Machining support and method for bipolar plates of electrolytic cell stacks

Abstract

The invention relates to the construction of certain parts of an electrolysis cell stack and to a tool designed to support these parts while they are being machined. The tool according to the invention is characterised in that there is a double plate support by means of which it is not necessary to turn the blank during machining.

Description

Technical Field

[0001] This invention relates to the technical field of dihydrogen electrolysis, and more specifically to certain parts of an electrolytic cell stack. More precisely, this invention relates to the design of certain parts of an electrolytic cell stack, and tools designed to support such parts during the machining of these parts. Background Technology

[0002] Membrane electrolysis devices typically consist of a stack of electrolytic cells (called an electrolyzer stack) within which the water electrolysis reaction takes place. These electrolytic cells are electrically connected in series and fluidly connected in parallel. (Reference) Figures 1 to 3The electrolytic cell 10 sequentially includes a bipolar plate 11, a space 125 enclosed by a flow field material mesh (or simply flow field material) 12, a first electrode 131 (in this case, the cathode), a membrane 14, a second electrode 132 (i.e., the anode), a second space 125 enclosed by the flow field material mesh 12, and a second bipolar plate 11. The space enclosed by the flow field material 12 (sometimes also called the electrode chamber) is designed for the circulation of electrolyte and electrolytic gas, and by means of the circulation of the electrolyte fluid, reactants (water and hydroxide ions) reach the surfaces of electrodes 131 and 132. The flow field material 12 is typically made of metal and provides a low resistivity path for the current between each bipolar plate 11 and its adjacent electrode 131 or 132. Electrodes 131 and 132 are typically made of doped metal (e.g., nickel), but other conductive metals may also be used. Membrane 14 (also called a diaphragm or porous diaphragm) ensures electrical isolation between the two electrodes 131, 132 and the transport of protons or hydroxide ions from one electrode to the other, while remaining impermeable to the electrolytic gas. The bipolar plate 11 (also called a current collector) functions to provide current and remove gas from the electrolytic cell 10. Therefore, the material of the bipolar plate 11 must have a sufficient level of electrical conductivity and good chemical inertness relative to the fluids (electrolyte, acid, gas) present in the electrolytic cell 10. Most commonly, the bipolar plate 11 is made of graphite, conductive composite materials, or metals (e.g., stainless steel). The bipolar plate 11 is typically provided with ribs or undulations to facilitate gas removal. Electrolyte (alkaline aqueous solution) from feed line 15 is introduced into space 125 through feed opening 121 in flow field material 12, while the resulting electrolyte / gas mixture is extracted from space 125 through a second opening 1221 or 1222 made in flow field material 12 for extraction. With space 125 arranged between bipolar plate 11 and cathode 131, the electrolyte / gas mixture extracted through extraction opening 1221 consists essentially of gaseous dihydrogen (H2), and the mixture is removed in extraction line 161. With space 125 arranged between anode 132 and bipolar plate 11, the electrolyte / gas mixture extracted through extraction opening 1222 consists essentially of gaseous hydrogen peroxide (O2), and the mixture is removed in extraction line 162. Extraction lines 161 and 162 transport the electrolyte / gas mixture to separate degassing devices (not shown) to recover dihydrogen and hydrogen peroxide, respectively. In space 125, electrodes 131 and 132 abut against bipolar plate 11, or a metal mesh (preferably a nickel mesh) is placed between bipolar plate 11 and electrodes 131 and 132.

[0003] Therefore, the electrolytic cell stack includes such a stack of electrolytic cells 10, with the bipolar plate 11 at the end of the first electrolytic cell 10 forming the starting point of the next electrolytic cell 10. Thus, the bipolar plate 11 of the first electrolytic cell 10 (upstream of the next one) is at a higher potential than the bipolar plate 11 of the second electrolytic cell 10 (downstream of the previous one), and therefore its surface in contact with the space 125 adjacent to the cathode 131 functions as the anode 132. Conversely, the surface of the bipolar plate 11 in contact with the space 125 adjacent to the anode 132 functions as the cathode 131.

[0004] Within the electrolytic cell stack, components in contact with the electrolyte are exposed to a particularly corrosive environment and can quickly become unusable due to significant corrosion. Furthermore, any surface roughness or defects in these components are potential sources of gas leakage, particularly dihydrogen. These two problems are addressed by electrolytically plating these parts with nickel. However, this electrolytic nickel plating requires that the components be perfectly machined.

[0005] Among components exposed to such conditions, bipolar plates are particularly important in terms of their key role in the operation of the electrolytic cell stack. Therefore, the nickel layer deposited on the bipolar plates must be completely homogeneous. To this end, the bipolar plates are machined to achieve the most perfect surface possible (smooth, without roughness). This machining is performed by milling and / or turning an unfinished part (called a blank). The blank is typically cut from a blank. The blank is placed flat on a support so that the machining tool can access the upper surface of the blank (on the side opposite the support). After the accessible surfaces of the blank have been machined, the blank is flipped on the support so that the machining tool can access the other side of the blank. This conventional technique is extremely time-consuming and difficult for operators who must flip the blank in hazardous environments.

[0006] Therefore, it is desirable to provide a solution for machining blanks intended to form bipolar plates, which allows for rapid machining of parts while avoiding the difficulties and dangers associated with blank flipping operations. Summary of the Invention

[0007] The purpose of the invention disclosed in this patent application is to solve this technical problem. To achieve this, a first aspect of the invention proposes a machined support comprising a turntable, an auxiliary table, and a support member. The turntable has a rotation axis, and the auxiliary table is arranged on the turntable in a plane orthogonal to the rotation axis of the turntable. The support member is used for one or more blanks and includes a lower plate and an upper plate arranged in mutually parallel planes orthogonal to the rotation axis of the turntable. The machined support member according to the invention has the following features:

[0008] - The auxiliary platform is equipped with multiple connecting devices, which are used to cooperate with the connecting devices of the lower plate of the support.

[0009] - Multiple zero points are set on the top of the auxiliary station;

[0010] - The lower and upper plates of the support are connected by a cylinder with a variable height, and one of the two plates can be translated relative to the other plate along the axis of the turntable; for example, the cylinder can be centrally located and coaxial with the axis of the turntable.

[0011] - The upper plate is provided with a plurality of internal fixed bearings distributed around its perimeter, each of which is provided with an internal clamping cylinder; the internal clamping cylinder body enables the workpiece to be machined to be held in a neutral position and also serves to prevent vibration.

[0012] - The lower plate is provided with multiple external fixed bearings distributed around its perimeter, and each of these external fixed bearings is provided with an external clamping cylinder.

[0013] The blank to be machined according to the present invention is generally made of steel or its alloy and is cut from a blank, but may also be forged or rolled and then welded. The blank to be machined can have any shape and is generally in the form of a ring, the outer diameter of which can be between 700 mm and 2500 mm, and the inner diameter of which can be between 500 mm and 2200 mm, wherein the thickness is between 7 mm and 20 mm.

[0014] An auxiliary table is a support that receives a machining support, the position and dimensions of which are fully known, thus allowing for the creation of a very precise reference for the machining support. The auxiliary table is often referred to as a "zero-point interface." The auxiliary table of this invention can have various configurations. Typically, the auxiliary table has a circular shape corresponding to a turntable and can be attached there without involving manual connection or adjustment; in other words, the auxiliary table enables "plug-and-play" replacement of machine supports.

[0015] Compared to prior art devices (e.g., known from documents FR3099072, FR2950276, FR3078911), which at most include a support for the workpiece, the device according to the invention includes a support comprising two plates. This particular configuration allows for three operating positions of the machining support: a first so-called upward position dedicated to a first machining operation by means of an upper plate movable relative to a lower plate; a second so-called downward position dedicated to a second machining operation by means of a fixed lower plate; and a third so-called intermediate position for transferring the workpiece to one or more of the machining positions. The transfer of the workpiece from the upper plate to the lower plate (and vice versa) can be fully automated by means of the vertical movement of the upper plate along the axis of rotation of the turntable by means of a central cylinder. The availability of the upward and downward positions is advantageous because it allows for machining of the first end of the workpiece on both sides without obstruction by the upper plate, and allows for machining of the two sides of the second end of the workpiece on both sides without obstruction by the lower plate, without having to perform a workpiece flipping operation. Prior art also includes documents DE-A1-102008037145 and EP-A1-1525944, which describe devices, in particular, without auxiliary tables. Such devices do not allow for continuous machining of both ends of the workpiece.

[0016] According to a preferred embodiment of the invention, the diameter of the circle defined by the rotation of the auxiliary stage about the axis of rotation R is between 1200 mm and 2500 mm.

[0017] According to another advantageous embodiment, the connecting device between the auxiliary platform and the lower plate of the support consists of pins that mate with holes. Advantageously, the auxiliary platform is provided with pins that mate with holes in the lower plate of the support.

[0018] According to an advantageous embodiment of the invention, the auxiliary platform is provided with at least 5 zero points, preferably at least 10 zero points. The number of zero points is arranged such that a limiting holding force (depending on the mass and dynamic range involved) can be achieved, with one zero point located at the center of the auxiliary platform. This point helps ensure precise positioning between the auxiliary platform and the support.

[0019] According to an advantageous embodiment of the invention, the cylinder is equipped with a protective shell to prevent damage to the cylinder from chips generated during the machining of the workpiece. This cylinder can be centered and coaxial with the axis of the turntable.

[0020] According to another preferred embodiment of the invention, the lower plate is fixed, and the upper plate is movable relative to the lower plate. In particular, the upper plate can be translated along the rotation axis of the turntable.

[0021] According to another preferred embodiment of the invention, a plurality of external fixed bearings are regularly distributed around the periphery of the lower plate. According to another preferred embodiment of the invention, a plurality of internal fixed bearings are regularly distributed around the periphery of the upper plate. In other words, for both the lower and upper plates, the fixed bearings are distributed at regular intervals and at angles around the periphery of the plates.

[0022] According to an advantageous variant of the invention, the upper plate is provided with a vibration damping device, preferably a radial vibration damping device and an axial vibration damping device. Advantageously, a clamping cylinder is arranged on the axial vibration damping device. In this way, the blank can be pressed onto the vibration damping device by the cylinder.

[0023] According to a second aspect of the present invention, the present invention relates to a machining method.

[0024] According to the present invention, the method comprises the following steps performed in sequence:

[0025] a) Provide machined support components as defined above;

[0026] b) Position the upper plate upward and open all internal clamping cylinders;

[0027] c) The blank is placed on at least two, preferably at least three, internal fixed bearings on the upper plate, which center the blank by the expansion of the inner cylinder, thus holding the blank in place by pressure;

[0028] d) Close the inner clamping cylinder on the inner fixed bearing of the upper plate;

[0029] e) Open the external clamping cylinder on the outer fixed bearing of the lower plate;

[0030] f) Machining the first end of the blank;

[0031] g) Lower the upper plate to the downward position so that part of the machined blank rests on the outer fixed bearing of the lower plate;

[0032] h) Open all the inner clamping cylinders on the upper plate, and optionally deactivate all vibration damping devices and their cylinders, if present.

[0033] i) Close the external clamping cylinder of the lower plate;

[0034] j) Machining the second end of the blank on the side opposite to the first machining end;

[0035] k) Open the outer clamping cylinder of the lower plate;

[0036] l) Open all the inner clamping cylinders of the upper plate so that the machined blank rests on the inner fixed bearing of the upper plate;

[0037] m) Raise the upper plate to the upward position;

[0038] n) Take out the machined blank.

[0039] According to a specific embodiment of the present invention, the blank is a bipolar plate.

[0040] Because the method ends when the upper plate is in the upward position and all the internal clamping cylinders are open, the machining support is ready to receive the new blank so that it can be machined without any time delay.

[0041] Advantageously, step c) is performed by a robot. Preferably, the robot moves away from the machining area before machining step f) begins.

[0042] Advantageously, steps h) and i) can be performed simultaneously.

[0043] According to an advantageous embodiment, a robot is used for the step of removing the machined bipolar plate.

[0044] Advantageously, machining steps f) and / or j) are performed simultaneously on both faces of the end of the machined blank.

[0045] According to an advantageous embodiment, machining can be performed using a machining tool, such as the machining tool described in French patent application FR23 / 13 027 filed in the name of the same applicant company. Attached Figure Description

[0046] The invention will now be described with reference to the accompanying drawings, which serve no purpose other than to illustrate the invention. These drawings schematically represent:

[0047] [ Figure 1 ] Figure 1 It is an electrolytic cell based on existing technology;

[0048] [ Figure 2 ] Figure 2 It is a flow field material based on existing technology;

[0049] [ Figure 3 ] Figure 3 It is a stack of existing electrolytic cells;

[0050] [ Figure 4 ] Figure 4 It is a machined support component according to the present invention;

[0051] [ Figure 5 ] Figure 5 It needs to be machined to provide blanks for bipolar plates;

[0052] [ Figure 6] Figure 6 This is the first machining stage;

[0053] [ Figure 7 ] Figure 7 This is the second machining stage;

[0054] [ Figure 8 ] Figure 8 It is a bipolar plate after machining. Detailed Implementation

[0055] Figure 4 This illustrates a machining support 200 according to the invention. The machining support 200 includes a turntable 400, an auxiliary table 300, and a support 201. The turntable has a rotation axis R, and the auxiliary table is arranged on the turntable 400 in a plane orthogonal to the rotation axis R. The support is for a workpiece 170. Figure 5 The diameter of the circle defined by the rotation of the auxiliary platform 300 about the axis of rotation R will be between 1200 mm and 2500 mm. The support member 201 includes a lower plate 500 and an upper plate 600, which are arranged in mutually parallel planes orthogonal to the axis of rotation R. A plurality of connecting devices 301 are provided on the upper part of the auxiliary platform 300, which cooperate with the connecting devices 501 of the lower plate 500 of the support member 201. Figure 4 In this configuration, the connecting device consists of three pins 301 on the auxiliary platform 300, which engage with an equal number of holes 501 on the underside of the lower plate 500 of the support member 201. Therefore, the support member 201 can be removably connected to the auxiliary platform 300. The support member 201 and the auxiliary platform 300 include connecting devices for attaching pneumatic and hydraulic feed sources (not shown). According to a variant of the invention, these connecting devices for attaching the feed sources can be connecting devices 301 and 501. A plurality of zero points 302 are provided on the upper surface of the auxiliary platform 300. The upper surface of the auxiliary platform 300 has been shown as having ten zero points 302, one of which is located at the center of the auxiliary platform 300.

[0056] The lower plate 500 and upper plate 600 of the support member 201 are connected by a cylinder 401, the height of which is variable. The lower plate 500 is fixed, and the upper plate 600 is movable relative to the lower plate 500. Here, the cylinder is centered and coaxial with the axis R. The central cylinder 401 is protected by a protective shell 402, which prevents machining chips from damaging the central cylinder 401.

[0057] The lower plate 500 is provided with a plurality of external fixed bearings 502 distributed at regular intervals around its periphery, and each of the external fixed bearings 502 is provided with an external clamping cylinder 503. Similarly, the upper plate 600 is provided with a plurality of internal fixed bearings 601 distributed at regular intervals around its periphery, and each of the internal fixed bearings 601 is provided with an internal clamping cylinder 602.

[0058] It can also be seen that the upper plate 600 is equipped with a radial vibration damping device 603 and an axial vibration damping device 604. The clamping cylinder 602 is arranged on the axial vibration damping device 604.

[0059] Figure 5 The blank 170 is shown to be machined. The blank 170 has a portion referred to as the first end 171 and another portion on the opposite side, referred to as the second end 172. These two portions 171 and 172 are separated by a stop distance 175, which is set by the operator according to the machining requirements of the bipolar plate 11. The bipolar plate 11 machined from the blank 170 is shown in transparent form. Figure 8 The fully machined bipolar plate 11 is shown.

[0060] Now we will rely on Figure 6 and Figure 7 To describe a method for machining bipolar plates 11 from blanks 170 using the aforementioned machining support 200.

[0061] By activating cylinder 401 and opening all inner clamping cylinders 602, the upper plate 600 is moved into the upward position, and the machining support 200 is ready to receive the blank 170.

[0062] The blank 170 is then placed on at least two, preferably at least three, inner fixed bearings 601 of the upper plate 600. The inner fixed bearings 601 center the blank 170 by matching the inner diameter of the blank with the diameter of the fixed bearing. Thus, the blank 170 is stabilized in the machining support 200 by its own weight. The blank 170 can be placed by means of an automated machine or robot (not shown). The inner clamping cylinders 602 on the inner fixed bearings 601 of the upper plate 600 are then closed. The outer clamping cylinders 503 on the outer fixed bearings 502 of the lower plate 500 are also opened.

[0063] The first end 171 of the blank 170 is then machined as far as the stop line or distance 175. Machining can be performed by any machining tool 700 (e.g., a roughing end mill). Both accessible surfaces 173 and 174 of the blank 170 can be machined simultaneously.

[0064] Once the first portion 172 of the blank 170 has been machined, the upper plate 600 is lowered back to the downward position, for example by disabling the cylinder 401 that lowers under its own weight, so that the partially machined blank 170 now rests on the outer fixed bearing 502 of the lower plate 500. It is advantageous to ensure that the upper plate 600 has indeed been lowered back to the downward position before proceeding to the next step. Therefore, a second or a few seconds can be waited to avoid any processing errors.

[0065] Then open all the inner clamping cylinders 602 of the upper plate 600 and deactivate all vibration damping devices 603, 604 and their inner clamping cylinders 605. Then close the outer clamping cylinder 503 of the lower plate 500.

[0066] The second end 172 can then be machined on the side opposite to the first end 171 of the blank 170 that has just been machined. Machining can be performed by any machining tool 700 (e.g., a roughing end mill). Both accessible surfaces 173 and 174 of the blank 170 can be machined simultaneously.

[0067] At this stage, after the machining operation, the thickness of the bipolar plate 11 is less than the thickness of the blank 170 initially placed on the machining support 200. For this reason, in order to avoid stress in the bipolar plate 11, the bipolar plate rests on the inner clamping cylinder 602 arranged on the upper plate 600.

[0068] Open the outer clamping cylinder 503 of the lower plate 500, and then open all the inner clamping cylinders 602 of the upper plate 600, so that the machined bipolar plate 11 is now resting on the inner fixed bearing 601 of the upper plate 600. Before removing the machined bipolar plate 11, raise the upper plate 600 back to the upward position by activating cylinder 401.

[0069] Because the method ends when the upper plate 600 is in the upward position and all the inner clamping cylinders 602 are open, the machining support 200 is ready to receive the new blank 170 for machining without any time delay.

[0070] Therefore, the bipolar plate 11 can be machined without having to perform the step of flipping the blank 170.

[0071] Figure Labels

[0072] 10 Electrolytic Cells

[0073] 11 Bipolar plates

[0074] 12 Flow Field Materials

[0075] 121 Electrolyte inlet opening

[0076] 1221 Extraction opening for electrolyte / dihydrogen mixture

[0077] 1222 Extraction opening for electrolyte / hydrogen peroxide mixtures

[0078] 123 Opening flared section

[0079] 125 Space

[0080] 131 Electrode (Cathode)

[0081] 132 Electrode (Anode)

[0082] 14 Membrane

[0083] 15 Electrolyte feed line

[0084] 161 Extraction line for electrolyte / dihydrogen mixture

[0085] 162 Extraction line for electrolyte / hydrogen peroxide mixture

[0086] 170 blank

[0087] 171 The first end of the blank

[0088] 172 The second end of the blank

[0089] 173 The top of the blank

[0090] 174 The bottom of the blank

[0091] 175 Stop distance

[0092] 200 machined support parts

[0093] 201 Support for blanks

[0094] 300 auxiliary stations

[0095] 301 Connecting device (pin)

[0096] 302 Midnight

[0097] 400 turntable

[0098] 401 cylinder

[0099] Protective casing for cylinder 402

[0100] 500 lower plate

[0101] 501 Connecting device (hole)

[0102] 502 External Fixed Bearing

[0103] 503 External clamping cylinder

[0104] 600 on board

[0105] 601 Internal Fixed Bearing

[0106] 602 Internal Clamping Cylinder

[0107] 603 Radial Vibration Damping Device

[0108] 604 Axial Vibration Damping Device

[0109] 605 Internal Clamping Cylinder

[0110] 700 Machining tools.

Claims

1. A machined support member (200), the machined support member comprising: a) A turntable (400) having a rotation axis R; and b) Support (201) for one or more blanks (170); in, - The support member (201) includes a lower plate (500) and an upper plate (600), the lower plate and the upper plate being arranged in mutually parallel planes orthogonal to the axis of rotation R; - The lower plate (500) is provided with a plurality of external fixed bearings (502) distributed around its periphery, and each of the external fixed bearings (502) is provided with an external clamping cylinder (503); and - The upper plate (600) is provided with a plurality of internal fixed bearings (601) distributed around the periphery of the upper plate (600), and each of the internal fixed bearings (601) is provided with an internal clamping cylinder (602). The machined support is characterized in that it further includes... c) An auxiliary platform (300) arranged on the turntable (400) in a plane orthogonal to the axis of rotation R. - The auxiliary platform (300) is provided with a plurality of connecting devices (301) on its upper part, the plurality of connecting devices being used to cooperate with the connecting devices (501) of the lower plate (500) of the support member (201); - The auxiliary platform (300) is provided with a plurality of zero points (302) on its surface; - The lower plate (500) and upper plate (600) of the support member (201) are connected by a cylinder (401) whose height is variable, and one of the two plates (600) can translate relative to the other plate (500) along the axis R.

2. The machined support member (200) as described in claim 1, wherein, The cylinder (401) is centered and coaxial with the axis R.

3. The machined support member (200) as described in claim 1 or 2, wherein, The diameter of the circle defined by the rotation of the auxiliary stage (300) about the axis of rotation R is between 1200 mm and 2500 mm.

4. The machined support member (200) as described in any one of claims 1 to 3, wherein, The connecting device between the auxiliary platform (300) and the lower plate (500) of the support member (201) consists of a pin (301) that mates with a hole (501).

5. The machined support member (200) as described in claim 4, wherein, The auxiliary platform (300) is provided with a pin (301), which engages with a hole (501) in the lower plate (500) of the support member (201).

6. The machined support member (200) as described in any one of claims 1 to 5, wherein, The auxiliary platform (300) has at least 5 zero points (302), preferably at least 10 zero points (302), with one zero point (302) located at the center of the auxiliary platform (300).

7. The machined support member (200) as described in any one of claims 1 to 6, wherein, The cylinder (401) is equipped with a protective shell (402).

8. The machined support member (200) as described in any one of claims 1 to 7, wherein, The lower plate (500) is fixed, and the upper plate (600) is movable relative to the lower plate (500).

9. The machined support member (200) as described in any one of claims 1 to 8, wherein, The plurality of external fixed bearings (502) are regularly distributed around the periphery of the lower plate (500).

10. The machined support member (200) as described in any one of claims 1 to 9, wherein, The plurality of internal fixed bearings (601) are regularly distributed around the periphery of the upper plate (600).

11. The machined support member (200) as described in any one of claims 1 to 10, wherein, The upper plate (600) is provided with vibration damping devices (603, 604), preferably radial vibration damping device (603) and axial vibration damping device (604).

12. The machined support member (200) as described in claim 11, wherein, The clamping cylinder (602) is arranged on the axial vibration damping device (604).

13. A method for machining a blank (170), the method comprising the following steps in sequence: a) Provide a machined support (200) as described in any of the preceding claims; b) Move the upper plate (600) into the upward position and open all the inner clamping cylinders (602); c) Place the blank (170) on at least two, preferably at least three, internal fixed bearings (601) of the upper plate (600); d) Close the inner clamping cylinder (602) on the inner fixed bearing (601) of the upper plate (600). e) Open the external clamping cylinder (503) on the external fixed bearing (502) of the lower plate (500); f) Machining the first end (171) of the blank (170); g) Lower the upper plate (600) to a downward position so that a portion of the machined blank (170) rests on the external fixed bearing (502) of the lower plate (500); h) Open all the inner clamping cylinders (602) of the upper plate (600), and optionally deactivate all the vibration damping devices (603, 604) and their cylinders (605), if present. i) Close the outer clamping cylinder (503) of the lower plate (500); j) Machining the second end (172) of the blank (170) on the side opposite to the first machined end (171); k) Open the outer clamping cylinder (503) of the lower plate (500); l) Open all the inner clamping cylinders (602) of the upper plate (600) so that the machined blank (170) rests on the inner fixed bearing (601) of the upper plate (600); m) Raise the upper plate (600) to the upward position; n) Remove the machined blank (170).

14. The method of claim 13, wherein, Step c) is performed by the robot, wherein the robot moves away from the machining support (200) prior to step f).

15. The method of claim 13 or 14, wherein, Steps h) and i) are executed simultaneously.

16. The method according to any one of claims 13 to 15, wherein, The machining step f) and / or step j) are performed simultaneously on both faces of the ends (171, 172) of the machined blank (170).

Images