Machining Process

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