Basic Fixture Design Concepts

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TOOL DESIGN
Basics & Concepts
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Contents:
Body in white (BIW)
Closures
Body Coordinate System (BCS), PLP & WP
Locating Principle, 4 way & 2 way pins
Unit, Station, Assembly line
Tools in the Assembly line
Fixtures, Hemming press, EOAT & Conveyors
Machining sequence
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BODY-IN-WHITE (BIW)
It is the automotive body without closure panels and without paint applied. It
consists of approximately 150-250 sheet metal parts.
CLOSURES
Front and Rear Doors, Hood, Deck-lid, Lift gate & Hinge gate.
CAR BODY
UNDER BODY BODY SIDE CLOSURES ROOF FENDER
Engine Compartment Front Doors (L & R)

Central or Front Floor Rear Doors (L & R)
Rear Floor Hood
Deck Lid
Lift Gate
Hinge Gate
Outer Panel
Inner Panel
Quarter Panel
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BODY COORDINATE SYSTEM (Part Locating System)

These datum schemes provide a reference system for all part surfaces and
features using body coordinates. Figure below illustrates a typical body
coordinate system. This system replaces the traditional X, Y, and Z directional
designations with fore/aft (X), in/out (Y), and up/down or high/low (Z). The 0,0,0
point of the car is the front, lower, and center position.
VEHICLE ORIENTATION
All vehicle product drawings are identified numerically relative to three vehicle
planes described and shown below.
1. Front “O” Line (FOL), “X”, Length (L)
2. Centerline of Body (C), “Y”, Width (W)
3. Bottom “O” Line (BOL), “Z”, Height (H)
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PLP & WP
PLP - Principle Locating Points are the spots over the panel having small area where
the product can be clamped. This information will be supplied along with the product.
WP - Weld Points are the spots over the panel where the product can be welded to
assemble two or more panels. This information will be supplied along with the product.
LOCATING PRINCIPLE
3-2-1 locating principle:
Holding fixtures used in assembly operations often follow a 3-2-1 locating
scheme to position parts. Under this scheme, three locators position a part in a
primary plane or direction (e.g., high/low). Two locators then position the part in a
secondary direction (e.g., in/out), leaving one locator for the tertiary direction
(e.g., fore/aft). This approach fixes the part in 3-dimensional space and satisfies
the six degrees of freedom constraint.
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So, the six-point locating principle is: the 6 DOFs of a work piece in a fixture
can be constrained by reasonably distributed 6 points, everyone of which
can constrain one DOF. For the primary locating datum, the area of the triangle
formed by the three locating points should be as large as possible. For the
secondary locating datum, the distance between the two locating points is as
large as possible, and the line segment connecting the two locating points should
be parallel to the primary locating datum if possible.
3-2-1 principle using the hole/slot combination:

For some product designs, manufacturers replace the three locators for the
secondary and tertiary directions using two round pins, one fitting a circular hole
and the other a slot. The pin locates the part in two directions (e.g., in/out and
fore/aft). The slot then becomes the other locator for the secondary direction
(e.g., in/out).
The lack of rigidity for many stamped components and metal assemblies,
however, often forces manufacturers to violate the 3-2-1 locating scheme and
use additional locators to position parts in a stable and repeatable manner. As a
result, the locating scheme for sheet metal is sometimes referred to as n-2-1.
The n denotes the three or more locators needed to position a parting a primary
plane. The number of additional constraints may vary greatly between
manufacturers.
The fixture design can be categorized into two groups:
Rigid parts like engines use 3-2-1 fixture design methodologies and compliant
sheet metal parts use n-2-1 fixture design methodologies for functional
configuration of fixtures.
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Four functional requirements for holding workpieces:

1. Locating stability – position and orientation
2. Deterministic workpiece location
3. Clamping stability – securing the workpiece under forces
4. Total restraint.
UNIT, TOOL, STATION & ASSEMBLY LINE

A unit, which may has NC block, Pressure foot, Locating pin, Shim sets, Blade,
Power clamp, Air cylinder, Riser, Rough locator, Weld gun, Frame etc. to hold or
clamp or locate or weld the product at the specified location.
Ex. Clamping unit, Locator unit, Locating pin unit, Weld gun unit, Base
A typical unit is shown below.
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A Tool may comprise a single or more units where the product will be placed
for holding or clamping or locating in order to perform operations like welding
or clinching or just to rest.
It is classified into unitized and Non-unitized tool
Unitized tool: Station having two or more units called unitized tool.
Ex. Geo fixture, Marriage fixture,
Non-unitized tool: Station, which cannot be split into units called non-unitized
tool
Ex. End effector, Holding buck (Hand off fixture)
A Station is the place where an operation is done by couple of tools. For

example, a station can contain one Geo set weld fixture (weld tool), robots, end
effectors, etc. to perform a single operation in the assembly line.
An Assembly line consists more no. of stations like weld stations, Hemming
press, Conveyors, Turn tables etc. to carryout all the operations to assemble a
complete closure.
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TOOLS IN THE ASSEMBLY LINE

Part load fixture Inner & Outer adhesive / weld
Inner geo fixture check slide
Hand off fixture Docking stand
Adhesive apply fixture Pedestal Mastic apply
Marriage fixture E/E Storage frame
Cure / Respot fixture Door Storage nest
Base frame (4) sided Hem press
(4) Station turntable Die changer
M/H Robot Hem die set
Welding Robot Induction cure inverter equipment
End effector Induction cure robot
Easel frame Air float table
Date scriber Cure head E/E
Pedestal welder Exit conveyor
FIXTURES, HEMMING PRESS, EOAT & CONVEYORS

Fixtures:
Part load fixture Adhesive apply fixture
Inner geo fixture Marriage fixture
Hand off fixture Cure / Respot fixture
Examples:
Fig. Hood Inner Geo Tool Base
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Fig. Hood Marriage Station (Belt load Hem Press)
Fig. Hood Inner Handoff Stand
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Hemming Press: Hemming press is used to hem the inner and outer panels
of the closures after welding together.
Fig. Robotic load press style Hemming system
Fig. Belt Load Hemming System
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Fig. Robotic Roller Hemmer
Fig. Fixture Style Hemming System
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Fig. Flexible Wheel House Hemming System
End of arm tools (EOAT): EoAT or End effector is attached at the end odf the
Robot arms and it is used to hold and handle the products like loading, unloading
and transferring between stations.
Fig. Door Hem Press Load EOAT

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Conveyors: Conveyors are used to transfer panels from one station to the
other where the distance is long. Gravity and Powered conveyors are the two
types.
Fig. Gravity Conveyor
MACHINING SEQUENCE
Machining sequence followed for all the make components except some cases is,
Cutting
Welding
Machining
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1

Basics & Concepts

Body in white (BIW)

Body Coordinate System (BCS), PLP & WP

Locating Principle, 4 way & 2 way pins

Unit, Station, Assembly line

Tools in the Assembly line

Fixtures, Hemming press, EOAT & Conveyors

UNDER BODY BODY SIDE CLOSURES ROOF FENDER

Engine Compartment Front Doors (L & R)

BODY COORDINATE SYSTEM (Part Locating System)

3-2-1 principle using the hole/slot combination:

Four functional requirements for holding workpieces:

UNIT, TOOL, STATION & ASSEMBLY LINE

A Station is the place where an operation is done by couple of tools. For

TOOLS IN THE ASSEMBLY LINE

FIXTURES, HEMMING PRESS, EOAT & CONVEYORS

Fig. Hood Inner Geo Tool Base

Fig. Hood Marriage Station (Belt load Hem Press)

Fig. Hood Inner Handoff Stand

Fig. Robotic load press style Hemming system

Fig. Belt Load Hemming System

Fig. Robotic Roller Hemmer

Fig. Fixture Style Hemming System

Fig. Flexible Wheel House Hemming System

Fig. Door Hem Press Load EOAT

Fig. Gravity Conveyor

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