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Metal fabrication is a process of producing a metal component by modifying a raw piece of material in a machine shop. These materials are processed on different temperatures and depending on the range of temperatures; the process is classified as cold, warm and hot. Precision sheet metal fabrication describes various different processes that form sheet metal into finished products. Objects that are fabricated and used for machinery and other instruments are among the daily used objects like paper clips, computers, bolts, nails, automotive parts and many more.
There are various factors like rate of production, desired geometry, and other physical requirements that influence the fabrication process. The benefits of the metal fabrication process are far and wide because it is used by all industries. Every precision sheet metal fabrication process undergoes three primary processes that include forming, cutting and finishing. Forming is a process that alters the form of the flat metal sheet. Forming can be done using various different processes like annealing, bending, cold rolling, drawing, forging, mechanical working, press forming, roll forming and welding. After forming, a metal sheet is cut to alter the shape by removing some unwanted material. The cutting process includes stamping, shearing, sawing, drilling, blanking and punching. Finally, the last stage is the finishing process. In this process, the shaped metal sheet is given a finished and soft surface using sanding and vibration techniques. Aesthetic considerations like painting and visual design applications are also few of the method applied to give the finishing touch. Some of the latest techniques in metal fabrication involve laser cutting, electro discharge machining, water jet cutting and wire cut EDM. In some cases CNC machining is also used.
There are various products that are created during precision sheet metal fabrication. The most common objects produced are metal cabinets, enclosures, ventilation shafts, hoods, exhaust systems, tanks and prototypes. Metal fabrication is also used by various other industries for food dispensing, food storage, communications, automotive, computer, medical, electronics, aerospace, telecommunication, pharmaceutical, residential and construction.
Some of the types of Precision Sheet Metal Fabrication include processes like Annealing (heating), Bending (straining), Cold forming, Cold rolling (shaping sheet metal using rollers), Drawing (material is forced into a die with a punch to form a cup-like shape), Forging hammering or pressing), Rolling (reducing thickness of the material), Extrusion (producing cylindrical bars or hollow tubes by forcing round billets through one or more dies) and Spinning (forms axially symmetrical shapes).
George is a well-known author who writes on the topics related with Precision Sheet Metal Fabrication, metal fabrication for the site www.emachineshop.com.
Related keyword - Precision Sheet Metal Fabrication, Custom Metal Fabrication, CNC, laser cut, water jet cutting, CNC machining, machine shop, CNC machine shop, machining,
Idealized Chip Formation
The figure below depicts an idealized, two dimensional view of the metal cutting process. The assumptions in this model are that the tool is perfectly sharp, that the cut depth t and the cutting speed V are constant, and that the cut depth is small compared to the cut width. In this idealized model, the material layer at the top is formed into a chip by a shearing process in the primary shear zone at AB. The chip slides up the rake face undergoing some secondary plastic flow due to the forces of friction. This idealized model correctly predicts that cutting force increases with cut depth, material hardness, and friction coefficient. Cutting forces are inversely propoortional to rake angle. Power required increases with the feed rate.
Idealized Chip Formation
Built Up Edge
One important effect that is not considered in the model above is built up edge. Under most cutting conditions, some of the cut material will attach to the cutting point. This tends to cause the cut to be deeper than the tip of the cutting tool and degrades surface finish. Also, periodically the built up edge will break off and remove some of the cutting tool. Thus, tool life is reduced. In general, built up edge can be reduced by:- Increasing cutting speed
- Decreasing feed rate
- Increasing ambient workpiece temperature
- Increasing rake angle
- Reducing friction (by applying cutting fluid)
Built Up Edge
Calculating Speeds and Feeds
Cutting speed refers to the speed at which the tool point of the cutter moves with respect to the work measured in feet per minute. Feed is the rate at which the work moves into the cutter measured in feed per tooth revolution. Feeds and speeds affect the time to finish a cut, tool life, finish of the machined surface, and power required of the machine. The cutting speed is mostly determined by the material to be cut and the material of the tool. To find the right speed for any task, refer to the Machinery's Handbook or other reference. To calculate the proper spindle speed, divide the desired cutting speed by the circumference of the tool (or of the part if it is rotating) expressed in feet. The feed rate depends on the width and depth of cut, finish desired and many other variables. To calculate the desired feed setting from the feed rate, multiply feed per tooth per revolution by number of teeth and rpm of the spindle.
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Temperature Considerations
At high temperature zones crater wear occurs. The highest temperature of the tool can exceed 700 °C and occurs at the rake face whereas the lowest temperature can be 500 °C or lower depending on the tool.ramEnergy Considerations
Energy comes in the form of heat from tool friction. It is a reasonable assumption that 80% of energy from cutting is carried away in the chip. If not for this the workpiece and the tool would be much hotter than what is experienced. The tool and the workpiece each carry approximately 10% of the energy. The percent of energy carried away in the chip increases as the speed of the cutting operation increases. This somewhat offsets the tool wear from increased cutting speeds. In fact, if not for the energy taken away in the chip increasing as cutting speed is increased; the tool would wear more quickly than is found.As every one knows, chips are formed during the machining of workpieces. The side of the chip in contact with the cutting tool is normally shiny, flat and smooth while the other side, which is the free workpiece surface, is jagged due to shear.
It is important to study the formation of chips during the machining process as the former affects the surface finish, cutting forces, temperature, tool life and dimensional tolerance. Understanding the chip formation during the machining process for the specific materials will allow us to determine the machining speeds, feed rates and depth of cuts for efficient machining and increased tool life in the specific actual machining operation.
During the machining process, three basic types of chips are formed. They are discontinuous chips, continuous chips, and continuous chips with built-up edge.
Discontinuous chip formation normally occurs during machining of brittle work material. This type of chips also occus in machining operation with small rake angles on cutting tools, coarse machining feeds, low cutting speeds. Discontinuous chip formation results in poor workpiece surface finish.
During continuous chip formation, a continuous "ribbon" of metal flows up the chip-tool zone. This is considered to be the ideal condition for efficient cutting action.
Continuous chip with built-up edge formation is basically the same process as continuous chip formation, except that as the metal flows up the chip-tool zone, small particles of the metal begin to adhere or weld themselves to the edge of the cutting tool. As the particles continue to weld to the tool, it affects the cutting action of the tool.
This type of chip formation is common in machining of softer non-ferrous metals and low carbon steels. Common problems are the built-up edges breaking off and being embedded in the workpiece during machining, decrease in tool-life and final poor surface finish of the workpiece.
Studies on the built-up edges have shown that the chip material is welded, deformed and then deposited onto the rake face of the tool layer by layer. It is thus possible to observe the presence of built-up edges by studying the back face of the chip during the machining process. This is normally used in micro or ultra precision machining operation.
To reduce built-up edges, improve the lubrication conditions, use sharp tools and better surface finish tool and also apply ultrasonic vibration during the machining process.
Author Ken Yap is a director of Suwa Precision Engineering in Singapore and represents niche manufacturers of metal stamping, swiss turning, pcb fabrication and gear hobbing from Suwa, Japan.
Almost everyone in manufacturing has heard about lean manufacturing. Most large corporations are in various stages of implementation. Many companies are currently applying the principles and building a lean foundation. Others are sustaining the implementation and continuously improving on the foundation. There are also many corporations wondering what went wrong or why they haven’t obtained the results they desired.
The primary key for success in lean is to understand that it is a journey. There is no “silver bullet” in any manufacturing or service industry. If there were, it would be sold and every company would have it.
Lean begins with the top management of the enterprise. Top management must have the vision to understand both the requirements and expected results, and commit the resources to achieving them. If the expected requirements and resources do not match, any system such as lean manufacturing will fail.
The requirements depend on the business. If the business has 5000 employees spread across 15 facilities in 20 different states, the requirements will be large. A small facility with 100 employees will require less.
Management needs to understand that lean manufacturing is a journey. It is a system of applied principles that leads the enterprise to a state of “lean”. If management is expecting to achieve “headcount reduction”, they are choosing the wrong system. Any headcount reduction should take place prior to implementing lean manufacturing.
Lean systems involve everyone in the enterprise to work diligently to remove all muda (waste) in the system. There are eight common types of waste defined in lean manufacturing. These wastes are so pervasive in organizations that everyone must pursue and eliminate them. People simply are not going to work themselves out of a job, and therefore everyone must be supportive of the journey.
Lean also involves continuous improvement through “kaizen”. Kaizen in Japanese means “small incremental improvement”. Kaizens involve employees from all functions to work together to eliminate waste, improve productivity, and improve the business in all aspects. Again, management must have employees empowered to improve the operation.
One piece flow is another system utilized in lean manufacturing. Therefore SMED (single minute exchange of die) systems to reduce changeover times must be employed.
Other lean concepts utilized in the journey include “pull systems”, “cellular manufacturing”, “kanban”, OEE (overall equipment effectiveness), TPM (total productive maintenance), error proofing, root cause elimination, and many others.
All of these systems require the effort of a large mass of employees to be successful. Therefore, employees must not be fearful of losing a job or lean manufacturing will not succeed.
Once employees feel they can trust management, the lean journey can begin. The journey begins with lean manufacturing training and it never stops.
Lean manufacturing is not a system that can be administered or implemented by a few individuals. It can be led by a few individuals, but the implementation will involve everyone.
Every person in the organization should first understand why the company is implementing lean manufacturing. Is it to have a competitive advantage? Is it to stay in business?
Since employees have always thought of management as “cost cutters”, it should be explained that costs are expected to come down in the long run. It should be explained why that is necessary, and what it will mean for the business. Lower costs enable the company to sell product or service. It might preserve existing jobs and lead to more hiring.
Once the overall goals of the company are explained, training should begin with the basics.
This will include an overview of lean manufacturing, 5S, 8 wastes (muda), problem solving techniques, and simple value stream mapping.
After initial training, individual concepts should be explained which apply to the company. For example, companies with machinery will be implement SMED, kanban, OEE, and TPM. Companies carrying inventory will want all employees to understand the waste involved in it.
Almost every company will begin with some type of “review” process. This review process will provide the “gap” analysis between where the company is in terms of lean versus where it wants to be. For example, setup times might average 12 minutes but need to be done in 3. Or cycle time might be 18 hours and it should be 6.
Once the analysis is completed, the training and implementation begins. Most companies begin training with 5S (workplace organization). Most implementations also begin with 5S while value stream mapping is often done simultaneously. As with all lean concepts, 5S, value stream mapping, and the review process never end.
Once these are implemented, the journey begins. Lean concepts are the arsenal to move the company to a state of lean. The lean leader utilizes the tools necessary to improve each part of the organization. Most often, many of the tools are utilized in every area.
When implemented correctly, lean is contagious. People in all functions from the plant or office floor to the executive suite are constantly looking for waste and non value adding activities. When they find them, they do everything possible to eliminate it forever.
A free lean manufacturing training primer of all major lean concepts in included at http://www.1stcourses.com |
As every one knows, chips are formed during the machining of workpieces. The side of the chip in contact with the cutting tool is normally shiny, flat and smooth while the other side, which is the free workpiece surface, is jagged due to shear.
It is important to study the formation of chips during the machining process as the former affects the surface finish, cutting forces, temperature, tool life and dimensional tolerance. Understanding the chip formation during the machining process for the specific materials will allow us to determine the machining speeds, feed rates and depth of cuts for efficient machining and increased tool life in the specific actual machining operation.
During the machining process, three basic types of chips are formed. They are discontinuous chips, continuous chips, and continuous chips with built-up edge.
Discontinuous chip formation normally occurs during machining of brittle work material. This type of chips also occus in machining operation with small rake angles on cutting tools, coarse machining feeds, low cutting speeds. Discontinuous chip formation results in poor workpiece surface finish.
During continuous chip formation, a continuous "ribbon" of metal flows up the chip-tool zone. This is considered to be the ideal condition for efficient cutting action.
Continuous chip with built-up edge formation is basically the same process as continuous chip formation, except that as the metal flows up the chip-tool zone, small particles of the metal begin to adhere or weld themselves to the edge of the cutting tool. As the particles continue to weld to the tool, it affects the cutting action of the tool.
This type of chip formation is common in machining of softer non-ferrous metals and low carbon steels. Common problems are the built-up edges breaking off and being embedded in the workpiece during machining, decrease in tool-life and final poor surface finish of the workpiece.
Studies on the built-up edges have shown that the chip material is welded, deformed and then deposited onto the rake face of the tool layer by layer. It is thus possible to observe the presence of built-up edges by studying the back face of the chip during the machining process. This is normally used in micro or ultra precision machining operation.
To reduce built-up edges, improve the lubrication conditions, use sharp tools and better surface finish tool and also apply ultrasonic vibration during the machining process.
Author Ken Yap is a director of Suwa Precision Engineering in Singapore and represents niche manufacturers of metal stamping, swiss turning, pcb fabrication and gear hobbing from Suwa, Japan.
Effects of Tool Geometrical Parameters on the Chip Formation and Cutting Force in Orthogonal Cutting
0 comments Posted by BMFRGuru at 11:50 AMAbstract.
The tool plays an important role in cutting process. The aim of this paper is to investigate
the effect of tool geometrical parameters on the chip formation and cutting force with orthogonal
cutting models. The large deformation Rigid-visco-plastic FEM program DEFORM-2DTM is used, and thermo-mechanical coupling effect are considered. The chip separation from workpiece is implemented by remeshing. Contrary to traditional cutting simulation, the workpiece is moved and the tool is fixed, which is consistent with actual process. The effects of tool rake angle on the chip geometry and cutting force are analyzed. The simulated cutting forces are compared with results in other references. The research results are a help to cutting process study and cutting tool design.
Introduction
Cutting processes, such as turning on lathe, drilling and milling, remove material from surface ofthe workpiece, thereby producing chips. The basic mechanics of chip formation is essentially thesame for all these operations. Although almost all cutting processes are three-dimensional in nature, the two-dimensional model shown in Fig. 1, known as orthogonal cutting, is still useful in studying the basic mechanics of cutting. In this model, the workpiece moves at a certain velocity V and a depth of cut t0. A chip is produced ahead of the tool by shearing the material continuously along the shear plane.
The major independent variables that we can change directly in the cutting process include tool
and workpiece material, tool shape, surface finish and sharpness, cutting conditions, cutting fluid,
machine, etc. They can influence the type of chip produced, force and energy dissipated in the
cutting process, temperature rise in the workpiece, the chip, the tool, wear and failure of the tool,
the surface finish produced on the workpiece after machining, etc. Among these independent
variables, the tool parameters play an important role in cutting processes，and some novel tools can improve the cutting quality. A cutting tool includes some dimensions parameters and angles
parameters, which can be mainly characterized by the rake angle, clearance angle, and cutting edge radius.
Analysis of the Cutting Force Components and Friction in High Speed Machining
0 comments Posted by BMFRGuru at 11:05 AMAn original experimental device is used to reproduce conditions of orthogonal cutting for a wide range of cutting speeds (from 15 to about 100 m/s) (Sutter et al.). Improvement of the initial device (Sutter et al.) makes it possible to record both values of normal and tangential forces in orthogonal cutting. An analysis of the tool–chip friction is then possible for a large range of cutting speeds. The evolution of cutting force components as well as the evolution of the friction coefficient are presented and analyzed. In addition, the process of chip formation during high speed machining is illustrated by photographic recording with a high speed camera.
In this study, temperature of cutting tool in high-speed milling was simulated using finite element method, and then the influences of cutting conditions and cutting edge geometry on tool temperature were studied. It was found out that a rapid temperature change is repeated in intermittent cutting, and the temperature around the cutting edge becomes very high within very short time. Combination of feed rate and radius depth of cut has a large influence on tool temperature. Thus it was suggested that maximum tool temperature becomes lower under the condition of high cutting speed and small radial depth of cut when the equal material removal rate is assumed. Also it was shown that the tool geometry such as rake angle and helix angle affect on tool temperature.
There are four basic design features that are incorporated into the design of all cutting tools, including taps. They include cutting face (hook), relief, base material, and surface treatment or coating. We will begin this series of tips with hook and relief.
The cutting face is that portion of the tap flute, between the major and minor diameter of the thread, that cuts or shears the workpiece material. The entry angle of the cutting face into the workpiece material is measured in degrees, from positive to negative, from a perpendicular reference line through the axis of the tool.
Positive hooks are used for soft materials that produce continuous (stringy) chips such are aluminum, mild steel, and stainless. Due to the positive angle, the cutting faces are fragile and may chip easily. Negative hooks are used for materials producing broken or powder chips, or those that have been hardened. This type of cutting face is much stronger and is also less prone to chipping.
Relief on a tap may be found on the chamfer's major diameter (required for tapping), or in the threads, in the form of radial clearance or back taper. Radial or thread relief is a thinning of the tooth from the cutting face to the heel to relieve cutting pressures and friction across the land of the tap. Thread relief is applied for materials that are tough, hard, or have high elastic memory (shrinks or squeezes the tap creating friction). Back taper is the reduction of the major, pitch, and minor diameters from the first thread at the front of the tap to the last thread near the shank. While thread relief is applied for specific applications, back taper is applied to all taps.
For tools or to be put in touch with a tap specialist www.pgstools.com
http://www.pgstools.com is a carbide insert cutting tool supplier. We offer articles for the purpose of troubleshooting tooling issues. All articles may contain information we have obtained through personal experience as well as reference from suppliers.
Magnesium has been used in manufacturing notebook computer frames, video cameras, digital cameras, PDAs and other consumer electronics products because of its high strength to weight ratio. When magnesium is alloyed with aluminum, the resultant material is very light and strong, and easily machinable.
The main concern in machining magnesium alloy is the danger of fire ignition when dry cutting. Fire may occur when the melting point of the alloy (400-600 degrees Celsius) is exceeded during machining. The small chips and fine dust generated during cutting are also highly flammable and pose a serious fire risk if not properly handled.
There are several points to note when machining magnesium:
Firstly, use a lower cutting speed when compared to cutting aluminum. The workpiece temperature goes up with an increase in cutting speed and also smaller undeformed chip thickness. In other words, the slower the machining speed and the larger the chips, the lower the workpiece temperature will be. Due to this reason, some companies have modified woodworking tools for machining magnesium so as to achieve larger chips and lower fire hazard.The cutting tools used should have relief and clearance angles that are sufficiently large to prevent unnecessary cutting tool-workpiece friction, thus lowering the heat generated during the cutting process.
Second, keep the machining center clean. Cleaning the machining centers regularly and storing the magnesium chips correctly are important aspects of machining magnesium. Keep a container of cast iron chips near by when machining magnesium, If fire occurs, smother the fire with the cast iron chips.
Thirdly, if coolants are necessary for high speed machining, do not use water-based lubricants. Instead use a light mineral oil, or a water-soluble cutting fluid such as Castrol Hysol MG specially formulated for machining magnesium. Some companies in Japan use semi-dry machining via a misting system.
The fourth point is to monitor the workpiece temperature during machining. Experiments were carried out using thermocouples mounted into the workpiece to monitor the workpiece temperature during machine. Dry cutting of magnesium alloy thin walls was achieved using cutting speed of 440m/min for roughing and 628m/min for fine finishing.
Despite the fire hazards, as competition from overseas low-cost production bases intensifies, and magnesium becomes increasingly used in electronics products, most machining job shops could very well find machining of magnesium a niche worth pursuing.
Author Ken Yap is a director of Suwa Precision Engineering Pte Ltd in Singapore and represents precision component manufacturers from Suwa, also called "The Oriental Switzerland" in Japan due to its Swiss resemblance for rich watch-making industry, its mountainous terrain and its precision component making industry. For more information on precision manufacturing, visit his homepage at http://www.suwaprecision.com.
