In: Operations Management
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 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 value stream map for the process. Over a period
of several days she collects the following information about the
process. 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 sheet-metal top. Demand for the tables is about
1000 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 1000 and brought to the assembly area and on average the
amount of table top inventory is 500. Cut tubes for the legs are
delivered by steel supplier, Steely Hollow, every week in batches
of 2000 tubes, so there are on average 1000 tubes in inventory.
(Since each tube has 2 legs that is equivalent to 500 table bases.)
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. Because
these other parts are purchased in bulk externally, Eileen decides
that she will make a note of them but not analyze them further. The
Manufacturing Process: To maintain correct alignment during
assembly, at each stage of the manufacturing process, processing is
done on tube pairs i.e. two tubes at a time since a table requires
two bent table legs. Hole punching: Holes for the hinge pins are
punched in the tubes. There is no set-up time for this operation.
Eileen observes that the punching station can produce 60
hole-punched tubes every hour. She notes that there are, on
average, approximately 750 pairs of 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 an U. There is no set-up required for this
operation. The bending operation requires 4 minute per tube pair
and there are two bending stations that work in parallel. There
are, on average, 750 pairs of bent legs waiting for the next
processing step Hinge Assembly: A pair of bent U-tubes are
assembled to form the folding base of the table by inserting hinged
pins. There are two hinge assembly stations and assembly, and each
table base requires, approximately, 2 mins for hinge assembly.
There are no setups required. Assembled bases are sent to Footer
assembly on roller conveyors as soon as they are assembled and
there is no intermediate inventory. Footer Assembly: Rubber footers
are attached to the assembled bases and it takes 30 seconds to do
operation. There is only one station for footer assembly. Eileen
observes that, on average, there are about 800 assembled table
bases waiting for final assembly. Table Assembly: The table top is
mated with the table base at the final assembly station. The
operation requires careful adjustments and takes 6 minutes per
table. There are three assembly stations. Assembled tables are
transported immediately on a rolling conveyor to packing to avoid
damage to the table. Packaging: The assembled table is packed in a
cardboard box for shipping. Each table requires approximately 90
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 250 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 learnt 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
Footer assembly and Packaging station. These two stations do not
need a schedule since they immediately process whatever is sent to
them by the previous process step. The planning department also
sends a weekly order for tubes to Steely Hollow, and table-tops to
the Sheetmetal forming plant. To assist Eileen please answer the
following questions. For all questions consider table equivalents -
a table equivalent is 2 table legs.
1) Draw a Value Stream Map for the table assembly line. Show all
activity steps, material flows, information flows and
inventories.
2) Draw a timeline showing processing times and waiting times. (You
may use any drawing package including powerpoint to create legible
chart. You can also use a package such as Visio or Lucidcharts to
draw your chart. You will need to make a free account to use
Lucidcharts software if you choose to use it.
https://www.lucidchart.com/pages/examples/value-stream-mapping) (6
points)
3) Calculate the Takt time in minutes for the table assembly
process.(1 point)
4) For each step of the process, calculate the cycle time in
minutes and the capacity utilization(2 points)
5) Calculate the total lead time and total processing time in days,
hours and minutes. (1 point)
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