1- Random sampling (in statistical quality control)/ (Quality Control)
Previous definition:
Taking a sample from a
population or lot in which each item has an equal change of being included in
the sample. Thus, when taking samples from a large bin, the inspector should
not take only those that happen to be within reach.
(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology,
Ed. 5th, p. 1121)
Current Definition:
The units selected for inspection from the
lot should be chosen at random, and they should be chosen at random, and they
should be representative of all the items in the lot. The random-sampling
concept is extremely important in acceptance sampling. Unless random samples
are used, bias will be introduced. For example, the vendor may ensure that the
units packaged on the top of the lot are of extremely good quality, knowing
that the inspector will select the sample from the top layer. ‘’Salting’’ a lot
in this manner is not a common practice, but if it occurs and
nonrandom-sampling methods are used, the effectiveness of the inspection
process is destroyed.
The technique often
suggested to draw a random sample is to assign a number to each item in the lot.
Then n random numbers are drawn, where the range of these numbers is from 1
to the maximum number of units in the
lot. This sequence of random numbers determines which units in the lot will
constitute the sample. Random numbers can be conveniently generated from a
computer, from many hand-held calculators, or from tables of random numbers
such as in Appendix IX. If products have serial or other code numbers, these
numbers can be used to avoid the process of actually assigning numbers to each
unit. Another possibility would be use a three-digit random number to represent
the length, width, and depth in a container. For example, the random number 482
could represent the unit located on the fourth level, eighth row, and second
column of the container.
In situations where we
cannot assign a number to each unit, utilize serial or code numbers, or
randomly determine the location of the sample unit, some other technique must
be employed to ensure that the sample is random or representative. Sometimes
the inspector may ‘’stratify’’ the lot. This consists of dividing the lot into
strata or layers and then subdividing each strata, into cubes, as shown in
Figure 13-1. Units are then selected from within each cube. While this
stratification of the lot is usually an imaginary activity performed by
inspector and does not necessarily ensure random samples, at least it ensures
that units are selected from all locations in the lot.
Introduction to Statistical Quality Control 2nd Edition , Douglas C. Montgomery, Pg. 555
Mustafa İnan Kütüphanesi
TS156 .M66 1991
2-
Scheduling (in flexible manufacturing
systems)
Previous
definition:
Because FMS involves a major capital investment, efficent
machine utilization is essential. Machines must not stand idle. Consequently,
proper scheduling and process planning are crucial. Scheduling for FMS is
dynamic, unlike that in job shops where a relatively rigid schedule is followed
to perform a set of operations. The scheduling system in FMS specifies the
types of operations to be performed on each part and identifies the machines or
manufacturing cells where these operations are to take place. Dynamic
scheduling is capable of responding to quick changes in product type; hence, it
is responsive to real - time decisions.
(Kalpakjian S. , Schmid
S.R. , Manufacturing Engineering and Technology, p. 1223)
Current Definition:
Scheduling is the process of organizing, choosing and timing resource usage to carry out all the activities necessary to produce the desired
outputs of activities and resources. In an FMS,
the objective of scheduling is to optimise the use of resources so that the overall production goals are met. A Fuzzy Based Scheduling Model for FMS which is developed here aims at making real-time control decisions that include dynamic scheduling and variable part routing used to solve
scheduling problems in FMS environments.
Attempts will be made to use a an industrial implementation for experimentation.
Otherwise the model will be verified using data from literature.
Process planning and scheduling are important manufacturing planning activities which deal with resource utilization and time span of the manufacturing operations. In order to cope with competitiveness and globalization of today’s business environment, supply chains become more complex, and manufacturing processes have become more advanced, however products have to be manufactured in higher varieties and smaller batches. It is essential to establish effective and efficient process plans and production schedules to cope with the highly dynamic manufacturing requirements. Some automobile manufactures are gradually adopting their production ways to support the diversity of the customer needs and increase the changing speed for the developing the new products [1].
1. Scheduling of Flexible Manufacturing
Systems Using Fuzzy Logic by Pramot
Srinoi
A/Prof. Ebrahim Shayan Dr.
Fatemeh Ghotb, School of Mathematical Sciences pg. 95
2.
Manufacturing
systems and technologies for the new frontier [electronic resource] : the 41st
CIRP Conference on Manufacturing Systems, May 26-28, 2008, Tokyo, Japan /
Mamoru Mitsuishi, Kanji Ueda, Fumihiko Kimura, editors, pg. 269
3-
Product quality /(Quality Control and Manufacturing)
Previous
definition:
In view of rhe
global economy and competition, a major priority in produckt quality is the
concept of continuous improvement as ezemplified by japanese term
kaizen,meaning never ending improvement.Still the level of quality that a
manufacturer chooses for its products depends on the market for whichthe
products are intended.Low cost,low quality products have their own market
niche,just as there is a market for high quality,expensive products,such as a
high precision machine tool, a rolls royce automoile, a private airplane or
yacht or sporting equipment.
Kalpakjian, S., Schmid, S. R., Manufacturing Engineering and
Technology, 5th ed., p. 1242
Current definition:
The collection of features and characteristics of a product
that contribute to its ability to meet given requirements. Early work in
controlling product quality was on creating standards for producing acceptable
products. By the mid-1950s, mature methods had evolved for controlling quality,
including statistical quality control and statistical process control,
utilizing sequential sampling techniques for tracking the mean and variance in
process performance. During the 1960s, these methods and techniques were
extended to the service industry. During 1960–1980, there was a major shift in
world markets, with the position of the United States declining while Japan and
Europe experienced substantial growth in international markets. Consumers
became more conscious of the cost and quality of products and services. Firms
began to focus on total production systems for achieving quality at minimum
cost. This trend has continued, and today the goals of quality control are
largely driven by consumer concerns and preferences.
McGraw-Hill Concise
Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.,pg. 559
4-
Interpolation /(Manufactoring / automation)
Previous definition is not found on the web page !!
Current definition:
Movement along the path (interpolation) occurs incrementally
by one of several basic methods (Fig. 37.11). Examples of actual paths in
drilling, boring and milling operations are shown in the Fig. 37.12.
In all interpolations, the path controlled is that of the center of
rotation of the tool. Compensation for different types of tools, for different
diameters of tools, or for tool wear during machining can be made in the NC
program.
·
In linear interpolation , the tool moves in a
straight line from start to end (Fig.37.11a) along two or three axes.
Theoretically, all types of profiles can be produced by this method by making
the increments between the points small (Fig.37.11b). However , a large amount
of data has to be processed in order to do so.
·
In circular interpolation( Fig. 37.11c), the
inputs required for the path are the coordinates of the end points, the
coordinates of the center of the circle and its radius, and the direction of
the tool along the arc.
·
In parabolic interpolation and cubic interpolation,
the path is approximated by curves using higher-order mathematical equations.
This method is effective in 5-axis machines and is useful in die sinking
operations for the sheet- forming of automotive bodies. These interpolations
also are used for the movements of industrial robots.
(Manufacturing
Engineering and Technology 5th Edition , Serope Kalpakjian, Steve R.
Schmid, Pg. 1158)
5-
Low cycle Fatigue/ (Material)
Previous definition
The cyclic loads are relatively high, significant amount of
plastic strain are induced during each cycle, and short lives or low numbers of
cycles to failure are exhibited if these relatively high loads are repeatedly
applied. This type of behavior has been commonly called low-cycle fatigue or,
more recently, cyclic strain-controlled fatigue. The transition from low-cycle
fatigue behavior to high-cycle fatigue behavior generally occurs in the range
from about 10^4 to 10^5 cycles, and many investigators now define the low-cycle
fatigue range to be failure in 50000 cycles or less.
Failure of Materials In Mechanical Design,
Jack A. COLLINS, John Wiley & Sons, 1993, Second Edition, p.393
Current Definition:
The phenomenon of
low cycle fatigue can be in principle described in terms of the theory of
plasticity. In fact, low-cycle fatigue is a cyclic elastoplastic deformation
occurring until the expenditure of plasticity reserves. The material behavior
at unloading and reversed loading, in particular the shape and size of
hysteresis loops, is of essential significance in low-cycle fatigue. The
relation between maximal stress and strain within a cycle generally differs
from that in monotonic quasistatic loading. The cycle-deformation relations
depend on the type of loading process. They change whether this process is
load- or displacement-controlled loading the maximal cycle stresses grow with
the cycle number. Other materials reveal a tendency to cyclic softening. An
intermediate place is occupied by the so-called plastically stabilizing
materials. Depending on the microstructural state and temperature, the same
material may behave in various ways. Typical diagrams of uniaxial
tensile/compression deformation σ(ε) are shown in Figure 1.8. They correspond
to symmetrical cycle loading with the given strain amplitude . Figure 1.8a shows the behavior of a
cycle-dependent hardening material; Figure 1.8b that of a softening material.
When the strain level
is high, cycle number at fatigue failure is comparatively small, and
significant one-sided residual deformations accumulate in the specimen. At a
moderate strain level, teat results are convenient to represent with fatigue
curves. Compared with high-cycle fatigue curves, low-cycle fatigue curves are
usually plotted on the plane of characteristic strain versus cycle number at
failure. Standard test in tension or tension/compression are usually performed
maintaining a constant range Δε of the nominal (average upon all the working
parts of a specimen) strain ε.
Mechanics of fatigue /
Vladimir V. Bolotin, Boca Raton : CRC Press, c1999 , pg. 9,10,11
Mustafa İnan
Kütüphanesi TA418.38 .B65
1999
