Machining Operations Part 1: Chapters 21, 22
Manufacturing Processes, 1311 Dr Simin Nasseri Southern Polytechnic State University
Material Removal Processes
A family of shaping operations, the common feature of which is removal of material from a starting workpart so the remaining part has the desired geometry. Material Removal Machining – material removal by a sharp cutting tool, e.g., turning, milling, drilling. Abrasive processes – material removal by hard, abrasive particles, e.g., grinding. Nontraditional processes - various energy forms other than sharp cutting tool to remove material, e.g. electrochemical and thermal energy processes.
Reasons to Machine Variety of work materials can be machined.
Most frequently used to cut metals. Variety of part shapes and special geometric features possible, Screw threads. Accurate round holes. Very straight edges and surfaces. Improve dimensional accuracy of: Castings, forming, or shaping processes. Produce features that cannot be produced by forming and shaping processes. External and internal profiles. Sharp corners. Flatness. Remove distortion & discoloration from heat-treatment. Reduce manufacturing costs (usually small quantities). Apply special surface characteristics or textures.
Wasteful of material Chips generated in machining are wasted material, at least in the unit operation Time consuming A machining operation generally takes more time to shape a given part than alternative shaping processes, such as casting, powder metallurgy, or forming More expensive for mass production. Consumes more energy. Can have adverse effects on surface quality & properties.
Classification of Machined Parts
Rotational - cylindrical or disk‑like shape Nonrotational (also called prismatic) - block‑like or plate‑like Figure Machined parts are classified as: (a) rotational, or (b) nonrotational, shown here by block and flat parts.
Or combination of the two.
Machining Operations and Part Geometry Each machining operation produces a characteristic part geometry due to two factors: 1- Relative motions between tool and workpart Generating – part geometry determined by feed trajectory of cutting tool 2- Shape of the cutting tool Forming – part geometry is created by the shape of the cutting tool Or combination of the two.
Part geometry determined by feed trajectory of cutting tool.
Generating Shape Part geometry determined by feed trajectory of cutting tool. Figure Generating shape: (a) straight turning, (b) taper turning, (c) contour turning, (d) plain milling, (e) profile milling.
Forming to Create Shape
Part geometry is created by the shape of the cutting tool. Figure Forming to create shape: (a) form turning, (b) drilling, and (c) broaching.
Forming and Generating
Part geometry determined by feed trajectory of cutting tool and is also created by the shape of the cutting tool. Figure Combination of forming and generating to create shape: (a) thread cutting on a lathe, and (b) slot milling.
Machining Processes Planing Traditional Chip Removal
Nontraditional Machining Ultrasonic Electrical Discharge Electro-arc Optical Lasers Electrochemical Chem-milling Abrasive Jet Cutting Electron Beam Machining Plasma Arc Machining Turning Milling Drilling Boring Reaming Shaping Sawing Broaching Planing Grinding Honing Lapping In the following slides, guess the machining processes based on the information given!
Figure 21.3 Three most common machining processes: (a) turning,
Single point cutting tool removes material from a rotating workpiece to form a cylindrical shape
Figure 21.3 (b) drilling, Drilling Used to create a round hole, usually by means of a rotating tool with two cutting edges
Two forms: peripheral milling and face milling
Figure (c) peripheral milling (Axis of the tool is parallel to the surface), and (d) face milling (axis of the tool is perpendicular to the surface). Milling Two forms: peripheral milling and face milling Rotating multiple-cutting-edge tool is moved across work to cut a plane or straight surface
Broaching Broaching operation. The tool is called a broach. The machine is called the broaching machine. This process is performed using a multiple tooth cutting tool. The tool is moved linearly relative to the work.
Figure 22.14 Machining operations related to drilling: (a) reaming
Used to slightly enlarge a hole, provide better tolerance on diameter, and improve surface finish.
Boring Internal turning operation which is performed on the inside diameter of an existing hole (Turning is performed on the outside diameter of an existing cylinder) Boring! Figure A vertical boring mill – for large, heavy workparts.
Counterboring Provides a stepped hole, in which a larger diameter follows smaller diameter partially into the hole. Figure Counterboring
Compare! Reaming Counterboring Boring
Tapping Used to provide internal screw threads on an existing hole
Figure (b) tapping. Tool is called a tap Tapping Used to provide internal screw threads on an existing hole
Tool is called a saw blade
Sawing Cuts narrow slit in work by a tool consisting of a series of narrowly spaced teeth. Typical functions: Separate a workpart into two pieces. Cut off unwanted portions of part. Sawing Tool is called a saw blade
Shaping & Planing Shaping: Planing:
Tool has a linear speed motion. Work has occasional feed motion. Planing: Work has a linear speed motion. Tool has occasional feed motion. Figure (a) Shaping (, and (b) planing.
Machinery In the following slides, guess the name of each machine based on the machining operation!
Figure 22.7 Diagram of an engine lathe, showing its principal components.
Vertical Boring Mill Boring:
Figure A vertical boring mill – for large, heavy workparts. Vertical Boring Mill Boring:
Drill Press Drilling: Upright drill press stands on the floor
Figure Upright drill press Drill Press Drilling: Upright drill press stands on the floor Bench drill similar but smaller and mounted on a table or bench
Radial Drill Drilling: Large drill press designed for large parts.
Figure Radial drill press (photo courtesy of Willis Machinery and Tools). Radial Drill Drilling: Large drill press designed for large parts.
Horizontal Milling Machine
Figure (a) Horizontal knee-and-column milling machine. Horizontal Milling Machine Milling: Axis of the tool is parallel to the surface of the part.
Vertical Milling Machine
Figure (b) Vertical knee‑and‑column milling machine Vertical Milling Machine Milling: Axis of the tool is perpendicular to the surface of the part.
Figure 22.30 Components of a shaper.
Shaping: The shaping machine is used to machine flat metal surfaces especially where a large amount of metal has to be removed. Other machines such as milling machines are much more expensive and are more suited to removing smaller amounts of metal, very accurately. As the disc rotates, the top of the machine moves forwards and backwards (reciprocating motion), pushing a cutting tool. The cutting tool removes the metal from work which is carefully bolted down.
Figure 22.31 Open side planer.
Shaping and Planing Two operations which are similar.
Both use a single point cutting tool moved linearly relative to the workpart. A straight, flat surface is created in both operations Interrupted cutting Subjects tool to impact loading when entering work Low cutting speeds due to start‑and‑stop motion Typical tooling: single point high speed steel tools Figure (a) Shaping (, and (b) planing.
Figure 22.35 (a) Power hacksaw
Sawing: Linear reciprocating motion of hacksaw blade against work.
Figure 22.35 (b) Bandsaw (vertical)
Sawing: Linear continuous motion of bandsaw blade, which is in the form of an endless flexible loop with teeth on one edge.
Figure 22.35 (c) Circular saw
Sawing: Rotating saw blade provides continuous motion of tool past workpart.
CNC 4‑axis turning center
Figure CNC 4‑axis turning center (photo courtesy of Cincinnati Milacron); CNC 4‑axis turning center Capable of turning and related operations, contour turning, and automatic tool indexing, all under computer control.
© 2023 SlidePlayer.com Inc.
All rights reserved.