Metal and Ceramic Injection Molded Parts

Index

• PIM Materials
• Kodak Experts/Contacts
• Advantages and Limitations of PIM
• Selected Mechanical Properties of PIM Metal Alloys and Ceramics
• PIM Design Guidelines and Tolerances

The powder injection molding (PIM) process has been developing since the late 1920's. In the 1950's ceramics were formed in the Soviet Union using wax binders.

The PIM business is expected to grow about 25% annually over the next several years.

Current annual PIM sales in North America exceed $100 million.

There are an estimated 40 companies in North America manufacturing PIM products either as job shops or in plant departments.

One of the limitations of injection molded polymer parts is relatively low strength. Injection molding of metallic or ceramic powders dispersed in a feed stock binder is a recognized route for improving strength. Given their relatively high final density, powder injection molded (PIM) products are suitable for high performance applications.

The high density results from the uniform powder packing attained in the PIM process.

The finished part and mold designs can be modeled by computer methods already established for thermoplastics.

A more familiar process for making powder metal and ceramic parts is die compaction. The wall friction between the powder and the die wall induces pressure gradients during compaction and ejection that lead to non-uniform powder density. Dimensional change during sintering depends upon the powder packing density. Low density regions shrink more than high density regions. Die compacted powders give non-uniform shrinkage. They are less dense because they are often sintered at lower temperatures where densification is minimized.

PIM is a hydrostatic forming operation in which the dispersion of the powder in the binder ensures uniform powder packing. The hydrostatic forming pressure minimizes density gradients and allows compacts to be sintered to densities approaching 100% theoretical, as compared with the 85% density attained in many die compacted materials.

Metal and ceramics components can be produced using the same machines and tooling that produce plastic parts. The difference being after the parts are molded the binding agent must be removed before the parts are sintered. Binders typically are polymers or waxes. Then the parts can be fired to complete the cycle. Note, that when the parts are removed from the molding machine they are in the green stage and require careful handling. Some newer processes are utilizing water based injection molding materials which do not require debinding.

Distortion during debinding and sintering is the largest contributor to dimensional variation. Computer simulation flow analysis studies can help the selection of gate size, gate placement, cooling pattern and molding conditions, thereby improving dimensional control.

As the cost of processing the raw materials declines, as it has started to do, powder injection molded parts cost will also come down. Different binder formulations are being researched to reduce the debinding time. A more efficient debinding system will result in better and larger parts.

PIM parts are now found in applications such as computer peripherals, printing and business machines, electrical, magnetic and semiconductor appliances, as well as the chemical, textile, automotive and bio-medical industries. Ceramics, metals, intermetallics and fiber reinforced composites can now be produced by the PIM process.

PIM Materials

Metals:

• copper, iron, gold, molybdenum, nickel, niobium, titanium, tungsten

Alloys:

• bronze, nickel-base, iron-nickel, cobalt-base, niobium (Nb-W-Ta), stainless steel, steel (Fe-C, Fe-Ni-C, Fe-Cu-C), super alloys, tool steel, tungsten heavy alloy

Ceramics and compounds:

• alumina, mullite (3Al2O3-2SiO2), nickel aluminide, silicon carbide, silicon nitride, titania, zirconia, silica

Cermets and composites:

• NbC-Ni, Ni3Al-Al2O3, Si3N4-SiC, TiC-Ni-Mo, WC-TaC-Co, W-Cu, WC-Ni

Index

• PIM Materials
• Kodak Experts/Contacts
• Advantages and Limitations of PIM
• Selected Mechanical Properties of PIM Metal Alloys and Ceramics
• PIM Design Guidelines and Tolerances

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Kodak Experts/Contacts

Advantages of PIM:

• Comolding of different materials, forming part of a component from one material and then another portion from a second material.
• Form low-cost complex shapes.
• High volume manufacturing method.
• Small production runs are possible, with as few as 5000 parts being economical.
• Reduced number of production steps due to the elimination of secondary operations such as milling, drilling, boring, grinding, etc.
• Material use is nearly 100%.
• Near-full density parts.
• For ceramics, the raw material cost is the same for PIM as for cold isostatic compaction or other forming approaches.
• Cemented carbides processed by PIM are widely used as wear and cutting parts.

Limitations of PIM:

• Usually applied to complex, small shapes with high values.
• Formation of a thick cross section is still a problem.
• Dimensional tolerances are typically in the range of +/- 0.3%. With care and effort, critical dimensions can be held within +/-0.1%.
• Largest dimension being below 3 1\2".
• Small powder particles used are often expensive to produce.
• Hours of development time are still required to bring a new PIM part into production.
• If the required properties can be satisfied by a thermoplastic polymer, then there is little justification in applying PIM.

Index

• PIM Materials
• Kodak Experts/Contacts
• Advantages and Limitations of PIM
• Selected Mechanical Properties of PIM Metal Alloys and Ceramics
• PIM Design Guidelines and Tolerances

Return to the Top

Selected Mechanical Properties of PIM Metals and Alloys

Selected Mechanical Properties of PIM Ceramics

Index

• PIM Materials
• Kodak Experts/Contacts
• Advantages and Limitations of PIM
• Selected Mechanical Properties of PIM Metal Alloys and Ceramics
• PIM Design Guidelines and Tolerances

Return to the Top

PIM Design Guidelines

Restrictions

• No inside closed cavities
• No undercuts on internal bores
• Corner radius greater than .008
• 2o draft on long parts
• Smallest hole diameter .004
• Minimum thickness .020
• Minimum weight 0.1 gram

Desirable features

• Gradual section thickness changes
• Symmetrical slots or holes
• Largest dimension below 3 1/2"
• Weight under 100 grams
• Wall thickness under 15/16"
• Assemblies in one piece

Allowed design features

• Holes at angles to one another
• Hexagonal, square, blind, and bottom holes
• Stiffening ribs
• Knurled surfaces
• Protrusions and studs
• External threads
• Part number or identification in the die

Index

• PIM Materials
• Kodak Experts/Contacts
• Advantages and Limitations of PIM
• Selected Mechanical Properties of PIM Metal Alloys and Ceramics
• PIM Design Guidelines and Tolerances

Return to the Top

References:
R.German, Powder Injection Molding
The 1995/1996 International Powder Injection Molding Sysmposium
International Journal of Powder Metallurgy