3D Finishing 2

AIM :

To study about the various design aspects regarding BIW fixtures.

OBJECTIVE :

• To perform 3D finish and create Rough locators for the Assembly design created earlier.

3D finishing process

• Hole concentricity & hole sizes.
• Machining area.
• Nominality.
• Holes colouring standard.
• Pneumatic lay-outing.
• Gaps checking.
• Fasteners implementation.
• Mylars Splitting as per panel profile.
• Proper renaming of parts/assemblies as per the standard.

Hole concentricity & hole sizes

• Hole concentricity and size of the component must be checked in order to make the assembly process easier.

Machining area

• The Machining area must be highlighted using a proper colour code.

Nominality

• Nominal dimensions must be used in the components in order to ensure proper fit in the assembly.

Holes colouring standard

• Standard colour code must be followed according to the customer requirements.
• Simple hole - Blue
• Threaded hole - Yellow
• Machined area - Cream
• Dowel hole - Blue

Pneumatic lay-outing

• It is the collective presence of various pneumatic pipes which work as an inlet to the pneumatic cylinder.

Gaps checking

• Proper gaps between components must be ensured in order to avoid any damage to the adjacent components.

Fasteners implementation

• Fastners must be implemented in the assembly as per the requirements.

Mylars Splitting as per panel profile

• Mylar splitting must be done with the given car panel.
• It must be ensured before the end of the design process.

Proper renaming of parts/assemblies as per the standard

• Proper renaming of part mus be done as per the standard for easy identification and to avoid confusion.

Once the 3D finishing is done, the entire assembly is further sent for simulation and 2D detailing.

3-2-1 principle

• The 3-2-1 method is a work-holding principle where three pins are located on the 1st principle plane, i.e., either XY, YZ, ZX. And two pins are located on the 2nd plane perpendicular to the 1st plane, and at last, one pin on the plane is mutually perpendicular to the 1st and 2nd planes.
• It represents the minimum requirement for the locating elements.
• The locators along with the clams which hold the part in place, provides equilibrium for all the forces.
• Stability is satisfactory if all three rest buttons are widely spaced and resultand cutting force lies within the triangular area between the buttons.
• If resultant cutting force lies outside the triangular area then it generates a moment which in turn lifts are overturns the component.

Locating Process in 3-2-1 method

We have two objectives when mounting a part in a fixture for machining
1. Accurately position the part at the desired coordinates.
2. Restrict all six degrees of freedom so that the part cannot move.
A widely used method of accomplishing these two objectives uses the 3-2-1 principle, so-called because it entails three steps that employ three, then two, then one fixed points of known location. Since that adds up to six fixed points, it’s also known as the six point method.
In the three steps of the 3-2-1 method, three mutually perpendicular planes, called datum planes, are introduced, one at each step. These three planes define the workpiece position, and together with opposing clamping forces fully constrain the part. Let’s take a look at the details of the 3-2-1 method

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.

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.

Rough locators

Rough locators are used to help locate workpieces in the automation process.

Locating refers to the desired location where you want the workpiece to be when it is getting worked on either by a person, team, or robot.

It is a device to establish and maintain position of a part in a jig or fixture.

It can also be called as fool proofing method as the rough locators are set according to the angle of their respective panels.

Thus the parts can be loaded in a defined direction and orientation.

The accuracy of the part locations are very crucial as they affect the final assembly.

Designing a Rough locator

The points need to be considered while designing a Rough locator are,

• It is used to guide the conponent to place it properly.
• It is generally placed at the edges.
• It must have an entry angle of 30 to 45 degree.
• It must guide the component at a distance of 10 to 15 mm before the engagement
• It is mounted on the base with slots for easy positioning.
• It must be placed at the same angle as the car panel.
• The slots must be in the direction of guiding the car part.
• These locators must be placed within two slots for making the mounting process simpler.

MODEL RESULTS :

Feature Tree

Car Panel

Base Unit

Pin Unit

Power Clamp Unit

Swivel Clamp Unit

Rest Unit

Rough Locator Unit

Assembly

Nominality Check