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Maintenance execution determines the overall outcome of any maintenance policy and strategy adopted to keep a facility in a reliable state. Once this is flawed, every other aspect of the maintenance process will not yield the intended result, hence the need to focus attention on the shopfloor execution of maintenance tasks with adherence to plans and schedules. There are two major aspects of maintenance execution: what to do and how to do it. What to do are a combination of original equipment manufacturer recommendations and other source of information relevant to maintenance planning, such as historical data, experience from technicians, and prognostic methodologies for data gathering. While this is almost unique to equipment, it is a prerequisite for proper maintenance planning and execution. The how-to-do aspect of maintenance execution involves the capability and ability of the shopfloor technicians to carry out the maintenance plan with the right knowledge, attitude, and tool set. By adopting the PDCA approach, a systematic approach to maintenance execution is developed that covers both planning and implementation of maintenance execution for sustaining reliability. The result shows a steady decline in waste trend with over 5% reduction in the amount of waste in less than 3 months.
*Address all correspondence to: okonta.christian@yahoo.com
1. Introduction
The aim of maintenance is to keep equipment function in basic condition defined by safety, quality, and productivity constraints. Continual usage of equipment leads to deterioration which can propagate to defect and subsequent breakdown. To detect and eradicate defects and anomalies, maintenance is carried out. Thus, maintenance is catholic term used to describe all activities carried out on a piece of equipment to prevent it from breaking down and resulting in unplanned downtime [1]. It could be cleaning, inspection, lubrication, tightening, adjustment, repairs or replacement.
In the manufacturing sector, maintenance cost is usually a major concern to the stakeholders, and optimization of this cost is a key performance index of the maintenance management team [2]. The ability to predict critical failures that may lead to long downtime is a key factor in reducing the overall cost along the supply chain [3]. Adequate maintenance is necessary as any malfunction that arises during manufacturing would cause a disturbance in the supply chain [4].
Different organizations adopt different policies for maintenance depending on the criticality of the expected failure. Preventive maintenance policy is usually implemented where equipment failure could result in huge downtime and production loss. In this situation, the cost of failure is high, and the aim is to reduce unplanned downtime to the minimum. Corrective maintenance policy is mostly common when the effect of failure is minimal, and the repair time is usually short or negligible; hence, no serious investment is made on inspection. In some production companies, there is a combination of both preventive and corrective maintenance policies which are implored to keep different machines in running state based on equipment complexity and criticality. The method of defect identification and determination of remaining useful life of an equipment is referred maintenance techniques, while the application maintenance policy and techniques to keep the facility functional is called maintenance strategy [5]. According to a study by Wang et al., [6] three competing failures may occur in a system, namely: a) shock failure as a result of environment shocks, b) soft failure which occurs when the deterioration is allowed to exceed a critical value, and c) out of balance when the difference value in alignment among components reaches the failure threshold. The ability to predict critical failures that may lead to long downtime is a key factor in reducing the overall cost along the supply chain [7]. Any breakdown that occurs during production will lead to a disruption in the supply chain, hence the need for adequate maintenance [8].
To create a good preventive maintenance system, a prerequisite is a standard roadmap to detail various action plans for maintenance execution with emphasis on what needs to be maintained and how the maintenance should be carried out. This is the process of finding the best possible maintenance strategy for every asset in your organization with the end goal of achieving consistently high levels of reliability at the lowest possible costs.
This work is structured in sections. Section 2 explains the WHAT of maintenance execution, while Section 3 gives a brief of the HOW. Section 4 elaborates on the adopted PDCA road map used to address the question arising from the WHAT section and also explains the HOW approach. Section 5 is the result obtained from the implementation of the approach using a food production factory as a case study. The results obtain are discussed in Section 6, while Section 7 is the conclusion.
Based on the principle of reliability-centered maintenance, understanding what needs to be done in order to keep equipment in a sustainable reliability state sets the maintenance process of identification of failure modes in motion for successful eradication through countermeasures. To get started, these questions must be addressed.
What is the working principle of the asset or equipment, and what are the associated performance standards?
What are the assemblies, components and parts of the machine that require maintenance? They are referred to as maintenance significant items (MSI).
In what ways can the maintenance significant items fail to provide the required functions? This involves failure mode identification.
What event can trigger each failure?
What are the noticeable signs and possible effects when each failure occurs?
What are the risks of failure?
What systematic proactive task can be done to prevent or diminish the consequence of the failure?
The next part in the maintenance execution journey is “How” maintenance should be carried out on the recognized items in order to sustain the reliability of the equipment at a standard safety and quality level. This is an explanation of required procedures in carrying out the WHAT of the maintenance execution. The two major aspects of the How in maintenance execution are the type and nature of maintenance required by these items. The type of maintenance could be time-based, condition-based, or prescriptive-based preventive maintenance depending on the accessibility, difficulty, and criticality of the machine/component. The nature of the maintenance is the actual action that needs to be performed on the maintenance significant item for accurate defect detection and restoration. This is where the failure modes of the component are being looked out for. The best approach is by asking questions around the possible effect of the identified failure modes on the MSI. The response to these questions together with recommendation from original equipment manufacturer (OEM) and historical experience becomes an insight into the creation of task list for inspection and maintenance. The next part is to prepare a detailed instruction and procedure for the WHAT part earlier identified with required tools, manpower, and enough training guide for technicians. For validation purpose, trigger the preventive maintenance as a corrective maintenance action and watch the execution. This second step is an opportunity to test your process and make possible adjustments before rolling out your maintenance task lists as a standard inspection and maintenance plan.
Maintenance is a continuous process and thus requires continuous improvement. In the 1950s, W. Edwards Deming developed a quality system for the continuous improvement of business processes. While Deming concentrated on industrial production processes, his approach and ideas could be applied just as readily for maintenance and other contemporary corporate operations [9]. Deming developed a model for use for constant improvement known as the PDCA (Plan-Do-Check-Act) cycle [10].
Implementation of the PDCA cycle for maintenance system execution is particularly important for the maintenance manager to remain focus on the basic of the maintenance program and not carried away by issues on the shop floor. It systematically provide answers to the relevant questions asked in the ‘WHAT’ section of maintenance execution, addressing each of them as a standard work process to developed and cascaded to the shopfloor. It also elaborates on the ‘HOW’ process of proactive maintenance execution. The implementation of the PDCA cycle for sustainable maintenance execution is elaborated in the following below.
4.1 Plan
Defining the issue or topic is the first step in finding long-term fixes. Creating an action plan, including the necessary resources and planning, is the final step in this process. This could be referred to as standard work process development of the maintenance system.
The first step is to develop preventive and corrective maintenance work order management route as shown in Figures 1 and 2.
Figure 1.
Preventive maintenance work order management route.
Figure 2.
Corrective maintenance work order management route.
The maintenance work order management route in Figures 1 and 2 is a definition of a systematic approach to upkeep the facilities and equipment, and it varies from facility to facility [11]. The selection of the best approach to sustaining a particular asset has been quite a challenge for the asset owner. The choice of the best maintenance strategy is a selection of the most suitable maintenance techniques for the policy to be operationalized. Maintenance techniques (MT) in this context are the methods used to forecast and predict the remaining useful life of an asset [12]. MT enables the application of maintenance policies. The available data as well as the possibilities for data collection and the required outcome determine what MT to select. Based on the classification [10, 11], five different forms of MTs can be distinguished as follows.
Experience-based: in the experience-based technique, forecasts of failure times are based on knowledge and experience outside or inside the organization (e.g., OEM). Occasionally, little or sparse data support them. Predictions are based on expert judgment (for example, facilitated by FMECA techniques). Such methods estimate the life span of an average variable operating under average historical conditions [13, 14, 15].
Reliability statistics: The prediction techniques for reliability statistics are based on historical (failure) records of comparable equipment without regard for specific component (use) variation. This method explains precisely the likelihood of population-wide failure. Such techniques also estimate the lifespan of an average item that operates under average conditions, for example, Distributions of Weibull [16].
Stressor based: stressor-based predictions are based on historical records with stressor data, for example, temperature, moisture, or speed, including environmental and operational variances, and produce predicted system life expectancy results in a specific environment. Pronouncements are based on a general direction derived from a physical model, built-in performance, or operating history [13].
Degradation based: degradation-based prognosis is based on the extrapolation of a general path to a failure threshold from a forecast parameter, a degradation measure. The system can be diagnosed by measuring symptoms of initial failure such as an increase in temperature or vibration. The prognostic parameter is also calculated by sensor measurements that are often dependent on measurement. The forecast starts from the current deterioration situation and results in a lifetime required of a particular system in a certain environment [17].
Model-based: model-based projections give the predicted remainder of the lifetime of a certain system. Two distinct categories of models exist:
Physical model-based: the prognostic parameter is computed based on a degradation mechanism physical model based on direct load-sensing or usage which governs individual components’ critical failure mechanisms.
Data model-based: data analytics approach that uses sensed load variations, utilization of process data or condition/health monitoring data as input to measure or extract the prognostic parameter. The algorithms are designed to extract or try to predict anomalies by comparing them with historical data.
The aim is to generate value adding preventive and corrective maintenance work orders to keep the equipment in basic condition. Automatic triggers such as condition monitoring and time base counter follows the preventive maintenance workorder management route in Figure 2, while work request from technicians and operators’ inspections follows the corrective maintenance work order management route in Figure 3.
Figure 3.
Breakdown analysis route.
Even with the best maintenance strategy, breakdown is almost inevitable but could be minimized through proper countermeasure. Thus, the next step in the planning phase of the PDCA cycle is to develop breakdown analysis route as shown in Figure 3 to ensure that breakdowns are not recurrent. The seriousness level of stoppage is determined by the company standard, and any downtime that is equal to or greater than the defined standard (say 30 minutes) is classified as a serious breakdown and thus selected for analysis. It is recommended to employ the Five Why (5 whys) problem-solving technique, which investigates the underlying causes and effects of specific issues. The main objective is to ask “Why?” repeatedly in order to identify the underlying source of a flaw or issue. Failures will recur if incorrect conclusions are drawn from breakdown data analyses that do not take into account the underlying processes of failure. Before any breakdown may be permanently eliminated by the application of suitable countermeasures, the failure mode of that breakdown must be connected to the root cause.
4.2 Do
This is the daily implementation of the planned actions. The objective of this step is to implement the plan defined above. The first action is the resource allocation.
Resource allocation is the process of assigning and managing assets in a manner that supports an organization’s strategic planning goals while also conferring a fitness benefit by contributing to a defined objective [18]. Resource allocation includes managing tangible assets such as hardware to make the best use of softer assets such as human capital. Resource allocation involves balancing competing needs and priorities and determining the best course of action to maximize the use of limited resources and get the best return on investment [19].
For illustration, using a premium tortilla production factor as a case study, the operational sequence is as follows;
Flour is received from the trucks delivered from the manufacturer to the plant into different silos with loadcells to determine the quantity and level of flour in each silo. Different flour such as whole wheat or white flour are stored in different silos. Once the facility is ready for production, the desired recipe is entered into the human-machine interface of the hopper. The hopper initiates ingredient call from the silo through the vacuum pump. Once the preset quantity is achieved, the vacuum pump cuts off. The ingredient is emptied from the hopper into the mixing bowl which is in turn clamped onto the mixing machine duck for mixing in order to achieve a homogenous quality dough at right elasticity, texture, and temperature. The prepared dough from the mixer is moved to the bowl lift which helps in conveying the bowl on the divider. The divider helps cut the dough into small oval shape of desired size and weight according the installed pocket of the divider drum. The next machine on the line is the proofer. The function of the proofer is to provide a controlled environment with respect to temperature and humidity for exothermic reaction of the enzymes on the dough and provide the right toughness for easy pressing. The autoloader helps to arrange the dough in arrays on the conveyor in preparation for pressing. The press is used to spread the dough ball into a circular flat tortilla of consistent size, ready for baking in the oven. The oven is a temperature-controlled baking system used to cook and bake the tortillas at desired temperature and time. The cooler is a long conveyor in a temperature-controlled room to reduce the temperature of the tortilla coming from the oven to less than 5 degree Celsius. The inspection/rejection system is a quality control installation that helps to inspect the shape, size, consistency, presence of spots and holes, and subsequent reject bad tortillas based on the specified pixel parameter. Counter stacker helps to count the good tortillas passed from the inspection system and stack them into different pockets according to the defined number ready for packaging. The indexing machine is used to press down the stacked tortillas. By pressing it together, it is easier to be transported on the conveyor and much easier for the bagging machine to handle. The function of the bagger is to put the pre-arranged stacks of tortillas into bags. Next is the metal detector, a critical control point for detecting the presence of metal in the tortilla by measurement of the electromagnetic radiation from the stacks. The printer is used for date and batch coding of the bags before being put into cartons and sent for delivering to the final consumers.
A summary of the flow chart of the production process with assigned mechanics is as shown in Figure 4.
Figure 4.
Resource allocation in a production plant.
The next step is the implementation of preventive maintenance daily agenda defining what must be done before the close of each business day. A guide to the maintenance team as shown in Figure 5.
Figure 5.
Preventive maintenance daily agenda.
This agenda serves as a workflow for managing the maintenance team on the shopfloor. It specifies the actions that must be performed on a daily basis to keep the system functional, responsive, and organized. Figure 6 states that runtime inspection must be carried out by technicians upon resumption followed by the execution of available workorders. These two actions serve as a strong preparation for the daily maintenance planning meeting which present an opportunity to get update from the previous 24 hours, follow-up with planned actions for the next 24 hours, and get update and feedback from the team as in Figure 6. Other maintenance scope meetings such as weekly, bi-weekly, and project planning meetings could also be integrated for forward planning. Work order execution is the aim of the “do” phase of the PDCA and must be given more attention. Time must be allotted for the documentation of executed workorders.
Figure 6.
Daily meeting critical agenda.
4.3 Check
CHECK Assess the measurements and report the results to the decision makers. Using measures, indicators, or observations, the effectiveness of measures implemented must be verified. If any modifications are needed, we return to the planning step. Maintenance metric should be clearly stated with target and explained during the weekly KPI review meeting. This objective metrics helps in visualizing the team performance on daily, weekly, or monthly review. Table 1 shows a standard metric for maintenance performance tracking.
Table 1.
Standardize maintenance metrics.
4.4 Act
This is the finalization of results, and their sustainable implementation involves development or updating of documents such as procedures, processes, good practice guides, or forms. ACT decides on the changes that are needed to improve the process. In maintenance, this basically involves review and update of task lists and training of technicians on inspections and maintenance. As a maintenance manager, requirements from maintenance technicians must be clearly stated as a written and documented work instructions. Maintenance work instruction can thus be defined as a written set of instruction that specifies how a maintenance task is to be performed and expected quality from the work order. The reason for work instruction is to manage/limit human error, reduce variability in task performance and ensure adherence to safety procedures. Maintenance work instruction is a living document that is subject to continuous improvement in a bit to finding the most efficient and safest way to perform the given task.
Focusing on the Dixon mixer for processing dry flour into consistent dough as a case study, the preventive maintenance of the mixer is written in detail in Table 2.
Table 2.
Procedure for monthly mixer maintenance.
This can be used for onsite training of technicians to ensure adept understanding of the working principle of the machine and execution of maintenance function as stipulated by the work instruction.
Using the case study of a premium food production plant in Canada as referenced in the DO section of the PDCA, the aim is to reduce waste from an average of 25% to less than 10% by implementation of a world class preventive maintenance strategy. By following this maintenance execution approach in three months, the result of the waste trend is shown in Table 3 and Figure 7.
Week of
Waste
Four-week avg.
5-Sep
26.00%
12-Sep
18.40%
19-Sep
19.80%
26-Sep
23.90%
22.0%
3-Oct
20.80%
20.7%
10-Oct
19.20%
20.9%
17-Oct
13.60%
19.4%
24-Oct
15.80%
17.4%
31-Oct
18.80%
16.9%
7-Nov
16%
16.1%
14-Nov
16.40%
16.8%
21-Nov
12.70%
16.0%
28-Nov
12.53%
14.4%
Table 3.
Waste trend data.
Figure 7.
Three-month waste trend.
The result from the check on the lagging and leading maintenance responsible for this reduction in waste is shown in Tables 4 and 5.
By following this maintenance execution approach, after 3 months, all the registered equipment of the computerized maintenance management system had been updated with weekly, bi-weekly, monthly, quarterly, semiannual, and annual maintenance plan. The maintenance metrics developed showed an improvement in waste from 25% to less than 15% within 3 months of introduction and adoption of the approach. The maintenance backlog was also reduced to less than 40. By adopting the PDCA approach, a systematic approach to maintenance execution is developed that covers both planning and implementation of maintenance execution for sustaining reliability. The CHECK shows the immediate performance of the maintenance function by elaborating on both the lagging and leading metrics in Tables 3 and 4. The result shows a steady decline in waste trend with over 5% reduction in the amount of waste in less than 3 months.
This chapter elaborates the PDCA approach to maintenance execution, focusing on what needs to be done and how maintenance execution should be carried out for the identified maintenance significant items. In the plan phase of the cycle, the preventive maintenance road map was presented for effective action plans based on the adoption of different maintenance techniques. The maintenance technique was used as a means of forecasting the remaining useful life of equipment hence, a trigger for the preventive maintenance workorder. A corrective maintenance route was also introduced to handle corrective work order request from inspections. As breakdown is almost inevitable, a breakdown route based on root cause analysis was introduced. The implementation phase focused on defined workflow is to be followed, specifying the maintenance team daily agenda. Standard leading and lagging maintenance metrics were presented as checks, guiding the maintenance function performance. As maintenance is a continuous process, work instruction must be revised and improved upon for onboarding and training technicians. The result of the implementation of this approach to maintenance is the establishment of a self-governing self-sustaining preventive maintenance system that is proactive in defect identification and eradication. The PDCA loop is able to carry out self-assessment of the system maintenance function performance, develop action plan for improvement, and evaluate the impact of the actions on the overall system.
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Written By
Christian Okonta, Ralphael Edokpia and Christopher Eboigbe
Submitted: 01 March 2024Reviewed: 05 March 2024Published: 14 June 2024
Open access peer-reviewed chapter - ONLINE FIRST
