Gearing

In a closed-loop system, gearing may be used to couple a high-speed, lowtorque
motor to a lower-speed, higher-torque load. The gearing must meet requirements
for accuracy, strength, and reliability to suit the application. In addition, the closed loop requires minimum backlash at the point where the feedback sensor is coupled. In a velocity- controlled system, the feedback sensor is a tachometer that is usually coupled directly to the rotor shaft. Backlash between motor and tachometer, as well as torsional compliance, must be minimized for stable operation of a high-performance system. Units combining motor and tachometer on a single shaft can usually be purchased as an assembly. By contrast, a positioning system may use a position feedback sensor that is closely coupled to the shaft being positioned. As with the velocity system, backlash between the motor and feedback sensor must be minimized for closed-loop stability. Antibacklash gearing is
frequently used between the gearing and the position feedback sensor. When the position feedback sensor is a limited rotation device, it may be coupled to a gear that turns faster than the output gear to allow use of its full range. Although this step-up gearing enhances it, accuracy is ultimately limited by the errors in the intermediate gearing between the position sensor and the output. When an appreciable load inertia is being driven, it is important that the mechanical stiffness between the position sensor coupling point and the load be high enough to avoid natural torsional resonances in the passband.

PHYSICAL CONSTANTS IN SI UNITS

Absolute zero of temperature – 273.15 °C

Acceleration due to gravity - g 9.807 m/s2

Avogadro’s number - NA 6.022x1026 /kmol

Base of natural logarithms - e 2.718

Boltzmann’s constant - k 1.381 x 10–26 kJ/K

Faraday’s constant - F 9.648 x 107 C/kmol

Universal Gas constant - R 8.3143 kJ/kmol K

Permeability of vacuum - μo 1.257 x 10–6 H/m

Permittivity of vacuum - εo 8.854 x 10–12 F/m

Planck’s constant - h 6.626 x 10–37 kJ/s

Velocity of light in vacuum - c 2.998 x 108 m/s

Volume of perfect gas at STP 22.41 m3/kmol

Application of CAD/CAM technology in Diecasting

1. Scanning of product to be die cast
Reverse engineering is one of the important methods to register the shape of a
product by scanning in die casting field. Hybrid products can be easily created out of
many products by scanning, modeling and super-imposing on each other. Features
can be selected from one part and can be married together to get hybrid product.
Model can also be created out of damaged part by scanning, surfacing and modeling.
This is the cheapest and fastest method of product development.
2. CAD/CAM (Computer added design and manufacturing)
CAD/CAM methodology means associated 3D modeling system to handle all the tool
design, manufacturing and analysis related activities with ease of use.
3. CAPP (computer added process planning)
In case of dies, 3D model of core, cavity and other die parts are further processed for
step-to-step working. All the features are divided in various steps to make easy
working for the operator on CNC/ conventional machines. Operators need not to
bother for many operations and their sequences. He has to perform only the operation
no. allotted to him. This way the inspection at each stage is easier, also operator will
not have a feeling of complicated machining. Complicated machining can be easily
achieved by using CNC and conventional machines, so CAPP is an important aspect
from cost, quality and time point of view of a die.
4. CAI (computer added inspection)
Computer added inspection (CAI) could be done with the help of scanned point cloud
data. It can be used for Comparison between CAD model and scanned model of the
product, produced by a die, can be done by superimposing to illustrate the warpage,
shrinkage and dimensional behavior. This method can be used for inspection and data
storage for large dies where manual work can also be registered as CAD data for
future.
5. 2D drawing To 3D modeling
Normally 2D drawings are being provided by customers, so 3D model can be made
with the help of 2D drawing supplied by the customer. Some time it is felt that few
dimensions are not correct, in that case modeling can be continued with assumed
dimensions. Model can be changes at any time after confirming the assumed
dimensions. This is an important aspect of concurrent engineering. In fact in
CAD/CAM creation of 3D model is only time consuming rest of the activities are just
pressing the button technology.
6. 3D model to 2D drawing
For normal shop floor working 2D drawing plays an important role. Creation of 2D
drawing out of 3D model is very easy with any no. of sections required to clarify the
details of the product. Software is capable enough to give any desired dimensions with
linear and geometrical tolerances.
7. Black-box designing (conceptual base designing)
CAD/CAM technology is very important tool for creating the new shape and design of
the product. Aesthetics of the product can be visualised from all aspects, which saves
lot of development time of a product. Earlier, finalisation of new shape was very
laborious job. Wooden patterns were being manufactured by pattern maker, which
takes lot of time. Latest black-box designing (styling) method is described as below:
Free hand sketching  Rendering  selection of styling part 
 make 3D model of selected style 
 (a) Make rapid prototype sample or
(b) CNC machining of wooden /acrylic prototype
8. Analysis & Simulation (stress, Strain, thermal analysis etc.)
Simulation is a computational algorithm, which has been developed to reduce the time
involved for the designing. Finite element analysis has been carried out for calculation
of different working conditions to optimise the material and design at the initial stage.
9. Analysis of Gate, runner, ejector pins and cooling line etc.
9a. Benefits of diecasting analysis:
 Shorter Design Lead time
 Reduced die trials
 Automatic Gating Feature creation
 Optimises runner and gate weight, resulting in improved yield
 Automatic Runner and Overflows creation
 Reduction in rejection rates due to better filling of casting
 Automatic calculation, systematic editing & built- in intelligence
 Shorter lead times - Die development
9b. DIECASTING PART WITH GATE AND RUNNER
10. NC data generation
CNC milling of core, cavity and other die parts to the final size can be done with help
of carbide cutters available in various shapes and sizes. Some time CNC machining is
required to be done on assembly of core / cavity, sliders, core inserts etc. to get better
matching. CAD/CAM software can Generate associated machining data for any CNC
machine. NC data should be made for core and cavities block of H13 / H11 material as
per following setup:
Roughing program - keeping 0.5 ~1.0 millimeter material
Semi finish program – keeping 0.2 ~0.3 millimeter material
Local area program (semi finish) - keeping 0.2 ~0.3 millimeter material
Finishing program - keeping 0.02 ~0.05 millimeter material for polishing if required
We must take care of sharp corners and keep provision for electrodes. Electrode can
be used in a single stage or multi stage as per requirement.
Die components with regular shapes can be made by conventional method, up to final
shape and size and can be fitted directly to the die.
11. Rapid prototyping
Rapid prototyping is a very strong tool in product development. CAD model can be
directly transferred in to a physical model in plastic, paper and copper etc.. this
physical model can be used as a part of the mechanism and various tests can be
performed to check the efficiency of the mechanism. In case some changes are
required to be done, CAD model is modified and cycle is repeated till the desired
efficiency is achieved. This is the cheapest method for any new development.
12. Concurrent engineering
CAD/CAM/CAE/CAI/CAPP and many other activities can go simultaneously after
preparation of 3D model. This saves lot of time in various activities.
References
1. DIECASTING PRODUCT DESIGN, DIE CASTING EDUCATIONAL PROGRAMME, THE
DIECASTING SOCIETY OF INDIA, NEW DELHI.
2. S.Sekar, system manager, graphics information systems, advanced technologies for design and
manufacture – by psg collage of technology, Coimbatore.
3. NEW TECHNOLOGY for die casting zinc;INTERNATIONAL LEAD ZINC RESEARCH
ORGANIZATION INC. NEW YORK, USA. DISTRIBUTED BY THE DIE CASTING SOCIETY OF
INDIA.
4. Jharna Majumdar, scientist, centre for artificial intelligence and robotics, banglore, advanced
technologies for design and manufacture – by psg collage of technology, coimbatore.
5. Forging and Casting, 8th edition, vol.5, American Society for Metals.
6. UMESH R KULKARNI, DIE DRESSING FOR GRAVITY & PRESSRE DIE CASTING,
REFRESHER COURSE ON PRESSURE DIE CASTING DIES, ORGANIZED BY THE DIE
CASTING SOCIETY OF INDIA.