Week 2:- BiW Fixture Basics Challenge
3) What is Resistance welding & its application in the automotive sector?
Resistance welding-
Resistance welding is the joining of metals by applying pressure and passing current for a length of time through the metal area which is to be joined. The key advantage of resistance welding is that no other materials are needed to create the bond, which makes this process extremely cost effective.
There are several different forms of resistance welding (e.g. spot and seam, projection, flash, and upset welding) which differ primarily by the types and shapes of weld electrodes that are used to apply the pressure and conduct the current. The electrodes, typically manufactured from copper based alloys due to superior conductive properties, are cooled by water flowing through cavities inside the electrode and the other conductive tooling of the resistance welding machine.
Resistance welding machines are designed and built for a wide range of automotive, aerospace and industrial applications. Through automation, the action of these machines is highly controlled and repeatable allowing manufacturers to staff production readily.
Types of Resistance Welding Applications:
(a)Spot Welding
Resistance Spot Welding, like all Resistance Welding Processes, creates welds using heat generated by resistance to the flow of welding current between the faying surfaces, as well as force to push the workpieces together, applied over a defined period of time. Resistance Spot Welding uses the face geometries of the welding electrodes themselves to focus the welding current at the desired weld location, as well as to apply force to the workpieces. Once sufficient resistance is generated, the materials set down and combine, and a weld nugget is formed.
RSW is automated and used in the form of robotic spot welding in automotive industries to weld the sheet metals to form car body. Industrial robots spot welding the car body in production line is shown in the photograph given
(b)Seam Welding
Resistance Seam Welding is a subset of Resistance Spot Welding using wheel-shaped electrodes to deliver force and welding current to the parts. The difference is that the workpiece rolls between the wheel-shaped electrodes while weld current is applied. Depending on the particular weld current and weld time settings, the welds created may be overlapping, forming a complete welded seam, or may simply be individual spot welds at defined intervals.Resistance seam welding is mostly applied in manufacturing of containers, radiators & heat exchangers etc.
(c)Projection Welding
Like other Resistance Welding Processes, Projection Welding uses heat generated by resistance to the flow of welding current, as well as force to push the workpieces together, applied over a defined period of time. Projection Welding localizes the welds at predetermined points by using projections, embossments or intersections, all of which focus heat generation at the point of contact. Once the weld current generates sufficient resistance at the point of contact, the projections collapse, forming the weld nugget.
Solid Projections are often used when welding fasteners to parts. Embossments are often used when joining sheet or plate material. An example of Projection Welding using material Intersections is cross-wire welding. In this case the intersection of the wires themselves localizes heat generation, and therefore resistance. The wires set-down into one another, forming a weld nugget in the process.
It is used mechanical fixing of Autobody structures eg. weldnut
4)What is fusion welding & types of fusion welding with its application in the automotive sector?
- Fusion welding is a process that uses heat to join or fuse two or more materials by heating them to melting point. The process may or may not require the use a filler material. External application of pressure is not required for fusion welding processes, except for resistance welding, where substantial contact pressure is required during welding for sound joining.
- Fusion welding processes can be grouped according to the source of the heat, for example, electric arc, gas, electrical resistance and high energy.
Shielded Metal Arc Welding (SMAW)
- also known as manual metal arc welding (MMA or MMAW), flux shielded arc welding or stick welding.is a manual arc welding process that uses a consumable electrode covered with a flux to lay the weld.
- An electric current, in the form of either AC or DC from a welding power supply, is used to form an elctric arc between the electrode and the metal to be joined. The workpiece and the electrode melts forming a pool of molten metal that cools to form a joint. As the weld is laid, the flux coating of the electrode disintegrates, giving off vapors that serve as a shielding gas and providing a layer of slag, both of which protect the weld area from atmospheric contamination.
- Because of the versatility of the process and the simplicity of its equipment and operation, shielded metal arc welding is one of the world's first and most popular welding processes. It dominates other welding processes in the maintenance and repair industry, and though flux cored arc welding is growing in popularity, SMAW continues to be used extensively in the construction of heavy steel structures and in industrial fabrication. The process is used primarily to weld steels (including stainless steel).
fig-shows SMAW welding
Metal Inert Gas Welding (MIG)/ Metal Active Gas Welding (MAG)
- Also known as Gas Metal Arc Welding (GMAW). MIG and MAG welding are the most common arc welding processes, in which an electric arc forms between a consumable wire electrode and the workpiece leading them to melt and join. Both use a shielding gas to protect the weld from airborne contaminants, or oxidation in the case of MIG welding.
- The process can be semi-automatic or automatic. A constant voltage, Direct current power source is most commonly used with GMAW, but constant current systems, as well as AC, can be used. There are four primary methods of metal transfer in GMAW, called globular, short-circuiting, spray, and pulsed-spray, each of which has distinct properties and corresponding advantages and limitations.
fig-shows MIG welding
Tungsten Inert Gas Welding (TIG)
- Also known as Gas Tungsten Arc Welding (GTAW). This arc process uses a non-consumable tungsten electrode to create the arc between the electrode and the base plate. An inert shielding gas is used to protect from oxidation or other atmospheric contamination.
- This process can be used autogenously on thin parts, but will require the addition of a wire, rod, or consumable to be added for thicker parts.
- A Constant current welding power supply produces electrical energy, which is conducted across the arc through a column of highly ionized gas and metal vapors known as a Plasma.
- GTAW is most commonly used to weld thin sections of stainless steel and non-ferrous metals such as aluminium.
fig-shows TIG welding
plasma arc welding: This process uses an electric arc created between an electrode and the torch nozzle. The electric arc ionises the gas (usually argon) in the chamber creating what is called a 'plasma.' It is then forced through a fine bore copper nozzle that constricts the arc and directs it to the workpiece, allowing the plasma arc to be separated from the shielding gas (which is usually made from a mixture of argon and hydrogen).
fig-shows plasma arc welding
Automobile application of arc welding -
- Arc welding is used to weld the chasis parts in automotive industry.
- Arc welding wire for automotive steel sheets
Solid wires suitable for robot welding that generate compara-tively small amounts of slag and fume are chosen for welding of au-tomotive parts.
- Arc welding is used to weld the body parts in Automotive industry-
Low heat input welding of thin steel sheetsPrevention of burn-through due to excessive heat input is im-portant in the welding of car body parts of thin sheets. For this rea-son, thin welding wire with a diameter of 0.9 mm, which enables stable welding at low currents, and low-heat-input welding power sources
- TIG welding is used to join thin stainless steel parts & various piping parts inautomobile industry.
- MIG welding is used for the repairing work in automobile industry wheather they are small, big, light or heavy.
First Plane
- Geometry tells us that three points are required to define a plane. This is the "3" in 3-2-1. So, three specific points are used to define the first plane.
- Fewer than three points cannot define a plane, and in the real world dimensional tolerances mean that four or more points will not be coplanar. A real-world, less than ideally perfect part placed on four or more reference points will, in fact, rest on only three of the points due to its less than perfect surface.
- Different parts may rest on different combinations of three points, resulting in variation between finished parts.
- A stool can be used to illustrate this concept. A two-legged stool would certainly be unstable. A three-legged stool sits rock-solid. A four-legged stool is often found to rock.
- In the illustration, a three dimensional part, represented by a cube, is placed on a datum plane defined by three support points. The part’s six degrees of freedom have now been reduced to three. It can still move along the X or Y axes, and it can still be rotated about the Z axis. (The part cannot move along the Z axis because it is held against the plane by clamping force.
TIPS
- Use the largest surface of the part for the first ("primary") reference plane.
- Position the three support points as far apart as possible.
- If more than three support points are required to prevent deflection, make the additional points adjustable.
Second Plane
- A second plane, if it is perpendicular to the first, can be defined by two points, the "2" in 3-2-1.
- The part is now constrained to one degree of freedom: movement along the Y axis. (The part cannot move along the X or Z axes because it is held against the planes by clamping force.)
Third Plane
- A third plane, if it is perpendicular to both of the first two planes, can be defined by one point, the "1" in 3-2-1. The part is now entirely constrained. It cannot move along or rotate about the X, Y, or Z axes. (Remember that the part is held against each of the three planes by clamping force.)
TIPS
- If more than one support point is required to prevent deflection, make the additional points adjustable.
Machined is Best
It’s best if the workpiece surfaces intended to contact the support points are machined. Cast surfaces are usable, but then tend to create tolerance problems. Machined holes are the number one choice. Two machined holes can be used to eliminate all but one degree of freedom.
Repeatability
- Repeatability is a paramount concern. It means that each part should be nearly identical to each other part coming off the same fixture. "Nearly identical" actually has a specific, quantifiable meaning: key dimensions of all parts produced on the same fixture must fall within defined tolerances.
- In order to stay within tolerances, it’s best if the workpiece surfaces intended to contact the support points are machined. Cast surfaces are usable, but they tend to create tolerance problems. Machined holes are the number one choice, because two machined holes can be used to eliminate all but one degree of freedom.
- The next best feature to use for consistent locating is machined surfaces at right angles. The "machined surface" desired here can simply be a tab or small flat specifically included for locating purposes.
- Repeatability is achieved through application of the 3-2-1 method to the three aspects of the locating process:
1. Supporting
2. Locating (positioning)
3. Holding
Supporting
- The part is supported from "below" with reference to the Z axis. (Introduction of the first reference plane.)
- Gravity positions the part against the support locator.
- Provide adjustable auxiliary support points as needed to prevent deflection.
- Vertical location with respect to the fixture is now established
- The part is positioned horizontally, in the X-Y plane. (Introduction of the second and third reference planes.)
Holding
- The part is clamped against fixed locators. Therefore, a known and unvarying position of the part is maintained with respect to the X, Y, and Z axes.
- One strap clamp or clamp arm will restrict the workpiece in three dimensions due to friction between the workpiece and clamp. However, friction alone may not be enough to prevent the workpiece from moving during machining.
- Cutting forces will not move a properly supported and clamped part.
Locating
- The part is positioned horizontally, in the X-Y plane. (Introduction of the second and third reference planes).
Summary: Clamping rules of thumb
- Define three reference planes on the workpiece and fixture.
- Provide one opposing clamping force opposite each plane to restrict movement.
- When in doubt, rely on additional cylinders to take up uncertainty.
6)Define Body coordinate system?
Coordinate system is a reference system Consisting of a set of point, Lines & surfaces used to define position of point in space either in 2 or 3 dimensions.
In general BCS is also called as car line or Body line
Car lines are the (Grid lines) shown on the fixture, which virtually represent the same location in the BIW. All the car line on fixture display the coordinate at corner for reference. With these lines one can easily relate the, location in BIW.
Some times single coordinate hole is given in the fixture, that also represent the car line coordinates, from that reference point fixture is made and can be inspected. Body coordinate are mentioned near the hole
-We should try that the co-ordinates of locating and clamping points should not be in three decimal (e.g. X=100.124, Y=245.127, Z=450.458).
They should be in the whole nos. or max upto 1 decimal . Once these co-ordinates are maintained automatically the BIW base structure is maintained.
All vehicle product drawings are identified numerically relative to three vehicle planes Description shown below.
1. ( X ) It is in width of BIW – 0 X - is Body Center Line
2. ( Y ) It is in length of BIW – 0 Y is Near Front Bumper
3. ( Z ) It is in Height of BIW - 0 Z is about Center of Wheel
7)Elaborate Body plane system & its essentials.
Body planes are three mutually perpendicular imaginary planes. These are reference planes in automotive car. These are used to define GD & T of all parts in automotive domain.
The measurement from body plane to parts are called bodyplane dimensions.
Bodylines dimensions are essential for below reason
- It defines exact position of each product in the vehicle w.r.t a fixed origin.
- It ensures flawless design for assembly.
- While designing lines, all the designs are carried out relative to the bodylines viz.fixtures, Turntables etc.
- It assist in easy location of different parts in the vehicle.
- It aims in creating a standardized system.
- It assist in quality checks.
Some examples which shows how we use body plane to define the exact position of part is shown below.
fig-shows the use of x plane to define the length
fig-shows the use of z plane to define the height
fig-shows the use of y plane to define the width