MET 33800 Manufacturing Processes Chapter 27 Workholding Devices for Machine Tools Before you begin: Turn on the sound on your computer. There is audio to accompany this presentation. Chapter 27-1 Workholding Devices Introduction Workholding device locates work in machine tool with respect to the cutting tool. Critical for repeatability. Trend toward flexibility: family of parts and manufacturing cells. Primary functions: Locating Clamping Chapter 27-2 INTRODUCTION Fixture Specialized workholding device that holds workpiece during machining or assembly operations and establishes size dimensions. Jig A special type of fixture that, through built-in features, determines both location and size dimensions that are produced by machining or fastening operations. Chapter 27-3 1
INTRODUCTION Fixture size Jig location and size Chapter 27-4 FIXTURE DESIGN Chapter 27-5 FIXTURE DESIGN Chapter 27-6 2
FIXTURE DESIGN 1. Locating function is to orient and position workpiece in the machine tool: Provides positive location for the 12 degrees of location freedom: o o Linear: X, Y, Z Rotational: A, B, C Location by 3 2 1 principle Chapter 27-7 3-2-1 FIXTURE DESIGN 3 Points 2Points 1 Points Chapter 27-8 FIXTURE DESIGN 1. Locating (continued): Repeatability: fool proofing. Low profile: clear cutting path. Chapter 27-9 3
FIXTURE DESIGN 1. Locating (continued): Cutting forces: press part into locators. Accommodation: allowing workpiece variance. Chapter 27-10 FIXTURE DESIGN Chapter 27-11 FIXTURE DESIGN 2. Clamping Function to hold and/or maintain location: Adequate: balance strength & deflection. Reliability: repeatable clamping forces. Clamping forces: toward locators. Loading/Unloading time: dependent on clamp type. Chapter 27-12 4
FIXTURE DESIGN 3. Other Design Factors: Chip disposal and removal: heat and interference concerns. Ruggedness Construction ease Ergonomics and safety Flexibility Chapter 27-13 JIG DESIGN 4. Additional Jig Functions: Location - position geometric shapes with respect to each other. Size - size of geometric shapes. Dimension control. Examples: Drill jig Welding jig. Chapter 27-14 JIG DESIGN Drill Bushings: Press Fit Slip Fit Chapter 27-15 5
TYPES of JIGS Plate jig - plate w/drill bushings and locating pins, clamped to part. Channel jig - part in open side, locate on outside of part. Ring jig - for end/surface of round parts. Diameter jig - for cylindrical surfaces. Leaf jig - hinged leaf or cover. Box jig - boxlike construction, tumble. Assembly jig - welding or riveting, open frame typically. Chapter 27-16 TYPES of JIGS Chapter 27-17 TYPES of JIGS Chapter 27-18 6
TYPES of FIXTURES Fixtures categories include: Vises Lathe chucks and collets Faceplate fixtures Milling and grinding fixtures Modular fixtures Chapter 27-19 TYPES of FIXTURES Chapter 27-20 TYPES of FIXTURES Chapter 27-21 7
TYPES of FIXTURES Chapter 27-22 TYPES of FIXTURES Example of a Lathe Faceplate Fixture Chapter 27-23 TYPES of FIXTURES Example of Multiple Parts on Single Fixture Chapter 27-24 8
MODULAR FIXTURES Modular fixtures provide versatility and adaptable to different workpieces. Chapter 27-25 MODULAR FIXTURES Chapter 27-26 MODULAR FIXTURES Chapter 27-27 9
MODULAR FIXTURES Chapter 27-28 MODULAR FIXTURES Chapter 27-29 ASSEMBLY FIXTURES Chapter 27-30 10
MASTER (GROUP) FIXTURES Used for part families: Group Technology (GT) concept. Chapter 27-31 MASTER (GROUP) FIXTURES Chapter 27-32 CLAMPING Chapter 27-33 11
CLAMPING Chapter 27-34 CLAMPING Fixture types which used other clamping methods: Magnetic chucks - ferromagnetic materials only. Electrostatic chucks - conductive materials only. Vacuum chucks. Chapter 27-35 CLAMPING Chapter 27-36 12
CLAMPING Permanent- Magnetic Chucks Chapter 27-37 CLAMPING Electro-Magnetic Chucks Chapter 27-38 CLAMPING Chapter 27-39 13
ECONOMICS of FIXTURES Chapter 27-40 ECONOMICS of FIXTURES Chapter 27-41 FIXTURING EXAMPLE Chapter 27-42 14
FIXTURING EXAMPLE Chapter 27-43 The End See Oncourse for Videos Chapter 27-44 15