Inspection Methodology:

First Article & Batch Processing

A new component must be completely machined through all its operations and inspected prior to any batch processing. Manufacturing processes cannot be verified until completion of a First-Article. It's better to use the time to completely verify a proposed process rather than losing material and lead-time over a failed process. First-Artical inspections at each operation is not a sufficient inspection method.

In-Process Probing

Inspecting critical features of a component is ideally done while in the machine with a probe system. A minimal number of inspection points should be run as a sub-program at a pre-determined frequency in order to avoid common process-related deficiencies. Such an inspection procedure should attribute no more than 2% of the component's cycle time.

End-of-Process CMM Probing

CMM inspection is intended to be a complete component inspection procedure of all manufacturing print features that can be checking with the CMM.

Frequency

The customer generally determines how frequent a CMM or In-Process inspection is performed for a particular batch of components. If the customer does not specify the inspection frequency, the manufacturing and quality engineers should collaborate and determine an efficient inspection frequency. Specific features may be inspected at more regular frequencies than others. Such a variable frequency method should be implemented into in-process probing programs using increment-based control variables and macros.

Milling Methodology:

Roughing Techniques

Shoulder Profiling: Shallow internal and external roughing in all materials; capable of inducing high stress and vibrations . All combinations and variations of axial/radial engagement may be used. Machine, workpiece, and tool rigidity/type/condition will govern the limits of tool engagement. Shoulder profiling generally sets a baseline for the establishment of tool-life.

High-Feed: Shallow internal and external roughing in tough materials; induces high stress and vibrations on machine, workpiece, and tool. Workpiece must be held very secure in all axes. Requires a large amount of spindle horsepower and a very rigid machine. This method is best utilized when requiring at least 60% radial stepover and a small axial depth of cut. Tool life is much better than profiling and plunging in relation to the amount of material removed.

Plunge: Deep internal and external roughing in tough materials; induces less stress and vibrations on machine, workpiece, and tool. Workpiece must be held very secure, especially in Z-axis. Requires a large amount of spindle horsepower. This method is best utilized for lighter machines that are more susceptible to undesirable harmonic vibration. Use the highest number of cutting edges available for the tool as long as chip evacuation does not become a problem. Must evacuate chips from internal pockets with thru coolant or air-blow. When plunging a ramped surface, start at the lowest z-depth and work upwards; otherwise the tool will enter a certer-cutting condition and damage the inserted cutter body. Tool life is generally better than profiling in relation to the amount of material removed.

Surface Feet per Minute (SFM)

SFM refers to the actual cutting speed of a cutter edge. This unit of cutting speed removes all other variables such as tool engagement, number of cutting edges, and cutting methodology. SFM strictly refers to how fast a cutting edge is moving through any given amount or engagement of material. The manufacturer's suggested SFM best reflects the ideal capacity of a cutting edge and where its break-down threshold begins. The cutting edge's material, grade, coating, and geometry determine its SFM capacity. Other factors such as tool engagement, workpiece/tool/machine rigidity, coolant type/pressure, and toolpath methodology influence the usable SFM capacity.

High-Speed Machining (HSM)

HSM refers to when the SFM is so high that heat escapes with the chip rather than into the cutting edge. Most machines are not HSM capable because of a lack of rigidity, spindle speed, and control/servo limitations. HSM generally requires a constant and relatively small radial of engagement on the tool, which reduces the amount of time the cutting edge is engaged with material. To observe the true benefits of HSM a higher axial depth of cut with lower radial engagement is required; this method tends to induce harmonic vibrations in light, undampened, or loose machines. An HSM machine requires a control capable of at least 40-block look-ahead, or otherwise able to read data into memory quick enough to process short-fast moves, be equipped with high performance servos and drives, and be rigid enough to support the particular HSM operation. Once the HSM threshold is meet, tool life and material removal rate dramatically increase. The overall process is a delicate balance of operating outside of the machine's natural harmonics for any given setup and working condition.