Creepfeed grinding offers a production method for manufacturing a wide range of 2-dimensional forms in both hard and soft materials. The traditional role of grinding has been to impart the required dimensional accuracy and surface finish to a component which has been subjected to preliminary stock removal operations such as milling or broaching. Creepfeed grinding extends grinding from this role to one which encompasses the preliminary stock removal as well as the finishing operation. Hence it provides a means for economically manufacturing precision forms on a number of different components.



Creepfeed grinding can be compared to the conventional surface grinding method also known as reciprocating surface grinding. Reciprocating grinding is characterized by a low depth of cut (0.001" to 0.005"/pass) at a high feed rate (3 - 15 inches/sec) and the grinding stock is removed in a number of passes. In contrast, creepfeed grinding is characterized by a high depth of cut (0.04" - 0.4"/pass) at a slow 'creep' feed rate (0.05 - 1 inch/sec) and generally the stock is removed in two or three passes. The two processes are depicted in the figures below:



TECHNICAL DESCRIPTION
Creepfeed Grinding Even when the depth of cut in surface grinding is increased by about 0.005" the wheel tends to burn the workpiece and hence you may wonder at the ability of creepfeed grinding to remove 0.4"/pass without thermal distortion of the workpiece. This high efficiency in creepfeed grinding is achieved by custom-building the grinding system to account for the burn limitation of the conventional process. The system features are discussed below:

Spindle Power - Due to the high arc of contact in creepfeed grinding, significantly high power in the range of 50-150 hp (as compared to 5 hp in the case of reciprocating grinding) is required for creepfeed grinding.

Machine Rigidity - As the grinding forces are high the machine has to be extremely rigid.

High Pressure Coolant - The higher arc of contact requires a highly effective coolant system with a flowrate of about 80 gallons/min at a high pressure of 100psi as compared to a flow rate of 1 gpm at atmospheric pressure for reciprocating grinding. The high pressure penetrates the air barrier created due to the high rotational speed of the grinding wheel and provides coolant in the grinding zone.

Induced Porosity of the Grinding Wheel - Normally grinding wheels are manufactured within a porosity range of 25 to 30%. Induced porosity wheels have about 50% porosity and this maximizes the amount of coolant in the grinding zone as well as minimizes loading of the grinding wheel.

Dressing Rolls - Creepfeed grinding uses a dressing roll mounted above the grinding wheel to impart the required form on the grinding wheel. Truing can be done by crush roll forming at low rpm's) using carbide rolls or dressed using a diamond roll even when the wheel is rotating at grinding speeds. The main advantage of diamond rolls is continuous dressing of the wheel during grinding so as to remove dull and worn out grains and this reduces the tendency to burn as well as improves form retention. CNC controls compensate for the reduction in grinding wheel diameter produced by dressing, resulting in precise straightness and size of the workpiece. This is particularly useful for long parts( or many smaller parts arranged in a line) which require to be within tight tolerances of width and straightness.

Holding Fixture - Due to the high depth of cut the grinding forces generated are extremely high. Hence the workpieces have to be held in place using rigid and well designed fixtures.

Last updated: 09/29/2006