Metallic bonding by infiltration is used mainly for dressing rollers and special applications [KLOC09]. Infiltrated bonds are also used for superhard honing sticks (bronze, Co-bonding), stone drilling crowns, or saws.
Grits, bond, and fillers are either mixed and filled into the die or the grits are fixed first onto the bottom of the die form and the matrix powder is added afterwards (Figs. 3.12 and 3.13). After then adding a defined amount of hard solder and flux (often copper, nickel or zinc alloys), the die form is heated in continuous ovens with inert gas or by induction [KLAU76, STOC86]. The solder has a relatively low melting point. Therefore, the molten solder penetrates the matrix powder by capillary forces. The resulting matrix is strong and highly wear-resistant [KLAU76]. The tool body can be connected to the abrasive layer simultaneously by brazing. Subsequent to the heating process, pressure can be applied to further influence the tool characteristics [STOC86] (Fig. 3.12).
The melting point of the solder defines the temperature of the infiltration process. Infiltration of copper-based solder takes place at 1000-1250 °C [YOUN66]. Die forms are made of graphite. This material has several tasks [KLAU76]:
• Building an air gap between die form and produced tool by different thermal expansion,
• Being multi-usable because of the two above described properties,
• Binding oxygen from the atmosphere and building of CO/CO2-atmosphere as
oxidization protection for diamond grits.
The appropriate choice of the graphite die material is important for a stable manufacturing process as reactions between tool bonding ingredients and graphite matrix can occur [KLAU76]. Graphite for the infiltration process should be easily machinable, be free of cracks and have low porosity, so no solder flows into the die material itself and destroys it. The generation of carbides between graphite and matrix powder ingredients can be suppressed by coating of the die form before each infiltration process. Coating materials can be e. g. Al2O3-powder and alcohol or natural graphite and glycol [KLAU76].