4. (25 points) Questions (circle your answer when necessary): When a square sect

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4. (25 points) Questions (circle your answer when necessary): When a square section of the same dimensions (TRUE-FALSE). Comminution: It is defined as the breaking up of large solid particles by mechanical means ic polymer of a square section through a die, the die opening must be (TRUE-FALSE) When working with powders, higher densities are achieved (at the same compacting pressure with smaller size particles ( TRUE-FALSE) Blow molding is a typical processused to produce a plastic ball ( TRUE-FALSE) In the same material, hot isostatic pressing (HIP) will give a material of higher and uniform density than by compact pressing and sintering ( TRUE-FALSE) Cutlery is mainly produced by hot forging (TRUE-FALSE) In a sheet metal, the material propensity to earing is determined by the planar anisotropy ratio (TRUE-FALSE ) The more isotropic is the steel sheet, the more suitable for its use as car chassis ( TRUE FALSE) For a material with a melting point of 1085oC, the sintering temperature is

Explanation / Answer

(1)FALSE

When a viscoelastic polymer melt is subjected to shear or extensional stresses in the die, there is an elastic recovery (memory) in the extrusion direction after the extrudate exits the die.

This elastic recovery manifests itself as a contraction on the length (not visible in a continuous process) and a corresponding expansion in the cross-section, producing an extrudate with cross-sectional dimensions greater than the dimensions of the die exit.

Die swell can vary from 10% to over 100% increase in dimensions, depending on the material, melt temperature, extrusion speed and die geometry.

(2) TRUE

  Comminution is the reduction of solid materials from one average particle size to a smaller average particle size, by crushing, grinding, cutting, vibrating, or other processes

(3)

  The density of the compacted powder increases with the amount of pressure applied. Typical pressures range from 80 psi to 1000 psi

(4)TRUE

mainly Injection molding is used. Gas-injection molding has been developed to save material, shorten cycle times and to improve the surface aspects of thick-walled injection-molded parts.

(5)TRUE

Uniform density: The resulting compacted piece will have uniform shrinkage during sintering or hot isostatic pressing with little or no warpage.

(6)FALSE

cutlery manufacture involves blanking the stainless steel or sterling silver to the proper shape. A series of rolling operations then gives the piece the correct thickness. After heat treatment and trimming, the piece has a pattern embossed on it in a stamping operation.

(7)TRUE

Deep drawn parts usually have different wall heights because of earing behavior. This behavior is due to the planar anisotropy (?r) of sheet metals. A measure of the variation of normal anisotropy with the angel to the rolling direction in sheet plane is known as planar anisotropy. If the magnitude of the planar anisotropy is relatively large as absolute value, the earing behavior becomes more effective so larger ears occur. Furthermore, the orientation of the sheet with respect to the die or the part to be formed will be important. In addition, cutting of scraps in the parts which have ears leads to material waste

(8)FALSE

The demand of automotive industries to reduce the fuel consumption and therefore the weight in vehicle construction are becoming more and more significant. The reduction of the weight in vehicle construction can be realized among other factors with lighter car bodies. Particularly the reduction of the sheet metal thickness in car bodies can provide a significant contribution to solve this problem.In this case the use of high-strength steel is necessary.Isotropic high-strength steels, so-called I-Steels (e.g. St250i) have been developed by the steel supplier SALZGITTER AG-Germany. These high-strength I-Steel sheets show direction-independent (“isotropic”) material qualities and a very good deep drawing behavior. With these I-Steels, interior components as well as outdoor panels can be produced

(9)FALSE

The infiltration process in which the aid of an external pressure or mechanical force governs theinfiltration of liquid metal into the porous reinforcement .

(10)TRUE

(11)FALSE

(12) C

  Anisotropy, is the property of being directionally dependent, which implies different properties in different directions

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