Tool Diameter Measurements

In this investigation, the initial tool diameter was measured online on the MAZAK machine by using the tool-setting probe (a physical contact tool-setter). This provided the input needed to start machining.

To provide a more accurate measure, the cutting tool dimension was acquired after machining using the CMM to measure a feature designed for this process [appendix

B]. It can be seen that C1 in H1 was formed using the portion of the cutter that had

undertaken minimal cutting. This hole was thus used as the reference to determine the initial tool diameter. Figure 4.10 represents this procedure and relates to the simple calculation given in equation (4.1). An exaggerated view of the tool wear effects on dimensions is shown for illustration discussion purposes. This was then utilised as the reference diameter for the entire series. It was used to define the diameter of the other holes at different depths. The assumption made was that the difference between diameter may treated as the tool flank wear.

Initial Tool Diameter Di = dnom - (Dnom - Dref) (4.1)

Where; Dnom= Nominal cylinder Diameter = 40 mm, Dref = Reference Diameter (reference point), and dnom= Nominal Tool Diameter =10mm or 16mm

Dref Dnom C1 C2 C3 C4

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It should be noted that dnom may have been set by a tool-setting probe but would still be updated in this manner. In this study, the Dnom was assumed to be 40 mm to start with, and that information was used to assess how much the tool wear has been.

4.4.1 Tool Wear Measurement

This section describes the tool wear measurement method based upon the assessment of the features and the metrology of the components.

After completion of the above-mentioned experiments, the flank wear (VB) of the cutting edge of the tool was adopted as the tool life criteria and measured indirectly based upon shape mapping. In general, when a tool is new, dimensional accuracy will be controllable and thus satisfactory. However, over time, as the tool gets worn out, dimensional accuracy may be reduced. This is particularly true in cases of uneven wear.

In this investigation, the dimension (i.e. diameter) and form (i.e. circularity and cylindricity) of the machined cylinders were assessed for each of the features indicated in the Table 4.3 using the CMM.

In order to operate the CMM, the CAD model was uploaded to the CMM’s controlling computer. From the uploaded file, a programme could be created using the CMM’s programming language. This used the geometries of the design as a reference. A program was then created that enabled the CMM to measure the required features.

The finished workpiece was located within a fixture that allowed for it to be positioned within the CMM. This meant that following tests would also be located in the same position each time.

The measurement process started with the operator using the joystick on the controller to manoeuvre the tip of the probe to follow the commands detailed in Figure 4.11. The reason for this initial operation was to locate its datum points, enabling it to reference the part. The heading at the bottom of Figure 4.11 ‘$$ CNC Alignment $$’ signals the

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beginning of the CMM’s auto-alignment, where these reference datums are determined more accurately.

The CNC alignment process used is performed for each measurement cycle. In this way, every test place is measured using the same initial reference datums, meaning more accurate measurements can be applied.

The next stage was the actual measurement process of the cylinders (C1–C4) in the holes (H1-H8). The probe first moved to the coordinates above the hole to be measured, then proceeded to lower into the hole.

Figure 4.11 CMM commands to the user to establish alignment of the test piece

As detailed in Figure 4.8, each hole was measured in eight positions to establish d1, d2, d3, and d4 for each of the four cylinders. Measurements were taken using a circular scan of the inside of the designated cylinders, and an average diameter was established. Then the tip of the probe ran around the circumference to determine the circularity. After each cylinder was completed the next cylinder 5mm down was measured for a total of 4 cylinders per hole, the programme represented in the Table 4.5 (the whole programme is in Appendix B). Once completed for all 8 Holes, the CMM provided an output for hole diameter directly into the separate excel sheet in the format of Figure 4.12. Figure 4.13 summarise the procedure of utilising CMM to measure one test piece.

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Table 4.5 CMM program

CMM program Meaning P(PArc8)=PATH/ARC,CART,0,0,0,0,0,1,20,0,360,1,0,0

P(PArc9)=PATH/ARC,CART,0,0,-2.5,0,0,1,20,0,360,1,0,0

In Cylinder 1, the two circles at 0.0 and 2.5mm depth have been scaned, and an average diameter was established. P(PArc10)=PATH/ARC,CART,0,0,-5.5,0,0,1,20,0,360,1,0,0

P(PArc11)=PATH/ARC,CART,0,0,-8,0,0,1,20,0,360,1,0,0

In Cylinder 2, the two circles at 5.5 and 8.0mm depth have been scaned and an average diameter was established. P(PArc12)=PATH/ARC,CART,0,0,-10.5,0,0,1,20,0,360,1,0,0

P(PArc13)=PATH/ARC,CART,0,0,-13,0,0,1,20,0,360,1,0,0

In Cylinder 3, the two circles at 10.5 and 13.0mm depth have been scaned and an average diameter was established.

P(PArc14)=PATH/ARC,CART,0,0,-15.5,0,0,1,20,0,360,1,0,0 P(PArc15)=PATH/ARC,CART,0,0,-18.5,0,0,1,20,0,360,1,0,0

In Cylinder 4, the two circles at 15.5 and 18.5mm depth have been scaned and an average diameter was established.

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Part alignment Creates PCS (part coordinate system

Figure 4.13 The flowchart of using CMM to measure the diameter of the holes (one set)

Uploading the CAD file to the CMM’s Controller

The Position of the Workpiece

SameDirection Different Direction

Fixed the Finished Part to a holder

Measured the two Circles to establish average Diameters Control the manoeuvre of the Probe

Output the measurements to an Excel File End No Yes Start I=0 J=0 J=4 I=8 One Hole One Set Move to the Next Position

Yes

Yes No

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The same procedure that utilised to measure the diameter of the four cylinders was used to assess the wear in the bottom cutting edge. The bottom of the hole was measured at three places and an average value was established. In this technique, the P0 ‘reference plane’ was used as a reference point to measure the depth of holes. The depth of the first hole H1 (normally 20 mm) was used as a reference depth for the entire series regarding to tool wear.

The assumption made was that the differece between the reference depth H1 and the other depth may treated as the tool wear in the bottom cutting edges.

After assessing the cylinder diameters of all the holes and calculating flank wear, it was possible to produce plots from which underlying trends could be determined. This process is considered in full in section 5.2.2.