Halil Kayhan_030070090_1st_week_answers

1- Segregation Induced Cracking, (Previous )(Manufacturing Failure):

Segregation induced cracking occurs when low melting point constituents such as phosphorus, zinc, copper and sulphur compounds in the admixture seperate during the weld solidification process. Low melting point components in the molten metal will be forced to the centre of the joint during solidification, since they are the last to solidify and the weld tends to separate as the solidified meatl contracts away from the centre region containing low melting point constituents.

(Bollinghaus, T., Hot Cracking Phenomena in Welds II, p. 116)

   Segregation Induced Cracking, (New):

Segregation-induced cracking occurs when low-melting-point constituents in the admixture separate during the weld solidification process. As the weld metal solidifies, element sand compounds with low melting temperatures are forced into the liquid phases that are next to the solidifying metal. The enrichment of the remaining liquid material (typically concentrated in the center of the weld cross section, or between solidifying grains of metal within the weld) with the low-melting-point materials, can lead to cracking.

When intermixed materials have a significantly different melting point than the basic iron-carbon weld metal, it is possible to have a liquid mixture in the center of the joint after the majority of the weld has solidified. When materials solidify, segregation may occur. The result is a change in composition throughout the cross section of the solidified material. The grains of steel have begun to grow, generally perpendicular to the fusion interface. As this solidification proceeds, segregation occurs. In an iron-carbon system, the first materials to solidify are typically lower in carbon con-tent because pure iron has a higher freezing point than iron-carbon mixtures .The degree of segregation is a complex issue and is a function of the solubility of the element or compound in liquid iron, as well as the rate at which solidification takes place. In general, however, the low-carbon layer that begins to form first results in higher levels of carbon being pushed into the still-liquid center of the weld bead. Other low-melting-point constituents can also be forced into this liquid center. Part of the cross section is solidified, while a portion remains liquid. In the case of some low-melting-point ingredients, the segregation takes place on a more localized basis, where individual elements segregate as individual grains form, expel-ling the still-liquid ingredients to the grain boundaries.

(Design guide 21/WELDED CONNECTIONS-A PRIMEE FOR ENGINEERS)

The new one is better, beacuse it has more detailed information

2- Bead Shape Induced Cracking, (Previous) (Manufacturing Failure):

This type of centreline cracking is associated with deep penetration processes like Submerged Arc Welding (SAW or method 121) and CO2 shielded Flux Cored Arc Welding (FCAW or method 136). When a weld bead is of a shape where there is more depth than width to the weld cross section, the solidifying grains growing perpendicular to the steel surface intersect in the middle, but do not gain fusion across the joint. To correct for this condition, the individual weld beads must have at least as much width as depth. The total wld configuration, which may have many individual weld beads, can have an overall profile that constitues more depth than width. If multiple passes are used in this situation, and each bead is wider than it is deep, a crack free weld can be made.

(Bollinghaus, T., Hot Cracking Phenomena in Welds II, p. 117)

Bead Shape Induced Cracking, (New):

The second type of centerline cracking is known as bead-shape-induced - cracking. This is illustrated in Figure 5–4 and is most often associated with deep-penetrating processes such as SAW (Submerged Arc Welding) and gas-shielded FCAW. When the cross-section of a single weld bead is of a shape where there is more depth than width, the solidifying grains grow gener-ally perpendicular to the steel and intersect in the middle, but do not gain fusion across the joint. To correct for thiscondition, the individual weld beads must have at least asmuch width as depth. Recommendations vary from a 1:1 to a1.4:1 width-to-depth ratio to remedy this condition. The finaloverall weld configuration, which may have many individualweld beads, can have a profile that constitutes more depththan width. If multiple passes are used in this situation, andeach bead is wider than it is deep, a crack-free weld can be made.

 

(Design guide 21/WELDED CONNECTIONS-A PRIMEE FOR ENGINEERS)

(The new one is better, because it has the figure)

3- Dedicated Machines (previous) (Machines):

Specialized and single-purpose machines were developed in the early 1990s for mass production of identical parts. Many different tranfer-type machines, each designed to producea specific product or perform a specific machining operation, were used in manufacturing. This process was not very flexible and as many as 150 different machines were required to produce a limited number of finished products. When the product mix changed, the machine had to changed,which was a costly, time-consuming process.

(Alavudeen & Venkateshwaran, Computer Integrated Manufacturing,pg.43)

(Dedicated Machines) (new):

The key to interchangeable parts, as we saw, lay in designing new tools that could cut hardened metal and stamp sheet steel with absolute precision. But the key to inexpensive interchangeable parts would be found in tools that could do this job at high volume with low or no set-up costs between pieces. That is, for a machine to do something to a piece of metal, someone must put the metal in the machine, then someone may need to adjust the machine. In the craft-production system-where a single machine could do many tasks but required lots of adjustment -this was the skilled machinist's job.

Ford dramatically reduced set-up time by making machines that could do only one task at a time. Then his engineers perfected simple jigs and fixtures for holding the work piece in this dedicated machine. The unskilled workers could simply snap the piece in place and push a button or pull a lever for the machine to perform the required task. This meant the machine could be loaded and unloaded by an employee with five minutes' training.(Indeed, loading Ford's machines was exactly like assembling parts in the assembly line: The parts would fit only one way, and the worker just popped them on.)

(James P. Womack,Daniel T. Jones,Daniel Roos, The machine that changed the world: the story of lean production, p33,34 )

(The new one is better, because it has also examples)

4- Rough-Cut Capasity Planning (Previous) (Production Planning):

Rough-cut capacity planning is used to check the feasibility of the master production schedule. The RCCP takes the master production schedule and converts it from production to capacity required, then compares it to capacity available during each production period. If the medium range capacity and production plans are feasible, the master production plan is firmed up. Otherwise, it is revised or the capacity is adjusted accordingly. Options for increasing medium range capacity include overtime, sub-contracting, adding resources, and an alternate routing of the production sequence.

(Principles of Supply Chain Management, Joel D. Wisner, Keah-Choon Tan, G. Keong Leong, page 194)

Rough-Cut Capasity Planning (New):

Rough-cut capacity planning is an approximate type of capacity planning using some load profiles (sometimes called “representative routings”) defined for the product families, focused on key or critical work centers, lines, departments, cells, suppliers, and support areas (engineering, distribution, shipping). For rough-cut capacity planning, “key” or “critical” resources are ones that are important, although not necessarily constant bottlenecks. Typical resources that might be planned as part of rough-cut capacity planning might include:

· Overall plant capacity

· Labor hours in total or for people with unique skills

· Assembly hours in a specific cell or bottleneck process

· Machine capacity in a key piece of equipment or unique or proprietary plant process

· Testing cell capacity

· Engineering hours needed to configure the final product to the customer’s specification

· Space required in a warehouse or storage area.

· Waste or effluent release, etc.

· Shipping labor

· Design time or credit release time

· Inspection or QC time

· Supplier capacity

The load profiles used in rough-cut capacity planning are a way to relate product families or individual master schedule items to the key resources required to produce them. The load profiles should contain the resource identifier, an indicator of which plan (supply, sales, inventory, etc,) drives the capacity projection, number of hours, pounds, molds, etc., and the approximate offset in time from the completion date of the plan. Typically this data is set based on historical records, but where this information is not available it may be set from estimates by knowledgeable people.

(Christopher D. Gray, Sales and Operations Planning Standard System, 2007, pg.59)

(The new one is better, because it has more information)

5) Alpha Prototype, (Previous)(Manufacturing method ):

Alpha prototypes are typically used to assess whether the product works as intended. The parts in alpha prototypes are usually similar in material and geometry to the parts that will be used in the production version of the product, but they are usually made with prototype production processes. For examply, plastic parts in an alpha prototype may be machined or rubber molded instead of injection molded as they would be in production.

(Kalpakjian S., Schmid S.R., Manufacturing Engineering and Technology,5th Edition, pg.261)

Alpha Prototype, (New):

– Represent “production intent” but do not attempt to replicate an actual

– While identical materials and configuration are used, the alpha prototype is not fabricated in the      actual processes to be used in production

– These are design discovery and risk reduction tools.

(John K. Gershenson, NASA ESMD Capstone Design, Michigan Technological University)

Both definiton have almost the same meanings.