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Questions and Answers
What is the primary motion in turning?
What is the primary motion in turning?
What is the purpose of chip breakers?
What is the purpose of chip breakers?
What is the type of chip formed during high-speed cutting of ductile materials?
What is the type of chip formed during high-speed cutting of ductile materials?
What is the machine used in turning?
What is the machine used in turning?
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What is the term for the distance the tool moves per spindle revolution?
What is the term for the distance the tool moves per spindle revolution?
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What is the process of removing unwanted material from a workpiece called?
What is the process of removing unwanted material from a workpiece called?
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What is the type of machining process that uses a rotating cutter to remove material?
What is the type of machining process that uses a rotating cutter to remove material?
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What is the term for the velocity of the cutting tool relative to the workpiece?
What is the term for the velocity of the cutting tool relative to the workpiece?
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What is the main purpose of workholding devices in machine tools?
What is the main purpose of workholding devices in machine tools?
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What does the location dimension determine in a workpiece?
What does the location dimension determine in a workpiece?
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What is the primary function of a jig?
What is the primary function of a jig?
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What is the first step in designing a workholding device?
What is the first step in designing a workholding device?
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What is the purpose of clamping in a workholding device?
What is the purpose of clamping in a workholding device?
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What is the final step in designing a workholding device?
What is the final step in designing a workholding device?
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What is the primary purpose of the 3-2-1 location principle in device placement?
What is the primary purpose of the 3-2-1 location principle in device placement?
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Which of the following is a consideration when designing clamping systems for machining?
Which of the following is a consideration when designing clamping systems for machining?
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What is the primary function of a jig in machining?
What is the primary function of a jig in machining?
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What type of jig is used for drilling rounded parts?
What type of jig is used for drilling rounded parts?
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What is the advantage of using modular fixtures in machining?
What is the advantage of using modular fixtures in machining?
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What is the primary advantage of using vacuum chucks in machining?
What is the primary advantage of using vacuum chucks in machining?
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Study Notes
CHIP REMOVING MACHINING
- Chip removing machining is a process of removing unwanted material from a workpiece, with the removed material referred to as chips.
- This process is versatile and can be applied to various materials such as plastics, metals, wood, composites, and ceramics.
Difficulties in Analyzing Machine Process
- Prior work hardening affects the machining process.
- Different materials behave differently during machining.
- The process is asymmetrical and unconstrained.
- High strain levels and rates are involved.
- The process is sensitive to variations in tool geometry, tool material, temperature, process dynamics (chatter and vibration), and environmental factors (cutting fluids).
Cutting Parameters for Turning
- Speed (v): primary cutting motion, measured in m/s, which is the velocity of the cutting tool relative to the workpiece.
- Feed (fr): axial distance the tool moves per spindle revolution, measured in inches per rev.
- Depth of cut (DOC or d): distance the tool is plunged into the surface.
- MRR (metal removal rate): calculated as Vfrd.
Cutting Tool Motion
- Rake angle (alpha): an important parameter in cutting tool motion.
- Shear angle (phi): another key parameter in cutting tool motion.
- Relief angle (epsilon): a significant parameter in cutting tool motion.
Milling
- Feed per tooth (f) is calculated as v/Nn, where v is velocity, N is rotational speed, and n is the number of teeth.
- Toolpath design involves contour parallel and direction parallel approaches.
- Contour parallel toolpath follows the direction of the shape, while direction parallel involves a zigzag pattern.
Chip Type
- Continuous chips: formed from ductile materials at high speeds, requiring chip breakers.
- Coils: not an ideal chip type.
- Discontinuous chips: formed from brittle materials at very low speeds.
7 Chip Forming Processes
Turning
- Rotating workpiece with a single point cutting tool that removes material.
- Uses a lathe machine.
Milling
- Rotating cutters that remove material as the workpiece is fed into the path of the tool.
Drilling
- Creates holes that are right circular cylinders.
Sawing
- Uses a tool with narrowly spaced teeth to create a narrow slit.
Broaching
- Removes metal using a tool with teeth that increase in size to remove more material.
Shaping v Planing
- Planing: uses a stationary tool, while shaping uses a stationary workpiece.
Grinding
- An abrasive machining process that uses a grinding wheel.
Workholding Devices for Machine Tools
- Ensure accuracy and precision in repeated manufacturing, have become more flexible, can hold more than one part, and can be changed rapidly.
Functions of Workholding Devices
- Locating: orients and positions part relative to cutting tool
- Clamping: holds the part in place
Dimensions
- Size Dimension: denotes geometrical shapes
- Location Dimension: determines position or location
Jigs vs. Fixtures
- Jig: specialized, determines location dimensions, guides tools and holds the workpiece
- Fixture: specialized, establishes size dimensions, holds the workpiece
Design Steps
- Plan the Machining: analyze the drawing, visualize machining steps, note key dimensions and tolerances
- Set Up: decide workpiece position relative to tools and table movements
- Force Analysis: estimate cutting force strength and direction
- Workholding: choose or modify standard clamps and workholders for the job
- Mental Picture: imagine workpiece secure in the machine, tools performing operations
- Detailed Sketch: draw the workpiece in the workholder with clamps, locators, etc.
- Machine Tool Sketch: sketch the workholder and workpiece in the machine relative to the tool
3-2-1 Location Principle
- Ensures that every part placed in the device occupies the same position
- Locate part on three fixed points on a plane
- Locate part on a second, perpendicular to the first, plane using two points
- Add another plane perpendicular to the first two, secure with single point
Clamping Considerations
- Clamping Forces: induce stresses, can cause some distortion, should be aligned with cutting forces
- Chip Disposal: jigs, fixtures need to accommodate chip removal, clearance needed for easy removal
Types of Jigs
- Plate Jigs: simplest
- Channel Jigs: for simple shaped parts
- Ring Jigs: for drilling rounded parts
- Leaf Jigs:
- Box Jigs:
- Universal Jigs:
- Master Jig: can be used to make a number of similar parts
- Intermediate Jig: jig that holds another jig for easy changing
Conventional Fixtures
- Vise: most common, general purpose, interchangeable jaws
- Chucks: general purpose fixtures for rotational parts, 3 jaw jacob, self-centering, collet, quick change
- Modular Fixture: more versatile, dowel points and t slots
- Increase Speed: master jig can be used to make a number of similar parts
Other Workholding Devices
- Assembly Jig: for final assembly
- Magnetic Workholders: no distortion, limited force
- Electrostatic Workholders: for non-ferromagnetic materials, similar to magnetic
- Vacuum Chucks: any material, initial set up hard
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Description
Learn about the chip removing machining process, its versatility, and the challenges faced in analyzing machine processes, including work hardening and material behavior.
