Lean Thinking and Methods: Total Productive Maintenance (TPM)
Total Productive Maintenance (TPM) seeks to engage all levels and functions in an organization to maximize the overall effectiveness of production equipment. This method further tunes up existing processes and equipment by reducing mistakes and accidents. Whereas maintenance departments are the traditional center of preventive maintenance programs, TPM seeks to involve workers in all departments and levels, from the plant-floor to senior executives, to ensure effective equipment operation.
Autonomous maintenance, a key aspect of TPM, trains and focuses workers to take care of the equipment and machines with which they work. TPM addresses the entire production system lifecycle and builds a solid, plant-floor based system to prevent accidents, defects, and breakdowns. TPM focuses on preventing breakdowns (preventive maintenance), "mistake-proofing" equipment (or poka-yoke) to eliminate product defects and non-de, or to make maintenance easier (corrective maintenance), designing and installing equipment that needs little or no maintenance (maintenance prevention), and quickly repairing equipment after breakdowns occur (breakdown maintenance).
The goal is the total elimination of all losses, including breakdowns, equipment setup and adjustment losses, idling and minor stoppages, reduced speed, defects and rework, spills and process upset conditions, and startup and yield losses. The ultimate goals of TPM are zero equipment breakdowns and zero product defects, which lead to improved utilization of production assets and plant capacity.
Method and Implementation Approach
TPM is focused primarily on keeping machinery functioning optimally and minimizing equipment breakdowns and associated waste by making equipment more efficient, conducting preventative, corrective, and autonomous maintenance, mistake-proofing equipment, and effectively managing safety and environmental issues. TPM seeks to eliminate five major losses that can result from faulty equipment or operation, as summarized below.
Six major losses that can result from poor maintenance, faulty equipment or inefficient operation
Unexpected breakdown losses
Results in equipment downtime for repairs. Costs can include downtime (and lost production opportunity or yields), labor, and spare parts.
Set-up and adjustment losses
Results in lost production opportunity (yields) that occurs during product changeovers, shift change or other changes in operating conditions.
Results in frequent production downtime from zero to 10 minutes in length and that are difficult to record manually. As a result, these losses are usually hidden from efficiency reports and are built into machine capabilities but can cause substantial equipment downtime and lost production opportunity.
Results in productivity losses when equipment must be slowed down to prevent quality defects or minor stoppages. In most cases, this loss is not recorded because the equipment continues to operate.
Quality defect losses
Results in off-spec production and defects due to equipment malfunction or poor performance, leading to output which must be reworked or scrapped as waste.
Equipment and capital investment losses
Results in wear and tear on equipment that reduces its durability and productive life span, leading to more frequent capital investment in replacement equipment.
Organizations typically pursue the four techniques below to implement TPM. Kaizen events can be used to focus organizational attention on implementing these techniques (see profile of the Kaizen lean method).
Efficient Equipment: The best way to increase equipment efficiency is to identify the losses, among the six described above, that are hindering performance. To measure overall equipment effectiveness, a TPM index, Overall Equipment Effectiveness (OEE) is used. OEE is calculated by multiplying (each as a percentage), overall equipment availability, performance and product quality rate. With these figures, the amount of time spent on each of the six big losses, and where most attention needs to be focused, can be determined. It is estimated that most companies can realize a 15-25 percent increase in equipment efficiency rates within three years of adopting TPM.
Effective Maintenance: Thorough and routine maintenance is a critical aspect of TPM. First and foremost, TPM trains equipment operators to play a key role in preventive maintenance by carrying out "autonomous maintenance" on a daily basis. Typical daily activities include precision checks, lubrication, parts replacement, simple repairs, and abnormality detection. Workers are also encouraged to conduct corrective maintenance, designed to further keep equipment from breaking down, and to facilitate inspection, repair and use. Corrective maintenance includes recording the results of daily inspections, and regularly considering and submitting maintenance improvement ideas.
Mistake-Proofing: Known as poka-yoke1 in lean manufacturing contexts, mistake-proofing is the application of simple "fail-safing" mechanisms designed to make mistakes impossible or at least easy to detect and correct. Poka-yoke devices fall into two major categories: prevention and detection.
A prevention device is one that makes it impossible for a machine or machine operator to make a mistake. For example, many automobiles have "shift locks" that prevent a driver from shifting into reverse unless their foot is on the brake.
A detection device signals the user when a mistake has been made, so that the user can quickly correct the problem. In automobiles, a detection device might be a warning buzzer indicating that keys have been inadvertently left in the ignition.
Safety Management: The fundamental principle behind TMP safety and environmental management activities is addressing potentially dangerous conditions and activities before they cause accidents, damage, and unanticipated costs. Like maintenance, safety activities under TPM are to be carried out continuously and systematically.
Focus areas include
the development of safety checklists (e.g., to detect leaks, unusual equipment vibration, or static electricity)
the standardization of operations (e.g., materials handling and transport, use of protective clothing, etc.)
and coordinating nonrepetitive maintenance tasks (e.g., especially those involving electrical hazards, toxic substances, open flames, etc.).
In many cases, equipment can be modified (see mistake-proofing) to minimize the likelihood of equipment malfunction and upset conditions.
Implications for Environmental Performance
Potential Benefits: Properly maintaining equipment and systems helps reduce defects that result from a process. A reduction in defects can, in turn, help eliminate waste from processes in three fundamental ways:
fewer defects decreases the number of products that must be scrapped;
fewer defects also means that the raw materials, energy, and resulting waste associated with the scrap are eliminated;
fewer defects decreases the amount of energy, raw material, and wastes that are used or generated to fix defective products that can be re-worked.
TPM can increase the longevity of equipment, thereby decreasing the need to purchase and/or make replacement equipment. This, in turn, reduces the environmental impacts associated with raw materials and manufacturing processes needed to produce new equipment.
TPM often attempts to decrease the number and severity of equipment spills, leaks, and upset conditions. This typically reduces the solid and hazardous wastes (e.g., contaminated rags and adsorbent pads) resulting from spills and leaks and their clean-up.
Potential Shortcomings: Failure to consider the environmental aspects or impacts associated with equipment during mistake-proofing and equipment efficiency improvement can leave potential waste minimization and pollution prevention opportunities on the table. For example, equipment can often be modified to reduce or eliminate spills, leaks, overspray, and misting that increase clean-up needs.
TPM can result in increased use of cleaning supplies, particularly if the route cause of unclean conditions are not addressed. Cleaning supplies may contain solvents and/or chemicals that can result in air emissions or increased waste generation.
Useful Resources Campbell, John Dixon. Uptime: Strategies for Excellence in Maintenance Management ( Portland, Oregon: Productivity Press, 1995).
The Japan Institute of Plant Maintenance, ed. TPM for Every Operator (Portland, Oregon: Productivity Press, 1996).
Leflar, James. Practical TPM: Successful Equipment Management at Agilent Technologies (Portland, Oregon: Productivity Press, 2001).
Robinson, Charles and Andrew Ginder. Introduction to Implementing TPM: The North American Experience (Portland, Oregon: Productivity Press, 1995).
Suzuki, Tokutaro, ed. TPM in Process Industries (Portland, Oregon: Productivity Press, 1994).
1. Comes from the Japanese words poka (inadvertent mistake) and yoke (prevent).
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