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Quality Parts Company

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1) Introduction

Quality Parts Company is an enterprise that supplies gizmos for a computer manufacturer. There are three products (X, Y, Z), and basically all of them need the same machines, except for product Z which has milling as the first operation. The demand can range from one hundred and twenty five to one hundred and seventy five products per month. Another important consideration to make about this enterprise is that it has a subassembly which gives products directly to the middle of the plant.

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The following chapter provides an overview of alterations planned by the manager of the company. We listed some changes that are not compatible in the lean manufacturing objectives and made suggestions to improve the results of the company.

2) Current situation

Doing the analysis of the changes that the manager considers to make in the company, it’s important to say that the first thing to do in the just in time is not to produce while the customer does not request the respective product.

By the principle of the kanban pull system, the worker only has permission to produce when a pull signal is sent to him, normally manifested through a card or an empty container. What we can see at the manager changes is that she wants to store a buffer of at least two days in front at the workstation, in order to try the worker to produce faster. In fact, this is bad for the company because that inventory it’s not giving profit for the company. Another important consideration to make it’s about hiring three workers to inspect the products after the production. The quality at the source is an important factor in the lean manufacturing. It refers to the theory of employees assuming the responsibility for the quality of their own work, they are expected to make a part of the final product correctly at the first time. Finally, it´s look like the manager have not seen that keeping the skids filled because of the high utilization of the machines and labor will provide a bad flow through the production line. Although her good intentions for the company, providing this change, probably the production will not attend the demand and it will result in fines and, worse, the company probable will lose that client.

3) Methodology

In order to change the reality of this company, notably characterized by high level of inventory, several quality problems and steady profit: a different approach should be utilized. The main technique that will be applied to reach this goal is the Lean Manufacturing. The Lean manufacturing approach is based on eliminating as most waste as possible and one of the major causes for waste in a factory is certainly inventory, including in Quality Parts Company. However, JIT has been successfully applied kanban to control inventory level. However to make more efficient recommendations, our analysis will not be limited to this approach. Therefore, other methods like Theory of Constraints, job sequencing, line balancing will be used. The Theory of Constraints is a way to find a control point to manage the flow of product through the system. Finding the constraint of the production line will allow time saving. It’s important to focus the analyses on this resource because it strikes the beat of the entire production. In order to understand how many workstations will be needed and consequently how many workers (assuming one worker for each workstation), the line will be balanced. Here the expectation is to reduce costs reducing the number of workers.

The purpose is to assign all tasks to a series of workstations in a way that prevent each workstation of having a bigger operation time than the cycle time. This will minimize the unassigned time across all workstations. One of the major difficulties is to respect the precedent relationship inherent of the assembly line itself. The job sequencing will be utilized to minimize flow time. This is one of the standard measures of schedule performance used to evaluate priority rules. With this choice of priority the most adequate rule is SOT (shortest operation time) because it is the one who minimize the MFT (mean flow time). It’s important to state that the due dates weren’t given which means that the option could have been another one. 4) Recommendations

4.1) Layout

The first area that this methodology is going to be applied is the factory layout. As can easily be seen, the entire layout of the plant is contributing to elevate the waste, mainly by the unnecessary movements between operations, besides it, the large distance among the machines requires larger batch sizes. The design below brings a substantial improvement:

Figure : Layout proposed

In this new layout we opted to adopt two U shaped manufacturing cells. The first one is composed by the lathe, mill and both drills. And the other line by the paint, oven and packing. This change allow us to reduce the number of employees from 13 (one of them a par-time worker) to 10 operators. The reason to achieve this improvement was that in the new layout several operators are doing more than one job: operator 2 works on the mill and the drill, operator 8 works painting and packing, operator 7 inspects before the assembly and also brings parts from the subassembly, finally, operator 10 inspects before the lathe and feed the mill and the lathe.

4.2) Line Balancing

The allocation of workers given above was done using line balancing and the benefits of the U shaped line. To achieve the best result the first thing done was to find the ideal cycle time in the worst scenario case. The demand for the three products is 175 units per month and assuming that the factory works in one shift of 8 hours and five day in a week, the ideal cycle time (C) found using the formula below was approximately 54,86 minutes.

With this cycle time and only using the balancing approach without a U shaped line, the result found is of one worker in each operation, given the total of 12 operators (remembering that we added one more inspection) more one worker to feed the machines. However, as can easily be seen in the layout above and with the table below, operator 2 have all conditions of work on drill and the milling.

Operation

Operation time(minutes)
Remaing unassigned time(minutes)
Station

Milling
20
34,86
1
Lathe
50
4,86
2
Drill 1
15
39,86
3
Drill2
40
14,86
4
Assembly 1
50
4,86
5
Assembly 2
45
9,86
6
Assembly 3
50
4,86
7
Inspection
30
24,86
8
Paint
30
24,86
9
Oven
50
4,86
10

Table : Line balancing approach

The final allocation of workers optimized with the U shaped line used is given below:

Worker
Tasks
1
Lathe
2
Drill 1 and mill
3
Drill 2
4
Assembly 1
5
Assembly 2
6
Assembly 3
7
Inspection 2 and supply subassembly products
8
Paint and packing
9
Oven
10
Inspection 1 and supply raw materials
Table : Final allocation of workes

4.3) Kanban Production Control Systems

A kanban system is responsible for control these buffers and works in a simple way: an employee withdraws material to work on it; this material is stored in boxes of four products. At the same time the operator puts the kanban card, which was in the box, in the kanban board. The employee of the previous operation checks the kanban board and if there is any kanban there he is allowed to produce in order to replace these 4 units. In order to determine the number of kanbans needed to fulfill the necessity of the bottleneck and the assembly, the follow formula:

The worst scenario demand (D) of these operations is 175 per month, the lead time (L) is 50 minutes, and the container assumed fits 4 units (C). Besides it, a safety stock (S) of ten hours is needed to protect the bottleneck and ensure that it will never stops. Putting all the terms in coherent units and applying the formula above three cards kanban (k) should be used.

4.4) Theory of Constraints

To determine which machine was our bottleneck it was necessary to calculate the level of utilization of each machine. We admit that the company works eight hours per day, five days per week. We assume to produce one product each time, until we fill the weekly demand, that’s why was adopted the minimum setups necessary.

Machine
Operation time (min)
Setup time (min)
Load (min)
Capacity (min)
Ratio
Milling
20
60
351,67
2400
0,1465
Lathe
50
30
2277,50
2400
0,9490
Drill 1
15
5
671,25
2400
0,2797
Drill2
40
5
1765,00
2400
0,7354
Assembly 1
50

2187,50
2400
0,9115
Assembly 2
45

1968,75
2400
0,8203
Assembly 3
50

2187,50
2400
0,9115
Inspection
30

1312,50
2400
0,5469
Paint
30
20
1372,50
2400
0,5719
Oven
50

2187,50
2400
0,9115
Packing
5

218,75
2400
0,0911
Table : Ratio of utilization of the machines

The greatest ratio between load and capacity indicates that we have a capacity-constrained resource in the Lathe machine because we have a ratio less than one, which indicates that the machine probably will stay stopped sometimes. In fact, our bottleneck is the demand of the market. Other progress was the change of the inspection from the end of the factory to two other places: before the kanban of the capacity-constrained resource and before the kanban of the assembly. This allows us not to waste bottleneck capacity and avoid working in products that are already scrapped. In both cases it’s also important to add an inventory buffer and a communication rope. The first one makes sure that capacity-constrained resource has always something to work on, the second keeps inventory from building up. The proximity between the machines also brings an improvement because it reduces the need for unnecessary movements and allows a better flow. Now it was implemented one piece flow between all operations and we have only to buffers positioned before the assembly and before the bottleneck in order to make sure that it will never stops.

4.5) Scheduling and Job Sequencing

The Scheduling was done using as reference the capacity-constrained resource that could restrict the production capacity of the enterprise system. It was established one week scheduling of the capacity-constrained resource to improve system efficiency by reducing unnecessary setups. The planning was based on the fact that from the 3 products, the products X and Y have the same throughput time and Z have one more operation making the throughput time higher, therefore, decisions were made taking into account the working day of eight hours, one hour break for lunch, five days per week and the same demand for the three products.

Monday
Tuesday
Wednesday
Thursday
Friday
Morning

setup
30
30
30
30

Operation X
200

200

Operation Y

200

200

Operation Z

250
Lunch Time

Afternoon

setup

30

Operation X
250

100

Operation Y

250
100

Operation Z

250
250
Table : Weekly Scheduling for the products X, Y and Z

The decision to produce first products X and Y was given to the fact that production would be more flexible to any changes in demand or delivery that might occur. This programming has 5 setups, reducing waste time and increasing the number of units produced. It wasn’t taken into account costs for or sales prices for each product nor due dates. This information is in fact very important to do a more accurate planning.

Monday
Tuesday
Wednesday
Thursday
Friday
Morning
8-11h50
8-11h50
8-11h50
8-11h50
8-12h10
Lunch Time
11h50-12h50
11h50-12h50
11h50-13h00
11h50-12h50
12h10-13h10
Afternoon
12h50-17h
12h50-17h
12h50-16h50
12h50-17h
13h10-17h20
Table : Weekly Scheduling Capacity-constrained Resource

The scheduling of the capacity-constrained resource (CCR) based on the planning seen before show a need for a slightly change from the normal shift. That means that other incentives have to be given to the CCR. The main changes occur on Wednesday, when utilization is just 7 hours and 40 minutes, and on Friday where the worker has to work 20 minutes of overtime. This means that the company will have to pay 4 extra hours per month to the CCR.

5) Conclusion

The main challenge was to outline a plan to introduce Just-In-Time (JIT) at Quality Parts Company. That was given in the chapter above called recommendations. Every one of them is a necessary step for a JIT implementation, seeking to achieve high volume production using minimal inventories of raw material, work-in-process and finished goods. With that purpose and as review of all the proposals the main points are: Layout:

Reduce de unnecessary movements between operations and batch sizes; The use of two U shaped manufacturing cells reduce the number of employees needed. Line Balancing:
The assignment of tasks to workstations was optimized, having in consideration the possibility of some workers do more than one task; The number of workers needed is in fact 10, meaning an improvement in the firm’s costs. Kanban:

The number of the Kanban cards required is 3.
Theory of Constraints:
The real bottleneck is the market;
We have a Capacity-constrained resource and that was taken into account in forthcoming analysis; The change of one final inspection for two, one before the CCR and the other one before the assembly; The need for two buffers and two communication ropes after the two inspections; Scheduling and Job Sequencing

In the attempt to have a more flexible production, combining with the JIT philosophy, the schedule was weekly; The weekly demand for the 3 products is produced weekly;
The products X and Y have a minor throughput time, therefore they are the first ones to be produced (SOT rule).

6) Bibliography

Chase, Richard B., Nicholas J. Aquilano, and F. Robert. Jacobs. Operations Management for Competitive Advantage. Boston, MA: McGraw-Hill, 2004. Just-In-Time Manufacturing. AIDT, Sept. 2006.

Cite this Quality Parts Company

Quality Parts Company. (2016, Jul 09). Retrieved from https://graduateway.com/quality-parts-company/

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