Process Capability

Question 1

What is process capability?

Answer 1

The capability of the manufacturing process to make a part, i.e. Selection of suitable process is based on part requirements and ability of the manufacturing process.

The multitude of the attributes of the parts that can be produced using a manufacturing process denotes it’s capability.

Successive manufacturing processes also contribute to the part’s realisation eg. Coupled

The number of possible combinations can be reduced as some processes aren’t compatible with some materials, some processes cannot be coupled, and some processes are specialised (eg. Superfinishing or roughing).

Question 2

The preliminary selection should be based on multiple criteria such as:

Answer 2

Accuracy aspects (eg. Dimensional/geometrical tolerance, surface quality)

Functionality aspects (eg. Appearance, need of assembly)

Volume of production (eg. Single product, batch or mass production)

Affordable expenditures for tooling and personnel

Process planning (eg. Succession of processes)

Question 3

What are depressions?

Answer 3

The ability of the process to generate cavities with specified radii or curvature

Question 4

What are uniform walls?

Answer 4

The ability of the process to generate walls with specific thicknesses, heights, and thickness-to-height ratios at required tolerances and surface qualities

Question 5

What are captured surfaces?

Answer 5

The ability of the process to generate reentrant surfaces eg. Bottle

Question 6

What is the process capability equation?

Answer 6

Cp = specification (or design tolerance) / process capability (or total process variation)

In other words:

Cp = (usl - lsl)/6(sigma)

Where usl - upper specification limit
Lsl - lower specification limit
6sigma - process variation from -3sigma to 3sigma
Sigma - standard deviation

Question 7

What are enclosed surfaces?

Answer 7

The ability of the process to produce hollow or enclosed surfaces