Manufacturing Task Sequence

Starting at the top, the assembly data object has one-to-many type of relationship with the part data object, whilst part object has one-to-one type of relationship with the assembly object. This determines the schema for the assembly objeet and bill of materials (BOM) is an example of it. The part object has one-to-one type of relationship with the task sequence object and it is the same viee versa. In practical terms this means that there is always a unique sequenee of tasks to manufacture the part dictated by the material and volume involved. The task sequence object has one-to-many type of relationship with the task object and the task object has a one-to-one type of relationship with the task sequence. This means that a task sequence often contains many different types of tasks. Finally, the task object has one-to-many type of relationship with the material object and equipment object, whilst the material and the equipment objects have a one-to-one type of relationship with the task object In practical terms this means that a task often utihses many different types of materials and equipment to make the parts. The determination of these relationships together with the object attributes lead us to the schema design that can hold all the information required for the manufacturing process design. The data relationships model of Fig. 3.2 integrates the key variables involved and their interactions... 

Availability constraints the macroscopic limits on material resources and the availability or up-time of equipment. Availability of raw materials is an obvious constraint at scheduling. Obviously, no catalytic hydrogenation can be done if the catalyst is unavailable. Simultaneous operation of certain tasks is restricted by the limited availability of common utilities such as steam, electricity, or labour. The priority sequence in a product chain needs to be respected by ensuring that intermediate products are manufactured in time to be available when required by a batch of the consecutive product. 

The first task is somehow to transfer the information from the DNA molecule contained within the nucleus to the site where the protein is to be assembled, that is, to the ribosomes attached to the endoplasmic reticulum. This is the job of m-RNA which is synthesized from DNA in a manner very similar to the synthesis of DNA itself, in a process called transcription. Transcription is controlled by RNA polymerase and because the DNA contains instructions for the manufacture of all the cell s proteins, only a few of which are likely to be needed at any one time, the enzyme must be able to recognize or select which particular DNA regions, representing the desired proteins, need to be transcribed at any one time. It probably does this by attaching to an area of DNA characterized hy having a specific nucleotide sequence - this is the... 

One of the main tasks of the DNA is to initiate the synthesis of proteins as and when they are needed. Proteins are synthesised in the ribosomes of the cell cytoplasm. DNA, however, is found in the cell nucleus. So how is the information contained in the DNA passed out of the cell nucleus and into the cytoplasm First, the DNA helix unfolds, and, in a process called transcription, a complementary strand of RNA is synthesised along a crucial part of one of the single DNA strands. This is the messenger RNA (mRNA) which leaves the cell nucleus and is transported into the manufacturing centres for proteins, the ribosomes. In the ribosome, transfer RNA (tRNA) delivers the amino acids required for polypeptide synthesis. The sequence of each group of three bases on the mRNA determines which amino acid is next in the peptide sequence. For example, the sequence AGC in the mRNA specifies the incorporation of the amino acid serine. This process is referred to as translation (Fig. 1.27). The genetic code, i.e. which sequence of bases in the DNA strand refers to which amino acid is given in Table 1.5. 

Narrow-Range Tasks If the system is configured so that each individual server only performs a narrow range of tasks, then this usually means that a number of different servers are required in order to perform all the required tasks for a customer. This means that the system will often be similar to a manufacturing flow line and so can be represented by queues in series. Of course, if there is some flexibility in the sequence in which tasks are done, then the system becomes more like a manufacturing job shop and can be represented by a network of queues. 

The production of high-value-added products (pharmaceutical active principles, agrochemicals, etc.) has stimulated investigations on batch processes for several decades. Generally, a batch plant can manufacture several products sharing standard equipment in a series of production campaigns, with the ability to adapt itself to variations of raw materials and to rapid market flucmations. A batch process involves discrete tasks embedded in an interconnected predefined sequence from raw materials to final products. The predefined sequence is commonly known as a recipe. The recipe consists of the amount of raw materials that are necessary to be involved in the individual tasks as well as their durations. It also includes the operating conditions of the tasks as well as additional constraints of the process (safety features for instance). 

The assembly sewing process is the most labour-intensive part of apparel manufacturing. The progressive bundle unit system is common in sewing room design. Recently, many manufacturers have installed unit production systems as a means to improve efficiency and effectiveness. Assembly involves a set of workstations in which a specific task of a pre-defined sequence is processed. 

Usually, for the production of small quantities of high-priced chemicals, such as in th manufacture of pharmaceuticals, foods, electronic materials, and specialty chemicals, batch fed-batch, and batch-product removal processes are preferred. This is often the case in bio processing, for example, when drugs are synthesized in a series of chemical reactions, eacl having small yields, and requiring difficult separations to recover small amounts of product This is also the case for banquet facilities in hotels, which prepare foods in batches, and fo many unit operations in the manufacture of semiconductors. As discussed in Chapters 3 am 4, these processes usually involve a recipe, that is, a sequence of tasks, to be carried out h various items of equipment. In the latter sections of this chapter, variations on batch proces schedules are discussed, as well as methods for optimizing the schedules. 

Manufacturing deals with the transformation of materials into forms. This is a creative process and demands considerable know-how of engineering processes. The material and the part form have a considerable influence on the manufacturing process and this starts with the attributes of part, they enable the development of sequence of tasks that generate the final form. 

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