Material Removal Processes PDF

Company LOGO www.company.com 1/100  Company LOGO Material Removal Processes Machining is a manufacturing process in which a sharp cutting tool is used to cut away material to leave the desired part shape. The p...

Company LOGO www.company.com 1/100  Company LOGO Material Removal Processes Machining is a manufacturing process in which a sharp cutting tool is used to cut away material to leave the desired part shape. The predominant cutting action in machining involves shear deformation of the work material to form a chip. As the chip is removed, a new surface is exposed. Machining is most frequently applied to shape metals. Click here to watch a video regarding the machining. Click here to watch a video regarding the shear deformation. www.company.com 3/100 Company LOGO Material Removal Processes Machining is important commercially and technologically for several reasons. These are: 1- Variety of work materials. Machining can be applied to most of work materials. Virtually all solid metals can be machined. Plastics and plastic composites can also be cut by machining. Ceramics pose difficulties because of their high hardness and brittleness; however, most ceramics can be successfully cut by the abrasive machining processes www.company.com 3/100 Company LOGO Material Removal Processes 2- Variety of part shapes and geometric features. Machining can be used to create any regular geometries, such as flat planes, round holes, and cylinders. By introducing variations in tool shapes and tool paths, irregular geometries can be created, such as screw threads and T-slots. By combining several machining operations in sequence, shapes of almost unlimited complexity and variety can be produced. www.company.com 3/100 Company LOGO Material Removal Processes 3- Dimensional accuracy. Machining can produce dimensions to very close tolerances. Some machining processes can achieve tolerances of ±0.025 mm, much more accurate than most other processes. 4- Good surface finishes. Machining is capable of creating very smooth surface finishes. Roughness values less than 0.4 microns can be achieved in conventional machining operations. Some abrasive processes can achieve even better finishes. www.company.com 3/100 Company LOGO Material Removal Processes Certain disadvantages are associated with machining and other material removal processes. These are: 1- Wasteful of material. Machining is inherently wasteful of material. The chips generated in a machining operation are wasted material. Although these chips can usually be recycled, they represent waste in terms of the unit operation. 2- Time consuming. A machining operation generally takes more time to shape a given part than alternative shaping processes such as casting or forging. www.company.com 3/100 Company LOGO Material Removal Processes Machining is generally performed after other manufacturing processes such as casting or bulk deformation. The other processes create the general shape of the starting work part, and machining provides the final geometry, dimensions, and finish. Machining is a group of processes. The common feature is the use of a cutting tool to form a chip that is removed from the work part. To perform the operation, relative motion is required between the tool and work material. This relative motion is achieved in most machining operations by means of a primary motion, called the cutting speed (V), and a secondary motion, called the feed (F). The shape of the tool and its penetration into the work surface, combined with these motions, produces the desired geometry of the resulting work surface. www.company.com 3/100 Company LOGO Types of Machining Operations There are many kinds of machining operations. Each of them is capable of generating a certain part geometry and surface texture. It is appropriate to identify and define the three most common types: turning, drilling, and milling. www.company.com 3/100 Company LOGO Types of Machining Operations In turning, a cutting tool with a single cutting edge is used to remove material from a rotating workpiece to generate a cylindrical shape. The speed motion in turning is provided by the rotating work part, and the feed motion is achieved by the cutting tool moving slowly in a direction parallel to the axis of rotation of the workpiece. Click here to watch a video regarding the turning. www.company.com 3/100 Company LOGO Types of Machining Operations Drilling is used to create a round hole. It is accomplished by a rotating tool that typically has two cutting edges. The tool is fed in a direction parallel to its axis of rotation into the work part to form the round hole. Click here to watch a video regarding the drilling. www.company.com 3/100 Company LOGO Types of Machining Operations In milling, a rotating tool with multiple cutting edges is Face milling fed slowly across the work material to generate a plane or straight surface. The direction of the feed motion is perpendicular to the tool’s axis of rotation. The speed motion is provided by the rotating milling cutter. The two basic forms of milling are peripheral milling Peripheral milling and face milling. Click here to watch a video regarding the milling. www.company.com 3/100 Company LOGO The Cutting Tool A cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate a chip from the parent work material. Connected to the cutting edge are two surfaces of the tool: the rake face and the flank. The rake face, which directs the flow of the newly formed chip, is oriented at a certain angle called the rake angle α. The rake angle is measured relative to a plane perpendicular to the work surface. www.company.com 3/100 Company LOGO The Cutting Tool The rake angle can be positive or negative. Positive rake angle Negative rake angle www.company.com 3/100 Company LOGO The Cutting Tool The flank of the tool provides a clearance between the tool and the newly generated work surface. The flank face protects the surface from abrasion, which would degrade the finish. This flank surface is oriented at an angle called the relief angle. Click here to watch a video regarding the cutting tool geometry. www.company.com 3/100 Company LOGO The Cutting Tool There are two basic types of the cutting tools. These are single-point tools and multiple-cutting-edge tools. Single-point tool Multiple-cutting-edge tool www.company.com 3/100 Company LOGO The Cutting Tool A single-point tool has one cutting edge and is used for operations such as turning. There is one tool point in the single point cutting tools. During machining, the point of the tool penetrates below the original work surface of the part. The point is usually rounded to a certain radius, called the nose radius. Multiple-cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the work part by rotating. Although the shape is quite different from a single-point tool, many elements of tool geometry are similar. Click here to watch a video regarding the single-point and multiple-cutting-edge tools. www.company.com 3/100 Company LOGO Cutting Conditions Relative motion is required between the tool and work material to perform a machining operation. The primary motion is accomplished at a certain cutting speed v. Cutting speed is defined as the speed at which the work moves with respect to the tool (usually measured in meter per minute). The tool must be moved laterally across the work. This is a much slower motion, called the feed f. Feed is defined as the distance the tool travels during one revolution of the part. The depth of cut is the penetration of the cutting tool below the original work surface. www.company.com 3/100 Company LOGO Cutting Conditions The speed, feed, and depth of cut are called the cutting conditions. The cutting conditions form the three dimensions of the machining process, and for certain operations and they can be used to calculate the material removal rate for the process. Material removal rate is the volume of material removed per minute. Cutting speed in mm/min Feed in mm/rev Material removal rate in mm3/min Depth of cut in mm www.company.com 3/100 Company LOGO Cutting Conditions Typical units used for cutting speed are mm/min. Feed in turning is expressed in mm/rev. Depth of cut is expressed in mm. In other machining operations, the cutting conditions may differ. For example, in a drilling operation, depth is interpreted as the depth of the drilled hole. www.company.com 3/100 Company LOGO Cutting Conditions Machining operations usually divide into two categories, distinguished by purpose and cutting conditions. These are roughing cuts and finishing cuts. Roughing cuts are used to remove large amounts of material from the starting work part as rapidly as possible. In order to produce a shape close to the desired form but leaving some material on the piece for a subsequent finishing operation. Roughing operations are performed at high feeds and depths—feeds of 0.4–1.25 mm/rev and depths of 2.5–20 mm are typical. Click here to watch a video regarding the roughing cuts. www.company.com 3/100 Company LOGO Cutting Conditions Finishing cuts are used to complete the part and achieve the final dimensions, tolerances, and surface finish. In production machining jobs, one or more roughing cuts are usually performed on the work, followed by one or two finishing cuts. Finishing operations are carried out at low feeds and depths—feeds of 0.125–0.4 mm and depths of 0.75–2.0 mm are typical. Cutting speeds are lower in roughing than in finishing. Click here to watch a video regarding the finishing cuts. www.company.com 3/100 Company LOGO Cutting Conditions A cutting fluid is often applied to the machining operation to cool and lubricate the cutting tool. Determining whether a cutting fluid should be used, and, if so, choosing the proper cutting fluid, is usually included within the scope of cutting conditions. Given the work material and tooling, the selection of these conditions is very influential in determining the success of a machining operation. Click here to watch a video regarding the cutting fluids. www.company.com 3/100 Company LOGO Machine Tools Conventional machine tools are usually tended by a human operator, who loads and unloads the work parts, changes cutting tools, and sets the cutting conditions. Many modern machine tools are designed to accomplish their operations with a form of automation called computer numerical control. A machine tool is used to hold the work part, position the tool relative to the work, and provide power for the machining process at the speed, feed, and depth that have been set. www.company.com 3/100 Company LOGO Machining and Part Geometry Machined parts can be classified as rotational or non-rotational (prismatic). A rotational work part has a cylindrical or disk-like shape. The characteristic operation that produces this geometry is one in which a cutting tool removes material from a rotating work part. Examples include turning and boring. A non-rotational (prismatic) work part is block-like or plate-like. This geometry is achieved by linear motions of the work part, combined with rotating or linear tool motions. Operations in this category include milling, shaping, planing, and sawing. Prismatic parts Rotational part www.company.com 3/100 Company LOGO Cutting Conditions in Turning The rotational speed in turning is related to the desired cutting speed at the surface of the cylindrical workpiece by the equation; Cutting speed in mm/min Rotational speed in rev/min Original diameter of the part in mm www.company.com 3/100 Company LOGO Cutting Conditions in Turning The turning operation reduces the diameter of the work from its original diameter (Do) to a final diameter (Df), as determined by the depth of cut (d): Final diameter Original diameter Depth of cut www.company.com 3/100 Company LOGO Cutting Conditions in Turning The feed in turning is generally expressed in mm/rev. This feed can be converted to a linear travel rate in mm/min by the formula Feed rate in mm/min Spindle speed in rev/min Feed in mm/rev www.company.com 3/100 Company LOGO Cutting Conditions in Turning The time to machine from one end of a cylindrical work part to the other is given by Length of the cylindrical workpart in mm Machining time in min Feed rate in mm/min www.company.com 3/100 Company LOGO Cutting Conditions in Turning A more direct computation of the machining time is provided by the following equation: Workpart diameter in mm Machining time in min Workpart length in mm Feed in mm/rev Cutting speed in mm/min *** As a practical matter, a small distance is usually added to the work part length at the beginning and end of the piece to allow for approach and overtravel of the tool. Thus, the duration of the feed motion past the work will be longer than Tm. www.company.com 3/100 Company LOGO Cutting Conditions in Turning The volumetric rate of material removal can be most conveniently determined by the following equation: Material removal rate in mm3/min Depth of cut Cutting speed in mm/min Feed in mm/rev www.company.com 3/100 Company LOGO Operations Related to Turning A variety of other machining operations can be performed on a lathe in addition to turning. Click here to watch a video regarding the operations related to turning. www.company.com 3/100 Company LOGO Operations Related to Turning Facing. The tool is fed radially into the rotating work on one end to create a flat surface on the end. Click here to watch a video regarding the facing. Taper turning. Instead of feeding the tool parallel to the axis of rotation of the work, the tool is fed at an angle, thus creating a tapered cylinder or conical shape. Click here to watch a video regarding the taper turning. www.company.com 3/100 Company LOGO Operations Related to Turning Contour turning. Instead of feeding the tool along a straight line parallel to the axis of rotation as in turning, the tool follows a contour that is other than straight, thus creating a contoured form in the turned part. Click here to watch a video regarding the contour turning. Form turning. In this operation, the tool has a shape that is imparted to the work by plunging the tool radially into the work. Form turning is performed with a specially designed tool called a form tool. Click here to watch a video regarding the form turning. www.company.com 3/100 Company LOGO Operations Related to Turning Chamfering. The cutting edge of the tool is used to cut an angle on the corner of the cylinder, forming a “chamfer.” Click here to watch a video regarding the chamfering. Cutoff. The tool is fed radially into the rotating work at some location along its length to cut off the end of the part. This operation is sometimes referred to as parting. Click here to watch a video regarding the cutoff. www.company.com 3/100 Company LOGO Operations Related to Turning Threading. A pointed tool is fed linearly across the outside surface of the rotating work part in a direction parallel to the axis of rotation at a large effective feed rate, thus creating threads in the cylinder. A threading operation is accomplished using a single- point tool designed with a geometry that shapes the thread. Click here to watch a video regarding the threading. Boring. A single-point tool is fed linearly, parallel to the axis of rotation, on the inside diameter of an existing hole in the part. Click here to watch a video regarding the boring. www.company.com 3/100 Company LOGO Operations Related to Turning Drilling can be performed on a lathe by feeding the drill into the rotating work along its axis. Drilling is accomplished by a drill bit. Click here to watch a video regarding the drilling Reaming is used to slightly enlarge a hole, to provide a better tolerance on its diameter, and to improve its surface finish. Reaming is accomplished by a reamer. Click here to watch a video regarding the reaming www.company.com 3/100 Company LOGO Operations Related to Turning Knurling is not a machining operation because it does not involve cutting of material. Instead, it is a metal forming operation used to produce a regular cross-hatched pattern in the work surface. Knurling is performed by a knurling tool, consisting of two hardened forming rolls, each mounted between centers. The forming rolls have the desired knurling pattern on their surfaces. To perform knurling, the tool is pressed against the rotating work part with sufficient pressure to impress the pattern onto the work surface. Click here to watch a video regarding the knurling www.company.com 3/100 Company LOGO Reference Groover, MP., Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, Wiley, 2014. 55/55 www.company.com 3/100 Company LOGO Thank you for your attention. 55/55 www.company.com 3/100