Material classification and characteristics of measuring needle lengthening rod

Material classification of needle measuring extension rod:

(1) steel

Needle measuring rod made of non-magnetic stainless steel is widely used in measuring ball/end diameter of 2mm or more, the longest length of 30mm needle. In this range, steel needle measuring rod has been available. * Good stiffness and weight ratio, excellent tolerance of measuring ball, measuring rod and thread, ensure the best rigidity of measuring needle.

(2) Tungsten carbide

The use of tungsten carbide rod is the best choice for small diameter rod or super long rod requiring large rigidity. Small diameter rod is required for measuring needle with ball diameter of 1mm or less, while super long rod can be up to 50mm in length. In addition, weight may become an issue or stiffness may be reduced as the joint between the rod and the body may be deflected.

(3) Ceramics

The stiffness of ceramic needle measuring rod with diameter larger than 3mm and length longer than 30mm is better than that of steel needle measuring rod, but the weight is much lighter than tungsten carbide.

The probe has additional collision protection for the probe because the needle rod will break in the event of a collision.

(4) Carbon fiber

Carbon fiber has many layers. In any case, RenishawGF it can provide the best stiffness characteristics in both stretched and twisted situations (which is very important for measuring needles in star-shaped structures) and very low weight. Carbon fiber is an inert material that combines with a special resin matrix to provide excellent protection in most very harsh machine tool environments.

Length greater than 50mm for measuring needle rod, rigid, high quality, light weight ideal material. It is a kind of high precision strain gauge gauge best measuring needle rod material with excellent vibration damping performance and negligible coefficient of thermal expansion.

Special characteristics of heat-stabilized extension rods

The connecting parts are made of titanium with a positive coefficient of thermal expansion, while the extended rod and tube are made of carbon fiber with a negative coefficient of thermal expansion. The two parts are designed to match, so the carbon fiber is reduced by the same amount during heating as the titanium.

As a result, these elongated rods barely expand even when the temperature changes are 15 to 40 ℃.

In contact scanning applications, the hard measuring ball needs to slide over a variety of surface materials to collect measurement data. In the absence of any lubrication, the shape of the measuring ball changes due to adhesion or wear of the surface material. This can lead to errors in the measurement data.

The degree of variation depends on the characteristics of the ball and the surface material and the distribution of the contact force, scanning distance and contact points on the ball.

No single sphere-measuring material has been found to avoid this phenomenon of common machined surfaces. Ruby is the best measuring ball material for most applications, but there are two cases where it is recommended to use measuring balls made of other materials.

The first case is the application of high-strength scanning aluminum. Because these materials are attractive to each other, a phenomenon called "adhesive wear" causes aluminum on the surface of the part under test to accumulate on the ball. Silicon nitride is a better material for this application.

The second type of application is one that does a high-intensity scan on cast iron. For example, using rubies can become a problem because the interaction between the two materials can cause wear and tear on the surface of the ruby ball gauge. A ball with the wrong oxidation is recommended.

Silicon nitride has similar properties to rubies. This is a very hard and wear-resistant ceramic material that can be machined into high-precision spheres.

It can also be polished to an extremely smooth surface finish. There is no adsorption between silicon nitride and aluminum, so there is no adhesion wear when ruby is used in similar situations. However, silicon nitride has obvious wear characteristics when it is scanned on steel surface, so its application is limited to aluminum workpiece.

Zirconia is a particularly hard ceramic material, with hardness and wear properties close to those of ruby. But its surface properties make it an ideal material for high strength scanning of cast iron workpiece.

The CMM lengthening rod increases the measuring depth by lengthening the distance between the measuring needle and the measuring head. However, due to the reduction of stiffness, the measuring needle lengthening rod will reduce the accuracy of the measuring head. This does not happen with an electronic measuring head because it has a very low trigger force, so it has a very low sensitivity to this error.

As with the selection of needle measuring assembly, the selection of extension rod material is equally important for measurement. Especially in the use of long extension rod, special attention should be paid to the thermal expansion characteristics of the material.