1.8 holes and slots
Holes and grooves, in addition to reducing part quality and forming uniform wall thickness, are a useful functional structural feature of MIM parts, and generally do not increase part prices.
However, adding holes and slots will increase the complexity of the mold, as shown in figure 8-a, which will increase the cost of the mold.Holes perpendicular to the parting line are easiest to form and cost the least.Holes parallel to the parting line, although easy to form, need to add sliders or hydraulic cylinders, which will increase the cost of early mold manufacturing.
The internal connecting hole can be formed, as shown in figure 8-b. In order to prevent the problem of sealing and burr, this design must be carefully considered.
If possible, a hole should be made into a d-hole to make a plane on the core rod, so as to enhance the sealing of the mold, otherwise, it is necessary to make an arc surface with the parts, and its thin edge will cause abnormal wear.
1.9 root cutting
With the open die, the external root cut as shown in FIG. 9 is easy to form on the parting line. Making this shape requires increasing the die parts, increasing the cost of the die and reducing the productivity.
Some internal root cuts can be made with sliders, others with movable cores.
In most MIM part designs, designers may decide to eliminate internal root cutting due to increased costs and possible flash problems.
1.10 casting system
The injection material enters the mold cavity through the sprue. Due to the high metal content of the MIM injection material, these sprue of MIM are generally much larger than those of plastic injection molding.
Since the gate usually leaves a mark where the finished part comes out of the molding cavity, the setting of the gate needs to balance the required craftsmanship, function, size control and aesthetics.
The gate is best set on the mold parting line, as shown in FIG. 10, so that the path of the injection material flow can impact the mold cavity wall or core bar.
In addition, for parts with different wall thicknesses, the sprue is usually set at the thickest cross section so that the injection material flows from the thick section to the thin section.This setting of the gate eliminates holes, grooves, stress concentrations and streamlines on the surface of the part.
If you want to produce parts with multiple cavities, you must also consider the size and configuration of the sprue to ensure that the same amount of injection material is supplied to each cavity with a uniform filling rate.
1.12 decorative features
Figure 12 shows the marking, embossing, number of parts and identification marks of die number and hole number, all of which can be easily formed in the proper position of the part without increasing the cost of the part.
These features can be highlighted or recessed, and the MIM process can produce high levels of feature detail, including sharper diamond embossing.
1.13 sintered parts support
In the process of degreasing and sintering, the green MIM parts shrink by about 20%. In order to minimize the possible distortion, the MIM parts must be properly supported during sintering.
Typically, MIM parts are placed on flat ceramic plates or trays.
As shown in FIG. 13, it is best to design the sintering plate or tray into a plane with large surface or common structural features of several parts, so that standard supports can be used.MIM parts with long spans, cantilevers or vulnerable areas may need to be supported by special brackets or fixtures for the parts.These production costs are very high.
