1.6 Sketches for Manufacturing Systems Adopted in Car
(c) protective coating and painting of the bodies (painting shop) (d) decking and final assembly of vehicles (general assembly shop)
(e) functional testing, sales lines and delivering (testing and delivering area).
In the following pages, the descriptions of the above process areas are described (Fig.1.9).
• Biggest sheet metal part printing, used for body assembly, is done in ‘‘press centres’’ integrated or close to the final assembly plants.
• The printing cycle of the principal elements of the vehicle bodies includes more operations (from a minimum of four to a maximum of six), performed under mechanical or hydraulic presses up to a printing strength of 2000 tons for single presses and up to 10,000 tons for multi-station transfer presses, in sequenced and continuous cycles.
• Equipment and systems used are different depending on set production levels:
(a) Transfer multi-station mechanical presses with a very high cadence (over 15 cycles/min) fitting with a very high production rate (over 600 series/day);
(b) Traditional mechanical or new generation hydraulic presses with a medium cadence (between 10 and 15 cycles/min), interconnected by automatic sys- tems, fitted for medium production rate (included between 60 and 600 series/day);
ENERGY
SERVICE SEWAGE
TREATMENT SHEET
MINOR BODY PARTS
RUCKS ILWAY
TOMATIC VEYORS
PRESS
SHOP BODY IN WHITE SHOP METAL RAW
MATERIAL
L T RA
AU CON
PAINTING SHOP OFFICES AND GENERAL SERVICES AREA
PRINCIPA FLOWS EXTERNAL SUPPLYING
GENERAL ASSEMBLY SHOP PAINT
SERVICES TESTING AND
DELIVERING
AREA ON AREAS REAS
CAR OUT-SOURCING
PARTS MECHANICAL
GROUPS
PRODUCTI AUXILIAR A
Fig. 1.8 General layout for a car assembly plant
(c) Traditional hydraulic or water forming presses, with manual loading/unload- ing, with low cadence, fitted for low production rate (less than 60 series/day).
Major factors influencing manufacturing costs are: press and mould deprecia- tions, maintenance costs and material handling. For these reasons, it is very important to reach and maintain a high level of OEE (Overall Equipment Effi- ciency) and a good utilization level (seeChap. 3) (Fig.1.10).
Furthermore, to keep product costs low, usage of sheet metal must be opti- mized. This depends on cutting schemes and printing methods and technology (‘‘sheet metal press’’ dimension). Overused metal parts are automatically conveyed in compacting equipment and transferred to where they can be reworked in met- allurgic processes.
• The manufacturing engineering plan defines printing directions and pressing strengths necessary for the single operations.
• Mouldings are built in two principal twin parts (matrix and die), characterized by complex shake and hydraulic and pneumatic leverages. Matrix and die are connected in order to the fixed lower part and upper pressing part of the press machine.
• Production is organized by batch, stocking elements in specific containers, engineered to avoid risk of damage.
• Even basic investments (press machines) as well as specific ones (moulds) are very high; so it is very important to assure the overall effectiveness of the best production systems. For this purpose:
FINISHED PARTS SUPERMARKET
METAL SHEET PARTS CUTTING
D E L I V E R I N G
SHEET METAL COILS WAREHOUSE
PRODUCTION FLOW
Cars Assembling Plant Press Shop typical Lay-out
PRESS LINES TRANSFERT PRESS
Fig. 1.9 Press shop layout
• it is necessary to provide efficient preventive maintenance of moulds and press machine parts and components;
• fast systems for the changeover of moulds must be used to assure short ‘‘set-up times’’
• (typically less than 15 min, from stoppage to restart of production).
• Geometric quality is statistically controlled through programmable measuring machines.
• Surface quality is normally checked through ‘‘on-line’’ visual controls, based on customer perception (Fig.1.11).
• Following the actual guidelines, for high or medium volume body in white welding and assembly, hard automation (robot-intensive-oriented) and flexible production systems are used.
• Assembling tools are specific to each part of each product and are used to assure the ‘‘process capability’’ level necessary for geometric and style characteristics.
• Systems flexibility/convertibility is achieved through the rapid interchange of specific tools, so that it is easy to set the mix model level on the same equipment or line.
Major factors influencing manufacturing cost are: specific equipment and tool depreciation, maintenance and material handling costs. Even in this area it is very important to achieve and maintain a high level of overall equipment efficiency and a good utilization level (seeChap. 3) (Fig.1.12).
MOULD
Typical tooling of a press machine: printing moulds equipped by automatic leverages integrated in mould structure, hydraulic or pneumatically driven
PRESS MACHINE
Fig. 1.10 Sheet metal parts printing process
Body-Framing Gate station is determinant for body geometric precision
Fig. 1.12 Body in white framing gate station
SPACEFRAME SUBASSEMBLING
SPACEFRAME ASSEMBLING
BODY FRAMING
MOBILE PARTS JOINING
MOBILE PARTS ASSEMBLING Body in white assembling and welding process starts with subassemblies and ends with the complete body frame (including doors, bunnet and trunk)
BODY SUBASSEMBLING
BODY IN WHITE FINISHING AND CHECKS
BODY IN WHITE WELDING OPERATIONS COMPLETING
Fig. 1.11 Body in white welding and assembling flow
• Joints are mostly formed through resistance welding performed by pneumatic and electro-mechanical welding guns. For aluminium structures, riveting and TIG (Tungsten Inert Gas) welding technologies are used. Recently, new joining technologies such as laser welding, with or without the material amount taking over, the riveting of hybrid joints, and structural gluing have been implemented.
• In the completion line of the body in white welding operation, mobile parts are joined to the body and rightly adjusted together with plastic parts that must be painted on the line with the body.
• For this technology, the manufacturing volume/investment ratio shows its best values when standard production capacity is set at 60/80 bodies/hour, depending on the dimension of the models.
• For ‘‘special bodies’’, small and medium series, the technological layout is set by working cells, with the manual loading of parts and only partial robot welding (Fig.1.13).
The body in white painting process is structured in sequenced phases, according to a continuous flow that can be divided into two macro areas:
(a) Pre-painting treatments, including washing, degreasing and phosphate treatment, which activates the sticking of the coating on metal, anti-corrosion coating applied by immersion of the body in an electro-chemical bath, application of polymeric materials for soundproofing and sealing.
WASHING / DEGREASING
BASIC PAINT APPLICATION
SEALING AND UNDERBODY SOUNDPROOFING
DEVICES APPLICATION
CAVITY WAX APPLICATION ANTI CORODAL
TREATMENT
EVENTUAL SURFACE REVISION
OWEN
Painting process flow
pre-painting treatments
painting
OWEN OWEN
PAINT AND TRANSPARENT
APPLICATION
OWEN WASHING AND
DRYING
Fig. 1.13 Body in white painting process
(b) Painting, applied by automatic robots with an electrostatic spray, in condi- tioned cabins with a high level of air change, controlled temperature and humidity, so as to assure the elimination of the ‘‘over spray’’ phenomenon and fast evaporation of solvent or basic water coating.
After each phase, polymerization is completed by layer exsiccation, obtained by continuous flow ovens, and followed by an accurate washing with deionised water.
Focal points for the correct management of the above processes are:
– material usage control (high quality and expensive ones);
– fluidic and filtering equipment preventive maintenance;
– a rigorous clearing of the above equipment;
– painting and spray systems logistic management;
– quality control by process parameters and quality of manual job leading.
– The gaseous, liquid and solid process materials rejected are also relevant, and must be treated before exhaustion according to strict legal guidelines.
For this technology, the manufacturing volume/investment ratio shows its best values when standard production capacity is set at 60/80 bodies/hour for part a) of the process and at 30/40 bodies/hour for part b). It is thus normal for the same pre-painting treatment equipment unit to supply enough work for two painting equipment units.
Major factors influencing manufacturing cost are: specific direct material and energy consumption, manpower necessary to manage the process and equipment maintenance costs (Fig.1.14).
For continuous flow in the general assembly of cars and commercial vehicles, or stop and go, lines with interconnected stations are used, managing fixed sequences of production. Lines can be divided into the following principal assembly sub-processes:
(a) Pre-Decking Assembly
It starts with doors disassembled from the painted body. The doors are removed to facilitate assembly of the operation inside the body and, once the dressing is completed, they are handled by automatic conveyors to the final assembly area; the subsequent operations are fluidic and electrical installa- tions, cockpit, instruments, steering leverage and fuel tank assembly on the vehicle.
The painted body is moved to assembly stations through a double rail chain conveyor or self-moving conveyor, equipped with a hanging hook able to rotate across the translation axle to facilitate the best ergonomic condition for underbody operations.
Completed cockpit module and instruments and door modules are prepared in dedicated stations to the side of the principal line, and conveyed directly to the point of installation on the vehicle, according to the production sequence scheduled through programmed systems.
(b) Mechanical Assembly and Decking
This important assembly phase of the process is made on line immediately after the previous one and includes the on-body assembly of the following mechanical groups: powertrain system, transmission groups, suspension sys- tems, and exhaustion pipes. These groups are prepared in the ‘‘mechanical assembly’’ area and transferred to the ‘‘decking’’ area by synchronic conveyor systems. The joining to the body is normally performed by multi-head auto- matic screwing systems, with controlled fastening torque.
(c) Final Assembly
This phase is also connected to the previous one, but the same ‘‘decking’’ line could feed two parallel ‘‘final assembly’’ lines, in case it is necessary to divide production flow for different models with the same space frame. Each ‘‘final assembly’’ line is divided into three sequential parts.
In thefirst part, preassembled bodies coming from the decking area are put on special supports to be transferred by a stop and go system to the next station. In the modern plants, the bodies are arranged across the line axle in this phase to facilitate ‘‘front-end’’ module assembly and to keep electric battery, air filters and engine connections operations ergonomic. Fixed glasses are also assem- bled by automatic systems in this part. For the subsequent operations, such as wheel assembly, the body is again arranged on the line axle.
HANGING CONVEYOR WITH VARIABLE TRIM Bodies input
SIDE LINE OVERHEAD CONVEYOR SCREWING SYSTEMS
Connessione al veicolo Applicazione
paraurti
Montaggio ruote Riempimento
fluidi Installazione
sedili
Completamento esterno veicolo
Completamento abitacolo
Completamento vano motore Spedizione
Applicazione vetri fissi
PRE -DECKING ASSEMBLY DECKING
FINAL ASSEMBLY FINAL TESTING,
FINISHING AND DELIVERY Wiring harnesses and insulating application
Steering leverages
assembling Fuel tank assembling Mechanical subsystems
assembling
Doors disassembling
Cockpit module assmbling Pipes assembling
Cockpit module pre-assembling
Doors module pre-assembling
Doors module assembling
Spaceframe mechanical groups pre-assembling
Powertrain system assembling
Suspension system
assembling Front-end module assembling
Final tests Dynamic tests Steering trims
adjustments Seats assembling Fixed glasses
application
Bumpers assembling
Front-end module application
Wheels assembling Engine space
completion Fluids filling
Internal dressing completion External dressing
completion On track statistic
testing Eventual finishing
Shipping
SALES LINE AND
DELIVERING ROLL CABIN UNDERBODY
STATIONS ONFLOOR CONTINUOUS CONVEYOR STOP AND GO CONVEYOR
WITH VARIABLE HEIGHT
Fig. 1.14 General assembly process flow
In thesecond part, the wheeled vehicle leans on a continuous moving con- veyor belt on the floor line; seats, garnishes, door modules (pre-assembled to the side of the line and conveyed to the same original body), lighting systems and the rest of the vehicle parts are assembled.
In the third part, work is done on the underbody, adjusting the vehicle sus- pension and steering wheel regulation.
(d) Final Testing, Finishing and Delivering
This phase includes a test of the quality conformity control of electrical connections and functional dynamics (performed through a roll test while on- line), in preparation for the final testing. Subsequent refining operations are made ‘‘off-line’’ and can be considered to be a critical phase of the process Truck or road testing is performed on 100 % of high performance cars and vehicles with a very high technical complexity, while, for cars and commercial vehicles of high production volume, only a set percentage are tested, following a statistical model. The latter assumes that a solid level of reliability has been reached through the entire production process, having passed the start-up phase of production.
Finally, vehicles are refined with accuracy and delivered to shipping, after the application of protections for avoiding damage during transportation and stocking phases.
Joining operations, screwing of mechanical groups and application of fixed glasses are generally performed by automatic systems, while the most labour intensive operations, such as application of the cockpit module, steering leverages, seats, and mobile parts, are done with the aid of partners to facilitate operations from an ergonomic point of view.
For manpower and investment productivity, the most effectively operative
‘‘decking’’ areas will average 60/80 vehicles/hour, while the ‘‘final assembly’’ areas will average 30/40 vehicles/hour. This means that the same ‘‘decking’’ line can supply two different ‘‘final assembly’’ lines. In this way, flows can be divided facilitating the supply of specific compo- nents and work loading for different models with the same space frame platform.
In this area of high logistic and organizational complexity, it is very important to use the modern product/process information technology known as ‘‘digital factory’’.
According to ‘‘lean production’’ principles, carmakers tend to organize body subsystems in preassembled modules to be tested separately (doors complete with moving windows, steering wheels with air-bag and electronic controls, cockpit modules fitted with air bag and instruments, front modules with thermal systems…). These modules are supplied ‘‘just-in-time’’ to the final assembly line. The modules have been tested beforehand, so that functional nonconformities that require ‘‘off-line’’ reworking operations decrease.
For components influencing vehicle dynamic safety, it is mandatory that the
‘‘traceability’’ of supplied batches be well-managed, assuring responsibility on
the part of the producers. Factors that most influence the processes of final assembly are: direct manpower, material handling, specific logistic informa- tion technology systems applied (Fig.1.15).
According to modern ‘‘make-or-buy’’ policies, the overall assembly and sub- assemblies are manufactured in engine assembling plants, together with engine blocks, heads and shaft machining.
For big series engines, with a modular structure, block machining is often performed on flexible transfer lines or interconnected machine centres. Particu- larly important for quality level are the boring and super-finishing operations on the engine shaft pivot location and head binding plane milling.
The machining of the head cylinder is often set-up in machining centres working at high speed and automatically interconnected to each other, with the ability to produce specific versions of engines belonging to the same family in a random way. Particularly important for quality level are the locations of shaft distribution and valve boring operations.
For the machining of the engine shaft, specific and precise machine tools, interconnected with each other, are used. For superficial gardening of ground and connecting rod pivots, on-line induction or carbon-nitrate treatments in heating ovens with a controlled atmosphere are used. Diameter and form ground and rod pivot precision and either dynamic regulation are very influential for the level of function quality.
Main components are manufactured by metal removing machining, starting from iron castings and steel microleagues forgings Fig. 1.15 Engine final
assembling
Head cylinder and short block (cylinder block with movement parts) subas- sembly is mostly effected by automation and integrated with cold testing opera- tions: fluid leakage test, right rotation of movement parts, right distribution of valve opening and closing phases. In this way, it is possible to avoid systematic hot testing in the power speed, which is performed only statistically.
The assembly operations of selected pistons and half-bearing coupling for engine shaft pivot location and even fuel rail and combustion rooms testing are very influential for the level of function quality, especially for diesel with direct injection ‘‘common-rail’’.
Final assembly of the complete engine includes assembly of auxiliary parts and relative activation controls, engine power supply and electric module integration;
these operations are normally performed manually on stop and go flow lines or on parallel independent modules, supplying component assembly kits by automatic guided vehicles (AGV).
For car engines that cover a generally wide range of models, the produceable volumes/investment ratio reaches optimal conditions within an interval of 80/120 series/hour production capacity. Otherwise, for commercial and industrial vehicle engines, this ratio is included in 40/60, even in relation to their major dimensions and to consistent diversification of the product. (Also taking agricultural, nautical and construction machines into consideration.)
Depreciation significantly influences transformation cost, and for this reason it is very important to reach the maximum degree of systems utilization (Fig.1.16).
BLOCK MACHINING
CYLINDER HEAD MACHINING ENGINE SHAFT MACHINING
• DISTRIBUTION SHAFTS
• VALVES
• DISTRIBUTION CONTROL PARTS
• INJECTION ORGANS
• IGNITION DEVICES
• PISTONS
• CONNECTING RODS
• HALF BEARINGS
• COOLING AND LUBRICATING PARTS
• TIGHT ELEMENTS
• COLLECTORS
• ELECTRONIC PARTS SENSORS
• TURBOCHARGER
• AUXILIARY ORGANS
• ELECTRICAL INSTALLATION
Production flow sketch for high volumes modern engine plants.
FINAL COLD TESTING
Fig. 1.16 Engine assembling process flow
The modern plant concept considers the making of parts: structural parts characterized by architecture and kinematic parts strictly related to the assembly of systems and requiring ‘‘on line’’ functional tests. The final producer delegates portions to specialized suppliers able to supply the total powertrain systems market, with the following parts made by hard automation production systems:
– pistons with tight rings (requiring metallurgic and finishing highly specialized technologies);
– connecting rods in micro-leagued or forged steel (requiring forming technolo- gies with high precision);
– cam axles in spheroid cast iron or steel composition;
– special metallic league bearings;
– valves and related opening and closing control components;
– injectors/collector groups and other components for fuel supply;
– suction collectors and butterfly parts;
– exhaust collectors;
– controlled ignition devices;
– turbo compressors;
– flywheels and torsion bumpers;
– ubricating system component;
– cooling system components;
– air conditioning compressors;
– belts, chains and pulley;
– composite elements for tight fluidics;
– electrical devices;
– temperature, pressure and oil level sensors.
Intermediate manufactured parts are farmed out to suppliers specializing in metallic league transformation:
• aluminium foundries for cylinder heads and blocks (car engines for upper intermediate product range);
– iron cast foundries for blocks (lower intermediate product range cars and industrial engines);
– special iron cast foundries for engine shaft (car engines of lower intermediate product range);
– forging centres specializing in micro-leagued steel engine shafts (car engines for upper intermediate product range and industrial engines).
To manage the product’s complexity effectively, and to assure constant control of the level of quality and overall equipment efficiency of the production systems, it is necessary to have information technology systems for flow management, overall equipment efficiency and quality parameter control and for assuring the traceability of those components influencing the vehicles’ availability and safety level (Fig.1.17).