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Coordinate Measuring Machine (CMM)
A coordinate measuring machine is a device that measures the geometry of physical objects by sensing discrete points on the surface of the object with a probe. Various types of probes are used in CMMs, including mechanical, optical, laser, and white light.
Depending on the machine, the probe position may be manually controlled by an operator or it may be computer controlled. CMMs typically specify a probe's position in terms of its displacement from a reference position in a three-dimensional Cartesian coordinate system (i.e., with XYZ axes). In addition to moving the probe along the X, Y, and Z axes, many machines also allow the probe angle to be controlled to allow measurement of surfaces that would otherwise be unreachable.
Coordinate measuring machineat present is not only a kind of laboratory measurement instrument, but is widely used in machining and assembly workshop. In the automotive industry, the CMM is the necessary measuring tool of product quality assurance and quality control.
OR
A coordinate measuring machine (CMM) works in much the same way as your finger when it traces map coordinates; its three axes form the machine's coordinate system. Instead of a finger, the CMM uses a probe to measure points on a workpiece. Each point on the workpiece is unique to the machine's coordinate system.
CMM. Full form: Cubic metres per minute. Definition: The volume of air in cubic metres that the fan can move in a minute at a defined speed. Another unit is CFM. Cubic feet per minute.
There are four basic types of coordinate measuring machines: bridge, cantilever, gantry and horizontal arm. Each one provides unique advantages based on the components being measured. Bridge. The bridge is the most popular style of coordinate measuring machine.
The typical 3D "bridge" CMM allows probe movement along three axes, X, Y and Z, which are orthogonal to each other in a three-dimensional Cartesian coordinate system. Each axis has a sensor that monitors the position of the probe on that axis, typically with micrometer precision. When the probe contacts (or otherwise detects) a particular location on the object, the machine samples the three position sensors, thus measuring the location of one point on the object's surface. This process is repeated as necessary, moving the probe each time, to produce a "point cloud" which describes the surface areas of interest.
A common use of CMMs is in manufacturing and assembly processes to test a part or assembly against the design intent. In such applications, point clouds are generated which are analysed via regression algorithms for the construction of features. These points are collected by using a probe that is positioned manually by an operator or automatically via Direct Computer Control (DCC). DCC CMMs can be programmed to repeatedly measure identical parts; thus an automated CMM is a specialized form of industrial robot.
Portable CMM: Whereas traditional CMMs use a probe that moves on three Cartesian axes to measure an object’s physical characteristics, portable CMMs use either articulated arms or, in the case of optical CMMs, arm-free scanning systems that use optical triangulation methods and enable total freedom of movement around the object.
Portable CMMs with articulated arms have six or seven axes that are equipped with rotary encoders, instead of linear axes. Portable arms are lightweight (typically less than 20 pounds) and can be carried and used nearly anywhere. However, optical CMMs are increasingly being used in the industry. Designed with compact linear or matrix array cameras (like the Microsoft Kinect), optical CMMs are smaller than portable CMMs with arms, feature no wires, and enable users to easily take 3D measurements of all types of objects located almost anywhere.
Certain nonrepetitive applications such as reverse engineering, rapid prototyping, and large-scale inspection of parts of all sizes are ideally suited for portable CMMs. The benefits of portable CMMs are multifold. Users have the flexibility in taking 3D measurements of all types of parts and in the most remote/difficult locations. They are easy to use and do not require a controlled environment to take accurate measurements. Moreover, portable CMMs tend to cost less than traditional CMMs.
The inherent trade-offs of portable CMMs are manual operation (they always require a human to use them). In addition, their overall accuracy can be somewhat less accurate than that of a bridge type CMM and is less suitable for some applications.
Wire Cutting EDM
EDM Wire Cutting uses a metallic wire to cut a programmed contour in a workpiece. Extrusion dies and blanking punches are very often machined by wire cutting. Cutting is always through the entire workpiece. To start machining it is first necessary to drill a hole in the workpiece or start from the edge. On the machining area, each discharge creates a crater in the workpiece and an impact on the tool. The wire can be inclined, thus making it possible to make parts with taper or with different profiles at the top and bottom. There is never any mechanical contact between the electrode and workpiece (see above). The wire is usually made of brass or stratified copper, and is between 0.1 and 0.3 mm diameter.
Depending on the accuracy and surface finish needed a part will either be one cut or it will be roughed and skimmed. On a one cut the wire ideally passes through a solid part and drops a slug or scrap piece when it is done. This will give adequate accuracy for some jobs but most of the time skimming is necessary. A skim cut is where the wire is passed back over the roughed surface again with a lower power setting and low pressure flush. There can be from one to nine skim passes depending on the accuracy and surface finish required. Usually there are just two skim passes. A skim pass can remove as much as 0.002" of material or a as little as 0.0001". During roughing ( i.e. the first cut) the water is forced into the cut at high pressure in order to provide plenty of cooling and eliminate eroded particles as fast as possible. During skimming (accuracy / finish cuts) the water is gently flowed over the burn so as not to deflect the wire.
Wire EDM is a method to cut conductive materials with a thin electrode that follows a programmed path. The electrode is a thin wire. Typical diameters range from .004"-.012" although smaller and larger diameters are available. The hardness of the work piece material has no detrimental effect on the cutting speed. There is no physical contact between the wire and the part being machined. Rather, the wire is charged to a voltage very rapidly. This wire is surrounded by deionized water. When the voltage reaches the correct level, a spark jumps the gap and melts a small portion of the work piece. The deionized water cools and flushes away the small particles from the gap.
The CNC machine can independently move four machines axes to generate taper cuts. A stamping die can be machined with 1/4 degree taper or a mold with one degree taper in some areas and two degrees in another with precision. Extrusion dies can be cut with the taper constantly changing. For example, a detailed shape on the top of the work piece can transition to a simple circle on the bottom.
Wire EDM can be accurate to +/-.0001". No burrs are generated. Since no cutting forces are present, wire EDM is ideal for delicate parts. No tooling is required so delivery times are short. Pieces over 16" thick can be machined. Tools and parts are machined after heat treatment so dimensional accuracy is held and not affected by heat treat distortion.
Heaters
HEATERS:
5. Vertical/horizontal male plug on the heater Max. Amp 16 at 250V.
6. Fiberglass wire exists between Inner and Outer sheath.
7. Post terminal option available at 19 mm length.
Plastics processing and heaters go hand in hand. Cylindrical band heaters are found on barrels of injection rnolding machines and extruders. Flat strip heaters are the heat source on flat surfaces of machines. Cartridge heaters are inserted in reamed holes of dies and other machinery parts. Tubular heaters may be cast in aluminium or strapped on barrels. When used in these applications, the heaters normally heat by conduction.
Radiant heaters are also used in plastics processing. They are found on roll leaf decorating machines, on thermoforming equipment, and in many packaging operations such as shrink packaging and heat sealing.
Heaters have a maximum manufacturers recommended watt density. Watt density is the watts/sq.in. of the active sheath area of the heater that is in contact with the machinery part or mold. Watt density of band heater is determined as follows:
WATTS DENSITY = watts/ID x 3.14 x width
Watt density of cartridge heater is determined as follows:
WATTS DENSITY = watts/(Length 0.05) x OD x 3.14
Maximum watt density of heaters should be used only if heat calculations indicate it is necessary. Excessive watts can waste energy, cause temperature problems and lead to shorter heater life.
Band heaters
Mica insulated band heaters are versatile and efficient. Many original equipment manufacturers pick these heaters since they are low cost, efficient, and easy to control American manufacturers as a rule choose narrow heaters for each zone. Reasoning that if one heater fails the machine probably can continue to operate. Offshore manufacturer choose one or two wide heaters per zone. Reasoning that the heat is more evenly distributed over the zone being heated. Both reasons have merit. As mica-insulated heaters heat by conduction is important they are properly installed in a clean, dry environment and tightened on the cylinder.
Ceramic insulated band heaters are energy efficient, offer long service life and easy to install. So they are the choice of many machinery builders and may be specified by the processor when ordering a new machine. They also may be chosen as replacement heaters for machines in the field. Ceramic insulated heaters incorporate a fibrous insulation that minimizes heat to the atmosphere and therefore, are more energy-efficient. , Many rebuilders of machine and energy conscious processors choose these heaters when retrofitting machine to meet current productivity demands. Interlocking ceramic insulators allow these heaters to flex and make installation easy. Ceramic-insulated heaters may be rated d with higher watt densities than many other heaters. Improved Ceramic-insulators now permit the manufacture of these heaters in the small sizes needed as nozzle band heaters on injection molding machines.
Mineral insulated heaters incorporate a refractory sheet insulation and similar in construction to mica-insulated heaters. They are, however, capable of higher watt density rating than are mica-insulated heaters. They are ridged in construction and are manufactured in close tolerance ID to match the OD of the cylinder being heated.
Refractory insulated heaters are also known as curved strip heaters. These heaters incorporate a compacted ceramic insulation and coiled resistance wire.
Cast in heaters are tubular heaters cast in aluminum and bronze and are used primarily on extruders. Cooling tubes can be cast in and connected to a chiller or heat exchanger where cooling is needed because of overheated cylinders caused by frictional heat from the screw. Cast-in heaters also have fins for air-cooling.
Tubular band heaters may be shaped and clamped on cylindrical shapes or placed in extruded aluminum profiles shaped and clamped on cylinders with straps. They are found on barrels of injection moulding machines and extruders.
Mica insulated nozzle band heaters continue to be choice of the injection. Molders, but their service life may be limited because of contamination, lead Breakage and high watt. Density. High heat requirements have contributed to the introduction of mineral insulated mini tubular and cartridge heaters for this application. Mini-tubular and cartridge heaters are used on nozzles and nozzle adaptors for hot runner mold systems as well.
1. Sheath material brass.
2. Max.operating temp 280°C.
3. Max.surface load 25w/sq. inch.
4. Fiberglass or Teflon insulated SS mixed wire terminals.
Nozzle band heaters may vary according to type, lockup. Flange, strap or key lock up wedge.
Many heater manufacturers will custom- build heaters to suit Specific applications. Custom heaters could be minor. Changes of standard heaters such as watts, volts, type lockup and electrical connections.
Versatile manufacturers will also build special shapes such as oval, rectangular,U shape and partial-coverage heater. Holes through heaters and cutouts can be incorporated in the heater design. Two-piece heaters for large diameters are a common request.
Recent developments include air-cool band heater Assemblies. These units are self-contained and include band heaters, a vent shroud, and a blower. They are available to OEMS or processors who need replacements for air-cooled extruders or water-cooling with air-cooling. Heat exchangers are not needed. Increased thermal and dielectric qualities of both mica insulation and mineral insulation allow higher ratings of heaters.
1. Plastic proof.
2. Sheathing material high grade steel or brass.
3. Operating temp brass 280°C - SS 350°C.
4. Max. surface load Brass 30w/sq. inch, SS sheath 45w/sq. inch.
5. Metal braided Fiberglas wire terminals.
Cartridge heaters are designed to fit into a reamed hole and are needed with many molds and platens. Packaging operations use them in heat-sealing of plastic containers. Stand diameters available are ¼,3/8, ½,⅝,3/4 and 1 inch. Metric sizes are also available. Minimum and maximum length vary depending on diameter and other tolerances.
Standard construction includes 12 in. leads exiting straight from one end of heater. Right-angle exit, longer leads, leads with metallic sleeving to minimize lead damage, or moisture-proof sleeving may be included in the heater design. Thermocouples may be built into the heater. They can incorporate fittings and be made moisture proof for immersion applications.
Strip and plate heaters are designed to be mounted (clamped on flat surfaces of machinery parts, molds, dies, etc.).Most heaters and their insulation medium can be constructed in flat shapes and called strip and plate heaters.
Installation can be via mounting bolts incorporated in the design, or via external clamping arrangements designed in.
Radiant heaters heat by radiation instead of conduction, as do most other heaters. Thermoforming and packaging machines usually incorporate radiant heaters.
Radiant panel heaters normally incorporate mica-insulated heat emitters evenly aligned in metal frame for mounting.Tubler heaters are used in many plastics applications calling for radiant heaters. They can be incorporated in panel heaters and all types of ovens. Flat or cylindrical ceramic- insulated heaters may also function as radiant heaters.
Leaf proof Nozzle Band Heaters
1. Plastic proof.
2. Sheathing material high grade steel.
3. Max.operating temp 600 °C.
4. Max.surface load 60 w/Sq. inch.
5. Insulation - high grade mineral insulation.
6. Metal braided fiberglass wire terminals.
Applications
1. Hot runner bushings.
2. Nozzles of plastic processing machineries.
Types of Terminals
1. 12" Lead or Post Terminals.
2. Junction Box
3. Two flexible fiberglass insulated lead wires without junction box.
4. Protected fiberglass Wires with G.I or SS flexible conduct..
8. Ceramic connectors Max. Amp - 25 A.
Mould Material Selection (Blow)
MOULD MATERIAL SELECTION FOR INJECTION AND BLOW MOULDS:
BERYLLIUM COPPER BLOW MOULD FOR PVC CONTAINER
BERYLLIUM COPPER BLOW MOULD FOR PVC CONTAINER
There is no core in blow mould, comparatively low clamping and blowing pressure required, and thus, need not be made of high tensile strength material. However, good thermal conductivity is necessary to reduce the cycle time and to produce quality product.
The Advantages of Aluminium Moulds
Following are some of the main advantages, which can be obtained by using Aluminium alloys for moulds. Some are well-known, other perhaps less:
1. The importance of machinability: equal to lightness
2. Extremely high thermal exchange capability: rapid cooling of the injected thermoplastic product
3. Liberty when designing the thicknesses of the thermoplastic moulded part
4. Elimination of many electroerosion operations
5. Actual utilisation of HSC and VHSC systems with Al alloys
6. Elimination (or drastic reduction) of fitting time
7. Durability and good maintenance of polished surfaces
8. Considerable weight reduction: easy-to-handle Al moulds and simplification of investments in infrastructures
9. Re-design flexibility
For blow moulding HDPE parts, aluminium is typically used for the base material, with BeCu or stainless steel inserts in the pinch off areas. For PVC parts, BeCu, ampcoloy or stainless steel as employed as the base material, with A-2 or stainless steel inserts in the pinch off areas. And for PET parts, the base mould is usually made of aluminium or BeCu, with A-2 or stainless pinch-offs.
When it comes to injection mould & blow plastic mould materials nothing speeds production like Copper alloys. Mipalloy 100's thermal conductivity is almost 10 times greater than Tool Steels, so it offers faster, more uniform heat dissipation. That means more than 20% shorter cycle times. But speed of production is not the only factor. Current research at Western Michigan University shows Beryllium Copper cores exceed most production requirements. For extreme conditions such as long runs of 30% Glass-filled Nylon, Beryllium Copper lasts longer than P-20 Steel cores.
The plastics industry has proven Mipalloy 100 as a material of choice for injection moulding & blow moulding applications.
The injection moulding cycle is made up of a number of elements. They include the filling portion, the cooling portion & the mould open portion. The cooling portion is always the longest & is usually 65% of the overall cycle. Therefore the longest element in the overall cycle is where the greatest benefit can be obtained in improving the injection moulding cycle & where Beryllium Copper works best.
In addition to its superior thermal conductivity Mipalloy 100 offers the following advantages;
1. Maintains high surface finish.
2. Accepts etching & texturing.
3. Requires no additional heat treatment. Supplied in heat treated condition.
4. Can be readily machined using conventional machining practices as well as Electrical Discharge Machining (EDM).
Mipalloy manufactures & stocks Beryllium Copper in various shapes & sizes;
1. Round rod from 6mm diameter to 145mm diameter.
2. Rectangular & Square bars from 1square upwards.
3. Large forgings weighing more than 1000 kgs single piece.
Recommended blow mould applications;
Blow pins : High thermal conductivity for efficient heat removal, reducing cycle time.
Mould Inserts : Inserts at pinch off & neck areas of Aluminium mould increasing both hardness & conductivity.
Complete moulds : resistant to attack in PVC applications. Mipalloy 100 alone or with hardened pinch offs for use in moulds with complex parting lines.
Recommended injection mould applications;
Core pins, cavity areas, sprue bushings, ejector pins & sleeves, manifold systems.
Advantages include;
Improved control of post mould shrinkage.
Better heat dissipation in areas of heavy wall sections or limited water channel access.
Improved dimensional stability in multi cavity tools or in large flat walled parts.
Excellent wear life when mated with standard tool steels.
Mould Life - Cycle
In the Processing shop, it is clear moulds dont last forever. There are three basic failure modes to permanent mould tooling.
1. Thermal fatigue manifested in cracking primarily
2. Erosion manifested in dimensional errors and/or texture problems
3. Damage due to improper handling or maintenance.
Molds may be retired for many reasons such as obsolescence but they fail for one or more of the three reasons above. It is also clear that molds, even of the same design, do not last for exactly the same number of shots. So mould-tooling life is not characterized by a single factor.
Life, as the saying goes, is more complicated than that.
Mould life cycle is dependent on various factors, which are
1. Plastic material to be moulded
2. Type of moulding operation viz. Injection,Blow etc.,
3. Complexity of the part
4. Type of machine used for moulding
5. Operators care in moulding and maintenance / handling
6. Type of material used in the construction of the mould.
The table below lists the average number of moldings to be expected dependent on the mould material.
Q: What happens in heat treatment ?
In heat treatment mechanical properties are altered by :
Changing the size of the grains of what it is composed or by
Changing its micro constituents
Q: Purpose of heat treatment?
1. To Improve Machinability
2. To Relieve Internal Stresses
3. To Change or Refine Grain Size
4. To Improve Mechanical Properties
5. To Improve Resistance to wear, heat & corrosion
6. To Produce a hard surface on a ductile interior
7. To improve magnetic & electrical properties
Q: DIFFERENT PROCESS OF HEAT TREATMENT?
1. Annealing is generally used to soften the steel
2. Normalising is used to eliminate coarse grain structure obtained during forging rolling and stamping and produce fine grains.
3. Hardening is done to develop high hardness to resist wear and enable to cut other metals
The hardness produced by hardening depending upon the carbon content of steel. Steel containing less than 0.15% C does not respond to hardening treatment.
Tempering is done to reduce internal stresses and reduce some of the hardness produced during
Special Hardening Techniques:
1. Vaccum hardening
2. Laser hardening
3. Plasma hardening
Mould Material Selection (Injection)
MOULD MATERIAL SELECTION FOR INJECTION MOULD:
It is well known that without proper mould material, proper tooling cannot be achieved. Wide ranges of mould materials are used for fabrication of moulds & dies for plastics.
Mould material selection should be carried out based on the requirements from Product / Mould designer, mould maker & molder.
Steel Requirements:
1. Product: Surface Finish, Photo Etching, Effect of Moulding Material, Production quantity.
2. Mould: Economy, Standard Sizes.
3. Mould maker: Free From Defects, Easy to machine & Polish, Stable in Heat treatment, Suitable for EDM / etching.
4. Moulder: Wear Resistance, Compressive Strength, Corrosion resistance, Thermal conductivity.
Product Design Requirements: A part from functional performance of the component, the moulding is required to meet the high standards of surface finish as well as dimensional tolerance over long production run. These requirements will meet only if we have good product design, good mould design, good mould making and proper selection of tool steels for the mould.
Mould Design Requirements: The mould designer can economize the tooling of the mould by selecting standard steel grades, standard steel sizes and standard machined plated. He along with the mould maker shares the responsibility of producing a mould, which will give reliable and economical production of the part visualized by the product designer. He has to see that the mould maker fabricates the mold as easily and economically as possible. This largely depends on specifying best mould steel and optimum hardness required for different mould parts. Selection of standard parts such as guide pillars, guide bushes, ejector pins etc., & standard mould bases along with other machined plates considerably reduces time and cost as these parts are now a days available at far more competitive price. This in turn helps in better planning, prompt mould delivery as well as in minimizing initial machining cost and material losses.
Mould Making Requirements: A substantial part of the total mould cost is that incurred in machining of the mould. Hence, one must see the mould making process is as straight forward as possible. A mould maker will see that the steel he is going to use has following properties.
Materials are free from any manufacturing defects
1. Good machinability
2. Good polishability
3. Good hardenability
4. Good dimensional stability
Moulder Requirements: A processor expects certain features in the mould such as:
1. Uniform and high rate of production
2. Uniform moulding quality
3. Longer mould life
4. Low mould maintenance cost
5. Lowest possible production cost
6. Easy components & material replacement
It can be summarized that the selection of tool steels for mould not only depends on the product/Mould design but a considerable thinking has to be done from mould maker and processor point of view. If all these factors are given through weightage, then only a mould can be manufactured and processed economically and effectively.
Essential Properties of Mould Materials:-
1. Excellent Machinability: The economic importance of machinability is very great indeed. Roughly 30 % of the total cost of a mould is accounted for by the machining costs.
2. High Compressive Strength Combined with Sufficient Toughness: In injection mould, it is estimated that a locking force of 1 ton per 3 - 4 cm2 (0.465-0.620sq.in.) of projected surface is required. When large items are being injection moulded the locking force, therefore, will be very great indeed. There is always a risk of indentation of the parting lines, but the risk decreases with increasing compressive strength on the part of the tool steel use.
High compressive strength is also desirable in view of the fact that the tools are liable to mechanical damage in course of transportation and installation. In some cases, the tools are nitrided to prevent the cavity from becoming scored or otherwise spoiled.
The compressive strength of the steels can be improved through nitriding.
3. Capacity for heat treatment without problems: A small change in hardening is unavoidable. It is nevertheless possible to limit the changes (warpage) through slow and even heating to the hardening temperature and by choosing a low hardening temperature and a suitable quenching medium.
The most satisfactory solution to the problem is to use hardened and tempered steels where no further heat treatment is necessary.
4. VG Good resistance to heat and wear: In order to improve the strength of the plastic product, an addition of glass fibre, asbestos, wood fibre, etc., is frequently made. These substances have an abrasive effect on parting lines, runner gates and inlet nozzles.
For such products, it can therefore be advisable to choose particularly wear-resistant tool steel.
5. High thermal conductivity: Every plastic manufacturer is anxious to maintain as high a production pace as possible. The limitation lies in the ability of the mould to conduct heat away from the plastic item. In this context, the thermal conductivity of the material is obviously important, but so is heat transfer between tool and coolant and heat transport through the coolant.
6. Ability to resist corrosion: Practically all moulds used for injection moulding come into contact with cooling water. Some plastics are also corrosive to the mould material. Certain plastics generate corrosive products such as hydrochloric acid from PVC plastics, acetic acids from acetate plastics and water from amino plastics. PVC plastics are well known for their tendency to produce hydrochloric acid when heated to high temperatures.
This type of corrosion attacks the surface of the mould. If the mould is then polished to high gloss, the corrosive attack necessitates expensive repolishing.
7. Good polishability: Polishing is a time-consuming and costly process. The result of polishing will depend in the first instance on the polishing technique used.
The polishability of steel depends on the homogeneity of the steel and on the type, distribution and size of slag inclusions. Hard, large slag particles are particularly troublesome. Polishability is also highly dependent on the hardness level and heat treatment of the material.
To receive the highest purity, the steel should be vacuum degassed or electro-slag refining (ESR).
Factors Governing The Choice of Mould Materials:
1. Length of Production Run
2. Injection Pressure Required
3. Type of Moulding Material
4. Dimensional Accuracy & Intricacy
5. Method of Manufacture
COST CONSIDERATIONS:
STEEL COST THE TIP OF THE ICEBERG
One of the major decision that can favorable influence overall mould performance and long term maintenance costs is to specify the best possible mould steel for the job. The cost of the tool steel in a mould usually represent only 10 - 15 % of the total cost, and offer savings made on buying cheaper mould steels turn out to be false encouragement.
Through Hardened Steels Applications
1. Moulds with long production runs
2. To resist abrasion from certain moulding materials
3. To counter high closing/injection pressures
Advantages
1. These steels are available in soft annealed & stress relieved condition.
2. Also available in hardened and tempered to the required harness (about 48-60 HRC)
3. These are used for core and cavity inserts
4. Better wear resistance, resistance to deformation and indentation & better polishability.
5. Improved wear resistance is important when filled or reinforced plastic materials are to be used.
6. Resistance to deformation & indention in the cavity, gate areas and parting lines helps in maintaining proper part quality.
Corrosion Resistant Mould Steels
Application
When a mould is likely to be exposed to a corrosive atmosphere, stainless steel is strongly recommended. The higher initial cost of the steel will be less than the cost involved in repolishing or replating of mould parts affected by corrosion.
Pre Hardened Steels
Applications
1. Large Moulds
2. Moulds with lower wear resistance requirement
3. High strength holder plates
4. Moulds with moderate production run
Advantages
1. These steels are available in the hardened and tempered condition having hardness about 25-30 HRC.
2. No heat treatment is necessary before the mould is put into use.
3. Flame hardening or nitriding can increase the surface hardness.
MATERIALS AND TREATMENTS FOR MOULD PARTS AT A GLANCE”
Service requirement, fabrication requirement & economical requirement of various products are different from one another. These input requirements are to be clearly understood before the selection of right material.
There are some common properties required in all parts such as good strength, less dimensional changes during Heat Resistance treatments, good machinability, good polishability etc.,
INJECTION MOULD:
The core and cavity inserts are the most important parts, which has to withstand various stresses continuously. There are various materials used for core and cavity inserts and the proper selection is a somewhat difficult task, since it decides the performance and life of the mould, along with other factors.
Steels Used For Different Mould Parts:
1. Constructional Steel- Used for mould bases & structural
2. Components such as blocks, spacers, ejector pins, support
3. Pillars, Backing plates & locating rings. Etc.,
Material for Guide Pillar, Bushes, Ejector Pins:-
EN-18, EN-19, EN-24, EN-32
PRE HARDENED STEELS:
AISI: P-20
PX-4 (JAPAN)
IMPAX SUPREME (ASSAB UDDEHOLEM)
BUDERUS 2311 ISO-BM (BUDERUS )
MOULD MATERIALS EQUIVALENTS:
EDM Milling
EDM Milling: is the process in which complex shapes are machined using simple shaped electrode. The simple shaped electrodes are rotated at high speeds and follow specified paths in the workpiece like the end mills. This technique is very useful and it makes EDM very versatile like the mechanical milling process. This process solves the problem of manufacturing accurate complex shaped electrodes for die-sinking of three dimensional cavities. EDM milling improves flushing due to the high speed electrode rotation. Moreover, the tooling problems involved with complex shaped electrodes is eliminated by the use of simple shaped electrodes. The electrode wear can be optimized in EDM milling because of the rotational and contouring motions of the electrode. EDM contouring and planetary EDM techniques are quite similar to EDM milling except that in the former cases, the electrode rotation is not present in some cases where electrodes other than cylindrical shapes are used.
In the case of EDM milling or contouring EDM, three types of motions with cylindrical electrodes can be distinguished. They are EDM profiling, EDM pocketing and EDM grooving as shown in the fig . These motions need distinction unlike in mechanical milling operations because of the different sparking gaps involved with the motions. In EDM profiling, the electrode is moved along the outer or inner contour of the workpiece. For pocketing operations, the generated toolpath comprises of several parallel or equidistant tracks in order to generate large two dimensional cavities. EDM grooving is a technique similar to wire EDM where the electrode travels along the specified contour in the workpiece.
EDM milling provides the most economic advantage where several electrodes would otherwise be used to produce a part by die-sinking EDM. An example is a piston for a circuit breaker mold, which required 50 electrodes for production by die-sinking EDM.
The need to manufacture electrodes resulted in an overall production time of 23 days for the part. EDM milling reduced this time to 11 days, with savings in electrode costs also cutting production cost. The figure below graphically compares the machining time of the slot usind Die-sinling and EDM milling.
EDM milling has the potential to simplify the planning process, by eliminating several traditional steps used in CNC die-sinking. The table below gives the process planning steps in EDM milling.
The rotation of the electrode and the tool path generated optimizes the electrode wear. However, it does not mean that EDM milling completely eliminates the electrode wear or reduces it to miniscule amount of 1%. The simplicity of electrode now permits an easier investigation on electrode wear and allows us to focus the research on developing a mathematical algorithm and compensate for electrode.
The main limitation in the EDM process is that complex shapes with sharp corners cannot be machined because of the rotating electrode.
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