MFGEN 481 Final Project Case Study 2023

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Brigham Young University *

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Mechanical Engineering

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Jan 9, 2024

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Process Improvement Case Study Door Assembly Process Plant Background The problem setting is a small furniture plant that primarily manufactures case goods, such as entertainment centers. Operating for a single eight-hour shift, the plant produces 150 to 200 cases each day. The plant makes approximately 30 unique case styles, and each case can be made from a variety of wood species including Oak, Cherry, Pine, etc. An example of one such case is shown below. Production Process: The production of a cabinet begins with the machining of a core of solid wood into a variety of machined parts, such as rails and moldings. In addition, front panels, shelving and side panels are cut from flat stock. This forming of parts takes place in the Machine Room. Also in the machine room, sub-assemblies, such as doors, are assembled. The parts for a two panel door are shown below:

The completed parts are then transported in batches to the Cabinet Room. In the Cabinet Room, the parts and subassemblies are assembled and take on the form of a cabinet. A Cabinet Room build schedule determines how many of each case to assemble. This build schedule generates the schedules of what to machine in the Machine Room as well. Once assembled, the case is placed on a continuously moving conveyor which transports the cabinet through the Finishing Room. In this room several operators use spray guns to apply paints, stains, and varnishes. The area also includes wiping and touch-up operations. Upon completion, the cabinets are offloaded onto a roller conveyor for the final assembly and packing. In the Packing Room, activities such as inserting glass panels for doors, installing electrical power strips, and adding door knobs are performed. Finally, the case is wrapped in protective material and placed in a cardboard box for shipping. The diagram below shows the basic flow of parts between the different processing areas.

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Process Description The process of interest in this case study is the door assembly operation. The reason for studying the door assembly process is that it requires 10 hours a day, and even some Saturdays to meet the daily cabinet room production schedule. The plant manager and machine room supervisor want the operation to produce the schedule during the normal shift (7.6 hours), working only 5 days a week. In the door assembly operation, cabinet doors are produced in batches. The plant produces approximately 60 different door styles. But in general, from a time to produce perspective, doors can be grouped into categories by the number of panels. There are one-panel, two-panel, four-panel, and six-panel doors. The figure below shows the parts that compose a door. Doors always have a top rail, bottom rail, and side rails. Doors also contain inserts (or panels), usually made from wood, but occasionally from glass. Rails separating the inserts are called center rails or munts. The side rails, top and bottom rails, and munts are all machined in the Machine Room and are delivered to the Door Assembly Operation in batches. Batch sizes are matched to the cabinet room build schedule. In the door assembly process, these parts are assembled, glued, and nailed together. The nailing process essentially holds the parts together until the glue dries. A layout of the door assembly process is shown below.

This process consists of three operations which are detailed with pictures and descriptions below. In addition to the assembly operations, a setup occurs between batches of doors. The setup consists of locating the rails and inserts for the new batch and stacking these parts at the first operation. Once all the parts are located, a single door is assembled so that the clamp can be properly adjusted for the new door. If a batch of parts has been incorrectly machined, the parts must be reworked. These setups can take anywhere from 20-60 minutes. However, if parts are missing, an even longer setup will occur. 1. Assembly Operations: First, two operators in parallel apply glue to the rails and assemble all the pieces together (side rails, end rails, inserts, and munts). Once assembled, the operator pushes the door to a holding fixture, shown as a V in the diagram above. If their side of the V contains a door, the operator will wait till that door is removed before pushing forward their most recent assembly. The operator will not begin assembling the next door until they have pushed the preceding door to the holding fixture.

2. Clamp Operations: Second, the clamp operator removes the assembled door from the V holding fixture and places the assembly into a pneumatic clamp. The operator activates the clamp with a foot pedal, which presses and "squares" the pieces together. The operator then applies nails to all joints using a nail gun. The clamp operator then releases the clamp and slides the door to the mud and stack operator. There is essentially an unlimited queue between the clamp operator and the mud & stack operator, because the clamp operator can stack up doors in front of the mud operator. 3. Mud & Stack : Finally, a single operator applies putty to the nail depressions and places the door on a cart to be sent to the next operation.

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Problem Statement The problem as stated earlier, is that the door assembly process is taking about 10 hours a day, and is often working 6 days a week, rather than 5, to keep up with the cabinet room schedule. Plant management wants to determine how to improve the process so that the schedule can be accomplished in 5 days during the normal 7.6 hour shift. After observing the process, a time study was performed and the following process data was collected. Also a representative door assembly schedule was generated which represents the door demand generated by a daily cabinet room build schedule. During the observation and time study of the process, the assembly operation itself ran smoothly. There were times when the clamp was not functioning properly, and times when the quality of the incoming parts impacted production. But in general, when the assembly team was producing parts, the workload appeared balanced and they produced at a constant and adequate rate. What became readily apparent was that the setup process was an extremely time-consuming task. Since setup time is essentially non-value added from the standpoint of producing parts, reducing setup time could dramatically increase the throughput of this process. Your Project: 1) Build a Simulation model to analyze each of the three scenarios below to determine the impact on setup time and time to produce the schedule. • Scenario 1 - use one of the assembly operators to begin a pre-setup • Scenario 2 - hire an operator dedicated to setup • Scenario 3 - increase the batch sizes 2) Provide a brief write up on each scenario that includes data from the simulation to support your conclusions. 3) Make a final recommendation which gives the most cost-effective solution for assembling doors during the normal shift.

The following summarizes the data collected during the time study: Assembly Operator 1 Cycle time ~ triangular(35,65,40)seconds * Difficulty Multiplier Assembly Operator 2 Cycle time ~ triangular (35,65,40)seconds * Difficulty Multiplier Clamp Operator Cycle time ~ triangular (20 ,60,41)seconds * Difficulty Multiplier Mud/Putty Operator Cycle time ~ triangular (15,30,20)seconds * Difficulty Multiplier Difficulty Multiplier* 1 panel door = 1.0 2 panel door = 1.2 4 panel door = 1.4 6 panel door = 1.6 * A Difficulty Multiplier is necessary since a single panel door is easier/quicker to assembly than a six-panel door. To account for this, a Difficulty Multiplier is applied to the cycle time distributions. Setup Setup time ~ triangular (20,65,30) minutes

Door Assembly Schedule Four different door types are manufactured at the facility. The type and number of doors are based on a build schedule. Directions for Operating the Schedule: A one-day schedule is listed below. You can rearrange the schedule to get the quickest time to finish the schedule. Then use your optimum schedule to run each scenario to determine the best option. Batch Number Batch Size Number of Panels 1 100 1 2 100 2 3 140 4 4 80 6 5 120 1 6 120 2 7 50 2 8 20 1 9 22 2 10 25 2

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Scenario 1 Use one of the Assembly Operators to begin a pre-setup Looking at a layout of the process, there are two assembly and glue operators that work in parallel. Theoretically, one assembly operator could leave and the operation would continue to run, although at a reduced rate. When the operator leaves, effects how long production will operate at the reduced rate, but will also impact how long the setup will take. Model Logic: Construct your model so that Assembler 2 can leave to perform setups based on the number of doors remaining in the current batch. The schedule below shows the setup times if Assembler 2 starts the setup with the associated doors remaining. Setup Schedule: Doors Remaining Set Up Time 0 triangular (20,65,30) 10 triangular (20,50,30) 20 triangular (20,45,25) 30 triangular (15,40,22) 40 triangular (13,40,21) 50 triangular (12,39,20)

Use the simulation model and the cost data below to determine the best time for Assembler 2 to be released to perform pre-setup tasks. Use the default daily door assembly schedule. Remember to run enough days in order to improve the confidence level of your results. Be sure to include the total costs (standard and over time) associated with each option in your report. Cost Data: Assembly Operator Standard Time $15.00/hr Over Time $20.00/hr Clamp Operator Standard Time $20.00/hr Over Time $27.50/hr Putty Operator Standard Time $15.00/hr Over Time $20.00/hr Note: Overtime begins after 7.6 hours Objective : Minimize overtime to reduce costs You need to determine: 1. Cost if Assembler 2 doesn't leave 2. Cost if Assembler 2 leaves with 10 doors remaining 3. Cost if Assembler 2 leaves with 20 doors remaining 4. Cost if Assembler 2 leaves with 30 doors remaining 5. Cost if Assembler 2 leaves with 40 doors remaining 6. Cost if Assembler 2 leaves with 50 doors remaining

Scenario 2 Hire an Operator dedicated to Setup Currently there is an unused door clamp machine in the building. A parallel door assembly line could be activated at very little cost. Therefore, a second scenario is to add an additional operator. His job would be dedicated to setting up the next batch on the parallel line while the other four operators are producing doors on the other line. When the four operators complete a batch, they could simply move over to the parallel line and begin the production of the next batch of doors with a significant reduction in their setup time. This additional operator will have a cost of $15/hr and $20/hr for standard time and overtime, respectively. By adding the operator, the setup time between production runs is reduced to a triangular (5,9,7)min distribution. Also, this operator only needs to devote 50% of his time to the door assembly setups. The rest of his time (and therefore his cost) will be applied to a nearby department. You need to : 1. Develop a cost comparison between Scenario 1 and Scenario 2.

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Scenario 3 Because of the long setup times, a third way to improve costs for the door assembly process is to increase the batch sizes and reduce the number of setups. To assess the impact of larger batches, you first need a little background on the scheduling process within the plant. Background: The door assembly schedule is based on the cabinet line schedule. For example, a model 9350 cabinet require two 2-panel and two 1-panel doors. So, if the cabinet line schedule called for 50 of the 9350 cabinets, a demand for one-hundred 9350 model 2-panel and one- hundred 9350 model 1-panel doors is generated for the door assembly schedule. A representative for a single day of the door assembly schedule has been included in the base simulation model. In addition, the plant manufactures up to thirty different cabinets, which translates to approximately 50 different doors. Therefore, the representative door assembly schedule may not repeat for a week or more. Currently, the door assembly schedule is synchronized with the cabinet line schedule. In other words, just enough doors are made to meet next day’s cabinet line schedule. So, if the batch size for the door assembly line is increased without increasing the batch size of the cabinet line, doors must typically be carried in inventory for at least a week before another build of that model will be called for by the cabinet line. Your task: Your task is to use the following data to determine how large to make the batch size. Assume the representative door assembly schedule requires no inventory control because the doors are immediately installed on the cabinets. Also, assume that the cabinet line schedule cannot be manipulated. Thus, increasing the batch sizes for the representative door assembly schedule requires a new mechanism (and cost) for managing assembled door inventory. Also, assume for simplicity sake that batch sizes can only be increased in integer multiples. Two costs are associated with carrying doors in inventory. The first cost is a onetime fixed cost for the equipment, procedures and controls put in place to establish the ability to physically carry doors in inventory. The table displays these costs as a function of the increase in the size of the representative daily door assembly schedule. Assume that there is only enough floor space to hold three weeks of inventory (quadruple the batch size). Batch Size Fixed Cost x1 $0 x2 $10,000 x3 $10,000 x4 $20,000 The second cost is associated with carrying the inventory. This is often referred to as a holding cost ( h ). The table below show the yearly holding cost for a single door by type.

Door Type Fixed Cost 1 panel $5.00 2 panel $6.50 4 panel $7.50 6 panel $8.50 You need to determine: 1. Costs associated with the base schedule 2. Costs of doubling the batch sizes 3. Costs of tripling the batch sizes 4. Costs of quadrupling the batch sizes Note: Don't forget that by increasing the batch size and reducing the number of setups, overtime and overtime costs will be reduced.