Increasing profit with machining.

Inside This Story:

* Castings often need additional features machined-in for their end-use applications.

* Many metalcasting firms have found success implementing a full-service machining operation into their facilities.

* By providing a one-stop shop, your firm could secure higher sales volume and profit margins while delivering finished castings at an accelerated rate.

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In an era when leadtimes have become tighter by the order, metalcasters should seize every opportunity to accelerate the delivery of finished cast components to their customers. One step is to consolidate the supply chain by performing in-house machining.

By nature, many cast components need additional grooves or bores machined-in to function in their end-use application. Customers often will purchase a casting from one source and then ship it to another firm for machining, leading to unnecessary time and shipping costs. However, by introducing machining capabilities at your facility to supply your customers with fully cast and machined products, you kill two birds with one stone.

With cast-and-machined components being produced solely at your plant, your firm becomes a full-service supplier to your customers. The additional operations can increase your profit margins as more customers come to your firm due to the central production. Customers, in turn, will save on their costs in the shortened leadtimes and fewer shipping expenses. Thus, your firm becomes a more valuable casting supplier and can gain higher sales volumes and more repeat customers with in-house machining.

A growing number of firms in the U.S. have this mindset, whether it is with a couple of manual drill press machines or state-of-the-art 5-axis CNC capabilities. From ferrous to nonferrous metalcasters, from one-ton components to palm-sized castings, these value-adding machining operations augment customers' components and improve overall part production from start to finish, resulting in shorter delivery times.

Providing One-Stop Shopping

When working with customers that require machined castings, having in-house machining can greatly improve your rapport with the purchasers. One of the best advantages they see in a one-stop shop is the limited search for additional firms, such as machine houses. This will expedite the production process and return the engineered cast component to your customer sooner.

"You're controlling the process (from casting to machining)," said Glen Laehn, president of Bremer Manufacturing Co., Elkhart Lake, Wis., an aluminum sand casting firm that provides secondary machining services with five 4-axis CNC machining centers. "From a delivery standpoint, it certainly helps a lot. We can schedule orders much tighter without sending things outside."

Wherever possible, Bremer likes to handle its machining requirements in-house; however, when requirements exceed those capabilities of either a capacity or technical nature, the firm utilizes several outside shops. According to Laehn, when Bremer outsources its machining operations, it gives those firms a timeframe of when the rough castings would be shipped to get into their queue. But there can be more benefits when the machining is done on-site.

"Maintaining quality is easier having a machine shop in-house, too, because if you have casting issues, the machine shop operators can make a point of it and get it back to the foundry right away," Laehn said.

Another bonus of in-house machining is the reduced risk of error. The interrelationship that exists between in-house metalcasters and machine shop operators ensures the final castings will not fail their expectations. Close communication is kept as to what features require machining and where they are needed. Additionally, customers are pleased by the elimination of needless shipping costs between a casting firm and machine shop. In-house machining also eliminates extra paperwork associated with purchasing.

"The one-stop shop is a win-win situation," said Neil Osborn, sales and marketing manager at Jencast (Jensen International Inc.), South Coffeyville, Okla., an iron casting firm that offers a range of options from single drilling to horizontal and vertical CNC machining work. "By providing a turnkey part, we utilize our equipment and capabilities, leadtimes can be reduced, freight costs between operations are reduced, and third party hassles over quality issues are eliminated."

Jencast currently machines its gray and ductile iron castings at its sister plant in Coffeyville, Kan., and plans to construct a new machining facility in South Coffeyville, adjacent to its casting operations.

Promoting Value

When considering implementing a machine shop, it's ideal to recognize all available capabilities. One casting might need the simplest machining, but the next casting could justify the most advanced techniques. "Our machining capabilities are driven by the customers and the jobs," said Todd Farrar, marketing and sales manager at Farrar Corp., Manhattan, Kan., which casts ductile iron components and offers an assortment of capabilities from horizontal and vertical CNC machines to broaches and lathes.

"Sometimes the need is very simple and shouldn't require a high-dollar piece of computerized equipment, but in other cases, the machining may be complex and/or a much higher quantity," Farrar said.

The training for such equipment varies for each metalcasting facility. Some firms have found success with people who have a vocational or technical education background, while others strive with several to have employees years' experience on CNC ma chines. But most of these facilities have found on the-job training to be an essential ingredient to employing competent machine operators. This training method allows the new employees to become accustomed to the firm's casting envelope, the setup processes, the blueprint readings and the measurement techniques of the machines to achieve the desired machined features.

Additionally, in case any difficulties occur or if tighter tolerances are needed, design engineers often are willing to collaborate on ideas with the machine operators to get the part completed faster.

When a customer requires machining, it should be noted that tolerances can play a key role that often depends on the type of casting process, Laehn said. For example, a typical green sand casting tolerance is [+ or -] 0.020-0.030 in./in. If the design calls for something closer, the casting must be machined to those tolerances or be made via another process. Having machining operations enables your plant to meet tighter tolerances, despite the differences in the size of castings your facility produces. For example, Jencast makes castings up to 1,500 lbs. (680.4 kg), while Bremer supplies parts that weigh ounces, yet both can achieve machining tolerances of [+ or -] 0.0005 in./in.

"If a part matches our capabilities, we will provide a three-to-five-piece sample including inspection documentation for a customer's approval," Osborn said. "Approval in writing is required before we proceed with regular production." Osborn noted that Jencast ensures an accurate machined part in the given leadtime by utilizing machining equipment in the fewest operations. Also during this process, the firm will examine a part's critical tolerances and then calculate leadtimes off management objectives, the backlog of orders and forecasts of incoming work.

In addition to showing physical part samples, discussing case studies with customers helps them gain more confidence in your operation. "Our job is to perform and show them we can be the entire supply chain, not just one link in it," said Farrar.

"In today's world, freight and leadtimes are becoming so critical for a lot of the manufacturers out there. Since we, in essence, control all of this, it helps in delivering the product our customers want in their hands."

For More Information

"The Market Driven Foundry--Part III: Survey Reveals Routes for Attracting Casting Business, Spending," M.J. Lessiter, MODERN CASTING, April 2003 p. 21-25.

"Uncovering the Path to Cast Iron Machinability Solutions," G. Goodrich, Engineered Casting Solutions, Winter 2003, p. 31-34.

RELATED ARTICLE: High-speed machining improves efficiencies.

A value-adding method that can augment castings significantly is high-speed machining (HSM). HSM can offer improved metal cutting efficiencies and reduced costs when machining castings. The key to HSM is how fast the unwanted metal can be removed, known as the metal removal rate (MRR).

In HSM, the high-speed capabilities of contemporary spindles are used to greatly increase the spindle speed and MRR. Today's modern cutting tool materials now can tolerate the tool temperatures generated at these speeds. A general rule with HSM is that spindle speeds accelerate within or above 5,000-10,000 rpm.

Investigations examined how the process performs with finished cast parts. Helicopter transmission castings with the transmission top made of A356-T6 aluminum alloy and the main transmission case made of magnesium underwent several milling methods for bores and surfaces via HSM processes with a machine tool that featured a 40-taper, 36,000-rpm, 35-horsepower spindle. The tool also had axis feed rates of 1,200 ipm.

It was found that with planetary milling for bores, HSM had a significant advantage in time savings over conventional boring when cutting tools with high dynamic stiffness were used, allowing for larger axial cut depths (Table A). MRR also increased greatly with spindle speed. When the endmilling of surfaces was compared to conventional practices, it was discovered that HSM also posed a quicker machining cycle time over conventional machines. Also, HSM was much faster for shallow bores that could be reached with out having to use long tools.

One issue of concern was found with planetary milling in which a poor surface was left on the bore, Such defects could lead to rejected castings. The cause of this was when a lack of parallelism existed between the cutting tool and the bore centerline or excessive deflection of the tool, which created a "sawtooth" surface (Fig. A). When the tool was fed into the bore as it proceeded around the bore. it would leave a single helical ridge; however, when the bore was generated in axial layers, the ridge appeared as a series of rings, Thus, the HSM process has yet to be perfected for high-production applications,

[FIGURE A OMITTED]

However, when applied to the ideal operations. HSM can be five times more productive than conventional practices (Table B) and could result in high-quality parts produced in a very quick manner.

The information provided was adapted from the article "High-Speed Machining Takes Flight," Engineered Casting Solutions, November/December 2005.

Table A. Planetary Milling of Bores

Aluminum Top Case

Feature                         Tool                           HSM Time

Large, very deep center bore    7 in. (17.9 cm), 2-flute,        173%
                                1 in. (2.54 cm) diameter
Center bore (reverse side)      5 in. (12.7 cm), 2-flute,        100%
                                0.75 in. (1.90 cm) diameter
Medium bores                    5 in. (12.7 cm), 2-flute,        42%
                                0.75 in. (1.90 cm) diameter
Shallow bores                   3 in. (7.62 cm), 4-flute,        15%
                                0.75 in. (1.90 cm) diameter

Magnesium Main Case

Feature                         Tool                           HSM Time

Large, deep bore                4 in. (10.16 cm), 4-flute,       47%
                                1 in. (2.54 cm) diameter
Large, medium depth bore        6 in. (15.24 cm), 4-flute,       26%
                                1 in. (2.54 cm) diameter
Shallow bores                   4 in. (10.16 cm), 4-flute,       4.0%
                                1 in. (1.90 cm) diameter
Shallow blind holes             4 in. (10.16 cm), 4-flute,       1.5%
                                1 in. (1.90 cm) diameter

Table B. Comparison of Overall Machining Time

                                Conventional    HSM Processes    HSM%

Aluminum Top Case                 3,327 sec      1,986 sec       59.7%
(All except deep center bore)                                   (15.1)

Magnesium Main Case              6,626 sec       1,232 sec        18.6