Because of the chemical nature of thermoplastic materials, injection molding has traditionally been the primary molding method for thermoplastics, and compression and transfer molding have been the primary molding methods for thermosetting plastics. Because of the greater molding cycle speeds and lower molding costs in injection molding, thermoplastics have had a substantial molding cost advantage over thermosets.
Advantages in equipment and in thermosetting molding compounds, however, have resulted in a rapid transition to screw-injection, in-line molding. This has been especially prominent with phenolics, but other thermosets are also included to varying degrees. The growth in screw-injection molding of phenolic has been extremely rapid. The development of this technique allows the molder to automate further, reduce labor costs, improve quality, reduce rejects, and gain substantial overall molding cycle efficiency. (Charles A. Harper, Edward M. Petrie, Plastic Materials and Processes- A Concise Encyclopedia, A John Wiley & Sons,Inc.Pub., 2003. p.560)
Thermoset Injection Molding
Injection Molding of Thermosets Injection molding is used for thermosetting (TS) plastics, with certain modifications in equipment and operating procedure to allow for Grim-linking. The machines for thermoset injection molding arc similar to those used for thermoplastics. They utilize a reciprocating-screw injection unit, but the barrel length is shorter to avoid premature curing and solidification of the IS polymer. For the sante reason, temperatures in the barrel are kept at relatively low levels, usually 50<12 to 125'C. (I2U'F-260P), depending on the polymer. The plastic, usually in the form of pellets or granules, is fed into the barrel through a hopper. Plasticizing occurs by the action of the rotating screw as the material is moved forward toward the nozzle. When sufficient melt has accumulated ahead of the sciew, it is injected into a mold that is heated to 1501C to 230PC (300P-450'T). where cross-linking occurs to harden the plastic. The mold is then opened, and the part is ejected and removed. Molding cycle times typically range from 20 sec to 2 mm. depending on polymer type and part size. Quinn. is the most time.consuming step in the cycle. In many cases, the part can be removed from the mold before curing is completed, so that final hardening ocethis due to retained heat within a minute or two after removal. An alternative approach is to use a multiple-mold machine, in which two or more molds are attached to an indexing head served by a single injection unit. The principal thermosets for injection molding arc phenolics, unsaturated polyesiers, melamines, epoxies, and urezoformaldehyde. Elastomers are also injected molded (Section 14.1.4). More than 50% of the phenolic moldings currently produced in the United States are made by this process [11], representing a shift away from compres-sion and transfer molding, the traditional processes used for thermosets (Section 13.7). Most of the TS molding materials contain large proportions of fillers (up to 70% by weight). including glass fibers, clay, wood fibers, and carbon black. In effect, these are “unposite materials that are being injected molded.
(Groover, M.P., Fundamentals Modern Manufacturing: Materials, processes and systems 4th Edition, pp. 284)
My definition is the best one. Because give every detail about thermoset injection. Also it can be much more undenstanable than older one.
Spray coating ( Manufacturing Technique)
spray coating is a widely used production method for spraying organic coatings.They process forces the coating liquid to atomize a fine mist immediately prior to deposition onto the part surface. When the droplets hit the surface,they spread andflow together to form a uniform coating within the localized region of the spray. If done properlyi spray coatig provides a uniform coating over the entire work surface.
(Mikell P. Groover,Fundamentals of Modern Manufacturing,p.682)
Spray coating
A sprayed coating can be characterized by a set of specified param-eters related to its future applications, such as wear resistance, heat isolation, electric resistivity, etc. These parameters are strongly depen-dent on the powder material and the spray process. The process may modify the properties of the initial material during the powder particle flight in a jet or a flame and at its 'splash' on a substrate. The modifica-tions can result (min material reduction, oxidation, rapid solidification, cooling and other phenomena. A wise choice of powder should include consideration of all of the possible modifications. Even 'smarter', is to take advantage of the deposition process to create an added value, i.e. coatings with particularly good properties. An example, from the area of thin film deposition, is the idea of mmoromposites proposed by Veprek (1999) which consists of deposition by Plasma-enhanced chemical vapour deposition (PECVD) of films with nano-dimensional reinforcements (e.g. TIN) inside an amorphous matrix (e.g. S13N1‘). The hardness of the films was shown to be greater than that of any nitrides, carbides or diamond-like coatings synthesized as films or coat-ings (Pawlowski, 2003). An example of such a 'smart design' in the area of thermal spraying is deposition of a self-bonding coating with the use of a powder that reacts exothermally at high temperatures. Such a reac-tion contributes by heating the interface between the sprayed lamellae and substrate and promotes good coating adhesion. An example of a powder that reacts exothermally is a mixture of Ni and Al (Dittrich, 196.5). Research into new smart materials is one of the tasks of engineers in powder manufacturing companies.
(Pawlowsk L. The Science and Engineering of Thermal Spray Coatings 2th Edt. Wiley page:2)
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Off-Line Programming (Process Improvement )
My definiton clarify all of abour off-line programing. And give improtant information about it.
Wire EDM (Manufacturing Technique)
Off-line programming provides an essential link between CAD and CAM. The development of off-line programming
systems should result in greater use of robots and accelerate the implementation of flexible manufacturing systems (FMS). It also offers an alternative for complex automated production lines and should allow rapid response to changing product:process issues.
Off-line programming is, by definition, the technique of generating a robot program without using a real machine. It presents several advantages over the on-line method, some of which are described below:
* Programs are prepared without interruptions of robot operation, resulting in reduction of robot down time, which means flexibility and an increase in productivity.
* Removal of the programmer from the potentially dangerous environment, as most of the program development is executed away from the robot. Thus, the time during which the programmer is at risk from aberrant robot behaviour is reduced.
* There is a greater possibility for optimisation of the workspace layout and the planning of robot
tasks.
* New programs can include previously developed routines.
* Program changes can be incorporated quickly by substituting only the necessary part of the program.
* Signals from sensors can be incorporated into programs.
* Information from the environment (i.e. computerintegrated-manufacturing system; CAD:CAM systems can be incorporated into programs.
* It permits verification of the robot behaviour through graphical simulation and allows for the correction of any error in the program.
(G.C. Carvalho, M.L. Siqueira, S.C. Absi-Alfar, Off-line programming of flexible welding manufacturing cells, Journal of Materials Processing Technology 78 (1998), pp.24–28)
Off-Line Programming
From its inception in 1983. ESPRIT (the European Strategic Programme for Research and Development in Information Technology) has aimed at improving the competitiveness of European industry and providing it with the technology needed for the 1990s. Esprit Project 623, on which most of the work presented in this book is based, was one of the key projects in the ESPRIT area, Computer Integrated Manufacturing (CIM). From its beginnings in 1985, it brought together a team of researchers from industry, research institutes and universities to explore and develop a critical stream of advanced manufacturing technology that would be timely and mature for industrial exploitation in a five year time frame. The synergy of cross border collaboration between technology users and vendors has led to results ranging from new and improved products to training courses given at universities. The subject of Esprit Project 623 was the integration of robots into manufacturing environments. Robots are a vital element in flexible automation and can contribute substantially to manufacturing efficiency. The project had two main themes, off-line programming and robot system planning. Off-line programming enlarges the application area of robots and opens up new possibilities in domains such as laser cutting, and other hazardous operations. Reported benefits obtained from off-line program-ming include:
- significant cost reductions because re-programming eliminates robot down-time;
- faster production cycles, in some cases time-savings of up to 85% are reported;
- the optimal engineering of products with improved quality.
Moreover, off-line programming techniques protect the operator, who under conventional systems of on-line programming, is at a risk of injury from having to work in the physical proximity of the robot. The integration of robots in manufacturing cells requires the integration of information concerning product design, plant availability and system layout. Project 623 has achieved this through the use of relational and knowledge databases which lead to large cost savings for vendors providing turnkey systems and users who need fast adaptation to production demands. The project has been an excellent example of a multi-disciplinary approach, combining the knowhow of mechanical and manufacturing engineers and computer scientists to push forward the frontiers of knowledge in an application domain which is at the leading edge of the major European economies.
(Bernhardt R. Dillman R. Integration of robots into CIM, Chapman & Hall, page:IV)
Wire EDM (Manufacturing Technique)
Wire cut EDM is an indispensable machine in tool rooms. This is used to make dies for blanking and piercing. The special feature of wire EDM is that the electrode is in the form of a thin wire of about 0.2 mm in dia. A small hole is drilled into the workpiece and the wire electrode is threaded through the workpiece onto a take-up roll. The movements of the work table through computer numerical control in X and Y directions enable cutting the component to the required shapes. In some cases where a relief is required for the die or the punch being machined, a 3-axis NC is used to tilt the wire axis relative to workpiece surface in the required direction. The direction of tilt varies with the contour and is controlled by the third axis of the CNC. Some of the latest wire EDM machines have the automatic drilling and self threading facility.
(P.Radhakrishnan,CAD/CAM/CIM,third edition page 369)
Wire EDM
Electrical discharge machining, the process normally referred to as EDM, came into industrial use shortly after World War II Ill. Its initially applications were in "tap-busting." the electrical erosion of broken taps in pans and die sections too valuable to discard. It was soon discovered, however. that the process of electrical erosion could be controlled to machine cavities and holes. After that, the wire EDM was used to execute the through cutting of EDM (2).
Wire cutting process is widely used for making stamping dies, tools, templates. extrusion dies, and progressive dies. It is also used for prototype production of parts to be made later by die stamping or CNC milling 131.
A computer support as an aid to part programming was not required during the early period of NC use in the wire-EDM. The parts to be machined were of two dimension configurations requiring simple mathematical calculation 141. With the increased use of NC systems and growth in complexity of production. the manual programming became a tedious work, time consumed. And Manual method depends to a very great extended on the experience of the operator, which leads to many human errors. And so. the part programmer was no longer able to calculate efficiently the required tool path. Therefore, the use of CAM systems as an aid to part programming became a necessity.
Many trails are achieved to develop the wire-EDM programming methods. Most current wire-EDM CAM systems neglected some of the wire-EDM technique. For example, the sequence of the wire path. the generation of the standard radius, the fixation stability. correction (wire offset), conical cutting. trim cut. No-Core cut. calculating the threading & breaking point of the wire, etc.
The development of a wire-EDM CAM system to overcome the previous limitations, was the aim of this work. The results of the proposed system show a great saving in time and the user effort. Precision & monitoring for all steps of the cutting process are illustrated.
(Imam F. I. Multiple approaches to intelligent systems: 12th International Conference, Page:889-890)
Self-directed work team
Self directed work team is a small number of people (7-15) with complementary skills who are committed to a common purpose,performance goals and approach for which they hold themselves mutually accountable.
(Paul C. Palmes, The magic of self directed work teams, 2006 page 31)
Self-directed work team
A self-directed work team combines the best aspects of the independent craft worker with mass production. It integrates the craft worker's inti-mate knowledge of the task with all the advantages of standardization. It provides an organizational structure that puts the employees in control of achieving their goals.
(Rose E. Buckley S. Self-directed work teams: a trainers role in the transition, ASTD, page:19)
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