10/11/2009 - Connecting rod in the kart
Connecting rod is a fundamental component of the engine, being part of the crank gear that is able to transform the reciprocating motion of the piston into the rotating crankshaft motion.. Due to the considerable entity of the inertia forces, connecting rod is a very stressed mechanical element and then it must have excellent mechanical properties. Connecting rod failure can in fact have disastrous consequences on engine and it must be absolutely avoided.
Connecting rod manufacture process vary as a function of the specific kind the application the component will be used on and, in particular, on the revolutions per minute of the particular engine. Higher revolution speeds involve higher inertia forces and then higher stresses in the connecting rod; is then necessary to trim the manufacture process in such a way to give to the component the needed mechanical strength. Another fundamental aspect is the geometrical and dimensional precision that can be obtained from a fabrication process and, in particular, parallelism condition between the two connecting rod axles, on which errors must be lower then 0.1 mm. It’s then clear how high performance applications need very tight tolerances while a lower manufacturing precision can be adopted in those fields characterized by lower engine rotation regimes.
Connecting rods can be obtained by foundry, sintering or forging, and in this last way the best features can be obtained. Forged connecting rods are then used in high performance automotive and motorcycle applications.
Connecting rods obtained by foundry are instead use on common automotive applications, while punched rods are used for agricultural engines.
Aside from the manufacturing method used to produce the raw piece, this is always subject to a series of operations until the realization of the finished product. In particular, the rod is first cut to obtain the rod head and then the needed profiles are realized on the rod sides by milling.
Then the connecting rod is drilled to obtain the holes on the head and on the basis and finally, by milling are created the planes on which the screw used for the connection of the two rod parts will be hosted.
Usually, steel with good fatigue strength is adopted for the production of connecting rods (fatigue is the primary cause of connecting rods failure ). Typically Chromium-Molibdenum steels are used, with various alloy elements, and the mechanical resistance is improved by means of sanding or shot blasting operation.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
20/11/2007 - Spindle in the kart
As everyone knows, spindle is that component of the steer kinematic chain that allows the mounting of the front wheels and also makes them steerable by means of the connection to the steering linkage. Spindle particular geometry, articulated in space according to two characteristic angles (A and in Figure 1), is relevant for vehicle performances. This particular geometry influences steering kinematics, acting on the magnitude of wheel vertical displacement when the steering angle is varied, and then influencing the raise of the inner back wheel during cornering. Furthermore, spindle pin, on which the wheel is mounted, has its own bending flexibility, determined by spindle geometry and material. Then spindle acts on vehicle torsional behaviour, on load transfers and also changing camber angle: the more the spindle is flexible the more ha camber angle will change during cornering.
Concerning fabrication, spindle is made by three main components: pin, bushing and the plate used for the connection to the steering linkage.
Pin is obtained from a block of material by turning, that is also used for the realization of the thread that is used for nut clamping. The bushing too is realized by turning, while the plate is obtained by sheet metal punching (in the case the plate is plain) or by forging (if the plate has a complex shape like the one in figure). In some kinds of spindles there is no bushing, and that component is substituted by a sheet metal “C”. The main spindle components are finally welded together to form the assembly.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
11/10/2007 - Steel in the Kart and others applications
Steel is the name commonly given to an alloy made by iron and carbon in addition to other elements that allows to trim material characteristics to the particular needs of the component that will be realized. Carbon, usually present in a percentage lower than 2.11% (beyond we are talking about cast iron, a material that is different in terms of characteristics and machinability), is present in the lattice structure of the material as iron carbide and, is able to block the motion of the dislocation, that are the primary material failure causes.
The add of carbon allows then to obtain better mechanical properties than that of pure iron, making this material suitable for a large number of applications. Another relevant factor is the relative low cost of the material, that makes steel one of the world’s most used construction materials each year being produced over five millions of tons.
Go kart chassis are generally made using low-alloyed steels, that are steels that contains, beyond carbon (in percentage ranging between 0.2 and ), some alloying elements that improve mechanical strength, quench penetration, tenacity and so on. Low-alloyed steels are characterized by an higher strength-to-weight ratio then normal carbon steels but they also have an higher price.
They are particularly indicated for mechanical components subjected to high dynamic stress.
The most used alloy elements are Chromium (Cr), Molibdenum (Mo), Manganese (Mn) and Nickel (Ni).
In particular, Chromium improves steel hardness and elastic limit. In percentages higher than 10% it makes the steel stainless, and resistant to atmospheric and chemical agents.
Molibdenum is used to enhance quench penetration and then to give a better efficiency to the quench process, in a similar way than with Manganese, that also improve hardness and wear resistance. Nickel is instead used to for its effects on the thermal dilatation coefficient, that is substantially reduced by the presence of this element.
From a mechanical point of view, the better steels are the Nickel-Chromium-Molibdenum that, with an ultimate tensile strenght of 1200 N/mm² are largely used for gears, cranks, connecting rods and motor components.
For the manufacturing of kart and bike chassis, but even for race car roll cages, chromoly (Chromium-Molibdenum) are the most used steels, for their very good resistance and weldability properties. One of the most diffused is the 4130, of which tables 1 and 2 depict main mechanical properties.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
08/10/2007 - Kart Braking system
In go kart there is a disc braking system that is a system in which wheel slowing down is obtained applying a braking torque by means of one or more couples of pads, that act on a disc, integral to the wheel, and then slow down the wheel by friction.
According to category, there are different kind of systems adopted in karting. In 100cc, there is only a disk, mounted on rear axle, while in 125cc there are brakes on both the front wheels. The differences depend on the different entity of engine powers and then to the different speeds reached, In 100cc, speeds are low and brake should not have an excessive effect, while in 125cc the higher speeds need a more effective braking action.
The system is made of three main components: discs, callipers and pads, plus all the system needed for the actuation (pedals, pumps and various connections).
Discs, normally produced in the measures 200mm for rear brakes and 125mm for front brakes, are made of a special carbon chromium steel, and are drilled to improve heat exchange. This is a fundamental aspect in braking system functioning. Actually we have braking powers of about 60-100 cv that transform vehicle kinetic energy in heat that must be quickly evacuated. Dissipation can be notably improved drilling the discs, obtaining also an increase in friction coefficient between pad and disc, and also using a pair of disc, in order to increase ventilation.
It’s mandatory that heat is correctly evacuated from the system. A non optimal heat exchange, in fact, can lead to pad material vitrification, with a fall in braking performance. Furthermore, if the heat is not properly evacuated, there can be a heat flow to the braking fluid and, if this reach the boiling point, the whole system can become useless.
The presence of holes on disc surface can also improve water evacuation, improving the performance on wet track.
Discs are produced from sheet metal, by means of laser cutting that allow to obtain an excellent finishing. Then discs are subject to an heat treatment to improve mechanical performance and the turned, milled and grinded.
Concerning pads, they are made of carbon-kevlar, a fireproof material made of a carbon based matrix (that provides friction) that hosts the kevlar fibres (that give solidity to the structure).
The production process is the following. Fibres are first put in a die and then compress together. Then they are inserted in an oven and then heated to 1000°C. A gas is then introduced in the furnace, to deposit carbon on fibres. After 500-800 hours, the material is dense and compact and is the machined to final dimensions.
Finally, let’s see calliper manufacture process. Calliper and disk carrier are realized from a block of anodized aluminium (usually ergal) by means of conventional machining operation, usually performed on numerically controlled machines.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - Numerically controlled machines
Numerical control is the result of the union between electronic/informatics and the mechanical material working technology. It was used for the first time in 1947, for the fabrication of the complex surface of military high performance aircraft and then has expected a huge diffusion until today, where it’s adopted in all the industrial realities.
As already known, all the machining processes are based on the reciprocating motion between the cutter and the workpiece. Numerical control technology allows to control these motion by means of a computer, minimizing (and in some cases cancelling) human intervention. This has a long series of advantages, ranging from an higher safety (the operator works away from the manufacturing area) to a considerable increase in manufacturing precision. Furthermore, very important is the complexity of the shapes that can be obtained, and the contemporary increase in the production rate, due to reduced machining times.
Numerically controlled systems are made essentially of a control unit (a computer) that controls a series of actuators that controls cutter and workpiece motions, plus a series of sensors, that record fundamental work parameters.
Numerically controlled work centers have a relevant importance, multi-purpose machines that can make a lot of machining operations with several kind of cutting tools.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - Grinding
Grinding consists in the metal removal from the workpiece by means of an abrasion mechanism. Actually metal is not removed by a cutter, but by the action of an high number of abrasive grains distributed inside the tool (that is the grinding wheel), where grains are maintained in cohesion by means of a particular binder. Grinding is the only conventional machining process that can be used for the machining of very hard materials (i.e. high hardness alloys) and metal treated steels (quenched or cemented). During grinding, special care must be dedicated at the cooling phase of the grinding wheel and of the workpiece. During machining in fact, high temperatures could be reached, that could lead to alterations in binding structure and then to tool failure. Concerning workpiece instead, high temperatures could lead to steel microstructural alterations (creation of fragile martensitic zones) and to residual internal thermal stresses.
The machine used for grinding is the grinder, and there are different kind of grinders that can be found in workshops.
The most common grinder is plain grinder (Figure 1) in which the workpiece is clamped on the workplane by means of a magnetic clamping system. The workplane can then be moved in both the horizontal direction while the grinding wheel can translate vertically, allow to change the machining deepness.
Another kind of grinding is the cylindrical grinding that can be performed on external and internal surfaces.
In the first case (Figure 2) the workpiece has center drilled ends that accommodate center points, and the work is rotated in the same direction of the tool, in such a way to have an opposite motion direction for tool and workpiece, in correspondence to the contact point.
In the second case instead workpiece is clamped and its internal surface is machined by means of a grinding wheel smaller than the hole to be ground. Grinding wheel is kept at high speeds in such a way to obtain an adequate peripheral speed at the contact point. Figure 3 depicts some kinds of internal grinding wheels.
Finally, there are universal grinder machines that are able to perform different kinds of machining operations.
Concerning the grinding wheels, as already said, these are discs in which an high number of abrasive grains bond together by means of a special binder. Grains can be natural (diamond, silica, etc.) or artificial (Alundum, Carburundum, Boron Nitride, etc.): most commonly binder are instead the ceramic one (clay and kaolin), silicon based, elastic binder (rubber based), resin based and metal based. The choice of the kind of grinding wheel to be used is a function of the workpiece material and of the desired surface finishing.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - Induction welding
Induction welding is a welding process in which the workpiece is bring to welding temperatures by means of electromagnetic induction principle. Is then a process suitable for conductor an ferromagnetic materials. Welding system is composed by an induction coil that generates an high frequency electromagnetic field. This field produces in conductor materials a rise in temperature, induced by currents (eddy currents) that are generated in the workpiece by the electromagnetic field.
In ferromagnetic materials instead, the rise in temperature is produced by material hysteresis. The application of the electromagnetic field generates distortions in the metal lattice structure, that lead to material heating. Actually, a large part of materials present an hybrid behaviour and then heating happens as a combination of both phenomena.
Even not magnetic materials can be welded via electromagnetic welding, putting inside this materials small particles of ferromagnetic material that are heated by the application of the external electromagnetic field and the transfer their heat by means of conduction to the surrounding material.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - MIG welding
MIG (Metal Inert Gas) welding is very similar to the TIG process, with the only difference consisting in the electrode, that is fusible and the actively participate to the welding process. Welding happens by means of an electric arc that is stroke in a protective atmosphere, generated using an inert gas (Argon). In the case of low carbon steels welding is anti-economic to use Argon and CO2 is used instead. In this case the process is named (Metal Active Gas).
MIG welding equipment is shown in figure 1. Arc is generated by means of a torch that contains the electrode, automatically fed, and the channels needed for gas flow. Furthermore, the whole torch can water cooled.
The system is powered by an electrical machine to which electrode and workpiece are connected.
In case of automatic welding, the torch is rigidly connected with the machine and the relative motion between torch and workpiece is obtained by means of actuators.
During welding, metal deposition mechanism depends on transition current, that is a parameter connected to many factors like, for example, the material used for the electrode, the kind of gas used and the current of the power supply.
In particular, with tensions lower than 20 V, we talk about short arc mode. In this case metal transport happens in the form of large drops, and the technique is particularly suitable for low thicknesses and for its capacity to be used in various angulations.
In spray arc mode, tensions are higher than 25 V, and metal transport happens by means of small drops. This mode is well suited for high thicknesses due to its good penetration, but can be used only for plain welding because welding bath is very fluid.
Finally there is a third technique that allows to utilize the advantages of both the previous techniques, the pulsed arc mode. In this functioning mode we have the superposition of two currents. One, continuous, is used to maintain the arc while the other, pulsed, is used to transfer material from the electrode to the workpiece. This is a very versatile method and can be used both for high and low thicknesses.
MIG process is simpler than TIG and is used when productivity is of primary concern, due to the high speed of welding creation. As a reversal, MIG suffers of a bulky equipment and could have problems in welding from difficult positions.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - TIG welding
TIG (Tungsten Inert Gas) is an electric arc welding process cunducted in an inert atmosphere. Electric arc is stroke between the base metal and a tungsten electrode that, sue to its high melting temperature (3422°C) doesn’t participate to the welding process. The filler metal (that is not present in the case of low thicknesses) can be provided by rods, if the welding is manual, or by wire, if the welding is conducted on automatic or semiautomatic machines.
Because arc is submersed in an inert gas atmosphere (usually Argon or Helium), metal oxidation is avoided and then it’s possible to weld metals that are not easy to weld, like aluminium alloys.
The equipment is composed of a power supply, needed for arc generation, gas bottles, and of the welding torch, depicted in figure 1. Inside the torch there is the tungsten electrode and the channels needed for water cooling and gas flow.
Depending on the polarity assigned to the electrode and the workpiece, two welding modes are possible: direct and inverse polarity. Usually the direct process is used (positive polarity assigned to the workpiece) that allows to obtain a well focused arc and a good penetration. Inverse polarity welding allows instead to obtain surface oxides destruction during welding, due to a ionic bombing, but the very high temperatures reached by the electrode limit the use of this kind of welding and the maximum current density that can be adopted.
An hybrid process is the one that use an alternate current. In this case we have a semicycle in which oxides are destructed and the other in which the electrode cools down, allowing then lower temperatures to be reached. The result of this kind of welding is the typical waved joint, that has a good aesthetic effect.
The field of use of TIG welding is that of particularly reactive materials, for which traditional welding could lead to problems in the welded joint, and for low thicknesses.
For high thicknesses the process is however uneconomic and different methods should be used.
The principal advantages of this welding methods are the high welding speeds, the easy control of the arc, the wide regulation range of the joint and finally the possibility to make the welding from every position.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - The Seat
Seat is a very important component of the vehicle due to its effects on the torsional stiffness of the chassis and then on the behaviour of the whole vehicle. It’s usually preferable to have a sufficiently rigid seat, to allow a good immediacy in vehicle diagonal load transfer during cornering.
Kart’s seats are usually made of glass reinforced plastic (but also often of carbon and Kevlar), a material that can both be handcrafted or deposed by automated industrial processes. Manual manufacturing is used for low scale productions or for details manufacturing, while automated productions are indicated with high production volumes.
Glass reinforced plastic (GRP) is a composite material, composed by fibreglass embedded into a thermoset plastic matrix, usually polyester or epoxy resin.
Glass fibre can be present in the form of long filaments and opportunely choosing the shape and orientation of these filaments it’s possible to increase mechanical properties of the material along some directions. Fibreglass can also be present in the form of chopped fragments randomly laid and held together by a binder.
The advantage of composite materials reside in the fact that the materials can compensate each other the defects they have. For example, in the case of GRP, matrix is able to resist to compression stresses contributes to stress repartition, while fibreglass are able to absorb traction stresses.
Manufacturing of glass reinforced plastic parts needs first of all the creation of a mold that copy the shape of the piece that has to be realized. GRP stripes are then laid inside the mold and some time must pass before the plastic matrix cures (i.e. become hard). Then the piece is extracted from the mold.
Due to its excellent structural properties, there are many applications of GRP, ranging from naval industry (hulls) to aeronautical industry to telecommunications and racing components.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
31/07/2007 - NEW REAR BRAKE COOLING SYSTEM by PAROLIN
At the last round of the WSK race, disputated in Lonato the 1st July, Parolin Motorsport equiped its Monza chassis with a new and impressive component: a fully-developed cooling system for the rear hydraulic caliper.
Designed by our Technical Department, this part is truly holding the reduction of the brake system heat through a turboventilation. Moreover it removes ferodo's surplus funds produced by breaking, operating a polish effect as well as a cooling one at the same time.
The new cooling fan, fixed to the disk carrier can reduce the brake system temperature of 25° celsius, it avoids additional air intake equipment reducing the kart's weight indeed, already limited in some categories by new regulations.
Presenting this innovate part, Parolin Racing maintains its leadership as a manunfacturer company of hight quality kart accessories and components, traded by Eurostar brand.
30/07/2007 - Piston
Piston, together with connecting rod, is the other fundamental element of each engine and its function is to compress the fuel-air mixture and then, after the combustion phase, to receive the motion that is then transferred to the crankshaft.
Beyond this function, piston can play a relevant role in engine internal fluid dynamics. Opportunely shaped it can optimize the motion of the mixture inside the cylinder, then obtaining a uniform combustion and an overall engine performance.
Similar to connecting rods, the piston is a very stressed component, in particular it’s subjected to severe thermal cycles during engine functioning. For this very reason pistons are realized using advanced materials like, for example, aluminium and titanium alloys.
Piston manufacturing starts from foundry, where the raw pistons are obtained from blocks of alloy. In this phase there should be particular attention to the scorification, degassing and grain refinement, that determine finished product performance and that must be performed with the maximum care. Furthermore, process temperatures must be severely controlled.
The so produce piece is the subject to several thermal cycle, in continuous-cycle automatic ovens, in order to decrease material internal stresses and to improve thermo-mechanical performance of the material.
After this delicate phase, the piston is then machined until the final shape is obtained. In particular, strips seats are obtained by turning and, using NC machines the head is shaped.
Finally, the hole for the connection with the connecting rod is drilled with tight dimensional and geometrical tolerances to obtain an optimal connection between hole and pin.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
30/07/2007 - SMAW - Shielded metal arc welding
Shielded metal arc welding represent the most diffused welding technology, due to its low costs and large use versatility. Furthermore, the process is well suited for open air applications, then for use in construction yards.
It comes from the arc welding process, developed at the beginnings of XX century, that however had a series of heavy disadvantages, related to weld oxidation and to impurity inclusion, that worsened structural performance of the welded joint.
To resolve these problems, nowadays electrodes are covered with appropriate deoxidizing agents, that increase welded joint characteristics.
Welding process (Figure 1) is performed striking an electric arc between the electrode and the workpiece, and operation control is demanded to the operator, that manually moves the electrode.
When the operation is finished, the weld needs to be chiseled, in order to remove scrap that forms during welding.
The manual character of this process, and the need for consumable electrode substitution, decrease the production rate of this process.
There are several types of electrodes that can be used, with different characteristics, and the choice must be based on the particular kind of application.
In particular, acid electrodes (silica and iron silicate) are used when materials with good weldability are joined (the electrode doesn’t have any depurating effect and then the weld is subjected to hot cracks) and usually aren’t used for horizontal welding, due to very high temperatures reached.
Basic electrodes (magnesium and calcium carbonates) depurates the weld joint, due to the reaction of magnesium and calcium with phosphorus and sulphur contained in the metal. This kind of electrodes works at relatively low temperatures and are the only that allow an overhead welding.
Another kind of largely diffuse electrodes are the cellulosic ones, that have an high penetration capacity and allow a strong projection of material from the electrode to the joint, and a welding from every position.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
30/07/2007 - The Drawing
Drawing is a cold plastic deformation process in which the workpiece is forced, by traction forces, to pass through successive matrixes of decreasing diameter that reduce its section.
This manufacturing process, that has its origin in the XI century, is nowadays widely used for the production of pipes, cylinders and wires, with high surface finishing and very good dimensional precision.
Figure 1 shows matrix geometry and the conical exit section of the finished drawn product.
Matrix is realized using very hard and resistant materials like, for example, alloyed steels, sintered carbides, hard alloys and, in some cases natural and sintetic diamond (for wires of micro dimension).
In the case non metallic materials are used for the matrix, this is usually inserted in a reinforcement support, usually a tungsten carbide ring, and than the assembly is assembled in a cylindrical steel frame.
Lubrication is of fundamental importance in the process, to reduce friction forces entity. Soaps and oils are used for this purpose.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
30/07/2007 - The Turning
Turning is a mechanical manufacturing process relatively simple and cheap, by means of which it’s possible to realize a wide range of mechanical components. By turning, that is one of the oldest manufacturing process the man knows, it’s possible to realize external and internal revolute surfaces, threads and ridged surfaces.
The machine used for turning is the lathe, that put tool and workpiece in relative rotation, and also to control motions in order to perform the required operation.
The characteristic turning motions are the circular cutting motion of the workpiece and the linear feeding motion of the tool.
The simplest kind of lathe is the traditional parallel lathe, but there are many kinds of lathes (turret type, automatic, etc.) of many different dimensions and manufacturing precisions, that are chosen depending on the particular application they will work on.
A wide family of machines is also constituted by numerically controlled machines, in which manufacture control is entirely committed to a computer.
A parallel lathe (Figure 1) is constituted by the following essential parts:
· A bed, that has the function to support all the other components and to guide apron and tailstock quill motions. Bed must have an adequate static and dynamic stiffness, in order to grant a sufficiently rigid support to the workpiece and also to insulate the whole system from vibration;
· A headstock, that hosts the spindle that determine the turning axle. Spindle receive the motion from an electric motor by means of a gear shift that allows the regulation of the revolution speed. Rotary motion is also transmitted to the feed rod and to the lead screw;
· A longitudinal apron, that can translate parallel to turning axle and on which a transversal and an adjustable slide are mounted. The cutter is installed on the adjustable slide and the whole system is controlled by the feed road and lead screw;
· A tailstock, that hosts the quill and has the function to sustain the rotating workpiece. In the case lathe is used for drilling or reaming the tailstock is used for tools mounting.
The cutter would need a special article on it, due to the wide literature on this subject and all the matters related to geometry, materials and on chip formation mechanism.
Nowadays, the materials use for cutter construction are special tool steels (carbon or alloyed steels), metallic sintered carbides, ceramic materials and, for special applications, diamond tools. Cutter choice must be lead by the application the cutter is need for, and by cutter material, in particular considering hardness, tenacity, wear resistance, heat conductivity and cost.
There are many operations that can be performed on a parallel lathe.
In particular we have:
· External cylindrical turning;
· Facing: operation performed to obtain plain surfaces, perpendicular to the turning axis;
· External complex surface turning: to obtain surface of straight and curve generator;
· Internal turning;
· External and internal threading;
· External and internal grooving;
· Drill machining;
· Other operations .
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - The bending
Pipes bending is a process by means of which a piece of straight pipe is bended according to a curvature radius arbitrarily chosen. There are multiple ways to bend pipes, and the choice of the method to use must account for different factors, first of all pipes dimensions, kind of desired bending, bending quality and, finally, process speed.
Apart from the used method, all methods have a common feature, that is to stretch the convex bending surface, operation that can be conducted in two different ways:
• Bending. External fibres are subjected to traction while internal are compressed;
• Stretch forming. External fibres are more stretched than internal.
Principal methods used in industry are rotary draw bending, compression bending, ram bending, stretch forming and roll bending.
In particular the one used for bending pipes for kart chassis is rotary draw bending (Figure 1) in which rotary machines are used, that can be actuated hydraulically, pneumatically or electromechanically. This kind of machines is used for almost 95% of bending operations, due to its large flexibility.
The equipment needed for draw bending consists in a rotating shape, a clamping end and a ram, that can be fixed or can be moved together with the workpiece to reduce friction.
This method allow a good control of material flow and is then suitable to make small radius bends. There are 5 different draw bending types, differencing for used equipment; the choice of one method depends on diameter and thickness of the pipe and on the desired bending radius.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Spheroidal cast iron
Spheroidal cast iron is a particular kind of cast iron (that is a steel-carbon alloy with a carbon content higher than 2.14%) in which carbon appears in the structure as spheroids (Figure 1). Spheroids are embedded in the metal matrix, that has a structure depending on chemical composition, cooling rate during the solidification phase and on thermal treatments.
Spheroidal structure is obtained adding to the melted metal some “nudulizing” agents like, for example, Magnesium, Cerium and Yttrium.
That particular spheroidal structure, brings a lot of advantages in terms of mechanical behaviour of the material. Spherical shape reduces stress concentrations inside material and, being the shape that has the lower surface (considering the same volume), is the one that produces less damage to the metal matrix, allowing the obtainment of better mechanical properties than cast iron. Furthermore, nodules are a stop point for crack propagation, and spheroidal cast iron is the only cast iron that is ductile.
Principal cast iron applications are pipes, automobile components, industrial machinery, valves, etc.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Kart foundry
The melting manufacturing process is one of the oldest techniques, by means of which it’s possible to produce raw components that then are finished by conventional manufacture process like turning, milling, drilling, etc. The melting process consists essentially in casting the melted metal into a cavity (mold) that is the negative copy of the piece to be produced. There are several foundry process used in industry but the main ones are sand casting, die casting and pressure die casting.
Sand casting is used mainly for limited productions when there is no justification for high investments in high cost equipments. In the process, the forming material is a mixture of granular silica, an argillaceous binding and various additives that has the function of improving mixture characteristics.
In this kind of process the shape is realized using a model that has the function of realizing the external surfaces of the component to be realized and with one or more cores used to generate the hollow shapes of the piece. Inside the sand die (Figure 1) there are also some elements, that are always present: the feeding canal, that has the role of conveying the melted metal inside the sand die, and the feedhead, that is used to compensate metal shrinkage during the solidification phase (that would lead to structure imperfections and porosity). During metal cooling, in fact, the piece undergo a volume reduction; it’s then mandatory to provide an extra quantity of metal to compensate this effect.
Sand casting process articulates in the following phases: the shape is first prepared using piece model, then cores are inserted for the creation of the hollow zones and then the feedhead and the feeding canal are inserted. Finally the metal is poured in the die. When the metal is solidified, the piece is extracted, the cones in excess are cut and then the piece is sent to the next machining operations.
When the quantity of pieces to be realized become relevant, the die casting process is better than sand casting. This process can happen by means of gravity or by the application of an external pressure. In the first case, die filling happens due to metal own weight, while, in the second case, an external pressure is applied. The last method allow to obtain complex shapes in high quantities, but is not suitable for stressed components because it has the tendency to form cavities in the piece. This effect doesn’t take place in gravity die casting, but the production rate is lower than pressure die casting.
As already said, die casting is used only with high production volumes. The die has in fact a very high cost. However, die casting offers the possibility to automate the whole process and also to obtain, due to the quick cooling of the metal, a fine lattice structure, with good effects on piece strength. Furthermore, a excellent surface finishing can be obtained.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Kart plastic parts manufacture
Go kart are equipped with some plastic parts that even if of minor importance have both an aesthetic and functional role. Hulls and tanks are an example.
The term plastic groups a large family of synthetic materials that are made of macro molecules (polymers), that are long carbon based molecules each one made by smaller molecules (monomers).
Nowadays there is a large number of available plastic materials, used in a bunch of different applications; the most diffused are polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP) and polyamide (PA or nylon).
The raw material for plastic production is petroleum from which, by means of cracking (that is the fractioning of long molecules in shorter ones) it is possible to extract the base monomer. Talking about polyethylene, that is adopted for kart components, it’s made of a chain of ethylene molecules, where ethylene is a carbon and hydrogen compound with formula H2C=CH2 (Figure 1). By means of the polymerization process a quantity n of this molecules (where n can be several millions) react in order to form a n interlaced and branched chain of polyethylene.
In industrial plastic parts manufacture process, raw polyethylene appears as small pellets (figure 2), that are sucked and transported to the machine that will make the particular component. The colour of polyethylene is translucid white but every colour can be obtained adding to white pellets a small quantity (<1%) of coloured pellets.
There are a large quantity of processes for the fabrication of plastic components. Focusing on process for the production of hulls and tanks, these are commonly produced by blow molding, process that is suitable for the production of hollow parts (the same technique is adopted for bottles fabrication).
In the process, material is first heated and melted at a temperature of about 200°C and then extruded with a shape similar to the final one. Then the material is wrapped in a steel mold, pierced with a needle and then inflated with a stream of compressed air, letting the material adhere to mold walls. When the piece has cooled down, the mold is opened and the component is extracted. Then the parts that are in excess are manually removed with a cutter.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - From pipe to chassis
The chassis of a kart is a fundamental element, for its function of mounting element on which all the others are assembled, and for its working features on which the whole dynamic behaviour of the vehicle depends. A go kart, has everyone knows, doesn’t have any suspension and differential, it’s then clear that this functions must be absolved by the chassis that, due to its elastic characteristics, must be able to insulate the driver absorbing, together with the tires, a portion of the stresses that comes from road roughness, granting an optimal weight distribution on the four wheels, and also to help the rising of the rear inner wheel during cornering, in such a fashion to avoid vehicle rear end slipping, that could result in loss of performance.
There are a lot of factors that influence chassis performances, and the choice of one chassis of one another must be based on considerations about the type of track, asphalt conditions and the expectations/requests of the driver.
A synthetic parameter that allow to compare the performances of different chassis is the torsional stiffness, that can be imagined as the inverse of the “flexibility” of the chassis. In scientific terms, the torsional stiffness is defined as the torque produced for a unit rotation of the chassis, and is commonly measured in Nmm/°.
In low grip conditions (i.e. wet asphalt), a flexible chassis should be used, that allows an adequate load transfer on the external wheels and further allowing the vehicle to have gradual and predictable reactions, so improving the vehicle control feeling, that is a must on a wet track.
In high grip conditions, instead, a more rigid chassis should be used, that allows the vehicle to have quicker reactions to trajectory changes and at the same time make the tires working better.
The need to adequate torsional stiffness of a certain chassis has pushed constructors to foresee the possibility of a connect to the chassis a series of stiffening rods, that can be mounted and unmounted, in such a way to adapt the elastic properties of the vehicle to track features and driver driving style. Furthermore, some chassis allows the possibility to vary torsional stiffness along the longitudinal axle of the vehicle, in order to calibrate not only the overall torsional stiffness but also the distribution of torsional stiffness along chassis length.
The importance of chassis stiffness is then clear. The stiffness of a chassis comes from the geometrical configuration of it, from the diameter of the pipes adopted, and from the mechanical characteristics of the material used for the construction, commonly a Chromium Molibdenum steel that grants a good flexibility, an high strength and a low weight, all features needed for a good vehicle performance.
Concerning the manufacturing process, that leads to the chassis, the starting point is constituted form the steel tubes, that can be, by regulation, of circular , oval, elliptic and also rectangular section.
Steel pipes are generally produced by roll forming, followed then by a drawing operation, in order to eliminate welding trace, and to improve dimensional precision and roughness of the workpiece.
A method that is widely adopted with Aluminium, is the extrusion, a mechanical process in which a block of metal is forced to pass along a matrix of the wanted shape by the application of a compression force.
Again, the pipe is subjected to drawing, to improve its roughness and dimensional precision.
Steel pipes are then subject to bending, in order to obtain the desired geometry, and then welded together using TIG or MIG. The chassis needs then to be subjected to a thermal treatment for the removal of structural imperfection due to the welding process, that are weak points of the structure.
Finally, for aesthetic and corrosion-protection purposes the chassis is subjected to painted, operation that close the production cycle of the chassis.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Kart Braking system
In go kart there is a disc braking system that is a system in which wheel slowing down is obtained applying a braking torque by means of one or more couples of pads, that act on a disc, integral to the wheel, and then slow down the wheel by friction.
According to category, there are different kind of systems adopted in karting. In 100cc, there is only a disk, mounted on rear axle, while in 125cc there are brakes on both the front wheels. The differences depend on the different entity of engine powers and then to the different speeds reached, In 100cc, speeds are low and brake should not have an excessive effect, while in 125cc the higher speeds need a more effective braking action.
The system is made of three main components: discs, callipers and pads, plus all the system needed for the actuation (pedals, pumps and various connections).
Discs, normally produced in the measures 200mm for rear brakes and 125mm for front brakes, are made of a special carbon chromium steel, and are drilled to improve heat exchange. This is a fundamental aspect in braking system functioning. Actually we have braking powers of about 60-100 cv that transform vehicle kinetic energy in heat that must be quickly evacuated. Dissipation can be notably improved drilling the discs, obtaining also an increase in friction coefficient between pad and disc, and also using a pair of disc, in order to increase ventilation.
It’s mandatory that heat is correctly evacuated from the system. A non optimal heat exchange, in fact, can lead to pad material vitrification, with a fall in braking performance. Furthermore, if the heat is not properly evacuated, there can be a heat flow to the braking fluid and, if this reach the boiling point, the whole system can become useless.
The presence of holes on disc surface can also improve water evacuation, improving the performance on wet track.
Discs are produced from sheet metal, by means of laser cutting that allow to obtain an excellent finishing. Then discs are subject to an heat treatment to improve mechanical performance and the turned, milled and grinded.
Concerning pads, they are made of carbon-kevlar, a fireproof material made of a carbon based matrix (that provides friction) that hosts the kevlar fibres (that give solidity to the structure).
The production process is the following. Fibres are first put in a die and then compress together. Then they are inserted in an oven and then heated to 1000°C. A gas is then introduced in the furnace, to deposit carbon on fibres. After 500-800 hours, the material is dense and compact and is the machined to final dimensions.
Finally, let’s see calliper manufacture process. Calliper and disk carrier are realized from a block of anodized aluminium (usually ergal) by means of conventional machining operation, usually performed on numerically controlled machines.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Magnesium
Magnesium is the eight most diffused element in nature, and third as dissolved quantity in sea waters. It’s an alkaline-earth metal, indispensable to the life of living cells and of engineering relevance when it’s combined with aluminium to form an alloy known as Magnalium (or even Magnelium).
Historically speaking, USA have been world’s principal magnesium producers with, until some decades ago, a market share of 45%. Actually scenario has changed. There’s only one US active magnesium producer and the US market share is now only at 7%. China has now the preponderance in Magnesium production with a market share of over 60% (was 4% in 1995).
In the USA magnesium is produced essentially by electrolysis of sea water, while in China it’s produce from the refinement of material extracted from caves.
Magnesium is the third material used for structural purposes after steel and aluminium. It has a large use in the vehicle sector, thanks to his strength and lightness properties.
There are several examples that witness the adoption of magnesium in the automotive field, ranging from Corvette SS (Figure 1), the first racing car built with magnesium panels, to the adoption for the construction of engine components (Porsche, Volkswagen). A very advantageous use of magnesium is for the manufacture of aluminium-magnesium alloy (typically ZK60 or its Russian equivalent MA14) wheel rims that, due to its lightness, allow to reduce unsprung mass then increasing vehicle handling and passenger comfort.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Extrusion
Extrusion is a metal manufacture process, that can be performed both in cold and in hot way, by means of which it’s possible to obtain (by plastic deformation) semi manufactured that can also have complex shape. The process consists in inserting a piece of bar, usually of circular section, in the machine; then, by means of compression forces, applied using an horizontal press, material is forced to pass through a matrix that has the same shape of the piece wanted. Extrusion is suitable both for deformable materials (i.e. aluminium alloys, brass) and for steels, and is characterized by a very high productivity rate and high section reductions.
As already said, the process can be performed at high temperatures (900-1300°C) as well as low temperatures, that lead to better surface finishing. In the first case, the advantage is the reduction in the magnitude of the forces involved in the process, but there are problems that must be resolved, related to the oxidation of the material and to high temperature lubrication. The first problem is resolved using a piston of dimension smaller then that of the bloom container, and then letting oxide adhere at container walls. The second one is solved using melted glass based lubricators.
There are two methods to realize extrusion: direct and inverse (figures 1 and 2). The fundamental difference between these two methods is the magnitude of the forces acting, that are lower in the inverse process due to the reduced friction between bloom and container. The main disadvantage of the inverse process is however the high cost of the hollow piston.
The most important component of the extrusion equipment is the matrix, usually made of sintered carbides or high strength steels.
The section of a simple matrix is depicted in figure 3, where we can see the presence of a first conical tract, followed by a cylindrical zone where section calibration happens and that also offer the material needed for the reworking of the matrix needed to correct wear effects.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Chromium plating
Chromium plating has the function of cover a metallic object with an hard chromium layer with both aesthetic and anticorrosion functions.
Under this point of view, chromium, that is deposed by means of galvanic deposition (similarly to the anodizing process) has the function to limit the activity of the micro electric cells at the metal grain borders, then limiting magnitude and speed of the corrosion process.
The plating thickness is a fundamental parameter. Chromium has a potential that is strongly less electronegative than steel (hat is the base metal); as a consequence, in case of break of the chromium film a strong, localized corrosion of the base metal would take place. Choice of the right plating thickness, as a function of the particular application, is then really important, to avoid a premature degradation of the piece.
As already said, deposition happens for electrolytic way: the component to be plated is first dipped into a solution of chromic acid (Cr03) and sulfuric acid (H2SO4) and then connected to the negative pole (cathode) of a power supply. At the positive pole (anode) is instead connected a chromium plate that is dipped in the electrolytic bath too.
Giving power to the system, the metal at the anode is oxidized and forms cations that combine with the anion present in the bath. Then at the cathode the cations are reduced and the metal deposit on the piece to be plated, making a film.
Film thickness is usually 10 micron when plating as only a decorative function while instead, in the case of hard chromium plating, it can reach a thickness of 1000 micron, with the purpose of reduce friction and wear of the component and to restore dimensions of wear pieces.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136
23/07/2007 - Bearings and chains in the kart
Bearings and chains are power transmission mechanical components. In particular bearings, of every type they are (the most commons are spherical, but there are mank kinds of bearings, cylindrical, tapered, etc.), are used to connect different components converting sliding friction in rolling friction, then reducing the magnitude of power losses.
Bearings are made of two rings that host, inside, the rolling elements that rolls in two grooves that are cut in the rings. Figure 1 depicts a cylindrical spherical bearing.
Spheres and rings are separately made, then bearings are assembled and sent to the quality control in order to check manufacturing goodness.
Bearings are usually made of chromium or stainless steels. Chromium steels are used in those applications whose implies high loads. This kind of steel has optimum machinability characteristics that allow to reach an high finishing of ball tracks and then an increase in fatigue life of the bearing.
Stainless steels are instead used when corrosion resistance is of primary concern. They are frequently used then for micro bearings in high precision applications.
Concerning chains, these are used to transfer power between different axles. The connection happens by means of sprockets that with an adequate choice of teeth number can also allow to a multiplication/demultiplication of RPM.
Chains are realized starting from punched sheet metal and then drilled to create pin seats. Holes are then reamed to improve surface finishing and then mails and pins are cold assembled together.
Ing. Fabio Renzi
TVK Project s.r.l.
Motorsport software and consulting
Via Ignazio Guidi, 44
00147, Roma
renzi@ing.uniroma2.it
fabio.renzi@tvk-project.com
www.tvk-project.com
Phone +39 0672597136