030070131 Mehmet Can Çapar- 1st week definitions



1-Plaster Molding (old) (Manufacturing Method)

By the use of plaster of Paris for molds, the process of casting soft metals can be brought within the range of the average home workshop. The process is simple and inexpensive.

            The pattern, from which the mold is to be made, may be of almost any material that will hold its shape long enough for the plaster to “set”; even wax or plastic (modeling) clay will serve the purpose.

            In the actual molding, the pattern, which should be smooth and have a good draft or taper to facilitate removal, is placed on a smooth flat surface such as plate glass and fastened with a bit of beeswax to prevent movement or “floating” when the plaster is poured on. Any undercuts should be built up with modeling wax so that the pattern will come from the mold freely, with as little hand relieving as possible.

            High grade plaster of Paris or dental plaster will serve for ordinary work, but if more than one or two castings are to be made from the same mold, it is the best to use half plaster and half powdered asbestos.

(Populer Science Magazine, May 1930, pg: 88)

(new)(better definiton)

            In plaster molding, the mold material is plaster of paris (also known as calcium sulfate or gypsum), combined with various additives to improve green strength, dry strength, permeability, and castability. Tale or magnesium oxide can be added to prevent cracking and reduce the setting time. Lime or cement helps to reduce expansion during baking. Glass fibers can be added to improve strength, and sand can be used as a filler.

            The mold material is first mixed with water, and the creamy slurry is then poured over a metal pattern (wood patterns tend to warp or swell) and allowed to set. Hydration of  the plaster produces a hard mold that can be easily stripped from the pattern. (Note: Flexible rubber patterns can be used when complex angular surfaces or reentrant angles are required. The plaster is strong enough to retain its shape during pattern removal.) The plaster mold is then baked to remove excess water, assembled, and poured.

            With metal patterns and plaster mold material, surface finish and dimensional accuracy are both excellent. Cooling is slow because the plaster has low heat capacity and low thermal conductivity. The poured metal stays hot and can flow into thin sections and replicate fine detail, which can often reduce machining cost. Unfortunately, plaster casting is limited to the lower –melting-temperature nonferrous alloys(such as aluminum, copper, magnesium, and zinc). At the high temperatures of ferrous metal casting, the plaster would first undergo a phase transformation and then melt, and the water of hydration can cause the mold to explode.

E. Paul DeGarmo,J. T. Black,Ronald A. Kohser, Degarmo's materials and Processes in Manufacturing, Eleventh Edition, pg:311








2-Vacuum Furnace (Manufacturing device)




Heating of metal parts in a vacuum furnace consists of carrying out various thermal operations in a heated chamber evacuated to a vacuum pressure suitable to the particular material and process desired. Although originally developed for the processing of electron-tube and space-age materials, it has been found to be extremely useful in many less-exotic metallurgical areas as vacuum technology has progressed. Vacuum heat treating can be used to:

Prevent reactions at the surface of the work, such as oxidation or decarburization, thus retaining a clean surface intact.

            Remove surface contaminants such as oxide films and residual traces of lubricants resulting from fabricating operations. The latter often are severe contaminants to the furnace.

            Add substances to the surface layers of the work, such as by carburization.

Remove dissolved contaminating substances from metals, using the degassing effect of a vacuum, such as hydrogen or oxygen from titanium.

Join metals by brazing or diffusion bonding.

Jon L. Dossett,Howard E. Boyer,2006,Practical heat treating, pg:67-68

Since induction melting is independent of the surrounding atmosphere, it is equally valid under vacuum. The melting furnace is entirely contained in a vacuum vessel. The electromagnetic stirring, combined with the vacuum, degasses the metal and there is no possibility of oxidation during either the melting or the casting. The inclusions are few number and are uniformly distributed in the product. Additives can be put in during the melt, without of reactions with the atmosphere, so that precise repeatability is guaranteed. These features ensure metals and alloys of very high purity with high resistance to corrosion, fatigue, and temperature-stress cracking

John Davies, Conduction and Induction Heating, 11th volume, pg:331

3-Multijet Modeling (Manufacturing Method)

Multijet Modeling (MJM) uses multiple print heads to deposit droplets of material in successive, thin layers. Two major MJM techniques can be distinguished (see http://www.3dsystems.com/ for more information): ThermoJet^TM. A 96element print head deposits droplets of wax. Because of its relatively fast production, this technique is marketed to the engineering or design Office for quick form studies (concept modeling). However, wax models can also be used as master patterns for investment casting, as will be explained later.

            InVision^TM. A print head jets two separate materials, an acrylic UV-curable photopolymer-based model material and a wax-like material to produce support structures for the models, production speed, and surface finish, applications rnge from preliminary prototypes to mock-ups for concept proposals or marketing models.

Vinesh Raja,Kiran Jude Fernandes, Reverse engineering: an industrial perspective, 2008, pg:109-110

 (the old one)(better)

The principle underlaying the Actua^TM 2100 is the layering principle used in other RP systems and the new MJM process. MJM builds models using a technique akin to inkjet or phase-change printing, applied in three dimensions, a “print” head comprising of 96 jets oriented in a linear array builds models in successive layers, with each jet applying a special thermopolymer material only where required. The MJM heads shuttle back and forthlike a line printer (X-axis), building a single layer of what will soon be a 3-dimensional concept  model. If the part is wider than the MJM head, the platform (Y-axis) will continue building that layer. When the layer is completed, the platform is distanced from the head (Z-axis) and the head begins building the next layer. This process is repeated until the entire concept model is completed.

            The main factors that influence the performance and functions of the Actua^TM 2100 are the thermopolymer materials, the MJM head, and the X, Y and Z controls

Cornelius T. Leondes, Computer Aided and Integrated Manufacturing Systems: Optimization methods, 2003, pg:171

4-Layering Technology (old one) (Better) (Plastic Manufacturing Work Principle)

Almost all RP Systems use layering technology in the creation of prototype parts. The basic principle is the availability of the computer software to slice a CAD model into layers and reproduce it in a "output" device like a laser scanning system. The layer thickness is controlled by a precision elevation mechanism. It will correspond directly to the slice thickness of the computer model and the cured thickness of resin. The limiting aspect of the RP system tends to be the curing thickness rather than the resolution of the elevation mechanism.

(Chua C., Leong K.F. and LIM C.S. Rapid Prototyping: Principles and Applications Page: 47-48)

(New one)

All industrially relevant rapid prototyping processes work in layers. Like the half-breadth-plan of a ship, known from classical model making, single layers are produced and joined to a component.

            In the strict sense, rapid prototyping processes are therefore 2 1/2 D processes, that is stacked up 2D contours with constant thickness. The layer is shaped (contoured) in an (x-y) plane two-dimensionally. The third dimension results from single layers eing stacked up on top of each other, but not as a continuous z-coordinate. The models are therefore three-dimensional parts, very exact on the build plane (x-y direction) and owing to the described procedure the stepped in the z-direction whereby the smaller the z-stepping is, the more the model looks like the original

 

(Gebhardt, Andreas. Rapid prototyping, pg:29-30)

Taguchi Method (Experimental Method)

(Old one) (Better)

Taguchi Methods have been used for improving the quality of Japanese Products with great success. Taguchi bases his methods on conventional statistical tools, together with some guidelines for laying out experiments and analyzing the results. Taguchi's approach to quality control applies to the entire process of developing and manufacturing a product - from the concept, through design and engineering, to manufacturing.

Taguchi suggests a three stage process:

1- Systems Design: New ideas, concepts, and knowledge in the areas of science and technology are utilizied by the designing team to determine the right combination of materials, parts, processes and design factors that will satisfy functional and economical specifications.

2- Parameter Design: Related to finding the appropriate design-factor levels to make the system perform less sensitive to causes of variation.

3- Tolerance Design: Tolerances of factors that have the largest influence on variation are adjusted only if, after the parameter design stage, he target values of quality have not yet been achieved.

(Computer Aided Manufacturing Second Edition, Chang T.C., Wysk R.A, Wang H., 1998, Pages: 599 - 601)

(New)

Experimental methods for determining sensitivity of design factors to

change. This allows designs to be made less sensitive to variations in the production

process.

(Hugh Jack, Engineer On a Disk, pg:39)