High Speed Grinding Reduces Total Processing Time From 8 Hours to 2.5 Hours

A mid-sized job shop that specialized in precision tooling, produced close tolerance form punches in close to one-quarter the previous processing time. This company had been producing 4 punches per 8 hours. This included rough milling and finish grinding. Their new CNC tool room grinding process reduced the processing time to 2.5 hours. In addition to the decrease in cycle time, the operator was free to run a second machine while the CNC grinder was grinding the punch.

The reduction of processing time was even more impressive because a tolerance requirement of +/- 0.000,050" (fifty millionths of an inch). The forming punch (pictured) is CPM M4, Rc 62-64. Formerly the punches were produced in a conventional fashion. Blanks were rough milled leaving 0.005 to 0.010 inch of stock in the form for the finish grind. This process, which required 3.5 hours, was completed on a manual mill. After hardening, the punches were finish ground on a manual surface grinder. The manual surface grinding took approximately 4.5 hours.

The punch had four identical teeth. Each tooth was comprised of five distinct forms. Each of these five forms was individually dressed into a wheel and ground into the part. Each step must be meticulously planned and executed. Dressing the wheel, locating the wheel, grinding, inspecting the workpiece, then finally grinding to size. The sequence repeats itself again and again for each for each detail, for each part, every time the wheel is redressed. The workpiece is handled more than twenty times for inspection.

The work is highly skilled and labor intensive. The Amada Wasino, MeisterPro CNC toolroom grinder was able to accomplish two major time savings.

First, high speed table reciprocation eliminated the roughing operation. The table, stroking at more then 250 reciprocations per minute, reduced the roughing operation to 12 minutes of uninterrupted grinding. Though extremely fast, the table remained free of vibration and the punch exhibited no chatter. The material removal was smooth and consistent.
Second, dressing of the wheel became a time saving feature. The process time was reduced every time the wheel was re-dressed. The MeisterPro can re-dress wheel forms and resume grinding with compensated positioning to within a "tenth" (0.000,1") all day. This effectively eliminates operator inspection after wheel re-dressing.

The process started with a blank wheel and a blue print of the form to be ground. The form of the tooth was quickly programmed through the conversation wheel dressing cycle. The blueprint style input screen made it simple to type in the required wheel shape. Once the data was input the canned cycle automatically roughed out the form into the wheel. When dressing, the graphic display shows the path of the dressing diamond as it is dressing. This display connects the operator to the machine in a comfortable way.

After roughing out the form into the wheel the finish dress was executed. The wheel was then inspected for wheel width calibration. A simple offset was used to "tweak" wheel width data. The wheel was then redressed to its correct grinding form. Confirmation inspection was performed and the wheel was ready for production. The entire wheel preparation took 30 minutes.

The punch was roughed out leaving approximately 0.003" of stock on the form. The punch was measured to assure location. This is the only inspection step required. After this inspection the location offset was input and the punch was then completely finish ground to final size.

Using the MeisterPro High Precision CNC Surface Grinder, the processing time was reduced from 8 hours to 2.5 hours. All form and location tolerances were held within 0.000,1".

Unattended grinding and dressing accuracy in combination with an effective "toolroom friendly" programming system makes CNC grinding productive for the tool room grinding.