If you’re fabricating parts out of bar metal, chances are it’s costing you a lot of extra time and money. And if those parts require extensive machining, you could be losing significant money in scrap, especially if you’re using pricey metals or alloys.
An increasing number of shops that make metal parts that are intricate, require extensive machining, or are produced repetitively or in limited quantities, are finding that investment casting is the ideal solution. Forming metal parts in disposable molds offers opportunities to create “near net shape” parts of virtually any metal, even in very low quantities.
Investment casting also offers broad flexibility of alloys while saving finishing time and material waste. The range of metals and alloys that can be investment-cast is very broad, including low-cost alloys such as carbon and many tool steels or costly alloys such as aluminum, stainless steel, hastalloy, cobalt, and Inconel.
As opposed to forming parts from bar metal, investment casting is also beneficial for fabricators who want to combine components into a single piece, or use pricey metals and want to avoid wasted material while minimizing machine time, which can run $85-$100 per hour including machine cost. If parts are between one ounce and 30 pounds in weight, they can be investment cast in remarkably close tolerances with surfaces that require little finishing.
Small-Lot Stainless Shafts
Several years ago Staten Island Machine Shop, Staten Island, NY began using parts supplied by Rimer Enterprises. This Waterville, OH state-of-the-art investment-casting specialist serves a variety of industries ranging from railroad to food processing.
“I suppose that some fabricators look at the somewhat higher initial cost and don’t realize all the savings of investment casting in time and materials, saving money in the long run. Plus they can produce a better part,” says Carl Johnson Jr., vice president of Staten Island Machine Shop Inc. Johnson, whose shop produces metal shafts as well as plate and sheet metal, explains that the stainless shafts he fabricates in relatively small lots are investment-cast rather than cut from bar stock or formed by sand casting and then finished.
“For one thing, in this part of the country it is becoming difficult to find qualified machinists,” Johnson says. “There are few machinists or CNC operators coming out of the schools today, and that – as well as the cost of equipment and labor – has become a problem for many machine shops. To an extent, investment casting alleviates this problem, because it eliminates some of the burden of machining.”
Johnson adds that the stainless steel gears his shop now gets from Rimer, typically for marine applications, are high-precision parts that slide over or under other components. In the past, when the gears were made from sand castings, there could be significant shifting or other movement.
“This problem is far less likely to happen with investment-cast gears because the rotations are right on, the holes are exactly where they should be, and all critical dimensions and tolerances are very close, which also minimizes the need for machining,” he says.
While reducing the demand on machine time is a significant savings, there is also substantial added savings in costly metals used to fabricate many parts. Chuck Myers, president of Rimer Enterprises, says depending on the metals and alloys used to make the castings, the differences in material costs could be stunning.
“For example, if you are machining a piece of stainless steel that costs $5 per lb, you might be machining 80% of the steel out for your finished product,” Myers explains. “By the time the part is finished you’ve got 4 lb of stainless steel chips that you end up selling to a scrap dealer for $2 per lb. If the same part is investment-cast, the near-net shape virtually eliminates the scrap, which could represent many dollars in savings per part in alloy cost as well as labor.”
Bar Stock Hard to Come By
The general manager of an Ohio-based machine shop says that one of the main reasons he buys investment castings is that he can’t get the needed material in bar stock and prefers not to use sand castings. However, the savings on materials is also significant.
“The advantage of getting a near-net shape means less machining and also material savings,” this general manager explains. “So, when you make parts with alloys, such as the nickel-based alloys that we use, there is a pretty significant cost savings because you don’t have to throw half of the metal away in chips. And of course, the machine time is less when you have parts that are cast pretty close to size.” This shop, which also has its investment castings made by Rimer, recognizes that the consistency of investment-cast products is a noteworthy benefit.
Cutting Turnaround Time
While investment casting may provide quantum savings in terms of time, material, and labor, some people have concerns about turnaround time. The GM mentioned above, for example, uses limited quantities of orifice rings that one of his glassmaking customers uses in making bottles.
“When we need castings it is usually because a customer is running the same part except that the dimension may change,” he says. “We try to stay ahead of the game but we can’t anticipate how long their production runs are going to be. So, if we get caught short, any delay in turnaround time can really hurt.”
In anticipation of such problems, Rimer made substantial new investments in its in-house capabilities when taking over ownership of the business several years ago. For example, in 2006, a robot dipping system was installed to reduce lead-time through the shop and improve the consistency of products. The newly expanded facilities also include a very modern CNC tooling shop and a CNC machine shop for machining castings.
“Turnaround time in our industry is often 10-12 weeks,” Myers says. “We have been able to cut that time more than 60%. In emergency situations, we will do everything we can to turn around the needed castings as quickly as possible.”
