique is generally to create as many parallel paths as possible. At this point, you can get involved with intermediate and holding jigs, automatic adjustments, and a huge volume of imaginative approaches to shorten the changeover time.
SMED and poka-yokes are two of the Lean techniques that are truly for the imagina- tive. This combination is a powerful set of tools to use as we reduce lead times and more fully utilize our processing equipment,
Much has been made of making a video of a changeover. I support this and have found it to be useful, but generally it is best to do it after you have applied SMED tech- niques at least once. The reason is this: When you apply SMED, the entire process will change, so it is not very worthwhile to view the old process. You will get some minor improvement ideas, but the majority of the ideas come from the development of the Gantt chart referred to earlier. However, there is one large benefit to be gained from making a video: Watching the old technique is usually humbling if not downright funny, and feeling a little humility as well as a good laugh are both good for the soul. At any rate, doing a video is easier than it used to be, so I do not discourage it completely.
The application of SMED technology is a key batch destruction technique and should not be underestimated in terms of its potential. It is one of the major efforts that must be undertaken if Lean is your objective. For further study, I suggest you go directly to the author of the tactic, Shigeo Shingo. He has written two major books. One is A Revolution in Manufacturing: The SMED System, (Productivity Press, 1985), his landmark book on the topic. In his other book, A Study of the Toyota Production System, (Productivity Press, 1989), he expanded his coverage on parts of his SMED system. He has refined his three stages into eight techniques. It is good reading for the Lean professional.
Cycle, Buffer, and Safety Stocks Cycle, Buffer, and Safety Stocks is the three-fold approach to inventory management used in Lean Manufacturing. Each of the three types of stock is calculated and marked separately. The common way to separate the stocks is to use color-coded kanban. For example, white cards are used for cycle, yellow for buffer, and orange for safety stocks. Red is normally reserved for emergency runs.
Consequently, when a colored kanban shows up at the heijunka board, the production