Manufacturing techniques for the test micro styl

As explained in chapter 2, there are several currently available technique capable of manufacturing a stylus system with dimensions below 100 µm. In summary, fabrication of stylus shaft might use the wire electro-discharge grinding (WEDG), and electro-chemical machining (ECM), while one pulse electro-discharge machining (OPED) or available glass micro-sphere technology is used for fabrication of the stylus tip. Therefore, for this project, four variant hybrid manufacturing techniques are used, namely:

Manufacturing technique Type 1: A combination of wire electro discharge grinding (WEDG) and one pulse electro discharge machining (OPED)[58]. The stylus shaft is manufactured by a WEDG process while the stylus tip is directly formed at the end of the stylus shaft using OPED, so creating a monolithic structure. This styli will be referred to as

Type 1 styli (Figure 5.1).

Manufacturing technique Type 2: Assembly of the stylus using an adhesive material to attach a stylus tip sphere on the end of the stylus shaft [76]. The stylus shaft is manufactured using a process similar to that for Type 1 styli and a commercially available micro-sphere made from glass is used as the stylus tip. Styli manufactured using this technique will be referred to as Type 2 styli (Figure 5.2).

Manufacturing technique Type 3: monolithic manufacture technique similar to manufacturing technique in Type 1 styli except that when manufacturing the stylus shaft, an electro chemical machining (ECM) process is introduced after the WEDG process. The ECM process is expected to increase the stiffness of the stylus by improving the surface and geometrical quality of the stylus shaft. The detail of this ECM process is well described in a previous paper [132]. Styli manufactured using this technique will be referred to as

Type 3 styli (Figure 5.3).

Manufacturing technique Type 4: The stylus shaft is made by only ECM process while the stylus tip is added monolithically using OPED. To date, ECM appears to be the promising technique for manufacturing stylus shaft with dimension below than 20 µm. Referred to as

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Type 1 styli and Type 2 styli have been tested previously to investigate their ultimate yield strength [133], while with the enhancement in the experimental setup and procedure,

Type 3 styli and Type 4 styli which are manufactured using new combination of manufacturing techniques, are tested here for the first time and their mechanical characteristics are compared to Type 1 and Type 2 styli. The result from these testing for Type 3 styli and Type 4

styli are vital in understanding the ECM process as it is a promising manufacturing technique in fabricating the stylus system with dimension in sub 10 micrometre.

Figure 5. 1: Type 1 styli – combination of WEDG and OPED manufacturing process

Figure 5. 2: Type 2 styli – Combination of WEDG manufacturing process for stylus shaft and commercial glass sphere for stylus tip

127 Figure 5. 3: Type 3 styli – combination of WEDG and ECM process for stylus shaft and OPED for stylus

tip

128 Table 5. 1: Geometrical dimension and analytical modelling data for the micro- styli manufactured using the variant hybrid manufacturing techniques (type1 to type4). * The value of effective maximum deflection are calculated based on the upper value of effective shaft diameter.

STYLUS GEOMETRICAL DIMENSION ANALYTICAL MODELLING

Stylus Name Stylus Code Effective Shaft

Diameter Stylus Tip Diameter Effective Length Effective Aspect Ratio Mechanical Aspect Ratio Allowable Probing Force Allowable Deflection (Wa) Effective Maximum Deflection* Effective Stiffness lower value upper value lower value upper value (µm) (µm) (µm) (µm) (mN) (µm) (µm) Nm-1 _Nm-1 TYPE 1 1a 0506-1-2 38 44 75 669 9 16 2.04 16 3.1 347 649 2a 0430-4-5 39 46 73 709 10 17 1.9 16 2.6 344 735 3a 0504-1-2 38 46 62 691 11 16 1.4 9 1.9 317 742 TYPE 2 2a 0509-1-2 34 40 68 720 11 20 9.66 16 26 182 361 2b 511-1-2 35 43 90 742 8 20 17 26 38 187 445 TYPE 3 3a 0517-4-5 31 39 49 593 12 16 0.9 7 1.8 188 475 3b 0521-3-4 34 42 77 642 8 16 2.1 18 3.6 249 586 3c 0521-9-10 36 43 73 713 10 18 1.9 16 3.85 235 509 TYPE 4 4a 0602-1-2 15 17 26 156 6 10 0.3 5.5 2.0 45 125 4b 0602-5-6 10 15 21 171 8.4 16 0.2 5 1.3 28 143 4c 0607-2-3 18 25 32 343 11 16 0.4 5.5 1.2 72 215 4d 0602-7 17 18 24 573 23 33 0.24 3.3 2.1 50 115

129 Table 5.1 shows the micro styli that have been manufactured using the four variants of hybrid manufacturing technique and used in the present experiment to examine their mechanical properties. These styli are selected based on their geometrical dimension which obey the design rules for geometrical consideration (discussed in section 3.2) including equation (3.5) in section 3.2.4. However Type 2 styli seem not to obey this equation, because their effective maximum deflection is larger than their allowable deflection. Therefore, to make these styli to obey to this equation, in the following experiments, it will be ensured that the force imparted to them will not exceed the allowable probing force and hence its deflection will not exceed the allowable deflection.

The geometrical dimension (diameter of the stylus shaft and stylus tip) for each of these styli have been measured using optical microscope made from Alicona Imaging GmbH [134]. During this measurement for each stylus, it is noticed that the diameter of the stylus shaft is varied along the effective length of the stylus shaft. Thus, in this work, the diameter is measured at different location of the stylus shaft and the upper and lower results value are recorded in the Table 5.1. Therefore, this upper and lower limits of stylus shaft diameter are used to determine the upper and lower limit of the calculated stiffness from this analytical model. Also, the mean value between the lower and upper value of stylus shaft diameter is used to calculate the mechanical aspect ratio.

The table provide information on the geometrical dimension and analytical modelling calculations for each stylus. Type 4 styli have the smallest geometrical dimension in this set. As required in the Thesis Aim for the characterisation of the stylus with dimension in sub-10 µm, Type 4 styli will be a major focus in this testing. Stylus 4b (stylus code 0602-5-6) has the smallest dimension of the styli while stylus 4d (stylus code 0602-7) has the highest aspect ratio among all the styli. The analytical modelling results are calculated based on the requirement that the stylus tip is contacting a test-workpiece made from the copper. This choice is because, pure copper is a soft material that has unfavourable material properties compared to tungsten and glass [131].

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