Revised Presentation Vlab on Manufacturing

Manufacturing Processes: Objective The intent of manufacturing processes is to produce acceptable parts and products. The machining process outputs, the dependent variables in the process models, have to do with both part and process characteristics. Machined part characteristics such as dimensional and form accuracy and part surface and subsurface characteristics are the primary concerns. Such part characteristics are the results of the fundamental mechanical and thermal processes that occur in the operation. The process models relating outputs to controllable process parameters are of two general kinds. First type relates measurable part characteristics to process parameters. E.g.: the effect of feed rate on machined surface roughness. The other kind relates more basic physical quantities that determine part characteristics to process parameters. Eg.: A mechanical model relating cutting forces to feed rate.

The forces are basic quantities that determine aspects of part dimension, surface roughness and, in conjunction with cutting speed, the power used and so energy dissipated as heat with the resulting temperature rise and its effects such as tool wear. All these aspects will be studied and analyzed through experiments during the course of Vlab on manufacturing. Manufacturing Processes: Objective

Process Variables The general goal of process model formulation is to quantitatively relate the dependent process variables to the independent variables. In lathe turning the independent variables are the process kinematics and other controllable aspects of running the process. –cutting speed –depth of cut –feed rate –cutting tool geometry –cutting fluid The process parameters determine process behavior.

Process performance is described by the dependent variables cutting forces cutting zone temperature tool-chip friction finished surface roughness Process Variables

Proposed Simulation Experiments 1.Turning operation on lathe and study of effect of speed, feed and depth of cut on surface roughness –In this experiment the students will learn effect of speed, feed and depth of cut on surface finish. –Background information will be given through power point presentations, videos and photograph to make them understand turning operation on lathe. –Effect of each of three parameters, keeping the other two constant will be discussed and shown through actual cutting operation. –Above information will be available to the student in a table on front end from where the student will pick requisite parameter and see the final cut piece and surface finish so obtained. 2.To perform taper turning on the lathe –Background information will be given through power point presentations, videos and photograph to make them understand about importance of taper and various ways of performing taper turning operation on lathe. –The student will be given a choice of selecting the taper turning method amongst Taper turning attachment, Tail stock offset Compound rest adjustment –Based on selection the student will be asked to set angle/offset, larger of two diameters and accordingly flash animation and videos of taper turning operation will be shown. –Exercises will be generated to set the parameters for a kind of taper turning and upload it.

3.To perform thread cutting on the lathe –Background information will be given through power point presentations, videos and photograph to make them understand about various types of threads, their use in practice and thread cutting. –Guidelines on setting of speed, feed, and direction for thread cutting will also be provided with examples. –Student will learn basics of cutting of metric and square threads through animations and videos. –Finally student will be shown the procedure to check correctness of the thread. 4.To perform milling operations, Profile milling, Pocket milling and Slot milling through basic operational differences and features –Background information will be given through power point presentations, videos and photograph to make them understand milling operations. –Details regarding up and down milling will be shown through animations. –Details of different milling cutters will be given to the students. 5.To study effect of the following process parameters during slot milling operation, –Cutting speed, –Depth of cut and –Feed rate.

6.To perform gear cutting operation on milling machine –Background information on gear geometry and calculation of number of involute tooth. –Details on indexing mechanism and procedure of setting it for the given profile will be explained and shown through diagram, photograph and videos. –Gear profile cutting operation will be shown by animation and videos. –Finally student will be shown the procedure to check correctness of the tooth profile. 7.Analysis of effect of the process parameters, cutting speed, feed rate and depth of cut on cutting forces during turning operation –Details of tool dynamometer will be given through power point presentation in terms of principle, working and data acquisition. –Cutting force measurement for a set of cutting parameters will be given. Student will be given choice to select a set among 15 sets 8.Effect of rake angle, clearance angle and nose radius on cutting forces, surface finish and chip formation –Details of tool signature and its importance will be given by power point presentation. –Students will be allowed to choose a set of tool signature. Based on selection an animation/video of turning on lathe will be shown. Finally, finished product, cutting forces, type of chip and surface roughness data will be provided to the student

9.Study on effect of work piece and tool materials on surface finish, chip formation and cutting forces –Basic aspects related to work piece material and tool material combination will be given by power point presentation. –Students will be allowed to choose a work piece material. Based on work piece students will be given a choice to select tool material. Based on the combination, analysis of their effect on cutting force, surface finish and type of chip will be carried out though comparative studies through photographs 10.Study of cutting tool geometry and its effect on cutting forces for up-milling and down-milling operations –Analysis of effect of up milling and down milling on cutting forces will be given to students through power point presentation. –Student will be given choice to select a set of milling parameters and tool geometry. Cutting force measurement for the given set will be shown.

Experiment 1 Turning operation on lathe and study of effect of speed, feed and depth of cut on surface roughness

11 Machining Turning Definition: A machining operation in which a single point cutting tool removes material from a rotating workpiece to form a cylindrical shape.

Basic Mechanics of Metal Cutting Metal ahead of the cutting tool is compressed. This results in the deformation or elongation of the crystal structure - resulting in a shearing of the metal. As the process continues, the metal above the cutting edge is forced along the “chip-tool” interference zone and is moved away form the work. Shear plane

Source: NPTEL Direction of feed motion decides type of turning – i)Feed motion parallel to axis – longitudinal turning ii)Feed motion perpendicular to axis – transverse turning

14 Machining –Orthogonal cutting model

Machining Terminology Speed – surface cutting speed (v, m/min) Feed – advancement of tool through the workpiece in one rotation of spindle (f, mm/rev) Depth of cut – distance by which tool penetrates in the workpiece (d, mm)

Process Parameters Any machining operation involves three basic parameters –Primary motion (cutting motion or Cutting Speed) v During the rotation of jobpiece, primary motion makes workpiece to approach cutting edge hence spindle rotates anticlockwise –Secondary motion (feed) f Distance travel along the axis –Depth of cut d Distance tool penetrates in the jobpiece. It is along raidial directoion Relative tool travel in 1 rotation =  D Cutting Speed = v =  DN/1000 m/min

Three process parameters are perpendicular to each other Process Parameters

Output Parameter: Surface Roughness Roughness: It is defined as closely spaced, irregular deviations on a scale smaller than that of waviness. Roughness is expressed in terms of its height, its width, and its distance on the surface along which it is measured. Waviness: It is a recurrent deviation from a flat surface, much like waves on the surface of water. It is measured and described in terms of the space between adjacent crests of the waves (waviness width) and height between the crests and valleys of the waves (waviness height).

Sample Plot: Surface Roughness v/s Cutting Speed

Cutting Speed Depends on number of rotations (rpm) of the chuck of a lathe Always expressed in meters per minute (m/min) Important to use correct speed for a given material to get desired surface finish –Too high: cutting-tool breaks down rapidly –Too low: time lost, low production rates

Cutting Speeds Using High-Speed Steel Toolbit Turning Rough CutFinish Cut Materialm/min Machine Steel2730 Tool Steel2127 Cast Iron1824 Bronze2730 Aluminum6193

Calculating Spindle Speed Given in revolutions per minute Cutting speed of metal and diameter of work must be known Proper spindle speed set by dividing CS (m/min) by circumference of work (mm)

Example: Calculate RPM required to rough-turn 50 mm diameter piece of machine steel (CS 27 MPM):

Effect of Cutting Speed v (m/min) f (mm/rev) 0.3 d (mm) 0.3 Rough Finish As speed increases surface finish increases

Feed Distance cutting tool advances along length of workpiece for every revolution of the spindle Feed of lathe dependent on speed of lead screw or feed rod –Speed of feed rod controlled by change gears in quick-change gearbox

Feed f – the distance the tool advances for every rotation of workpiece (mm/rev)

27 Analysis of Turning –Feed & Feed rate: Both are used to specify the same quantity which is the amount of travel in secondary motion direction in a specified amount of time. Time unit is revolution of workpiece for feed while feed rate is defined in terms of second. Feed

Effect of Feed on Roughness

Rough and Finish cut Generally two cuts are employed - Roughing cut –Purpose to remove excess material quickly –Coarse feed: surface finish not too important to 0.4-mm Finishing cut –Used to bring diameter to size –Fine feed: Produce good finish to mm

Effect of Feed At low feed surface finish is good. v (m/min)25.9 f (mm/rev) d (mm)0.3 Rough Finish

Feed High-speed steel cutting tool feed per revolution of spindle Rough CutsFinish Cuts Materialmm/rev Machine Steel Tool Steel Cast Iron Bronze Aluminum

Depth of Cut Distance tool penetrates in the workpiece It is equal to half the difference between the initial diameter and the final diameter. Generally only one roughing and one finishing cut is used –Roughing cut should be as deep as possible to reduce diameter to within 0.75 to 1 mm of size required –Finishing cut should be less than mm

Depth of cut on a lathe

Depth of Cut perpendicular distance between machined surface and uncut surface of the Workpiece d = (D 1 – D 2 )/2 (mm)

Effect of Depth of Cut At low depth of cut surface finish is good. v (m/min)25.9 f (mm/rev)0.3 d (mm)

Material Removal Rate MRR Volume of material removed in one revolution MRR =  D d f mm 3 Job makes N revolutions/min MRR =  D d f N (mm 3 /min) In terms of v MRR is given by MRR = 1000 v d f (mm 3 /min)

37 Note that undeformed chip thickness is equal to feed! MRR

Calculating Machining Time Factors such as spindle speed, feed and depth of cut must be considered

Example: Calculate the time required to machine a 2-in. diameter machine-steel shaft 16 inch to diameter finish size Roughing cut Roughing feed feed =.020 Finishing cut: Finishing feed =.003 Total Time 29.1 min