Mehmet Can ÇAPAR 030070131, 4th Week Definition


1-Open Mold (Manufacturing type)
 (old answer) 
The distinguishing feature of this family of FRP( fiber-reinforced polymer composites) shaping processes is its use of a single positive or negative mold surface to produce laminated FRP structures. Other names for open mold processes include contact lamination and contact molding. The starting materials (resins, fibers, mats, and woven rovings) are applied to the mold in layers, builging up to the desired thickness. This is followed by curing and part removal. Common resinds are unsaturated polyesters and epoxies, using fiberglass as the reinforcement. The moldings are usually large( e.g., boat hulls). The advantage of using an open mold is that the mold costs mych less than if two matching molds wew used. The disadvantage is that only the part surface in contact with the mold surface is finished; the other side is rough. For the best possible part surface on the finished side, the mold itself must be very smooth.

There are several important open mold FRP processes. The differences are in the methods of applying the laminations to the mold, alternative curing techniques, and other variations. The family of open molf processes for shaping fiber-reinforced plastics: (1) hand lay-up, (2) spray-up, (3) automated tape – laying machines, and (4) bag molding. We treat hand lay-up as the base process and the others as modifications and refinements.

(Groover, M.P., Fundamentals of modern manufacturing: materials, processes, and systems, 4th Edition, pg.331-332)

(new answer) (better)

Instead of applying pressure in a closed mold the mix of liquid resin and reinforcing fiber may be laid into an open mold, and optionally pressed gently at room temperature until cured. To accelerate low-temperature cure, more active catalyst systems are added Alternatively, the assembly may be UV or oven cured. This requiresless capital investment but more skilled labor, so it is useful for prototype and small pro-duction runs, It permits unlimited size, so the largest reinforced thermoset products are made in this way, for example, large tanks and whole boat hulls.

Hand Lay-Up (Contact Molding). 

A layer of liquid resin is applied to the surface of the mold. A layer of glass fiber mat (low strength) or fabric (high strength) is hand laid over it. Liquid resin is poured over It, and brushed or rolled (squeegeed) into it. The process ls repeated to build up the desired thickness of the product. The assembly is allowed to stand until cured.

Spray-Up

 Instead  of hand  lay-up,  continuous  glass roving  and liquid resin are  fed into a  gun,  which  chops  the  glass  fiber,  mixes  it with  the  resin,  and  sprays  it  into  the  mold. This  can  be  automated  for  lower  labor  cost and greater  uniformity  Spraying  is  often  followed by hand-rolling  to  expel air and  densify the  assembly, Then  it is allowed  to stand  until cured  Products  are  similar  to  those  from simple  hand  lay-up. 

Vacuum-Bag Molding.  After hand lay-up, the assembly is covered with an air-tight film, typically  polyvinyl  alcohol,  occasionally nylon or  other material. Then  a  vacuum is pulled  on  the  underside  of  the film,  to  let atmospheric  pressure  squeeze  om  air  and excess resin. Use of a hand-held paddle may help. The assembly is allowed to stand until cured. Products are void-free. and quality is better than simple hand lay-up. 

Pressure-Bag Molding.  This  is similar  to vacuum-bag  molding,  but  345 kPa (50 psi) air pressure  is applied  to the  outside  of the  cover film.  A rubber  bag  may  he  used  to  facilitate the  process.

Autoclave  Molding.  s  is similar  to  pressure  bag  molding,  but  it  is  carried  out  in  an autoclave  to  apply the  pressure  to  the  outside of the  cover mm. 

Rubber Plug Molding. Liquid silicone rubber  is  cast  into  a  female mold  cavity  and cured. The plug is removed and layers of mat or fabric are built onto the plug. This assembly  is  then  inserted  into  the  mold  cavity, pressed  and heated until cured.

(James A. Kent, Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology, pg:685,686)

2-FAST Diagram (Analysis technique)

(old answer) (better)

Fuctional Analysis System Technique (FAST) is provided alternative to the function tree that is a hierarchical functional breakdown structure starting with a system function or a system mission. The FAST diagram is drawn from left to right. We start with a system function on the left side and ask how this funtion is (or may be ) accomplished. The functions on the first level are than identified and entered into the diagram. We continue asking how until we reach the intended level of detail. The lower level functions can be connected by AND or OR relations. Functions that have to be performed at the same time may be indicated by vertical arows. 

( Marvin Rausand, Arnljot Hoyland, System Reliability Theory: Models, Statistical Methods and Aplications,John Wiley & Sons, Inc. Pub., 2004, Second Edition, p.80-81)

(new answer)

The Function Analysis System Technique, commonly referred to by the acronym

FAST, is a powerful  diagramming  technique for analyzing the relationship of functions, FAST diagrams have the following uses

      Show the specific relationships of all functions with respect to one another

      Test the validity of the functions under study

      Help  identify  missing  functions
      Broaden  the  knowledge of all team members with respect to the project 
The Function  Analysis  System  Techique  was  developed  by  Charles  W, By the way of the Sperry  Rand Corporation and was first introduced in a paper presented  at  the  1965  National  Conference  of  The Society of American Value Engineers. Subsequently. FAST has been widely used by governmental  agencies, private firms, and  value consultants.

(Robert B. Stewart, Value Optimization for Project and Performance Management, pg:155,156)

3-Repetitive Design (a design method)

(old answer) (better)

The first of the repeittive design functions has to create a definition of the problem being solved for which the next five develop a set of design (across the system’s life cycle). The seven functions that comprise this first desing function defining the desing problem , are :

*Develop operational concept

*Define system boudary with extermal system didagram

*Develop the system objects hierarchy

*Develop, analyze , and refine requirements

(The engineering design of systems: models and methods; Dennis M. Buede, pg. 51 , 2nd Edition)

(new answer)

It would be difficult to draw a strict line between texture and pattern. Pattern is usualy defined as a repetitive design with the same motif apearing again and again. Texture, too, often repeats, but its variations  usually do not involve such perfect regularity. The difference in the two terms is admittedly sligth. The texture of a material such as burlap would be readily identified by touch, yet the surface design is repetitive enough that a photograph of burlap coud be called pattern.

The essential distinction between texture and pattern seems to be whether the surface arouses our sense of touch or merely provides designs appealing to the eye, in other words, altough every texture makes a sort of pattern, not every pattern could be considered a texture. Some suggestion of a three-dimensional aspect to the surface such as shadows or glassiness, no matter how subtle, will visually evoke texture.

 (David A. Lauer,Stephen Pentak, Design Basics, pg:184)

4-Automatic Welding (a welding method)

(old answer)

Traditionally, welding processes have been manually operated and are based on trial and error and/or on operator's experience. When improved control is required under manual control, an automatic welding procedure or control is established.

Automatic welding, simply means that some aspects of the welding operation is performed without the intervention of human such as welder or welding operator. In most of automatic welding operations, a welder is required to make initial preparations and then monitors the overall operation. The advantages of an automatic welding system include the following:

• Consistency in welding quality
• Increased welding production and consequent reduction of production costs
• Integration with other automatic operations of the industry
• Absence of human fatigue and/or error
• Absence of loss of human life in case of severe accidents

However, automatic welding also has some disadvantages such as listed below:

• Extensive planning of procedural steps
• Higher capital investments leading to uneconomic investment for small operations

(Naidu D.S., Özçelik S., Moore K.L., Modeling, Sensing and Control of Gas Metal Arc Welding, pg.148,)

(new answer) (better)


     Automation  in Welding  because of the hazards of manual welding and in efforts to
increase  productivity and improve product quality, various forms of mechanization and
automation have been, developed. The categories include machine welding, automatic
welding, and robotic welding.


     Machine welding can be defined as mechanized welding with equipment that
performs the operation under the continious supervision of an operator, It is normally
accomplished by a welding head that is moved by mechanical means relative to a stationary work, or by moving the work relative to a stationary welding head. The human worker must
continually observe and interact with the equipment to control the operation
     If the equipment  is capable of performing the operation without control by a human
operator, it is referred to as automatic welding. A human worker is usually present to
oversee the procces and detect variations from from normal conditions. What distinguishes
automatic welding from machine welding as a weld cycle controller to regulate the arc
movement and workpiece positioning without continuous human atention. Automatic welding requires a welding fixture and/or positioner to position the work relative to the welding head. It also requires a higher degree of consistency and accuracy in the component parts used in the weldment. For these reasons, automatic welding can be justified only for large quantity production.


(Mikell P. Groover, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, pg:697)










5-Computer Assisted Part Programming (programming)
(old answer)

     The use of CAD/CAM takes computer-assisted part programming a step further by using a computer graphics system (CAD/CAM system) to interact with the programmer as the part program is being pre­pared. In the conventional use of APT, a complete program is written and then entered into the computer for processing. Many programming errors are not detected until com­puter processing. When a CAD/CAM system is used, the programmer receives immediate visual verification when each statement is entered, to determine whether the statement is correct. When part geometry is entered by the programmer, the element is graphically displayed on the monitor. When the tool path is constructed, the programmer can see exactly how the motion commands will move the tool relative to the part. Errors can be corrected immediately rather than after the entire program has been written. 
(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.906)



(new answer) (better)

     Computer  assisted  part programming  is used for complicated point-to-point  and contour profile
applications. In  computer  assisted  part  programming, the  part  programmer defines the work
piece  geometry and  then  specifies  the  operation sequence  and  tool  path. This tool  path
specification involves a detailed step by step sequence  of cutter movement. Figure 14.12 shows
the cutter offset of a contour part programming.

     The computer's job in computer assisted  part programming  consists of the following steps:
-Input translation
-Arithmetic calculations
-Cutter offset computation
-Post-processor
     The  part programmer enters the  program in  an  NC  language. The  input  translation
component converts the coded instructions contained in the program law computer usable form
for  further  processing. The  arithmetic  calculations  unit  of  the  system  consists  of  a
comprehensive set of subroutines for solving  the  mathematics required to generate the part
surface. These subroutines are called by the various part programming language statements.
     The actual tool path is different from the part outline because the tool path is defined as the
path taken by the centerof the cutter. It is at the periphery of the cutter that machining takes place. The purpose of the cutter offset compensations is to offset the tool path from the desired part surface by the radius of the  cutter
     The  post-processor is a separate computer program that has been written to  prepare the
punched tape for a specific machine tool. The input to the post processor is the output from the
other three components, a series of  cutter locations and other instructions. The output of the
post-processor is the NC tape written in the correct format for the machine on which it is to
housed.

 (Lalit Narayan Et Al., Computer Aided Design And Manufacturing,pg:302,303)