Casting call: forming metal parts in disposable molds can save time, material.
If an operation is fabricating parts out of bar metal, chances are it's costing extra time and money. If those parts require machining, there could be a loss of significant money in scrap, especially if expensive metals or alloys are used.
Investment casting offers flexibility of alloys while saving finishing time and material waste. The range of metals and alloys that can be investment-cast is wide: aluminum, stainless steel, cobalt, and Inconel.
The process can also combine two or more parts into a single piece, saving on fabrication, welding or assembly, and machining time.
Parts between 1 ounce and 30 pounds in weight can be investment-cast in close tolerances with surfaces that require little finishing.
A growing number of operations that make intricate metal parts, or parts requiring repetitive, extensive machining, are finding that investment casting is a solution.
Savings in the long run
"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" says Carl Johnson Jr., vice president of Staten Island Machine Shop Inc. of Staten Island, NY. "Plus they can produce a better part."
Johnson, who produces metal shafts as well as plate and sheet metal, explains that the stainless shafts he fabricates 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," he 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--bas become a problem for many machine operations.
"To an extent, investment casting alleviates this problem, because it eliminates some of the burden of machining."
Several years ago, Staten Island Machine Shop began having some of the parts it previously had sand-cast instead supplied by Rimer Enterprises of Waterville, OH, a state-of-the-art investment-casting specialist that serves industries ranging from railroad to food processing.
Jonnson adds mat me stainless steel gears his operation 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.
Savings in metal
While reducing the demand on machine time is a savings, there is also added savings in costly metals used to fabricate many parts. Chuck Myers, president of Rimer Enterprises, says that 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 pound, you might be machining 80 percent of the steel out for your finished product," Myers explains.
"By the time the part is finished, you've got four pounds of stainless steel chips that you end up selling to a scrap dealer for $2 per pound. 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."
The general manager of another Ohio-based machine operation 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 are also significant.
"The advantage of getting a near-net shape means less machining and also material savings," he 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 hall 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 operation, which also has its investment castings made by Rimer, recognizes that the consistency of investment-cast products is a noteworthy benefit. While investment casting may provide quantum savings in terms of time, material and labor, some have concerns about turn-around rime.
"When we need castings, it is usually because a customer is running the same part except that the dimension may change," the general manager 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 it took over ownership of the business several years ago. For example, the company installed a robot-dipping system to reduce lead-time and improve the consistency of products. The newly expanded facilities also include a 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 percent. In emergency situations, we will do everything we can to turn around the needed castings as quickly as possible." Rimer Enterprises, www.rsleads.com/806tp-151
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|Title Annotation:||managing for tomorrow|
|Publication:||Tooling & Production|
|Date:||Jun 1, 2008|
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