Small-quantity/High-mix Tube Manufacturing

In the US, many high volume tubing suppliers have moved production facilities overseas to low cost producers like China or Mexico. Minimum buys are now the rule, leaving many US manufacturers with a quandary – How to get small quantities of a wide variety of tubing needed for research and development or smaller production runs. Into this void have stepped a few purveyors of "small quantity, high mix" tubing, providing high quality products without requiring purchase of thousands of pounds. How do they make the business model work? By taking what major mills produce and redrawing it quickly to meet customer specifications. With a mix of raw materials, a large selection of dies, and using lean manufacturing principles to level-load the facility, niche tubing manufacturers are maximizing efficiencies to meet customer demands.

Major mills produce massive quantities of tubing in stainless steel, copper, and nickel in standard industry sizes. Those looking for quarter-inch stainless steel tubing could go to a host of small-volume tubing distributors and get standard sizes in any quantity they need. But what if they need tubing that is not a standard size, or if they need a variety of alloys to test a concept? That's when the average distributor would tell them that such an order would require the purchase of a minimum number of feet, and it would take several weeks or even months. By comparison, the small quantity/high mix model can provide quick turnaround for a range of alloys in a variety of sizes so customers can see what works best in a particular application.

Profitable small quantity/high mix tube manufacturing depends upon efficiently running manufacturing operations. For example, at A.T. Wall, we have developed the capability to take what the major mills produce and redraw it into specific sizes without sending it overseas. And we do it quickly, with a frequent changeover in machines. We take the customer requirement and resize the tubing into specific tightly held tolerances, specific surface requirements, and specific sizes. The facility produces tubing made from precious metals, nickel-iron alloy, tantalum and niobium, as well as Kovar, Invar, and stainless steels.

This way of selling tubing is a form of distribution, but has the advantage of not locking the facility into only inventory already on the shelf. And how do we operate profitably doing this? It comes down to how efficiently you run the facility. It is critical to understand the product you are running through and use skill sets learned on the manufacturing floor to maximize efficiencies for running the product.

The key is to level load the facility using lean principles. With a small quantity/high product mix, on any given day you could be producing any one of many products, so it is essential to understand how to do a very quick changeover from one product to the next using single minute exchange of die (SMED).

Another key consideration is the ability to conduct secondary operations in house, for example heat treating/annealing. The more times you have to send out a product for secondary operations, the harder it is to level load, and the more difficult it is to keep an efficient facility. Keeping more secondary operations in house speeds up production, and gives you more control over the product.

In addition, a cold working process can be used to change surface finish, the OD/ID, and tube hardness. For example, if the customer needs to bend the part, the facility can temper the material; if they are going to flare the tube at their facility, alloys with softer composition are suggested. Consultation is available on whether tubes fitting in machined components will meet all required tolerances.

Research and development facilities, especially larger centers like Lockheed Martin, NASA's Jet Propulsion Laboratory (JPL), as well as other similar facilities, frequently need small quantities of a range of alloys (typically stainless steel and Kovar) to test a concept. They are not in a position to procure the minimum quantity of several thousand pounds required by most major mills.

Working with R&D engineers as they prove out a theory can be extremely exciting. Large centers' budgets tend to be flexible enough to make it possible to work with them to procure the alloys they need. Many research engineers have found procuring alloys for R&D to be challenging – one unique capability A.T. Wall has is the ability to take plate stock in squares, cut it into a circle, and then press the stock into tubing in a technique called "cupping." This is appealing to R&D engineers, who can use the process rather than having to procure say 15,000 pounds of tubing for an untested concept. While not the most efficient process, it is a way of getting a heavier wall-to-OD relationship, and is used by national laboratories as well as medical, aerospace, and chemical processing engineers.

One example of a good candidate for this cupping technique is Kovar, used in many applications where thermal expansion rates are critical. Kovar is used in the electronics industry as a glass to metal sealing alloy for keeping electronic components hermetically sealed. Widely used as tubing in which to run fiber optics, Kovar is extremely expensive (about $30 a pound), so using a machine shop to hollow out the tube wastes a tremendous amount of the costly alloy. This makes the alternative method particularly attractive.

Other examples of applications that have taken advantage of the small quantity/high mix model include nickel tubes used in X-ray imaging technology, tubes used for oil drills, incubators, double wall tubing for high pressure testing, rectangular nickel tubes used for battery cans, as well as Invar and stainless tubing used in cryogenics equipment.

The use of precious metals in industrial applications is another area where small quantity/high mix tubing comes into play. In most cases, customers do not need a lot of the material but it has to be extremely precise. Another interesting example is the use of coined silver (90 percent silver and 10 percent copper) for production of slip rings. The alloying of this material supplies the electrical conductivity and hardness needed for high efficiency motors. Fine silver, usually found in purity greater than 99 percent, is used in the forming of linear explosive cord. This product is extremely important in aerospace applications. For example, it is used in emergency evacuation systems tubing found in the ejection mechanism of helicopter and fighter jet cockpits. A relatively soft extruded tube is drawn, and the added cold work increases its strength. After it gets to the specific required strength, the customer takes the tubing and packs it with explosives. Since silver vaporizes when it explodes, the component blows off the canopy to allow the pilot to eject safely.

Creating products customers need and offering them affordably in amounts they can use, carrying a variety of alloys in an extremely wide range of different sizes and shapes, using an efficient manufacturing process, and being open to the full range of industrial uses, has been a successful and profitable path for this proud American manufacturer of precision tubing.