Rapid prototyping technology and its application in casting

Knowledge sharing by Guangdong Shunde Teamwork Model Technology Co., Ltd, whom with over 20 years rapid prototyping experience.

Email: ken@gdtwmx.com

Website: www.gdtwmx.com

2.1 Introduction

Rapid Prototyping (RP) technology is a new high-tech achievement developed internationally, referred to as rapid prototyping technology. Its core technologies are computer technology and materials technology. Rapid prototyping technology eliminates the traditional machining method, controls the 3D CNC forming system according to the geometric information of the parts generated by CAD, and builds the parts by laser beam or other methods. Forming in this way eliminates the need for time-consuming, costly mold or special tool design and machining, greatly increasing production efficiency and manufacturing flexibility.

In casting production, the manufacture of stencils, core boxes, wax-types, die-casting dies, etc. is often done by mechanical processing, sometimes requiring trimmers to be trimmed, time-consuming and costly, and not highly accurate. Especially for some thin-walled castings with complicated shapes, such as blades of aircraft engines, marine propellers, cylinders of cylinders for automobiles, tractors, cylinder heads, etc., the manufacture of molds is a difficult problem. Although some large-scale foundries also import some advanced equipment such as Cnc Machine tools and copy milling, in addition to the expensive equipment, the mold processing cycle is also very long, and because there is no good software system support, the machine programming It is also very difficult. Faced with the competition in the economic market in the world today, the upgrading of products is accelerating, and the current status of casting mold processing is difficult to adapt to the current situation. The emergence of rapid prototyping manufacturing technology provides a promising new path to solve this problem.

2.2 Rapid prototyping method

The main methods used in rapid prototyping devices that have been put into use in the world are as follows:
(1) SL (Stereo Lithography) method - stereolithography;
(2) SLS (Selective Laser Sintering) - laser layered sintering method;
(3) LOM (Laminated Object Manufactu-ring)--layered wheel gallery molding method;
(4) SGC (Sold Ground Curing) - photomask method;
(5) FDM (Fused Deoposite Manufacturing) - melt deposition method;
(6) DSPC (Direct Shell Production Casting) - ceramic shell method.

The specific processes of the above various methods have their own characteristics, but the basic process of the process is the same. In addition, there are still some methods still under study. Among the six methods, the SL method is the most mature and the largest occupant of the market.

Application of laser forming technology in casting

At present, the international application of laser forming technology in casting mainly has the following three aspects.

Direct casting casting

This method is suitable for single-piece production with complex shapes, such as special castings in the aerospace industry, or one or two castings for further testing during the trial production of new products. The specific operation is to cast the casting by resin molding or by investment casting, or to directly cast the casting by the lost foam casting method. When molding by the SLS method, when the paraffin powder is used as a raw material to directly produce a paraffin prototype, it is convenient to cast the casting.

2. Cast the casting with the prototype and then cast the casting

This method can be applied when the number of castings is large. It is first turned into a casting mold by a silicone rubber method, a gypsum type method or a self-hardening sand type method, and then a wax mold or a direct casting into a casting. The raw materials used in the SLS method are paraffin, nylon or polycarbonate. Sintered with polycarbonate material, it is superior to paraffin in many properties and can be used for many complex high-precision parts.

Chrysler Corporation and General Machines Inc. of the United States use the SLS method to reduce development costs for new automotive engine parts. Chrysler used the SLS method to make wax patterns to produce complex in-vehicle intake and exhaust pipes. General Machines also used this method to make complex parts on spacecraft. Rorketdyhe of the United States even used wax and nylon to make a complex six-cylinder cylinder block shape, and then used investment casting to produce castings.

3. Using the prototype to make molds

This aspect is the most widely used and can be used for mass production of castings.

1) The most direct mold application is on the formwork and core box for sand casting. The prototype is prepared by using a suitable Resin Material, and then the surface is sprayed, or the ceramic prototype is sintered by the LOM method, and then the pattern is directly mounted on the template and the core box. This can reduce the manufacturing cycle of the mold, and the cost is lower than that of the CNC machine tool.

Ford Motor Company of the United States used the LOM method to manufacture a 685mm long crankshaft model, which was first divided into three pieces and then assembled into a sand casting template with a dimensional accuracy of ±0.13mm.
2) Spray some low-melting alloy on the surface of the prototype, which can be used as a wax mold, or as a core box or a wax mold with epoxy resin and prototype.
3) The mold pattern can be directly designed through the 3D CAD system, and then the mold prototype can be obtained by laser rapid prototyping technology, and the metal mold can be directly cast by the above various methods.