Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 1
Topic - Tool Design
Lecture
onJigs and Fixtures for Machine Shop
By
Abhishek Tevatia
MAE, MAIT, Delhi
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 2
Topic - Tool Design
This lecture will cover
(i) Definition of Fixture and Jig (that aid machining)
(ii) Conceive the purposes of use of jigs and fixtures
(iii) State the design considerations for jigs and fixtures
(iv) illustrate the methods of
(a)locating
(b)supporting and
(c) clamping of jobs in jigs and fixtures
(d) guidance of cutting tools by bushes in jigs
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 3
Topic - Tool Design
DEFINITIONFixtures Mechanical (strong and
rigid) devices and used (in machine
shop) to enable easy, quick and
consistently accurate locating,
supporting and clamping, blanks
against the tool for higher productivity
and product quality in batch
production
Jig is a fixture having an additional feature of tool guidance.
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 4
Topic - Tool Design
Steps usually followed in machining without fixture
Marking & Punching Mount and fix the blank on the
machine bed or in a vise with
proper alignment, support and
clamp
Adjust the tool-work position byshifting job, vice or tool
Initiate machining andcheck/correct tool work
position,
Complete machining Inspect / measure the
machined features
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 5
Topic - Tool Design
BASIC PURPOSES OF USING JIGS & FIXTURES
To eliminate tedious marking, punching, mounting trial - basepositioning and repeated checking
Easy, quick and consistently accurate locating, mountingand clamping blank against the tool
Guidance of cutting tool (drill, reamer etc)
To raise productivity and maintain quality consistently
To reduce operators labour and skill requirement
To attain close tolerances and interchangeability
To reduce rejection and overall cost
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 6
Topic - Tool Design
Economic application of jigs and fixtures
Mode of machining
in ordinary machine without fixtures
in ordinary machines using jigs and fixtures
In automatic machine without or with special
fixturing
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 7
Topic - Tool Design
DESIGN OF JIGS & FIXTURE
Salient elements to be designed Base and body Locating elements/ system Supporting system Clamping system/ elements Tool guides framing & bushing Indexing system, if needed Auxiliary elements (fasteners etc)
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 8
Topic - Tool Design
Factors essentially considered during design of
jigs and fixtures
Easy, quick & consistently accurate locating Provide strong, rigid and stable supporting Quick , strong and rigid clamping Tool guidance for accuracy and safety Easy, quick and uninterrupted loading and unloading Use of minimum and standard parts Adjustable locating for part size variation Chip removal Simple but accurate indexing, if required Ergonomics and safety Manufacturability Service life and cost
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 9
Topic - Tool Design
DESIGN OF FIXTURE AND JIGS
Major functions requiring proper design
(a)
Locating
Supporting
Clamping of blank
(b) Tool guidance in jigs
There may be several methods of locating etc depending upon
job-shape, size, material
machining requirement
cutting tools-type, size & shape
But some basic rules are followed during design
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 10
Topic - Tool Design
Fundamental requirements for locating,
supporting and clamping
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 11
Topic - Tool Design
Locating Blanks in Jigs or Fixture Design Principles or Rules
o one or more pre machined surface holes are to be used for
reference
o The reference surface or holes should be important features
based on which other dimensions are laid
o Locating should be easy, quick and accurate
o Locating pins should be strong, rigid and hard.
o Locating pin should be wide apart
o V-block and cones are preferable for cylindrical jobs.
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 12
Topic - Tool Design
Design Locating cont
o Sight location for jobs of irregular surfaces
o Pivoted arms may be used for locating and supporting
large jobs
o adjustable pins or screws are to be used to accommodate
the part size variation
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 13
Topic - Tool Design
General methods of locating
Locating work piece for machining in lathes
o By fitting into self centering chuck
o By fitting into collets
o Mounting in between centers
o Fitting in a fixture mounted on faceplate
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 14
Topic - Tool Design
General methods of locating cont..
Locating work piece for machining in other than lathes
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 15
Topic - Tool Design
General methods of locating cont..
Locating by holes
Locating by holes and V-block
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 16
Topic - Tool Design
General methods of locating cont..
Locating by mandrel or plug
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 17
Topic - Tool Design
SUPPORTING PRINCIPALS AND METHOD
Design principals or rules for supporting
o Minimum 3 point contact required to support at flat surface
o Supporting pins or plugs should be strong, rigid and hard
o Unsupported span-should not be much wide
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 18
Topic - Tool Design
SUPPORTING Cont..
o supporting should keep job stable under forces
o Recess to be provided within wide contact area.
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 19
Topic - Tool Design
SUPPORTING Cont..
o cylindrical jobs are to be supported (and located) on V block
o additional (over 3) pins are to be usedto compensate part size variationto support large and heavy jobsto prevent deformation of job by forces
o additional pins should be adjustable
o Mandrel may be used to support land (and locate) ring
type blanks
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 20
Topic - Tool Design
SUPPORTING Cont..
Common methods of supporting
Supporting on vices Supporting at flat surfaces Supporting by fixed pins or plugs
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 21
Topic - Tool Design
SUPPORTING Cont..Common methods of supporting
Extra supporting by additional adjustable pins.
Supporting (& locating) on V-block and mandrels
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 22
Topic - Tool Design
Design for Clamping
Design principles or rules of clamping
Clamping must be strong, rigid and stable
Should be easy, quick and adequate.
Should not hinder loading and unloading work
Clamping force should act against rigid part and not damage the job
Minimum and standard parts are to be used for clamping
Wear parts have to be hard and replaceable
Reliability, safely and low cost.
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 23
Topic - Tool Design
Methods of clamping in fixtures
(a) Ordinary (b) Quick acting
Ordinary (Slow) Methods
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 24
Topic - Tool Design
Ordinary Methods Cont..
Clamping from side for through machine of top surface
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 25
Topic - Tool Design
Ordinary Methods Cont..
Clamping using swing plates
Other common clamping methods
Vice, magnetic chucks, chucks and collets
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 26
Topic - Tool Design
Quick Clamping Method
Quick acting nut
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 27
Topic - Tool Design
Quick Clamping Cont..
Clamping using Cam
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 28
Topic - Tool Design
Quick Clamping Cont..
Multiple clamping of cylindrical jobs
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 29
Topic - Tool Design
Quick Clamping Cont..
Quick acting screw (bayonet type)
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 30
Topic - Tool Design
DRILL JIG BUSHINGPurposes of using bush
To reduce or eliminate runoutTo locate the tool in positionTo prevent buckling and breaking of toolsTo attain and maintain accuracy, safety and economy
Desired characteristics
Material - hard or hardened steel (Rc >= 60)Finishing inside and outside by grindingBushes length >= 2d and diameter d+ (d is drill diameter)Quick fitting, removal and replacementDo not slip unwantedly
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 31
Topic - Tool Design
Types of bushes
According to fittingpress fit
slip type with linerscrew type with/ without liner
According to headwithout head
with head
with flange
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 32
Topic - Tool Design
Types of bushes Cont
Frequently replaceable bushes
Metal Cutting and Tool Design (ETME-310)
Abhishek Tevatia, Mechanical & Automation Engineering Department 33
Topic - Tool Design
Types of bushes Cont
Special types of bushes