Engineering Metrology

Question 1

What is a Co-ordinate measuring machine

Answer 1

CMM is an electromechanical system designed to perform co-ordinate metrology

CMM uses a probe that can be positioned in three dimensions relative to the surfaces of a workpiece

x, y, and z coordinates of the probe can be accurately and precisely recorded to obtain dimensional data about the part geometry

Question 2

What are the 2 types of Co-ordinate systems?

Answer 2

Machine Co-ordinate System
With the co-ordinates of x-y-z referring to the machine’s motions

Part Co-ordinate System
Where the 3 axes relate to the datums or features of the workpiece

Question 3

What are the methods of operating and programming CMMs ?

Answer 3

Manual drive – operator physically moves the probe along the machine’s axes to make contact with the part and record measurements

Motor- driven and computer-assisted data processing – operator uses joystick or similar to operate electric motors moving the probe

Direct computer control (DCC) – operates like a CNC machine tool and the motorised movements are controlled by a computer (manual leadthrough method, off-line programming)

Question 4

Applications of CMM?

Answer 4

• Post-process (off-line) inspection
• Elimination of repetitive manual inspection
• Elimination of multiple inspection setups
• Complex part geometry or high part variety
• Repetition of works orders
• Reverse Engineering

Question 5

Advantages of CMM?

Answer 5

Complex measurements for linear, circular and angular measurements; can also check geometric features

Flexibility – inspection of a variety of different part configurations with minimal change-over times

Reduced inspection time – allows early warnings of dimensional errors and helps to reduce number of rejects

Avoidance of multiple setup – single setup ensures higher accuracy and higher throughput

Reduced operator errors due to automation (TTPs eliminate operator feel, calculations are performed by the computer)

Greater inherent accuracy and precision

CMM are compatible with CIM methodologies and can be easily incorporated into manufacturing systems

Storage of measurement data for subsequent statistical analysis