2nd week Ebubekir Çantı 030070154

1) Kevlar(Material)

Kevlar  is  an  aromatic  polyamide,  (aramid). It  is  a  para  isomer  that  is  produced  from p-phenylenediamine  with  isophthaloyl  chloride. Kevlar has very high strength and is used  as a tire cord  and,  with  short  fibers,  as  a  substitute  for 

asbestos, for example, in high-temperature gaskets. It  is  also  used  as  reinforcement  in  bulletproof vests. To make kevlar fabric, rods of the polymer, polyparaphenylene  terephthalamide, are extruded  through  spinnerets  to  produce  fine  fibers  which  are  spun  together o  make  yarns  that  can  be woven. 


Handbook of Manufacturing Process, James  G.  Bralla, p.703 


(Previous description)(better)

Kevlar

The most widely known aramid is Kevlar, formed by the reaction between 1,4-diaminobenzene and benzene—1,4-dioyl chloride. Molecules of Kevlar consist of benzene rings linked together by amide groups at diametrically opposed carbon atoms. For this reason Kevlar is classified as a para aramid, “para” being the term used to identify the relative positions of chemical groups on opposite sides of the same benzene ring.

Kevlar is resistant to abrasion, mildew, most solvents, and many common chemicals, such as fuels and lubricants. It retains most of these properties a temperatures as high as 350˚F (180˚C) and is difficult to ignite. Kevlar decomposes at around 7200˚F (4000˚C) without melting.

While the strength of Kevlar makes it an extremely useful material, it also makes it a difficult substance to cut and machine. Conventional cutting tools –serrated scissors, shears, and saws, for example- can be used provided due attention is paid to sharpness and the conditions of use. Advanced cutting tools, such as lasers and high-energy water jets, are better suited to the job.

A weak point of Kevlar, its low compressive strength, which makes it prone to crumble under large compressive forces, can be overcome by using Kevlar in composites with materials of high compressive strength, such as glass fiber.

(Cavendish M., How It Works: Science And Technology, 3^rd Edition, page 1805)

2)Value Analysis(better)(Production)

The  value  analysis approach  requires, first  of  all, that  valid  and  complete answers be developed for the following five questions:

1. What is the item or service?

2.  What does it cost?

3. What does it do?

4. What else would do the job?

5. What would that alternative cost?

These basic questions serve the  end  of  uncovering needed pertinent facts. With the establishment of  answers to them, the foundation is  laid for developing objective  data  for presentation  to the  decision makers. Hence the importance of  understanding  and effectively using these questions cannot be overemphasized. W hat is the item or  service?  This question is usually quite readily determined from objective data. What  does it cost? Here the answer is often obtainable from effective and meaningful cost data, but sometimes such costs  are dacult  to obtain. This will  be further  developed in technique 2 of  the more results techniques presented in Chapter 8. What  does it do?  For the moment, all else except precisely the question, "What  does it do?"  must be disregarded. This means that  we  put aside such questions as:

What machines does the factory have?

What processes does the factory customarily use?

What special skills do the factory people have?

What special skills  are available in the drafting  and planning organi-

zations?

Admittedly, all these additional questions embrace considerations that 

will  enter into  decision making,  but  at this stage of  value  analysis, the  

establishment of  sound criteria for decision making is handicapped if  any 

of  these questions are allowed to interfere with the  effective generation 

of  objective data such  as,  "It conducts current,"  "It excludes dust," "It 

supports  the  operator," "It separates  dials,"  "It mounts the motor,"  "It 

mounts the control." 

What else would  do the job?  This is not a superficial question; it is a 

penetrating  one.  The  comprehensiveness  of  the  answer  to  that  simple 

question  governs, to  a high degree,  the  effectiveness and the  grade  of 

value work being done. No matter how skilled the searcher and no matter 

how diligent and creative his search, there will always remain alternatives 

which  he  did not bring  into focus, many  of  which would have  accom- 

plished the total performance reliably at very much lower cost. To ensure 

good  value content,  many  of  the special techniques  and  much  of  the 

special knowledge of  value  analysis must be  used in  getting substantial 

answers to this question. The approach here is  to search intensively for 

alternatives by: 

Studying handbooks 

Perusing trade literature 

Telephoning people who might have pertinent information 

Writing to specialists and to  companies who might  know  of  effective 

alternatives 

Focusing intense creativity sharply  on the  precise task to  be  accom- 

plished 

Refining the results of  these creative sessions and searching further for 

additional information 

Unless  this phase  of  the  work  is  effectively and  penetratingly done, it 

cannot be hoped that the product will have more than an average degree 

of  value. 

What would  that  alternative cost? Handbooks are full of  information 
on the properties  of  various  products  and materials and suggested uses 
for them. Notably absent from most of  these is  cost. This is quite under- 
standable. Costs vary from time to time while the properties of  materials 
and their functions are relatively stable. Furthermore, as our civilization 
has  developed,  it  has been a  basic necessity  to  find  materials which, 
within  the  appropriate size  and  weight range, accomplished the neces- 
sary functions. Therefore, the handbooks contain the information needed.



for these pursuits. When value is the objective, it becomes vital to have 
meaningful costs for decision making. Hence the question of  the cost  of 
alternatives must be effectively and objectively answered. 
Meaningful costs may  be obtained from a variety of  sources or from a 
combination of  sources: 
The cost department 
Cost analyses 
Catalogues 
Suppliers of  products or materials 
Special cost studies 
But  since,  in  many  instances of  good  value  work,  materials, products, 
and  processes will  be  utilized in different ways, really meaningful costs 
often  must  be  worked  up  for  the  job.  This  does  not  mean  that it  is 
necessary to have perfection in cost data at this stage in the cycle. Costs 
within a range of  plus or minus 5 per cent will usually be suflicient, and 
often,  costs  within  a  range  of  plus  or  minus  10 per cent  will  help  to 
determine whether  the  particular  value  alternatives are  of  sdficient in- 
terest to warrant  more  exact  cost  determination and further study. 
At  the risk  of  appearing too emphatic about this important point, the 
value specialist must not be too concerned about the comment, "Beware 
of  the  situation  in  which precise  costs  are  not provided."  His  concern 
must  rather center on statements such as, "Tools  are too costly; it is not 
even worthwhile to provide an estimate on them" or "The  quantities are 
so small that we  know the process will not  be practicable; therefore we 
will not provide an estimate" or "We have studied this a number of  times 
and  always found it impracticable; it is therefore not worthwhile to pre- 
pare an estimate on it now." Such beliefs and habits of  the past often lock 
in large amounts of  unsuspected and unnecessary costs. 

Techniques of Value Analysis and Engineering 3rd Edition, Lawrence D. Miles, p.18


(Previous description)


Value Analysis:

Value analysis is a system that evaluates each step in design, materials, process, and operations in order to manufacture a product that performs all of its intended functions and does so at the lowest possible cost.
The value of a product defined as:
Value = Product function and performance / Product cost
Value analysis generally consists of the following six phases:
1. Information phase: to gather data and determine costs.
2. Analysis phase: to define functions and identify problem areas as well as opportunities.
3. Creativity phase: to seek ideas to respond to problems and opportunities without judging the value of each of these ideas.
4. Evaluation phase: to select the ideas to be developed and to identify the costs involved.
5. Implementation phase: to present facts, costs, and values to the company managament; to develop a plan, and to motivate positive action, all in order to obtain a commitment of the resources necessary to accomplish the task.
6. Review phase: in which the overall value-analysis process is reviewed and necessary adjustments are made.

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, 1266)

3) Ergonomics(better)(Manufacturing)

The subject of ergonomics is equally important to both types of designer and represents the

overlap between industrial and engineering design. The word 'ergonomics' stems from two

Greek words; 'ergos' meaning work and *nomos' meaning the laws. In the USA *human

engineering' finds favour and in continental Europe the expression *biotechnics' is often

used.

Engineering ergonomics is concerned with ways of designing machines, operations and

work environments to match human capacities and limitations. During the Second World

War a new category of machine appeared which made demands on sensory, perceptual,

judgemental and decision-making abilities rather than muscular power. This new class of

machine posed some interesting questions about human abilities that could no longer be

answered by common sense and time and motion studies. Consider the design of a manned

space vehicle. Almost everything known about human beings is important: body

dimensions; physiological reactions; sensory capacities; control abilities; eating, drinking

and waste disposal; psychological effects of fatigue and emotion. Happily, for most

designers, we are only usually concerned with a restricted part of the human sensory

repertory.

Engineering Design Principles, Ken Hurst, p.76


(Previous description)

Ergonomics

Ergonomics is the study of people while they use equipment in specific environments to perform certain tasks. Ergonomics seeks to minimize adverse effects of the environment upon people and thus to enable each person to maximize his or her contribution to a given job.

(Cherie Berry,A Guide of Ergonomics, pg6)

 4) Design for Manufacturing and Assembly (DFMA)(better)(manufacturing)

Any engineering designer, whether or not working as part of a team with manufacturing

engineers, requires a working knowledge of manufacturing methods. Good practice

dictates that during all stages of the design process advice is sought from manufacturing

experts and the designer should attempt to utilize existing machinery and tooling where

possible.

Assuming that possible interference of components or gross errors in the 'logic' of

assembly are detected during the execution of the scheme drawing, a design should be

suitable for machining and assembly if the following are critically appraised:

• ease of machining

• economy

• use of existing machinery and tooling

• avoidance of redundant fits

• accessibility

• ease of assembly.

In designing for ease of machining it is important not to simply consider the functiona-

lity of the design but also to consider manufacturing process requirements. Although not

exhaustive. Figs 5.8, 5.9, 5.10 and 5.11 give some examples which illustrate the principles

involved in simplifying manufacture.

Figure 5.8 illustrates provision of runouts for cutting tools. A poor finish may result or a component may be impossible to manufacture without runouts. The decision to provide 

such undercuts must be taken at the design stage since the smaller diameter may have 

strength reduction implications. 

The simplification of machining can also be achieved by the placing of features in the 

components which are easiest to machine and subsequently inspect. This is true of the 

grooves which are required for some sort of rubber sealing ring in the example shown in 

Fig, 5.9. If the grooves are designed to go on the inside of the housing then access for 

machining is difficult. If it is functionally acceptable to insert the grooves in the shaft then 

this should be done because turning the grooves in the shaft is much more straight forward. 

In order to facilitate drilling, clearance must be provided for the drill to break through 

fully, drills should encounter equal resistance on their cutting edges so should not enter on 

a sloping surface and the centre of holes should be at least a full diameter away from the 

edge of a component to avoid breaking out. 

Engineering Design Principles, Ken Hurst, p.73


(Previous description)

Design for Manufacturing and Assembly (DFMA)

Design for Manufacturing and Assembly is a natural outcome of developments which recognizes the inherent interrelationship amont the manufacturing of components and their assembly into a final product. (manufacturing engineering and technology-Serope kalpakjian, page 16)

5) Design  for   Assembly (better)(manufacturing)

Large  numbers  of  engineering  components 

and  machines  fail  simply because  they  are  not  assembled  properly.  Precision  rotating

machines  such  as  engines,  gearboxes  and  turbines  have  closely  specified  running

clearances  and  cannot  tolerate  much  misalignment  in  assembly.  This  applies  even

more  to  smaller  components  such  as bearings,  couplings  and  seals.  Reliability  can  be

improved  therefore  by  designing  a  component  so  that  it  can  only  be  assembled

accurately.  This  means  using  design  features  such  as  keys,  locating  lugs,  splines,

guides  and  locating  pins  which  help  parts  assemble  together  accurately.  It  is  also

useful  to  incorporate  additional  measures  to  make  it  impossible  to  assemble

components  the  wrong  way round  or back-to-front.  Accurate  assembly  can  definitely

improve  reliability  (although  you  won't  find  a  mathematical  theory  explaining

why).

Case Studies in Engineering Design, Clifford Matthews, p.137


(Previous description)


Design for Assembly:
Assembly is an important phase of the overall manufacturing operation and requires consideration of the ease, speed and the cost of putting parts together. Furthermore, products must be designed so that disassembly is also possible, in order to enable the product to be taken apart with relative ease for maintenance, servicing and recycling of its components. Because assembly operations can contribute significantly to product cost, design for assembly, as well as design for disassembly, are important aspects of manufacturing. Typically, a product that is easy to assemble is also easy to disassemble. Further important developments include design for service, the goal of which is that individual parts or sub-assemblies in a product be easy to reach and service.
(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, pg 15)