5.1
Background of company X.
Company X is a global leader in the production of
centrifuges for use in laboratories worldwide. It has been in existence for close
to 100 years and over this period it has concentrated on building a variety of
products to meet customers’ laboratory needs. It has also pioneered several
technologies during this period. X is an ISO 9000 certified company and also
meets several standards for companies dealing in centrifuges (IEC 1010-2-020,
CE Mark, CSA). X’s supplier base has been approved on the basis of its past
performance and the current operating systems. This has enabled the
establishment of a vendor certification program that ensures delivery of
quality parts to X. Company X is a wholly owned subsidiary of a larger
scientific equipment manufacturer with annual revenues of about $ 400 million.
The parent company handles some aspects of distribution and development for X.
In addition to doing direct sales and using its parent company’s sales network,
company X also distributes its products through Fisher Scientific
International, the world’s leader in distributing scientific products. Fisher serves about 250 000 customers and boasted
sales of $2.47 billion in 1999. Fisher uses a direct sales force and
customer-service organization consisting over 2,600 technicians as well as a
2500 page catalog and a website that hosts a digital version of the catalog
with real time information. These three distribution networks form the basis of
company X’s forecasting function.
5.1.1
What do they make?
Company X’s primary product line is centrifuges. As of
January 2000, it offered 36 different models broadly categorized into a
table-top version and a floor based version. A typical centrifuge has about 200
different components (this value was reduced from 300 mainly due to design
improvements) with some of these components being interchangeable between
models. In addition to complete centrifuges, company X also sells centrifuge
accessories such as rotors, buckets, adapters, heating jackets, tubes and
carriers. Collectively, these accessories constitute 316 different parts with
over one third of them being rotors. For each major piece of equipment, company
X uses a serial number to monitor its motion through all the stages of the
manufacturing cycle by using markings, labeling and accompanying documentation.
5.1.2
Who are their
customers?
Company X has two categories of customers. The first is the
US government which can be categorized as a single large customer that deals
directly with company X and offers
predictable forecasts. The second customer constitutes individuals and
scientific institutions who place their orders with company X. Through its
Fisher representatives, company X ‘s sales force also deals indirectly with
customers. The prices for the items sold by company X range from less than $10
for some components to as much as $10 000 for
a complete centrifuge. All orders are handled through the sales
department which then creates the demand for the manufacturing department.
5.1.3
How long have they been
using MRP and what did they have before?
Company X has had its manufacturing system set up for close
to one century but it’s not until 1991 that they started running an MRP based
system. Immediately before this, they used a card system to control their
manufacturing process. These cards had different types of information such as
lot purchasing details, the vendors involved in securing a part and the part
number. These cards were stored in alphabetical order at a central location on
the plant floor and they never traveled with the parts as they went through the
various processes. There were three copies of each card with the first being
maintained at the central location and the second being kept by a receiver. In
addition to handling the cards, the receiver was also responsible for
travelling with the raw material. The information generated in the system was
usually run on computers and stored in the form of punched cards that were
processed near the company premises.
5.1.4
Are they making any
attempts to integrate with lean?
Company X has recently embarked on efforts to make its
system lean. They already have a
version of cellular manufacturing at the assembly stage of production although
the cells do not operate strictly on the principles of lean manufacturing.
Another area they have worked on is the reduction of inventory. This inventory
has been halved from about 6 million to 3 million parts over the last 3 years.
The company has the potential to convert its system from MRP to lean and there
are several part families that would easily be used for a pilot study.
5.2
Description of Company
X’s MRP II system based on one product line
The MRP system at company X was analyzed by studying the
manufacturing processes for the base plate (part A) that goes into one of the
table-top centrifuge models (model B). The model B centrifuge comes in
twenty-two different specifications based on the operating voltage and the type
of rotor used. As mentioned before, the centrifuge would has close to 200
different components including part A. When fully assembled it weighs about
11kg and has dimensions of about (30-60cm height, 35cm width and 40 cm depth).
5.2.1
Product types and sizes
Part A is made of aluminum and arrives at the shop floor in
its cast form. It subsequently undergoes 5 different manufacturing processes
before it is used in the final process of assembling model B. Part A moves in
lot sizes of 125 pieces. A stack of
these pieces can be seen in the attached photos in appendix 2. A planner work
order accompanies each lot and every time an operation is completed, the
machine operator signs off. The machines at the various workstations are
arranged in a departmental format. Part
A consequently has to travel a lot as it moves between workstations.
5.2.2 Value stream of part A and model B from
forecast to shipping
The value stream for part A shows the various stages it goes
through from the moment it is received from the vendor to the stage when it is
assembled into the model B centrifuge. This information is presented in figure
6 which shows the value stream for part A as it goes through the different
workstations on the shop floor. The information flow is also indicated.
Figure 6. Value Stream of part A of the Model B
centrifuge
1. Purchase based on forecasts
The first step involves the purchase of the cast aluminum
parts. These parts are obtained from the vendors by the buyers based on
information received from the planners. The plans are developed based on the
projected forecast of demand. At
company X, the planners spend about 4hrs every 3 weeks doing long term plans
and 4 hours a day re-planning and doing shorter term planning. Currently one
planner is shared by several buyers but company X would like a system where
each buyer is assigned their own planner. This relationship is summarized in
the flow map shown in figure 7.
Figure 7. Relationship between Forecasts, the MPS and
the MRP modules at company X.
The biggest problem facing company X right now is that the
Forecast and MPS modules do not run the MRP module and hence the system is never
in control. This problem is characteristic of push systems and particularly MRP
as pointed out by Cochran in chapter 4. Company X has a ‘Dock-to-Stock’ time (the time interval between the arrival
of the ordered part at the dock and its arrival at the first workstation for
processing) of 1 day. All the inventory representing received stock is housed
in one central section near the section of the shop floor that contains the
various machines. There is usually a turnover of one month but some of the pieces
have as much as a 6 month turnover. Order preparation by the buyer takes about
5 days. The sales team works with an average lead time of 14 days and therefore
promise customers a delivery time of two weeks from the time they receive an
order for a model B centrifuge. However, manufacturing works with a lead time
of about 60 days which in reality reduces to 30-45 days. For the rest of this
analysis I shall use the sales lead time of 14 days.
2. Machining
The first process involves turning part A on a lathe until
it achieves the desired dimensions. The process uses an automated puma 10
Daewoo machine which is manned by a worker at all times. The entire lot of 125
parts takes up a total of 18.625 hours at the work station. This time includes
a set up time of 3 hours and a run time of 0.125 hours per part.
3. Milling
The second process is a milling operation during which holes
are drilled in part A and certain sections are milled to their finished
quality. The process uses an automated Hitachi Seiko HC 500 machine which is
also manned by a worker. The lot takes 55.5 hours to be processed which
includes a 3 hour set up time and a run time of 0.42 hours per part.
Before part A proceeds to the next process, a small metallic
bracket is fixed onto the milled part using a small portable rivet gun that is
located on one of the worker’s tables. The time taken is negligible and is
therefore ignored in this analysis.
4. Washing
This process uses a large industrial size Typhoon Proceco
washer. Since it operates as a batch process, it is possible to handle more
than 125 pieces at a go. This process has no set up time. Therefore the entire
lot takes 2.4 hours, which roughly translates into a runtime of 0.0192 hours
per part.
5. Pre-finish
This process includes all the steps that have to be taken to
prepare for painting. The run time is 0.06365 hours which translates into a
processing time of 7.95625 hours.
6. Painting
Part A is spray painted by hand in special booths. Several
booths lie adjacent to each other and the process just requires the lot to be
wheeled to one of these booths. A worker manning the booth uses a spray gun to
paint each part individually. There is no set up time for this process but the
run time for each part is 0.0926 hours translating into a total processing time
of 11.575 hours for the entire lot. Usually the parts are heated so as to
reduce the drying time. When there is not enough capacity at company X, outside vendors are sometimes used to do the
painting.
7. Assembly
Once part A has been painted, it is delivered to the
assembly area. There are 4 different assembly cells at company X. Each cell
handles a different family of centrifuges and they are color coded as follows:
yellow (large floor models), green (refrigerated and non- refrigerated models),
red (large table top models) and blue (small non-refrigerated models). Model B
is assembled in the blue cell. The
assembly process is done in four steps. During all the stages, each centrifuge
is accompanied by an inspection sheet that indicates any problems that are
encountered during assembly. In the first step the base is assembled. This is
the stage where part A is incorporated into the centrifuge. In refrigerated
models, the refrigeration unit would be added next but this step is not
necessary for model B. Next, the cabinet that forms the centrifuge housing is
added followed by the transformer for voltage conversion. The final step
involves testing the centrifuge for performance. Centrifuges that pass the test
are packaged and sent to the shipping dock ready for delivery to the customer.
In case problems are encountered for a given part during
assembly, the workers will try to resolve it themselves. If that fails, the
part will be put aside and the manufacturing or design engineers will be called
in to rectify the problem. This ensures uninterrupted production. The
manufacturing engineer is also responsible for obtaining feedback from the
workers in the cell and using that information to effect the necessary changes.
The workers in the assembly cell are cross-functional and can consequently
cover for a missing worker. However
they remain tied to one assembly process in the cell at all times. It takes
about one week to train a new worker. To facilitate this, a folder containing
information about the assembly process is kept at the cell. Also within the
cell is a computer terminal that is used to enter information into the MRP
system. Typically, each worker will update the records every time they finish
working on a part.
8. Shipping and Delivery
Parts are shipped and delivered on a daily basis. UPS makes
deliveries in the morning and collects shipments in the afternoon. They pick up
all the items that they find at the shipping dock and deliver them to the
various locations based on the information provided by the sales office.
5.2.3
The MRP Process at
company X
The MRP system at company X is designed to meet the demand
for the finished product while minimizing inventory. It therefore has the role
of determining the levels of intermediate good inventories needed to ensure
that the finished product demand will be met. This premise is what has led to
the design shown in figure 7. As mentioned before the sales forecasts and the
MPS module at company X do not run the MRP module. Typically when new orders
are received, they tend to use up all the forecast parts.
The MRP system at company X is based on the Glovia ERP
system produced by Miracle Information Systems of the UK. The Glovia system
incorporates both client/server technologies and object oriented standards. Company X has a modular system with
financial, sales and operation modules. It runs on Windows and uses an Alpha
Server system with an Oracle database. Company X made the upgrade to Windows in
mid 1999. This is an example of how companies normally solve MRP problems
through software improvements as discussed in Chapter 2. The operations module
is further subdivided into three parts: Inventory Management, Master Production
scheduling and Material Requirements Planning. This module integrates closely with
the sales module and it provides data to the financial side. The following is a
description of the key parts of the MRP system designed by Glovia showing how
control is effected on the shop floor. This information is based on appendix 3 which shows the various interfaces of
company X’s MRP system, a purchase order form, an exception report, the
schedule of one of the cells and a work order.
Options
and Location Table
There are two versions of this table, one for the MPS module
(version i) and the other for the MRP module (version ii). Both versions
indicate if there is inventory on hand.
The MPS module has a planning horizon of 365 days and a
review time of (time bucket) of 7 days. An increase in stock is indicated as a
replenishment while a decrease is noted as a requirement. Replenishment of the MPS is carried out
using five documents; Purchase Order (PO), Computer Planned Order (CO), Work
Order (WO), Forecast Planned Order (FPO) and Supplier (Sup). Requirements of
the MPS are determined by four documents: Forecast (Fcst), Sales Order (SO),
Forecast Planned Order (FPO) and Demand (Dem).
Version i also indicates whether or not the forecast of demand has been
used. It indicates when the MPS regeneration was done and indicates the person
responsible.
The MRP module also has a planning horizon of 365 days but
it has a time bucket of 14 days. The documents that determine replenishment of
the MRP are identical to those of the MPS with the exception of the Computer
Planned Order (CO). The documents for determining requirements are identical to
those of the MPS.
MRP/MPS
Planning Detail Inquiry
This table is used in netting so as to determine if there is
sufficient material to meet the demand. It offsets the requirements from the
replenishments to give the net number of items available. In addition it gives
a reference number for the item(s) in question, the delivery date of the
replenishments, the due date of the requirements and the quantity of each
desired. The attached tables show the netting calculations for the model B
centrifuge (version iii) and a component (part C) of the centrifuge, which is
not the same as the aluminum base studied earlier (version iv).
Version iii uses the sales order and the forecasts to
determine the requirements. Note that the net available stock for this case is
always a negative value meaning that the shop floor is short of material. This
is a characteristic of MRP that results form its effort minimize inventory such
that material from the vendors is held back until the last possible moment.
Version iv uses the work order, the MPS and forecasts to
determine requirements and purchase orders to do replenishments. Note that
there is initially a net positive amount of stock as of the 10th of
February but this quantity gradually declines to a negative value on the 7th
of March as requirements are met. The first replenishment is not made for
another 14 transactions until the 17th of March when an order for
135 pieces of part C are made. However the stock remains negative until the 6th
of April when the second replenishment is made. The remaining appendices show
copies of the purchase order form, the MRP exception report, the schedule for
the red cell and a work order form. Note that the exception report is typically
eighty pages long and the sheet shown is from page 44.
5.3 General observations
Company X does not pay attention
to the capacity of the plant. Although a detailed capacity planning module that
tells what the actual situation on the shop floor exists, it is not used.
Instead they use an excel spreadsheet that is updated frequently to assign jobs
to the various machines. This was pointed out in chapter 2 as one of the
weaknesses of MRP system.
In spite of
company X doing their planning a month ahead, it was noted that the mix of
orders placed wasn’t usually met. However, their sales targets were often successfully
met. This inaccuracy shows that the MRP system does a bad job of leveling the
orders and this can be attributed to the large lot sizes and the long
throughput time.
In summary,
company X’s MRP system did not work very well because it had to deal with the
randomness of the shop floor. To do this, it needed certain conditions to exist
on the shop floor, which wasn’t necessarily the case at company X i.e.: A large
backlog, excellent forecasts, vendors who didn’t miss quality targets, vendors
who kept to schedule, existence of large inventories and short material lead
times. These can easily be correlated to the various constraints highlighted
using the decomposition in chapter 4.
Company X should
try to establish a lean system on its shop floor. Based on the solutions
suggested by Uday Karmakar in Chapter 2, company X could try implementing a
‘Tandem Push-Pull system’ or a ‘Requirements driven Kanban’ system. A proposed
design that meets the requirements of a lean system is discussed later in the chapter. The infrastructure to enable this transition
currently exists. A pilot cell can be based on a family of centrifuges for
example those assembled at the blue cell.
The throughput
time of part A is very high mostly as a result of lot delays and the long setup
times. Based on the processing and setup times provided, the throughput time is
96.05625 hours (about 4 days). This does not take into account transport delay
or machine downtime. The actual value adding time is less than an hour
(0.72045hr). This could have been predicted by the analysis provided in chapter
4 using the Manufacturing System Design Decomposition. This information is
shown in figure 5. This delay is clearly illustrated in figure 8 which compares
the delay processing time for a run size of one and a run size of 125.
The performance of the MRP system
at company X can be illustrated using the following real life data for a part A
order. On February 10th, an order was opened for 136 bases. By the
time the order was closed on April 6th, 132 bases had been completed
and 4 remained. Starting April 14th, the parts started being used in
the assembly process.
5.4 New and improved value stream map with linked cell system
A new and improved design for
company X’s shop floor is presented in figure 9. In the lean design with linked
cells, the plant floor is divided into three main processing areas. There is a
set of cells that carry out the primary processing of part A i.e. milling and
turning on a lathe. In this area, there are four almost identical sets of
machines that contain either two mills and a lathe or two lathes and a mill.
Before and after each of these machines, there exists a decoupler where the
unprocessed / processed part is placed
Figure 8. Excel Spreadsheet showing the delay introduced into the
system due to the large lot size (125 parts) compared to a lot size of 1 part.
in between cycles. When a part is
placed on the decoupler located after one of the milling machines, the metal
bracket that was described earlier in the chapter can be fixed as the part
waits on the decoupler before it’s next process. The cell cycle time for this
area will be determined by the slowest machine (or the longest process to be
done on part A which in this case would be the milling operation). Since all
the machines would be running in parallel, a complete part would be produced
from the cell after each cycle time.
Figure 9. New and improved value stream map
with linked cell system
The second area
constitutes the washing process and the painting process. Sincere there is only
one washer available and it has a large capacity, the parts can be brought to
it in given batch sizes that ensure downstream processes are not kept waiting.
Given the small processing time for the washer, this process can easily be
coordinated to match the cycle time in the previous and subsequent cells. The
part from the previous cell is carried from the last decoupler and taken to the
decoupler next to the washer where other parts from the other cells on the shop
floor are also assembled so as to build up volume. An ideal washer design would
use a conveyer belt such that the part never has to wait on other parts in order
to get processed.
The third area
is the assembly area. This area would have all the four cells (blue, red, green
and yellow). Parts coming from the washer would be placed on the appropriate
decoupler in each of these cells. As soon as a part is pulled out of the cell
to shipping, the part coming in from the washer would go into the cell and be
assembled into the centrifuge. Company x currently has these cells set up and
the only challenge would be to design their location so as to minimize
transport time to the shipping dock.
The information
system would work as follows. A customer would make an order to the sales
office which would then coordinate with the manufacturing department to provide
the right mix and volume of parts to meet the demand of the various customers
for a given day. The customer can give
this information electronically through the web based system discussed earlier
in the chapter or using regular purchase order forms sent directly to company X.
The ‘heijunka’ is a system that carries out the role of distributing demand in
terms of volume and mix. Information from the ‘heijunka’ is then communicated
to the four assembly cells using a signal kanban which tells the cells what to
produce. The four assembly cells pass this information backwards to the washer
and painting area and subsequently to the four primary processing cells. In
this way production is driven by the customer demand. When the completed part
is pulled out of the assembly cell and is sent to shipping, it is picked up
daily whenever the delivery services comes by to collect parts to be delivered
to the customer. The parts delivered from the vendor are also delivered daily to company X based on parts that have
been pulled out of the four primary processing cells. This arrangement ensures
that sales targets are met both in terms of mix and volume.
The customer
demand can be used to determine the takt time which is simply the total
customer demand divided by the available manufacturing time. The goal is to
ensure that each of the cells on the shop floor has a cell cycle time that is
equal to or less than the takt time. In this way, company X’s shop floor will
be designed to keep pace with the customer demand. The arrangement in cells has
the added advantage that various parts for any of the four centrifuges can be
processed at any of the four primary processing cells provided the number of
milling or turning operations is known. For processes requiring more than three
operations, two cells can be combined to provide more machines for the
additional operations. The speed of the cells can be varied by adding or
reducing the number of workers operating the cell since they would each be
cross-trained to handle any of the machines in their cell. Note that the
workers are not tied to a given machine.