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 Also, the metallic core is to be withdrawn immediately after solidification, otherwise, its extraction becomes difficult because of shrinkage.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.    

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.

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.

 5．It must be possible to remove the casting from the mold so a permanent mold must be made in two or more sections.

  6．After 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.

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.

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.

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.

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...