First you must ensure that all elements being measured can be accessed by the styli.
It must be possible to position the workpiece firmly on the support so that it cannot be deformed or moved.
Your workpiece should not be seated too tight or too loose. Your workpiece will then still be able to “function” regardless of temperature fluctuations, i.e. react without becoming overtensioned.
Clamping fixtures are the ideal solution for part inspectors who must position and stabilize workpieces for precise results. This quick reference guide explains the basics and terminology; specific solutions for applications such as contact, optical and CT measurement will be examined in the coming articles.
Exact, stable positioning before and during the measurement is decisive. Even changes in the μm range affect the results. Workpieces are either clamped or held depending on the situation. Here is the difference between the two:
Clamping: Temporary securing of a part in a defined orientation and position using force closure. Clamping fixtures are used in measurement technology whenever probing forces take effect or machine movements can influence the position of the workpiece (e.g. active damping).
Holding: Bringing a body into a defined position without exerting force. Holding devices are usually used in optical measurement technology or for CT applications (see VDI Directive 2860).
A system or body can move in six different ways: in three directions (translationally) and about three axes (rotationally). A total of six degrees of freedom therefore exist.
If one or more degrees of freedom of a workpiece is/are not fixed, this is referred to as "static underdetermination". This always must be avoided in measurement technology.
If all six degrees of freedom of a workpiece are fixed, this is referred to as "static determination". Always strive for static determination if you work with stable, nondeformable workpieces in measurement technology.
Static overdetermination occurs if multiple adjustment planes are assigned to a single reference plane in one direction. Static overdetermination is used if "soft" workpieces made of e.g. sheet metal or plastic are deformed prior to assembly, e.g. so that they correspond to the installation situation. You can look forward to future items featuring special fastening solutions for contact, optical and X-ray applications.
Using the center-clamping vises, the widest variety of workpieces can be securely clamped. Due to the clamping pins and changeable jaws, this can be achieved flexibly even for a wide range of different geometries. They are especially easy and flexible to use: Whether on pallets, grid plates or machine tables (thread size M6 or larger) - the vise fits the widest variety of measuring machines and, due to its center clamping, can be used even on rotary tables.
OmniFix vises also can be used for optical applications. Please note here that vises with black anodized material should be used to avoid reflections. Another advantage of the vises is that they guarantee optimal accessibility in the Z axis and are therefore well suited to optical applications.
For CT applications, make sure that the clamping fixtures only have a low density, so that there is a substantial difference between them and the part. It also is important that the material is translucent. The foam blocks with steel holder ensure the user that his workpiece will be held securely without influencing the measurement.