6.6 Control Mechanisms in Operative Management
6.6.1 Occurrence of an Planned Activity or Unplanned Event
Limiting the occurrence and duration of known material-waste-causing activities or operating states presents one lever to reduce material waste.
The feasibility of limiting the occurrence frequency of material waste activities and the extent to which factory management has authority to do so
needs to be examined on a class-by-class basis. For that reason, both planned activities, namely activities that are a result of proactive operative decision-making, and unplanned activities, which occur due to an unintentional change in system parameters or reactive efforts to counteract these activities or operating states, are examined in the following section.
The piece-processing or machine batch interval (planned activity, work state): Waste occurring when processing a single workpiece in a machine or in a fixed machine batch size can be is described as occurring every piece interval or batch interval respectively. Under ideal conditions, the accumulated material waste is proportional to the production volume. The piece interval is assumed rigid, in that, it cannot be changed by changing the total production volume (throughput) of the factory, and it is beyond the authority of OM to refuse production orders. However, by avoiding overproduction, piece-processing activities can also be avoided. Similarly, by avoiding defects, repeating the piece processing to replace or repair parts is avoided.
The stock-material processing interval (planned activity, work state):
Material waste in the stock-material cycle, describes material waste occurring with every raw material unit that is processed in the factory, and regardless of the number of parts that are ordered. Examples include the ends of coils or trim loss from the cutting of stock-sheets. Depending on the cutting technology and process specifications, it may be possible to make the occurrence of trim loss less frequent by using larger stock units (e.g. longer coils).
Setup interval: Assuming customer orders can be filled from a finished goods warehouse, warehouse costs and capital lock-up are negligible, and the product is not subject to deterioration, setups on multiproduct machines can be performed at low frequencies by bundling multiple orders to large lots.
before, during or after a setup activity. Examples include startup and shutoff losses, discarded auxiliary material, and cleaning solvent consumption.
Maintenance intervals (planned activity, preventative maintenance state): Maintenance cycle waste describes the materials that are used by maintenance staff during routine maintenance activities, including lubricants and cleaning solvents, as well as the shutdown losses (process defects) occurring when the machine is prepared for maintenance. Bundling the maintenance activities and performing all maintenance jobs for one workstation at once reduces the frequency of maintenance-related shutdowns.
Transport intervals (planned activity, peripheral module): Waste linked with the transport-cycle describes the lump-sum waste with the transport of a set of parts, which may not be proportional to the number of pieces or batches produced. Loading more pieces on transport vehicles would reduce the frequency of transport activities. Depending on the distances travelled and the organization type, multiple handling activities may occur between two successive workstations. Reducing these activities can be achieved through organizational (e.g. suppliers deliver directly to shop floor) and technological changes (e.g. direct conveyors to point of use).
Destructive testing intervals (planned activity, peripheral module):
Material loss linked with the test cycle describes the material destroyed in destructive testing. As destructive testing is assumed to be a strategic decision, this form of material loss is fixed for a given production system. Management can merely avoid unnecessary testing by limiting overproduction.
Housekeeping intervals (planned activity, peripheral module): The housekeeping cycle describes waste that occurs when tidying up a work station as a part of a daily housekeeping routine, and therefore may consist of cleaning solvents and any materials that are to be discarded at the end of the shift (open paint containers). Cleaning activities can be avoided by preventing waste from occurring e.g. through closing doors and following handling procedures to
prevent spills, as well as encouraging cleaning only in certain times, when enough dirt has collected to warrant the use of cleaning materials.
Machine breakdown interval (unplanned event, error state): The machine breakdown cycle describes how frequently the main process module falls into an error state, causing out of range process parameters and causing material waste to occur. Mean time to failure (MTTF) is a key performance indicator describing the error-free runtime (time in work-state) that can be achieved before entering an error state. A number of maintenance strategies can be utilized to lengthen the mean time to failure, including more frequent and extensive preventative maintenance activities and lessened machine loading, though constraints of the machine system, including its age and the current production load, prevent measurable gains.
Machine idling intervals (unplanned event, idle state): As shown in Figure 38, machine idling occurs for a variety of reasons. In linked workstations working in one-piece flow, short “starved” or “blocked” periods can occur in every tact. Idling due to starving or blocking can be prevented by ensuring a minimum buffer level and not limiting the maximum level, respectively. Preventative maintenance for machine feeding technology or awareness training for employees can help prevent starving conditions. Lack of orders can be remedied by ensuring a minimum number of orders are available in the queue.
Material aging (unplanned activity, peripheral module): Material aging describes instances of exceeding the material lifetime within a manufacturing facility. Instances of material aging in the factory occur less frequently if employees are adequately trained to maintain cutting-fluid systems, and the influence of external factors, e.g. contaminants, is limited. Limiting the holding time of deteriorating or fashion goods reduces the risk of waste.
Material mishandling (unplanned activity, peripheral module): Inventory
aging), can be prevented through staffing and qualifying employees, enforcing standard work procedures, and limiting the transport or storage of goods under suboptimal conditions.
6.6.1.1 Potential for Limiting Waste-Causing Activities in the Factory
Based on the evaluation criteria described in 6.6, the perceived potential for activity avoidance shown in Table 16, along with the waste forms that generally are triggered by the occurrence of these activities or operating states.
While avoiding overproduction is within the authority of factory management, reducing the number of workpieces processed below customer demand is not possible, therefore the potential, especially in contract manufacturing is low.
Processing machine batches can be limited by making sure the batch container (e.g. a paint shop rack) is full and avoiding over production of batches;
however, undercutting the minimum number of batches necessary to produce the customer demand may not occur. Therefore the potential for avoidance is also estimated to be low.
The setup interval presents comparatively high potential to reduce material waste, though potential trade off with inventory deterioration and sluggishness of the system cannot be disregarded. Manufacturers are free in setting maintenance intervals, though undercutting a lower limit leads to increased risk of breakdown and quality defects. While a minimum number of transport activities are required, multiple touches regularly occur between value-adding processes. Therefore, avoiding transport activities presents an opportunity for many manufacturers. Similarly avoiding idling states presents an opportunity within the authority of OM, because idling can be through increasing inventory levels in many cases. The likelihood of inventory deterioration can be avoided by using a fitting dispatch policy (FIFO or LIFO), reducing inventory levels and consequentially the material holding time.
Comparing the potential to avoid material-waste-causing activities with the material waste intensity of these activities (based on the number of waste forms, the certainty of their occurrence, and typical quantities), setups present the most opportunity for improvement. Setups are one of the most waste-producing processes in injection molding and paint shop processes, and one of the few intervals defined by decision-makers in the factory. The occurrence of destructive testing is an example outside of the authority of operative decision makers.
Table 16: Waste prevention through activity occurrence avoidance
Tactics Addressed activity and
linked waste forms
Scope of material savings Feasibility within operative decision- making
Planned activity intervals
Avoid workpiece processing:
- Defect avoidance - Avoiding overproduction
- Better utilization of batch containers (e.g. paint racks)
Workpiece processing or batch processing: defects, trim loss, chips, byproducts, aux., cutting fluids, cleaning materials, lubricants
◐ ◔
Avoid material unit replenishment:
- Larger stock units (e.g. longer coils)
Material unit replenishment:
trim loss ◔ ◔
Avoid setups:
- Bundling orders/ larger lots
Setups: defects, cleaners,
auxiliary materials ◐ ◕
Avoid maintenance activities:
- Bundling activities Maintenance: lubricants ◔ ◐
Avoiding storage:
- Immediately processing/ inventory reduction
Storage: intermediate
packaging ◔ ◐
Avoiding transport:
- Loading more pieces on vehicles - Avoiding excessive handling
Transport: transport loss ◔ ◐
Avoiding destructive testing:
- Avoiding overproduction
Destructive testing: defects
(startup/ shut-off) ● ◔
Avoiding housekeeping:
- Prevent spills and messes
- Clean only at management designated times
Housekeeping: cleaning materials, auxiliary materials
◐ ◕
Unplanned activity intervals
Avoiding machine breakdowns:
- Preventative maintenance - Reduced loading
Machine breakdown:
defects (startup/shut-off) ◐ ◐
Avoiding machine idling:
- Higher inventory levels (decoupling) - Preventative maintenance on feeder technologies
- Employee awareness training
Machine idling: defects
(startup/shut-off) ◔ ●
Avoiding material aging:
- Limit holding times - Employee qualification
Material aging: inventory shrinkage, closed loop operating materials, auxiliary materials
◐ ◐
Avoiding mishandling:
- Employee awareness and safety training
Mishandling: inventory
shrinkage ● ◐
Total score ◐ ◐