Turn-Mill Enhance Productivity

In recent years, shops have experienced market changes that continue to impact how parts are manufactured. Shorter lead times, reduced lot sizes and the drive to eliminate inventory have conspired to change the manufacturing process.

In the current manufacturing process adapted for the machining of metal parts needs a milling machine to mill, a turning machine to turn, a drill press to make holes and so on. Each operation was an incremental step in the manufacturing process--ultimately resulting in a completely machined part. Shorter lead times, reduced lot sizes and the drive to eliminate inventory have conspired to change the manufacturing process.

The Turn/Mill technology will enable to complete most of the operations on a workpiece in a single setting. The turn-mill machine brings advantages of access to part geometric features that previously would require secondary operations. This reduction of clamping time avoids the error accumulation caused by the conversion of positioning datum. Thus improving the machining accuracy resulting in enhancement of throughput yield.

Additionally this technology provides the ability to reduce production leadtime, improve machining accuracy, reduce floor space, lower operating expenses, reduce operator requirements and improve the work environment.

Metal Working - Cutting Oil Selection and Functions

Metal cutting fluid is utilized as a part of metalworking and machining for various purposes, mostly as a lubricant and for cooling. It comes in the different type of forms including synthetic fluids, semi-synthetic fluids, oils and solvent oils.

Synthetic fluids are made of alkaline mixes and compounds that avert erosion. They are utilized as a part of weakened water and are the critical part of cooling. Semi-synthetic fluids are a blend of soluble oils and manufactured fluids and its attributes show up in the two constituents.

Undiluted Oils are used only when making cutting fluids. They offer the best friction yet bad cooling. Solvent oils are solute with water and give great lubrication and cooling contrasted with alternate items. They are the most cost-effective and are hence are very popular among the heavy metal cutting industry.

In order to select the best oil, you need to gather some basic information relevant to the selection criteria. For purposes of simplicity, you need to know the metals in use, the predominant machining operations, basic machine types, tooling specifics, plant processes and chemical restrictions for your facility.

Metals

Some metals are more difficult to machine than others. Stainless steel, exotic alloys and very hard metals demand a very high level of performance from the cutting oil. Other metals, like brass and aluminum, are easy to machine with general-purpose oils.

Where tough, low-machinability metals are involved, you will need highly additized cutting oil with excellent extreme-pressure (EP) and anti-weld capability. Most often, these oils contain active sulfur and chlorine to protect the tooling and ensure good parts finish.

For brass, aluminum, many carbon steels and low-alloy steels, a cutting oil with lubricity additives, friction modifiers and mild EP/anti-weld performance is sufficient. These oils are generally formulated with sulfurized fat (inactive) and/or chlorinated paraffin. Active cutting oils (containing active sulfur) should not be used for brass and aluminum, as they will stain or tarnish the finished parts. Oils formulated for brass and aluminum are often called "non-staining" oils.

Machining Operations

Easy machining operations (turning, forming, drilling, milling, etc.) can be performed at higher speeds and require high levels of cooling with only modest EP capability. The milder operations can be performed with lower viscosity, lightly additized fluids.

Difficult machining operations must be run at lower speeds and require a great deal of anti-weld protection. Oils designed specifically for the most difficult operations, like thread-cutting or broaching, are generally higher in viscosity and loaded with EP additives like active sulfur and chlorine.

Basic Machine Types

The type of machinery will also dictate some of the cutting oil characteristics. For example, screw machines experience heavy cross-contamination between the lube oil and cutting oil. For this reason, these machines frequently run on dual-purpose or tri-purpose oils that can be used in the lube boxes, hydraulics and cutting oil sumps.

Grinders, gun drills and deep-hole drilling machines require lighter viscosity oils for high rates of cooling, good chip and swarf flushing, through-the-tool delivery and high-pressure application without foaming. CNC OEMs may place restrictions on the cutting oil due to potential incompatibility between the cutting fluid and machine components, such as seals. Centerless grinders may require a tougher fluid than surface grinders.

Qualities and Functions of a Good Metal Cutting Fluid:

·       The principle trademark is its ability to keep the metal and apparatus temperature stable to abstain from obliterating the metal because of high temperatures or even a fire on nearby materials.

·         It ought to give appropriate lubrication to boost the life cycle of the cutting tip and lessen the amount of heat created by reducing contact.

·         It ought to have the ability to stop rust from getting on the metal cutters and important metal parts.

·         The cutting fluid must be safe to operate and also environmental friendly to discard.

·         Fluid should be able to wash out bits of metal away from the cutting area.

·         The diverse metal cutting fluids require distinctive application techniques; these incorporate brushing, flooding, spraying, misting, and dripping. The most widely recognized and used technique is a Jet method in which liquid is being sprayed to the cutting workpieces.

Non-Cutting Functions

·     The selection of a fluid/coolant should also consider its effect, not just on the part being ground or machined or however upon the nearby condition of the operation. These contemplations would incorporate the:

·         Addition of rust inhibitors to control consumption

·         Stink (scent) protection from keeping the development of poisonous vapor

·         Adhesive resistance to prevent waste formation on the finishing product

·         Operator health and nature-friendly

·         Disposability which, contingent upon synthetic substance, may go under certain ecological restrictions

Cutting Fluid Maintenance

Cutting fluids lose its quality after some time because of oil system contamination. Most common type of degradation in the form of tramp oil, otherwise called sump oil, which is undesirable oil that has blended with cutting fluid. It begins as grease oil that leaks out from the sideways and washes into the coolant blend, as the protection film with which a steel provider coats their items to avert rusting, or as pressure driven oil spills.

Skimmers are utilized to isolate the tramp oil from the coolant. These are typically slowly rotating vertical disks that are partially submerged beneath the coolant level in the primary supply. As the disk turns the tramp oil sticks to each side of the plate to be scratched off by two wipers previously the plate goes back through the coolant. The wipers are a channel that at that point diverts the tramp oil to a holder where it is gathered for waste disposal. Floating waste is additionally utilized as a part of these situations where temperature or the amount of oil in the water becomes too much.

Support and checking of the fluids are essential for helpful fluid life. Some portion of this is in the care and tidiness of the machine apparatuses themselves. Monitoring involves health and safety checks utilizing the proper test, including:

·         Refractometers, which are utilized to decide the aggregate sum of soluble in a solution.

·         Tests for PH levels and alkalinity (corrosive parts) are additionally valuable.

·         Titration Kits, who are utilized to break down fluid concentration in metal-cutting fluids sullied with tramp oils.

MODELING IN ANSYS

MODEL GENERATION

The ultimate purpose of a finite element analysis is to re-create mathematically the behavior of an actual engineering system. In other words, the analysis must be an accurate mathematical model of a physical prototype. In the broadest sense, this model comprises all the nodes, elements, material properties, real constants, boundary conditions, and other features that are used to represent the physical system.

In ANSYS terminology, the term model generation usually takes on the narrower meaning of generating the nodes and elements that represent the spatial volume and connectivity of the actual system. Thus, model generation in this discussion will mean the process of defining the geometric configuration of the model's nodes and elements. The ANSYS program offers you the following approaches to model generation:

• Creating a solid model within ANSYS.
• Using direct generation.
• Importing a model created in a computer-aided design (CAD) system.

STEPS INVOLVED IN MODEL GENERATION WITHIN ANSYS

A common modeling session might follow this general outline (detailed information on italicized subjects can be found elsewhere in this guide):

• Begin by planning your approach. Determine your objectives, decide what basic form your model will take, choose appropriate element types, and consider how you will establish an appropriate mesh density. You will typically do this general planning before you initiate your ANSYS session.
• Enter the preprocessor (PREP7) to initiate your model-building session. Most often, you will build your model using solid modeling procedures.
• Establish a working plane.
• Generate basic geometric features using geometric primitives and Boolean operators.
• Activate the appropriate coordinate system.
• Generate other solid model features from the bottom up. That is, create keypoints, and then define lines, areas, and volumes as needed.
• Use more Boolean operators or number controls to join separate solid model regions together as appropriate.
• Create tables of element attributes (element types, real constants, material properties, and element coordinate systems).
• Set element attribute pointers.
• Set meshing controls to establish your desired mesh density if desired. This step is not always required because default element sizes exist when you enter the program. (If you want the program to refine the mesh automatically, exit the preprocessor at this point, and activate adaptive meshing.)
• Create nodes and elements by meshing your solid model.
• After you have generated nodes and elements, add features such as surface-to-surface contact elements, coupled degrees of freedom, and constraint equations.
• Save your model data to Jobname.DB.
• Exit the preprocessor. 

3D PRINTING

According to a Wikipedia article, 3D printing is a process of making a three-dimensional solid object of virtually any shape from a digital model. 3D printing is achieved using an additive process, where successive layers of material are laid down in different shapes. 3D printing is also considered distinct from traditional machining techniques, which mostly rely on the removal of material by methods such as cutting or drilling (subtractive processes). A 3D printer is a limited type of industrial robot that is capable of carrying out an additive process under computer control. 

The 3D printing technology is used for both prototyping and distributed manufacturing with applications in architecture, construction (AEC), industrial design, automotive, aerospace, military, engineering, civil engineering, dental and medical industries, biotech (human tissue replacement), fashion, footwear, jewelry, eyewear, education, geographic information systems, food, and many other fields. 

Casting Defects And Their Inspection Methods

There are numerous opportunities for things to go wrong in a casting operation, resulting in quality defects in the cast product. In this section we compile a list of the common defects that occur in casting and we indicate the inspection procedures to detect them

Casting Defects

Some defects are common to any and all casting processes. These defects are briefly describe in the following points

Misruns 

Misruns are the castings which solidify before completely filling the cavity. Typical cases includes

• Fluidity of molten metal is insufficient

• Pouring temperature is too low

• Pouring is done too slowly

• Cross section of the mold cavity is too thin

Cold Shuts 

Cold shuts occurs when two portions of the metals flow together but there is a lack of fusion between them due to premature freezing. Its causes are similar to those of a misrun

Cold Shuts

Cold shuts results from splattering during pouring, causing the formation of solid globules of metal that entrapped in the casting. Pouring procedures and gating system designs that avoid splatting can prevent this defects

Shrinkage Cavity

Shrinkage cavity is a depression in the surface or an internal void i  the casting caused by solidification shrinkage that restricts the amount of molten metal available in the last region to freeze. It often occurs near the top of the casting, in which case it is referred to as a pipe

Micro-porosity

Micro-porosity consists of a network of small void distributed throughout the casting caused by localized solidification shrinkage of the final molten metal in the dendritic structure. The defects is usually associated with alloy, because of the protracted manner in which freezer occurs in these metals

Hot Tearing

Hot tearing also called hot cracking occurs when the casting is restrained from contraction by a unyielding mold during the final stages of solidification or early stages of cooling after solidification. The defect is manifested as a separation of the metal at a point of high tensile stress caused by the metal inability to shrink naturally. In sand casting and other expendable mold processes, It is prevented by compounding the mold to be collapsible. In permanent mold process hot tearing is reduce by removing the part from the mold immediately after solidification

Defects Found Primarily In Sand Casting

Some defects are related to the use of sand mold and therefore they occur only in sand casting. To a lesser degree other expendable mold processes are also susceptible to these problems.

Sand blow

Sand wash is an irregularity in the surface of the casting that result from erosion of the sand during pouring and the contour of the erosion is formed in the surface of the final cast part.

SCABs

SCABs are rough areas on the surface of the casting due to encrusting of sand and melt. It is caused by portions of of the mold surface flaking off during solidification and becoming imbedded in the casting surface.

PENETRATION

PENETRATION to the surface defect  that  occurs when the fluidity of the liquid metal is high and it penetrates into the sand mold or sand core. Upon freezing, the casting surface consists of a mixture of sand grains and metal. Harder packing of the sand mold helps to alleviate this condition.

MOLD SHIFT

MOLD SHIFT refers to a detect caused by a sidewise displacement of the mold cope relative to the drag the result of which is a step in the cast product at the parting line.

CORE SHIFT 

CORE SHIFT is a similar to mold  shift , but it is the core that is displaced and the displaced and the displacement is usually vertical. Core shift and mold shift are caused by buoyancy of the molten  metal.

MOLD CRACK 

MOLD CRACK occur when more strength is insufficient and a crack develops into which liquid metal can seep to form a ‘fin’ on the final casting.

INSPECTION METHOD 

Foundry inspection producing include 

• visual inspection to detect obvious defect such as misruns , cold shuts, and serve surface flaws; 
• displacement measurements to ensure that tolerances have been met; and (3) metallurgical , chemical, physical and other tests concerned with the inherent quality of the cast metal 

Tests in category include ; 

• pressure testing- to locate leaks in the casting; 
• radiographic methods , magnetic practical tests, the use of fluorescent penetrants; and supersonic testing-to detect either surface or internal defect in the casting; the and 
• mechanical testing to determine properties such as tensile strength and hardness. If defects are discovered but are not too serious it is often possible to save the casting by welding, grinding, or other salvage methods to which the customers has agreed.

Significance of Water in Cooling Tower

Quality water plays a significant role in cooling water system. It is considered that cooling towers and its mechanical components represent the cooling system hardware and the water flowing through the cooling system is the system software as shown in figure 1. The cooling-water system normally has highly efficient pumps supplying both the process and the cooling system. Amount of flow to the process always related to the demand by pump sequencing with multiple pumps or using variable-speed drive controllers with pressure and flow rate as a control signal.

Figure 1 Flow of water in a cooling tower;Tangram Technology

As many researchers have agreed that cooling towers control temperature by rejecting heat from hot equipment or from air-conditioning systems. This is possible by the use of significant amounts of water.

Proper operation, thermal efficiency and longevity of the water cooling system rely solely on the quality of water and its reuse potential.In a cooling tower, water is lost throughbleed-off, drift and evaporation. In order to replace such amount of water lost and retain its cooling function, there is a need for more make-up water which must be added to the tower system. Occasionally water used for other equipment within a system can be reused and recycled for cooling tower make-up with little or no pre-treatment (Homel, 2007).

One of the most potential variables of cooling system is quality of water. The condition of water is often not considered as a potential variable over time. However, if cooling water is left unattended, itsupports biological growth, corrodes or scales equipment.  In the case of efficient process and operation, there must be proper treatment of water for cooling tower usage. An approach commonly employed to remove waste heat from the cooling tower is known as cooling loop. It allows water to evaporate to the environment or atmosphere. The evaporated water should be replaced always by fresh make-up water (Lee, 2005).

Heikkila and Milosavljevic (2001) stated that water play an important role in the operation and performance of cooling tower. In their report, it was described that in heat rejection in cooling tower is convectional transfer between water droplets and the air surrounding the environment. Also evaporation allows small portion of water to evaporate into the atmosphere.

Tyagi et al (2007) also revealed that in hostile weather conditions, the exhaust of the cooling tower remixes with the cooler ambient air and when it cools down the leftover moisture condenses in small fog droplets which creates visible plume.

In another development, (ASHRAE, 1996:Tyagi et al 2007) the plume can travel at few hundreds of meters which can led to visibility and darkness issues.

Furthermore, the operation of cooling tower system depends on water quality of the make-up source. Different sources have different challenges. Typical examples include of surface water sources include rivers, lakes and streams. Also groundwater sources are wells or aquifers. In fact, the location of surface water sources are a major factor because of it high level of suspended debris or silts that can cause fouling if not removed by pre-filtration systems.

In figure 2 represents a schematic water-side free cooling system which consist of two flows; the primary and condenser water flows. The cooling tower chills a flow of condenser water that is passed through a plate-and-frame heat exchanger. The free cooling heat exchanger, the condenser water from the cooling tower absorbs heat from the primary water flow.  Also, the chilled primary flow is used in the same way as the primary flow normally supplied by the chillers. Effectively, the water-side free cooling system permits the cooling towers to work as the building’s chillers. However, the cooling towers engaged atmospheric conditions, rather than a mechanically driven refrigeration cycle, as a heat sink to cool the primary water flow.

Figure 2 Water side flow systems

However, the groundwater sources do not have the seasonal variations which surface water sources have, but depending on the geology of the region. The groundwater can have high levels of dissolved minerals which pose as a problem to many cooling tower systems. The water reuse is one of the wise resources option, where consideration should be given to the quality of water and also how that will affect the efficient operation of the cooling tower system and the system ability to meet the required cooling demand.

Natural and Mechanical Drafts Cooling Towers

The difference between natural and mechanical cooling towers is the flow of air which passes through the tower. The natural draft tower is that the packing area is design to locate inside the base of large chimney as shown in figure 1. When the packing is in contact with warm cooling water, it makes the density of the air above the packing to be 5% or less than that of the atmosphere. The driving force to overcome the pressure losses that resist the flow of air through the tower is due to the difference between the air in the chimney and the air outside.

Figure 1 Natural draft cooling tower

In the case of mechanical draft towers mainly use fans which are driven by electric motors to produce the flow of air as represented by figure 2, 3 and 4. The location of the fan determines the type of draft cooling tower. The types of mechanical draft cooling tower include; Force draft; that is when the fan is located in the air passage at the base of the tower. Induced draft; that is when is located in the air passage at the top of tower. This type of draft tower uses both axial and centrifugal flow fans. However, the axial fans are normally with induced draft (Singham, 1990).

Figure 2 Forced draft

Figure 3  Induced draft,  mixed flow

Figure 4 Induced draft, cross flow

Figure : Mechanical draft cooling tower layouts