Week 1:- Introduction to BiW and Fixtures Challenge
1.BIW:
The stage in automotive ndesign or manufacturing in which the car body sheet metel components are been assembled by welding and other joining process.In this stage in automobile manufacturing in which a car body's frame has been joined together, that is before painting and before the motor, chassis sub-assemblies, or trim (glass, door locks/handles, seats, upholstery, electronics, etc.) have been integrated into the structure.
3-2-1 Principle in BIW:
The 3-2-1 principle of location (six point location principle) is used to constrain the movement of workpiece along the three axes XX, YY, and ZZ. This is achieved by providing six locating points, 3 pins in base plate, 2 pins in vertical plane and 1 pin in a plane which is perpendicular to first two planes.
BIW:
- Body Sides.
- Under Body.
- Closures.
- Roof.
- Fender.
Nomenclature is basically choosing names for thing. BIW have no. of parts in it. All parts have different names.As automotive industry is spread worldwide. Every nation has its own language. So the same part in BIW have different name in its region.For example, One component of BIW is called suspension tower in UK & same component called shock tower in U.S. BIW nomenclature.
3.FIXTURE:
Fixtures are work-holding devices and locating elements that locate, hold, and support the workpiece in a fixed, proper position during the machining process with respect to the machining tools. The most common type of fixture is the vise jaw found in nearly all workshops.
Advantages:
- Increased productivity
- Increased machining accuracy
- High-speed manufacturing process
- Maintained interchangeability
- High clamping rigidity for CNC and turning operations on large parts
- The increased quality level of the finished product.
Types
Turning Fixtures:
They are usually mounted on chucks of the machine spindle during turning operations, like on lathes. Depending on the part that’s being machined, turning fixtures may be equipped with counterweights to balance an unbalanced fixture.
Milling Fixtures:
Milling fixtures are usually mounted on machining tables facing the faceplate or the spindle of the milling machines. The workpiece is placed at the base of the fixture and clamped before starting milling operations. However, during operation the cutting tool remains in place while the machining table, alongside the piece, shifts in relation to the cutter.
Boring Fixtures:
Boring fixtures incorporate the principles of drill jigs since the boring bar is guided through a pilot bushing, similar to drill bushing. Its main function is to hold the workpiece in the correct position relative to the boring bar. Since they aren’t subject to strong cutting forces, boring fixtures don’t need to be as study.
Grinding Fixtures:
There are several different forms of grinding fixtures used in grinding machines to hold, locate, or support workpieces that are subject to grinding operations. Regardless of their form, however, these should have provisions for the supply and exit of coolant.
Tapping Fixtures
These work holding devices are specifically designed to position and secure workpieces for tapping operations — cutting internal threads in drill holes. They’re primarily used on odd-shaped and imbalanced parts, especially in mass production, for drilling, tapping and reaming.
Welding Fixtures:
Welding fixtures are designed to hold and support different components intended for welding operations and to prevent any possible distortions in welded structures. The structure of these fixtures has to be rigid and stable, and the clamping elements need to be positioned clear of the welding area.
Assembly Fixtures:
These are used to hold various parts and components together for assembly purposes. They’re similar to welding fixtures, but instead of hot joining, these are used for mechanical assembly.
4. Basic principle of fixture design:
Fixtures are workholding devices designed to hold, locate and support workpieces during manufacturing operations. Fixtures provide a means to reference and align the cutting tool to the workpiece but they do not guide the tool.
A fixture designer major portion of design time is spent deciding how to locate the work piece in fixture. For any free body there are total twelve degrees of freedom as below.
6 translation degrees of freedom: +X, -X, +Y, -Y, +Z, -Z
And 6 rotational degrees of freedom
-Clockwise around X axis (CROT-X)
-Anticlockwise around X axis (ACROT-X)
-Clockwise around Y axis (CROT-Y)
-Anticlockwise around Y axis (ACROT-Y)
-Clockwise around Z axis (CROT-Z)
-Anticlockwise around Z axis (ACROT-Z)
Fix all the 12 degrees of in order to locate work piece in fixture. The main motive of fixture is to hold work piece so that it cannot move or distort when operation is being done. It must hold work piece rigidly & stable.illustrate degrees of freedom of any body.
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. Below fig. show 3-2-1 locating principle.
5.Types of BIW Stations:
In BIW assembly line is in where different types of panel are joined together in each specified zones. Each panel categories will have individual zone. As under body zone, door zone, hood zone etc. These zones are further divided into stations. There are following types of station in BIW.
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. So there will be proper flow of inventory.
TYPES:
- Tool stations
- Gripper stations
- Stand stations
- Miscellaneous station.
TOOL STATION:
a) Geo station- Geo tool is a fixture in which geometry of the panels which are welded together are defined accurately. The pin tolerance for geo pin will be of closure tolerance i.e.-0.15 in general. For example, consider panel hole size 20mm, the pin diameter should be 19.85mm.
All parts must be located with two locating pin. Tolerance level in all terms should be very less with geo fixture. Pin should be undersize & pin tolerance for geo pin will be closer.
b) Re-spot station
Re-spot tool or station is fixture in which the remaining weld spot which are not achieved in geo tool are welded for the pre welded panel from the geo tool. The pin tolerance for re-spot pin will be of tolerance with -0.28 in general.
Suppose in assemble we need 50 weld stack. On one station we cannot complete all these operation because it will take more time & other station relative to assembly in idle condition
In this type of case we carefully choose some weld tack points which will define geometry of the part and also assembly will not get deformed after opening clamp or in transportation due to welding stresses. The remaining weld spot are completed in re-spot fixture.
C) Framer station
Framer fixture is next station after marriage station. In framer fixture roof is attached to output of the marriage fixture and it form like frame hence it is called as framer tool.
c) Hemming/ marriage station
A marriage or a hemming tool is fixture in which the inner panel assembly and outer panel assembly are joined together. These are done by welding or hemming in case of closure panels. spot & marriage
e) Checking station
A checking station tool is fixture which is used to check the automotive parts or assemblies, ensuring all the co-ordinate, relative dimension and position as per the tolerances.
A checking station can be a gauge type, fixed type & automated checking fixture. A checking gauge is tool where work piece is hold & various measuring gauges are introduced to ensure the dimensions and repeatability
2.Gripper station
A gripper is device or a fixture which holds the car panel & is fixed to the manipulating end of robot or an end effector. Also known as EOAT ( End of arm tooling)
a) Material handling grippers
Material handling grippers is designed for handling the car panel from one station to other. Below fig. shows material handling gripper.
b) Process Grippers
Process grippers are designed for handling the car panel one station to other & in addition to that it under goes process like pedestal welding, pedestal riveting, gluing, sealing etc.
c) Combo gripper
Combo gripper is designed for handling car panel from one station to other also with combination of weld gun at another side of gripper for welding. It is multiple tasking types.
Weld gun + Gripper
d) Dual gripper
Dual gripper is designed for handling car panel from one tool (station) to other, with two sided gripper. It can hold two panel simultaneously one RH & one LH side.
3.Stand station:
a) Pedestal stand
Weld gun is mounted to the floor permanently. The gripper can carry the panel under the stand to do some operation.
b) Gluing & sealer stand
Gluing or sealer gun is attached to standard stand which is grouted to floor permanently fixing is required. So stand should not move due to vibration or other factors
c) Docking stand
When robots are selected of multitasking like material handling & welding, which cannot carry both due to some limitations (payload capacity of robot or space constraint. It is also called as parking stand for gripper.
d) Date stamp stand
Every manufactured product have some data to stamped or to be embossed on it like serial no, batch no, date etc. For some future reference or for data collection.
4.Miscellaneous station-
a) Curing
After gluing it needs some time to cool down, so we put assembly on some belts & it will take the panel to another station & meanwhile gluing will cool down.
b) Buffer stand
After some operation we can put the no. of assemblies in this stand which is buffer stock & it can be transported to another station in easy way. They are also used to store the inventory while the machine is undergoing for some maintenance.
c) Take out trolley
It is used to take out some panels for inspection to rectify the process is going in right or not between the cycles.
d) Conveyor
Conveyor is material handling. They are used to transfer panel from one station to another station. It can be of two types gravity & powered.
6.Basic terminologies used in the BIW fixture:
1.NC/MYLARS
These are parts are used to hold panel. They are globally called as mylar. Top side mylar is called as clamping mylar & bottom side is called resting mylar. Every clamping mylar should have resting mylar. It is jaw type. It prevent panel from deforming while welding.
2.Principle locating point (PLP)
These are point which are used for the accurate location of part to maintain the geometry of assembly. means principle locating points are those where we use pin for locating panel. These are defined in drawing. The positional dimensions or relative dimensions are very precise in stamping & in fixture also.
3.Risers
Risers can be of L-type, welded or square tube or frame type. These are basically manufactured parts are used to give height to assembly.
4.Blades
Blades are plates attached to riser. Other part likes cylinder, arms etc are mounted on the blade.
5.Shims
In fixture we are providing tolerance to each part mostly manufactured. Those tolerance tend to stack up & reflect together. In order to avoid that we use shims so we can easily adjust after assembly so whatever stack up there we will rectify it through shims. Shims come in thickness of 0.1, 0.2, 0.5 etc.
6.Rough locators
Rough locators are those used majorly for manual fixture. There is chance that operator can place part in wrong orientation mistakenly. The rough locator will work as a guide while placing the part in the fixture & part will be loaded in desired orientation.
7.Hardwares
Hardwares are like the hex head bolts, allen bolt, hex nuts, spring washers, self locking nuts etc.
8.CMM
CMM stands for coordinate measuring machine. It is a device that measures the geometry of physical objects by sensing discrete points on the surface of object with probe. It generates report by comparing the data with the CAD file data.
9.Units
The fixture is assembly of different types of units to form a fixture. There are different unit like pin unit, base unit, clamping unit etc
10.Number plates
Number plate is the aluminum embossed plate placed on each unit to recognize the unit.
11.Co-ordinate plate
When we discuss about fixture on every fixture we have tooling hole which is called master hole through all fixture checked on CMM mastering that particular hole. Cover that hole so that it won’t get other impurities & hole does not get any wear, tear & distortion.
12.Name plate
The plate on which basic information described like company name, fixture name, fixture weight, panel name are embossed & joined to fixture.
13.Clamp arm
Clamp arm is part of clamp unit which moves about axis. Over clamp are mylars are mounted
14.Pivot
It is axis about which clamp arm will rotates.
15.Class ‘A’ surface/ skin surface
The outer panels of car like hood, door, backdoor, fender, roof etc are visible to customer. The outer panels should be aesthetically very good. No any scratches or dent mark is acceptable over it. While designing fixture to the skin surface the clamping material should be soft, so that it could not able to left any impression or dent over skin. Generally nylon or PU material is used for clamping purpose.
16.Reed switches & sensor
These are the electric components used in automated fixtures. The sensor & reed switches are used only in that situation where fixture is fully automatic or semiautomatic that run through PLC, control panel etc. Sensor are used to detect part present or not, clamp is close or open whereas reed switches confirms position of piston i.e. it is at top or down.