Micro-plastic parts

In combination of die-sinking EDM and wire-cut EDM, high precision inserts can be manufactured for the production of micro-plastic parts. Figure 4.43 shows the compiexity and precision of this type of process on the example of micro-stamping. Figure 4.44 iilustrates another combination part. 

Machining of micro molds and dies for a variety of applications including plastic parts mass manufacture... 

Before electroless plating plastic parts, the surfaces have to be treated to ensure good adhesion. The etching process usually involves the use of a chromic acid solution to provide a microscopically roughened surface to the plastic part. The catalytic process is sometimes referred to as seeding. Here very small particles of an inactive noble metal catalyst, normally palladium, are deposited into the micro-cracks created during the etching process. The palladium will act as active catalyst sites for chemical reduction of the electroless... 

The stress-strain curves simulate a homogeneous deformation process of the polymer. However, on the microscale above the linear part of the stress-strain curve (see Fig. 1.15, curves (b), (c), (d)), localized heterogeneous deformation mechanisms occur. Depending on the polymer chemical structure and entanglement molecular weight Mg and on the deformation conditions (temperature and strain rate), several types of heterogeneous deformation are observed micro plastic zones, crazes, deformation zones, and shear bands. Their main features are sketched in Fig. 1.18. 

Micro plastic zones occur even in the brittle fracture of polymers in front of the crack tip. Crazes are localized bands of plastically deformed polymer material, which always appear perpendicular to the stretching direction. They are constituted hy polymer fibrils of about 5 -15 nm diameter, which are stretched in the loading direction and separated by elongated voids with diameters up to about 50 nm. The craze-bulk interface is relatively sharp and only about 10 nm thick. Crazing is connected with volume increase of the material. In Part II, Figs. 1.4 and 1.5 and those figures that follow show typical examples of crazes in PS. Crazes in other polymers can also possess a coarser internal structure. 

Dirt or debris can adhere to the surface of almost any plastic part, or it can accumulate in micro-cracks caused by heat, light, or mechanical stress. Microorganisms can grow on the debris and produce metabolic products that can stain the plastic and give rise to odors. 

In either case, different tolerance, surface features, and accuracy may be required. Eor the micro injection molded parts themselves, the same rules apply (e.g., avoidance of sink points, etc.) as for normal plastic parts. Experience in micro-mold making and preliminary testing is mostly necessary. Here, the collaboration with the customer is a priority, much more so than in the area of standard shapes. 

Telecommunications, the watch industry, medical applications, and the automotive and chemical industries are asking for smaller and smaller parts and components made of plastic. Standard injection machines are unsuitable for micro-parts. Here we describe, without claiming to be ejdiaustive, two examples of special machinery developed by Battenfeld and Medical Murray. 

Fillers, stabilisers and colorants can be inorganic or organic, and are added as part of identification, stability and durability, they must be non-leaching and meet health requirements. Some plastics products are required to keep moisture and air out of sensitive products and these are usually high-density plastics with low permeation properties. Some products require plastics with high permeability to allow air (oxygen) as part of product stability, e.g. anaerobic adhesives. Healthcare products require that some containers do not allow air or moisture to permeate the surfaces (bacteria or other micro-organisms) and in some extreme cases may require that the inside be coated with an inner layer of approved lacquer or other very low permeable material. 

The method of molecular dynamics (MD) provides a remarkable opportunity for the observation of various mechanisms of processes taking place on a micro-(nano-) level, and for the evaluation of the probability of such processes by repeating experiments dozens of times. Figure IX-37 shows the MD simulation of the deformation and fracture of a two-dimensional crystal. Plastic deformation and formation of a dislocation (AB) at elevated temperature (upper part) and the formation of a brittle crack at low temperature (lower part) are shown in Fig. IX-37, a, while simultaneous processes of crack nucleation influenced by the presence of foreign atoms, and their propagation to the tip of the crack, taking place at elevated temperature, are illustrated in both lower and upper portions of Fig. IX-37, b [40,41]. 

Scanning acoustic microscopy (SAM) is an ideal nondestructive method for revealing internal flaws within materials or between material interfaces. SAM is extensively used in detecting voids, delamination, and other separations that can occur in adhesive-attached parts, especially after thermal cycling. SAM is particularly useful in the analysis or evaluation of many types of electronic parts, including ceramic and plastic-encapsulated ICs, plastic-encapsulated microcircuits (PEMs), hybrid micro-circuits, CSPs, PBGAs, and printed-wiring boards. 

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