workholding principles // workholding...
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MFG 316 Chapter 4 //Workholding Principles
�All devices that grip, hold, chuck,
or retain a workpiece in order to perform a manufacturing
operation.
�Force=hydraulic, pneumatic, electrical, mechanical
�Force multiplication by levers-
H=a/bxF
Workholding Principles
MFG 316 Chapter 4 //Workholding Principles
�Chuck-used during turning, boring, drilling, grinding...
�Vise-simplest workholder, with special jaws, special capabilities, varied methods of actuation
MFG 316 Chapter 4 //Workholding Principles
�Position or locate-definite relationship to the cutting tool
�Must withstand cutting forces and maintain location
�Workholder elements
⌧Locating element-position workpiece
⌧Structure/tool body-withstands forces
⌧brackets-attach workholder to machine
⌧Clamps, screws, jaws-apply holding force to workpiece
�All functions must have
⌧Required firmness of holding
⌧Accuracy of positioning
⌧Safety for operator and equipment
Purpose and function of workholders
MFG 316 Chapter 4 //Workholding Principles
�Physical characteristics
�Support against cutting
force
�Location of workpiece
�Strength of workholder
�Production requirements
�Safety Requirements
�Foolproofing
�Standard parts
�Repeatable location of
workpiece
�Required strength
�Flat-flange, step, face
�Cylindrical-holes, curved
�Irregular-all else
General Considerations Locating Principles
Workpiece Surfaces
MFG 316 Chapter 4 //Workholding Principles
� Plane-wrt a particular plane
� Concentric-wrt internal or external diameter
� Radial-supplemental to concentric
� Combined
Types of Location
MFG 316 Chapter 4 //Workholding Principles
�Degrees of Freedom
�Movement in plane, along major axes with the addition of roll,
pitch, yaw (12deg)
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MFG 316 Chapter 4 //Workholding Principles
3-2-1 Method�Base plane (3 points)�Secondary plane (2 points)�Tertiary plane (1 point)�3 degrees remain-for loading
and unloading
MFG 316 Chapter 4 //Workholding Principles
�Simplest fixture
�restrains 9 degrees
�added radial restrains 11
degrees
Concentric and Radial
MFG 316 Chapter 4 //Workholding Principles
� Position and number of Locators
� Redundant Locators
� Locational Tolerances
� Foolproofing
Basic Locating Rules
MFG 316 Chapter 4 //Workholding Principles
�External Locators
�Integral Locators
�Assembled Locators
�V Locators
�Adjustable Supports
Basic Types of Locators
MFG 316 Chapter 4 //Workholding Principles
�Locators
�Commercial Pin Locators
�Relieved Locators
�Conical , self adjusting
�Spring Locators, stop buttons
�Locating Pins
MFG 316 Chapter 4 //Workholding Principles
�Locating Nests
�Adjustable Locators
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MFG 316 Chapter 4 //Workholding Principles
�Cause wear and disturb proper location
⌧Make locators easy to clean
• raised above surface
⌧Make locators self-cleaning
• edges or projections to wipe part
⌧Protect locators
• entirely covered by workpiece
⌧Air blast, suction, gravity slides used to remove chips
�Burrs can cause jamming in the fixture
⌧Minor burr at entry to part
⌧Major burr at exit from part
Chip and Burr Problems
MFG 316 Chapter 4 //Workholding Principles
MFG 316 Chapter 4 //Workholding Principles MFG 316 Chapter 4 //Workholding Principles
� Clamps matched to the operation-simple best
� Purpose to exert force to hold part against locators and resist machining forces
�Simple clamps preferred
�Proper clamp for job
�Rough parts may require longer travel or digging in of clamp
�Clamp type determined by operation performed
�Clamps should not obstruct load and unload or cause problems
�Clamps that move or slip should not be used in production
�Clamps should be selected by frequency of setup
Clamping Principles
MFG 316 Chapter 4 //Workholding Principles
�Clamping and location for
drilling
⌧Must resist torque and pull-out force
Tool Forces
MFG 316 Chapter 4 //Workholding Principles
�Clamping and location for
tapping
⌧Must resist torque and pull-out forces
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MFG 316 Chapter 4 //Workholding Principles
�Clamping and location for broaching
⌧Cutting tool works with cutting force
MFG 316 Chapter 4 //Workholding Principles
�Clamping and location for milling
⌧Use of fixed jaw to resist cutting force
⌧Use of friction to resist cutting force
MFG 316 Chapter 4 //Workholding Principles
� Clamps hold against a locator
� Mechanical methods to multiply force
� Must counteract tool force
� Must be consistent with material
� Must be appropriate to operation
� Directed parallel to the operation
Clamping Forces
MFG 316 Chapter 4 //Workholding Principles
�Positioning clamps
�Must not distort part
�Contact part at most rigid point
�Clamp over a locator
�Use secondary supports when required
MFG 316 Chapter 4 //Workholding Principles
�Rigid vs. Elastic
�Strap Clamps
�Screw Clamps
�Cam Clamps
�Toggle Clamps
�Wedge Action Clamps
�Specialty Clamps
Types of Clamps
MFG 316 Chapter 4 //Workholding Principles
Chucks and Vises
�Chucking
Operations
⌧External/External
⌧Endwise/Centers
⌧Combination
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MFG 316 Chapter 4 //Workholding Principles
Chucks and Vises
�Chucking Nomenclature
⌧Arbor and Mandrel
�Lathe Chucks
�Solid Arbor and Mandrel
�Straight Mandrel
�Collets
MFG 316 Chapter 4 //Workholding Principles
�Vises
⌧Special Vise Jaws
⌧Independent Jaws
MFG 316 Chapter 4 //Workholding Principles
�Magnetic Chucks
�Vacuum Chucks
�Electrostatic Chucks
�Power Clamping
�Multiple Part Clamping
Nonmechanical Clamping
MFG 316 Chapter 4 //Workholding Principles
�Tool Bodies
�Cast Tool Bodies
�Welded Tool Bodies
�Built-up Tool Bodies
MFG 316 Chapter 4 //Workholding Principles
�Tooling Materials
�Precision Ground Material
�Aluminum Tooling Plate
�Precast Brackets/Shapes
�Structural Sections
⌧C-channel best
MFG 316 Chapter 4 //Workholding Principles
�Screws and Bolts
�Nuts, Washers, Inserts
�Dowels and Pins
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