2016-10-07
Production Management
Course Outline: 1. Introduction 2. Need for Flexible Manufacturing Systems 3. Organizational categories of flexible manufacturing 4. Functional structure of flexible manufacturing system 5. Machining subsystem 6. Tool management 7. Workpiece subsystem 8. FMS logistic system (automated material movement and storage) 9. FMS information system 10. FMS supervising and diagnostics system 11. FMS availability
Flexible Manufacturing Automation (2) 4. Functional structure of flexible manufacturing system 5. Machining subsystem
Wacław Skoczyński room 2.17 B-4, tel. 71 320 26 39
[email protected]
FLEXIBLE MANUFACTURING SYSTEM
4. Functional structure of flexible manufacturing system The main goal of a Flexible Manufacturing System can be formulated as follows: „economically effective part processing by wide part variety, randomly schedule and variable batch size". To achieve this goal, in general case of a complex system, the fallowing should be ensured: • Sufficient inventory of parts and tools, • Automated part moving, • Automated tool movement to and from the processing stations with transfer of tooling data, • Remote distribution to machine control units and actuating of NC programs, • Automated chip disposal, • Automated cleaning of parts, fixtures and pallets on machine tool or in wash-station, • Automated workpiece inspection on machine tool or inspection station (coordinate measuring machine), • If necessary, a main computer and/or DNC system, • In accordance with needs, central monitoring and diagnostics system.
FLEXIBLE MANUFACTURING SYSTEM
TECHNICAL SYSTEM
INFORMATION SYSTEM
FMS STAFF
- material flow - information flow - person flow and intervention interfering
Figure 4.1. The main functional subsystems of a flexible manufacturing system
FLEXIBLE MANUFACTURING SYSTEM
TECHNICAL SYSTEM
INFORMATION SYSTEM
TECHNICAL SYSTEM
TECHNICAL SYSTEM
INFORMATION SYSTEM
FMS STAFF
- material flow - information flow - person flow and interfering
INFORMATION SYSTEM FMS STAFF
- material flow - information flow - person flow and interfering
Machining system
Tool management system
Part management system
Supporting systems
Production planning and control
Data distribution and collection
Energy management system Control system
Auxiliary materials management Chip disposal system
Figure 4.2. Subsystems in FMS technical system
Control technical system
Planning system
Control organization system
Figure 4.3. Components of information system
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Components of information system (1)
Components of information system (2)
The information subsystem realizes functions necessary to control and supervision of processes running in FMS. There can be distinguished from it two main subsystems: data distribution and collection and short-term planning and control of manufacturing process.. The data distribution and collection subsystem ensures: • Storage and retrieval of all data connected with part machining planning and control in flexible system. Therefore, watched must be the condition of each part being machined in a given moment in the system. The matter is, to manage the technological process (together with demand for tools for particular machining operations and suitable NC programs), and to watch the machining course. • Management of tool matrices and tool cycle time expectancy. • Collecting data stored at the machine control unit to maintain a historical maintenance and cumulative run time log. The short-term planning and control subsystem includes managerial and execution functions necessary to ensure coordinated course of part processing, handling and moving in FMS.
Planning system includes, with regard to the actual condition of FMS, tasks connected with loading of the technical system with realization of work-orders released by the system manager. It defines an individual work order to the FMS and describes its station processing sequence. In the control system there may be distinguish two subsystems: the technical and the organizational subsystems. The technical subsystem ensures: • Sending the part programs • Control of part and tool flow (e. g. watching the positions of AGV’s with the aim to avoid collision). • Synchronization of machine tools and transport control, as well as, • Control of particular machine tools. The role of organizational subsystem is on the other hand short-term planning (machine tools operation, using transport means, changing the dispositions in case of failure in working of the system), and run time log. As far as in the conventional manufacturing, the last problem is very often omitted, but in flexible manufacturing systems, its realization is considered as a necessary condition of its operation.
FMS staff subsystem FMS staff subsystem covers the personnel directly engaged in operation of FMS. In many cases in planning of the flexible manufacturing systems it is assumed, that FMS can be operated fully unmanned. This is however possible only during limited period of time (unmanned shift). The work-task of FMS staff sub-system covers: • preparing of parts and tools (building of pallet and fixture assemblies, • loading of parts on pallets, • building up and tear down of tool assemblies, • tool preset, • tool delivery, • tool allocation, • supervision of manufacturing process, • maintaining of all facilities and also in many cases (computer aided) control. It happens namely, that the interference of a man in the process running is necessary, although there is a tendency to minimize the division of work-task among the personnel of the FMS staff. It increases markedly its flexibility, but requires appropriate training of workers so, that they would be able to perform various operations. FLEXIBLE MANUFACTURING SYSTEM
TECHNICAL SYSTEM
INFORMATION SYSTEM
FMS STAFF
Chip disposal
- material flow - information flow - person flow and interfering
Tool delivery system Tool room
CNC machining center 2
CNC machining center 3
Milling machine
Part moving system
Coordinate measuring machine
• Manufacturing installations according to the requirements of FMS; provided with standard part and tool interfaces, • Feeding system for machined parts; equipped with means of part transportation, handling and storage, • Feeding system of machine tools being in the system, with tools, together with necessary means of transport thereof, handling and storage, • Control and supervision system
Example - the task and requirements for the subsystem flow tools
Central coolant recovery system
CNC machining center 1
The most important components of the FMS
Fixture-topallet mounting
Fixture-topallet mounting Compensation store-area
Wash station
Material flows in an exemplary flexible manufacturing system
Machined parts
The task: in a specific time on the machine should appear the tool necessary to perform the machining tasks and the machine control system should include the adequate information about this tool. Requirements for the subsystem: • specify the system demand for tools, • each tool must be assigned to data set, • a sufficient number of tools at the workplace should be collected, • a possibility of tolls exchange should be provided, • a solution to the problem of transport of tools from a central store to individual workstations, • high speed of tools exchanging (in accordance to the planned process), • control of tool wear and appropriate reactions of the system.
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Shape creating system
5. Machining subsystem
The aim of this system is:
The main goal of machining subsystem is: „to give the workpiece suitable properties defined in design documentation, i.e. first of all, the required shape, dimensions, and surface quality” In order to achieve the above goal, there must be realized several functions which may be shown in three areas: • shape creating process (covers the realization of all relative motions of the workpiece and tool necessary to give the workpiece assumed shapes and dimensions), • machining process (functions, which are bound with the physical process of removing of allowance from the workpiece and to give the assumed properties to the surface of the processed part), • auxiliary functions (application of cutting fluids and chips removal).
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“Creating of the part shape trough realization of relative movements of the workpiece and cutting tool in accordance with specification of the design and technological documentation”.
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Units which realize the movement are generally named “NC axes”. A NC axis consist of: • controllable drive, • measurement system, and mostly, at least one, • feedback loop.
Figure 5.1. NC axes of a cross-table: 1 - cross-table, 2 - NC axes , 3 - machine control unit
End position signal Overload signal Feed rate
Carriage (table) Carriage (table)
NC NC axis axis
xs xs
Amplifier 1 Amplifier 1
-
xj xj
xw xw
JJM M
Amplifier 2 Amplifier 2
-
F F
Resisting Resisting force force
Transmission Transmission Drive system Drive system
JJred red
i i Measuring Measuring system system
Tachometer Tachometer
y y
Position signal
x x
Limit switch Guideway Screw rolling
Overload safety coupling
Motor Indirect position measuring system
Drive: electric servomotor Position measurement: encoder mounted coaxially (indirect measurement) Rotational speed measurement: electronically differentiating displacement or additionally tachogenerator attached to the motor (not shown in figure)
Electrics / Electronic
Mechanics
Mechatronics Position signal End position signal Overload signal Feed rate
Feedback loops
Limit switch Guideway Screw rolling
Figure 5.2. Structure of a NC axis: JM - motor moment of inertia, Jred – reduced transmission moment of inertia
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Overload safety coupling
Motor Direct position measuring system
Drive: electric servomotor Position measurement: separate linear encoder (direct measurement) Rotational speed measurement: electronically differentiating displacement or additionally tachogenerator attached to the motor (not shown in figure)
Electrics / Electronic
Mechanics
Mechatronics
Scheme of typical servo feed drives with indirect and direct position measuring system
Z
B
c w
Y
X
Figure 5.3. A vertical machining center with NC axes: four linear and two rotational Common feed drive motors with applications and characteristics
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22 a)
33
11
b) X
+C
Axis of revolution
Z
+X + Z
U W
Headstock of the center lathe TMC 250 (TRAUB):
Figure 5.4. NC axes of turning centers: a) lathe and b) turret
1 - spindle, 2 - spindle drive pulley, 3 - spindle positioning worm gear (backlash-free)
Requirements for feed drives in CNC machine tools: •
• • • • • •
High accuracy and repeatability of reaching a position adjusted by numerical control of machine tools, regardless of the existing cutting forces, friction and inertia; required resolution of measuring system is 0.001 mm for linear movements and 0.001 with respect to angular movements, Torque on the motor shaft: 5 to 100 Nm, High-speed driving over the set position and short positioning times; (HSC proliferation) Overload capacity during acceleration or braking of sliding units, High equability of movement the entire rev range, High stability to maintain the position reached by the NC axis (usually one does not apply mechanical clamps) High drive dynamics (response time to the adjusted speed changes from 10 to 50 ms).
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Scheme of feed drive system with an electric motor
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2
1
3
7
5 5
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DC motor for the feed drives:
AC motor (brushless servo):
1 - rotor, 2 - permanent magnets, 3 - brake, 4 – tachometer, 5 - junction box
1 - package of stator segments, 2 - winding, 3 - permanent magnets, 4 - brake, 5 - tachometer, 6 - coupling of the measuring system, 7 - bearing seal, 8 - mains connection
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Comparison of DC and AC servomotors (both engines, despite the large difference in the overall dimensions have the same power)
The design principle of a linear motor
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The differences between linear motors 3
•
•
•
5 2
Synchronous linear motors are straightened versions of permanent magnet rotor motors
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The linear asynchronous motor is an induction motor, which means that they have in it additional losses associated with the exciting currents in the inductor (the primary winding) and the currents induced in the tread (the secondary winding). In the asynchronous motors seasonal variation of forces is associated with the poles and grooves and it is present in every state of the engine operation. In synchronous motors this occurrence is present only during the movement, because at rest conditions in the windings only constant currents flow. Permanent magnets occurring in the synchronous motors require shields only the secondary part which is associated with significant expenditures. This is especially important when machining ferrous materials (such as cast iron or ferrous steel). The linear asynchronous motor when deenergized of current is free from the force and magnetic field
NC axis drive with synchronous linear motor: 1 - machine carrier, 2 - primary winding, 3 - primary winding cooler, 4 – secondary winding, 5 - position measuring system
Measurement systems
Measurement systems
The criteria determining the choice of the measuring system: • • •
• •
Length of measuring distance (the larger the length the greater dependence of the measurement system’s costs on the choice of this system), Required resolution (the most frequent resolution 0,001 mm is possible to obtain generally with all measurement system), Maximum speed and acceleration are limited to maximum frequency of the measurement signal processing and permissible rotation (taking into account mechanical acceleration of sensor), Insensitiveness to interferences, both mechanical and electrical (such as selfinduced vibration, acceleration spikes, induced voltage), Resistance to pollution (it is obtained by the use of encased sensors and scales, as well as protection against oil spraying or damages to the chips.
Position (absolute)
Position (absolute)
Displacement (incremental)
Analog
Analog
Digital
Rotational
Linear
Periodically digital
Linear
Incremental encoder
Optoelectronic incremental en Periodically digital
Resolver
Resolver
Inductosyn
Inductosyn
Code disc
Classification of movement and position measurement systems used in machine tools
Digital
Rotational
Incremental encoder Optoelectronic incremental encoder
Displace (increme
(absolute encoder)
Linear encoder with absolute code
Laser interferometer
Code disc (absolute encoder)
Linear encoder with absolute code Laser interferometer
Classification of sensors for movement and position measurements used in machine tools
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a)
b)
The principle of the direct (a) and indirect (b) measuring of machine tool table displacement
1 2 3 4 7
Photoelectric measuring system for incremental measurements:
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A five-track binary-code optical absolute linear encoder
1 - source of light (light-emitting diode - LED) 2 - condenser, 3 - tracking plate, 4 - glass scale, 5 - reference mark 6 – photo elements, 7 - scale
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1 Machining centers
FOR PRISMATIC PARTS
MILLING
horizontal
BORING AND MILLING
FOR ROTATIONAL SYMMETRIC PARTS
GRINDING
TURNING
vertical general-purpose horizontal
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VARIOUS
Design structures of centers are characterized by: • High rigidity of spindle system, • High bed rigidity, • Thermo symmetric frame structure, • Spindle structure enabling repeatable conditions of tool fixing, • Good flow of chips and cutting fluids, • Enclosed workspace.
SPECIAL PURPOSE
GRINDING
vertical
Figure 5.5. Classification of machining centers acc. to L.T.Wrotny
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Figure 5.6. Basic module of horizontal machining center used in flexible manufacturing systems : 1 - machine tool, 2 - tool magazine, 3 - pallet changer
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Methods and equipment for deburring and surface finishing Deburring is a particular machining operation. It relies on removal of burrs, which usually remain on edges of machined parts, on casting parting plane, or on edges of sheet metal after shearing or cutting. Need for part deburring results from many reasons: • Burr may cause product malfunction in use and increase the wear of interacted parts, • Burrs, particularly on hole edges, may disturb or make impossible automatic assembly, • Burr sharp edges may cause injuries by assembly or use of product. • Burrs worsen the product appearance.
Example of location of burrs formed during the milling operation
a)
b)
Location of burrs in the case of different order of the machining operations: a) negative, b) preferred due to the availability of deburring process The dependence of the burr’s cross section on depth of cut ap by milling of steel (h - height of burr , b - width of burr’s base)
Effectiveness and division of deburring methods In situation where burrs cannot definitely be eliminated in the process of machining, they must be removed in a separate operation. The economic effectiveness of defined deburring methods depends on the following factors: • Required accuracy of this operation, • Number of machined workpieces, • Time of duration of burrs removal of one part, • Workshop area necessary to arrange a workstation on which the operation will be realized, • Safety rules and environment protection.
Figure 5.7. Components of a comprehensive approach to burr prevention and minimization acc. to Dornfeld and Lee
During the last 30-35 years, many such and associated equipment appeared including NC machine tools. The most often deburring methods can be divided into five groups: 1. Mechanical, 2. Thermal energy, 3. Electrochemical, 4. Vibratory, 5. Jet method.
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Mechanical methods
Abrasive Flow Machining (AFM)
Deburring using wire brushes
The possibility of using appropriate kind of mechanical treatment depends on material and geometry of machined workpiece as well as on quantity and type of burrs. There are applied the following methods: • machining, • grinding, • loose abrasive treatment, • using of the wire brush. The use of loose abrasives belongs to intensively developed and finding still widening industrial application in mechanically removal of burrs. The feature of these methods is integration in one operation the finishing treatment of workpiece surface and burrs removal on its edges. It has elaborated several methods belonging to this group: • Abrasive Flow Machining (AFM) – consists on pressing through the holes and channels of subject (or around it) a viscous-elastic abrasive polymer, • Orbital Polishing (OP) – in which the same abrasive material is used, • Ultrasonic Polishing (UP)
Deburring by grinding Mechanical deburring using a special boring bar
Advantages and limitations of mechanical deburring by cutting: • It is possible to use conventional cutting tools • Burr size has only a limited impact on tool to be used, • Method can be used for any machinable materials, • Machined edges must be geometrically defined, • Thanks to the numerical controlled tool paths and the possibility of using interchangeable tools one can machine specified range of parts, • There is a simple possibility of integration into automated manufacturing systems, • There is no thermal loads, whereas mechanical loads exist only to a small extent, • During milling and grinding small secondary burrs are formed, • Mechanical deburring is largely restricted by the diameter and depth of holes in the case of the inner edges of these holes intersections The effects of using scanner to recognize the shape of the casting burr
Deburring using wire brushes Robotic deburring in gear wheels
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Methods of using loose abrasives : •
•
•
Abrasive Flow Machining (AFM) also known as abrasive flow deburring or extrude honing, is characterized by flowing an abrasive-laden fluid through the holes and slots of workpiece (or around the part ); this fluid is viscoelastic abrasive polymer; Orbital Polishing (OP), controlled removal of the material allowance by an oscillating rotation of the part (mounted on the front surface of the piston) that takes place in a horizontal plane; workpiece is immersed vertically in a cylindrical container with the abrasive medium , the same as those used in Abrasive Flow Machining; Ultrasonic polishing (UP) is the vibration influence of the brittle abrasive particles, such as graphite or glass on the surface of the workpiece; vibrations of the particles are characterized by high frequencies and relatively small amplitudes, the abrasive is fed to the treatment zone in the form of a suspension.
The principle of Abrasive Flow Machining using the device with two cylinders and pistons
Scheme of the device for one-way Abrasive Flow Machining
Abrasive Flow Machining
Deburring using Abrasive Flow Machining
Application of the Abrasive Flow Machining to deburring in cylindrical gear
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Deburring using Abrasive Flow Machining
The principle of Orbital Polishing using abrasive polymer
Thermal energy deburring Parts to be processed are sealed in a chamber that is pressurized with a mixture of combustible gas and oxygen that completely envelopes the parts and surrounds burrs and flash, regardless of external, internal, or blind hole location. This gaseous mixture is then ignited by a spark plug, which creates an instant burst of intense heat (temperature from 2500 to 3500 °C), and burrs and flash, because of their high ratio of surface to area mass, burst into flame. Burrs and flash are instantly oxidized and converted to powder in a total floor cycle time approximately 25 to 30 seconds. Part can then be cleaned with solvent. Thermal energy is a unique and consistent deburring process because it removes undesirable material from all surfaces, even inaccessible internal recesses and intersecting holes. It is effective on a wide range of dissimilar parts of both ferrous and nonferrous material The principle of treatment using Ultrasonic Polishing
Sparking plug
Cylinder of combustible gas batcher Cylinder of gas injector
Work chamber
Cylinder of oxygen injector
Sealing device Base plate for part holding Pressure plate
Figure 5.8. Functioning principle of thermal energy deburring
Deburring using thermal energy method
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Stand for thermal energy deburring (Bosch) 1 - working chamber, 2 - link mechanism for locking of the chamber, 3 - rotary table, 4 - gas mixer, 5 - device body, 6 - hydraulic power unit, 7 - control cubicle
Deburring using thermal energy method
Advantages and limitations of thermal energy deburring method: • • • • • • • • • Automated stand for thermal energy deburring
•
Workpiece material must be well oxidized, In a reliable manner are removed burrs inside holes, All adhering chips and dirt are also removed, Workpiece edges are also slightly rounded, The devices are universal and do not require a special tooling, The method is very flexible due to usefulness to the variety of parts, The device can be easily automated and integrated with manufacturing system, Burrs need not be geometrically determined, Workpieces are subject to thermal and mechanical loads, but without causing structural changes in the material, Workpiece size is limited to the volume of the working chamber.
Electrochemical method of burrs removal The „electrochemical” method of burrs removal consists on anodic digestion of material. Electrochemical deburring machines can deburr and contour parts through an electrochemical reaction that dissolves metal from a workpiece into an electrolyte solution. Direct current is passed through the electrolyte solution between the electrode tool (the shape of the cavity desired), which has a negative charge, and the workpiece, which has a positive charge. Chemical reaction caused by the direct current in the electrolyte dissolves the metal from the workpiece. Although electrochemical deburring is a slow process, it has several advantages. The tool (electrode) never touches the part, so no tool wear occurs. No heat is created during the process; therefore, thermal or mechanical stress cannot distort the part. And electrochemical deburring is applicable across a wide range of material types and hardness variations. One should however take into consideration, that the wasted liquids strongly load the environment and require neutralization, thus increasing the cost of operation.
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Influence of unevenness on the surface of the current density distribution: 1 - electrode, 2 - workpiece, 3 - gap, 4 - burr
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Advantages and limitations of electrochemical method: 1
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6 5
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Scheme of the electrochemical deburring: 1 - the power supply to the workpiece, 2 - contact with the workpiece, 3 - the workpiece (the cathode), 4 - electrode (anode) fitted to the workpiece geometry, 5 - the power supply to the electrode, 6 - delivering of electrolyte, 7 - workpiece chuck
• It can be applied to any conductive materials, • Workpieces are not subjected to thermal or mechanical interactions, • The value of the radius of the workpiece edge can be controlled by the current values and the processing time, • The method is suitable for deburring on the inner edges of the workpiece, • There is possible to machine the edges of any shape, selecting the shape of the electrode (tool) • The method is suitable for difficult machining materials • The electrochemical devices can be automated and integrated into production lines • Machined edges must be geometrically defined, • The tool must be adapted to the workpiece, ie each geometrically different part requires special tools, • the workpieces can not have a deep and confined spaces in which the electrolyte could be stay (due to the risk of corrosion).
Recommendations for use of electrochemical deburring: • • • •
Small volume of burrs and hence the expectation of short-time machining, Small dimensional tolerance of the surface on which burrs occur; so it can be obtained a repeatable gap between the electrodes, No oxides and fat on the surface of the workpiece, No components of the workpiece material structure of the significantly different properties (such as iron, graphite, and cementite, in the case of cast iron).
Vibratory method of deburring Vibratory deburring machines are designed for relatively small rotational or prismatic workpieces. Parts systematically enter a large bowl container filled with ceramic pebbles commonly referred to as media. The size of the ceramic media can vary depending on the type, size, and material of the parts to be deburred. As parts enter the bowl, sometimes via a conveyor, the rapid vibratory back and forth, motion agitates the parts in the ceramic media, removing burrs, descaling, and gently polishing the parts. Eccentric weights are mounted on each end of the container support shaft to vibrate the bowl in a controlled but adjustable manner. As media can also used pieces of plastics, hard wood and crushed corncobs. The duration of treatment is 5 to 25 minutes. The effectiveness of this process may be increased by the use of water bath with the addition of synthetic washing means, detergents and corrosion inhibitors. An additional effect is obtained in this way in the form of clean workpiece and abrasive elements and through rinsing from the system the treatment remainders. Duration of the process may by shortened even by 80 to 90%, decreasing also in the same grade the use of abrasive elements, using addition of chemically active means.
The shapes of abrasive elements used in the vibratory method
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Vibrator of vertical axis of rotation
The shapes of steel abrasive elements used in the vibratory method
Vibrator of horizontal axis of rotation
Vibrator of vertical axis of rotation
Vibrator of horizontal axis of rotation
Vibratory deburring method
Vibratory deburring method
Vibratory deburring method
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Complex automated stand for deburring and finishing: 1 – input conveyor, 2 - vibrator, 3 – washing stand, 4 - conveyor, 5 - dryer, 6 - output conveyor
Deburring from the crankshaft lubricating holes using high pressure fluid jet
Principles of deburring method selection
High-pressure, automated device for washing and deburring on the body of the ABS system. The individual units are used for treatment of: • the front and rear sides of the surface (Unit 1), • narrow lateral sides of the surface (Unit 2), • the upper and lower sides of the surface (Unit 3).
Figure 5.9. Investment in deburring systems as a function of part complexity and total investment in manufacturing system acc. to Dornfeld and Lee
The selection of most suitable, in a given case, method of burrs removal depends on a range of factors such as material of machined parts, part dimensions, position of edges being treated (external, hidden), geometrically defined edge (in case of castings, there is a great diversification in particular pieces) geometric form of burr (its length and crosssection), allowed actions on the part’s surface, operations made before and after burrs removal, possibility to change the sequence of operation due to removal of burrs; and also on the answer such questions as: • Can the thermal and/or mechanical stress influence the part? • Is the thermal treatment planned? • Which range of burrs removal is necessary (if it will be sufficient to remove the protruding burrs, or it will be necessary also to break the edges)? Taking in consideration both the mentioned factors, as well as the response on given questions, it allows to take optimal method of the process of burrs removal, having in view the cost of operation and its durability. The costs associated with burrs removal are substantial. The typical costs as a percentage of manufacturing costs varies up to 30% for high precision components such as aircraft engines, etc.
Figure 5.39. Infrastructure of the flexible manufacturing system with other functional subsystems
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COOLANTS
Realization of auxiliary function
Coolants on the water basis
Nonemulsifiable technological oils
- mineral oils - synthetic and vegetable esters + water - polyglycols
- mineral oils - synthetic and vegetable esters - polyglycols
Machining process requires realization of several auxiliary functions:
+ Antiwear (AW) additions - reducing tool abrasive wear - fatty acid esters - polyglycols
- phosphorus compounds - sulfur compounds
1. Coolant supply,
+ EP (extreme pressure) additions
2. Part cleaning before next operation, inspection, storage and assembly,
- improving coolant resistance against extreme pressure - polysulfide - fatty acid esters
- phosphorus and sulfur compounds
+
3. Chip disposal.
Corrosion inhibitors - fatty acid esters - polyglycols
- phosphorus compounds - sulfur compounds
+ Dodatki Antifoam and antifog additions - silicones, polysiloxanes - organic polymers
- hydrocarbon polymers
+
Figure 5.9. Coolant components
Emulsifiers - sulfonates - fatty acid amids - aliphatic alcohols
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Cutting fluid on the CNC machine tool
+ Conservation additions (biocides) -
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- formaldehyde (derivative)
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Function
Lubrication
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of contact zone workpiece / tool edge
1
Coolant 7 12
Cooling of temperature zone workpiece / tool edge
Flushing
2 5
of chips
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Effect
Advantage
friction reduction
- tool life increasing
minimizing of heat release carrying heat from the cutting edge and part
- prevention of material structure changes
cleaning of cutting zone
- surface quality improvement
- dimensional accuracy assurance
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Figure 5.11. The role of coolant in machining
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Figure 5.10. Central coolant recovery installation: 1 – contaminated coolant sewer, 2 – central tank, 3 - pumps, 4 – coolant filter, 5 – clean coolant tank, 6 - pumps, 7 – pick-up flowing impurities, 8 – centrifugal separator, 9 – impurities to be burned, 10 – water softening, 11 – complementary additive feeder, 12 – additives container, 13 – installation of draining the used coolant from work stations, 14 – installation of feeding the processing stations with recovered coolant , 15 – water supply installation.
a)
The costs of using the coolant by part machining, includes also the outlays for neutralization after the use, reach to 20% of the costs of tools.
b)
Figure 5.12. Installation cleaning the workspace air from oil fog: a) installation placed on the machine, b) cleaning device (filter)
Cleaning cutting fluid from the chips by magnetic method
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Batch washers are available to handle workpiece weighing thousands of kilograms and as large as a 2 meter cube. Batch wash stations are generally used in low- to mid-volume applications to provide a clean part for downstream inspections, assembly or further processing.
Part cleaning Part cleaning may be realized: - in the machine’s work zone, - in the wash stations There are : 1. batch wash stations, and 2. in-line conveyorized wash stations.
In-line conveyorized washers are used for high-volume production where rapid part throughput is a high requirement. With an in-line conveyorized washer, parts are loaded at one end of the system, cleaned as they pass trough the machine, and removed at the opposite end. Separate roller conveyors can be added at the load-unload sections for interfacing with a robot or pallet shuttle mechanism. Multiple stages can be added for rinsing, rust prevention, or part blow-dry.
We distinguish two kinds of part washing - jet washing, and - bath washing.
Selection of either a batch or in-line conveyorized wash station is function of: • Workpiece type, size, weight, material, and configuration, • Throughput rate required, • Material to be removed (chips, cutting oil, tapping compound, und the like), • Succeeding operation type (inspection, stocking, assembly, or another machining operation), • Method of part loading, unloading, transport, and delivery.
MACHINING CENTER INSTALLATIONS
HIGH PRESSURE JET ASSIST HIGH PRESSURE
COOL JET SYSTEM
LOW PRESSURE FEED SUMP PUMP
BYPASS RETURN COOLANT RESERVOIR
Figure 5.13. High-pressure washing installation Figure 5.14. Part washing in the working space of machining centers
Rotating jet washing machine for workpieces
Figure 5.15. Tunnel type modular conveyor washers: 1 – nozzles, 2 – steel net, 3 – nozzles of hot and cold air, 4 – conveyor belt made of stainless steel wire net, 5 – first section of washers, 6 – optional subsequent section, 7- optional heater of parts before leaving the washer.
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3
2
To part cleaning is also used a method of blowing with a stream of air (the blow-off method). Blow-off reduces drying time of the washed workpiece by blowing off the excess coolant or wash solution, prevents spillover to other machines and other areas of the manufacturing system, and helps, keep the area clean and neat. Some machines use convector heated air blowoff generated by gas, steam, electricity in 7 order to speed up the blow-off and part drying cycle and to remove moisture. An advantage of blow-off method is also low cost of installation.
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Jet washing machine with rotating spraying nozzles and contrary rotating container with workpieces
Figure 5.16. Schematic diagram of air stream cleaning installation: 1- working chamber, 2 – nozzles, 3 – machined part, 4 – air cooler, 5 – compressor, 6 – filter, 7 – oil
Basic shapes of chips: Chip disposal system For solution of chip disposal problem there is necessary to meet the fallowing conditions: 1. suitable form of chips, 2. suitable construction of machine tool bed, 3. chip removal and preprocessing system.
Winding type
Short
Double-sided
Lateral
Frontal
• Discontinuous chips (splintering) formed by machining brittle materials; during formation thereof, there are present great variations of machining force what results negatively on the surface and are easy to convey behind the area of machining. • Stepped chips (segment), are formed by machining hard materials with week thermal conductivity (such as e.g. high alloy steels, titan alloys); their formation is also associated with considerable changing if machining force. As a rule, they do not afford problems with removal beyond the machining area though they occupy greater volume of space than the discontinuous chips. • Continuous chips are formed by machining materials of lower limit of plasticity (e.g. steel, bras, aluminum). Variations of machining force are in this case not great, obtained surface roughness is the least, but these chips occupy the greatest volume and are most difficult to remove.
Straight
Favorable chip shapes
Unfavorable
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chip shapes
Figure 5.17. Classification of chip shapes from the point of view of their disposal suitability
The design of the lathe bed enabling free fall of chips: 1 - headstock, 2 - turret, 3 - bed, 4 - chip conveyor
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Figure 5.18. Chip disposal conveyor installation placed under the floor Chip removal system for machining center
Chip conveyor
Chip conveyor
Conveyor for transport chips and their separation from the coolant Figure 5.19. Suction of chips and transporting them by pipe installation
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Chips, before sending them as a scrap metal are subjected to initial processing. This is realized in special chips workstation. This includes the following: • Crusher to chopping up the chips, • Centrifuge to drying the chips, • Briquetting machine.
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3
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Crushing the chips is aimed to decrease their volume making transport easier and further proceeding. The need to clean the chips out of the coolant is caused by many reasons: • There are to be gained considerable amounts of machining liquid (especially oil as its constituent) which can be used again; chips contain 8% of the whole capacity of coolant used during processing, • The weight of chips is decreasing (essential because of transport costs); (in the slime left after grinding there is 40 to 45 % of liquid. • The procedure fulfils the requirements of environmental protection, because cutting fluids getting out of chips stored on open air may penetrate to the soil and water causing pollution. Briquetting does to decrease the capacity of chips in a radical way, meaning significant simplification of storing and transport, thus decreasing the associated costs.
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Scheme of the chips reshaping station: 1 - crusher, 2 - centrifuge, 3 -, briquetting machine, 4 - container, 5 – conveyor
Crusher for chips comminuting
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1 5 6 1 1
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Construction of centrifuges for cleaning chips: 1 - chips supply, 2 - hopper, 3 - acoustic insulation, 4 - a double sheath, 4 - vibration damper, 5 – oil outflow, 6 - oil tank, 7 - chips container, 8 - control box
Centrifuge to separate the chips from the coolant
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Chip conveyor with briquetting press for extraction the coolant
Chip briquetting press
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