Programming of CNC Machines. Ken Evans
from available machining libraries.
The Feedrate
Feedrate is defined as the distance the tool travels along a given axis in a set amount of time, generally measured in inches per minute in/min (formerly known as IPM) for milling or inches per revolution in/rev (formerly known as IPR) for turning. This factor is dependent upon the selected tool type, the calculated spindle speed, and the depth of cut. Refer to the Machinery’s Handbook and cutting tool manufacturer data for the chip load recommendations and review the formula below that is necessary to calculate this aspect of the metal-cutting operation.
F = R × N × f
where:
F = Feed in in/min or mm/min
R = r/min calculated from the preceding formula
N = the number of cutting edges
f = the chip load per tooth recommended from the Machinery’s Handbook
The Depth of Cut
The depth of cut is determined by the amount of material to be removed from the workpiece, cutting tool flute length or insert size, and the power available from the machine spindle. Always use the largest depth of cut possible to ensure the least effect on the tool life.
Cutting speed, spindle speed, feedrate, and depth of cut are all important factors in the metal-cutting process. When properly calculated, the optimum metal-cutting conditions will result. Refer to the Machinery’s Handbook, tool and insert ordering catalogs, and online applications from the tool and insert manufacturers for more information on recommended depths of cut for particular tooling.
Certain steps must be followed in order to produce a machined part that meets specifications given in an engineering drawing or blueprint. These steps need to be organized in a logical sequence to produce the finished part in the most efficient manner. Before machining begins, it is essential to go through the procedure called process planning. The following are the steps in the process:
1. Study the engineering drawing or blueprint.
2. Select the proper raw material or rough stock as described in the engineering drawing or blueprint.
3. Study the engineering drawing or blueprint and determine the best sequence of individual operations needed to machine the required geometry.
4. Transfer the information onto planning charts.
5. While the part is still mounted on the machine, use in-process inspection to check dimensional values as they are completed.
6. Make necessary corrections and deburr.
7. Perform a 100% dimensional inspection when the part is finished and log the results of the first article inspection on the quality control check sheet.
8. Take corrective action if any problems are identified.
9. Begin production.
Planning Documents
An engineering drawing or blueprint may be thought of as a map that defines the destination. This destination is the end product. The roads available to get to this destination may be numerous. We do not start the trip without first determining what the destination is and how we are going to get there.
Planning sheets resemble the required path to the destination. They are written descriptions of how to get there (to the end product). The following are descriptions of sample planning documents.
The Engineering Drawing or Blueprint
The information given on the engineering drawing or blueprint will include the material, overall shape and the dimensions for part features (Figure 1-7). The geometry determines the type of machine (mill or lathe) to be used to produce the part. By studying the engineering drawing or blueprint, material and operations (drilling, milling, boring, etc.) can be identified. The tools and work holding method can also be determined. Occasionally, the geometry will require multiple machines to manufacture the part, and thus additional operations will be necessary.
Figure 1-7 Machined Part Engineering Drawing
Chart 1-1Process Planning Operation Sheet
| Date | Prepared By | ||
| Part Name | Part Number | ||
| Quantity | Sheet ___of ___ | ||
| Material | |||
| Raw Stock Size | |||
| Operation Number | Machine Used | Description of Operation | Time |