for small and large production runs
Conventional Grinding
▪Long cycle times – multiple setups (chucking) required
▪Danger of workpiece thermal damage because of heat buildup
▪High machine and grinding wheel wear
▪Frequent grinding wheel dressing cycles required
▪Inconsistent quality parts due to wheel wear
▪Complex formed wheels minimize the range of part contours that can be ground
SUMMARY
The grinding process has been under fire for some time now. Many shops are looking at alternative methods to reduce or eliminate grinding from their process. Hard turning is one example.
▪Single-point grinding may be a way to use the accuracy and surface finish benefits of the grinding process in a way that has a lower impact on the material flow in the shop.
▪In virtually all metalworking operations including milling and turning, many businesses are looking to perform more operations in a single workpiece handling.
▪For medium volume production grinding of complex workpieces, the single-point grinding process may be a way to accomplish this for shops that rely on grinding for a living.
For more information on SINGLE-POINT OD GRINDING see the Website: www.junker-machinery.com
(Dirk Smits, President – Bethel Technologies, Inc.)
Grinding is a metal-removal process that uses an abrasive cutting tool to finish a part to an accurate size and produce a high surface finish. The most common abrasive tool used is a grinding wheel that consists of many thousands of abrasive grain bonded together. In a grinding process, a revolving grinding wheel is brought into contact with the surface of the part to be ground. As each abrasive grain on the periphery of the wheel contacts the part surface, it acts as a cutting tool and removes a minute (very small) chip of metal, Fig. 2-3-1.
Cylindrical grinding may be defined as grinding the periphery of a rigidly supported, revolving part. Cylindrical grinders fall into three general classes: plain cylindrical, universal cylindrical, and special cylindrical grinders. The centerless grinder, one of the special grinders, makes it possible to grind cylindrical parts without supporting the part between centers or holding it in some from of fixture, Fig. 2-3-2. Centerless grinders are precision machine tools capable of mass-producing countless numbers of parts held to close tolerances of size, shape, and surface finish. The modern grinding machine is capable of finishing soft or hardened parts to tolerances of .0002 in. (0.005 mm) or less on high-production machines, while producing very fine surface finishes.
The goal of every manufacturing operation is to produce quality products as quickly and accurately as possible. To accomplish this goal, it is important that every component in the manufacturing process be in top condition so that inaccurate parts are not produced. Inaccuracies in manufacturing result in parts that may have to be repaired, replaced, or scrapped, which affects the productivity and profitability of any operation.
Virtual Reality and certain software programs can be used to simulate a manufacturing operation on a computer before starting to actually manufacture a product. This allows any potential manufacturing errors or operational sequences to be corrected before spending time, material, and labor on a process that may not produce satisfactory results.
Fig. 2-3-1 The cutting action of abrasive grains in a grinding wheel. (Carborundum Abrasives, Div. Saint-Gobain Abrasives.)
CYLINDRICAL GRINDING SIMULATOR
The Grinding Simulator is a software package that can predict production rates for the cylindrical part to be ground in a mass production grinding operation. The calculations are based on macroscopic grinding principles and not based on microscopic principles. A macroscopic method is an averaging effect of combining data from many grinding operations. The advantage of this method is that it can be used to predict productivity. A microscopic approach is to calculate certain grinding parameters from an abrasive cutting into the metal. The disadvantage of a microscopic approach is that it is unable to predict productivity since each abrasive grain in the wheel is different and requires a different calculation.
Before testing is done on any machine tool, the machine spindle and slides should be checked to see that they are in good condition, otherwise the test results would be not be accurate.
Fig. 2-3-2 Parts pass between the grinding and regulating wheels during Thrufeed grinding. (Cincinnati Machine, A UNOVA Co.)
GRINDING PARAMETERS DEFINITIONS
Before writing any code, the grinding parameters must be defined. The difficulty with grinding is that every abrasive grain has its own geometry.
Specific Metal-Removal Rate
The parameter that combines all grinding operations, no matter what size and length, is the Specific Metal-Removal Rate. The Specific Metal-Removal Rate, defined as Q prime, is
| (1) |
The unit for this parameter is in.3/min/in. This equation can be simplified to
| (2) |
In center-type infeed grinding, the effective wheel width is equal to the part length, and the stock divided by time equals the infeed rate. This results in
| (3) |
The importance of Q′ is that one has a parameter that can compare with different operations, of which the part geometry and wheel width is different. As can be seen from Equation 3, if the part diameter is changed by a factor of 2 and the infeed rate is the same, It is possible to grind twice as aggressively.
Surface Finish Calculations
Knowing the definition of Q′ and having a method of measuring its value, it is necessary to obtain a relationship between the specific metal-removal rate and the surface finish (Ra). Whenever data is taken, be sure that equilibrium has been reached before making any analytical conclusions. The relationship between Q’ and surface finish (f) is logarithmic.
| fQ-n3 = C3 | (4) |
where C3 and n3 are depending on the conductivity coefficient of the material, material hardness, and fluid type. For the influence of metal-working fluids on the
