INTRODUCTION
Introduction
According to the latest report just released by the Vietnam Steel Association (VSA), in September 2022, finished steel production reached 2.446 million tons, an increase of 23.41% compared to August 2022 and an increase of 1.7 million tons % over the same period in 2021; steel consumption of all kinds reached 1.998 million tons, down 7.19% over the previous month and down 9.9% over the same period in 2021
After a long time of use, steel can be worn, rusted, cracked, reducing strength and hardness, greatly affecting the stability of the overall structure There are also special cases need the material with the appropriate adjusted hardness There are many methods that can solve that problems, in this topic we plan to do it with the heat from welding electrode, directly increase the surface temperature of the steel cylinder, then cool it down with water pumping system
Using the chuck with the form of CNC turning machine, which can maintain fixed location for the steel cylinder while processing We also use drivers and PLC for step motors in order to precisely control the speed of spindle and welding electrode’s position, avoid damaging the surrounding areas Start with a raw steel cylinder part, uneven hardness, substandard positions and end up with even, improved one has suitable hardness, which can response given standards
1.1.2 Structure, general mechanical properties of steel:
Steel, alloy of iron and carbon in which the carbon content ranges up to 2 percent (with a higher carbon content, the material is defined as cast iron) By far the most widely used material for building the world’s infrastructure and industries, it is used to fabricate everything
The main reasons for the popularity of steel are the relatively low cost of making, forming, and processing it, the abundance of its two raw materials (iron ore and scrap), and its unparalleled range of mechanical properties
The major component of steel is iron, a metal that in its pure state is not much harder than copper Omitting very extreme cases, iron in its solid state is, like all other metals, polycrystalline - that is, it consists of many crystals that join one another on their boundaries A crystal is a well-ordered arrangement of atoms that can best be pictured as spheres touching one another They are ordered in planes, called lattices, which penetrate one another in specific ways
Tempering leads to the release of carbon inside by heating the steel This allows the structure to deform plastically and increase some of its internal stresses This increases hardness and decreases toughness, but it also tends to increase tensile strength The degree of tempering is dependent on temperature and time; temperature having the greatest influence If the welding temperature profile for a typical weld is plotted against the carbon equilibrium diagram, a wide variety of transformation and heat treatments will be observered
Steel containing a carbon content of 0.77 percent begins to solidify at about 1,475°
C (2,660° F) and is completely solid at about 1,400° C (2,550° F) From this point down, the iron crystals are all in an austenitic - i.e., fcc - arrangement and contain all of the carbon in solid solution Cooling further, a dramatic change takes place at about 727° C (1,341° F) when the austenite crystals transform into a fine lamellar structure consisting of alternating platelets of ferrite and iron carbide
Figure 1.4 Steel structure from low to high temperature[13]
1.1.3 Carbon steel and effect of carbon content on the properties of steel:
There are 4 main types of steel: Carbon, alloy, stainless and tool Carbon steel is the most popular one base on its advantages and low costs, easy to produce The reason for the existence of carbon steel is the pure form of iron is soft and generally not useful as an engineering material; the principal method of strengthening it and converting it into steel is by adding small amounts of carbon In solid steel, carbon is generally found in two forms Either it is in solid solution in austenite and ferrite or it is found as a carbide The carbide form can be iron carbide (Fe3C, known as cementite), or it can be a carbide of an alloying element such as titanium (On the other hand, in gray iron, carbon appears as flakes or clusters of graphite, owing to the presence of silicon, which suppresses carbide formation.)
Carbon steel is highly versatile, and its uses and properties can vary depending on its carbon content As the carbon content rises, the steel becomes harder and stronger However, it does become less ductile, more brittle and harder to weld Also, the higher the carbon, the lower the melting point of the steel Carbon steel is further broken down into four groups based on its carbon content: low, medium, high, and ultra-high
Low carbon steel (mild steel): contains approximately 0.04–0.3% carbon, it is malleable, ductile, tough, and very easy to weld But it is not readily tempered and has a relatively low tensile strength
Medium carbon steel: the carbon content of this metal ranges from 0.31–0.6%, this grade has ductility, strength, and good wear resistance It is stronger and harder than mild steel, but it is more difficult to weld and form
High carbon steel: has a range of 0.61-1.5% carbon High carbon steel is extremely hard and brittle But because of this it is very difficult to bend, weld, or cut
Ultra-high carbon steel: With a carbon content ranging from 1.51-2%, this metal can be heat treated to exceptional hardness
1.1.4 Heat-treating and its advantages:
Improve the hardness and wear resistance of steel, increase the working life of wear-resistant parts The hardness of hardened steel depends on the amount of carbon Low carbon steel < 0.25% when harden is not high enough, not wear resistant enough
So, to achieve this goal, hardened steel must have a medium and high carbon content of 0.3% carbon or more Improve the durability and load capacity of steel materials Thanks to this property, people conduct steel for important details: heavy load, resistance to wear, fracture and service life
Adjusting the carbon content is the simplest way to change the mechanical properties of steel Additional changes are made possible by heat-treating—for instance, by accelerating the rate of cooling through the austenite-to-ferrite transformation point, shown by the P-S-K line in the figure (Figure 1.5) This transformation is also called the Ar1 transformation, r standing for refroidissement, or “cooling.”
Figure 1.5 Iron-carbon equilibrium diagram.[13]
The urgency of the topic
Steel details account for about 95% of the total metal production worldwide, because this metal is very commonly used It can help structure hard, high bearing capacity, and low cost iron and steel become a common material in both life and especially in construction that uses a lot Because of the demand, steel details are usually used for a long time and hard for maintenance, it leads to the material quality degraded, cause damage on local and total structure, danger is present
Heavy industry evolution put demands on develop higher grade materials, steel is the most important one to be research Testing and simulating the change of steel’s hardness require specific machine model with specific design and method That model need to be compact, cheap, simple, accurate and effective
This is why we choose the topic: Design and fabrication of a welding electrode moving model around a cylinder part.
Objection of the project
We already mentioned about the advantages of our method With the criterion of creating a heat-treating machine in CNC turning form to heat the steel cylinder by positions
So that, our project will focus on these following aim:
- Built a machine with the main functions of a CNC turning machine
- Control the speed of electrode by drivers and PLC
- Make sure the steel cylinder part reaches the desired hardness
- Ensure the durability of the machine and the whole system.
Research method
The topic is approached based on the actual need to process heating materials create steel parts to achieve the hardness and durability according to customer demand From studying and observing some realistic CNC turning machine in school, the team take advantage of the basic functions of the CNC turning system, improve with a welding electrode for heating, simplify the frame for lower cost In order to do that, our team using these methods:
- Experimental analysis for gathering input data and testing machine after manufactured
- Theoretical calculation for design and calculating machine component
Aim, mission and scope of the project
- Aim of the project: welding electrode heat-treating machine, testing report, technical drawings, 3D models
- Mission of the project: Design and implement fully functional prototype of CNC turning machine, replace the knife with welding electrode for heating Serve the research of steel hardness, provide heat-treated steel which achieved the desired standard
+ Appling theatrical knowledge about mechanical design and machine manufacturing to built
+ Time for designing and manufacturing is 5 months.
Input data
- Steel cylinder with diameter (60mm-100mm)
1.6.2 Define input data about steel cylinder:
Using a hollow round steel tube whose diameter is 76cm and length is 100cm from building materials store The material is steel ASTM A53 - a carbon steel alloy, used as structural steel or for low-pressure plumbing The alloy specifications are set by ASTM International, in specification ASTM A53/A53M
Expecting output data
- Heat-treated steel cylinder with no deformed, no cracked
- Obvious hardness survey positions, not affect non-heating areas due to processing demand.
LITERATURE REVIEW
Machine overview and principle
The overview of the machine is based on CNC lathes, metal cutting machines, used to process parts with round surfaces such as: Cylindrical, conical, screw thread, face shaping… The device works based on the circular motion of the workpiece and the movement of the tool In particular, the movement of the tool is divided into two types: The tool runs along the axial direction of the workpiece and the tool runs horizontally in the radial direction of the workpiece
Currently, CNC lathe is a device favored by many businesses thanks to its multi- function, automatic operation through installation on computer software As a result, the quality of the product to be processed no longer depends on the skill level of the workers, and the enterprise also solves the economic problem during operation
Includes the following main parts:
- Main shaft system: Has the function of guiding the tool head in the Z direction and is also the part that generates the product cutting speed In the spindle chuck includes:
- Main shaft, stepper motor, detailed chuck, hydraulic or pneumatic system
- Main shaft: Used to attach the system of motor
- Body: Supports the components of the device
Some improvements in this project:
- PLC control system and step driver: control and change operating parameters by laptop and wire, encode immediately and can be changed during operation
- Arranged with a welding electrode to replace the original turning tool for heating
- Move the working table by automatic software instead of manual
The common turning machine works based on the rotation of the workpiece and the tool feed movement, where the rotation of the workpiece generates cutting speed The tool feed movement determines the feed, shapes the machined surface The feed movement includes:
- Longitudinal feed: the cutter moves in a reciprocating direction parallel to the centerline of the lathe
- Transverse feed: the cutter moves in a reciprocating direction perpendicular to the lathe centerline
- Tilt feed: the direction of cutter movement forms an angle to the centerline of the lathe (applicable when machining taper faces)
- Curve tool path: applicable when machining profiled surfaces
Basically, the part to be machined is mounted on the chuck for circular motion, and the cutter is mounted on the tool holder (or tool table) to perform turning according to the cutting mode from the operator
Based on the above principle and structure, the machine designed in this topic changes the cutting operation by heating operation Do not apply force to the work piece
A welding electrode locates at the knife position, the tips of it maintain a distance 2 mm to the workpiece’s surface The heating system selected is the Jasic TIG 200A W233 welding machine, used for materials with thickness from 0.5 to 8mm, 220V input power, manufactured and assembled according to European standards (CE), arc priming by high frequency (HF) method Smooth welding, concentrated arc, less spatter, stable arc current Good weld quality, deep penetration Suitable for welding many different materials such as steel, stainless steel, copper, titanium, nickel or many other metals
Figure 2.4 Jasic Tig 200A W233 welding machine
Protecting gas is Argon, electric provider independent The welder has some information in the table below:
Rated input voltage AC220V±15% 50 HZ
Rated power: Tg 6.6 kva/ MMA 7.2 KVA
Welding current/rated output voltage TIG: 200A/17.2V MMA: 180A/26.4V
Imax load cycle (40°C): TIG:30% MMA:20%
Dimensions (with handle) 430mm×168mm×312mm
Machine Structure
Based on the purpose of the project and the desired function, the machine will be designed to bear a small load no torque because it does not perform the turning process The frame material must be light enough for easy assembly and portability And the aesthetics of the machine is also considered
The type of material selected is aluminum profiled into bars Model ATV6-2040-
01 (20x40mm) produced on modern production lines, meets the standards of durability and hardness, the aluminum surface is shiny anodized V-track for moving slider There are different models and sizes to meet the needs of customers
Some basic information of model ATV6-2040-01 are:
Figure 2.5 Standard dimensions of ATV6-2040-01 and real model
The chuck must ensure a higher mounting accuracy than the chucks on the conventional universal machine To ensure the installation accuracy, the standard must be selected so that the standard error is zero, the clamping error must have the minimum value, the setting point of the clamping force must avoid causing deformation to the work piece
Depending on the object of processing, the chuck is composed of two, three, and four-spoke types Two-spoke, three-spoke chucks are usually self-centering Except in special cases, it is common for four-spoke chucks to be non-centering Because the chuck rotates with the same details, sometimes at a very high speed, people often choose the structure of the chuck with a circular, symmetrical shape, ensuring a firm assembly with the main shaft, with a firm clamping mechanism and stable centering to meet the requirements of dynamic balance
The 3-spoke chuck is the most common chuck on lathes in small, medium and single production, used for clamping when machining rotating objects whose centerline coincides with the main axis of the machine Use this chuck to install simply and quickly When controlling, all three chucks enter or exit together, creating clamping and centering forces for the work piece
Depending on the shape and structure of the workpiece, there are ways to use clamps to fit the workpiece The figure below shows how to use the chuck on the chuck when mounting workpieces with a diameter smaller than that of the chuck with the forward chuck (Figure a) When machining jigs with large diameters and compartments, install the clamps backwards (Figure b) When mounting a workpiece with a large diameter and with a hole, insert the clamp upside down and insert it into the hole of the workpiece (Figure c)
The chuck selected for this topic is the 3-spoke chuck with 80mm diameter model K11-80, this is a small 3-spoke chuck commonly used on mini lathes to clamp small diameter products It has a weight of 1,8kg and parameters shows in figure below:
A stepper motor is a type of motor that uses electricity but has a very different principle and application compared to ordinary 1-phase electric motors and 3-phase electric motors In essence, this is a type of synchronous motor, capable of transforming the control signals of machines in the form of discrete electrical pulses emitted in succession, forming rotational movements Sometimes it is the movements of the rotor, which help the user to fix the machine's rotor into the required position
Rated Current/ phase 2.0 A Phase Resistance 1.4 Ω
In general, a stepper motor ( stepper motor ) is a type of motor that you can specify its rotational frequency The smaller its step angle, the greater the number of steps per revolution of the motor and the greater the accuracy of the position we obtain The step angles of the motor can reach a maximum of 90 degrees and a minimum of 0.72 degrees However, the most commonly used motor stepping angles are 1.8 degrees, 2.5 degrees, 7.5 degrees, and 15 degrees
The operating principle of the stepper motor does not rotate according to the usual mechanisms, because the step motor rotates step by step, so it has a high accuracy, especially in terms of cybernetics Stepper motors work thanks to the operation of electronic switches These electronic circuits will put the signals of the control command running into the stator in sequential numbers and a certain frequency The total number of rotations of each rotor corresponds to the number of times the motor is switched At the same time, the rotation direction and rotation speed of the rotor also depend on the conversion sequence number as well as its switching frequency
Figure 2.8 The operation of electronic switches.[16]
The model of stepper motor chosen in this topic is NEMA23 57H1876 for the spindle rotation and NEMA23 57STH56 for the table sliding Both of them are 2 phase motor with 8mm shaft diameter, 20mm long 2A-1,5Nm for 57STH56 and 4.2A-1.8Nm for 57H1876
Slider is the moving part for the welding electrode, suitable for 2020 aluminum bar, or 2040 aluminum bars aluminum edge The product set includes 4 wheels V-Slot,
1 aluminum frame, hexagon screws, bushings, long temples just enough for 1 set
Pulley is an important part to attach the belts to transmit torque to help operate the system In fact, the pulley is the part of the pulley roller, which is responsible for transmitting the moving torque, helping the machine to operate Pulley for our human life is also very important, it brings a lot of benefits and is very convenient Usually pulleys are used to move objects from one place to another, in this case we use a big pulley system for spindle rotation and small one for the slider movement
Spindle receives rotation from the stepper motor by a pulley system includes a big gear at spindle and small one at motor shaft
Electrical and electronic system
With the purpose of the topic, the best choice for electricity supplier is switching source or pulse source, has overcome the disadvantages of the classical linear source Instead of using a ferromagnetic transformer to lower the voltage and then use a rectifier combined with a linear source IC to create the required DC voltage levels such as: 3.3V, 5V, 6V, medium heavy, both cumbersome and costly… The honeycomb source transforms the power source by means of a pulse oscillation created by an electronic circuit combined with a compact and lightweight pulse transformer, increasing the durability of the power supply
Currently, there are many different types of honeycomb sources such as: 12V pulse source, 24V pulse source, 12V 30A pulse source, 5V 60A pulse source, 24V 25A pulse source Each type will be specially designed computer, separate specifications to suit a variety of purposes of users We use 24V pulse source
Meanwell 24V source is a power supply with superior characteristics, no less than the 12V pulse source There are many products with 24V pulse power supply, such as: 24V 5A pulse power supply, 24V 10A pulse source, 24V 20A pulse source, 24V 30A pulse power supply And almost every electrical cabinet has a set convert 220V to 24V power to power devices
As a power supply used in large billboards, this power supply is designed with a cooling fan system to help prevent the source from overheating and protect the product's life
Used a lot in applications that provide power to the system High efficiency, stable output voltage within the allowable power limit (no voltage drop when the current is large) Overload protection, short circuit, over voltage protection, cooling fan Output voltage: 24V/10A
The TB6600 4A 42V stepper motor driver circuit uses the TB6600HQ/HG IC, used for stepper motors: 42/57/86 2-phase or 4-wire with a load current of 4A/42VDC Application in machine making such as CNC, Laser or other automatic machines The TB6600 4A 42V stepper motor driver circuit uses the TB6600HQ/HG IC, used for stepper motors: 42/57/86 2-phase or 4-wire with a load current of 4A/42VDC Application in machine making such as CNC, Laser or other automatic machines
+ Input with optical isolation, high speed
+ Built-in over-current and over-voltage measurement
DC+: Connect to the power source from 9 - 40VDC
DC- : Negative (-) voltage of the source
A+ and A -: Connect to the winding pair of stepper motor
B+ and B- : Connect to the remaining windings of the motor
PUL+: Speed control pulse (+5V) signal from BOB for M6600
PUL-: Speed control pulse (-) signal from BOB for M6600
DIR+: Reverse pulse supply signal (+5V) from BOB for M6600
DIR-: Reverse pulse supply signal (-) from BOB for M6600
ENA+ and ENA -: when giving signal to this pair, the motor will no longer have holding and rotating torque
A common positive (+) signal or a common negative (-) signal can be connected
Limit switch is a type of switch used to limit the travel of certain moving parts in a mechanism or system It has the same structure as a normal electrical switch, still has the function of opening and closing, but has an additional need to act to let moving parts affect and change the state of the contacts inside it The limit switch will not maintain the state, when it is no longer active they will return to the original position Compared to other normal switches, when activated, they will remain in the state until they are activated again The limit switch can be used to switch circuits used in low voltage grids It has the same effect as a push button, the manual action is replaced by the impact of the mechanical parts, making the mechanical motion into an electrical signal
A limit switch will be composed of the following parts:
- Actuator receiver: this is a pretty important part of a limit switch, what sets them apart from other types of switches They are mounted on the top of the switch and are responsible for receiving impacts from moving parts to trigger the switch
- Switch body: the body of the switch will include internal components with a plastic shell to help them crash, protecting the internal electrical circuits from physical impacts
- Connector: This is considered the output signal for the switch because it is responsible for transmitting signals to other devices when affected by the actuator.
MECHANICAL DESIGN
Block diagram
- Electrical box: stand as a power supply as well as the control circuit for the whole mechanical system Electrical box includes in transformer (convert 220V to 24V), 2 driver for 2 step motor and PLC circuit (distribute signal to 2 motor)
+ Aluminum base product: fixing and holding the entire machine
+ Main shaft: with the chuck, this system transfers the mechanical power from step motor to rotating workpiece and holds workpiece while working
+ Slider: holding the welding gun and cooling system, using the linear motion system with belt drive transfers the mechanical power from the second step motor to drive along side with the length of the workpiece
+ Cooling system: water pump, faucet and gutter (holding cooling water)
+ Tailstock: not only uses for supporting the longitudinal rotary axis of a workpiece but also connects with the welding cable mass to produce an electric arc and the heat source
To heat treatment a cylinder part using a welding electrode, we applied the mechanism of the simple lathe machine However, the tool post system will change to slider carrying the welding gun
Like the CNC lathe machine, we can control the speed of the headstock and slider to fit with the heat and the heat affected zones Moreover, with the PLC circuit, we can set the slider to home position in everytime we start to activate the program from the PLC circuit
To choose a step motor we based on the working condition and parameters
- To heat treatment the cylinder part, the welding gun move to heat slowly along side of the part that why we choose step motor for slow working condition In addition, we can determine the speed we need without using gearbox and move the slider steadily without losing precision
- Because of working with welding machine to heat the part, we have to separate the power source of welding machine (220V) and control circuit (24V) to protect the control circuit from short circuit
Slider at the start position
Slider automatically run to the NO contact (home position)
Main shaft starts running at the speed
Slider starts to move with velocity v (mm/rev)
Slider run to the NC contact (at the end of the workpiece)
+ Theoretical Velocity of slider: 0,1 mm/min
+ Theoretical Speed of main shaft: 10 rpm
+ Weight of main shaft includes in:
Choose step motor based on the weight of mainshaft
Principle of servo type selection:
1 Continuous working torque < motor rated torque
2 Instantaneous MAX torque < MIN torque of servo motor (when accelerating)
3 Load inertia < 3 times motor rotor inertia
4 Continuous working speed < rated speed of motor
Inertia, or more specifically, inertia ratio, is one of the most important factors in sizing a servo system Inertia is defined an object’s resistance to change in velocity, and in servo-driven systems, it can be used as a measure of how well the motor is able to control the acceleration and deceleration of the load The yardstick by which this is judged is the inertia ratio, which is defined as the inertia of the driven component(s) divided by the inertia of the motor
𝐽 𝐿 : inertia of load reflected to motor
An inertia ratio that is too low means the motor is likely oversized, leading to higher than necessary cost and energy usage An inertia ratio that is too high means the motor will have a difficult time controlling the load, which results in resonance and causes the system to overshoot its target parameter (position, velocity or torque)
While it seems logical that an inertia ratio of 1:1 would be the goal, it’s not always achievable or cost-effective Most servo motor manufacturers recommend that the inertia ratio be kept to 10:1 or less, although there are many applications that operate successfully at much higher ratios The best inertia ratio for an application comes down to the dynamics of the move and the accuracy required
Load inertia includes the inertia of all rotating parts, including the drive (such as a belt and pulley system, screw, or rack and pinion), the load being moved, and the coupling between the load and the motor
𝐽 𝐿 : inertia of load reflected to motor
𝐽 𝐷 : inertia of drive (ball screw, belt, rack and pinion)
𝐽 𝐸 : inertia of external (moved) load
Because the weight of workpiece and weight of the chuck is co-axis with the driven pulley so that we calculate the inertia of workpiece and chuck by formula:
Inertia of hollow cylinder(workpiece):
𝑟 0 = 38𝑚𝑚: outer radius of hollow cylinder
𝑟 𝑖 = 36𝑚𝑚: innerr radius of hollow cylinder
Inertia of solid cylinder (chuck):
Inertia of load with belt reduction:
4 2 = 132,81𝑘𝑔 𝑚𝑚 2 𝑖: belt ratio based on the number of teeth on the drive pulley (10 teeth) as well as the driven pulley (40 teeth)
With load inertia < 3 times motor rotor inertia:
We choose NEMA 23 stepper motor with parameter like below:
Holding Torque: 1.5 Nãm (150 Nãcm, 212.5 Oz.in)
Choose the step motor for slider
Like all the step we have mentioned above, we based on the inertia of load reflected to motor to choose the motor with condition: the load inertia < 3 times motor rotor inertia
Inertia of load driven by belt:
𝑚 = 1,425𝑘𝑔: mass of load(slider(0,35kg) and TIG torch(0,975kg)) + mass of belt (0,1kg)
𝑟 = 5𝑚𝑚: the radius in this case is the outer radius of the pulley, since this is the axis around which the belt and load are being rotated
With load inertia < 3 times motor rotor inertia:
We choose NEMA 23 stepper motor with parameter like below:
Calculating belt drive for mainshaft
Timing belt is a flat belt made into a closed ring, with teeth on the inside When coming into contact with the pulley, the teeth of the belt will engage with the teeth on the pulley Due to the geared belt force transmission, the toothed belt drive has the following advantages: No slippage, large transmission ratio(𝑢 < 20), high efficiency, no need for large initial tension, small shaft force
Timing belts are made of a flexible polymer over a fabric reinforcement Originally this was rubber over a natural textile, but developments in material science have had a substantial effect in increasing the lifetime of these belts This included changes from natural to synthetic rubber and polyurethane and also the adoption of steel, nylon, Kevlar (or other aramid fibres), and/or carbon fibres in their reinforcement
In this case, we choose the belt made from the natural rubber to reduce the cost but still remain the efficiency and avoid the high voltage from the welding machine
Our motor type is servo motor and NEMA23 series is usually used in printing machine
Figure 3.3 Speed multiplication correction factor[2]
Because of the machine working in high temperature, the rest in every operation is needed So that the operation duration is 1 or more less than 1,25
Figure 3.4 Operation time correction factor[2]
Figure 3.5 Start/stop correction factor[2]
Our machine is used to experience welding electrode heating the cylinder part so that the start/stop frequency is around 11 we choose 3GT timing belt series Determine belt width
We calculate an approximated belt width using the following formula, and then select a belt width that is the nearest value to the approximated value
𝑍 𝑑 : number of teeth of small pulley
So that we choose timing belt have:
Calculating belt drive for slider
𝐺 = 1,425𝑘𝑔: net weight of load placed on the belt surface (total weight of slider and TIG torch)
𝜇 = 0,42: Friction coefficient of belt vs table
Figure 3.10 Typical friction coefficient of belt vs table[2]
𝐻 = 0𝑚𝑚: Lift (belt working on horizontal direction)
𝐾 = 𝐾 1 + 𝐾 2 + 𝐾 3 = 1,3 with 𝐾 1 = 1: correction factors for daily operation hours
Figure 3.11 Correction factor for daily operation hours[2]
Figure 3.12 Belt length correction factors[2]
Figure 3.13 Belt speed correction factors[2]
When we calculate belt drive for slider, we used conveyer belts selection procedure because of the similarity mechanism to the slider However, manufacturer from supplier company recommended when using belts for other purpose than conveyance (e.g transmission), for polyurethane belt S3M; design with 1/2 of the allowable tension in the table; for XL, L, H, S5M, S8M, T5 and T10, design with approximate 2/3 of the allowable tension in the table
Figure 3.14 Table on open-end belts allowable tension[2]
Conclusion: We choose S3M belt type because it is satisfied the condition for open-end belts allowable tension with the belt width is 6mm and the length we used for the machine is 164mm
Calculating main shaft
Shaft design calculation including steps:
- Choose material: Because shaft only work in slow speed (around 10 rpm) and load the weight of chuck and workpiece about 2,5kg Therefore, CT5 would be a perfect material for this type of working condition
- Shaft design in terms of durability:
Our main shaft design based on some available part in the market so that the diameter and length like the dimension from picture above The only job we done is calculate the fatigue strength and static strength test whether the shaft can stand in front of force from the timing pulley and the weight of chuck
𝑣 = 10𝑟𝑝𝑚 = 0,02𝑚/𝑠: Speed of the motor with diameter of the smalll pulley is 10mm
In case the line connecting the center creates an 𝛼 = 194 0 angle with the y-axis, divide 𝐹 𝑟 into 2 components that are perpendicular to each other
𝐹 𝑥𝑟 = 𝐹 𝑟 sin 𝛼 = 1140 × sin 194 0 = −800,72𝑁 From the drawing above, we will have free body diagram of the shaft:
- Determine the forces and moments acting on shaft:
- Calculate bending moment at dangerous cross-section:
- Calculate torque acting on shaft:
- Equivalent moment at cross section A:
= 40080,68𝑁𝑚𝑚 Verify the strength condition for shaft:
- At dangerous cross section: Bearing assembly cross section
𝜏 −1 = 0,58𝜎 −1 = 0,58 × 218 = 126,44𝑀𝑃𝑎 with tensile strength of CT5 is 500MPa
For the axis of rotation, the bending stress varies with the period of symmetry, so that:
- Calculating 𝜏 𝑚𝑗 and 𝜏 𝑎𝑗 : When the shaft rotates in 1 direction, the torsional stress changes with the dynamic circuit period, so that:
- Finally, calculating 𝑠 𝑗 : The newly designed shaft structure ensures fatigue strength if the safety factor at dangerous sections satisfies the following conditions:
Choosing bearing and verifying the bearing condition
- Total forces acting on bearing:
Notation d (mm) D (mm) C (kN) 𝐶 0 (kN)
Verify the bearing based on dynamics load:
- m = 3: Degree of fatigue curve in bearing test with ball bearing
- 𝑉 = 1: Coefficient about the number of rotation
Verify the stress based on static load
In order the prevent the residual deformation, the ball bearing need to satisfy the condition:
MANUFACTURING
Manufactured details
Main shaft used to support and fix the chuck, which needs to be carefully machined to satisfy the mounting dimensions and maintain the rotational stability of the workpiece Because the load of the shaft is not too large, there is no cutting moment, the main shaft will be machined at the mechanical workshop from a round steel bar with a diameter of 80mm with the following parameters:
The main shaft is the most important of our mechanism It received the rotational motion and moment from motor through belt drive It stability maintained by bearings and the rotational speed is affected by the stepper motor
- Tolerances for assembly: At the step diameter we need to assembly bearing In this case we use clearances fit then fixed it by the screws of bearing
Material removal allowances and machining methods:
- Material removal allowances: the largest diameter is 40mm and the leght ofshaft is 80 mm So we choosing the C45 cylindrical structure steel with diameter and length are 80mm and 120mm respectively
- Machining method: Turning on engine lathe
No Routes Steps Machine Cutting tool Fixture
Carbide insert tool 3 jaw chuck Drilling center
Face turning Carbide insert tool 3 jaw chuck Drilling center
Rough turning to 80mm Rough turning to 25mm for step diameter
Rough turning to 17mmfor step diameter Rough turning to 16mm for step diameter Rough turning to 16mm for step diameter
3 jaw chuck and tailstock and driving center tip
6 Finishing Finishing Carbide 3 jaw turning ∅17 and ∅16 turning to
∅17 and ∅16 insert tool chuck and tailstock
4.1.2 Parts used to fix assembly details:
Detail used for the purpose of fixing the motor holder to the frame Need material that is light, durable, not too hard, relatively machined by vertical milling machine Mounting with custom jigs We design 2 pieces for 2 motor, the parameters shown in the drawings below:
Figure 4.3 Main motor holder locating bar
- Tolerances for assembly: 2 holes we need to assembly hexagon screws In this case we use clearances fit then fixed it by the screws
Material removal allowances and machining methods:
- Material removal allowances: the longest dimension is 62mm and the thickness of part is 2mm So we choosing 2 C45 structure steel sheets with length and width are 65mm and 25mm then weld together
- Machining method: Turning on engine mill, welder
Figure 4.4 Side motor holder locating bar
Figure 4.5 Side motor holder locating bar technical drawing
- Tolerances for assembly: slot we need to assembly hexagon screws In this case we use clearances fit then fixed it by the screws
- Material removal allowances and machining methods:
- Material removal allowances: the longest dimension is 100mm and the thickness of part is 5mm So we choosing C45 structure steel sheet with lenght and width are
- Machining method: Turning on engine mill
Detail used for the purpose of fixing the welding electrode holder to the slider system Need material that is light, durable, not too hard, relatively machined by vertical milling machine Mounting with custom jigs The parameters shown in the drawings below:
Figure 4.6 Electrode holder locating bartechnical drawing
- Tolerances for assembly: 4 holes we need to assembly hexagon screws In this case we use clearances fit then fixed it by the screws
Material removal allowances and machining methods:
- Material removal allowances: the longest dimension is 64mm and the thickness of part is 3mm So we choosing C45 structure steel sheet with lenght and width are
- Machining method: Turning on engine mill
Detail used for the purpose of fixing the bearings for mainshaft and tailstock Need material that is light, durable, relatively machined by cutting and grinding machine Using standard mica 20mm thickness The parameters shown in the drawings below:
Figure 4.8 Mica sheet for main shaft
Figure 4.9 Mica sheet for tailstock
- Tolerances for assembly: 1 holes we need to assembly bearing In this case we use clearances fit then fixed it by the bearing
- Material removal allowances and machining methods:
- Material removal allowances: using the standard mica sheet then cutting down to the desired dimensions and grinding to the desired thickness
- Machining method: Turning on cutting and grinding machine.
MACHINE ASSEMBLY PROCEDURES
Machine assembly
In order to facilitate the assembly of the frame in the most accurate way, we divided
ELECTRICALBOX the structure into 5 separate assemblies then assemble them together in the sequence as shown in the diagram below
Aluminum frames are linked together by right angles and hexagon screws The water trough is fitted into the groove of the aluminum bar and can be adjusted to fit
Figure 5.4 Assembling the profile frame and water trough
After completing the aluminum frame next will be the roller assembly The slider is connected to the roller with a trapezoidal aluminum plate to increase the rigidity when the roller moves The slide lock is fitted with the torch holder which can be adjusted in height depending on the size of the workpiece.
Figure 5.5 Slider cluster front view
Figure 5.6 Slider cluster back view
The front of the main shaft is fitted with a 3-spoke chuck and is fixed with a hex nut In the middle of the shaft body fitted with the bearing has been fitted with a plastic plate the end of the main shaft is fitted with a pulley for connection to the belt
Figure 5.7 Main shaft cluster front view
Figure 5.8 Main shaft cluster topview
Figure 5.9 Slider cluster top view
In the motor of the main shaft, the motor locating part is designed with a groove that helps to adjust the position of the motor, and at the same time helps to tighten the belt
Figure 5.10 Motor assembly and spindle belt
- For the slider's motor, the open belt is held by a belt pillow
- To adjust the tension of the belt we use a hex nut combined with a pulley mounted on the rails of the aluminum profile
- The motor locating part is also designed with a groove so that the height of the motor can be adjusted to a suitable position
Figure 5.11 Assembling motor and shaft belt of roller table
Electrical box wiring and assembly
The machine is geared towards industrial design, so we chose the main control circuit as PLC With many advantages such as:
- Easy operation inspection and repair
- Easy plc programming function, easy to understand programming language, easy to learn Easily change the program at will
- Perform complex algorithms with high accuracy Large program capacity to accommodate many complex programs
- Good anti-interference ability, long life, small size Completely reliable in industrial environments
- Because the components all use DC power, the power source we choose is a 24V honeycomb source to transfer the current
- In addition, the power cord in the electrical box is connected to the jack makes it easier to separate the electrical box from the chassis as well as to maintain and repair it flexibly
Figure 5.15 Jack to connect the electrical box to the motor
RESULT AND ANALYSIS
Result
Final look of the machine:
Dimensions and weight of the machine:
Min: 8,7kg (without electrical box)
6.1.2 Result after testing the machine with TIG machine:
- The machine ensures rigidity after attaching the torch
- The machine works safely after starting the TIG welding machine, successfully insulating the control circuit and the power source of the welding machine
- The machine can withstand heat from the electric arc.
Analysis
With the application of PLC circuit, we can control the speed of mainshaft and the velocity of the slider based on the diameter of the workpiece
For stepper motors, usually controlled by the pulse frequency emitted by the driver, so we have to calculate the relationship of the pulse frequency with the speed of both motors
Stepper motors move in discrete steps, or fractions of a revolution For example, a stepper motor with a 1,8 degree step angle will make 200 steps for every full revolution of the motor (360 ÷ 1,8) This discrete motion means the motor’s rotation isn’t perfectly smooth, and the slower the rotation, the less smooth it is due to the relatively large step size One way to alleviate this lack of smoothness at slow speeds is to reduce the size of the motor’s steps This is where microstepping comes in
Microstepping control divides each full step into smaller steps to help smooth out the motor’s rotation, especially at slow speeds For example, a 1,8 degree step can be divided up to 256 times, providing a step angle of 0,007 degrees (1.8 ÷ 256), or 51,200 microsteps per revolution
Microstepping is achieved by using pulse-width modulated (PWM) voltage to control current to the motor windings The driver sends two voltage sine waves, 90 degrees out of phase, to the motor windings While current increases in one winding, it decreases in the other winding This gradual transfer of current results in smoother motion and more consistent torque production than full- or half-step control
For this machine, we choose a step angle of 0,225 degrees which means we divide a 1,8 degree step to 8 times so that we will have 1600 microsteps per revolution
The stepper motor speed can be estimated using:
𝑀𝑜𝑡𝑜𝑟 𝑠𝑡𝑒𝑝𝑠 𝑝𝑒𝑟 𝑟𝑒𝑣𝑙𝑢𝑡𝑖𝑜𝑛 For the speed of mainshaft:
Through belt drive with transmission ratio 4:1, the speed of mainshaft is
4 = 2,34 𝑟𝑝𝑚 For the speed of slider:
1600= 0,1875 𝑟𝑝𝑚 Calculate the velocity of slider:
The diameter of the pulley used for move the slider is 10 mm so that when the motor finish one revolution, the slider will move 10 × 𝜋 (mm) on the scroll bar
𝑟𝑒𝑣) = 5,89 𝑚𝑚/𝑚𝑖𝑛 Parameters of TIG machine while operation:
- Flow rate of argon: 5 l/min
Figure 6.2 After testing the machine
CONCLUSION
Overall, our machine was finished with fully functioned like a mini lathe The machine generally reaching 80% of our expectation However, the reason we make this machine is for further experiment to test whether the TIG welding machine can be used as an option for heat treatment metal cylinder part
Although we have tried our best in both design and implementation, the lack of time and financial problems made us having a few disadvantages First of all, the design of slider for holding TIG torch is quite poor, when we attached the TIG torch, we have to use bandage and nylon cable tie Secondly, when the machine starts to operation, the welding machine can not automatically perform without physical impact to button from TIG torch Thirdly, because of our mistake while designing, our cooling system does not have a way out for water in the tank Finally, our PLC program can be developed for better operations such as we can calculate the position on the workpiece and nominate the TIG torch go to that exact position
For the future improvement, we want to adding some more feature and upgrade our machine including:
- Changing fixture for TIG torch
- Improve the water cooling system
- Adding position sensor and upgrade the PLC program
[1] Trinh Chat, Le Van Uyen "Tính toán thiết kế hệ dẫn động cơ khí" Vietnam Education Publishing House, 2012
[2] Misumi Configurable Timing Pulleys and Timing Belts Catalog - 1st edition
[3] Choosing step motor https://www.machinedesign.com/motors-drives/article/21827541/choosing-a- step-motor-real-example
[4] Microstepping for motor https://www.motioncontroltips.com/faq-what-is-microstepping/
[5] Servo calculation and selection http://www.winmo.top/en/m/news/425.html
[6] Effect of Heat Treatments on the Mechanical Properties of Welded Joints of Alloy Steel by Arc Welding https://www.researchgate.net/publication/335146383_Effect_of_Heat_Treatme nts_on_the_Mechanical_Properties_of_Welded_Joints_of_Alloy_Steel_by_Arc_Weld ing
[7] Hướng dẫn trình bày luận văn https://fcft.hcmute.edu.vn/Resources/Docs/SubDomain/fcft/Quy%20dinh%20tri nh%20bay%20luan%20van_CNMT.pdf
[8] Hướng dẫn làm luận văn tốt nghiệp https://www.youtube.com/watch?v=wwm8ZbRmFCk
[9] Effects of Microstepping in Stepper Motors https://www.youtube.com/watch?v=tRoT3qpndbU
[10] Program for PLC mitsubishi https://dl.mitsubishielectric.com/dl/fa/document/manual/plc_fx/jy997d16801/jy 997d16801k.pdf https://tanhieptienphat.com/upload/baiviet/fx3u3uc-lap-trinh-plc-tieng-viet-
4127.pdf https://plctech.com.vn/huong-dan-lap-trinh-plc-mitsubishi-phat-xung-dieu- khien-servo/
[11] https://vneconomy.vn/kho-khan-cua-nganh-thep-co-the-keo-dai-den-quy-2- 2023.htm#:~:text=Theo%20b%C3%A1o%20c%C3%A1o%20m%E1%BB%9Bi%20n h%E1%BA%A5t,4%25%20so%20v%E1%BB%9Bi%20c%C3%B9ng%20k%E1%BB
[12] https://www.youtube.com/watch?v=eohKyqrZnyI
[13] http://www.gowelding.com/met/carbon.htm
[14] https://www.alibaba.com/product-detail/C6163B-Bochi-BaoJi-Gap-Bed- Horizontal_60721705219.html
[15] https://vi.aliexpress.com/item/32921778642.html?gatewayAdapt=glo2vnm
[16] https://www.electronics-tutorials.ws/io/io_7.html
[17]https://shopee.vn/linhkien_ktshop?categoryId0637&entryPoint=ShopByPDP& itemId#21225566
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
Full Name Sign Date Design P.T.TINH
DESIGN AND FABRICATION OF A WELDING ELECTRODE MOVING MODEL AROUND A CYLINDER PART
1 Heat treatment reaches hardness 52 HRC
3 Unless otherwise specified, limiting deviations of all dimensions as chosen as follows:
Switch Motor carrier Welding electrode
Belt b=8mm Nut M6 Pulley M6 Step motor M5 Hexagon screw Motor support bar Angle locating Aluminum bar
24v Supply Step driver PLC Belt bmm