**5. Conclusion**

128 Some Critical Issues for Injection Molding

sub-micron pores, because both debinding and oxidizing have not been completed at the low temperature. Then the microscopic structures are kept in accurate shape. In general the sintered parts processed at higher temperature shrink more, and the corner of microscopic structures becomes dull correspondingly. However the sintered parts processed at 973K keep the edge sharpness under optimized debinding-sintering conditions. The green compacts have slight concave portions on the top face of microscopic structure, but it was attained to fill the feedstock into SP-mold with sufficiently high transcription. On the other hand, the sintered parts processed at 973K shrank 20% in both height and width, and became round at the top and bottom of corner portions. As the sintering temperature is raised, the shrinkage ratio increased remarkably up to 873K and further increased gradually. It was also seen that the shrinkage ratios of L/S=5µm structures are larger than that of

The processability of a variety of μ-SPiMIM processes as above-described is summarized in Fig.36 in compared with the other precision processing and machining methods. A conventional rapid plot typing is difficult to manufacture SP-mold with micro-scale structure and high dimensional accuracy. Then RP/μ-SPiMIM method is not superior compared to micro machining such as micro-cutting, micro-EDM and micro-casting on the size of products, but it has a great potential to manufacture complex shaped parts such as micro-impeller shown in Fig.17. Further micro-miniaturization and surface quality improvement of rapid plot typing are required for μ-SPiMIM process, micro rapid plottyping using stereo-lithography and 3D-printing technology is a prospective method for manufacturing of fine structured SP-mold. On the other hand, LIGA/μ-SPiMIM and Resist/μ-SPiMIM are very hopeful combined methods for manufacturing metallic microstructured parts with high aspect ratios. The size possible for manufacturing is ranged from hundreds micrometers to tens micrometers. The problems are included high manufacturing cost and shape limitation of SP-mold. Furthermore, NIL techniques has a possibility for

1 10 100 1000

50μm

200μm

**Ultra-Precision Processing** (Laser, E-beam, UV, etc)

Width (µm)

Photo-etching

Micro-cutting, Micro-EDM, Micro-Casting, etc

**Mechanical & Physical machining**

**RP/µ-SPiMIM**

L/S=10µm ones and the whole bodies.

Fig. 36. Processability of a variety of µ-SPiMIM processes.

1

10

**NIL/µ-SPiMIM**

10μm

5μm **Resist/µ-SPiMIM LIGA/µ-SPiMIM**

100

Height (µm)

1000

10000

In this chapter, a general characteristic of MIM process on materials and conditions for manufacturing of small metallic parts with high quality was described utilizing actual data, and the complex flow characteristics of MIM were introduced on two kinds of small components, such as micro gear and micro dumbbell specimen. Then the technical problems to be solved for micro-miniaturizing of MIM parts were addressed, and the effectiveness of sacrificial plastic mold in micro-MIM process was shown by citing some example productions of micro-structured parts. A variety of methods for fabricating of the sacrificial plastic mold such as rapid proto-typing, plastic injection-molding, LIGA process and nanoimprint lithography process, were introduced by showing the investigation results on the effects of metal particle size and processing conditions. The use of nano-sized metal powder was applied in micro MIM process inserted sacrificial plastic molds made of resist or nanoimprint lithography, the results that the decreasing of particle size improved the surface roughness and shape-transcription of sintered parts were shown obviously. In collusion, micro sacrificial plastic mold insert metal injection molding, named as μ-SPiMIM method has a great potential to solve technical problems occurring in the μ-MIM process, it can be produced precisely the 3 dimensional complex metallic metal components with single-digit micrometer structures.

#### **6. Acknowledgment**

Author deeply appreciated for research foundation supports and understandings to President Dr. Shigeo Tanaka from Taisei Kogyo Co., Ltd., and great efforts of experimental works to many former graduated students from Osaka Prefectural College of Technology.

#### **7. References**


**6** 

*IRITEL A.D., Republic of Serbia* 

**Ceramic Injection Molding** 

Zdravko Stanimirović and Ivanka Stanimirović

Powder injection molding (PIM), which encompasses metal injection molding (MIM) and ceramic injection molding (CIM), is a net-shaping process which enables large scale production of complex-shaped components for use in a diverse range of industries. It combines plastic injection molding techniques and performance attributes of ceramic and metal powders. Ceramic injection molding (CIM) uses ceramic powders such as alumina, zirconia, titania, ferrite powders, etc. It was introduced in 1940's, but for the next thirty years it was of minor interest to ceramic industry. In 1970's and 1980's CIM provided cost-effective fabrication method for mass production of ceramic parts for automotive industry. Today more than 300 companies practise PIM. Most of them practise MIM technology (>70%). Small percentage (5%) produce metals, ceramics and carbide components and about 25% practice CIM technology. This positive tendency can be attributed to unique properties of ceramic materials. They have excellent mechanical properties and low specific weight. Also, they are suitable for applications under extreme conditions (high temperatures, corrosive atmospheres, abrasive conditions, high loads at high temperatures). This combination

The ceramic injection molding process consists of four basic steps: feedstock preparation, injection molding, debinding process and sintering (Fig. 1).When powder technologies are in question, the key step in production process is choosing the adequate ceramic powder. Specific surface area, particle size, size distribution, particle shape and purity of the powder influence properties of the feedstock. Typical particle sizes in CIM are 1-2µm, but also much finer particles down to submicron or nano region are being used in advanced CIM. CIM uses a feedstock of composite granulate. A high concentration of ceramic powder is mixed with a thermoplastic binder system to form moderate viscosity feedstock - homogenous powder-binder mix that is free of agglomerates, has optimum ceramic/binder content and

The feedstock is molded using injection molding equipment similar to that used for polymer injection molding. Injection molding involves concurrent heating and pressurization of the feedstock. It requires close monitoring in order to minimize molding defects. As a result, a green body is obtained (Fig. 2). After molding, the binder is extracted from the green body. Debinding usually takes place in two steps. Immersion is the first step. Soluble component of the binder is removed and system of pore channels develops to allow removal of the remaining component. The second step is thermal debinding and the insoluble component

is being removed by thermal decomposition thus resulting in brown body (Fig. 2).

makes them interesting for a wide variety of applications.

still maintains sufficient fluidity (Rak, 1999).

**1. Introduction** 

