030070127 Sinan Sever 6th Week Definitions

Electrochemical Buffing

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Fig. 2 shows a principle of ECB schematically. In the method of ECB, a rotating disk with abrasive fine particles where the electrolyte is supplied is pressed against the work piece. The disk and the work function as a cathode and an anode, respectively and an aqueous solution of sodium nitrate is used for the electrolyte. The practical situation is shown in Fig. 3 where a rotating ECB head with 100 mm in a diameter gradually moves on a work which is larger than the head.

(Appication of Electro Chemical Buffing Onto Niobium SRF Cavity Surfaces, Proceedings of IPAC’10,; S. Kato et al.; pg. 2930)

OLD

Mechanical buffing is a slow finishing process used for achieving smooth,bright, and mirrorlike surfaces. The process is carried out under dry conditions, which raises dust and makes the working environmental conditions unsuitable. Electrochemical buffing (ECB), uses a carbon fiber cloth that rubs the anodic specimen against a revolving cathode fiber buff. Electrolytes of NaCl or NaNO3 are supplied to the machining zone using a suitable pump. The machining current flows from the workpiece to the cathode through the carbon cloth. ECD of the anodic specimen mainly takes place on the surface of the specimen where it is rubbed by the carbon cloth buff. The current density, the type of electrolyte, and the workpiece material control the polishing speed. For high-speed polishing, an NaCl electrolyte is used where high current density is ensured. The addition of Al2O3 abrasives (200 mesh number) to the machining medium increases the amoun of material removal; however, surface smoothing and brightness are decreased. During ECB, a passive oxide film is normally formed on the surface of the stainless steel workpiece. MA and hence the removal of such a film on the high spots of the surface irregularities enhances thedissolution phase to prevail in these spots, which in turn makes the surface smoother and brighter.

(Advanced Machining Processes, Hassan El-Hofy; Page:196)

Liquid Thermal Polymerization

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Liquid thermal polymerization (LTP) uses thermoset instead of photo-polymer, which is normally used in stereolithography. Solidification occurs by heat dissipation rather than by the impact of laser light. Heat dissipation might make it difficult to control the accuracy, thermal shrinkage, and part distortion. The system employs two jets for the plastic object and the wax like support materials. The liquids are fed to the individual jetting heads, which squirt tiny droplets of the materials as they are moved in x-y coordinates to form a layer of the object as shown in Fig. 8.4. The materials harden by a rapid drop in temperatures they are deposited. After an entire layer of the object is formed by jetting, a milling heads passed over the layer to make it a uniform thickness. As the milling head cuts, particles are vacuumed and collected. The process is repeated to form the entire object. The wax support material is either melted or dissolved away. The most outstanding characteristic of LTP is the ability to produce extremely fine resolution and surface finishes that are equivalent to CNC machining. However, the technique is very slow for large objects. While the size of the machine and materials used are office-friendly, the use of a milling head creates noise which may be objectionable in an office environment. Materials selection also is very limited.

(Advanced Machining Processes, Hassan El-Hofy, pg. 264)

OLD

LTP process is quite similar stereolithograpy in a way that the part is built by solidification of successive layers of liquid polymer. However, polymers used in LTD process are thermosetting polymers instead of photopolymers and hence the solidification is induced by thermal energy rather than light energy. The thermal nature of the process is expected to make the control of the size of the voxels difficult due to dissipation of heat.

(Narendra B. Dahotre, Sandrip P. Harimkar, Laser Fabrication and Machining of Materials, Spr,nger Pub., 2008, p.356)

Beam Interference Solidification

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Beam interference solidification (BIS) is the most versatile polymer-based RP process. In beam interference solidification (Fig. 8.2) part creation occurs by point-by-point solidification of the liquid at the intersection of two laser beams having different frequencies. All the liquid hit by laser beam 1 is excited so that it polymerizes upon the impact of laser beam 2. Forming the part in the z axis no longer needs to be done in layers. Initializing the laser beam movements in any set of x, y, z coordinates makes it possible to trace the part in three dimensions rather than in two in a small prototyping time. The process has a limited industrial application because of the following problems:

1. Light absorption (drop of intensity with depth)

2. Shade effects of parts already solidified

3. Beam intersection problems due to the light diffraction caused by local temperature variation or solidification

(Advanced Machining Processes, Hassan El-Hofy, pg. 261)

OLD

This process is based on the point-by-point solidification of photosensitive polymers (contained in transparent vat) at the intersection of two laser beams having different wavelengths. The first laser excites the liquid polymer to the reversible metastable state which is subsequently polymerized by the radiations from the second laser. The process is associated with various technical limitations such as insufficient absorption of laser intensity at higher depths, shadowing effect of already solidified material, and diffraction of laser lights leading to difficulties in obtaining the precise intersection of the beam.

(Narendra B. Dahotre, Sandrip P. Harimkar, Laser Fabrication and Machining of Materials,Spr,nger Pub., 2008, p.356)

Holographic Interference Solidification

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Holographic interference solidification (HIS) is based on photopolymerization. The idea is that projecting a holographic image of a modelin a vat of liquid photosensitive monomer could solidify a whole three-dimensional surface at once, rather than to build it up point by point.This process saves the prototyping time. Reported applications includethe production of lost wax models for copper EDM electrodes.

(Advanced Machining Processes, Hassan El-Hofy, pg. 261)

OLD

Holographic interference solidification is a subtitle of liquid base rapid prototyping process. In this

proces a holographic image is projected on a liquid photosensitive polymer contained in a vat such

that the entire surface of the polymer is solidified instead of poin by point solidification.

(Narendra B. Dahotre,Sandip P. Harimkar, Laser fabrication and machining of materials, p.356)