Procesos Industriales

Homework exercises - 1

PROCESSES DESIGN AND ANALYSIS

Flow charts and capacity analysis

Question 1.

Consider the following flow diagram that describes a process of manufacturing a piece of furniture:

a) Suppose that the firm employs three different workers, each assigned to one of the tasks. Using a Gantt chart, calculate the time used to produce three units and answer the following questions:

1. Assuming that the worker of the first task does not postpone the process of polishing any unit, at what time will he finish his job?

2. How much time has passed since the painter started to paint the first unit until he finished painting the last unit?

3. What percentage of time was the painter working?

Suppose now that the firm has decided to hire a fourth worker to help in the second task. For this, they established two job stations so that the two workers are able to assemble in parallel. Suppose that the second worker takes 9 minutes to assemble a unit. The new process can be described according to the following diagram:

(b) Using a Gantt Chart, calculate the time necessary to produce three units using this new process and answer the following questions:

1. Assuming that the worker of the first task does not postpone the process of polishing in any unit, at what time will he finish his job?

2. How much time has passed since the painter started to paint the first unit until he finished painting the last unit?

3. What percentage of time was the painter working?

Suppose now that the firm has decided that the fourth worker, instead of working in parallel, will help the worker to assemble faster. The two workers, as a whole, take 5 minutes in assembling a unit. In this way, the process can be described according to the following diagram:

(c) Using a Gantt chart, calculate the time that takes producing three units using this new process and answer the following questions

1. Assuming that the worker of the first phase does not postpone the process of polishing in any unit, at what time will he finish his job?

2. How much time passed since the painter started to paint the first unit until the end of the last painting?

3. What percentage of this time was the painter working?

(d) Considering the two options above: if you had to make the decision, how would you use the fourth worker? If you were producing four units instead of three, would you change your decision?

(e) Which system has greater capacity? Calculate the necessary time to produce units 5, 6, 7 and 8.

Question 2.

An agricultural producer has four people to perform the packing of raspberries. The input of the process is a container of raspberries recently harvested from the field, and the output is another container with small baskets of 100 grams of high quality raspberries packed for export. The process of packing consists of the following stages: first one must select raspberries that fit with the standards of export. For this end, there are two people who work together and are able to select 10 grams of raspberries per second and pass them on to a container of raspberries of high quality. The second stage consists of picking raspberries in this high quality container and placing them in small baskets containing 100 grams of raspberries each. In this stage, a person is able to set up one basket every fifteen seconds. The third stage consists of packing each basket, wrapping these in plastic, and adding a sticker indicating the brand and place of harvest of raspberries. For this last stage there is a worker capable of packing 12 baskets per minute.

1. Analyze the process, putting together a flow diagram, and indicate:

Production time of the first basket of 100 grams,

the cycle time of each process,

each stage’s capacity,

the system’s bottleneck,

the system’s capacity,

Capacity utilization of each one of the workers, assuming that the demand is 4 baskets per minute.

2. Assuming that the process starts from time zero, answer the following questions:

How long does it takes to complete the first basket?

After exactly one hour of work, how many baskets have been completed?

Suppose now that one of the workers of the first stage misses one day of work. How many baskets can be finished in the first hour of work?

3. Arriving the high season of production of raspberries, the Manager of the packing process decides to triple the capacity of this system. He proposes to increase the number of workers from 4 to 12. However, after consulting with an "expert" in operations, they discover that it is only necessary to hire four additional workers to achieve this increase in capacity.

Show how you can be triple the capacity of the process using four additional workers.

How do you explain that doubling the number of workers triples the throughput of the system?

Analyze the system after hiring these four workers, as referred to in (a).

4. To increase the productivity of the system, the administrator of the packing considers buying a machine to speed up the second phase, allowing the person to fill a basket every 12 seconds. Suppose that:

each additional basket provides a gain of 100 pesos

a workday lasts 8 hours,

the machine costs 200,000 pesos,

In how many days is the machine paid?

Question 3.

"Uncle Eduardo" is a small business that sells steaks to order. They are currently analyzing the production process in their store. To sell steak the following stages are performed sequentially:

1. Take the order (1 minute per order).

2. Cut the bread and add the meat/cheese (3 minutes per order).

3. Add the vegetables and seasonings (4 minutes per order).

4. Prepare tray with napkins, services, and dish (2 minutes per order).

There is a separate person working on each of the stages of the process. Make a flow diagram and indicate the capacity of each stage and the amount of time it takes to produce the first unit. Then, help Eduardo answer the following questions:

What is the capacity of the local?

If we add a worker to the production line, in which stage should we add him? What would be the benefit?

Is there any benefit in reducing the time of the second stage in a minute, and adding it to the first stage?

Is there any advantage in reducing the time of the third

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