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Machining Tungsten Alloys

Sometimes, you can have it all. Our high-density tungsten alloys are extremely strong and durable (typical hardness ranges from 24-32 RC), yet easy to work with. (They machine much like gray cast iron.) Tungsten alloy's low-thermal expansion rate and resistance to breakage and chipping allow you to achieve very close tolerances and hold fine finishes. Coolants are optional, reducing your processing costs and, in most cases, your carbide tools will machine our high-density alloys well.

Turning and Boring

Carbide inserted cutters are suggested. Roughing - Cutting depth of .030" to .125" and .008" to .015" feed, at speeds of 200 to 300 SFM. Finishing - .010" to.015" cutting depth and .004" to .010" feed, at speeds of 250 to 400 SFM.

Tapping

Use high-speed steel or carbide, two flute plug spiral point taps. A light tapping fluid is recommended.

Drilling and Grinding

Carbide drills usually work best. Increasing clearance angles and using automatic feeds are often helpful to prevent inadvertent binding and seizing. Carbide drills give a better tool life.

For grinding applications, we recommend using aluminum oxide or silicon carbide wheels of medium hardness.

Milling

Carbide cutters are suggested.
Roughing - Feeds of .007" to .015" per tooth at speeds of 200 to 400 SFM.
Finishing - Feeds of .003" to .010" per tooth at speeds of 300 to 700 SFM.

Sawing or Cutting

Despite the incredible strength of our high-density alloys, materials can be cut nicely using a bi-metal blade. Blade pitch should be relative to the thickness of the material. Coarse blades can be used at low speeds; finer blades can be used at higher speeds. Coolant, though not usually necessary, can be used. Tungsten alloys can also be cut using high-speed abrasive cutoff wheels.

Stress Relieving

To perform stress relieving on high-density alloy machined parts, we suggest heating at 600°F in air for two hours and cool in air or in a protective atmosphere at 900°F for 30 minutes.

Mechanical Joining

Mechanical joining is the best option for joining high-density alloy material. Standard fasteners such as bolts and pins are often used, as is threading a tungsten alloy to mate to itself.

Copper Brazing

Copper brazing may also be used to join tungsten alloy to itself or another material; the resulting joint strength is comparable to that of the parent material. Unfortunately, although it is a very successful method of joining high-density alloys, the tightly controlled conditions required for copper brazing often make it impractical.

Diffusion Bonding

Diffusion bonding is an ideal way of joining tungsten alloy material to itself, but because it is performed at very high temperatures and tightly controlled conditions, it has to be done by the material manufacturer. If parts are finished, the extreme temperature may cause some distortion.

Silver Soldering

Another practical and efficient way of joining tungsten alloy material to itself or to steel is silver soldering. Easy-Flo 45 (BAg-1) is commonly used. Typically, at least .002" clearance between the parts to be joined is required (larger parts require greater clearance). Parts should be cleaned thoroughly (sometimes sandblasting is used), fluxed and heated carefully until the solder flows smoothly. For greatest joint strength it's also important to facilitate slow, uniform cooling.

Shrink Fitting

Shrink fitting is another good method to join tungsten alloy to steel. Depending on the size of the part, .005"/.007" interference per side is recommended. The high-density alloy is chilled in dry ice or nitrogen while the steel is heated. The resulting joint is usually reinforced with a pin or fixture and allowed to cool slowly.

Contact a Mi-Tech Metals professional for more information on which method would be best for your application.