2015年1月30日星期五

Sand Casting

              Sand Casting
 China precision machining  Casting is used to make metal products of almost any desired shape by the pouring of molten metal into a reshaped hollow mold. As the metal freezes, the mold is removed. This technique was learned thousands of years ago when it was discovered that damp sand could be packed by hand into almost any shape.
    Generally speaking, clean, fine sand is placed in a wooden or steel box and packed around a preformed wooden pattern or actual object. When the pattern is
removed, its imprint remains in the sand.  China precision machining  Molten metal is then poured into the hollow mold. Castings made from sand molds have a rough surface. They must be cleaned,
trimmed and, at times, machined. Sand molds must be repacked after each casting to obtain additional parts. Therefore, the casting of many pieces using sand molds requires much time and labor. 
 Permanent Mould Casting
   The mould material is selected on the consideration of the pouring temperature, size of the casting and frequency of the casting cycle. They determine the total heat to be borne by the die. Fine grained grey cast iron is the most generally used die material. Alloy cast iron, C20 steel and alloy steel (H11 and H14) are also used for very large volumes and large parts. Graphite mould may be used for small volume production from aluminum and magnesium. The die life is less for higher melting temperature alloys such as copper or grey cast iron.    
   For making any hollow portions, cores are also used in permanent mould casting. The cores can be made out of metal, or sand. When sand cores are used, the process is called semi-permanent moulding. The metallic core cannot be complex with under-cuts and the like. Also, the metallic core is to be withdrawn immediately after solidification, otherwise, its extraction becomes difficult because of shrinkage. For complicated shapes, collapsible metal cores (multiple-piece cores) are sometimes used in permanent moulds. Their use is not extensive because of the fact that it is difficult to securely position the core as a single piece as also due to the dimensional variations that are likely to occur. Hence, with collapsible cores,  China precision machining  the designer has to provide coarse tolerance on these dimensions.    

2015年1月28日星期三

Casting Terms

   Casting Terms
China precision machining  In the following sections, the details of sand casting process which represents the basic process of casting would be seen. Because going into the details of the process, defining a number of casting vocabulary words would be appropriate. Reference may please be made to Fig. 2.1


     
 ds the sand mould intact. Depending upon the position of the flask in the mould structure it is referred to by various names such as drag-lower moulding flask, cope-upper moulding flask and
cheek-intermediate moulding flask used in three-piece moulding. It is made up of wood for temporary applications and more generally of metal for long-term use.
Pattern:
 Pattern is a replica of the final object to be made with some modifications. The mould cavity is made with the help of the pattern.
Parting Line:
  This is the dividing line between the two moulding flasks that makes
up the sand mould. In split pattern it is also the dividing line between the two halves of the pattern.
Bottom board:
 China precision machining This is a board normally made of wood which is used at the start of
the mould making. The pattern is first kept on the bottom board, sand is sprinkled on
it and then ramming is done in the drag.
Facing sand:
The small amount of material sprinkled on the inner surface of the moulding cavity to give a better surface finish to the castings.
Moulding sand:
 It is the freshly prepared refractory material used for making the mould cavity. It is a mixture of silica, clay and moisture in appropriate proportions to get the desired results and it surrounds the pattern while making the mould
 Backing sand: 
 It what constitutes most of the refractory material found in the mould. This is made up of used and burnt sand.
Core: It is used for making hollow cavities in castings.
Pouring basin:
 A small funnel shaped cavity at the top of the mould into which the molten metal is poured.
Sprue:
 The passage through which the molten metal from the pouring basin reaches the mould cavity. In many cases it controls the flow of metal into the mould.
Runner: The passageways in the parting plane through which molten metal flow is regulated
Gate: The actual entry point through which molten metal enters mould cavitybefore they reach the mould cavity.
Chaplet:
 Chaplets are used to support cores inside the mould cavity to take care of its own weight and overcome the metallostatic force.
chill:
 Chill are metallic object which are placed in the mould to increase the cooling rate of casting to provide uniform or desired cooling rate.
Riser:

 It is reservoir of molten metal provided in the casting so that hot metal can flow back into the mould cavity when there is a China precision machining reduction in volume of metal due to solidification.

2015年1月26日星期一

Casting Processes of Metals

      Casting Processes of Metals
   China precision machining A casting may be defined as a "metal object obtained by allowing molten metal to solidify in a mold ", the shape of the object being determined by the shape of the mold cavity. Casting is basically melting a solid material, heating to a special temperature, and pouring the molten material into a cavity or mold, which is in proper shape. Casting has been known by human being since the 4th century B.C.    
 Casting Procedure
   In all casting processes six basic factors are involved. These are as follows:     
 1.   China precision machining A mold cavity, having the desired shape and size and with due allowance for shrinkage of the solidifying metal, must be produced. Any complexity of shape desired in the finished casting must exist in the cavity. Consequently, the mold material mustsuch as to reproduce the desired detail and also have a refractory character so that it will not be significantly affected by the molten metal that it contains. Either a new mold must be prepared for each casting, or it must be made from a material that can withstand being used for repeated castings, the latter being called permanent molds.                 
  2. A suitable means must be available for melting the metal that is to be cast, providing not only adequate temperature, but also satisfactory quality and quantity at low cost.
  3. The molten metal must be introduced into the mold in such a manner that all air or gases in   the mold, prior to pouring or generated by the action of the hot metal upon the mold, will escape, and the mold will be completely filled. A quality casting must be dense and free from defects such as air holes.
 4. Provision must be made so that the mold will not cause too much restraint to the shrinkage   that accompanies cooling after the metal has solidified. Otherwise, the casting will crack while its strength is low. In addition, the design of the casting must be such that solidification and solidification shrinkage can occur without producing cracks and internal porosity or voids.
 5It must be possible to remove the casting from the mold so a permanent mold must be made in two or more sections.
  6After removal from the mold, finishing operations may need to be performed to remove extraneous material that is attached to   China precision machining the casting as the result of the method of introducing the metal into the cavity, or is picked up from the mold through contact with the metal.

2015年1月24日星期六

The surface of the mold heat treatment to strengthen the quality and impact on life

The surface of the mold heat treatment to strengthen the quality and impact on life  
  China precision machining Mold heat treatment the nature and quality of life of the mold a great impact. Practice shows that the die parts of the quenching distortion and cracking, early fracture during use, while the metallurgical and materials quality, forging quality, mold structure and process related, but related more to die of heat treatment. According to statistical analysis of failure causes of mold, heat treatment failure due to improper accounting for more than 50%. Practice shows that the mold material must be accompanied by high heat treatment process properly, can really play a material's potential. Parts surface hardening mold work purpose is to obtain the effect of external hard tough inside, so be hardness, wear resistance, toughness, good resistance to fatigue with. Many ways to die surface hardening, surface treatment technology of new technologies developed rapidly. In addition to Nitrocarburizing and ion nitride, boride, seepage niobium, vanadium permeability, hard chrome plated and spark strengthening, the chemical vapor deposition (CVD) and physical vapor deposition (PVD) has been gradually adopted. By CVD and PVD treatment, the mold surface covered with super-hard material, such as TiC, TiN, etc.. High hardness, wear resistance, corrosion resistance, adhesion is very good, can improve the die life several times to several times. 
 Manufacturing precision of the die parts of die life 
   China precision machining Precision die manufacturing and life in it in particular, mold surface roughness on the mold a great impact. If using Crl2MoV steel blanking die, if the surface roughness value R = 1.6 m, its life span is about 30,000. Such as polished by the precision, surface roughness value R = 0.4 m, life can be increased to 4-5 million. Therefore, the working parts of the mold surface, the general must go through grinding, grinding, polishing and other finishing and fine processing. 
  Other aspects of the impact of die life  
 (1) Press the accuracy is not high, but also easy to make die damage.
 (2) die in the press or not installed properly and the operator's technical level, on the tool life is also greatly affected.  
 (3) dies in the custody and maintenance of good and bad, and the use of lubricant condition also affects mold life.
  Conclusion 

  In actual production, sheet metal dies for use, rare case of non-normal wear and tear. But when the die plate was found prone to irregular wear, we always study for the problems summarized. Because of a cold die, from the design, manufacture, assembly, commissioning and installation and use, all spent many hours, while the convex die, die material used, mostly high-quality alloy steel. Therefore, the die cost is relatively high. Therefore,  China precision machiningin the production of understanding the factors that affect the die life and take the appropriate measures to guide the production of great practical significance.

2015年1月22日星期四

Die with life and Countermeasures of 2th

      Die with life and Countermeasures of 2th
China precision machining  The impact of cold stamping materials, cold stamping materials selected should meet the design requirements of workpieces and stamping process requirements, or easy to mold damage and reduce mold life. Poor surface quality of cold stamping, punching, cracking when the workpiece is also easy to scratch mold. Bad cold stamping plastic materials, deformation is small, easy to press when the workpiece rupture, but also easy to scratch mold. In addition, the material thickness tolerances shall comply with national standards. Die because of a certain thickness of material suitable for forming, bending, flanging, drawing die of the male and female die structure gap is directly determined by the thickness of the material. China precision machining Therefore, uneven thickness, will result in waste generation and mold damage.
 2. Die Die Life of  

 Die Die Life of a mold material properties, chemical composition, structure, hardness and comprehensive reflection of metallurgical quality. Among them, the material properties and heat treatment affect the quality of the most obvious. Mold material properties on the impact of die life is great. If the same workpiece, using a different mold material of the bending test, the test results: The 9Mn2V material, the life of 5 million; with Crl2MoV nitriding, the life of up to 40 million. Therefore, the choice of materials, the batch size should be based on workpiece, rational use of mold materials. The hardness of the die parts to Die Life a great impact. But not the higher hardness, longer die life. This is because the hardness and strength, toughness and abrasion resistance are closely related. Some die demands of high hardness, long life. Such as the use of T10 steel dies, hardness 54 ~ 58HRC, only washed thousands of times a burr on the workpiece great. If the hardness to 60 ~ 64HRC, the grinding life of up to 2 to 3 million. However, if continue to improve hardness, fracture occurs earlier. Some die hardness should not be too high, as the die manufacturing using Crl2MoV 58 ~ 62HRC hardness, the general life of 2-3 million, invalid form of chipping and cracking, and if the hardness down to 54 ~ 58HRC, life expectancy increased to 5 ~ 60 000, but decreased to 50 ~ 53HRC hardness appears easy to blunt the die edge phenomenon. Thus, mold hardness must be based on material properties and failure modes may be.China precision machining  Should enable the hardness, strength, toughness and wear resistance, resistance to fatigue strength needed to achieve a particular stamping process the best match.

2015年1月20日星期二

Die with life and Countermeasures

  Die with life and Countermeasures
  China precision machining  Die with the life of the workpiece by punching out the number of terms. Many factors affect the life Die. There are die structure design, manufacture molds used in the punch and die materials, die quality and surface hardening heat treatment, precision die manufacturing parts and cold stamping materials selection. In addition, there are die installation, adjustment, use and maintenance. 
 1. Die Design on Life 
  (1) Layout design of layout methods and take the boundary value a great impact on the die life, too small to take the boundary value, often causing rapid wear and convex mold, die bite wounds on the. Starting from material savings, take the boundary value smaller the better, but take the edge is less than some value, the cut surface of the mold and the quality of life adversely. There will be left behind in the blanking die Q-gap were to produce spare parts glitch, or even damage the die edge, reduce die life. Therefore, consider increasing the material utilization of the same time, parts must yield, quality and life expectancy to determine the layout methods and take the boundary.  
 (2) die structure prone to stress concentration on the cracking of the die structure, composite structure can be used or mosaic structure, and prestressed structure to enhance the mold life.  

 (3)   China precision machining the impact of clearance when the gap is too small, compressed extrusion of interest, increased friction, increased wear, the wear side of aggravated discharge and push pieces after blanking time, materials and convex, the friction between die will cause wear and tear than the end edge on the side of the grinding much, but also easily lead to convex, concave mold temperature is high, the adsorption of metal debris in the side edge to form a metal tumor, so that male and female die chipping or expansion occurs crack phenomenon. Therefore, the gap is too small to Die Life very bad. Gap is too large will increase the punch and the die face the edge of the concentration of stress, resulting in a sharp increase in stress, so blade edge quickly lose angular yield deformation. Therefore, addition of blanking force, thereby enabling faster edge edge wear, reduce die life. But in order to reduce the male and female die wear, extending mold life, while ensuring quality of stamping pieces under the premise that larger space designed properly it is necessary.   (4) Die-oriented structure of the life of a reliable guide for the working parts reduce wear, prevent male and female die bite wound is very effective. In particular, non-small-Q gap Q gap or Die, compound die and multi-position progressive die even more important. To improve the die life, must be based on processes and the demand of precision,   China precision machining the correct choice-oriented form and orientation accuracy, the choice should be higher than the accuracy-oriented convex, concave mold with precision.

2015年1月18日星期日

Renoho Precision Machinery Technology Co.,Ltd: Die with the development of

Renoho Precision Machinery Technology Co.,Ltd: Die with the development of:                 Die with the development of   China precision machining  Since reform and opening, with the rapid development of the nati...

Die with the development of

                Die with the development of  
China precision machining Since reform and opening, with the rapid development of the national economy, the market demand with the growing Die. In recent years, Die with the industry has been around 15% growth rate of the rapid development of industrial enterprises with ownership Die components also changed dramatically, in addition to the professional mold factory outside of state-owned, collective, joint ventures, wholly-owned and private has been a rapid development.  
 As with the accelerating pace of international integration, the increasing competition in the market, it has been increasingly recognized product quality, cost, and new product development capacities. The cold die manufacturing is the most basic elements of the chain, one of the cold die manufacturing technology to measure a country's manufacturing sector has become an important symbol of the level, and largely determine the viability of enterprises. 
  Die with enterprises to increase in recent years many technological advances for investment, technological progress will be seen as an important driving force for enterprise development. Some domestic enterprises have popularized the two-dimensional mold CAD, and gradually began to use UG, Pro / Engineer, I-DEAS, Euclid-IS and other international common software, individual manufacturers have also introduced Moldflow, C-Flow, DYNAFORM, Optris and MAGMASOFT etc. CAE software, and successfully applied in stamping die design.  
 A car cover mold as the representative of a large stamping die manufacturing technology has made great progress, Dongfeng Motor Corporation mold factory, mold manufacturers such as FAW mold center has been able to produce some car cover mold. In addition, many research institutions and universities to carry out technology research and development of mold. After years of effort, in the mold CAD / CAE / CAM technology has made remarkable progress; in improving quality and reducing mold die design and manufacturing cycle, and so contributed.  
 Although China Die with the industry over the past decade has made remarkable development, but in many ways compared with the industrialized countries there is still a large gap. For example, the precision machining equipment, processing equipment in Die with the relatively low proportion; CAD / CAE / CAM technology penetration is not high; many advanced mold technology not widely so, resulting in a considerable number of large, sophisticated, complex and long Die life with dependence on imports.     
 China precision machining With the continuous progress of science and technology, modern industrial production of increasingly complex and diverse, product performance and quality is ever increasing, thus the cold stamping technology put forward higher requirements. In order to adapt to the cold stamping technology industry needs, cold stamping technology itself also in innovation and development. cold stamping technology idea is to improve and expand as much as possible the advantages of the cold stamping process, to overcome its shortcomings. in the cold stamping technology development, should note the following aspects: 
  (1) cold stamping technology process parameters should be properly identified and Die with the work of some of the shape and size, to improve the quality of stamping parts and shorten the new product production cycle should be in strengthening the metal forming the basis of theoretical studies, to metal forming theory to practice can produce a direction, and gradually establish a close connection with the actual production of the advanced process of calculation. abroad have begun to use plastic finite element method, automobile parts forming process of the stress and strain analysis and computer simulation to predict the forming part of a process plan on the possibilities and potential problems. 
 (2) to accelerate product replacement, mold design to overcome the shortcomings of a long cycle. Should vigorously carry out computer-aided design and manufacture of molds (CAD / CAM) Research. In my country, paying particular attention to strengthening the multi-position progressive die CAD / CAM Technology. 
 (3) to meet the needs of mass production, and reduce labor intensity. Should strengthen cold stamping of mechanized and automated, so that the average, small pieces of high-speed presses in a multi-position progressive die production, production reached a high degree of automation to further improve stamping productivity. 
 (4) expand the scope of application of cold stamping production. So cold pressing both suitable for mass production, but also for small batch production; both the general accuracy of product production, but also can produce precision parts. Should pay attention to development such as fine blanking (especially thick material fine blanking), forming high-energy, soft mold forming, pressure and processing new superplastic forming process, but also promote the easy mode (soft mode and the low melting point alloy mold), Universal Hybrid model, the use of CNC punch press and other equipment.  

 In addition,China precision machining the performance improvement of sheet metal stamping, mold new material, die development of new processing methods should be further strengthened.

2015年1月16日星期五

Die with the main parts

      Die with the main parts 
  China precision machining Die stamping tools is the main process equipment, stamping rely on the relative movement under the mold completed. Processing time because the upper and lower mold between the constant division and, if continued operation of the fingers of workers to enter or remain in the mold closed, there will certainly pose a serious threat to their personal safety.     (A) of the mold main parts, function and safety requirements 
  1. Working parts is a direct punch to blank forming the working parts, therefore, it is the key to mold parts. Punch not only sophisticated and complex, it should meet the following requirements: 
  (1) be of sufficient strength, can not be broken or destroyed during stamping.
  (2) should be appropriate to its material and heat treatment requirements, to prevent too high hardness and brittle fracture. 
  2. Positioning parts positioning part is to determine the location of the parts installed blank, there are pins (board), gauge pin (plate), lead is sold, guide plate, knife set from the side, side pressure etc.. Design should be considered when positioning parts easy to operate and should not have had orientation, location to facilitate observation, preferably in the forward position, contouring to correct the pin location and positioning.
  3. Binder, unloading and discharging parts binder components are blank holder, binder board. 
  China precision machining Blank holder pressure can drawing blank holder force, thereby preventing billets under the action of the tangential pressure arch formed folds. The role of pressure plate to prevent movement and bounce blank. Top of the device, discharge board's role is to facilitate the pieces and clean up waste. Them by the spring, rubber and equipment, putting on the air-cushion support, can move up and down, knocking out pieces of the design should have enough top output, movement to the limited
spaces. Stripper plate area should be minimized or closed position in the operating groove milling out empty-handed. Exposure of the stripper plate should have protection around the plate, to prevent finger inserted into or foreign objects inside, exposed surface edges should be blunt down.  
 4. Guide parts and guide sleeve guide pin is the most widely used part of a guide.
  Its role is to ensure punch the punching clearance when accurate match. Therefore, the guide posts, guide cover the gap should be less than the blanking clearance. Guide Post located next mold base, to ensure that the stroke bottom dead center, the lead column in the template on the face over the top for at least 5 to 10 mm. Guide columns should be arranged far away from the module and the pressure plate in the area, so the operator's arms do not get to take over the lead column material.
 5. Supporting and clamping the upper and lower parts which includes templates, die handle, fixed plate punch, plate, stopper, etc.. 
  Up and down the template is the basis of the cold die parts, other parts are respectively fixed at the top. Template plane size, especially around the direction to be compatible with the workpiece, too large or too small are not conducive to action. 
 Some molds (blanking, punching type mold) to the pieces of convenience, be set up under the mold plate. At this time the best and the template plate connected between the screw, the two plate thickness should be absolutely equal. Plate spacing out the pieces to be able to prevail, not too much, so as not to break the template. 

 6.China precision machining  Fastening parts which includes screws, nuts, springs, pins, washers, etc., are generally used standard parts. Die more with the amount of standard parts, design choice and flexibility should be tightened to ensure the top out of the need to avoid exposure to the surface fastener operating position, the staff and impede operation to prevent bumps.

2015年1月14日星期三

Overview of stamping die

            Overview of stamping die
   China precision machining Stamping Die - Stamping in the cold, the material (metal or non-metallic) processing into parts (or half) of a special technical equipment, called cold stamping die (commonly known as Die). Press - is at room temperature, using the die installed in the press to put pressure on the material to produce a separation or plastic deformation, and thus to obtain the necessary parts of a pressure processing method.  
 Stamping die in the form of many, the general categories according to the following main features: 
  1. According to the technical nature of 
   (1) Die along the closed or open contour the material are derived from mold. If blanking die, punch die, cut off the mold, cut mode, cutting mode, split mode, etc.. 
  (2) bending mode to blank or blank sheet along a straight line (curved line) to bend, deform, and thus obtain a certain angle and shape of the workpiece in the mold.  
  (3) The drawing die is made of the blank sheet opening hollow, or hollow pieces of further changes to the shape and size of the mold. 
  (4) Die rough or semi-finished workpiece is convex according to plan, direct copy the shape of the die shape, the material itself, generate only local plastic deformation of the mold. Such as the bulging mode, reducing the die, expansion die, forming die rolling, flanging mold, plastic mold.
  2. According to the degree classification process combination 
  (1) single process model in a press tour, just completed a die stamping process.
  (2) composite model is only one station, in a press tour, at the same station at the same time to complete more than two or two die stamping process. 
  (3) Progressive Die (also known as the modulus of continuity) in the feeding direction, rough, with two or more of the station, at the press of a visit,  China precision machining work in different places on the completion of two or two successive Road over stamping die process.  
 Chong called cold stamping die Die-wide. 

  Cold stamping die is used in cold stamping die mold industry, and accessories required for high-performance structural ceramic materials, preparation methods, high-performance ceramic materials, molds and accessories from the zirconium oxide and yttrium aluminum powder increases, Pr element composition, Preparation is the solution of zirconia, yttria solution, praseodymium oxide solution, according to a certain percentage of alumina solution when mixed liquor, ammonium bicarbonate infusion, by co-precipitation synthesis of ceramic materials, molds and accessories needed for raw materials, reaction precipitate generated by the treatment, drying, calcining and accessories by high performance ceramic mold material superfine powder, and then after forming, sintering, finishing,  China precision machining they will have high-performance ceramic materials, molds and accessories. Advantages of this invention is the invention made of cold stamping dies and parts and long service life, the process does not appear in the press and its parts and stamping die bond generated the phenomenon of stamping surface is smooth, no glitches, can replace traditional high-speed steel, tungsten steel.

2015年1月13日星期二

Types of Casting And manufacturing process

Types of  Casting  And manufacturing process

    China precision machining Casting is a manufacturing process in which molten metal is poured or injected and allowed to solidify in a suitably  shaped mold cavity. During or after  cooling, the cast part is removed from the mold and then processed for delivery.
    Casting processes and cast-material technologies vary from simple to highly complex. Material and process selection  depends on the part’s complexity and function, the product’s quality specifications, and the projected cost  level.
     Castings are parts that are made close to their final dimensions by a casting process. With a history dating back 6,000  years, the various casting processes are  in a state of continuous refinement and evolution as technological advances are being made.
A:Sand Casting  
    Sand casting is used to make large parts (typically iron, but also bronze, brass, aluminum). Molten metal is poured into a mold cavity formed out of sand (natural or synthetic).
    The processes of sand casting are discussed in this section, including patterns, sprues and runners, design considerations, and casting allowance.
    The cavity in the sand is formed by using a pattern (an approximate duplicate of the real part), which are typically made out of wood, sometimes metal. The cavity is contained in an aggregate housed in a box called the flask.
    Core is a sand shape inserted into the mold to produce the internal features of the part such as holes or internal passages. Cores are placed in the cavity to form holes of the desired shapes. Core print is the region added to the pattern, core, or mold that is used to locate and support the core within the mold.
    A riser is an extra void created in the mold to contain excessive molten material. The purpose of this is to feed the molten metal to the mold cavity as the molten metal solidifies and shrinks, and thereby  prevents voids in the main casting.
    In a two-part mold, which is typical of sand  castings, the upper half, including the top half of the pattern, flask, and core is called cope and  the lower half is called drag,  The parting line or the parting surface is line or surface that separates the cope and drag.
     China precision machining The drag is first filled partially with sand, and the core  print, the cores, and the gating system are  placed near the parting line. The cope is then assembled to the drag, and the sand is poured on the cope half, covering the pattern, core and the gating system.
    The sand is compacted by vibration and mechanical means. Next, the cope is removed from the drag, and the pattern is carefully removed. The object is to remove the pattern without breaking the mold cavity.
    This is facilitated by designing a draft, a slight angular offset from the vertical to the vertical surfaces of the pattern. This is usually a minimum of 1.5mm(0.060in.), whichever is greater. The rougher the surface of the pattern, the more the draft to be provided.
    The molten material is poured into the pouring cup, which is part of the gating system that supplies the molten material to the mold cavity.
    The vertical part of the gating system connected to the pouring cup is the sprue, and the horizontal portion is called the runners and finally to the multiple
points where it is introduced to the mold cavity called the gates.
   Additionally there are extensions to the gating system called vents that provide the path for the built-up gases and the displaced air to vent to the atmosphere.
  The cavity is usually made oversize to allow for the metal contraction as it cools down to room temperature. This is achieved by making the pattern oversize. To account for shrinking, the pattern must be made oversize by these factors on the average. These are linear factors and apply in each direction.
  These shrinkage allowances are only approximate, because the exact allowance is determined by the shape and size of the casting. In addition, different  parts of the casting might require different shrinkage allowances.
Sand castings generally have a rough surface sometimes with surface impurities, and surface variations. A machining (finish) allowance is made for this type of defect.
   In general, typical stages of sand casting operation include :
   1. Patterns are made. These will be the shape used to form the cavity in the sand.
   2. Cores may also be made at this time. These cores are made of bonded sand that will be broken out of the cast part after it is complete.
   3. Sand is mulled (mixed) thoroughly with  additives such as bentonite to increase  bonding and overall strength.
   4. Sand is formed about the patterns, and gates, runners, risers, vents and pouring cups are added as needed. A compaction stage is typically used to ensure good coverage and solid molds.
  Cores may also be added to make concave or internal features for the cast part. Alignment pins may also be used for mating the molds later. Chills may be added to cool large masses faster.
  5. The patterns are removed, and the molds may be put through a baking stage to increase strength.
  6. Mold halves are mated and prepared for pouring metal.
  7. Metal is preheated in a furnace or crucible until is above the liquidus temperature in a suitable range (we don’t want the metal solidifying before the pour is complete). The exact temperature may be closely controlled depending upon the application.
  Degassing, and other treatment  processes may be done at this time, such  as removal of impurities (i.e. slag). Some  portion of this metal may be remelted scrap from previously cast parts—10% is reasonable.
 8. The metal is poured slowly, but continuously into the mold until the mold  is full.
9. As the molten metal cools (minutes to days),  the metal will shrink and the volume will decrease. During this time molten metal may backflow from the molten risers to feed the part and maintain the same shape.
10. Once the part starts to solidify small dendrites of solid material form in the part. During this time metal properties are being determined, and internal stresses are being generated. If a part is allowed to cool slowly enough at a constant rate then the final part will be relatively homogenous and stress free.
11. Once the part has completely solidified below the eutectic point it may be removed with no concern for final metal properties. At this point the sand is simply broken up, and the part removed. At this point the surface will have a quantity of sand adhering to the surface, and solid cores inside.
12. A bulk of the remaining sand and cores can be removed by mechanically striking the part. Other options are to use  a vibrating table, sand/shot blaster, hand 
labor, etc.
13. The final part is cut off the runner gate system, and is near final shape using cutters, torches, etc. Grinding operations  are used to remove any remaining bulk.
14. The part is taken down to final shape using machining operations. And cleaning operations may be used to remove oxides, etc.
B.Investment casting
   Investment casting is also known as the lost wax process. This process is one of the oldest manufacturing processes. The Egyptians used it in the time of the Pharaohs to make gold jewelry (hence the name Investment) some 5,000 years ago.
   Intricate shapes can be made with high accuracy. In addition, metals that are hard  to machine or fabricate are good  candidates for this process. It can be used to make parts that cannot be produced by normal manufacturing techniques, such as turbine blades that have complex shapes, or airplane parts that have to withstand  high temperatures.
 The mold is made by making a pattern using wax or some other material that can be melted away. This wax pattern is dipped in refractory slurry, which coats the wax pattern and forms a skin. This is dried and the process of dipping in the slurry and drying is repeated until a robust thickness is achieved.
   After this, the entire pattern is  placed in an oven and the wax is melted away. This leads to a mold that can be filled with the molten metal. Because the mold is formed around a one-piece pattern (which does not have to be pulled out from the mold as  in a traditional sand casting process), very intricate parts and undercuts can be made.
  The wax pattern itself is made by duplicating using a stereo lithography or similar model—which has been fabricated using a computer solid model master.
   The materials used for the slurry are a  mixture of plaster, a binder and powdered silica, a refractory, for low temperature melts. For higher temperature melts, sillimanite or alumina-silicate is used as a refractory, and silica is used as a binder.
  Depending on the fineness of the finish desired additional coatings of sillimanite and ethyl silicate may be applied. The mold thus produced can be used directly  for light castings, or be reinforced by  placing it in a larger container and reinforcing it more slurry.
   Just before the pour, the mold is pre-heated to about 1,000(1,832) to remove any residues of wax, harden the  binder. The pour in the pre-heated mold  also ensures that the mold will fill completely.
    Pouring can be done using  gravity, pressure or vacuum  conditions. Attention must be paid to mold  permeability when using pressure, to  allow the air to escape as the pour is  done.
     Tolerances of 0.5% of length are routinely possible, and as low as 0.15% is possible for small dimensions. Castings  can weigh from a few grams to 35kg (0.1oz to 80lb), although the normal size ranges from 200g to about 8kg(7oz to 15 lb). Normal minimum wall thicknesses are about 1mm to about 0.5mm(0.040~ 0.020  in.) for alloys that can be cast easily.
       The types of materials that can be cast  are aluminum alloys, bronzes, tool steels, stainless steels, stellite, hastelloys, and  precious metals. Parts made with  investment castings often do not require  any further machining, because of the  close tolerances that can be achieved.
  C .Centrifugal Casting
   Centrifugal casting as a category includes centrifugal casting,  semi-centrifugal casting and centrifuging. In centrifugal casting, a permanent mold is rotated about its axis at high speeds (300 to 3,000rpm) as the molten metal is poured.
   The molten metal is centrifugally thrown towards the inside mold wall, where it solidifies after cooling. The casting is usually a fine grain casting with a very fine-grained outer diameter, which is resistant to atmospheric corrosion, a typical situation with pipes. The inside diameter has more impurities and inclusions, which can be machined away.
   Only cylindrical shapes can be produced with this process. Size limits are  up to 3m(10feet) diameter and 15m(50 feet) length. Wall thickness can be 2.5mm to 125mm(0.1~5.0in.). The tolerances that can be held on the OD can be as good as 2.5mm (0.1in.) and on the ID can be 3.8mm(0.15in.). The surface finish ranges from 2.5mm to 12.5mm(0.1~0.5in.) rms(root-mean-square).nless  steels, and alloys of aluminum, copper and nickel. Two materials can be cast by introducing a second material during the  process. Typical parts made by this process are pipes, boilers, pressure  vessels, flywheels, cylinder liners and other parts that are axis-symmetric.
    Semi-centrifugal casting. The molds used can be permanent or expendable, can be stacked as necessary. The rotational speeds are lower than those used in centrifugal casting.
   The center axis of the part has inclusion defects as well as porosity and thus is suitable only for parts where this can be machined  away. This  process is used for making  wheels, nozzles and similar parts where the axis of the part is removed by subsequent machining.
   Centrifuging. Centrifuging is used for forcing metal from a central axis of the equipment into individual mold cavities that are placed on the circumference.
This provides a means of increasing the filling pressure within each mold and allows for reproduction of intricate details. This method is often used for the pouring of investment casting pattern.
  Full-mold casting is a technique similar to investment casting, but instead of wax as the expendable material, polystyrene foam is used as the pattern. The foam pattern is coated with a refractory material. The pattern is encased in a one-piece sand mold. As the metal is  poured, the foam vaporizes, and the metal takes its place.
    China precision machining This can make complex shaped castings without any draft or flash. However, the pattern cost can be high due to the expendable nature of the pattern. Minimum wall thicknesses are 2.5mm, tolerances can be held to 0.3% on dimensions. Surface finish can be held from 2.5μm to 25μm(0.1μin. to 1.0μin.) rms(root-mean-square).  Size limits are from 400g(1lb) to several tons. No draft allowance is required. Typical materials that can be cast with this process are aluminum, iron, steel, nickel alloys, copper  alloys. Types of parts that can be made using these processes are pump housings, manifolds, and auto brake components.



     

2015年1月12日星期一

Automatic Fixture Design

               Automatic Fixture Design
    China precision machining  Assembly equipment used in the traditional synchronous fixture put parts of the fixture mobile center, to ensure that components from transmission from the plane or equipment plate placed after removal has been scheduled for position. However, in certain applications, mobile mandatory parts of the center line, it may cause parts or equipment damage. When parts vulnerability and may lead to a small vibration abandoned, or when their location is by machine spindle or specific to die, Tolerance again or when the request is a sophisticated, it would rather let the fixture to adapt to the location of parts, and not the contrary. For these tasks, Elyria, Ohio, the company has developed Zaytran a general non-functional data synchronization West category FLEXIBILITY fixture. Fixture because of the interaction and synchronization devices is independent, The synchronous device can use sophisticated equipment to replace the slip without affecting the fixture force. Fixture specification range from 0.2 inches itinerary, 5 pounds clamping force of the six-inch trip, 400-inch clamping force. 
  The characteristics of modern production is becoming smaller and smaller quantities and product specifications biggest changes. Therefore, in the final stages of production, assembly of production, quantity and product design changes appear to be particularly vulnerable. This situation is forcing many companies to make greater efforts to rationalize the extensive reform and the previously mentioned case of assembly automation. Despite flexible fixture behind the rapid development of flexible transport and handling devices, such as backward in the development of industrial robots, it is still expected to increase the flexibility fixture. In fact the important fixture devices -- the production of the devices to strengthen investment on the fixture so that more flexibility in economic support holders.
   China precision machining  According to their flexibility and fixture can be divided into : special fixture, the fixture combinations, the standard fixture, high flexible fixture. Flexible fixture on different parts of their high adaptability and the few low-cost replacement for the characteristic.
   Forms can transform the structure of the flexible fixture can be installed with the change of structure components (such as needle cheek plate, Multi-chip components and flake cheek plate), a non-standard work piece gripper or clamping elements (for example : commencement standard with a clamping fixture and mobile components fixture supporting documents), or with ceramic or hardening of the intermediary substances (such as : Mobile particle bed fixture and heat fixture tight fixture). To production, the parts were secured fixture, the need to generate clamping function, its fixture with a few unrelated to the sexual submissive steps:
  According to the processing was part of that foundation and working characteristics to determine the work piece fixture in the required position, then need to select some stability flat combination, These constitute a stable plane was fixed in the work piece fixture set position on the clamp-profile structure, all balanced and torque, it has also ensured that the  work features close to the work piece. Finally, it must be calculated and adjusted, assembly or disassembly be standard fixture components required for the position, so that the work piece firmly by clamping fixture in China. In accordance with this procedure, the outline fixture structure and equipped with the planning and recording process can be automated control. 
  Structural modeling task is to produce some stable flat combination, Thus, these plane of the work pieces clamping force and will fixture stability. According to usual practice, this task can be human-machine dialogue that is almost completely automated way to completion. A man-machine dialogue that is automated fixture structure modeling to determine the merits can be conducted in an organized and planning fixture design, reduce the amount of the design, shortening the study period and better distribution of work conditions. In short, can be successfully achieved significantly improve fixture efficiency and effectiveness. 

 China precision machining  Fully prepared to structure programs and the number of material circumstances, the completion of the first successful assembly can save up to 60% of the time.      
   Therefore fixture process modeling agencies is the purpose of the program have appropriate documents.

2015年1月11日星期日

Grinding process and Type of Grinding

              Grinding process and Type of Grinding
      China precision machining Grinding is a manufacturing process that involves the removal of metal by employing a rotating abrasive wheel. The latter simulates a milling cutter with an extremely large number of miniature cutting edges.
Generally, grinding is considered to be a finishing process that is usually used for obtaining high-dimensional accuracy and  better surface finish. Grinding can be performed on flat, cylindrical, or even  internal surfaces by employing specialized  machine tools, which are referred to as grinding machines.
Obviously, grinding machines differ in construction as well as capabilities, and the type to be employed is determined mainly by the geometrical shape and nature of the surface to be ground, e.g., cylindrical surfaces are ground on cylindrical grinding machines.
Type of Grinding Operations
1. Surface grinding. As the name surface grinding suggests, this operation involves grinding of flat or plane surfaces. Fig.8.1 indicates the two possible variations, either a horizontal or vertical machine spindle.
In the first case (horizontal spindle), the machine usually has a planer-type reciprocating table on which the workpiece is held. However, grinding machines with vertical spindles can have either a planer type table like that of the horizontal-spindle machine or a rotating worktable.
Also, the grinding action in this case is achieved by the end face of the grinding wheel, contrary to the case of horizontal-spindle machines, where the workpieces ground by the periphery of the grinding wheel.
During the surface-grinding operations, heavy workpieces are either held in fixtures or clamped on the machine table by strap clamps and the like, whereas smaller workpieces are usually held by magnetic chucks.
2. Cylindrical grinding. In cylindrical grinding, the workpiece is held between centers during the grinding operation, and the wheel rotation is the source and cause for the rotary cutting motion, In fact, cylindrical grinding can be carried out by employing any of the following methods:
 (1) The transverse method, in which both the grinding wheel and the workpiece rotate and longitudinal linear feed is applied to enable grinding of the whole length. The depth of cut is adjusted by the cross feed of the grinding wheel into the workpiece.
 (2) The plunge-cut method, in which grinding is achieved through the cross feed of the grinding wheel and no axial feed is applied. As you can see, this method can be applied only when the surface to be ground is shorter than the width of the grinding wheel used.
 (3) The full-depth method, which is similar to the transverse method except that the grinding allowance is removed in a single pass. This method is usually recommended when grinding short rigid shafts.
3. Internal grinding. Internal grinding is employed for grinding relatively short holes, The workpiece is held in a chuck or a special fixture. Both the grinding wheel and the workpiece rotate during the operation and feed is applied in the longitudinal direction.
Any desired depth of cut can be obtained by the cross feed of the grinding wheel. A variation from this type is planetary internal grinding, which is recommended for heavy workpieces that cannot be held in chucks.
In that case, the grinding wheel not only spins around its own axis but also rotates around the centerline of the hole that is being ground.
4. Centerless grinding. Centerless grinding involves passing a cylindrical workpiece, which is supported by a rest blade, between two wheels, i.e., the grinding wheel and the regulating or feed wheel.
The grinding wheel does the actual grinding, while the regulating wheel is responsible for rotating the workpiece as well as generating the longitudinal feed. This is possible because of the frictional characteristics of that wheel, which is usually made of rubber-bonded abrasive.
the axis of the regulating wheel is tilted at a slight angle with the axis of the grinding wheel. Consequently, the peripheral velocity of the regulating wheel can be resolved into two components, namely, workpiece rotational speed and longitudinal feed.
These can be given by the following  equations:
          VworkpieceVregulating wheel×cosα
          Axial feedVregulating wheel×c×sinα
Where c is a constant coefficient to account for the slip between the workpiece and the regulating wheel (c=0.94~0.98).
   The velocity of the regulating wheel is controllable and is used to achieve any desired rotational speed of the workpiece. The angleαis usually taken from 1°to 5°and the larger the angle, the larger the longitudinal feed would be.
Whenαis taken as 0°, i.e., the two axes of the grinding and regulating wheels are parallel, there is no longitudinal feed of the  workpiece.
5 Grinding Wheels
       China precision machining Grinding wheels are composed of abrasive grains having similar size and a binder. The actual grinding process is performed by the abrasive grains. Pores between the grains within the binder enable the grains to act as separate single-point cutting tools.
These pores also provide space for the generated chips, thus preventing the wheel from clogging. In addition, pores assist the easy flow of coolants to enable efficient and prompt removal of the heat generated during the grinding process.
Grinding wheels are identified based on their shape and size, kind of abrasive, grain size, binder, grade (hardness), and structure.
     Shape and size of grinding wheels. Grinding wheels differ in shape and size, depending upon the purpose for which they are to be used. include the following types:
1)Straight wheels used for surface, cylindrical, internal, and centerless grinding.
2)Bevelled-face or tapered wheels used for grinding threads, gear teeth, and the like.
3)Straight recessed wheels for cylindrical grinding and facing.
4)Abrasive disks for cutoff and slotting operations. (thickness 0.02 up to 0.2in. (0.5 to 5mm)).
5)Cylinders, straight cups, and flaring cups are used for surface grinding with the end face of the wheel.
  The main dimensions of a grinding wheel are the outside diameter D, the bore diameter d, and the height H. These dimensions vary widely, depending upon the grinding process for which the wheel is to be used.
   Kind of abrasive. Grinding wheels can be made of natural abrasives such as quartz, emery, and corundum or of industrially prepared chemical compounds such as aluminum oxide or silicon carbide (known as carborundum).
Generally, silicon carbide grinding wheels are used when grinding low-tensile-strength materials like cast iron, whereas aluminum oxide wheels are employed for grinding high-strength metals such as alloy steel, hardened steel, and the like.
 Grain size of abrasive used. As you may expect, the grain size of the abrasive particles of the wheel plays a fundamental role in determining the quality of ground surface obtained.
  The finer the grains, the smoother the ground surface is. Therefore, coarse-grained grinding wheels are used for roughing operations, whereas fine-grained wheels are employed in final finishing operations.
The grade of the bond. The grade of the bond is actually an indication of the resistance of the bond to pulling off the abrasive grains from the grinding wheel. Generally, wheels having hard grades are used for grinding soft materials and vice versa.
  If a hard-grade wheel were to be used for grinding a hard material, the dull grains would not be pulled off from the bond quickly enough, thus impeding the self-dressing process of the surface of the wheel and finally resulting in clogging of the wheel and burns on the ground surface.
In fact, the cutting properties of all grinding wheels must be restored periodically by dressing with a cemented carbide roller or a diamond tool to give the wheel the exact desired shape and remove all worn abrasive grains.
  Structure. Structure refers to the amount of void space between the abrasive grains. When grinding softer metals, larger void space are needed to facilitate the flow of the removed chips.
  The binder. Abrasive particles are bonded together in many different ways. These include bond, silicate, rubber, resinoid, shellac, and oxychloride. Nevertheless, the bond is the most commonly used one.
   China precision machining In fact, the standard marking system is employed for distinguishing grinding wheels, by providing all the preceding parameters in a specific sequence.



2015年1月10日星期六

Wears of Cutting Tool

               Wears of Cutting Tool
  China precision machining  We already have been processed and the rattle of the countless cracks edge tool, we learn that tool wear are basically three forms : flank wear, the former flank wear and V-Notch wear. Flank wear occurred in both the main blade occurred vice blade. On the main blade, shoulder removed because most metal chip mandate, which resulted in an increase cutting force and cutting temperature increase, If not allowed to check, That could lead to the work piece and the tool vibration and provide for efficient cutting conditions may no longer exist. Vice-bladed on, it is determined work piece dimensions and surface finish. Flank wear size of the possible failure of the product and surface finish are also inferior. In most actual cutting conditions, as the principal in the former first deputy flank before flank wear, wear arrival enough, Tool will be effective, the results are made unqualified parts. 
 As Tool stress on the surface uneven, chip and flank before sliding contact zone between stress, in sliding contact the start of the largest, and in contact with the tail of zero, so abrasive wear in the region occurred. This is because the card cutting edge than the nearby settlements near the more serious wear, and bladed chip due to the vicinity of the former flank and lost contact wear lighter. This results from a certain distance from the cutting edge of the surface formed before the knife point Ma pit, which is usually considered before wear. Under normal circumstances, this is wear cross-sectional shape of an arc. In many instances and for the actual cutting conditions, the former flank wear compared to flank wear light, Therefore flank wear more generally as a tool failure of scale signs. But because many authors have said in the cutting speed of the increase, Maeto surface temperature than the knife surface temperatures have risen faster. but because any form of wear rate is essentially temperature changes by the significant impact. Therefore, the former usually wear in high-speed cutting happen. 
    China precision machining  The main tool flank wear the tail is not processed with the work piece surface in contact, Therefore flank wear than wear along with the ends more visible, which is the most common. This is because the local effect, which is as rough on the surface has hardened layer, This effect is by cutting in front of the hardening of the work piece. Not just cutting, and as oxidation skin, the blade local high temperature will also cause this effect. This partial wear normally referred to as pit sexual wear, but occasionally it is very serious. Despite the emergence of the pits on the Cutting Tool nature is not meaningful impact, but often pits gradually become darker If cutting continued the case, then there cutter fracture crisis.

   If any form of sexual allowed to wear, eventually wear rate increase obviously will be a tool to destroy failure destruction, that will no longer tool for cutting, cause the work piece scrapped, it is good, can cause serious damage machine. For various carbide cutting tools and for the various types of wear, in the event of a serious lapse, on the tool that has reached the end of the life cycle. But for various high-speed steel cutting tools and wear belonging to the non-uniformity of wear, has been found : When the wear and even to allow for a serious lapse, the most meaningful is that the tool can re-mill use, of course, In practice, cutting the time to use than the short time lapse. Several phenomena are one tool serious lapse began features :   China precision machining the most common is the sudden increase cutting force, appeared on the work piece burning ring patterns and an increase in noise.