Related Problems in Wax Model Manufacturing in Precision Casting
Various fields have different regulations for precision casting. In order to meet the requirements,Precision castingTechnicality shows its universal adaptability, such as mainly manifested in the diversification of raw materials, the diversification of appearance, the batch nature of manufacturing, the accuracy of specifications, uniformity, reliability and surface precision, etc., in this characteristic , Today all have new progress and improvements. For example, the material is a stainless steel plate with a net weight of 40g, and the outline specification is a precision casting with a length of 55mm, a width of 3216mm, and a thickness of 13mm. The roughness must consider the requirements of the Japanese Industrial Standards (JIS); ③The 4 holes around the hole axis cooperate with another member. In addition to considering the requirements of JIS, the relevant specifications stipulate that the casting cannot be stretched and deformed; ④The minimum standard tolerance of castings is ±012mm ⑤The depth of the text, marks, etc. cast is 013mm, and the wire frame is clear; ⑥The minimum standard tolerance between the plan drawings is 011mm ⑦Fin, arc, roughness, shrinkage, deformation, etc. The last unique and specific items are implemented in accordance with the manufacturing company's specifications. As an example of precision castings, it can be seen from this that the current industrial production of precision castings and the standards that operators can exceed. From the contemporary investment casting production process, it can be understood that it is not very easy to ensure the stated regulations. Therefore, it is very difficult to exceed the stated objectives if strict requirements, proper practical operations, and mutual cooperation are not carried out from each process, each stage, and each position. This article only discusses the related problems of wax model manufacturing.
1. Wax
Wax is the first stage in precision casting manufacturing. Everyone knows that because of the development trend of casting manufacturing, the regulations on wax are relatively diverse. The easiest way for the operator is to use it in the wax materials on the market, and it can also configure it by itself, and can authorize and entrust a technical professional processing factory to manufacture in accordance with the regulations. But no matter what kind of wax material, its specified characteristics are the same, namely: melting point, freezing point, softening point, heat transfer, circulation, shrinkage, shrinkage, compressive strength, strength, ductility, separation Shape, paintability, recyclability, specification reliability, and residual ash content after high-temperature burning, etc. Basically, people use a kind of wax material in the actual manufacturing of castings, and stipulate that the wax material has the characteristics of some aspects, once the owner and once; in addition, it is a key element from many aspects of cost. In order to achieve the actual requirements of various castings, wax materials are divided into liquid, semi-liquid, semi-solid, and solid; with and without filling masterbatch; water-soluble and non-water-soluble; remanufactured and non-remanufactured ; For wax models, pouring system software, bonding, repairing, sealing, epoxy resin waxes, etc. From the perspective of wax materials for wax models alone, there are many types of them, and they are developing again. Fillerwax with filler masterbatch is more commonly used. Common filler masterbatches are powdered high-pressure polyethylene, polyethylene, citric acid, oleic acid and tapioca starch. Its addition amount is 30% to 45% of the total output. This wax material has very good thermal insulation, that is, it will be formed at a lower temperature, its circulation is good, and the details of the wax mold can be clearly reproduced. For example, adding heat-forced butadiene, adding isophthalic acid, and adding three wax materials called P2FILLER, the time from 104°C to 49°C is 59 seconds, 62 seconds and 99 seconds, respectively. It shows that the type of filler masterbatch has great harm to wax performance. The shrinkage rate of this wax is about 5% less than that of the unfilled masterbatch. The problem closely related to wax performance is the harm of wax preparation, application and solution methods to wax performance.
1. Avoid over-temperature wax in the whole process of melting
(1) Apply indirect heating oil bath furnace and compulsory circulation system of high temperature heat transfer oil, the melting temperature is controlled in the range of 84～98℃, and it is stirred from beginning to end, except for making the temperature uniform. , It also has the effect of avoiding settling for wax containing filler masterbatch. Excessive temperature and some over-temperature will affect the wax's performance due to problems such as air oxidation and carbonization of the wax. The main manifestation of over-temperature is the change of the color tone of the wax, the cavity of the wax bucket causes the macula, which is transparent due to the separation of the filler masterbatch, and the thick smoke or volatile matter is caused in the wax bucket.
(2) When the wax is recycled and reused, in order to remove the residue and water, it must be heated to about the melting point of the wax. Generally, it is operated below 120°C. In addition to ensuring that the wax has a certain fluidity and working ability to remove the residue, The moisture content will be enough to volatilize due to the stirring of the stirring device.
(3) For the wax sticks used under the thermal insulation of the thermal insulation cylinder, the heating temperature only needs to be 2～3℃ higher than the injection temperature.
(4) When the wax material is removed in the high-pressure reactor (pressure tank), the steam temperature can reach about 150°C. This type of standard is the key stage that causes the performance of the wax material to be affected, so try to reduce the dewaxing temperature and reduce the dewaxing Working pressure to maintain wax performance.
2. Maintain the natural environment temperature
In the wax model manufacturing room, whether it is winter or summer, the temperature in the room should be maintained within 20-25, so that the specifications of the wax model are in a stable natural environment, and in addition to the natural process of dipping the shell Environmental standards complement each other to ensure the quality of the shell.
(1) Heating and heat insulation of wax material
The wax material enters the profile plate from the wax bucket under the working pressure, and condenses in the mold. In the whole process here, the temperature difference is a key element that harms the appearance, specifications and reliability of the wax model. Therefore, when the wax barrel is used to heat and heat the wax material to carry out the wax pressing, the uniformity of the wax barrel temperature is extremely important. The same as the poor heat transfer of the wax material, it is difficult to rely on the heat generation of the wax barrel to make the wax material evenly symmetrical. , The wax bucket with uneven temperature makes an imperfect wax mold. Therefore, heat insulation tanks are generally used to heat and heat the wax buckets, and the heat insulation tanks can generally be set at 58-62°C, which is slightly higher than the injection temperature. It can be applied for a long time, at least 8 hours or so after heating and evenness. The thermal insulation tank is an oil bath heating equipment. The high-temperature heat transfer oil circulates the fluidity of the system under the working pressure of the gasoline pump, so that the wax bucket is heated and insulated at a uniform temperature. The temperature control board of the thermal insulation tank can be as required Set the required temperature. When the wax bucket with uneven temperature is pressed, the wax mold will cause shortcomings such as underfill, cold partition, granular surface layer, flow pattern and network structure pattern.
(2) The molding method of wax mold
According to the size, appearance and technical standards of castings, different molding methods are created. Different molding methods are complemented by different wax materials. From the driving force of the wax, there are manual, electric, pneumatic, hydraulic, etc.; from the working pressure, there are bottom pressure, high pressure, high pressure, etc.; from the wax condition, there are liquid, semi-liquid, semi-solid , Solid, etc.; from the profiled board, there are metal material type, vulcanized rubber type, plaster of paris, etc., from the casting parts, there are industrial products, handicrafts.
2. Wax pressing machine (wax pressing machine)
The wax material is rolled into a wax mold in the wax press, which means that the characteristics of the wax mold are restricted by the main parameters of the wax press at a very large level. This is related to the design, structure and performance of the wax press. For example, for a vertical high-pressure semi-solid wax press, before starting the actual operation of wax pressing, be sure to check the wax material temperature, injection working pressure, injection time, refrigeration time, and pressure plate temperature. Then carry out the actual operation according to the requirements of the processing technology card. The performance of the wax press molding machine is specifically manifested in the main parameters of the processing technology that it can adjust, mainly including hand-drawn and fully automatic; wax barrel temperature adjustment, wax injection port temperature adjustment; closing force adjustment, closing stroke arrangement adjustment; Injection working pressure adjustment, injection rate adjustment, injection time adjustment; round-trip rate adjustment, etc. For example, some castings have 2 orifice rings on both sides of the wax mold. Because the connection between the orifice ring and itself is relatively weak, it is easy to produce micro cracks visible to the human eye at the connection, and then adjust the shooting rate according to And maintenance time, this kind of shortcomings are eliminated. It can be seen that the main parameters of the processing technology that can be adjusted by the wax press, as well as the adjustment range, adjustment method and proper operation are extremely important for the production and manufacture of wax molds. Part of the management center of the wax press is the wax cylinder. Its specification is< 100mm×400mm.="" it="" is="" used="" to="" place="" wax="" sticks.="" the="" fully="" heated="" wax="" sticks="" are="" placed="" in="" the="" wax="" cylinder.="" the="" wax="" cylinder="" uses="" an="" electric="" heater="" to="" maintain="" the="" temperature="" at="" the="" injection="" temperature.="" after="" the="" inlet="" is="" put="" into="" the="" wax="" injection="" port="" (injection="" inlet)="" of="" the="" wax="" cylinder="" (the="" wax="" injection="" side="" has="" a="" separate="" heating="" and="" thermal="" insulation="" system="" software),="" the="" gasoline="" pump="" can="" be="" started,="" forcing="" the="" upper="" piston="" rod="" to="" move="" down,="" and="" the="" wax="" is="" pressed="" into="" the="" mold="" medium;="" after="" holding="" the="" pressure="" for="" a="" certain="" period="" of="" time,="" fold="" the="" profiled="" plate="" and="" remove="" the="" wax="" mold.="" the="" basic="" parameters="" of="" the="" process="" are:="" ①the="" temperature="" control="" of="" the="" semi-solid="" wax="" material="" is="" slightly="" higher="" than="" the="" injection="" temperature,="" generally="" 55～60℃.="" in="" order="" to="" make="" the="" temperature="" of="" the="" wax="" cylinder="" uniform,="" the="" surface="" and="" the="" inside="" are="" consistent,="" the="" wax="" cylinder="" must="" be="" retained="" in="" the="" thermal="" insulation="" tank.="" 8="" hours="" or="" so;="" ②the="" working="" pressure="" of="" the="" injection="" is="" adjustable,="" generally="" 214～218mpa="" ③the="" tightening="" force="" of="" the="" wax="" press="" to="" the="" pressure="" plate="" is="" adjustable,="" generally="" 310～315mpa="" ④the="" injection="" rate="" is="" executed="" by="" the="" injection="" time="" yes,="" it="" is="" different="" because="" of="" the="" different="" wax="" patterns.="" it="" has="" a="" lot="" to="" do="" with="" the="" closed="" state="" of="" the="" wax="" patterns,="" which="" in="" turn="" harms="" the="" quality="" of="" the="" wax="">
3. Disadvantages of wax mold
For various reasons, the wax mold produced by the wax molding machine can cause