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The present invention further comprises the steps of receiving a maneuver command signal from a manually controllable device. The manually controllably device can be a joystick or a plurality of push buttons which an operator can activate to convey a maneuver command to a controller of the present invention. The present invention further comprises the step of calculating a first magnitude of thrust for the first marine propulsion unit as a function of the maneuver command and calculating a second magnitude of thrust for the second marine propulsion unit as a function of the maneuver command.
The first and second magnitudes of thrust are calculated to create a resultant force vector imposed on the marine vessel in combination with a resultant moment about an instantaneous center of turn of the marine vessel which will achieve the maneuver command received from the manually controllable device.
Certain embodiments of the present invention further comprise the steps of causing the first marine propulsion unit to provide the first magnitude of thrust and causing the second marine propulsion unit to provide the second magnitude of thrust. The causing steps of the present invention can comprise the steps of changing the operating speeds of engines which are associated with the first and second marine propulsion units. In other words, if the first and second marine propulsion units are outboard motors or stem drive systems with individual internal combustion engines, the operating speed of the two or more engines, measured in revolutions per minute, can be changed to appropriately affect the magnitudes of thrust produced by the first and second marine propulsion units.
Alternatively, the causing steps of the present invention can comprise the steps of changing the pitch of each of two controllable pitch propellers associated with the first and second marine propulsion units.
Certain embodiments of the present invention can further comprise the steps of changing the relative position of the first marine propulsion unit relative to the transom in order to change the direction of the first magnitude of thrust relative to the marine vessel.
Similarly, this embodiment of the present invention would also comprise changing the relative position of the second marine propulsion unit relative to the transom in order to change the direction of the second magnitude of thrust relative to the marine vessel.
In other words, two outboard motors can be steered in a direction other than straight ahead in certain embodiments of the present invention while other embodiments can leave the two outboard motors positioned as they would be for straight ahead travel of the marine vessel. The first and second marine propulsion units can be stem drive systems, outboard motors, or inboard drives. The manually controllable device can be a joystick or a device which comprises a plurality of push buttons.
An apparatus made in accordance with the present invention comprises first and second marine propulsion units which are attachable to a transom of a marine vessel. It further comprises a manually controllable device which has an output that is representative of a maneuver command provided by a marine vessel operator.
It also comprises first and second means for calculating a first magnitude of thrust and a second magnitude of thrust, respectively, for the first and second marine propulsion units, respectively, as a result of the maneuver command received from the manually controllably device.
The first and second calculating means are typically incorporated as part of a micro-processor. The micro-processor can be included as a component within an engine control unit. The present invention can further comprise means for causing the first and second marine propulsion units to actually provide the first and second magnitudes of thrust. This can be accomplished either by changing the operating speeds of the two engines associated with the two marine propulsion units or, alternatively, by changing the pitch of the blades of the controllable pitch propellers of the two marine propulsion units.
The two marine propulsion units can be directed in a straight ahead configuration or, alternatively, can be positioned at directions other than perpendicular to the transom of the boat. These positions can provide parallel thrusts or, alternatively, thrust vectors which are not parallel to each other.
Throughout the description of the present invention, it should be clearly understood that the two or more marine propulsion devices are capable of providing thrust in either of two opposing directions, forward and reverse. The present invention will be more fully and completely understood from a reading of the description of the preferred embodiment in conjunction with the drawings, in which:.
Throughout the description of the preferred embodiment of the present invention, like components will be identified by like reference numerals. A manual controller 10 is provided to allow a marine vessel operator to provide an input representing a desired maneuvering activity.
The manual controller 10 can be a joystick or a plurality of buttons by which the marine vessel operator is able to convey certain commands to an engine control unit 14 which represent maneuver commands. These commands can be relatively simple, such as straight ahead, reverse, rotate counterclockwise, and rotate clockwise. The engine control unit ECU 14 receives the commands from the manual controller 10 , as represented by arrows 21 and It a typical arrangement, the signals received on lines 21 and 22 would represent a choice between full speed ahead and full speed reverse on line 21 and between full speed counterclockwise and full speed clockwise on line With these two inputs, the ECU 14 calculates the appropriate thrust values for the two marine propulsion units attached to the transom of the marine vessel and provides speed control commands for both units and direction control commands for both units.
These are provided on lines 31 and 32 , respectively. It should be understood that the present invention contemplates two distinctly different potential modes of operation. For example, the direction control for both units represented by box 42 in FIG. In this mode of operation, with both marine propulsion units restricted to a straight ahead position relative to the transom, the speed commands for the two units, as represented by box 41 in FIG. Alternatively, the direction control for both marine propulsion units can provide commands which cause the two marine propulsion units to turn either to the left or right relative to the transom in a parallel maneuver or, alternatively, the two engines can be directed independently of each other.
Instead of using cables or mechanical linkages, as are common in many marine vessels, the marine vessel on which the present invention is used provides electronic signals which convey both steering and propulsion commands from the operator station to the marine propulsion units. In this type of system, no direct mechanical connection is provided between the operator's station and the marine propulsion units.
As a result, the two marine propulsion units can be operated independently from each other, under the control of the ECU 14 , in terms of both speed of operation and direction of the thrust vectors provided by the two marine propulsion units. Typically, the stick 52 can be moved left and right and forward and backward relative to the base The operation of joysticks is very well known to those skilled in the art and will not be described in detail herein.
A forward pad 61 and a reverse pad 62 can be incorporated to provide the signal on line 21 of FIG. Similarly, a counterclockwise rotation pad 63 and a clockwise rotation pad 64 can be combined to provide the signal on line 22 of FIG. With the four buttons shown in FIG. Throughout the description of the preferred embodiment, it should be understood that the force vectors, F 1 and F 2 can be positive or negative.
Points 81 and 82 represent the points about which the marine propulsion units can rotate while remaining attached to the transom Point 90 represents the instantaneous center of turn of the marine vessel 70 in response to forces exerted on the marine vessel.
In other words, the instantaneous center of turn 90 is a function of several factors which comprise the speed of the vessel as it moves through the water, the hydrodynamic forces on the hull of the marine vessel 70 , the weight distribution of the load contained within the marine vessel 70 , and the degree to which the boat is disposed below the waterline.
The location of the instantaneous center of turn 90 can be empirically determined for various sets of conditions. For purposes of describing the operation of the present invention, it will be presumed that the location of the instantaneous center of turn 90 is known by the software operating within a micro-processor of the engine control unit A centerline 94 of the marine vessel 70 is drawn through the instantaneous center of turn Centerlines, and , are shown extending through the first and second marine propulsion units, 71 and 72 , co-linearly with the first and second thrust vectors, and , produced by the first and second marine propulsion units, 71 and With continued reference to FIG.
By appropriately selecting the first and second magnitudes of thrust, and , the marine vessel 70 can be maneuvered in response to a maneuver command received from the manually controllable device In a normal situation, where the two marine propulsion units are spaced equally apart from the centerline 94 , each of the two thrust vectors, and , will produce a moment about the instantaneous center of turn 90 that is equivalent to the force of the vector multiplied by dimension X.
The first magnitude of thrust will produce a clockwise moment about the instantaneous center of turn 90 while the second magnitude of thrust will produce a counterclockwise moment about the instantaneous center of turn If the first and second magnitudes of thrust, and are equal to each other, a forward movement of the marine vessel 70 will result and there will be no rotational movement about the instantaneous center of turn However, if the first and second magnitudes of thrust are unequal in either magnitude or direction, the marine vessel 70 will be caused to rotate about the instantaneous center of turn This will result in a rearward movement of the marine vessel 70 if the two thrust vectors are equal in both direction and magnitude.
If both marine propulsion units, 71 and 72 , produce reverse thrust, but the two magnitudes of thrust are unequal, rotation of the marine vessel 70 about the instantaneous center of turn 90 will result. In step 2, we examined how effort variables such as mesh size, season month , and fishing location were related to the observed landings profiles, and how all data could be combined for identifying trip clusters.
A Multiple Correspondence Analysis MCA was applied to the data matrix, built with fishing trips as individuals, and the effort and landings profile as categorical variables. Finally, an HAC analysis with the same criteria as for step 1 was applied on all the factorial coordinates from the MCA. In step 3, the final definition of fisheries was set. This was done by arbitrarily pooling some of the clusters obtained in step 2.
The aim of this procedure was to decrease the number of combinations without losing meaningful information on the structure of the data set. Various criteria were considered, including cluster size, similarity with other clusters, seasonal patterns, difference in current management practices, and consistency with the ad hoc classification used by DIFRES.
Describing the fisheries was not deemed sufficient to understand the mechanisms involved in the dynamics of fishing activity. That required also analysis at the scale of the fishing vessel, not just at the trip level. We therefore constructed groups of fishing vessels that had similar activities, regardless of their physical characteristics and home port.
Vessel groups were identified using the same multivariate procedure as used for the identification of landings profiles step 1. A normalized PCA was applied to the data matrix, built with vessels as individuals, and the percentage of trips spent in each fishery as variables. The identified clusters vessel groups were named after the fishery with the highest percentage of trips within the cluster. That fishery was referred to as the main fishery of a given vessel group.
The flexibility of vessel groups is a generic term underlining the fact that fishing vessels are able to switch between fisheries at a trip level, i. This flexibility was quantified by two indices: polyvalence, and seasonality. The index of seasonality IS, by year y and vessel group vg, reflects the seasonal pattern of the main fishery.
It is expressed as the maximum number of consecutive months during which the main fishery of the vessel group which was identified at the year level was also the main fishery in terms of number of trips over the period analysed.
An index close to 12 indicates that vessels operated in their main fishery throughout the year, whereas one closer to 1 indicates that vessel activity was more seasonal, with the main fishery being operated during a limited period, and secondary fisheries being operated during the balance of the year.
These rules were subsequently applied to trip data for the period � Each trip was allocated to just one fishery, and each vessel was allocated to only one vessel group per year. The use of fixed rules allowed comparison of the dynamics of the various fisheries and vessel groups independently from the natural fluctuations in species assemblages. Temporal trends for fisheries were described in terms of number of trips per year. For vessel groups, they were described in terms of number of vessels, average number of trips, average percentage of trips spent in the main fishery, and index of polyvalence.
For any two consecutive years, we calculated transition matrices that described shifts between vessel groups. Vessels entering or leaving the fishery were also included.
This allowed measuring the extent to which vessels tended to stay within the same vessel group throughout the study period, i. The median value of the percentage of vessels staying in the same vessel group i between two consecutive years was referred to as the index of stability S i. Only the case of Kattegat longlines, from which landings were exclusively cod, was not analysed but introduced directly as a fishery in step 3.
In all cases, one or two species were highly characteristic of each cluster, which was then named after them. Choice of the number of clusters was made on the basis of the thresholds of variance explained, and on the relevance of clusters, in particular of the dominant species. For example, other levels were possible for Danish seiners in the Skagerrak e. Among them, only those considered to be indicators of real target species e.
Three-step approach for identifying Danish fisheries by area and gear during Areas are displayed in geographical order. The Eastern and the Western Baltic herring and industrial midwater trawl fisheries were pooled.
Various preliminary trials were run during step 2 to decide which effort data should be retained among mesh size, month, and ICES rectangle. Given that the analyses were already performed by area, the fishing location expressed by ICES rectangle was not relevant for describing fisheries, especially in the smaller areas such as the Skagerrak, the Kattegat, and the Western Baltic. Final runs were performed with mesh size aggregated into a limited number of classes and landings profiles as active variables.
The cases where a single mesh size class was identified Danish and purse-seine cases were not analysed in this step, but were introduced directly as fisheries in step 3.
These high levels of explained variance indicated that species assemblages, and in particular dominant species, were strongly related to the mesh size used. Some combinations showed redundancy between variables i. However, the landings profile was also necessary to discriminate between combinations using the same gear and mesh size class, specifically when the technical characteristics of the gear were not available in the data set e.
They represented the highest level of disaggregation obtained when selecting combinations that could be interpreted. Finally, some of the combinations were pooled in step 3. The resulting pools were considered as relevant fisheries. In total, 1�6 fisheries per case were retained, the largest numbers for otter trawl cases. Finally, one miscellaneous fishery per area was assigned to gather all trips not included in the other fisheries.
This led to a total of 54 fisheries for the whole Danish fleet Table 2. Typology of Danish fisheries in Area, descriptive name, with the type of gear used, mesh size range, main species and average percentage value, total number of trips.
Emboldening indicates the parameters used for allocation rules. The importance of these fisheries in terms of number of trips differed widely. The smallest was Kattegat longlining eight trips in , and the largest was groundfish trawling in the Western Baltic 16 trips.
The PCA�HAC analysis of fishing vessels in terms of the percentage of trips spent in each fishery led to the identification of 31 clusters, explaining For each cluster, one fishery was highly characteristic and referred to as the main fishery. Six clusters had fewer than five vessels, and showed strong similarities with some other clusters regarding the main fishery.
They were arbitrarily pooled. This led to a total of 25 clusters, referred to as vessel groups Table 3. Vessel groups contained between 2 Skagerrak longliners and North Sea gillnetters fishing vessels. Few vessel groups were characterized by operating in a single fishery e.
Crangon beam trawling, Baltic longlining ; most operated in three or more different fisheries in The index of polyvalence H reflected this diversification of activity. It is remarkable that gillnetters in each area, and Danish seiners off eastern Denmark Skagerrak to the Baltic Sea , were not statistically split into several vessel groups.
This indicated a high level of complementarity between the fisheries. Typology of Danish vessel groups in Main fishing area, name describing the type of main activity, number of vessels and average number of trips, main and secondary fishery with percentage of trips, polyvalence and seasonality indices.
Half the vessel groups showed no seasonal pattern, operating in their main fishery throughout the year Table 3. These were essentially the Danish seiner and Nephrops trawler vessel groups.
The number of trips by fishery varied greatly for all areas Figure 2. The average number of trips, along with the coefficient of variation and slope of the linear regression over the time period of all fisheries, are displayed in Table 4. Some fisheries were more active during the early s Kattegat and Skagerrak Nephrops trawling , others were more active during the mids, when the number of trips was greatest Baltic longlining, Western Baltic gillnetting, Kattegat sole and plaice gillnetting, North Sea cod gillnetting.
Overall, the number of trips increased in 23 fisheries positive slope , but often with large variations between years. Fisheries with increasing trends included all fisheries in the Western Baltic, and most fisheries with fixed gears.
Other fisheries with towed gears decreased in number of trips, except for Baltic industrial midwater trawling and Danish seining, Kattegat and North Sea mixed trawling, and Crangon beam trawling.
Dynamics of Danish fisheries between and , in terms of total number of trips per year. Three different scales are used on the y-axis because of large differences in effort across fisheries.
Fishery coding is defined in Table 2. Summary statistics for fisheries temporal trends number of trips per year between and The temporal dynamics in the number of vessels and number of trips during the past decade differed between vessel group and between areas Figure 3. General results were that most vessel groups decreased in terms of number of vessels, but increased in terms of number of trips per vessel Table 5.
The slope of the index of polyvalence decreased for most vessel groups, indicating that they became less polyvalent with time. However, the slope of average percentage of trips spent in their main fishery was also negative or close to zero in most cases, indicating no increasing activity in the main fishery. This means that the progressive loss of polyvalence took place rather through the loss of some secondary activities. Dynamics of Danish vessel groups between and , in terms of number of vessels, and average number of trips.
Two different scales are used on the y-axis for the number of vessels. Vessel group coding is defined in Table 3. Summary statistics for vessel group temporal trends between and Only a few vessel groups failed to follow these general trends.
The number of vessels increased in some small vessel groups, but also in some more important ones such as Western Baltic demersal trawlers.
The index of polyvalence increased for some vessel groups Baltic Sea longliners, and North Sea Danish seiners and demersal trawlers. The large variations in the number of vessels in the Western Baltic and Kattegat gillnetter vessel groups between and were due to changes in the regulations: to protect inshore vessel groups, small boats were allocated a fixed proportion of the cod quota in This contributed to the registration of a large number of small boats in an attempt to increase individual catch shares.
The system lasted until , when the Danish Fisheries Directorate decided to control the activity of registered vessels, and to suppress the fishing rights of less active ones F. The stability over two consecutive years differed widely among vessel groups, both in median value S i , and in interannual fluctuations Figure 4. Other than that, no general pattern could be observed in terms of stability by area or type of gear. The interannual fluctuations were obviously larger for the small vessel groups e.
Western Baltic gillnetters. The properties mentioned in the text include hardness, strength, and thermal diffusivity. Costs tend to increase when better surface finish is required because additional operations such as grinding, lapping, or similar finishing processes must be included in the manufacturing sequence.
The factors that affect surface finish are 1 geometric factors such as type of operation, feed, and tool shape nose radius in particular ; 2 work material factors such as built-up edge effects, and tearing of the work surface when machining ductile materials, which factors are affected by cutting speed; and 3 vibration and machine tool factors such as setup and workpart rigidity, and backlash in the feed mechanism.
The ideal surface roughness is determined by the following geometric parameters of the machining operation: 1 tool nose radius and 2 feed. In some cases, the end cutting edge and end cutting edge angle of the single-point tool affects the feed mark pattern on the work surface. Steps to reduce vibration in machining include 1 increase stiffness or damping in the setup; 2 operate at speeds away from the natural frequency of the machine tool system; 3 reduce forces in machining by changing feed or depth and cutter design e.
The factors are 1 type of tooling e. What is the fourth term? The fourth term is the cost of the tool itself purchasing the tool and grinding it, if applicable. Cutting speed for minimum cost is always lower because of the fourth term in the unit cost equation, which deals with the actual cost of the cutting edge. This term tends to push the U-shaped function toward a lower value in the case of cutting speed for minimum cost.
Multiple Choice QuizThere are 14 correct answers in the following multiple choice questions some questions have multiple answers that are correct.
A material supplier is pushing a new material that is supposed to be more machinable while providing similar mechanical properties. The company does not have access to sophisticated measuring devices, but they do have a stopwatch. They have acquired a sample of the new material and cut both the present material and the new material with the same band saw settings. In the process, they measured how long it took to cut through each material. To cut through the present material, it took an average of 2 minutes, 20 seconds.
To cut through the new material, it took an average of 2 minutes, 6 seconds. ProblemsSolution: a Since a material with a shorter cutting time is better, it should have a higher machinability rating. To achieve this the cutting time of the base material needs to be in the numerator and the time of the tested material needs to be in the denominator. For the base material B , test data resulted in a Taylor Based on this information, and machinability data given in Table Compute an estimate of the surface roughness for this cut.
From Fig. Determine the surface roughness for this cut. The part is made of a free-machining aluminum alloy. Determine the feed that will achieve the specified surface finish. The part is made of a aluminum. The cutting speed is 1. The work material is cast iron. The nose radius of the cutting tool must be selected. Determine the minimum nose radius that will obtain the specified finish in this operation.
The cutter uses four inserts and its diameter is 3. Solution Solution6 Solution: a Changes in cutting conditions: 1 decrease chip load f, 2 increase cutting speed v, 3 use cutting fluid. Items 2 and 3 will have a marginal effect.
Determine the speed and feed combination that meets these criteria. Increasing speed will increase R MR and reduce R a. Therefore, it stands to reason that we should operate at the highest possible v. Solution:Starting with Eq. Important reasons include 1 applications on all types of materials, 2 very fine finishes, and 3 close tolerances.
The parameters are 1 abrasive material, 2 grit size, 3 bonding material, 4 wheel structure, which refers to the relative spacing of grains, and 5 wheel grade, which refers to the bond strength of the wheel in retaining abrasive grains. The principal abrasive grit materials include 1 aluminum oxide, 2 silicon carbide, 3 cubic boron nitride, and 4 diamond.
The bonding materials in grinding wheels are 1 vitrified bond -clay and ceramics, 2 silicate, 3 rubber, 4 resinoid, 5 shellac, and 6 metallic. Wheel structure indicates the relative spacing of the abrasive grains in the wheel.
An open structure is one in which the grains are far apart, and a dense structure indicates that the grains are close together. Wheel grade refers to the wheel's ability to retain abrasive grains during cutting. It indicates the bond strength of the bonding material used to shape the wheel. A soft grade indicates that the grains are released easily from the bonding material. A hard wheel is one which retains the abrasive grains.
Reasons for higher specific energy in grinding include: 1 size effect -smaller chip size means higher specific energy; 2 extremely negative rake angles on the abrasive particles in a grinding wheel; and 3 not all of the grains in the wheel surface are engaged in cutting; some are plowing or deforming the surface while others are simply rubbing and creating friction at the surface of the work. How is temperature harmful in grinding? High temperatures in grinding create surface burns and cracks.
High temperatures can also soften the surfaces of workparts that have been heat treated for high hardness. The mechanisms are 1 grain fracture, in which a portion of the grain breaks off during cutting; 2 attritious wear, in which the grains become dull during cutting; and 3 bond fracture, in which the grains are pulled out of the bonding material. Dressing is a procedure applied to worn grinding wheels to break off dull grits and expose fresh grits, and to remove chips of work material that have become clogged in the wheel.
It uses a rotating disk or abrasive stick held against the wheel while it rotates. Truing is similar to dressing, but it also restores the ideal cylindrical shape to the wheel. It uses a diamond-pointed tool fed slowly and precisely across the wheel while it rotates. Choose a diamond wheel. Functions of a grinding fluid include 1 reducing friction, 2 removing heat, 3 washing away chips, and 4 reducing workpiece temperature. Centerless grinding is a grinding operation in which cylindrical workparts e.
In creep feed grinding, the depth Mod Small Boats 1.7.10 Iso of cut is very high -several thousand times higher than conventional grinding -and the feed rates are lower by about the same proportion. How does abrasive belt grinding differ from a conventional surface grinding operation? Instead of a grinding wheel, abrasive belt grinding uses abrasive particles bonded to a flexible cloth belt loop which is moved around a pulley system to obtain the speed motion.
Parts are pressed against the belt to accomplish grinding. High finish abrasive processes include honing, lapping, superfinishing, buffing, and polishing.
Video Describe a wheel ring test. Answer: A wheel ring test is performed by suspending the wheel and lightly striking it with a solid, non-metal object, similar to striking a bell. The wheel should ring a clear long tone. If it has cracks, it will not ring properly. Video List two purposes of dressing a grinding wheel.
Answer: Two purposes of dressing a grinding wheel are 1 to renew the wheel surface by fracturing abrasive particles and 2 to remove tiny pieces of embedded workpiece material. Answer: According to the video, the purpose of using coolant in the grinding process are threefold: 1 to reduce grinding power required, 2 to maintain work quality, and 3 to stabilize part dimensions over long production runs. Each omitted answer or wrong answer reduces the score by 1 point, and Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted.
The workpiece is mm long, 30 mm wide, and 75 mm thick. It is desired to remove 25 mm of material from the surface. When traditional grinding is used, the infeed is set at 0.
There is no crossfeed since the wheel width is greater than the work width. When creep feed grinding is used, the depth is increased by and the forward feed is decreased by How long will it take to complete the grinding operation It is desired to make the wheel appear softer by making changes in cutting conditions.
What changes would you recommend? Solution:A hard wheel means that the grains are not readily pulled from the wheel bond. The wheel can be made to appear softer by increasing the force on the individual grits as given by Eq. According to this equation, the force on the abrasive grains will be increased by increasing work speed v w , decreasing wheel speed v, and increasing infeed d.
Specify the appropriate grinding wheel parameters and the grinding conditions for this job. For the following application, identify one or more nontraditional machining processes that might be used, and present arguments to support your selection.
Assume that either the part geometry or the work material or both preclude the use of conventional machining. The application is a matrix of 0. The matrix is rectangular, 75 by mm 3. Solution:Application: matrix of holes in 0. The application is an engraved aluminum printing plate to be used in an offset printing press to make by mm 11 by 14 in posters of Lincoln's Gettysburg address. Solution:Application: engraved aluminum printing press plate for 11 in by 14 in posters.
Possible process: photochemical engraving; making a negative of the speech and transferring this to either a silk screen or directly to the photoresist would seem to be the most straightforward methods. The application is a through-hole in the shape of the letter L in a The size of the "L" is 25 by 15 mm 1. Solution:Application: through-hole in the shape of the letter "L" drilled through 0.
Possible process: USM works on glass and other brittle non-metallic materials. This is probably the best process. The application is a blind-hole in the shape of the letter G in a 50 mm 2.
The overall size of the "G" is 25 by 19 mm 1. Solution:Application: the letter "G" drilled to a depth of 0. Manual methods based on portable saws are currently used to perform the cutting operation, but production is slow and scrap rates are high.
The foreman says the company should invest in a plasma arc cutting machine, but the plant manager thinks it would be too expensive. What do you think? Justify your answer by indicating the characteristics of the process that make PAC attractive or unattractive in this application. Solution:In plasma arc cutting, the workpart must be an electrically conductive material. Fiber glass is not electrically conductive.
PAC is therefore not an appropriate process for this application. Many of these fabrics are strong and wear-resistant, which properties make them difficult to cut. Justify your answer by indicating the characteristics of the process that make it attractive. Solution:Water jet cutting would be an ideal process for this application. WJC cuts through fabrics quickly and cleanly, and the process could be readily automated. Electrochemical Machining In an electrochemical machining operation, the frontal working area of the electrode is 2.
The material being cut is pure aluminum, whose specific removal rate is given in Table 26 The hole is 25 mm on each side, but the electrode used to cut the hole is slightly less that 25 mm on its sides to allow for overcut, and its shape includes a hole in its center to permit the flow of electrolyte and to reduce the area of the cut.
This tool design results in a frontal area of mm 2. Table 26 The block is 2. To speed the cutting process, the electrode tool will have a center hole of 3. The outside diameter of the electrode is undersized to allow for overcut. The overcut is expected to be 0. Electric Discharge Machining Determine the amount of metal removed in the operation after one hour at a discharge current of 20 amps for each of these metals.
What metal removal rate would be achieved on nickel in this EDM operation, if the same discharge current were used?
Estimate the melting temperature of 0. It is anticipated that the overcut will be 0. Solution SolutionSolution: Using Eq. However, in preliminary cuts, the surface finish on the cut edge is poor. What changes in discharge current and frequency of discharges should be made to improve the finish?
Solution: As indicated in Figure Chemical The reader might be tempted to select d because the Jominy test plots hardness as a function of distance from the quenched surface of the test specimen. However, the reason for measuring hardness in the Jominy test is to indicate hardenability. Multiple Choice QuizThere are 20 correct answers in the following multiple choice questions some questions have multiple answers that are correct.
Advantages: 1 it provides a permanent joint, 2 joint strength is typically as high as the strength of base metals, 3 it is most economical in terms of material usage, and 4 it is versatile in terms of where it can be accomplished. Disadvantages: 1 it is usually performed manually, so labor cost is high and the skilled labor to perform it is sometimes scarce, 2 welding is inherently dangerous, 3 a welded joint is difficult to disassemble, and 4 quality defects are sometimes difficult to detect.
The two discoveries of Sir Humphrey Davy were 1 the electric arc and 2 acetylene gas. The faying surfaces are the contacting surfaces in a welded joint. A fusion weld is a weld in which the metal surfaces have been melted in order to cause coalescence. In a fusion weld, the metal is melted. In a solid state weld, the metal is not melted. An autogenous weld is a fusion weld made without the addition of filler metal.
Most welding operations are carried out at high temperatures that can cause serious burns on skin and flesh. In gas welding, the fuels are a fire hazard. In arc welding and resistance welding, the high electrical energy can cause shocks that are fatal to the worker. In arc welding, the electric arc emits intense ultraviolet radiation that can cause blinding. Other hazards include sparks, smoke, fumes, and weld spatter. An automatic welding operation uses a weld cycle controller that regulates the arc movement and workpiece positioning; whereas in machine welding, a human worker must continuously control the arc and the relative movement of the welding head and the workpart.
Five joint types are 1 butt, 2 corner, 3 lap, 4 tee, 5 edge. For sketches see Figure A fillet weld is a weld joint of approximately triangular cross section used to fill in the edges of corner, lap, and tee joints. A groove weld is a weld joint used to fill in the space between the adjoining edges of butt and other weld types except lap. Because it does not join to distinct parts, but instead adds only filler metal to a surface. Because the heat is concentrated in a small region for greatest efficiency and minimum metallurgical damage.
The unit melting energy is the amount of heat energy required to melt one cubic inch or one cubic mm of metal. The Smallboats 1.7.10 Iso factors on which it depends are 1 specific heat, 2 melting point, and 3 heat of fusion of the metal. Heat transfer factor is the ratio of the actual heat received at the work surface divided by the total heat generated by the source.
Melting factor is the ratio of heat required for melting divided by the heat received at the work surface. The HAZ is a region of base metal surrounding the fusion zone in which melting has not occurred, but temperatures from welding were high enough to cause solid state microstructural changes.
Welding can be accomplished between certain combinations of dissimilar metals using solid state welding processes. Which one of the following heat sources is most consistent with this objective: a high power, b high power density, c low power, or d low power density? Failures also occur in the heat-affected zone because metallurgical damage often occurs in this region.
Problems Power Density Is the resulting power density enough to melt metal? This power density is most probably sufficient for melting the metal. Assume the power density provided in , Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted.
What are the power densities in , Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted. The U-groove is prepared using a milling cutter so the radius of the groove is 3. During welding, the penetration of the weld causes an additional 1.
The final crosssectional area of the weld can be approximated by a semicircle with a radius of 4. The length of the weld is mm. The melting factor of the setup is 0. Assume the resulting top surface of the weld bead is flush with the top surface of the plates. Assume the cross section of the weld bead approximates a right isosceles triangle with a leg length of 4. Determine the rate of heat generation required at the welding source to accomplish the weld.
The operation required the power to be on for 4 sec. Determine the rate of heat generation that was required at the source to accomplish this weld. The filler metal to be added is a harder alloy grade of steel, whose melting point is assumed to be the same. A thickness of 2.
The surface will be applied by making a series of parallel, overlapped welding beads running lengthwise on the plate. Assume the welding bead is rectangular in cross section: 5 mm by 6 mm. Ignore the minor complications of the turnarounds at the ends of the plate.
Solution: FromSolution: a From Table In order to restore it, the diameter was turned to 3. Next the axle was built up so that it was oversized by the deposition of a surface weld bead, which was deposited in a spiral pattern using a single pass on a lathe.
After the weld buildup, the axle was turned again to achieve the original diameter of 4. The weld metal deposited was a similar composition to the steel in the axle. The length of the bearing surface was 7. During the welding operation, the welding apparatus was attached to the tool holder, which was fed toward the head of the lathe as the axle rotated.
The axle rotated at a speed of 4. The width of the weld bead was 0. Assuming the heat transfer factor was 0. Multiple Choice QuizThere are 23 correct answers in the following multiple choice questions some questions have multiple answers that are correct. The arc is sustained in arc welding processes by the transfer of molten metal across the gap between the electrode and the work: a true or b false?
The arc is sustained, not by the transfer of molten metal, but by the presence of a thermally ionized column of gas through which the current flows. The fitter takes 5. Every mm of weld length, the welding stick must be changed, which takes 0.
While the fitter is working, the welder is idle resting ; and while the welder is working, the fitter is idle. With two fixtures, fitter and robot work simultaneously, the robot welding at one fixture while the fitter unloads and loads at the other.
At the end of each work cycle, they switch places. The electrode wire spool must be changed every five workparts, which task requires 5. Determine a arc time and b production rate for this work cell. The welding voltage is 22 volts and the current is amps. The heat transfer factor is 0. If filler metal wire of 3.
The welding voltage is 21 volts and the current is amps. Using tabular data and equations given in this and the preceding chapter, determine the likely value for travel speed v in the operation. The melting factor of the steel is 0. The welding current is 75 amps and the voltage is 16 volts. The diameter of the electrode is 0. There is a core of flux running through the center of the electrode that has a diameter of 0. The rate at which the filler metal is added to the weld is 0.
The tube is slowly rotated under a stationary welding head. The cross-sectional area of the weld bead is 0. The weld duration will be set at 0. Based on the electrode diameter, the weld nugget will have a diameter of 0. If the electrical resistance between the surfaces is micro-ohms, what is the thickness of the weld nugget assuming it has a uniform thickness? The unit melting energy for a certain sheet metal is 9.
The thickness of each of the two sheets to be spot welded is 3. To achieve required strength, it is desired to form a weld nugget that is 5.
If it is assumed that the electrical resistance between the surfaces is micro-ohms, and that only one-third of the electrical energy generated will be used to form the weld nugget the rest being dissipated , determine the minimum current level required in this operation. In stitching the U-shaped fasteners are formed during the assembly process.
In stapling, the fasteners are preformed. What are integral fasteners? Integral fasteners make use of a forming operation on one of the parts to be joined to interlock the components and create a mechanically fastened joint. Some of the general principles and guidelines in design for assembly include the following: 1 Use the fewest number of parts possible to reduce assembly required.
Use threaded fasteners only where justified, e. Some of the principles and guidelines that apply specifically to automated assembly include the following: 1 Use modularity in product design.
Each module to be produced on a single assembly system should have a maximum of 12 or 13 parts and should be designed around a base part to which other components are added. The ideal is for all components to be added vertically from above. Poor quality components cause jams in feeding and assembly mechanisms.
Answer e might also be given, but it is not mentioned in the text. All of the other answers go against design-for-assembly principles. Problems Threaded Fasteners However, this bolt is too large for the size of the components involved, and a higher strength but smaller bolt would be preferable. The hole has a diameter of 2. The pin has a diameter of 2. The base of the machine is 4 ft x 8 ft.
Determine a the radial pressure between the pin and the base and b the maximum effective stress in the interface. Solution Solution: a 3 The seed and tang ends are removed, which reduces the length to mm. The diameter is ground to mm. A mm-wide flat is ground on the surface which extends from one end to the other. Assuming that the seed and tang portions cut off the ends of the starting boule were conical in shape, determine a the original volume of the boule, mm 3 ; b how many wafers are cut from it, assuming the entire mm length can be sliced; and c the volumetric proportion of silicon in the starting boule that is wasted during processing.
This is a principal motivation for using larger wafer diameters. The IC chips that will be fabricated on the wafer surface are square with 20 mm on a side.
However, the processable area on each chip is only 18 mm by 18 mm. The density of circuits within each chip's processable area is circuits per mm 2. The IC chips that will be fabricated on the wafer surface are square with 0. However, the processable area on each chip is only 0.
The density of circuits within each chip's processable area is , circuits per square inch. Next, it will be sliced into wafers 0. The wafers thus produced will be used to fabricate as many IC chips as possible for the personal computer market. Each chip is square with 15 mm on a side.
Solution:First determine the number of wafers that can be obtained from the cylinder. Each wafer takes 0. Thus, the number of wafers is given by: Answer: The features sizes range from less than 1 nm to nm. Answer: Products mentioned in the text include computers, flat screen displays, and batteries based on carbon nanotubes; nanodots and nanowires as reinforcing agents in composite materials; cancer drugs designed to match the genetic profile of cancer cells; surface films that absorb more solar energy than current photovoltaic receptacles; nanoscale coatings to increase scratch resistance of surfaces and stain resistance of fabrics; portable medical laboratories, and light sources that are more energy efficient.
What is a buckyball? Answer: A buckyball is the carbon molecule C 60 , a molecule containing exactly 60 carbon atoms and shaped like a soccer ball. The 60 atoms are arranged symmetrically into 12 pentagonal faces and 20 hexagonal faces to form a ball.
What is a carbon nanotube? Answer: A carbon nanotube is another molecular structure of carbon atoms possessing the shape of a tube. It has a typical size of a few nm in diameter and a length of nm or so. Of interest are its mechanical and electrical properties. It can possess strength and stiffness properties exceeding those of steel, and it can be a conductor of electricity or a semiconductor.
Answer: The main disciplines include chemistry, physics, various engineering disciplines, computer science, biology, and medical science. Answer: The close association of biology derives from the fact that the building blocks of biological organisms are in the same size range.
For example, proteins range in size between about 4 nm and 50 nm. What are those two factors? Answer: The two factors mentioned in the text that differentiate nanoscale objects from much larger ones are 1 surface properties become much more important because a much higher proportion of a nanoscale object's atoms or molecules are at the surface, whereas in a larger object the internal atoms and molecules are relatively much more numerous; and 2 material behavior of nanoscale objects is influenced by quantum mechanics rather than bulk properties.
Answer: A scanning probe instrument uses a very sharp probe, whose tip approaches the size of an atom, that moves along the surface of the specimen at a distance of only one nanometer in order to measure properties of the surface.
This type of instrument is important because it permits images of the surface to be constructed that are on the scale of the surface atoms. The probability of electrons being in this space beyond the surface decreases exponentially in proportion to the distance from the surface. This sensitivity to distance is exploited in the scanning tunneling microscope by positioning the probe tip very close to the surface and applying a small voltage between the two.
This causes electrons of surface atoms to be attracted to the small positive charge of the tip, and they tunnel across the gap to the probe.
Answer: The two basic categories are 1 top-down approaches, which adapt the microfabrication techniques to nanoscale object sizes and 2 bottom-up approaches, in which atoms and molecules are manipulated and combined into larger structures.
Answer: Because the wavelength of visible light is to nm, well beyond nanoscale. Answer:The lithography techniques discussed in the text are 1 extreme ultraviolet lithography, 2 electron beam lithography, 3 x-ray lithography, and 4 nano-imprint lithography.
Answer: Nano-imprint lithography is the same basic process as micro-imprint lithography except the deformed features of the resist are of nanoscale proportions. These limitations make it a very slow and expensive process. What is self-assembly in nanofabrication? Answer: The desirable features of atomic or molecular self-assembly processes include the following: 1 they can be carried out rapidly, 2 they occur automatically and do not require any central control, 3 they exhibit massive replication, and 4 they can be performed at or near atmospheric pressure and room temperature.
Multiple Choice QuizThere are 18 correct answers in the following multiple choice questions some questions have more than one correct answer.
To achieve a perfect score on the quiz, all correct answers must be given. Each omitted answer or wrong answer reduces the total score by 1 point, and each additional answer beyond the correct number of answers reduces the score by 1 point.
The percentage score on the quiz is based on the total number of correct answers. In powered leadthrough, a teach pendant that controls the drive motors of the individual joints is used to move the manipulator into the desired joint positions, which are then recorded into memory. In manual leadthrough, the manipulator is physically moved through the desired sequence of positions, which are recorded into memory for later execution.
Flexible automation is an extension of programmable automation in which there is virtually no lost production time for setup changes or reprogramming: a true or b false. The data is binary, not analog. The leadscrew is powered by a stepping motor which has step angles.
Determine a the number of pulses required to move the table the specified distance and b the required motor speed and pulse rate to achieve the desired table speed. An optical encoder is connected to the lead screw. The optical encoder emits pulses per revolution. Determine a the control resolution of the system for the x-axis only, b the corresponding rotational speed of the motor, and c frequency of the pulse train emitted by the optical encoder at the desired feed rate.
The joint must have an accuracy of 0. The motor is attached to a leadscrew through a gear reduction 2 turns of the motor for 1 turn of the leadscrew. The pitch of the leadscrew is 5. Specify the number of step angles that the motor must have in order to meet the accuracy requirement. The accuracy of the joint-link combination, expressed as a linear measure at the end of the link which results from rotating the joint, is specified as 0.
It is assumed that the link is perfectly rigid, so there are no additional errors due to deflection. In addition, human workers are required to manage the system, and workers may be used to operate the individual workstations and machines. The principal material handling functions in manufacturing are 1 loading and positioning work units at each workstation, 2 unloading work units from the station, and 3 transporting work units between workstations.
The five main types of material transport equipment are 1 industrial trucks, which includes fork lift trucks, 2 automated guided vehicles, 3 rail-guided vehicles, 4 conveyors, and 5 hoists and cranes.
In fixed routing, all of the work units are moved through the same sequence of stations, which means that the processing sequence required on all work units is either identical or very similar. In variable routing, different work units are moved through different workstation sequences, meaning that the manufacturing system processes or assembles different types of parts or products.
A production line is a sequence of workstations at which individual tasks are accomplished on each work unit as it moves from one station to the next to progressively make the product. Advantages of the mixed model line include 1 no downtime between the different models due to line changeovers; 2 production rates can be matched to demand rates for the different models, and thus 3 inventory fluctuations can be avoided in which there are high inventories of some models while there are stock-outs of other models.
Limitations of a mixed model line include 1 the line balancing problem is more complex, 2 scheduling the models is more difficult, and 3 getting the right parts to each workstation is more complicated because more parts are involved.
The manual methods include 1 work units are simply passed by hand along a flat worktable from one station to the next, 2 work units are collected in boxes and then Minecraft Small Boats Mod 1.7.10 passed between stations, and 3 work units are pushed along a non-powered conveyor between stations.
The three work transfer systems are 1 continuous transfer, in which parts move on a conveyor at a steady speed; 2 synchronous transfer, in which parts all move simultaneously from station-to-station with a stop-and-go action; and 3 asynchronous transfer, in which parts move independently between stations with a stop-and-go action.
Because all production lines suffer a certain amount of nonproductive time due to reliability problems. The repositioning time is called the transfer time; it is the time to move parts from one station to the next. The entire work cycle is performed at one station, so single station cells usually operate at relatively slow production rates. Reasons for downtime on a machining transfer line include tool changes, unpredictable mechanical and electrical failures, and normal wear and tear on the equipment.
Define group technology. GT is a general approach in which similarities among parts are identified and exploited in design and manufacturing. Cellular manufacturing involves the production of part families using groups of machines generally manually operated to produce a certain part family or a limited set of part families.
The concept is useful in designing cells to produce the part family. A flexible manufacturing system FMS is an automated group technology cell consisting of processing stations interconnected by an automated handling system and controlled by a computer.
FMS software and control functions include 1 NC part programming, 2 NC part program download, 3 production control, 4 machine control, 5 workpart control, 6 tool management, 7 work transport control, and 8 general system management. Advantages include 1 higher machine utilization, 2 reduced work-in-process, 3 lower manufacturing lead times, and 4 greater flexibility in production scheduling. Computer integrated manufacturing CIM refers to the pervasive use of computer systems throughout a manufacturing organization, not only to monitor and control the operations, but also to design the product, plan the manufacturing processes, and accomplish the business functions related to production.
Design for life cycle means that factors relating to the product after it has been manufactured should be taken into consideration in design. These factors include ease of installation, reliability, maintainability, serviceability, upgradeability, and disposability. Multiple Choice QuizThere are 19 correct answers in the following multiple choice questions some questions have multiple answers that are correct.
Make-to-stock is the case in which the company produces to replenish inventories of products. Production rate is greater than demand rate, and it is appropriate to carry inventory. Aggregate planning is scheduling by general product line; the master production schedule indicates how many and when of each product model within the product line are to be produced.
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