Chairvana’s Table Assembly Operations: Chairvana Inc. manufactures metal tables and chairs at its plant in Paxton,...

Chairvana’s Table Assembly Operations:

Chairvana Inc. manufactures metal tables and chairs at its plant in Paxton, Illinois. Recently hired general manager, Bob Behar, is concerned about the large inventories and manufacturing inefficiencies in the plant. The Paxton plant has two separate assembly lines – one for chairs and one for tables. Demand for chairs is significantly larger than tables, so Bob decides to tackle the table assembly process for first. Bob has recently hired a summer intern, Eileen Mayer, who he asks to study the table assembly line and suggest ways to improve the process. Having recently completed a course on operations management, Eileen decides to create a value stream map for the process. Over a period of several days, she collects the following information about the process.

Features Descriptions
The Assembly Line The assembly line operates one 8-hour shift per day, 5-days a week.
The Product Chairvana makes one type of folding table. The table has two bent metal tubes that form the legs and a formed sheetmetal top.

Demand for the tables is about 2000 tables per week.

Raw material storage Raw material for the table assembly line consists of the formed sheet-metal tops which are manufactured in the sheetmetal forming department elsewhere in the plant, and steel tubes for the legs. The tabletops are made in batches of 2000 and brought to the assembly area and on average the amount of tabletop inventory is 1000.
Cut tubes for the legs are delivered by steel supplier, Steely Hollow, every week in batches of 4000 tubes, so there are on average 2000 tubes in inventory. In addition, there are hinge pins, fasteners, rubber feet and cardboard boxes that are required. These are ordered in large bulk quantities and stored at the respective assembly stations.
Hole punching Holes for the hinge pins are punched in the tubes. There is no set-up time for this operation but tubes are punched in batches of 100. Eileen observes that the punching station can produce 120 hole-punched tubes every hour. She notes that there are approximately 2500 hole-punched tubes in a work-in-process storage area waiting for the bending operation
Leg Bending In this operation, the hole-punched metal tubes are bent in the shape of a U. There is no set-up required for this operation. The bending operation requires 1 minute per tube and there are two bending stations that work in parallel. There are approximately 3000 bent tubes awaiting assembly.
Hinge assembly Two bent U-tubes are assembled to form the folding base of by inserting hinged pins. There are two hinge assembly stations and assembly requires approximately 2 minutes for each table base. There are no setups required. Eileen observes that there are about 1200 assembled table bases waiting for final assembly.
Table Assemble The tabletop is mated with the table base at the final assembly station. The operation requires careful adjustments and takes 3 minutes per table. There are three assembly stations. Assembled stations are transported immediately on a rolling conveyor to packing to avoid damage to the table.
Packaging The assembled table is packed in a card box for shipping. Each table requires approximately 45 seconds to be boxed and there are two packaging stations. Packaged tables are shipped to BigMart twice a week. On average, therefore there are about 500 packaged tables waiting to be shipped.
Planning and Scheduling To understand how the different stations received instructions about their daily schedules, Eileen spent a day with the production planning department. She learned that BigMart sends a monthly forecast of demand for tables electronically on the 25th of each month. In addition, a firm order for the week’s requirement is faxed to Chairvana on the previous Wednesday. Chairvana’s, planning department then looks at inventories and creates a work order for the week and a paper schedule is given to each station, except the Packaging station. Packaging does not need a schedule since it immediately packs whatever is made by Table assembly. The planning department also sends a weekly order for tubes to Steely Hollow, and tabletops to the sheetmetal forming plant.

To assist Eileen please answer the following questions

Calculate the Takt time for the table assembly process.

For each step of the process, calculate the cycle time in minutes and the capacity utilization

Calculate the total lead time and total processing time in hours and minutes.

Homework Answers

Answer #1

Tact time = Least time taken to make every table.

Let us look at time taken for every step of table:

1. Opening punching = Eileen sees that the punching station can deliver 120 gap punched tubes each hour. So time taken for punching openings in cylinders = 2 tubes for every moment. Each table requires 2 tubes. So politeness time for opening punching of cylinders = 1 minute.

2. Leg bending = 1 minute for two tubes (two machines are available in parallel)

3. Hinge Assembly = 2 mint for each table base

4. Table Assembly = 3 mint per table

5. Packaging = 45 sec per table

So Total Tact time = 1+1+2+3+0.75 = 7.75 mint of 7 mint and 45 sec

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