There are two types of machine static stiffness
tests: thrufeed, and infeed.
1. Thrufeed Instruction
Grind
enough components with total stack length larger than twice the wheel width.
Operate the grinder at a power consumption that is larger than 60% of the
available power. Take one component in the middle of the stack out of the flow.
Measure its diameter accurately and record this number for the first
measurement input of the program.
After
taking the part out of the flow, the flow can be stopped, however leave the
machine running but do not change any settings. Use the measured component and
feed it through the grinder again. Measure its diameter and record it for the
second measured input of this program.
2. Infeed and Internal Instruction

Grind
one component at an infeed rate with high enough power consumption (60% or
more of available power); keep spark out time to zero. Measure the
diameter of the component and record the net actual power consumption.

Grind
a second component in the same setup with spark out set to 10 seconds or
more. Measure the diameter of component.
There
is more to grinding than only the basic principles covered, but this will serve
as an introduction to the capabilities of the software.
GRINDING SIMULATOR SOFTWARE
There
are eight different types of grinding operations built into the Grinding
Simulator, Fig. 233A to D:

Thrufeed
grinding with one machine (A)

Thrufeed
grinding with multiple machines in line

Centerless
Infeed (B)

Centertype
Infeed

Microcentric

Angular
(C)

MultipleDiameter
Centerless Infeed (D)

MultipleDiameter
Centertype.
A
B
C
D
Fig. 233
Types of centerless grinding: A.
Throughfeed (Cincinnati Machine, A UNOVA Co.) B. Centerless infeed (Carborundum
Abrasives, Div. SaintGobain Abrasives.) C. Angular (Cincinnati Machine, A
UNOVA Co.) D. MultiDiameter Infeed (Carborundum Abrasives, Div. Saint Gobain
Abrasives)
It
would be difficult to discuss all these grinding operations in detail since the
same basic principles apply to all. Therefore for this example, the focus will
be on Thrufeed Grinding for one machine with multiple passes.
Part Information
Figure
234 shows the
Part Information
page, which lists various
material groups, each containing several specific materials. There are a total
of eighty different types of materials and other materials can be added,
provided that its thermal conductivity at 300°C is known.
Fig. 234
The Part Information page of the
Thrufeed One machine with multiple passes.
There
are different types of tolerances that play a role in the grinding process and
are related to each other. In the Part Information Page, the print final size
tolerance is an input, and automatically the expected roundness tolerance and
cylindricity tolerances are calculated. The software allows users to type in
their own roundness or cylindricity tolerance. This would then initiate a
reverse calculation for the final size tolerance. Another important input is
the CPK (Capability Index). The print tolerance and the shop tolerance are not
the same when the CPK is larger than one. The relationship between shop
tolerance and print final size tolerance is
(8)
For
each input where there are metric and inch units, each unit system can be used.
The green label shows the converted value from one unit to the other.
The
part’s information can be saved in a database and be reloaded or modified at
any time.
Machine Information
Figure
235 shows the
Machine
Information
page. The speed
ratio is defined as
(9)
Fig. 235
The Machine Information page of
the Throughfeed One machine with multiple passes. (Bethel Technologies, Inc.)
The
user can enter the Speed Ratio, or it can be selected from the general ranges. A
highspeed ratio means a low workpiece speed that makes the chip length larger.
This would then make the grinding process more sensitive for surface damage due
to heat. A speed ratio higher than the
High
Speed Ratio
selection will
result in burning of the workpiece. The selection of High Speed Ratio should be
used in cases where workpiece outofbalance takes place or where the machine
dynamic stiffness does not allow higher work speed.
A
selection of
Typical
means an average moderate work speed that is
used on most grinding operations. The selection of
Low
speed
ratio means a high workpiece speed and can be selected when the machine has a
high static stiffness. With weaker machines, a low speed ratio may cause
chatter on the workpiece. The practical speed ratio has a correlation between
the wheel speed, workpiece speed, and with the part diameter. When the user
enters in a wheel speed, the wheel r/min is automatically calculated. It is
possible to enter the wheel r/min that would result in a wheel speed
calculation. The workpiece r/min is automatically calculated when the speed
ratio is selected. The user can enter the workpiece r/min at which time the
speed ratio selection will go to
None
. There is an important correlation between
workpiece r/min and wheel r/min. The ratio between wheel r/min and work r/min
is called the Beta ratio. It is defined as
This
relationship is important when the grinding process results in triangle or
other nonround parts. When the Beta Ratio is exactly 3 or close to 3, then it
could indicate a triangle part problem. Another important calculation that
depends on the workpiece r/min and the speed ratio is the regulating wheel
r/min. Whenever the workpiece r/min is changed, the regulating wheel r/min is
changed accordingly.