Lean Manufacturing and Simulation for New Products


ISE Magazine May 2019 Volume: 51 Number: 5

By Rosa Hilda Félix-Jácquez, Alfonso Alejandro Lara-Negrete, Daniel Torres-Ramírez, María Merced Cruz- Rentería, Ma. Dolores Delgado-Celis

The following is the case study of a repair shop at a rail company facing a critical economic situation, with lean manufacturing and simulation providing the solution.

The repair shop’s man-hours of yearly work were reduced drastically in recent years due to the lack of new product introductions (NPI). Having a smaller number of working hours means a higher cost of labor, with all business expenses divided by the total work hours to obtain the annual labor cost rate. The increased labor costs have made it harder to justify investment projects that are less than a year’s return of investment (ROI) as the corporation needs.

This is why the company has the objective to gain more working hours for the shop, become more productive and reduce labor costs through the introduction of new products. The implementation of good practices such as lean manufacturing and process simulation model both support the new compressor repair line in the supply chain business unit.

Facts analysis

The air compressor is one of the main components for the locomotive operation as it supplies air to the braking system. It primarily consists of a high-pressure head, two low-pressure heads, an aftercooler, two intercoolers, a crank-case, an electric motor and the air flow lines.

The first phase was an action work out to develop a process for the remanufacturing of the air compressor. Repair activities were carried out in different areas of the plant, according to the customer’s needs, with cycle time of 20 hours required to meet demand. This did not make it feasible to achieve the expected cost by the primary customers, nor the benefit projected by the company.

The opportunity areas identified included a lack of the necessary documentation in process sheets for standardization of operations and a quality plan for the regulation and the measurement of critical to quality (CTQ) items; the identification of potential risks and their safety precautions at work; process failure mode effect analysis (FMEA) to prevent effects and failure modes in the process; the design of the layout that would indicate the flow of the compressor within the line, as well as the standard work combination sheets for each station and operator training for this NPI.

The next phase of the project was to create a benefits matrix to identify the area where the compressor line will be installed, taking into consideration the needs for the process and the investment needed for the facility prep. This matrix contains the most important facts that should be considered, as well as the equipment and space availability, distance to the warehouse and investment required.

The team evaluated three different criteria to choose the best option: 1 point for poor, 3 for regular and 9 for good. The matrix results showed the first area got 59 points and the second 91 points, making it the optimal work area for the process installation.

There are two kinds of work scopes for the air compressor. One of them is the light version, where the highpressure head, low-pressure heads crankcase, aftercooler and intercoolers are tested, and all the gaskets and seals changed. The other is the heavy repair on the full disassembly, qualification of principal parts, nondestructive testing (Magnaflux) and the complete set of seals in the gaskets. This project was based on the planning for the light process line of work scope repair.

By using the value stream mapping (VSM) tool, the complete process of value-added and nonvalue-added operations were laid out. This tool allowed identification of the main waste sources and opportunity areas, including the lack of exclusive space for the installation of the line and unfamiliarity with the necessary tools. The operator did not know the sequence of activities required by the absence of process sheets, among other things. All this caused the percentage of nonvalue-added operations to increase more than the 20.81 percent of the cycle time that represents 20 additional working hours.

The future mapping of the process was designed to reduce or eliminate the nonvalue-added operations, and strategies were planned to reduce the cycle time by 25 percent to get 15 hours. The primary approach to reduce cycle time took into account the use of process sheets and identification of the necessary tools, layout design, process flow and component transportation.

Environmental health and safety (EHS) risks, nonconforming products and long cycle times are the leading waste sources created by transportation and material handling. A spaghetti diagram is helpful to measure the total distance the component travels from a workstation to another. By using this tool, the materials flow and interference in the process line were identified, leading to a redesign of the process flow to avoid EHS problems and minimize traveling distance.

The spaghetti diagram measured the number of meters both the operator and compressor travel to perform the remanufacturing process in different areas of the plant. It measured 411 meters, high-lighting that the distances were too long due to the lack of a defined production line. Once the layout was designed and the compressor/operator route was analyzed, the distance measured decreased to 40.1 meters.

The next step was to define the takt time that, in theory, describes the total available time and customer demand. There are two scenarios, best case and worst. In the first case, the cycle time for every workstation was calculated by the average number of failures during a static test. In the second case, it was estimated by considering the greatest time of static analysis, causing a bottleneck; being the most critical workstation in the line, it could not meet the weekly demand. That demand required by the customers was 25 compressors weekly; the takt time indicated that every few hours, a compressor must exit the line ready to be delivered to the customer to achieve the goal of five per day.

Inside the process, we identified a variation in workload for each station, mainly in static tests that caused the cycle time to exceed the takt time and not allow the objective to be reached. Due to this, a redistribution of tasks at each station was performed to balance the workload for each operator. According to the line balance, we deter-mined the number of operators needed for the line is three, and on two work shifts.

A detailed analysis of each task for the remanufacturing process that we performed was assigned according to its urgency, considering the in-formation described above. Additionally, we took care of the distances the operator has to walk along the line and EHS factors while handling the component.

Improvement approaches

For layout design, an assessment of the available facilities was completed, considering requirements such as crane availability, washing and painting equipment, electrical and pneumatic connections and square feet. Once the work area was selected, the design of the layout was made with the relevant dimensions for each workstation considering the standards for a safe and ergonomic workplace.

Once we completed the initial design of the layout, we started adding lean manufacturing principles. The production line was designed in a “U” shape to reduce the transportation and movement of the component and avoid material crossings by using production “pull” system and minimizing work in process (WIP).

With the design of the layout, the total distance decreased 370.9 meters and the impact on safety risks was a 90.24 percent reduction in the probability of an accident during the compressor transports.

For the air compressor remanufacturing process, we developed two simulation models that emulated the compressor flow through the workstations. The first model developed on a two-dimensional space demonstrated there was an existing bottleneck in the static test’s workstation. This was blocking the fulfillment of the weekly demand because this station cycle time was longer than takt time due to the variability of com-pressor failures.

For the second model, a three-dimensional layout was created using a computer-aided design (CAD), where different simulation elements were used such as cranes, operators and status indicators. Once done, the balance and workload of the operators was better distributed; the simulation model was again defined to meet customer’s demand.

To achieve standardization of working methods, we introduced process sheets with information to help the operators perform the activities with the correct tooling and specifications and in the proper sequence.

Process sheets are very helpful for the operators when the activities are too repetitive or when the operator must check any parameter along the process, such as pressure, dimension and temperature. These documents also help train new operators for the air compressor line.

Regarding the quality plan, this assured compliance and a record of critical-to-quality factors that were the primary customer requirements measured during the remanufacturing process.

The quality plan the team developed includes different types of information as CTQs – measuring gauges, tolerances, completion date, operator name and shift – to control the air compressor in-formation. The quality plan is also called a “traveler sheet” because this document goes on with the component during its remanufacturing process at each work-station.

One of the essential principles of the lean manufacturing philosophy is the standardization of work. That is why the elaboration of the standard work combination sheets (SWCS) helps to accomplish this goal. They show every operation per workstation and the interaction with the operator during the process. The standardization of work is crucial to provide a proper flow to the line, making it possible to view the production sequence graphically and change it to improve capacity. This tool also is useful to balance the labor for each operator and outlines the tasks, machinery, waiting time, transportation and walking time.

The job safety analysis (JSA) identifies the risks operators are exposed to while working along the line. It indicates why some operations are dangerous and the preventive actions to be taken to avoid accidents. Moreover, the ergonomic research for the correct positions is required. This document determines the needs in each workstation and analyzes the personal protective equipment required. It also contains general information, required training, workstation name, emergency phone numbers and unsafe activities the operator must know before starting work. The JSAs are located near each workstation for operator query in case of any incident.

The failure mode and effect analysis was made to detect possible failures and their potential effects on the process. This document is a tool used to identify and eliminate a potential product or process failures or defects. The FMEA was discussed with a multidisciplinary team including members from the quality, engineering, materials, logistics, projects, EHS and manufacturing departments. One of the main tasks of an interdisciplinary team is to recommend actions, if necessary, and assign the owner to implement each one.

With FMEA, the teamwork analyzes every step in the process and prioritizes each with a standard rating according to the risks encountered by both the product and operator safety while working on the line. Each possible failure has a score that indicates how many times it could happen in the process (occurrence); a score that indicates if the fault is difficult or easy to be found (detect-ability); and a score that shows how dangerous a failure is for the product and operator safety (severity). Based on the FMEA, the risk priority number (RPN) helps to determine the most dangerous steps and required action for their control.

Within the premises of a new production line, it is fundamental to implement a visual management system that allows identification of work areas, risks and mandatory protective equipment. Among the main signs deployed are for an emergency exit, workstation identification, classification of air, water and steam lines, fire extinguisher location, leak-proof kit and containers for scrap and garbage.

The purpose of the visual management system is to transmit information about safety rules and process distribution, visual aids designed according to the minimal size, color and form regulations to match company standards.

Finally, it was necessary to create a control plan for project sustainability. This document includes actions, planned dates, owner, completion date and frequency. The new workstation was involved in the annual quality audit program, where process compliance was revised, a proper quality plan recorded and the measuring gauges calibrated. It also was considered in safety tours where the line conditions, 5S and ergonomics were verified, as well as the preventive maintenance plan.

After the implementation of lean manufacturing philosophy and simulation throughout the project, we executed a total of 19 kaizens. The financial benefit was that labor costs decreased from $52.5 to $47.5 per man hour, a difference of $5 that represents a 9.5 percent cost reduction, an efficiency increase of 21 percent, a distance reduction of 380 meters and annual savings of $384,000.

The development of this remanufacturing line is the baseline for the management and implementation of future projects at the company. It is founded on the lean manufacturing philosophy and represents a model for the other rail sites to follow.