030090704 MÜGE BAŞARAN 4th week

   1)           WORK SAMPLING:‘’process management’’

Old definition:

Work sampling is the process of making sufficient random observations of an operator’s activities to determine the relative amount of time the operator spends on the various activities associated with the job. Although it is not the express purpose of work sampling to determine how long specific tasks should take, work sampling data, when coupled with historical production data for key volume indicators and performance levelling, can provide information that can be used to establish standards. The major goal of work sampling, however, is to determine the proportion of the workday spent on certain types of work.

(Hwaiyu Geng, Manufacturing Engineering Handbook, p. 53.12)

NEW DEFINITION:

Work sampling is a technique for estimating the proportion of time that a worker or machine spends on various activities. Work sampling does not require direct timing of an activity. Rather, observers make brief observations of a worker or machine at random intervals over a period of time and simply record the nature of the activity (Stevenson, 20021 p. 331). The resulting data are simply counts of the number of times that each category of activity or nonactivity was observed. Work sampling has two purposes: to estimate the percentage of unproductive or idle time for repetitive jobs, and to estimate the percentage of time spent on the various tasks in nonrepetitive jobs—for example, estimating the time an RN spends on direct, on indirect, and on professional or nonprofessional tasks of patient care.

Work sampling has several advantages over time study. The observations are spread over a period or time, so results are less susceptible to short-term fluctuations. There also is little or no work disruption, and workers are less resentful. Work sampling studies are less costly and less time-consuming, and many studies can be conducted simultaneously. Observers do not need extensive skills, as long as they are trained properly to conduct the observation.

Despite the advantages, there are certain shortcomings of work sampling studies. First of all, they provide less detail on the elements and tasks of a job and often no record of the worker's method. Sometimes workers alter work patterns, which invalidates the results. If observers do not adhere to the random observation schedule, that further taints results. Work sampling studies should not be used for short, repetitive tasks.

 (Quantitative Methods in Health Care Management: Techniques and Applications, Yasar A Ozcan Phd,Yasar A. Ozcan, PhD,pg.235)

My definition is more detailed but the older may be considered as more understandable 

     2)           HACKSAW BLADES:’’cutting process tool’’

Old definition:

Hacksaws have straight blades and reciprocating motions. Developed in the 1650s, they generally are used to cut off bars, rods, and structural shapes. They may be manual or power operated. Because cutting takes place during only one of the two reciprocating strokes, hacksaws are not as efficient as band saws. Power hacksaw blades are usually 1.2 to 2.5 mm (0.05 to 0.10 in.) thick and up to 610 mm (24 in.) long. The rate of strokes ranges from 30 per minute for high-strength alloys to 180 per minute for carbon steels. The hacksaw frame in power hacksaw is hacksaw is weighted by various mechanisms, applying as much as 1.3 kN (300 lb) of force to the workpiece to improve the cutting rate. Hand hacksaw blades are thinner and shorter than power hacksaw blades, which have as many as 1.2 teeth per mm (32 per in.) for sawing sheet metal and thin tubing.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, Ed. 5th, p. 747)

NEW DEFINITION:

Hacksaw blades are made either of cast (high-carbon) steel or high-speed steel. Cast steel blades are quite satisfactory for general purposes, but for some work—for example, cutting cast steel—a high-speed steel blade is required. High-speed steel blades break quite easily; they are also considerably more expensive than cast steel blades. Cast steel blades may be all hard or flexible. The flexible blades, though softer, are less brittle. High speed steel blades contain a high percentage of tungsten. The east steel blades have a very small amount of tungsten. Flexible blades are hardened only along the teeth. 

Hacksaw blades are specified by: (1) the length of blade (203, 254, or 304 mm); (2) the number of teeth per inch (t.p.i.)—this may be 14, 18, 24, or 32 t.p.i.; (3) whether hard or flexible, and whether cast or high-speed steel.

 The teeth of a hacksaw blade are given a slight set, and this makes the saw cut slightly wider than the blade. The blade should always he put in the saw to cut on the forward stroke. For cutting very large-section mild steel, a blade of 14 t.p.i. may be used. Blades of 18 and 24 t.p.i. are useful for general-purpose work. For sheet metal, tubing, and soft non-ferrous metals, a blade of 32 t.p.i. is suitable.

 The expression t.p.i. will probably continue for some time after metrication as it has continued in countries with well-established metric systems of measurement.

(P. F. Lye , Metalwork theory, 1. Kitap ,P. F. Lye, pg. 11) 

My definition includes more specific information about the materials used for hacksaw blades

     3)           DEPENDENT DEMAND‘’ requirement planning’’

Old definition:

Dependent Demand (or derived demand) items are those components that are become part of some parent item or in some similar way become part of a set of components. Dependent demand inventories typically are consumed within the production system, not by some outside demand. Materials requirements planning (MRP) adn just in time (JIT) inventory management are two methods for managing derived demand inventories.

 (Financial Management, Third Edition, Shim&Siegel, p241)

NEW DEFINITION:

Dependent demand is the internal demand for parts based on the demand of the final product in which the parts are used. Subassemblies, components, and raw materials are examples of dependent demand items. Dependent demand may have a pattern of abrupt and dramatic changes because of its dependency on the demand of the final product, particularly if the final product is produced in large lot sizes. Dependent demand can be calculated once the demand of the final product is known. Hence, material requirements planning (MRP) software is often used to compute exact material requirements.

(Joel D. Wisner,Keah-Choon Tan,G. Keong Leong ,Principles of Supply Chain Management: A Balanced Approach, pg. 218)

The MPS and RCCP fix the production plan for all finished products, or decoupling items. Using a similar approach, that is, planning the production to meet uncertain forecasts, does not make sense for the other items in the BOM structure. One can do much better.

Once the production plan for finished products is fixed, one knows exactly when and in what quantity the components entering in the final production stage are required. This information has been called the dependent demand. So, we can replace uncertain forecasts by certain dependent demands, computed using the BOM structure. This eliminate: the major source of uncertainty from the planning process, and hence the major reason to hold huge safety stocks. Then, we can plan the production of these components to meet their dependent demand. These production plans determine in turn the de-pendent demand of their immediate predecessors.

This process can be repeated, level by level in the BONI structure, all the way through, from the finished products back to the raw materials. It is known as the Material Requirements Planning process. Its sequential aspect is illustrated in Figure 2.8 on the BOM structure from Figure 2.4, assuming a NITS policy. Observe for instance that the total dependent demand and the production plan of item C can only be computed after the production plans of both FP and A have been fixed.

(Yves Pochet,Laurence A. Wolsey, Production planning by mixed integer programming. Pg. 59)

My definition is prepared by using two sourcebook that’s why it is more clear to understand what is the word means.

4)           KNUCKLE-JOINT PRESS ‘’manufacturing process ''

Old definition: 

Knuckle-joint presses are customarily used for both coining and swaging because they combine high tonnage and a slow squeezing action to the workpiece rather than the sharp impact of a conventional press.

(Design for manufacturability handbook, James G. Bralla, p. 3.17)

NEW DEFINITION:

The knuckle joint, with a relatively small connecting rod force, generates a considerably larger pressing force. Thus, with the same drive moment, it is possible to reach around three to four times higher pressing forces as compared to eccentric presses. Furthermore, the slide speed in the region 30 to 40° above the bottom dead center is appreciably lower. By inserting an additional joint, the kinematic characteristics and the speed versus stroke of the slide can be modified. Knuckle-joint and modified knuckle-joint drive systems can be either top or bottom mounted. For cold forging, particularly, the modified top drive system is in popular use. Figure 11.22 illustrates the principle of a press configured according to this specification. The fixed point of the modified knuckle joint is mounted in the press crown. While the upper joint pivots around this fixed point, the lower joint describes at curve-shaped path. This results in a change of the stroke versus time characteristics of the slide, compared to the largely symmetrical stroke-time curve of the eccentric drive system (fig. 11.19). This curve can be altered by modifying the arrangement of the joints (or possible by integrating an additional joint).

                (Cold and hot forging: fundamentals and applications, 1. Cilt,Taylan Altan,Gracious Ngaile,Gangshu Shen, pg.130)
Because of adding pictures my definition becomes more understandable against the older one

 5)           PARTS EXPLOSION:‘’DFM cost estimation’’

Old definition:

The process of determining gross requirements for component items, that is, requirements for the subassemblies, components and raw materials for a given number of end-items units is known as parts explosion. Therefore, parts explosion essentially represents the explotion of parents into their components.

(Nanua Singh, Computer-Integrated Design and Manufacturing 1996, pg. 409)

NEW DEFINITION:

In a parts explosion (also called a bill of materials), the nodes are assembly units that eventually resolve down to individual parts from inventory, and each edge is the "is made or relationship. The top of the tree is called the root. In an organizational chart, it is the highest authority; in a parts explosion, it is the final assembly. The number of edges coming out of the node is its outdegree, and the number of edges entering it is its indegree. A binary tree is one in which a parent_node can have at most two children; more generally, an n-ary tree is one in which a node can have at most outdegree n. The nodes of the tree that have no subtrees beneath them are called the leaf nodes. In a parts explosion, they are the individual parts, which cannot be broken down any further. The descendants, or children, of a node (the parent_node) are every node in the subtree that has the parent_node node as its root. There are several ways to define a tree: It is a graph with no cycles; it is a graph where all nudes except the root have indegree I and the root has indegree zero. Another defining property is that a path can be found from the root to any other node in the tree by following the edges in their natural direction. The tree structure and the nodes are very different things and therefore should be modeled in separate tables.

(Joe Celko, Joe Celko's SQL for Smarties: Advanced SQL Programming ,pg. 665)

Older definition can be assumed as more clear but my definition is more satisfactory