Flexible Manufacturing System Design, Modelling and Evaluation

FLEXIBLE MANUFACTURING SYSTEM DESIGN, MODELLING AND EVALUATION 8

FlexibleManufacturing System Design, Modelling and Evaluation

Spurgears emerge as the most usual type of gear and are utilized in allindustries. Spur gears are cylindrical gears that have straight teethcutting parallel to the axis of the gear. These gears give a highdegree of efficiency and due to their straight teeth do not produceend thrust. In their manufacture, there are three chief manufacturingprocesses, which include planning, shaping, and hobbing (Davis,2005). The aim of this assignment is to discuss the manufacturingprocess of spur gearbox. Machines required in the manufacturingprocess will also be discussed.

Inthe manufacture of spur gearbox, three processes are followed. Theseprocesses are planning, shaping, and hobbing. In the followingparagraphs, each of these processes will be covered together with themachines that are used in every process.

PlanningProcess

Inthe planning process, rack cutter is used. The cutter is usuallymounted on a vertical slide, while the work piece axis is placedhorizontally. The cutter navigates vertically downwards duringrolling movement of generation. In the generation of spur gears, thecutter responds horizontally along a line parallel to the workingaxis. The cutter usually has an exact shape of the finished geartooth. Only meager amounts of material become removed through arolling and reciprocating action. This process is usually fast, butexpensive generally because of the cost of tooling and machinery.This process is as illustrated in the following diagram the motionof the cutter is indicated and the setting of the work piece in ahorizontal axis is also indicated.

Itis critical to note that the shape of the cutter must conform to theshape of the gear. This is an important consideration because ithelps in coming up with gears that have the required shape. Thecutter must be in a machined form in order to cut the required geartooth space. The planning process is usually repeated until all teethfor the gear are formed. This process is usually deemed to have adisadvantage in that the tooth space profile can be clearly differentfor gears that have different modules and varied number of teeth.This problem is such that for every module, through permitting someinaccuracy of form, around eight cutters are required for the entirerange for gear teeth from ten teeth to the rack form.

ShapingProcess

Spurgearbox teeth are usually generated through the use of areciprocating cutter, which is a rotating pinion form or a rack form.During this process, the rack cutter is usually reciprocated across ablank-face. After every cut, the rack cutter is moved some distancealong the teeth line and the blank becomes rotated through a meagerangle. This process is repeated till end of the rack becomes reached.At this point, the blank and rack have to be repositioned. Shaping ofspur gears using a circular pinion shaped cutter having the requiredrake angles in cutting the teeth is faster compared to using the rackform of cutter. The cutter and blank are usually set in a verticalplane and rotated in way such that the two become like gears in mesh.The shaping of gear cutter is faster compared to using a rack sincethe cutting process is continuous. Besides, the cutter need not bestepped back, which gear cutter shaping faster. In this process, thecutter that is utilized is virtually a gear that is provided withcutting edges. The tool is usually rotated at the needed velocityratio that is relative to the spur gear and a single manufacturedgear tooth space becomes formed by one whole cutter tooth. There is alimitation in using pinion shaped teeth during this process since thegenerated gear profile is directly reliant on the tooth profile anyerror on any tooth of the cutter becomes directly transferred to thespur gear being cut (Bawa,2004).

HobbingProcess

Thisprocess utilizes a hobbing machine that has to skew spindles. One ofthe spindles is mounted with a blank work piece while the other ismounted with a hob. The angle amid the work piece’s spindle andthat of the hob’s spindle differs. During the production of spurgear, the hob is usually angled being equal to that of the helixangle. During the process, two shafts become rotated at a comparativeratio this is critical in determining the number of teeth that areon the blank. For instance, in case the gear ratio is established tobe 40:1, this implies that the hob is estimated to rotate 40 timesfor every turn made by the blank. This also implies that 40 teethwould be produced in the blank. This example can only apply in thecase of a single threaded hob. In this process, the hob becomes fedup into the work piece till the appropriate tooth depth becomesobtained. It is after this that the hob becomes fed up through thework piece being parallel to the axis of rotation of the blank. Gearhobbing entails a continuous generation process, where tooth flanksof the continually moving work piece become formed through equallyspaced cutting edges of hob. This process has an advantage in that itcan be relied upon on high productivity rates.

Everyhobbing machine comprises of tailstock and a chuck for holding thework piece and a spindle. For a tooth profile, the principal rack isstraight-sided having sides that are inclined at a pressure angle ofa tooth form the top and bottom are flat. The required addendumcorrection so as to permit the use of small-numbered pinions may beobtained through appropriate modification of the rack. Hobbingmachines are usually characterized by the pitch diameter they canproduce. Most of the hobbing machines are vertical hobbers, whichimply that the blank is vertically mounted.

Thehob entails a rotating cutting tool, which has the shape of a worm.The teeth of the hob have straight sides. The axis of the hob shouldbe rotated through the lead angle in order to cut spur gear teeth.Basically, the hob is a straight cylindrical tool that has a threadhaving the same cross section as that of the rack tooth, which ishelically wound. The blank and the hob must be rotated at anappropriate angular velocity ratio (Jadon&ampVerma,2010). The cutting teeth of the hob have grooves, which run acrossthe length of the hob. The grooves are critical for cutting andremoval of chip. The cross sectional profile of the hob teeth isusually similar to the profile of the teeth of a rack gear, which isutilized with the finished product. Every tooth of the hob isrelieved on the back side so as to mitigate friction. Most the hobsare single-threaded however, when double and triple threaded hobsare used, production rates are increased. The problem with usingdouble and triple threaded hobs is that they are not accurate as thesingle-threaded hobs. There are different types of hobs, whichinclude worm wheel hobs, chamfer hobs, spline hobs, and serrationhobs among others (Bangalore,2004).

Theproduction process of the spur gear cannot be complete withoutundergoing through the last processes of heat treatment and grinding.After passing through the cutting process, heat treatment is appliedon the gears. The chief reason for letting the gears pass through theheat treatment is to harden the gears (Sharma,2013). It is after passing through the heat treatment that the spurgears are passed through the grinding process. It is from thegrinding step that one gets a finished spur gearbox. In order todetermine the time that can be used in manufacturing spur gearbox, itcan be assumed that the time taken would depend on the cuttingmachine used and the gear ratio. In case the gear ratio is high, thenthe production rate can also be high. Therefore, the number of spurgearboxes produced in a period of one year will depend on theproduction rate.

Conclusion

Spurgears are the most common type of gear and are utilized in allindustries. Spur gears are cylindrical gears that have straight teethcutting parallel to the axis of the gear. These gears give a highdegree of efficiency and due to their straight teeth do not produceend thrust. In their manufacture, there are three chief manufacturingprocesses, which include planning, shaping, and hobbing. During theplanning process, rack-cutter is used. The cutter is usually mountedon a vertical slide, while the work piece axis is placedhorizontally. The cutter navigates vertically downwards duringrolling movement of generation. In the generation of spur gears, thecutter responds horizontally along a line parallel to the workingaxis. The shape of the cutter must conform to the shape of the gear.This is an important consideration because it helps in coming up withgears that have the required shape. During the shaping process, therack cutter is usually reciprocated across a blank-face. After everycut, the rack cutter is moved some distance along the teeth line andthe blank becomes rotated through a meager angle. This process isrepeated till end of the rack becomes reached. In the hobbingprocess, process utilizes a hobbing machine that has to skewspindles. One of the spindles is mounted with a blank work piecewhile the other is mounted with a hob. The angle amid the workpiece’s spindle and that of the hob’s spindle differs. During theproduction of spur gear, the hob is usually angled being equal tothat of the helix angle. During the process, two shafts becomerotated at a comparative ratio this is critical in determining thenumber of teeth that are on the blank. The hob describes a rotatingcutting tool, which has the shape of a worm. The teeth of the hobhave straight sides. The axis of the hob should be rotated throughthe lead angle in order to cut spur gear teeth.

References

Bangalore,H. M. T. (2004).&nbspProductiontechnology.New Delhi: Tata McGraw-Hill.

Bawa,H. S. (2004).&nbspManufacturingprocesses.New Delhi: Tata McGraw-Hill.

Davis,J. R. (2005).&nbspGearmaterials, properties, and manufacture.Materials Park, Ohio: ASM International.

Jadon,V. K., &amp Verma, S. (2010).&nbspAnalysisand design of machine elements.New Delhi: I.K. International Pub. House.

Sharma,P. C. (2013).&nbspAtextbook of production engineering.NewDelhi: S. Chand &amp Company PVT.LTD.