RU2487779C1 - Plant for making parts by layer-by-layer synthesis - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to powder metallurgy, particularly, to materials intended for production of parts by layer-by-layer synthesis. It may be used in various branches of machine industry. Proposed plant comprises worktable, desk for fritting, mechanism to feed powder onto worktable, device to collect excess powder and powder layers levelling device including carriage with blade displace by drive above worktable surface. Said carriage represents a rectangular structural part with L-like brackets secured to its ends and arranged in two parallel slots made in worktable edges and levelling blade case arranged at its front edge. Sliders are arranged at L-like brackets ends, on guides secured to worktable bottom surface. Worktable is equipped with slot protective devices.

EFFECT: simplified design, reliable laser fritting.

2 cl, 15 dwg

Description

Technical field

The invention relates to technological processes, namely to powder metallurgy, in particular, to the technology of laser layer-by-layer synthesis of complex parts from metallic finely divided powder and can find application in various branches of engineering.

State of the art

Currently, in the aerospace, engineering and other industries, more and more products are manufactured using rapid prototyping technologies. Basically, BP processes consist of the following steps: preparing a geometric image of a three-dimensional object, forming cross sections of the manufactured object, layer-by-layer superposition of these sections in the synthesis process and combining layers of a specific material. BP technologies have obvious advantages: they accelerate the design process with improved development quality (possible errors are eliminated at an early stage); small series of products, spare parts can be manufactured economically and flexibly; manufacturers can respond to market changes with minimal delay and without the risk of high investments.

One of the most promising BP methods is selective laser sintering (SLS) technology, which allows you to create prototypes to evaluate the design and performance of the product, models for the further production process, finished functional products.

Known installation of SLS Sinterstation HiQ ^TM company 3D Systems (USA). Sources of information are: patents US 2006/01190112 A1 and US 2009/0169664 A1, the book "Rapid Prototyping: Principles and Applications" p. 199-213 (authors: S.K. Chua K.F., Leong, CS, Lim) available on the Internet at http://www.google.com/books?id=4OYcyiDUpsQC&lpg=PR4&hl=en&pg=PR7#v=twopage&q&f=false dated 02/29/2012, 3D Systems advertising brochure available on the Internet at http : //www.3dsvstems.com/products/datafiles/sinterstation hiq / datasheets / DS_Sinterstation_HiQ_rev0606.pdf. from 02.29.2012. According to sources, the installation is designed to create products from plastic and metal powders by the SLS method.

The main components of the installation are: a fixed frame on which all other components of the installation are mounted; laser optical system consisting of a CO ₂ laser and a beam delivery system; sintering table on which the creation of the product / products with a vertical displacement drive, powered by an electric motor; two powder feeding devices (located symmetrically to the right and left of the sintering table) with vertical displacement drives powered by electric motors; powder heating devices; a sinter layer making apparatus representing a roller that levels, compacts and removes excess powder. The roller moves along the guides thanks to the electric drive. The workspace in which the product is created has dimensions of 381 mm × 330 mm × 457 mm. Laser power 30 W or 50 W (depending on configuration), maximum scanning speed 5 m / s. The control system includes a mobile remote control and control cabinet, CAD / CAM software. File input in * STL format. Each type of material in the installation has its own mode of operation.

Closest to the proposed invention in technical essence and the achieved result is the installation of Phenix PM250 company Phenix System (France). Sources of information are: site http://www.techbuss.ru/prototipirovanie/sls metod.php dated 02.29.2012 and US patent 7,789,037. According to sources, the Phenix PM250 selective laser sintering machine consists of the following main parts:

- the machine part with the mechanisms and devices included in it;

- a laser with a scanning system;

- control system.

The machine part of the Phenix PM250 installation is made in the form of a box structure with high rigidity for basing all the other nodes. The machine part of the complex includes the following main components and equipment:

- frame

- powder leveling device;

- working platform;

- powder feed device;

- oven;

- gas equipment and cooling;

- electrical equipment.

The frame mounted on the foundation is the base unit. It is a box-shaped structure consisting of square metal pipes. All basic units (furnace, fencing chamber, etc.) are installed on the frame.

The fencing chamber consists of panels fixed outside the frame.

The powder leveling device reciprocates in the horizontal direction due to the electric drive. The main component of the powder leveling device is a roller with a V-neck. The cutout is located along the axis of rotation of the roller. The roller, making reciprocating movements, drags, levels and compacts the powder on the working platform. The roller at the edges is attached to the carriages. The carriages ride on the rolling bearings (sliders) along the rail type guides. Guides are installed on the upper plane of a high-precision plate. Due to this arrangement of the rails, it is necessary to use structurally complex protective devices, as the powder can get into the guides. The upper plane of the high-precision plate is parallel to the plane of the working platform and the plane formed when moving the axis of rotation of the roller. Powder material: any ceramic and metal powders (granule diameter 5-20 microns).

The working platform is fixed at the bottom of the high-precision plate of the powder leveling device. The working platform has the shape of a well, inside which the desktop moves up or down. On the desktop is the "growing" of the product. The table moves on four round guides with the help of a precision ball screw pair. Ball screw pair rotates by an electric motor. Desktop positioning accuracy ± 0.001 mm. The size of the working area: diameter 250 mm, height 300 mm, usable volume 1.5 l.

The powder feed device is attached to the bottom of the high precision plate of the powder leveling mechanism. The powder feeder has the shape of a well, inside of which the powder feeder table moves up or down. The powder feed table is driven on four circular guides using a precision ball screw pair. Ball screw pair rotates by an electric motor. Powder feed table positioning accuracy ± 0.001 mm.

The furnace is fixed on top of a high-precision plate of the powder leveling mechanism. It forms a closed space into which gas can be supplied (argon, nitrogen, etc.). The space in the furnace can be heated up to 900ºС.

Gas equipment and cooling. Gas equipment creates the necessary atmosphere in the furnace (argon, nitrogen, etc.). The unit’s cooling system cools a 50 or 100 W fiber laser (depending on configuration).

The fiber laser is connected to a scanning system that allows you to control the laser beam in two spatial directions. Build speed: 1-10 mm ³ / sec.

The disadvantages of these settings are:

1. The complex design of the powder leveling device, namely the installation of rail-type guides on the upper plane of a high-precision plate. Therefore, the need arises for the use of complex protective elements (corrugations, boxes, etc.) that protect the guides from clogging with powder.

2. The use of an electric drive in a powder leveling device also complicates the design, because you have to use a ball-screw rolling pair, parts securing the electric motor, coupling, etc.

A device for the manufacture of parts by the method of layer-by-layer synthesis is known, comprising a rigid frame, a laser-optical system with a sintering laser optical head, a working chamber with a working table, a container with powder and a powder dosing mechanism. (RF patent for utility model No. 89011, B23F 3/16, 2006)

The device is also equipped with a carriage with a horizontal movement drive. The device is equipped with a hopper for collecting excess powder located in the device plate and made in the form of an opening with a depth of at least 200 mm, equipped with a receiving device with the possibility of its extraction from the hopper.

The mechanism of storage, dosing, transportation and leveling of the powder layer contains a hopper, a vertical knife with a servo drive, and an electric drive. Vertical knives are made in the form of flat plates with a working edge.

The carriage is welded from metal plates and has a rectangular cross section, connected to the servo rod. The carriage along horizontal guides made of parallel metal plates rigidly connected to the frame plate moves the servo.

The device is made in the form of an experimental stand, not intended for mass production, the carriage, made in a rectangular shape in cross section, moves in guides also of rectangular cross section, difficult to manufacture, the guides are not protected from ingress of powder used for sintering, which leads to insufficient reliability in work.

A device for leveling powder layers for sintering parts by layer-by-layer synthesis technology is known, comprising a leveling mechanism made in the form of a cylinder pivotally mounted on a carriage driven by a drive, a mechanism for storing and supplying powder to a work table, a knife fixed on a carriage and equipped with a regulation mechanism. (RF patent for utility model No. 88592, B23F 3/16, 2010)

The cylinder mounted on the carriage moves along the surface of the desktop. At the same time, both the cylinder and the table are not protected from ingress and sticking of the powder, which leads to a decrease in the accuracy and reliability of the device.

The above disadvantages of the plants reduce the reliability of the process of selective laser sintering, and also increase the cost of manufacturing the installation.

SUMMARY OF THE INVENTION

The objective of the invention is to develop a layered synthesis unit for laser sintering of powder materials, which can be used in any industry where there are problems of modeling and rapid prototyping of functional single products of complex shape with unique physical, chemical and / or biological properties.

In addition, the installation must be reliable in operation, have a low cost of manufacture.

This object is achieved by the fact that in the installation for the manufacture of parts by the method of layer-by-layer synthesis, containing a working table, a sintering table, a powder supply mechanism to the working table, a device for collecting excess powder and a device for leveling powder layers, including a carriage with a knife, moved above the surface the desktop using the drive, the carriage, made in the form of a body part of a rectangular shape, is equipped with L-shaped brackets mounted on its ends, placed in two parallel grooves, in filled in the desktop on the sides of its working area, and the leveling knife body mounted on its front edge, while the L-shaped brackets at their ends carry sliders mounted on rails mounted on the bottom surface of the desktop, and the desktop is equipped with devices groove protection.

In addition, in the installation for the manufacture of parts by the method of layer-by-layer synthesis, the groove protection devices are made in the form of endless tapes mounted on rotating drums, mounted on the bottom surface of the working table, passed over the slots and mounted on the ends of the carriage, while the rotating drums are equipped with devices for moving them to adjust the tension of the tapes.

This installation allows you to increase the reliability of its work, reduce costs.

List of figures

The invention is illustrated by drawings, in which:

Figure 1 is a sectional view of the front view of the installation for the manufacture of parts by layer synthesis.

Figure 2 - cross section DD from figure 1.

Figure 3 is a front view of a device for leveling layers of powders.

Figure 4 is a top view of a device for leveling layers of powders.

Figure 5 is a view along arrow A of figure 3.

6 is a section bB with figure 3.

Fig.7 is a cross-section EE of Fig.3.

Fig.8 is a section bb in Fig.4.

Fig.9 is a cross section GG with Fig.4.

Figure 10 - section FJ with Fig. 8.

11 is a cross section ZZ with Fig. 8.

12 is an enlarged local view K of FIG.

13 is a plan view of a high precision plate 22.

Fig.14 is a cross-section MM from Fig.13.

FIG. 15 is an enlarged local view of FIG. 5.

The implementation of the invention.

Installation for the manufacture of parts by the method of layer-by-layer synthesis (hereinafter installation) consists of the following main parts:

- the machine part with the mechanisms and devices included in it;

- a laser with a scanning system;

- control system.

The machine part of the installation is made in the form of a box structure with high rigidity for basing all other nodes. The machine parts of the installation include the following main components and equipment:

- base 1;

- frame 2;

- fencing chamber 3;

- desktop 22;

- a device for leveling the layers of powders 4;

- sintering table 5;

- a mechanism for supplying powder to the desktop 36;

- a device for collecting excess powder 7;

- a working camera 8;

- pneumogas equipment and cooling;

- electrical equipment.

The base 1 (figure 1, figure 2), mounted on the foundation, is the base node. The base 1 is a box-shaped structure welded from square metal pipes. On the basis of 1, the following basic units are installed: frame 2, work table 22, laser 46, pneumatic cylinder 10, etc.

Frame 2 (figure 1, figure 2), a welded box-shaped structure. The frame 2 is installed on the base 1 using screws 102 (figure 2). The frame 2 is welded from metal corners and together with the base 1 forms a power "skeleton" of the installation.

The fencing chamber 3 (Fig. 1, Fig. 2) consists of panels fixed outside the base 1 and the frame 2 with screws. The panels are made of steel sheets. The fencing chamber 3 is necessary to protect all components and equipment of the installation from external influences, such as dust, dirt, etc., as well as for safe operation of the installation.

The working table 22 (Fig. 1, Fig. 2, Fig. 4, Fig. 13) is intended for basing and functioning of such units as: a device for leveling the layers of powders 4, a sintering table 5, a powder supply mechanism to the working table 36, the device to collect excess powder 7, the chamber is working 8. The working table 22 (Fig. 4) is installed on the base 1 with screws 82. The working table 22 (Fig. 13) is a high-precision plate with a large number of grooves and holes. The through hole 29 (Fig. 13) is necessary for passing through, if necessary, the table 38 (Fig. 1), which is part of the mechanism for supplying powder to the working table 36. The through hole 31 (Fig. 13) is necessary for passing through the table if necessary -platform 24, which is part of the sintering table 5. A through hole 33 (Fig.13) is necessary for pouring excess powder into the device for collecting excess powder 7 (Fig.1). The groove 25 (FIG. 13, FIG. 14) has a width of 42 mm and a depth of 1 mm and is made on the upper plane of the working table 22. The groove 25 is necessary so that the tape 23 (FIG. 4) of the powder leveling mechanism 4 slides freely Also, a through groove 15 is made in the groove 25 (Fig. 13, Fig. 14), the width of which is slightly larger than the width of the bracket 21 (Fig. 6). The groove 15 has the length necessary to move the bracket 21 to the working stroke of the carriage 14 (figure 4) 1000 mm long. Through holes 27 (Fig.13) are necessary for the functioning of the protection device of the guides 55 (Fig.4, Fig.5).

A device for leveling the layers of powders 4 (figure 1, figure 2, figure 3, figure 4) is intended for applying and leveling the layers of powder. A device for leveling the layers of powders 4 is located on the upper plane of the working table 22 and contains the main components and parts: carriage 14, leveling knife 16, housing 18, rail type guides 20, an actuator in the form of a pneumatic cylinder 10, guides protection device 55.

The carriage 14 (Fig. 4, Fig. 6, Fig. 9) is made in the form of a rectangular-shaped body part at the ends of which the L-shaped brackets 21 are fixed (Fig. 4, Fig. 6) with screws 88. The brackets 21 have the other end attached to the sliders 19 using screws 87 (Fig.6). Thus, the carriage 14 is mounted on the sliders 19 using the intermediate bracket 21 (Fig.6). Also on the bracket 21 is rigidly fixed frame 52 (Fig.9). During operation of the device for leveling the layers of powders 4, the brackets 21 are moved in the through groove 15 of the working table 22 together with the carriage 14 (Fig.6).

The leveling knife 16 (Fig. 3, Fig. 8, Fig. 9) is intended for gripping, dragging and leveling the powder layers. The leveling knife 16 is made in the form of a metal part of a rectangular shape, one of the sides of which is sharpened at the required angle from 170º to 90º. The leveling knife 16 is mounted in the housing 18 (Fig. 3, Fig. 4, Fig. 9) using screws 84 (Fig. 9). When the device for leveling the layers of powders 4, the leveling knife 16 must move in parallel and at a certain distance relative to the upper plane of the working table 22, all this is achieved by adjusting the position of the leveling knife 16 using screws 85 (Fig. 4, Fig. 9).

The housing 18 (FIG. 3, FIG. 4, FIG. 9) is necessary for securing and moving the knife 16 together with the carriage 14. Since the housing 18 is attached to the carriage 14 using standard screws 86 (FIG. 4), it can always be easily replaced to the leveling roller (or some other device used to level the layers of powders).

The guides 20 (Fig. 3, Fig. 5, Fig. 6, Fig. 8, Fig. 9) of the rail type are mounted on the lower plane of the working table 22 and have the length necessary to ensure the carriage stroke of 1000 mm

The pneumatic cylinder 10 (Fig. 1, Fig. 3, Fig. 4) serves as a source of motive force for moving the carriage 14 per 1000 mm stroke. The front end of the pneumatic cylinder 10 (Fig. 1) is mounted on the working table 22, and the rear end of the pneumatic cylinder 10 is mounted on the base 1. The rod of the pneumatic cylinder 10 (Fig. 9) moves the carriage 14 due to the bracket 12 (Fig. 4, Fig. 9), which rigidly mounted on the carriage 14.

The protection device for the guides 55 (Fig. 4, Fig. 5) protects the guides 20 from the ingress of powder particles and is installed on the lower plane of the working table 22. The protection device for the guides 55 consists of a mechanism for tensioning the tape 56 and tape 23. The installation design provides two guiding protection devices - one device per rail 20.

The mechanism of tension of the tape 56 (Fig. 1, Fig. 5, Fig. 7, Fig. 15) is fixed on the lower plane of the working table 22 with four screws 66 with four washers 67 (Fig. 15) and is necessary to ensure the necessary tension of the tape 23 The main details of the belt tensioning mechanism 56 (Fig. 7, Fig. 15) are: housing 58, axis 60, deep groove ball bearings 62, reel 64, screws 66, washers 67, strap 72, stud 71, nut 74, lock nut 76, frame 52 (FIG. 9, FIG. 10, FIG. 12).

The housing 58 (Fig. 15) is a housing part with grooves 68 within the length of which the housing 58 can move. Also, the housing 58 has landing holes for the axis 60 (Fig.7) and a through hole for mounting the stud 71.

The axis 60 (Fig.7) is installed in the housing 58. On the axis 60 are mounted radial ball bearings 62, on which, in turn, a drum 64 is mounted.

The drum 64 (Fig.7) can rotate in any direction around the axis 60. The drum 64 has a cylindrical shape with a groove on the outer surface under the tape 23 and an inner hole for landing bearings. The dimensions of the drum 64 are selected so that the tape 23 coming off from it clearly falls into the groove 25, i.e. the bottom of the outer groove of the drum 64 coincides in height with the bottom of the groove 25 of the working table 22.

The bar 72 (Fig. 15) is made in the form of a rectangular part and is rigidly fixed on the lower plane of the working table 22. In the bar 72 there is a through hole through which the pin 71 passes.

The stud 71 (Fig. 15) is designed to move the housing 58 together with the drum 64 (Fig. 7). The pin 71 has the shape of a cylinder at one end of which there is a cap of a larger diameter than the body of the pin itself, and a thread is cut at the other end and a place for a wrench is provided. One end of the pin 71 (on which there is a cap) is inserted into the hole in the housing 58, and the other end passes through the hole in the bar 72 and is clamped by the nut 74 and the lock nut 76. Thus, holding the pin 71 from turning with a wrench and rotating the nut 74 at the same time the lock nut 76, the pin 71 will move along its axis and carry the body 58 along with the drum 64. Moving the two bodies 58 together with the drums 64 in opposite directions, you can stretch the tape to the required effort (figure 3). The movement of the housing 58 is provided by the length of the grooves 68.

The tape 23 (Fig. 3, Fig. 7, Fig. 15) slides together with the carriage 14 into the groove 25 of the working table 22 and closes the groove 15 in the working table 22. The tape 23 is a steel tape with a thickness of 0.2 mm and a width 40 mm. The tape 23 is stretched between the reels 64 (Fig. 8) for the best glide in the groove 25. The ends of the tape 23 are attached to the frame 52 (Fig. 10, Fig. 11, Fig. 12) using the clamping plate 50, as well as the screws 53 and the screw 54.

The frame 52 (Fig. 9, Fig. 10, Fig. 12) is rigidly fixed to the bracket 21 and moves together with the carriage 14. The frame 52 has a rectangular shape with a rectangular hole cut inside, sufficient to be worn on the bracket 21. Moving together with the bracket 21, the frame 52 also moves the tape 23, i.e. makes the tape 23 slide into the groove 25. Thus, with the entire working stroke of 1000 mm of the carriage 14, the steel tape slides together with the carriage 14 and at the same time closes the groove 15 from the ingress of powder particles, thereby protecting the guides 20 from premature wear.

The sintering table 5 (Fig. 1, Fig. 2) is fixed on the lower plane of the working table 22 with screws 94 (Fig. 4). Sintering table 5 is intended for sintering layers of powder on it. The casing of the sintering table 5 has the shape of a well of rectangular cross section, inside of which the platform table 24 moves up or down (FIG. 1, FIG. 2). The platform table 24 moves on four circular guides 26 (Fig. 1) using a precision ball screw pair 28 (Fig. 1, Fig. 2). Ball screw pair 28 is rotated by an electric motor 30 (figure 2) through a toothed belt drive 32 (figure 2). The positioning accuracy of the platform table 24 is ± 0.005 mm. The size of the working area: length 300 mm, width 300 mm, height 350 mm. The platform table 24 has the ability to heat up to 100ºC due to the electric heating element 34 (figure 1, figure 2).

The powder supply mechanism to the working table 36 (Fig. 1) is fixed on the lower plane of the working table 22 using screws 92 (Fig. 4). The housing of the mechanism for supplying powder to the working table 36 has the shape of a square well, inside which the table 38 moves up or down (Fig. 1). Table 38 moves on four circular guides 40 (FIG. 1) using a precision ball screw pair 42 (FIG. 1). Ball screw pair rotates by an electric motor. The positioning accuracy of table 38 is ± 0.005 mm. The size of the powder loading zone: length 300 mm, width 300 mm, height 350 mm.

A device for collecting excess powder 7 (figure 1) is mounted on the lower plane of the working table 22 and is a welded structure. The device for collecting excess powder 7 is designed to collect excess powder remaining after applying the next layer to the table platform 24 (figure 1, figure 2).

The working chamber 8 (FIG. 1, FIG. 2) is installed on top of the working table 22. The working chamber 8 is designed to create an enclosed space into which gas can be supplied (argon, nitrogen, etc.). The working chamber 8 is a prefabricated structure consisting of four walls that fit snugly against each other and are pulled together by screws 96 (Fig. 1). In front, the working chamber 8 is closed by a sealed door 11 (Fig.2). The space in the working chamber 8 can be heated up to 300 ° C due to electric heating elements 31 (figure 2).

Pneumogas equipment and cooling. The complex’s pneumatic system (not shown in the figures) purifies the compressed air and supplies air to the pneumatic cylinder 10 that moves the carriage 14 with the knife 16. The gas equipment of the complex (not shown in the figures) delivers inert gas to the working chamber 8. The cooling system of the installation delivers distilled water to the laser 46 (figure 1) and the scanner 48 (figure 1, figure 2).

The fiber laser 46 (FIG. 1) through the optical fiber 49 (FIG. 1) transmits radiation to the scanner 48 (FIG. 1, FIG. 2), which allows controlling the laser beam in three spatial directions. Laser power 200 watts.

Electrical equipment with a control system (not shown in the figures) based on the Windows XP operating system ensures the operation of the installation in automatic mode according to the program. The control system has a touch screen, which is the interface between the installation and the operator. The touch screen is integrated into one of the panels of the fencing chamber 3. The input data of the file are in the * STL, * STEP format. Manufacturing accuracy up to 0.05 mm.

The device operates as follows:

The installation works automatically according to the program.

Prepared powder is loaded into the powder supply mechanism to the working table 36 (Fig. 1), then the powder is heated to the required temperature by electric heating elements 31 (Fig. 2). The product is built in layers, and each layer is calculated by the program according to the data from the * STL file. A device for leveling the layers of powders 4 (FIG. 1) shifts with a knife 16 (FIG. 1, FIG. 3) a layer of powder from the powder supply mechanism to the work table 36 on the platform table 24 (FIG. 1), and racks excess powder into the device to collect excess powder 7 (figure 1). The laser beam 46 (Fig. 1), controlled by the scanner 48 (Fig. 1, Fig. 2), sinteres the powder particles between them along the calculated contour of the section. After sintering the layer, the table 38 (figure 1) rises, and the table platform 24 is lowered by the thickness of the working layer. The entire cycle is repeated until the product is ready. When the product is ready, it is removed from the working chamber 8 (figure 1), and excess powder is removed by shaking or mopping with a special spatula. Product formation can occur in a gas environment (argon, nitrogen, etc.).

Using the proposed device provides an increase in the reliability of the selective laser sintering process due to the simplified design of the device for leveling powder layers. Simplification of the design of the device for leveling the layers of powders is achieved by using steel tape guides as protection, and not, for example, corrugations or protective boxes. Also, a pneumatic cylinder is used as a drive of the device for leveling the layers of powders, which allows you to abandon the ball-screw rolling pair, parts securing the electric motor, coupling, etc.

Claims (2)

1. Installation for the manufacture of parts by the method of layer-by-layer synthesis, comprising a working table, a sintering table, a powder feeding mechanism to the working table, a device for collecting excess powder and a device for leveling the powder layers, including a carriage with a knife, moved above the surface of the working table using a drive characterized in that the carriage is made in the form of a body part of a rectangular shape and is equipped with L-shaped brackets mounted on its ends, placed in two parallel grooves, made in the working roofing on the sides of its working area, and the housing screed blade mounted at its front edge, wherein the ends of L-shaped brackets located slides mounted on rails attached to the bottom surface of the desktop, and desktop protection provided with grooves devices. 2. Installation according to claim 1, characterized in that the groove protection devices are made in the form of endless tapes mounted on rotating drums, mounted on the lower surface of the working table, passed over the slots and mounted on the ends of the carriage, while the rotating drums are equipped with devices for moving them to adjust the tension of the tapes.

Images