1. Introduction
“CDVD enter prises” is a customer driven optical storage m edia producer making about
90.000.000 CDs, Blu -rays and DVDs per year serving about 31.500 different customer s.
Production is divided into five sections: pre -manufacturing, manufacturing, graphics, printing and
packaging. In general, the production can be described as follows:
Pre -manufacturing : Each customer sends an email (or a CD) containing the data to be reproduced
by CDVD enterprises. This data is written to a unique mould a so -called “stamper” which is us ed
to make a disc ingot for further replication. The stamper consists of silicone or glass with a
diameter of about 20 centimeters. The data is written to a silicone – or glassmaster with a laser
beam that “records” the information that is going to be replicated . The information is recorded to
the disc by producing tiny indentations to the polycarbonate known as “pits” and “lands”.
Manufacturing: After the stamper is made the disc replication starts by using molding machines.
Here a syringe injects a he ated liquid polycarbonate (approx. 360 degrees Celsius) producing the
disc which already contains digital information, but cannot be scanned since at this stage the disc
is completely transparent . After a short cooling of the disc , one side of the disc (co ntaining the
information) is covered with a silver, aluminum or gold layer and thereafter is covered with
lacquer which reflects the laser beam in order to read the information from the disc. After a
quality inspection the discs are collected on a spindle.
Graphics: Within the graphics department the covers of the discs are produced according to the
customer’s provided graphic design. Here print stencils are made for the different printing
technologies (serigraphy or offset printing).
Printing: Depending on the quality requirements (high quality offset) the di scs are printed at a
serigraphy – or an offset machine. The difference between these two techniques is mainly that for
the serigraphy printing machines the mesh has to be cleaned after eac h order and that the colors have to be prepared beforehand. The offset printing machines contain the CMYK (cyan, magenta,
yellow, black) colors and therefore only the stencils need to be changed after each order.
Packaging: Within the packaging department , all orders are sent to machines which are either
fully – or semiautomatic. Here the covers, booklets, inlays etc. are a dded to the discs and are
pack ed according to the customer’s need ( boxes, paper bags, trays, etc.).
Since t he pre -manufacturing and grap hics section are very flexible and do not state a planning
pro blem these two sections are not included in the following description. Figure 1 depicts the
workflow through the shop floor which is organized as a flexible flow shop.
Figure 1: Structure of the production system
Work flows from left to right, each product moves through these sections and i n t otal there are 35
machines on the shop floor. The manufacturing section is divided into two parts: CD and Blu –
Ray, DVD production (thereafter DVD) . These two parts consists of seventeen machines; six can
be assigned to the CD and eleven to the DVD division . The machines are fully substitutable
within the two segments which means all DVD -orders can be made on every DVD machine, but an DVD -order cannot be transferred to the CD part . The printing section is structured into three
parts since three technologies are available to print the media: serigraphy division (SD),
kammann – (KOD) and metronic offset division (MOD) . These three parts consists of ten
machines, six of them are serigraphy, three are kammann offset and one is a metronic offset
machine. The SD machines are partly substitutable and the KOD machines are fully substitutabl e.
The packaging section is structured into four parts, the V1 (CD boxes), V2 (shrinking), V3 (DVD
boxes) and V4 (paper, cardboard and plastic bags) packaging and consists of 8 machines (2 for
each part) whereas the machines in V1, V3 and V4 are partly sub stitutable and V2 machines are
fully substitutable. The production operates 16 hours per day , seven days a week in two shifts,
bottlenecks work stations are in the printing and packaging section due to the varying product
mix. The next section describes th e (production) planning tasks and problems at CDVD
enterprises .
2. Production planning and control tasks and problems at CDVD enterprises
In general, p roduction planning and control at CDVD enterprises follows a hierarchical approach.
Figur e 2 shows the hierarchical structure and the planning tasks at the company .
Figure 2. Planning tasks as described in Fleischmann et al. (2008) In the following we will focus on four different problems (problem sets) that the CDVD
enterprises faces. These problem sets should form the basis for student projects which should
develop models or techniques to improve the situation at CDVD enterprises.
2.1 Mid -term problem sets
1) Customer inquiry management
For customer driven manufacturers – like CDVD enterprises – an additional task is included
within the mid -term planning level, namely customer inqui ry management (also see figure 3 ).
Figure 3. Process of a customer driven company
At first, the customers inquiry at the company by stating the desired quantity of product(s)
(CD, DVD, Blu -ray and the corresponding type of packaging) and their desired delivery date.
Here, t he main decisions are whether to accept or reject the customer order s (order
acceptance/rejection) and whether the desired due date of the customer is feasible or whether it
should be renegotiated (due date assignment or also due date setting) .
1.1) Order acceptance/rejection – Problem set 1:
By now the employee in charge of customer inquiry management at CDVD enterprises does
not reject any order which , as a consequence, leads to overutilization of certain machines and
a low service level. Therefore, the task is to analyze the effect of rejecting orders and to show
the potential improvement of certain performance measures.
1.2) Due date assignment / due date setting – Problem set 2:
One has to differentiate between the external due date which is set by the customer (which
might be negotiable) and the internal due date which needs to be calculated by the company in
order to decide whether to accept the external due date. By now , CDVD enterprises uses forward scheduling to set the internal due d ate. Start ing with
the expected date that the customer places the order (Email with the data for the CD/DVD/Blu
ray production) they add a fixed planned lead time of 6 days (3 days production, printing and
packaging , 2 days transport and 1 day buffer) and thereafter accept or renegotiate the due date
with the customer . A major weakness of this approach is that the capacities of the production
departments are not taken into account and thus the 6 days (fixed) lead time are mostly a bad
estimation of the actual lead ti mes.
2.2 Short -term problem sets
2) Shop floor control: o rder release – Problem set 3 :
After order acceptance and due date setting all (accepted) orders are collected in an order pool
(see figure 3 above) . This order pool is a (digital list ) of orders provided to the production
planner who decides (each day) which orders to release to the shop floor .
At CDVD enterprises orders are automatically released by an infinite backward scheduling
approach. Thus, the release date is calculated by subtracting a fi xed lead time of 3 days from
the given (external) due date of an order. Capacities of the machines are not considered which
leads to time -varying loading and thus to changing utilization levels at the machines and as a
consequence to shifting bottlenecks . Thus, high WIP levels and therefore long lead times are
observed which, as a consequence, le ad to a poor service level . The management seeks for an
improved order release mechanism; they are especially fond of an order release mechanism
based on workload c ontrol.
3) M achine scheduling – Problem set 4:
On the shop floor , supervisors need to decide on the schedule of orders on specific machines
that is – allocating orders to resources at a specific time.
Especially at the printing department, scheduling of orders to the nine different printing
machines is important. By now, supervisors make scheduling decisions using a rule of thumb.
Thus the managers and the supervisors request a decision support tool for detailed scheduling
at least for the six serigraphy machines.
Extra problem set – supply of polycarbonate :
In order to guarantee a smooth production, polycarbonate need s to be on stock when needed,
acquired in time and in good quality. Currently, the responsible employee forecasts the
demand for polycarbonate over a planning horizon of 14 days. Therefore, she looks at the
order book, the stock of the material and uses his torical data (simple average) in order to
anticipate the demand. The company looks for an inventory control policy that determines a
reorder point and quantity (the mean lead time of the supplier is 3 days).
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